Nanostructured Smart Materials: Synthesis, Characterization, and Potential Applications 9781771889742, 9781774637814, 9781003130468, 2021001483, 2021001484

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NANOSTRUCTURED SMART MATERIALS Synthesis, Characterization, and Potential Applications

NANOSTRUCTURED SMART MATERIALS Synthesis, Characterization, and Potential Applications

Edited by V. R. Remya H. Akhina Oluwatobi Samuel Oluwafemi Nandakumar Kalarikkal Sabu Thomas

First edition published 2022 Apple Academic Press Inc. 1265 Goldenrod Circle, NE, Palm Bay, FL 32905 USA 4164 Lakeshore Road, Burlington, ON, L7L 1A4 Canada

CRC Press 6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487-2742 USA 2 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN UK

© 2022 Apple Academic Press, Inc. Apple Academic Press exclusively co-publishes with CRC Press, an imprint of Taylor & Francis Group, LLC Reasonable efforts have been made to publish reliable data and information, but the authors, editors, and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors, editors, and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged, please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, access www.copyright.com or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. For works that are not available on CCC please contact [email protected] Trademark notice: Product or corporate names may be trademarks or registered trademarks and are used only for identification and explanation without intent to infringe. Library and Archives Canada Cataloguing in Publication Title: Nanostructured smart materials : synthesis, characterization, and potential applications / edited by V.R. Remya, H. Akhina, Oluwatobi Samuel Oluwafemi, Nandakumar Kalarikkal, Sabu Thomas. Names: Remya, V. R., editor. | Akhina H., editor. | Oluwafemi, Oluwatobi Samuel, editor. | Kalarikkal, Nandakumar, editor. | Thomas, Sabu, editor. Description: First edition. | Includes bibliographical references and index. Identifiers: Canadiana (print) 20210110104 | Canadiana (ebook) 20210110112 | ISBN 9781771889742 (hardcover) | ISBN 9781774637814 (softcover) | ISBN 9781003130468 (ebook) Subjects: LCSH: Smart materials. | LCSH: Nanostructured materials. | LCSH: Nanotechnology. Classification: LCC TA418.9.S62 N36 2021 | DDC 620.1/15—dc23 Library of Congress Cataloging‑in‑Publication Data Names: Remya, V. R., editor. | Akhina H., editor. | Oluwafemi, Oluwatobi Samuel, editor. | Kalarikkal, Nandakumar, editor. | Thomas, Sabu, editor. Title: Nanostructured smart materials : synthesis, characterization, and potential applications / edited by V.R. Remya, H. Akhina, Oluwatobi Samuel Oluwafemi, Nandakumar Kalarikkal, Sabu Thomas. Description: First edition. | Palm Bay, FL : Apple Academic Press, 2021. | Includes bibliographical references and index. | Summary: "This new volume presents various research studies that focus on the development of advanced nanomaterials and their composites and blends for different applications in sensing, electrical, biomedical, coating, industrial applications, etc. This book includes detailed discussions on the synthesis, properties, processing, and potential applications of nanomaterials and their blends and composites. Some chapters also explain the basic theoretical aspects of these nanostructured materials and systems, which help readers to develop a better understanding various application areas, including construction. Nanostructured Smart Materials: Synthesis, Characterization and Potential Applications responds to the need for advanced polymeric materials and nanostructured materials with ultimate performance and enhanced qualities and properties for varied applications. The chapters highlight information and research that will be valuable for development of new smart materials. This book will be a useful reference source for universities, colleges, researchers from R&D groups, scientists, postdoctoral fellows, industrialists, graduate and postgraduate students, and faculty"-- Provided by publisher. Identifiers: LCCN 2021001483 (print) | LCCN 2021001484 (ebook) | ISBN 9781771889742 (hardcover) | ISBN 9781774637814 (paperback) | ISBN 9781003130468 (ebook) Subjects: MESH: Nanostructures | Smart Materials | Nanotechnology Classification: LCC R855.3 (print) | LCC R855.3 (ebook) | NLM QT 36.5 | DDC 610.285--dc23 LC record available at https://lccn.loc.gov/2021001483 LC ebook record available at https://lccn.loc.gov/2021001484 ISBN: 978-1-77188-974-2 (hbk) ISBN: 978-1-77463-781-4 (pbk) ISBN: 978-1-00313-046-8 (ebk)

About the Editors V. R. Remya, MSc, CSIR‑UGC NET Research Fellow, Department of Chemical Sciences, Centre for Nanomaterials Science Research, University of Johannesburg, Doornfontien Campus, South Africa V. R. Remya is a Research Fellow in the Department of Chemical Sciences, Centre for Nanomaterials Science Research, University of Johannesburg, Doornfontien Campus, South Africa. She has successfully completed a three-year Defence Research and Development Organisation, Indiasponsored project on nanostructured polymer blends at the International and Inter University Center for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, India. She has published several articles in professional international and national journals and has presented her work at various international and national conferences as well. She has authored and co-authored several book chapters. She received several best paper and best poster awards. Her research interests include polymer blends and composites, nanocomposites, synthesis and applications of quantum dots, and fabrication of super tough and fluorescent material for nanotechnology industrial applications, etc. H. Akhina, PhD Assistant Professor (Guest), Department of Chemistry, MSM College, Kayamkulam, Kerala, India H. Akhina, PhD, is currently working as an Assistant Professor (Guest), Department of Chemistry, MSM College, Kayamkulam, Kerala, India. She was a Senior Research Fellow (CSIR) at the International and Inter University Center for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, India. She has published articles in professional international and national journals and has presented her work at various international and national conferences as well. She has co-authored several book chapters and has experience in editing books. Her research interests include the synthesis of nanomaterials such as graphene and polymer nanocomposites, etc.

vi

About the Editors

Oluwatobi S. Oluwafemi, PhD Professor, Department of Chemical Sciences, Centre for Nanomaterials Science Research, University of Johannesburg, Doornfontein Campus, South Africa Oluwatobi Samuel Oluwafemi, PhD, is a National Research Foundation-rated researcher and is actively involved in research in the area of nanotechnology. He is a Full Professor at the Department of Chemical Sciences, Centre for Nanomaterials Science Research, University of Johannesburg, Doornfontein Campus, South Africa. He has published many papers in internationally recognized journals and has presented at several professional meetings both locally and internationally. He is a fellow of many professional bodies, a reviewer for many international journals, and has received many awards for his excellent work in material research, both local and international. His current research interests include green synthesis and application of nanomaterials in medicine, water treatment, and fabrication of devices. Nandakumar Kalarikkal, PhD Director, International and Inter University Centre for Nanoscience and Nanotechnology; Professor, School of Pure and Applied Physics, Mahatma Gandhi University, Kerala, India Nandakumar Kalarikkal, PhD, is the Director of the International and Inter University Centre for Nanoscience and Nanotechnology as well as a Professor and Chair in the School of Pure and Applied Physics at Mahatma Gandhi University, Kerala, India. His current research interests include synthesis, characterization, and applications of various nanostructured materials, laser plasma, and phase transitions. He has published more than 200 research articles in peer-reviewed journals and has co-edited more than 25 books. Prof. Kalarikkal obtained his master’s degree in Physics with a specialization in Industrial Physics and his PhD in Semiconductor Physics from Cochin University of Science and Technology, Kerala, India. He was a postdoctoral fellow at NIIST, Trivandrum, Kerala, India, and later joined Mahatma Gandhi University. Prof. Kalarikkal is also a visiting Professor at the University of Lorraine, France, and CNRS Professor at ILM, Lyon, France.

About the Editors

vii

Sabu Thomas, PhD Professor, Polymer Science and Engineering, School of Chemical Sciences; Director, International and Inter University Centre for Nanoscience and Nanotechnology, Mahatma Gandhi University, Kottayam, Kerala, India Sabu Thomas, PhD, is currently working as the Vice-Chancellor of Mahatma Gandhi University, Kottayam, India. He is a Professor of Polymer Science and Engineering at the School of Chemical Sciences and Director of the International and Inter University Centre for Nanoscience and Nanotechnology at Mahatma Gandhi University, Kottayam, Kerala, India. The research activities of Professor Thomas include surfaces and interfaces in multiphase polymer blend and composite systems; phase separation in polymer blends; compatibilization of immiscible polymer blends; thermoplastic elastomers; phase transitions in polymers; nanostructured polymer blends; macro-, micro-, and nanocomposites; polymer rheology; recycling; reactive extrusion; processing-morphology-property relationships in multiphase polymer systems; double networking of elastomers; natural fibers and green composites; rubber vulcanization; interpenetrating polymer networks; diffusion and transport; and polymer scaffolds for tissue engineering. He has supervised 68 PhD theses, 40 MPhil theses, and 45 master’s theses. He has three patents to his credit. He also received the coveted Sukumar Maithy Award for the best polymer researcher in the country for the year 2008. Very recently, Professor Thomas received the MRSI and CRSI medals for his excellent work. With over 800 publications to his credit and over 35,765 citations, with an h-index of 100, Dr. Thomas has been ranked fifth in India as one of the most productive scientists. He received his BSc degree (1980) in Chemistry from the University of Kerala, BTech (1983) in Polymer Science and Rubber Technology from the Cochin University of Science and Technology, and PhD (1987) in Polymer Engineering from the Indian Institute of Technology, Kharagpur, India.

Contents

Contributors.............................................................................................................xi Abbreviations .......................................................................................................... xv Symbols .................................................................................................................. xix Preface ................................................................................................................... xxi 1.

Metal Oxide Embellished on Polymer Functionalized Reduced Graphene Oxide for Electrochemical Detection of Hydrogen Peroxide ....1 S. Yuvashree and J. Balavijayalakshmi

2.

Photoluminescence Investigations of UV, Near UV, and Visible Light Excited CaS:Eu Nanophosphors ...................................13 S. Rekha and E. I. Anila

3.

Nanomaterial Aspect of Drug Delivery Towards Cancer Therapy ..........29 Ahmaduddin Khan and Niroj Kumar Sahu

4.

Polymer Functionalized Reduced Graphene Oxide‑Based Nickel Nanoparticles as Highly Efficient Dye Catalyst for Water Remediation .......................................................................................61 V. Ramalakshmi and J. Balavijayalakshmi

5.

Fabrication of Interdigitated Electrodes (IDEs) by Screen Printing Technology and Their Structural Studies .......................77 A. Akshaya Kumar, S. K. Naveen Kumar, and Almaw Ayele Aniley

6.

Photocatalytic Effect of Tin Oxide‑Zinc Oxide Nanocomposites Prepared by the Solvothermal Method .......................................................89 K. J. Abhirama and K. U. Madhu

7.

MMT Intercalated Pd Nanocatalyst for Heck (Mizoroki‑Heck) Reaction ..........................................................................109 Prashant Gautam and Vivek Srivastava

8.

A Novel Approach for Production and Characterization of Al‑Mg Eutectic Alloy Nanopowder by Electrical Explosion of Thin Plates ......131 C. Mohammed Iqbal, S. R. Chakravarthy, R. Jayaganthan, R. Sarathi, and A. Srinivasan

x

Contents

9.

Investigation on Wear and Corrosion Behavior of Ti2N Thin Films ......141 J. Menghani, K. B. Pai, M. K. Totlani, and N. Jalgoankar

10. Structural Study of Ethylene Glycol‑Assisted Solution Combustion Synthesis of Strontium Doped LaMnO3 ..............................159 P. V. Jithin and Joji Kurian

11. Molecular Dynamics Study of Single Crystal Metallic Nanowires.........171 Jit Sarkar

12. Low‑Temperature Gas Sensing Properties of Reduced Graphene Oxide Incorporated Perovskite Nanocomposite.......................................185 N. Vidyarajan and L. K. Alexander

13. Synthesis and Characterization of LFO‑BFO Multiferroic Nanocomposites ...........................................................................................193 Ayekpam Kiranjit Singh, T. H. David Singh, and Ibetombi Soibam

14. Mycobacterium tuberculosis Diagnosis with Conventional, Molecular Probe, and Nanobiosensing Techniques .................................203 Deepak V. Sawant and Shivaji H. Pawar

15. Physical Aging in PS‑MWCNT Composite: An Enthalpy Relaxation Study .........................................................................................223 Md. Amir Sohel, Abhijit Mondal, and Asmita Sengupta

16. Dual Probe Heat Pulse (DPHP) Method Soil Moisture Sensor Using Advanced Materials‑Based Thermistor and Fluorine Doped Tin Oxide (FTO) Thin Film Electric Heater ................................233 Almaw Ayele Aniley, S. K. Naveen Kumar, and A. Akshaya Kumar

17. Indium Doped Tin Oxide (ITO) Nanopowder‑Based Electric Heater Fabrication and Characterization ................................................253 Almaw Ayele Aniley, S. K. Naveen Kumar, and A. Akshaya Kumar

18. Optimization and Performance of Nanomaterials in Cement Concrete .........................................................................................265 Mainak Ghosal and Arun Kumar Chakraborty

Index .....................................................................................................................289

Contributors

K. J. Abhirama

Physics Research Centre, S. T. Hindu College, Nagercoil–629002, Tamil Nadu, India, E-mail: [email protected]

L. K. Alexander

Department of Physics, University of Calicut, Kerala–673635, India

E. I. Anila

Optoelectronic and Nanomaterials Research Laboratory, Department of Physics, Union Christian College, Aluva–683102, Kerala, India, E-mail: [email protected]

Almaw Ayele Aniley

Department of Electronics, Mangalore University, Mangalagangothri–574199, Mangalore, Karnataka, India; Department of Electrical and Computer Engineering, Debre Markos University, Debre Markos, Ethiopia

J. Balavijayalakshmi

Assistant Professor, Department of Physics, PSGR Krishnammal College for Women, Coimbatore, Tamil Nadu, India, E-mail: [email protected]

Arun Kumar Chakraborty

Associate Professor, Department of Civil Engineering, Indian Institute of Engineering Science and Technology, Shibpur, West Bengal, India

S. R. Chakravarthy

Department of Aerospace Engineering, IIT Madras, Chennai–600036, India, E-mail: [email protected]

Prashant Gautam

Basic Sciences, Chemistry, NIIT University, NH-8 Jaipur/Delhi Highway, Neemrana, Rajasthan –301705, India

Mainak Ghosal

PhD Research Scholar, Indian Institute of Engineering Science and Technology, Shibpur, West Bengal, India

C. Mohammed Iqbal

Department of Aerospace Engineering, IIT Madras, Chennai–600036, India, E-mail: [email protected]

N. Jalgoankar

Multi-Arc India Ltd., Umargoan, Gujarat, India

R. Jayaganthan

Department of Engineering Design, IIT Madras, Chennai–600036, India, E-mail: [email protected]

P. V. Jithin

Department of Physics, Nirmalagiri College, Nirmalagiri P. O., Kannur–670701, Kerala, India

Ahmaduddin Khan

Centre for Nanotechnology Research, VIT, Vellore–632014, Tamil Nadu, India, E-mail: [email protected]

xii

Contributors

A. Akshaya Kumar

Department of Electronics, Mangalore University, Mangalagangothri–574199, Mangalore, Karnataka, India, E-mail: [email protected]

S. K. Naveen Kumar

Department of Electronics, Mangalore University, Mangalagangothri–574199, Mangalore, Karnataka, India

Joji Kurian

Department of Physics, Nirmalagiri College, Nirmalagiri P. O., Kannur–670701, Kerala, India, E-mail: [email protected]

K. U. Madhu

Physics Research Centre, S. T. Hindu College, Nagercoil–629002, Tamil Nadu, India

J. Menghani

Mechanical Engineering Department, SVNIT Surat, Gujarat, India, E-mail: [email protected]

Abhijit Mondal

Department of Physics, Visva-Bharati Central University, Santiniketan, West Bengal–731235, India

K. B. Pai

ITM Universe, Vadodara, Gujarat, India

Shivaji H. Pawar

Center for Interdisciplinary Research, D. Y. Patil Education Society, Kolhapur–416 006, Maharashtra, India; Center for Innovative and Applied Research, Anekant Education Society, TC College Complex, Baramati, Maharashtra, India

V. Ramalakshmi

Department of Physics, PSGR Krishnammal College for Women, Coimbatore, Tamil Nadu, India, E-mail: [email protected]

S. Rekha

Department of Physics, Maharaja’s College, Ernakulam, Kerala, India; Optoelectronic and Nanomaterials Research Laboratory, Department of Physics, Union Christian College, Aluva–683102, Kerala, India

Niroj Kumar Sahu

Centre for Nanotechnology Research, VIT, Vellore–632014, Tamil Nadu, India, E-mail: [email protected]

R. Sarathi

Department of Electrical Engineering, IIT Madras, Chennai–600036, India, E-mail: [email protected]

Jit Sarkar

Boldink Technologies Private Limited, Howrah, West Bengal–711110, India, E-mail: [email protected]

Deepak V. Sawant

Center for Interdisciplinary Research, D. Y. Patil Education Society, Kolhapur–416 006, Maharashtra, India, E-mail: [email protected]

Asmita Sengupta

Department of Physics, Visva-Bharati Central University, Santiniketan, West Bengal–731235, India, E-mail: [email protected]

Ayekpam Kiranjit Singh

Department of Physics, NIT Manipur, Imphal–795004, Manipur, India

Contributors

xiii

T. H. David Singh

Department of Chemistry, NIT Manipur, Imphal–795004, Manipur, India

Md. Amir Sohel

Department of Physics, Visva-Bharati Central University, Santiniketan, West Bengal–731235, India

Ibetombi Soibam

Department of Physics, NIT Manipur, Imphal–795004, Manipur, India, E-mail: [email protected]

A. Srinivasan

Division of Material Science and Technology (NIIST) Trivandrum, Kerala, India, E-mail: [email protected]

Vivek Srivastava

Basic Sciences, Chemistry, NIIT University, NH-8 Jaipur/Delhi Highway, Neemrana, Rajasthan–301705, India, Phone: +91-1494660623, E-mail: [email protected]

M. K. Totlani

Associated with BARC, Mumbai and Later on was Independent Consultant, Mumbai, Maharashtra, India

N. Vidyarajan

Department of Physics, University of Calicut, Kerala–673635, India, E-mail: [email protected]

S. Yuvashree

PhD Scholar, Department of Physics, PSGR Krishnammal College for Women, Coimbatore, Tamil Nadu, India, E-mail: [email protected]

Abbreviations

ADR AF AFM AFM AOP AR BIS BSA C2H6O2 CA CAE CDs CEC CIE CMR CNTs COF Cp CPT CS C-S-H Cu CuO NPs CV CXR DLS DMF DMSO DNA DRS DTT EDS EDX EGF

amplitude domain reflectometry acid-fast antiferromagnetic atomic force microscopy advanced oxidation processes analytical reagent Bureau of Indian Standards bovine serum albumin ethylene glycol coarse aggregate cathodic arc evaporation cyclodextrins cation exchange capacity Commission Internationale de l’Eclairage colossal magnetoresistance carbon nanotubes coefficient of friction specific heat capacity camptothecin chitosan calcium silicate hydrate copper copper oxide nanoparticles cyclic voltammetry chest x-ray dynamic light scattering dimethylformamide dimethyl sulfoxide deoxyribonucleic acid diffuse reflectance spectrum DL-dithiothreitol energy-dispersive x-ray spectroscopy x-ray spectroscopy epidermal growth factor

xvi EPR FA FD FDR FE-SEM FM FT-IR FWHM GBM GCE GO H2O2 HD HMT HPC HPLC HRTEM HSA HSC ICP-OES IDEs IIT ILs IONPs IoT ITO ITS ITZ KFT KMnO4 KWW LAMMPS LAMP LCST LDHs LFO LMO MAA MD

Abbreviations

enhanced permeability and retention folic acid frequency domain frequency domain reflectometry field emission scanning electron microscopy ferromagnetic Fourier transform infrared full width at half maximum glomerular basement membrane glassy carbon electrode graphene oxide hydrogen peroxide hydrodynamic diameter hexamethylenetetramine high-performance concrete high-performance liquid chromatography high-resolution transmission electron microscopy human serum albumin high-strength concrete inductively coupled plasma atomic emission spectroscopy interdigitated electrodes Indian Institute of Technology ionic liquids iron oxide magnetic nanoparticles internet of things indium-doped tin oxide internal transcribed spacer interfacial transition zone kidney filtration threshold potassium permanganate Kohlrausch-Williams-Watts large-scale atomic/molecular massively parallel simulator loop-mediated isothermal amplification test low critical solution temperature layered double hydroxides LaFeO3 LaMnO3 methacrylic acid molecular dynamics

Abbreviations

MDR MEA MHT MMT MnO2 MSN MTBC MWCNTs NAAT NALC NaNO3 NaOH NCCRD NIR NM NMP NMRI NPs NRs NTM O PBS PCB PCL PCN PCR Pd NPs PEG PL PLA PLGA PM-FM PM PMA PNCs POC PS PT PTFE

xvii

multidrug resistance monoethanolamine magnetic hyperthermia montmorillonite manganese dioxide mesoporous silica nanoparticles M. tuberculosis bacilli complex multi-walled carbon nanotubes nucleic acid amplification N-acetyl-L-cysteine sodium nitrate sodium hydroxide National Centre for Combustion Research and Development near-infrared radiation neutron moderation method N-methyl-2-pyrrolidone nuclear magnetic resonance imaging nanoparticles nanorods nontuberculosis mycobacteria oxygen phosphate buffer solution printed circuit board polycaprolactone polymer caged nanobin polymer chain reaction Pd nanoparticles polyethylene glycol photoluminescence polylactic acid polylactic-co-glycolic acid paramagnetic to ferromagnetic magnetic phases poly(methacrylic acid) polymer nanocomposites point-of-care polystyrene phase transformation polytetrafluoroethylene

Abbreviations

xviii PTX QDs RES RFLP RGO ROS RPS RT SAED SAXS SCE SE SEM SLNPs SNP SPION Sr Sr(NO3)2 SWCNTs Ta TB TBAB TC TDR TEM Tg TL TMA TPP TSILs TST UPV VPTT WHO XRD XRF ZN Zn ZnO

hydrophobic paclitaxel quantum dots reticuloendothelial system restriction length polymorphism analysis reduced graphene oxide reactive oxygen species research promotion scheme room temperature selected area electron diffraction small to medium angle X-ray scattering saturated calomel electrode super-exchange scanning electron microscope solid lipid NPs single nucleotide polymorphism superparamagnetic iron oxide nanoparticles strontium strontium nitrate single-walled CNTs aging temperature tuberculosis tetra butyl ammonium bromide temperature time-domain reflectometry transmission electron microscope glass transition temperature transmission line trimethylamine tripolyphosphate task-specific ILs tuberculin skin test ultrasonic pulse velocity volume phase transition temperature World Health Organization report x-ray diffraction x-ray fluorescence Ziehl-Neelsen zinc zinc oxide

Symbols

τ=

π α λ1 A1 Bo C∞ Cw DB DT I K Le M Nb Nt P Pr Rd T∞ Tw u uw v v vw γ μ∞ μo ρf σ τ1

( ρ c) p ( ρ c) f

the ratio between the effective heat capacity of nanoparticle material and heat capacity of the fluid second invariant strain tensor thermal diffusivity Williamson parameter First Rivlin-Erickson tensor magnetic field ambient fluid concentration stretching surface concentration Brownian diffusion coefficient thermophoresis diffusion coefficient identity vector thermal conductivity Lewis number magnetic parameter Brownian motion parameter thermophoresis parameter pressure Prandtl number radiation parameter ambient fluid temperature stretching surface temperature velocity component along x-axis velocity component at the wall kinematic viscosity velocity component along y-axis velocity component at the wall angle of inclination limiting viscosity at an infinite shear rate limiting viscosity at zero shear rate density of the fluid electrical conductivity extra stress tensor

Preface

The world is seeking advanced new materials with ultimate performance qualities in science and technology, health, industry, and all aspects of the environment, and the need for new nanosystems leads to the study of new developments in nanotechnology. Recently, advanced polymeric materials and nanostructured materials have gained much more attention because people are looking for these types of excellent and smart materials with enhanced properties in their applications. Nowadays, the use of advanced nanostructured and polymeric materials is increasing due to their wide variety of properties and tunability. Scientists, researchers, engineers, industrialists, etc., are exploring a new world by using advanced nanomaterials rather than conventional materials. The major goal of this book is to present various research to develop advanced nanomaterials and their composites and blends for different applications for sensing, electrical, biomedical, coating, industrial applica­ tions, etc. This book gives a detailed discussion on the synthesis, properties, processing, and potential applications of nanomaterials and their blend/ composites. Some chapters also explain the basic theoretical aspects of these nanostructured materials and systems, which help readers to develop a better understanding of various application areas, including construction. Technology that is close to nature is necessary, and therefore, the need of these kinds of advanced materials and their application in the 21st century is essential. The present book starts with a chapter discussing the simple, costeffective, and sensitive synthesis of copper oxide nanoparticles (CuO NPs) and decorated reduced graphene oxide (RGO)-chitosan (CS) nanocomposites for the determination of H2O2 in a real water sample. The second chapter deals with Europium doped CaS nanophosphors having an average crystallite size of 40 nm that were synthesized using the solid-state diffusion method. The optical bandgap of the prepared nanophosphors is found to increase compared to that of bulk CaS due to the Burstein-Moss effect. The tunable emission of these phosphors finds application in solid-state lighting technology and various display devices.

xxii

Preface

The third chapter gives a detailed discussion of nanomaterial-based drug delivery in cancer therapy and targeting. Later it covers the synthesis, properties, processing, and potential applications of various nanoparticles and nanocomposites like CD/GO nanocomposites, ZnO NRs modified IDEs sensor, zinc oxide (ZnO) nanocomposites, Williamson nanofluid, nanopowder of Al-Mg alloy, metal nitride thin films, single-phase LaMnO3 (Lanthanum manganite) and Sr (Strontium) doped LaMnO3 samples, singlecrystal FCC metallic nanowires, perovskite LaFe0.8Al0.2O3 (LFAL) with Pbnm crystal structure, nanocomposites having the compositional formula (1–x) BFO-xLFO with x = (0, 0.25, 0.50, 0.75, 1.0) in versatile fields like the textile industry, sensors, catalysis, coating, aerospace, and defense, shooting, etc. The last part of this book reveals the traditional and molecular probe methods available for TB diagnosis, PS-multi wall carbon nanotube (MWCNT) composite film, which has been studied by monitoring enthalpy relaxation; DPHP method soil moisture content estimation using thin-film heater as a heat source; nanoceramic powder-based thermistor as a temperature sensor; low power and cost-effective electric heaters fabrication by using simple and economical techniques from ITO nanopowder-based electric heater and nano­ silica (nS); and carbon nanotubes (CNTs)-based concrete treatment in detail. This book will be a very important and valuable reference source for universities, colleges, researchers from R&D groups, scientists, postdoctoral fellows, industrialists, graduate and postgraduate students, and teachers for studying the basics and for developing new advanced smart materials. In short, the editors would like to express their sincere gratitude to all the contributors of this book, who extended their wonderful and excellent support for the successful completion of this venture. We are really thankful to them for the sincerity and commitment they have given toward their contributions to the book. This volume happened only because of their enthusiasm and great support. We would also like to thank all reviewers who have taken their valuable time to give critical comments on each chapter. We express our sincere thanks to the publisher, Apple Academic Press, for recognizing the demand for such a book in advanced nanostructured smart materials and realizing the necessity and importance of such a project in the current and upcoming century. —V. R. Remya, MSc, CSIR‑UGC NET H. Akhina, PhD Oluwatobi S. Oluwafemi, PhD Nandakumar Kalarikkal, PhD Sabu Thomas, PhD

CHAPTER 1

Metal Oxide Embellished on Polymer Functionalized Reduced Graphene Oxide for Electrochemical Detection of Hydrogen Peroxide S. YUVASHREE1 and J. BALAVIJAYALAKSHMI2 PhD Scholar, Department of Physics, PSGR Krishnammal College for Women, Coimbatore, Tamil Nadu, India, E-mail: [email protected]

1

Assistant Professor, Department of Physics, PSGR Krishnammal College for Women, Coimbatore, Tamil Nadu, India, E-mail: [email protected]

2

ABSTRACT In this study, copper oxide nanoparticles (CuO NPs) decorated reduced graphene oxide (RGO)-chitosan (CS) nanocomposites are prepared for reliable detection of hydrogen peroxide (H2O2). The reduced GO-CS­ copper oxide nanocomposites are synthesized by the chemical reduction method. The morphological and chemical structures of the nanocomposites are systemically evaluated by Fourier transform infrared spectral analysis (FT-IR), x-ray diffraction (XRD), scanning electron microscopy (SEM), and Raman analysis. A potential application of reduced GO-CS-copper oxide nanocomposites-modified electrode as a biosensor to monitor H2O2 has been investigated. The electrochemical properties of the biosensor are investigated by cyclic voltammetry (CV). After optimizing all the experimental parameters, the reduced GO-CS-copper oxide nanocomposites on modified glassy carbon electrode (GCE) showed a good performance towards the electrocatalytic reduction of H2O2. This method is simple, cost-effective, sensitive, and also can be used for the determination of H2O2 in a real water sample.

2

Nanostructured Smart Materials

1.1 INTRODUCTION Graphene, a single layer of sp2 hybridized carbon atoms packed into a dense honeycomb crystal structure, has attracted significant research interest because of its unique structure and extraordinary properties like high conductivity, high surface area, and hardest material [1]. Graphene possesses various mate­ rial parameters such as superior mechanical stiffness, strength, and elasticity, very high electrical and thermal conductivity that has versatile applications in the areas of the supercapacitor, transistor, solar cells, batteries, fuel cells, hydrogen storage, nanoelectronics, electrocatalysis, sensors, electrochemical devices, electromechanical resonator [2]. Chitosan (CS) is a linear b-1,4­ linked polysaccharide that possesses distinct chemical and biological proper­ ties, because of its reactive amino and hydroxyl groups in its linear high molar mass poly glucosamine chains, which are amenable to chemical modification [3]. CS has a lot of excellent characteristics, including film-forming ability, biocompatibility, non-toxicity, good water permeability, high mechanical strength, and adhesion. Graphene and its nanocomposites have been widely exploited in biomedicine for drug/gene delivery, cancer therapy, tissue engi­ neering, and biosensing. In recent years, noble metal nanoparticles have been used widely due to their interesting electronic, optical, mechanical, magnetic, and chemical properties, which differ greatly from those of bulk substances. Among various metal nanoparticles, copper oxide nanoparticles (CuO NPs) have been widely used in many fields due to their excellent physical and chemical properties, easy preparation, and low synthetic cost [4]. Hydrogen peroxide (H2O2), a chemical widely used in pharmaceutical, clinical, environmental, mining, textile, and food manufacturing industries [5], is the by-product of oxidases such as lactate oxidase, urate oxidase, and so on. It is one of the reactive oxygen species (ROS) that plays a vital role in signaling molecules, mainly regulating DNA damage, protein synthesis, cell apoptosis, etc., and it affects cell proliferation and thus leads to cancer, diabetes, and cardiovascular disorders [6, 7]. It is also a relatively stable molecule that makes it highly suitable as a diffusible signaling molecule [8]. Most importantly, the high concentrations of H2O2 initiate neurotoxic events such as Parkinson’s and Alzheimer’s disorders. It is critically important to monitor H2O2 levels in biological environments, especially in the cellular environment. However, the electrochemical technique is an optimal choice to actualize the accurate and sensitive determination of H2O2 depending on its inherent advantages, such as low cost, practicality, simplicity, high sensitivity, and fast response [9]. Recently a large range of nanomaterials such as metals, metal oxides, carbon nanotubes (CNTs), graphene, oxide,

Metal Oxide Embellished on Polymer Functionalized

3

and nanocomposite materials have been used for the electrochemical detection of H2O2. Additionally, few numbers of polymer-based graphene nanocomposites have been employed for H2O2 sensing [10]. In this present work, CuO NPs decorated on CS functionalized RGO nanocomposites have been synthesized using a chemical reduction method for the electrochemical determination of H2O2. The cyclic voltammetry (CV) is employed to investi­ gate the analytical performance of H2O2. 1.2 EXPERIMENTAL 1.2.1 REAGENTS Graphite powder, conc. sulfuric acid (98% H2SO4), potassium permanganate (KMnO4), hydrogen peroxide solution (30% H2O2), sodium nitrate (NaNO3), sodium hydroxide (NaOH), cupric chloride (CS), and sodium borohydride are purchased from Sigma Aldrich and are used as received without further purification. 1.2.2 PREPARATION OF REDUCED GRAPHENE OXIDE (RGO)/ CHITOSAN (CS)/COPPER OXIDE NANOCOMPOSITES Graphene oxide is synthesized from natural graphite by the modified Hummer’s method. Graphite (1 g), NaNO3 (0.5g), and concentrated H2SO4 (25 mL) are first stirred together in an ice bath for 1 hour. KMnO4 (6 g) is slowly added into the solution and stirred for 12 hrs at a temperature of 35°C, and the mixture is then gradually turned into brown. Then, the whole system is removed from the ice bath, and 500 ml-distilled water is added into the reaction mixture. H2O2 (5 ml) is finally added into the solution to remove excess KMnO4. The resultant mixture is washed with distilled water for several times and dried in an oven at 60°C for 12 hours. The rGO/CS/copper oxide nanocomposites are synthesized by dispersing GO (50 mg) in 25 ml distilled water by ultrasonication for 1 hour to form the GO solution. An aqueous solution of CS is prepared by stirring 25 mg CS in 2% acetic acid, which is then added dropwise into the dispersed GO solution, and about 0.006 M of cupric chloride solution is added, followed by dropwise addition of NaBH4 (25 mg) solution and stirred for 4 hrs at 60°C. Thus the formed solution is left undisturbed for overnight and dried at 60°C for 12 hours (Figure 1.1).

Nanostructured Smart Materials

4

FIGURE 1.1

The possible reaction mechanism.

1.3 RESULTS AND DISCUSSION 1.3.1 FTIR ANALYSIS The FT-IR spectra of GO, RGO, RGO/CS/CuO nanocomposites are shown in Figure 1.2(a–c). The broadband at 3143 cm–1 corresponds to O-H stretching vibrations of hydroxyl groups, and the band at 1424 cm–1 is assigned to C-OH bending vibrations of carboxyl groups. The bands at 1403 cm−1 and 1053 cm−1 may be assigned to the deformation vibration of O–H and stretching vibration of C–O, respectively, which confirms the formation of GO. The reduction of GO into rGO could be clearly evidenced by the absence of the oxygen-containing groups as shown in Figure 1.1(b) [10], and the presence of amino groups is confirmed by the band around 1554.69 cm–1 as shown in Figure 1.1(c) [11]. It is further observed that the intensity of the bands at 3143 cm–1 and 1424 cm–1 decreases, and this may be due to the addition of CuO nanoparticles. The band appeared at 576 cm–1 corresponds to the Cu–O stretching vibration that confirms the presence of CuO NPs onto the surface of polymer functionalized GO [12]. 1.3.2 XRD ANALYSIS Figure 1.3 shows the x-ray diffraction (XRD) patterns of GO, RGO, RGO/CS/ CuO nanocomposites. A strong peak at 11.45° corresponds to the (002) plane and the interlayer distance of 0.85 nm, confirms the successful preparation of GO from graphite powder through oxidation, and the diffraction peak at

Metal Oxide Embellished on Polymer Functionalized

5

42.3° corresponds to the (001) plane may be due to the incomplete oxidation of graphite materials as shown in Figure 1.3(a). The disappearance of the diffraction peak at 11.45° and the appearance of a broad peak at 23.83° corresponding to the (002) plane indicates the complete reduction of GO to RGO as shown in Figure 1.3(b) [13]. In Figure 1.2(c), the broadening of the peak at 23.83° may be due to the amorphous nature of the polymer, and in addition, the diffraction peaks observed at 2θ values of 36.4°, 42.8° and 61.4° corresponding to (110), (112), (113) planes confirms the formation of CuO nanoparticles and are well-matched with the JCPDS Card no. 89–2530 [14]. The crystallite size of CuO nanoparticles is found to be around 20.9 nm. The sharp crystalline peaks ascribe the good incorporation of copper oxide into the polymer functionalized GO.

FIGURE 1.2

FT-IR spectra of (a) GO, (b) RGO, and (c) RGO/CS/CuO nanocomposites.

1.3.3 SEM ANALYSIS The surface morphology of the synthesized GO, RGO/CS/CuO nanocom­ posites are studied by SEM. In Figure 1.3(a), the synthesized GO is of a paper-like structure. Figure 1.3(b) shows that the spherical-shaped CuO nanoparticles are homogeneously distributed over the paper-like surface

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6

of rGO/CS nanosheets, thereby conforming the embellishment of CuO nanoparticles into the rGO/CS nanocomposites [15] (Figure 1.4).

FIGURE 1.3

XRD pattern for GO, RGO, RGO/CS/CuO nanocomposites.

(a) FIGURE 1.4

(b)

SEM images for GO, RGO/CS/CuO nanocomposites.

1.3.4 EDAX ANALYSIS EDAX spectra reveal the presence of elements in the synthesized GO and RGO/CS/CuO nanocomposites. Figure 1.5(a) shows carbon and oxygen

Metal Oxide Embellished on Polymer Functionalized

7

presence and confirms the formation of GO nanosheets. Figure 1.5(b) shows the presence of carbon, oxygen, and copper elements without any impurities confirm the formation of RGO/CS/CuO nanocomposites [16].

(a) FIGURE 1.5

(b)

EDAX spectra for (a) GO and (b) RGO/CS/CuO nanocomposites.

1.3.5 TEM ANALYSIS The morphology of the synthesized RGO/CS/CuO nanocomposites is investigated by TEM analysis. Figure 1.6(a–b) shows the TEM images for RGO/CS/CuO nanocomposites with different magnifications. Figure 1.6(a–b) shows the detailed texture of particles, and the spherical shaped CuO nanoparticles are well incorporated and closely anchored onto the surface of RGO/CS nanosheets. This result is in good agreement with the SEM images [17]. The selected area electron diffraction (SAED) pattern of the synthesized RGO/CS/CuO nanocomposites is shown in Figure 1.6(c). It is observed from Figure 1.6(c) that the prepared nanocomposites are polycrystalline in nature with distinct rings, which implies the high degree of crystallinity of CuO nanoparticles as evidenced by XRD analysis. 1.3.6 RAMAN SPECTROSCOPY The information on structural defects, residual stress, and the presence of additional functional groups is further investigated by Raman spectroscopy. Figure 1.7 shows the Raman spectrum for (a) GO and (b) reduced GO. The two intense characteristic bands of GO is observed in Figure 1.7(a). The

Nanostructured Smart Materials

8

band at 1359 cm–1 corresponds to D-band, which is due to the defects and disorder in the hexagonal graphitic layers, and another band at about 1593 cm–1 corresponds to G-band, which is due to the stretching of C-C vibration of the sp2 bonded carbon atoms in a two-dimensional hexagonal lattice. By comparing the band of GO with reduced GO, the intensity of the D-band increases with a decrease in the intensity of the G-band. It clearly shows that GO has been successfully reduced [18].

(a)

(b)

(c) FIGURE 1.6 (a, b) TEM images with different magnifications and (c) SAED pattern for RGO/CS/CuO nanocomposites.

1.4 ELECTROCHEMICAL STUDIES The electrochemical activity of the RGO/CS/CuO nanocomposites towards H2O2 detection is studied by CV [19]. It is carried out in the electrolyte

Metal Oxide Embellished on Polymer Functionalized

9

solution of 0.1 M phosphate buffer solution (PBS) from –1.5 V to 0.5 V, with a scanning rate of 20 mV/s at pH 7. The electrochemical activity is studied using three-electrode systems, and the surface of GCE is modified using the prepared RGO/CS/CuO nanocomposites. By the addition of 1 mm H2O2, no redox peaks are found for bare GO, and in contrast, a pair of redox peaks are observed at a potential about –0.3 V and 0.1 V for RGO/CS/CuO nano­ composites modified GCE as depicted in Figure 1.8(a), which shows that CuO nanoparticles enhance the electrochemical activity [20–23]. It is also observed that the current increases on further addition of H2O2 from 1 mM to 6 mM, indicating the good electrocatalytic activity of the as-synthesized nanocomposites towards the detection of Hydrogen peroxide. Thus the enhanced electrocatalytic activity is due to the synergistic contribution of the efficient conductivity of RGO/CS and high loading of CuO nanoparticles onto the RGO/CS sheets. These results indicate that the prepared nanocom­ posites showed a good response over the detection of H2O2.

FIGURE 1.7

Raman spectrum for (a) GO and (b) RGO.

1.5 CONCLUSION RGO/CS/CuO nanocomposites are synthesized by the chemical reduction method. The RGO/CS/CuO nanocomposites are characterized by XRD,

Nanostructured Smart Materials

10

FT-IR, SEM, and EDAX. The band appeared at 576 cm–1 corresponds to the Cu–O stretching vibration that confirms the presence of CuO NPs. XRD revealed that the formed GO and RGO/CS/CuO nanocomposites are crystal­ line in nature. The crystallite size of CuO nanoparticles is found to be around 20.9 nm. The SEM images revealed that CuO nanoparticles are well-formed and closely anchored at RGO/CS nanocomposites’ surface. EDAX analysis further confirms the presence of elements in the prepared nanocomposites without any impurities. The electrochemical measurements showed that the synthesized nanocomposites have high electrocatalytic activity for H2O2 detection, and the proposed sensor may find its practical application in H2O2 detection.

(a)

(b)

FIGURE 1.8 Electrochemical behavior for bare GO, RGO/CS/CuO nanocomposites modified GCE.

KEYWORDS • • • • • •

aminophenol chitosan electrochemical studies graphene oxide reactive oxygen species x-ray diffraction

Metal Oxide Embellished on Polymer Functionalized

11

REFERENCES 1. Chao, X., Xin, W., & Junwu, Z., (2008). J. Phys. Chem. C., 112, 19841–19845. 2. Lin-Jun, H., Yan-Xin, W., Jian-guo, T., Hui-Min, W., Hai-Bin, W., Jian-Xiu, Q., Wang, Y., Ji-Xian, L., & Jing-Quan, L., (2012). Int. J. Electrochem. Sci., 7, 11068–11075. 3. Jiang, Y., Ji-Hyuk, Y., Rudi, S. J., Woo-Jin, C., & Sundaram, G., (2013). Biosensors and Bioelectronics, 47, 530–538. 4. Jonghoon, C., Hana, O., Sang-Wook, H., Seokhoon, A., Jaegeun, N., & Joon, B. P., (2016). Current Applied Physics, 17, 137–145. 5. Binbin, L., Xueming, L., Jianchun, Y., Xianli, L., Longping, X., Xiaolin, L., Jiakun, G., et al., (2014). Anal. Methods, 6, 1114–1120. 6. Yuanyuan, Z., Xiaoyun, B., Xuemei, W., Kwok-Keung, S., Yanliang, Z., & Hui, J., (2014). Anal. Chem., 86, 9459−9465. 7. Guangxia, Y., Weixiang, W., Xiaoqi, P., Qiang, Z., Xiaoyun, W., & Qing, L., (2015). Sensors, 2709–2722. 8. Ruizhong, Z., & Wei, C., (2016). Biosensors and Bioelectronic, S0956–5663(16), 30088–30084. 9. Kangfu, Z., Yihua, Z., Xiaoling, Y., Jie, L., Chunzhong, L., & Shaorong, L., (2010). Electrochimica Acta, 3055–3060. 10. Abdollah, N., Mohmmad, K., Mohammad, R., Ensiyeh, S., & Mohammad, M., (2017). Electroanalysis, 29, 1–12. 11. Indranil, R., Dipak, R., Gunjan, S., Amartya, B., Nayan, R. S., Soumya, M., Sutanuk, P., et al., (2015). RSC Adv., 1–8. 12. Wenjing, L., Su, L., Jinghua, Y., Jie, L., Min, C., Wei, X., & Jiadong, H., (2013). Biosensors and Bioelectronics, 44, 70–76. 13. Chandrama, S., & Swapan, K. D., (2015). RSC Adv., 5, 60763–60769. 14. Guogang, Z., Haijun, Z., & Shuang, L., (2013). Int. J. Electrochem. Sci., 8, 6269–6280. 15. Xiaolin, W., Enli, L., & Xiaoli, Z., (2014). Electrochimica Acta, 130, 253–260. 16. Selvama, S., Balamuralitharana, B., Jegatheeswaran, S., Mi-Young, K., Karthick, S. N., Anandha, R. J., Boomi, P., et al., (2012). Journal of Materials Chemistry A., 1–3. 17. Youcheng, Z., Xinyu, S., Qisheng, S., & Zhilei, Y., (2012). Cryst. Eng. Comm., 14, 6710–6719. 18. Isaac, C., Luis, A. J., Wonjun, P., Helin, C., & Yong, P. C., Chapter 19; Raman Spectroscopy of Graphene and Related Materials, 1–20. 19. Riyaz, A. D., Gowhar, A. N., Pramod, K. K., Lily, G., Farid, K., Shashi, P. K., & Ashwini, K. S., (2015). Electrochimica Acta, 163, 196–203. 20. Minmin, L., Ru, L., & Wei, C., (2013). Biosensors and Bioelectronics, 45, 206–212. 21. Fariba, M., Asadpour-Zeynali, K., Susana, C., Yanez-Sedeno, P., & Jose, M. P., (2017). Electrochimica Acta, 246, 303–314. 22. Muhammet, G., Vedat, T., Ahmet, B., & Mehmet, Z., (2018). Electrochimica Acta, S0013–4686(18), 30075, 30076. 23. Bibi, S., Sharifah, M., Siti, N. A. H., Ninie, S., & Abdul, M., (2018). Sensors and Actuators B, 254, 1148–1156.

CHAPTER 2

Photoluminescence Investigations of UV, Near UV, and Visible Light Excited CaS:Eu Nanophosphors S. REKHA1,2 and E. I. ANILA2 1

Department of Physics, Maharaja’s College, Ernakulam, Kerala, India

Optoelectronic and Nanomaterials Research Laboratory, Department of Physics, Union Christian College, Aluva–683102, Kerala, India, E-mail: [email protected] (E. I. Anila)

2

ABSTRACT Rare-earth doped alkaline earth sulfides have been investigated extensively during the past few decades since they are promising candidates for electronic and optical applications. Of these alkaline earth sulfides, calcium sulfide (CaS) is an excellent luminescent material having a wide bandgap (4.5 eV) and size-tunable optical properties. CaS nanoparticles are cadmium-free nanoscale semiconductors, and tailoring the nanoparticles’ color output plays a vital role in their application as light-emitting displays, field emission displays, and various other optoelectronic devices. Here we report the synthesis of CaS nanophosphors, doped with the rare earth element europium using the solid-state diffusion method. The phase and particle size of the synthesized nanophosphors were determined from x-ray diffraction (XRD) data. Morphology of CaS:Eu nanophosphors were studied using scanning electron microscopy. The optical properties of the samples were studied by photoluminescence (PL) and UV-Vis absorption spectroscopy. We observed a variation in the PL emission color from yellow to red on excitation of the samples with UV, near UV, and visible light. The PL emission peaks are attributed to the 5D0→7FJ (J = 0, 1, 2, 3, …) electronic transitions of Eu3+ ions incorporated into the CaS host lattice. The optical band gap is calculated from the diffuse reflectance spectrum (DRS),

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and its value is found to be 5.3 eV. The improved optical properties of the synthesized phosphors can be exploited in various optoelectronic devices, including displays and white LEDs. 2.1 INTRODUCTION Sulfide based luminescent materials have gained considerable attention because of their wide range of photoluminescence (PL) and electrolumi­ nescence applications [1–5]. Alkaline earth sulfides are excellent phosphor materials, and they have fascinated many researchers owing to their stimu­ lated PL and electroluminescence properties. The luminescence of rare earth and transition metal ion-doped alkaline earth sulfides like MgS, SrS, CaS, and BaS has been studied extensively during the last few decades [6]. Of these alkaline earth sulfides, CaS is an excellent luminescent material having a wide bandgap (4.5 eV) and size-tunable optical properties. Lehman studied the effect of a large number of activators and coactivators on the luminescence properties of CaS [7, 8]. Lehman's studies on CaS rejuvenated the investiga­ tions on alkaline earth metal sulfides and led to many works, which gave an insight into the various intrinsic point defects in these sulfides. Intrinsic point defects play a significant role in determining the luminescence properties of CaS. It has a face-centered cubic structure with space group Fm  3̅ m. CaS based phosphors find applications in TV screens, fluorescence lamps, thermoluminescence dosimetry, and high-pressure mercury lamps [9–11]. Alkaline earth sulfide phosphors are also good candidates for LED applica­ tions because all of them have strong absorption in the blue region that is suitable for blue LED pumping [12–14]. To generate white light of LEDs, the methods needed are (i) the combination of three diodes (red, green, and bluechip), (ii) accumulated yellow, green, or red phosphors on the blue LED chip, and (iii) integrated three phosphors (red, green, and blue) on the UV chip. Sulfide phosphors could be the phosphors in the future for color conversion for white LEDs [13, 14]. With the development of nanotechnology, nanophosphors are being extensively investigated due to their potential applications in various fields. The technological developments in the synthesis of semiconductor nano­ phosphors and the understanding of their optical properties have opened new application areas from display devices to biomedical detection, imaging, and treatment of various diseases [15]. CaS nanoparticles are cadmium-free nanoscale semiconductors, and tailoring the nanoparticles’ color output plays an important role in their application as light-emitting displays, field

Photoluminescence Investigations of UV, Near UV

15

emission displays, and various other optoelectronic devices. On doping with various dopants like rare-earth ions, the luminescence of CaS can be varied over the entire visible region. Rare-earth ions, also known as lanthanides, comprise an interesting group of elements including Europium, Cerium, Terbium, and Samarium, whose optical properties are determined by the inner 'f' electrons. Europium is an important rare earth element whose optical properties are derived from the incompletely filled 4f shell electrons. These electrons are shielded by the 5s and 5p closed shells, and hence they do not participate directly in bonding and interact much less strongly with the environment. Europium ions have been explored due to their PL properties, which result in the emission of sharp atomic bands corresponding to f → f transitions in the central metal ion. Eu3+or Eu2+ ion incorporation into the host lattice can be identified from the characteristic PL they exhibit. Eu2+ emission arises from the lowest band of 4f65d1 configuration to 8S7/2 state of 4f7 configuration. Eu3+ ions give unique narrow emission and absorption band, which arises due to the 5D0 → 7 FJ (J = 0, 1, 2, 3,…) electronic transitions of Eu3+ ions. Many simpler, cheaper, and eco-friendly synthesis routes such as wet chemical co-precipitation [16, 17], solvothermal [18], alkoxide [19], sol-gel [20], microwave [21], solid-state diffusion [22], and single-source precursor [23] methods have been employed by various researchers for the preparation of CaS nanophosphors. Sun et al. [16] have synthesized Europium doped CaS nanoparticles by wet chemical method for the first time. They examined the various factors that affect the fluorescence properties of the nanoparticles, like the concentration of dopant, annealing time, and temperature. The fluorescence intensity was found to increase with the increase in Europium concentration, and the highest quantum yield was obtained for a europium concentration of 0.85 mol.%. When the Europium concentration was higher or lower than this, a decrease in fluorescence intensity was observed, which shows concentration quenching. The nanoparticles formed had very low fluorescence intensity because of poor crystallinity, and therefore the samples were annealed at different temperatures. Both annealing temperature and time were varied, and it was found that for the synthesis of CaS:Eu nanoparticles with the highest fluorescence intensity, the optimal annealing condition was at 700°C for 2 h. The luminescence properties of micrometer-sized europium doped CaS synthesized using solvothermal method was studied by Haecke et al. [18]. The SEM images of uncapped CaS:Eu nanoparticles consisted of aggregates with sizes ranging from 500 nm to 1.3 μm, which are composed of 20–50 nm large grains. To control the growth of the crystallites, thioglycerol was

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added as a capping agent. The SEM images of CaS:Eu capped with 0.1 mL of thioglycerol consisted of monodispersed particles with a diameter in the range 600 nm to 1.5 μm. CaS:Eu phosphors were prepared by varying the amount of thioglycerol, and it was observed that thioglycerol does not restrict the size of the particles formed. Rather it acts as a catalyst for improving the reactivity of elemental sulfur. The as-obtained suspensions were strongly photoluminescent, pointing at proper Eu2+ incorporation. The CaS:Eu phosphors showed a PL emission band with an emission peak at 663 nm which is attributed to the transition between the excited state (T2g) of the 4f6 5d configuration and the ground state (8S7/2) of the 4f7 configuration of Eu2+ respectively. Here no post-deposition annealing was required to incorporate Eu2+ ions into the host lattice. CaS:Eu2+ nanoparticles were prepared by Sawada et al. [19] using two wet chemical procedures: (i) alkoxide method, (ii) co-precipitation method. From the dynamic light scattering (DLS) method, the particle size of the samples synthesized by the alkoxide method was found to be around 22 nm. The TEM micrographs of the sample prepared by the alkoxide method indicate that the diameter of primary particles is in the range 20–30 nm. The as-prepared samples did not show any emission. While heating samples prepared by both methods at 700°C in N2 atmosphere Eu2+ ions are incor­ porated into the CaS lattice and both samples exhibited red emission (628 nm) corresponding to the 4f65d1→4f7 transition of Eu2+. A slight blue shift in the emission peaks from the bulk value (633 nm) was observed due to a change in crystal field strength with nanosizing. The excitation peak corre­ sponding to the interband transition of CaS was observed at 268 nm for the alkoxide method prepared sample and at 254 nm for the sample prepared by co-precipitation method. These wavelengths were smaller than 273 nm obtained for bulk CaS. The intensity of the peak due to the interband transi­ tion for the sample prepared by the co-precipitation method was three times greater than that of bulk. Quantum size effect is confirmed by the increase in the probability of interband transition of CaS as well as the blue-shift of excitation peak due to its transition. Game et al. prepared CaS:Eu2+ nanoparticles by the carbothermal reduction of CaSO4:Eu, which was synthesized by wet chemical co-precipitation method [24]. The PL emission spectrum consisted of an emission band with a peak at 631 nm, which corresponds to an intense red emission. Burbano et al. reported the persistent and near-infrared photostimulated optical properties of CaS nanoparticles, CaS:Eu2+ and CaS:Eu2+, Dy3+ nanophosphors. They proposed a mechanism for the electron trapping after UV irradiation, and for persistent and near-infrared photostimulated luminescence for CaS,

Photoluminescence Investigations of UV, Near UV

17

CaS:Eu2+ (0.02 mol.%) and CaS:Eu2+ (0.02 mol.%) Dy3+ (0.002 mol.%) nanophosphors [25, 26]. Studies on the effect of rare earth dopants on the structural and optical properties of CaS nanoparticles are required in order to increase the scientific knowledge regarding their future PL applications. Only a few reports are available on the synthesis of nanosized Eu3+ doped CaS phosphors. In this paper, we report the tunable emissions of Eu3+ doped CaS nanophosphors synthesized by the solid-state diffusion method for different excitation wave­ lengths. The structural and optical characterization of the prepared samples is done using various experimental techniques. The Commission Internationale de l'Eclairage (CIE) coordinates have been evaluated, and the chromaticity diagram is also plotted. 2.2 EXPERIMENTAL A solid-state diffusion method was employed to synthesize europium-doped CaS nanophosphors. The solid-state diffusion method involves the mechanical mixing of solid constituents with repeated grindings and annealing at high temperatures, generally over a long duration. Calcium sulfate (CaSO4.2H2O, 99%, Merck), sodium thiosulphate (Na2S2O3.5H2O, extra pure, SRL, India), europium acetate [Eu(OOCCH3)3, Alpha caesar 99.9%], and carbon powder were the starting materials used for the synthesis. Sodium thiosulphate (15 wt.%) acts as the flux for the reaction, and carbon acts as the reducing agent that reduces calcium sulfate to calcium sulfide at high temperatures. The calculated quantities of calcium sulfate, sodium thiosulphate, europium acetate, and carbon powder were mixed by adding a small amount of 2-propanol by using an agate pestle and mortar. The mixture was dried in an oven at 80°C for some time. The mixture was then transferred to a clean alumina crucible, covered with another similar crucible, and fired at a temperature of 950°C for 2 hours to obtain the nanoparticles. The schematic diagram of the solid-state diffusion method for the synthesis of Europium doped CaS nanoparticles is shown in Figure 2.1. The x-ray diffraction (XRD) patterns were recorded to characterize the phase and crystal structure of the synthesized phosphors using a Bruker AXS D8 Advance X-ray diffractometer by using Cu-Kα lines (λ = 1.5406 Å). The morphology of the particles was studied using a Tescan VEGA 3 SBH model scanning electron microscope (SEM). The samples’ PL emission spectra were obtained using a Flouromax4C spectrofluorometer having a 150 W ozone-free Xenon lamp as an excitation source. The diffuse reflectance

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spectrum (DRS) was recorded with the help of a UV-Vis-NIR spectropho­ tometer (Varian, Cary 5000).

FIGURE 2.1 Schematic diagram of the solid-state diffusion method for the synthesis of europium doped CaS nanophosphors.

2.3 RESULTS AND DISCUSSION 2.3.1 STRUCTURAL ANALYSIS The XRD pattern of Eu (5 wt.%) doped CaS phosphors is displayed in Figure 2.2, which is in good agreement with the standard data available in JCPDS card No: 78–1922. The XRD pattern reveals that the products are well crystallized in a cubic structure. The average crystallite size of the particles formed was obtained from the Debye-Scherrer formula given by: D=

0.9λ β cos θ

(1)

where, D is the average crystallite size of the particles, λ is the wavelength of the Cu-Kα (1.5406 Å) radiation, β (in radian) is the full width at half maximum (FWHM), and θ is the Bragg angle [27]. Using the above formula, the average crystallite size of Europium doped CaS nanophosphors was calculated to be 40 nm. There are also some foreign peaks in the XRD pattern, which are due to the presence of minute impurities of Ca (OH)2 and CaO in the prepared samples. The structure of CaS was found to be cubic, and the lattice parameter was calculated using the equation:

Photoluminescence Investigations of UV, Near UV

d hkl =

a 2

h + k2 + l2

19

(2)

where, dhkl is the interplanar distance, a is the lattice parameter and h, k, l represents the Miller indices. The lattice parameter of the prepared samples was obtained to be 5.697 Å which is slightly greater than the literature value given by 5.689 Å which may be attributed to the strain experienced by the host lattice due to the addition of the dopant.

FIGURE 2.2 XRD pattern of Eu (5wt.%) doped CaS nanophosphors (starred peaks represents impurities).

The SEM micrographs of CaS nanophosphors doped with 5wt.% of europium are shown in Figure 2.3(a) and (b), which shows that the particles do not have a definite shape. SEM images show that the majority of the particles have flake-like morphology along with some hair-like projections. Also, there is a certain degree of agglomeration, which makes it difficult to determine the exact particle size. However, we can conclude that the crystal­ lites are of nanometer size, and they join together to form bigger particles. 2.3.2 OPTICAL STUDIES PL spectroscopy gives information about bandgap energy and various defect levels of nanostructures. Wide bandgap semiconductors are ideal materials for studies on trap states. Such localized energy states can be due to various types of imperfections present in the crystal-like vacancies, interstitial atoms, and dangling bonds, atoms at surface and grain boundaries.

20

FIGURE 2.3

Nanostructured Smart Materials

SEM images of Eu doped (5 wt.%) CaS nanophosphors.

The f-f transitions of Eu3+ are forbidden and PL emission of Eu3+ is in general weak unless there is excitation by charge transfer or energy transfer from a sensitizer. When they are incorporated into a host matrix, the luminescence can be improved by the intermixing of the 4f states with the ligands of the host matrix and excitation to d electronic states due to crystal field effects [28, 29]. The luminescence of Eu3+ ions can be efficiently sensitized via the energy transfer from the CaS host lattice to Eu3+, which thereby overcomes the inefficient direct absorptions of the parity forbidden 4f-4f transitions of Eu3+ ions. The emission lines for the Eu3+ ion usually appear in the visible region. These lines correspond to transitions from the excited 5D0 level to 7FJ (J = 0, 1, 2, 3, 4) levels of the 4f6 configuration of Eu3+ ions. In general, narrow emission bands may be observed at about 570, 590, 610, 650, and 700 nm corresponding to transitions 5D0 to 7F0, 7F1, 7F2, 7F3, 7 F4, respectively. Of these, three transitions which are of prime importance are 5D0 to 7F0 (around 570 nm), 5D0 to 7F1 (around 595 nm), and 5D0 to 7F2 (around 610 nm). The 5D0 to 7F1 transition is forbidden as electric dipole but allowed as magnetic dipole. This is the only transition when Eu3+ occupies a site coinciding with a center of symmetry. When Eu3+ ion is situated at a site, which lacks the inversion symmetry, then, the transitions corresponding to even values of j (except 0) are electric dipole allowed, and red emission can be observed [28]. The PL emission studies of CaS:Eu nanophosphors for excitation with UV, near UV and visible light were carried out at room temperature (RT). Figure 2.4 gives the PL emission spectrum of Europium doped CaS phosphors for an excitation wavelength of 290 nm. The PL spectrum at 290 nm consists of sharp peaks, which are a characteristic feature of rare-earth doping. The

Photoluminescence Investigations of UV, Near UV

21

emission peaks at 370 nm and 408 nm are due to the various defect levels present in the host lattice whereas the peaks at 572 nm, 590 nm, 614 nm and 758 nm originates due to the transition from the 5D0 levels to the 7FJ (J = 0, 1.2, …) levels in the 4f6 configuration of Eu3+ ions [30, 31].

FIGURE 2.4 290 nm.

PL emission spectrum of CaS:Eu nanophosphors at excitation wavelength

Figure 2.5 depicts the PL emission spectrum of europium doped CaS phosphors for an excitation wavelength 395 nm which consists of peaks at 536 nm (5D1→7F1), 590 nm (5D0→7F1), 614 nm (5D0→7F2), 650 nm (5D0→7F3) and 696 nm (5D0→7F4) respectively [29]. The peak at 590 nm corresponds to magnetic dipole moment transition, and it reflects the site symmetry of Eu3+ ions. The strongest emission band centered at 614 nm is an electric dipole transition (5D0→7F2) which indicates the absence of center of symmetry on activator incorporation [30–32]. It is observed that the intensity of the orange emission (590 nm) decreases while the intensity of the red emission (614 nm) increases with excitation wavelength. The emission spectrum of CaS: Eu at an excitation wavelength of 465 nm (Figure 2.6) consists of a broad peak centered at 635 nm with a shoulder around 590 nm. Here the ratio of intensities of the emission peaks due to (5D0→7F2) transition to the (5D0→7F1) transition is increased so that we obtain good quality red emission. So the defect state-related emissions are suppressed under an excitation wavelength of 465 nm, which implies an efficient energy transfer between the host and the rare earth ion.

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FIGURE 2.5 395 nm.

PL emission spectrum of CaS:Eu nanophosphors at excitation wavelength

FIGURE 2.6 465 nm.

PL emission spectrum of CaS:Eu nanophosphors at excitation wavelength

Commission Internationale de I'Eclairage (CIE), which was established in 1931, is an internationally accepted standard for quantifying visible colors. Luminescence spectrum from the sample can be represented by means of CIE color coordinates on a two-dimensional plane which gives the CIE

Photoluminescence Investigations of UV, Near UV

23

chromaticity diagram. The CIE chromaticity diagram of 5 wt.% of europium doped CaS phosphors for various excitation wavelengths are depicted in Figure 2.7. Table 2.1 gives the values of the chromaticity coordinates and the emission color for excitation wavelengths 290 nm, 395 nm and 465 nm. The chromaticity coordinates for an excitation wavelength 290 nm (0.38, 0.40) falls in the yellow region (point a) since the defect level emissions are also dominant as observed in the PL spectrum (Figure 2.4). For an excitation wavelength 395 nm, the chromaticity coordinates (0.33, 0.27) lie in the white region (point b) which is close to the standard white light point given by (0.33, 0.33) even though the emission spectrum consists of an intense peak in the red region (614 nm). This may be due to the overlapping of the red emission with the orange emission at 592 nm and defect-related emissions. The chromaticity coordinates for excitation wavelength 465 nm (0.57, 0.39) is in the red region (point c), and it agrees well with the PL emission spectrum shown in Figure 2.6.

FIGURE 2.7 CIE chromaticity diagram of CaS: Eu nanophosphors for excitation wavelengths (a) 290 nm (b) 395 nm and (c) 465 nm.

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TABLE 2.1 CIE Coordinates and Emission Color of CaS:Eu Nanophosphors for Different Excitation Wavelengths Excitation Wavelength (nm)

CIE coordinates

Emission Color

x

y

290

0.38

0.40

Yellow (point a)

365

0.33

0.27

White (point b)

465

0.57

0.39

Red (point c)

DRS have been extensively used as one of the most crucial tools for studying the bandgap energy (Eg) and band structures of semiconductors. When a material, consisting of nanoparticles is illuminated, some of the incoming radiation penetrates the sample and some are reflected from its surface. The part of the radiation that penetrates the sample is scattered by a large number of points in its path as well as it is transmitted through the particles several times. The portion of this radiation that returns back to the surface of the sample and emerges out is considered as the diffuse reflection. The DRS of CaS:Eu phosphor is measured in the wavelength range 300–800 nm at RT. The spectrum is depicted in Figure 2.8, which shows about 90% optical reflection in the visible region. From the DRS spectrum, the optical bandgap of the samples can be calculated from the plot of [k/s × hv]1/2 versus energy hv by employing the Kubelka-Munk relation [33, 34] which is given by: F ( R) =

(1− R ) 2R

2

=

k s

(3)

where, F(R) is the Kubelka-Munk function, R is the reflectance, k is the absorption coefficient and s is the scattering coefficient. The optical bandgap of CaS:Eu nanophosphors can be estimated from the plot of [k/s × hv]1/2 versus hv, which is given in the inset of Figure 2.8. The linear region of this curve is extrapolated to [k/s × hν]1/2 = 0 and the intersection between the linear fit and energy axis gives the value of the optical bandgap Eg. The optical bandgap of CaS:Eu nanophosphors is found to be 5.3 eV. An increase in bandgap compared to the bulk value of CaS (4.5 eV) is observed which may be attributed to the Burstein-Moss effect [35, 36] that comes into play at high concentration of the dopant ions. In nominally doped semiconductors, the Fermi level lies between the conduction band and the valence band. As the doping concentration is increased, the Fermi level is pushed to higher energy and will lie inside the conduction band. An electron from the top of

Photoluminescence Investigations of UV, Near UV

25

the valence band can only be excited into conduction band above the Fermi level, and an increase in bandgap will result. This is called Burstein-Moss effect. The shift in Fermi energy level prohibits the intermediate transition or interband transition through Pauli’s exclusion principle.

FIGURE 2.8

DRS [Inset: hυ vs. [(k/s) hυ]1/2 plot] of CaS:Eu nanophosphors.

2.4 CONCLUSIONS Europium doped CaS nanophosphors having an average crystallite size of 40 nm were synthesized using the solid-state diffusion method. SEM images of the nanophosphors consist of large aggregates composed of smaller crys­ tallites. The prepared samples exhibit yellow, white, and red luminescence depending on the excitation wavelengths. The PL emission peaks originate from the 5D0–7FJ (J = 0.1, 2.3…) transitions in the 4f6 configuration of the europium ions. Both defect-related emissions and dopant emission bands are observed for excitation wavelengths 290 nm and 395 nm. The defectrelated emissions from the host lattice are suppressed under an excitation wavelength of 465 nm and we obtain good quality red emission. The optical bandgap of the prepared nanophosphors is found to increase compared to bulk CaS due to the Burstein-Moss effect. The tunable emission of these

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26

phosphors finds application in solid-state lighting technology and various display devices. KEYWORDS • • • • • • •

alkaline earth sulfides bandgap diffuse reflectance spectrum morphology nanophosphors photoluminescence solid state diffusion

REFERENCES 1. Poelman, D., Van, H. J. E., & Smet, P. F., (2009). Advances in sulfide phosphors for displays and lighting. J. Mater. Sci: Mater. Electron., 20, S134–S138. 2. Jia, D., & Wang, X., (2007). Alkali earth sulfide phosphors doped with Eu2+ and Ce3+ for LEDs. Opt. Mat., 30, 375–379. 3. Yamamoto, H., Megumi, K., & Kasano, H., (1987). An orange emitting phosphor (Ca, Mg)S.Mn for terminal display tubes. J. Electrochem. Soc., 134, 1571–1573. 4. Poelman, D., Vercaemst, R., Vanmeirhaeghe, R. L., Laflere, W. H., & Cardon, F., (1995). The influence of Se-co-evaporation on the emission spectra of CaS:Eu and SrS:Ce thinfilm electroluminescent devices. J. Lumin., 65, 7–10. 5. Pham-Thi, M., (1995). Rare earth calcium sulfide phosphors for cathode ray tube displays. J. Alloys Compd., 225, 547–551. 6. Ghosh, P. K., & Ray, B., (1992). Luminescence in alkaline earth sulfides. Prog. Crystal Growth and Charact., 35, 1–37. 7. Lehman, W., (1972). Activators and coactivators in CaS phosphors. J. Lumin., 5, 87–107. 8. Lehman, W., & Ryan, F. M., (1971). Cathodoluminescence of CaS: Ce3 + and CaS: Eu2 + phosphors. J. Electrochem. Soc., 118, 477–482. 9. Kumar, V., Mishra, V., Biggs, M. M., Nagpure, I. M., Ntwaeaborwa, O. M., Terblans, J. J., & Swart, H. C., (2010). Electron beam induced green luminescence and degradation study of CaS:Ce nanocrystalline phosphors for FED applications. Appl. Sur. Sci., 256, 1720–1724. 10. Van, H. J. E., Smet, P. F., & Poelman, D., (2005). The formation of Eu2+ clusters in saturated red Ca0.5Sr0.5S: Eu electroluminescent devices. J. Electrochem. Soc., 152, H225–H228. 11. Kumar, V., Kumar, R., Lochab, S. P., & Singh, N., (2006). Thermoluminescence studies of CaS:Bi nanocrystalline phosphors. J. Phys. D: Appl. Phys., 39, 5137–5142.

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12. Game, D. N., Ingale, N. B., & Omanwar, K., (2016). Converted white light-emitting diodes from Ce3+ doping of alkali earth sulfide phosphors. Materials Discovery, 4, 1–7. 13. Rao, C. A., Rao, N. V. P., & Murthy, K. V. R., (2015). Synthesis, characterization, and photoluminescence properties of CaS:Eu3+ and SrS:Eu3+ for white LED. Adv. Phys. Lett., 2(4), ISSN online 2349–1108. 14. Oh, S. I., Jeong, Y. K., & Kang, J. G., (2009). Synthesis and luminescence properties of CaS: Eu2+, Si4+, Ga3+ for a white LED. Bulletin Korean Chemical Society, 30(2), 419–422. 15. Chander, H., (2005). Development of nanophosphors: A review. Mater. Sci. Eng., R49, 113–155. 16. Sun, B. Q., Yi, G. S., Chen, D., Zhou, Y., & Cheng, J., (2002). Synthesis and characterization of strongly fluorescent europium doped calcium sulfide nanoparticles. J. Mater. Chem., 12, 1194–1198. 17. Rekha, S., Martinez, A., Safeera, T. A., & Anila, E. I., (2017). Enhanced luminescence of triethanolamine capped CaS nanophosphors synthesized by wet chemical method. J. Lumin., 190, 94–99. 18. Haecke, J. E., Smet, P. F., De Keyser, K., & Poelman, D., (2007). Single crystal CaS:Eu and SrS:Eu luminescent particles obtained by solvothermal synthesis. J. Electrochem. Soc., 154, J278–282. 19. Sawada, N., Chen, Y., & Isobe, T., (2006). Low-temperature synthesis and photolumi­ nescence of IIA-VIB earth ions. J. Alloys. Comp., 408–412, 824–827. 20. Yang, P., Lu, M., Song, C., Gu, F., Liu, S., Xu, D., Yuan, D., & Cheng, X., (2002). Luminescence of CaS and MnS nanocrystallites co-activated sol-gel derived silica xerogel. J. Non-Cryst. Solids, 311, 99–103. 21. Roy, A., & Bhattacharya, J., (2012). Microwave-assisted synthesis of CaS nanoparticles. Int. J. of Nanoscience, 11, 125007–1250027(1–6). 22. Kumar, V., Pitale, S. S., Mishra, V., Nagpure, I. M., Biggs, M. M., Ntwaeaborwa, O. M., & Swart, H. C., (2010). Luminescence investigation of Ce3+ doped CaS nanophosphors. J. Alloy Compd., 492, L8–L12. 23. Zhao, Y., Rabouw, F. T., Donega, C., Meijerink, A., & Walree, C., (2012). Single source precursor synthesis of colloidal CaS and SrS nanocrystals. Mat. Lett., 80, 75–77. 24. Game, D. N.,. Katore, B. K., Ingale, N. B., & Omanwar, S. K., (2012). Synthesis and luminescent properties of europium doped calcium sulfide. Sci. Revs. Chem. Commun., 2(3), 305–307, ISSN: 2277–2669. 25. Burbano, D. C., Rodríguez, E. M., Dorenbos, P., & Capobianca, J. A., (2014). The near-IR photostimulated luminescence of in CaS:Eu2+/Dy3+ nanophosphors. J. Mater. Chem., C2, 228–233. 26. Burbano, D. C., Sharma, S. K., Dorenbos, P., Viana, B., & Capobianca, J. A., (2015). Persistent and photostimulated red emission in CaS:Eu2+, Dy3+ nanophosphors Ad. Opt. Mat., 3, 551–557. 27. Cullity, B. D., (1978). Elements of X-ray Diffraction (2nd edn., p. 102). Addison-Wiley Pub Co, Reading: Massachusetts. 28. Luo, W., Liu, Y., & Chen, X., (2015). Lanthanide doped semiconductor nanocrystals: Electronic structures and optical properties. Sci. China Mater., 58, 819–850. 29. Binnemans, K., (2015). Interpretation of europium III spectra. Coordination Chemistry Reviews, 295, 1–45.

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30. Huo, Q., Tu, W., & Gio, L., (2017). Enhanced photoluminescence property and broad color emission of ZnGa2 O4 phosphor due to the synergistic role of Eu and carbon dots. Opt. Mat., 72, 305–312. 31. Wani, J. A., Dhoble, N. S., Kokode, N. S., & Dhoble, J. S., (2014). Synthesis and photoluminescence property of Re3+ activated Na2Ca P2O7 phosphor. Adv. Mat. Lett., 5(8),459–464. 32. Xu, B., Li, D., Huang, Z., Tang, C., Mo, W., & Ma, Y., (2018). Alleviating luminescence concentration quenching in lanthanide-doped CaF2 based nanoparticles through Na+ ion doping. Dalton Trans., 47, 7534–7540. 33. Kubelka, P., & Munk, F., (1931). Ein beitrag zur optik der farbanstriche. Zh. Tekh. Fiz., 12, 593–620. 34. Kubelka, P., (1948). New contributions to the optics of intensely light-scattering materials: Part 1. J. Opt. Soc. Am., 38, 448–457. 35. Selloum, D., Henni, A., Karar, A., Tabchouche, A., Harfouche, N., Bacha, O., Tingry, S., & Rosei, F., (2019). Effects of Fe concentration on the properties of ZnO nanostructures and their application to photocurrent generation. Solid-State Sciences, 92, 76–80. 36. Sharma, G., Chawla, P., Lochab, S. P., & Singh, N., (2011). Burstein-Moss effect in nanocrystalline CaS: Ce. Bull. Mater. Sci., 34, 673–676.

CHAPTER 3

Nanomaterial Aspect of Drug Delivery Towards Cancer Therapy AHMADUDDIN KHAN and NIROJ KUMAR SAHU Centre for Nanotechnology Research, VIT, Vellore–632014, Tamil Nadu, India, E-mails: [email protected] (A. Khan), [email protected] (N. K. Sahu)

ABSTRACT Biodistribution of anticancer drugs in the human body is the main problem due to its detrimental impact on the normal tissues. The conventional cancer treatments have a lot of drawbacks, and hence nanomaterial mediated drug delivery systems are getting importance due to their targeting abilities either by passive enhanced permeability and retention (EPR) effect or by active targeting with attached moieties. Multifunctional nanoparticles (NPs) can carry an optimum quantity of drugs to achieve a high local concentration at the tumor location, facilitating cancer treatment. This book chapter discusses the basics of drug delivery, different nanomaterials used as cargo for drug delivery, and subsequent stimulus-responsive delivery for chemotherapy of cancer. 3.1 INTRODUCTION Cancer is characterized by uncontrolled growth and spread of abnormal cells. Millions of new cancer cases arise year by year. Cancer is the second most common reason for death in the United States, which is only behind heart ailments [1]. Many different types of therapies are available for cancer treatment, like radiation therapy, surgery, hormonal therapy, chemotherapy, immunotherapy, and hyperthermia. There are basically four stages of cancer. In stage-I, the tumor is in small size and remains in the organ from where it

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has been generated. In stage-II and III, the size becomes larger and grows into lymph nodes and the surrounding tissues. In stage-IV, cancer gets metastasized and spreads to other body organs. In radiation therapy, ionizing radiation like X-ray/γ-ray is used to kill cancer cells and to shrink the tumors. Surgery can cure if the cancer cells haven’t metastasized. Immunotherapy utilizes an immune system of the person to fight against cancer. In hormonal therapy, either administering or blocking hormones would be beneficial to inhibit tumors whereas, in hyperthermia, tissues are exposed to higher temperatures of about 42–45°C, resulting in the death of malignant cells. Cancer that spreads to different parts of the body needs more rigorous and inclusive therapies which require chemotherapy as the first line of treatment [2–4]. Chemotherapy is a kind of cancer therapy which uses anticancer drugs to kill the quickly dividing cancer cells. With respect to that, nanomaterials are of great interests and are getting substantial attention for the progress of a new generation of drug delivery systems. Nanoscale science and engineering gives unparalleled knowledge and control of matter at its fundamental level of atomic and molecular scale. The nanoscale materials are gaining plenty of attention due to their uncommon magnetic, optical, and electronic properties [5–7]. Further, nanomaterials are ideal for surface modification with various functional groups. Due to their small size, the nanostructures are having distinctive biological and physicochemical properties such as higher reactive surface area and capability to go across the cell and tissue barrier that makes them suitable material for specific biomedical applications [8]. Nanoparticles (NPs) are the particles having an average size in the range of 1–100 nm in any of its dimensions. The advantage of using NPs for drug delivery systems is that its surface can be modified with various organic moieties, which help to load different types of drugs and delivers to the exact tumor site with or without the help of any targeting agent. The NPs of optimum size allows ease of interaction with the biological system while the NPs material framework gives stability, specificity, and self-assembly, which are essential for encapsulation of drug and biocompatibility [9, 10]. Different kinds of nanocarriers generally used in preclinical and clinical studies are given in Figure 3.1(a). To make nanocarrier stealth for avoidance from reticuloendothelial system (RES), its surface can be modified with polyethylene glycol (PEG), gelatin, dextran, chitosan (CS), pullulan, etc., and can be surface functionalized with different targeting ligands. Recent developments in the area of cancer nanotechnology has paved the way for the development of NPs based cancer therapy depending upon the patient’s molecular profile [9, 10]. This chapter consists of an overview of

Nanomaterial Aspect of Drug Delivery

31

the different conventional and nanomaterial-based drug delivery cargo used for precise cancer therapy and their pros and cons.

FIGURE 3.1 (A) Different nanomaterials used in preclinical and clinical studies and (B) PEGylated and ligand attached NPs. Source: Reprinted with permission from Ref. [11]. © 2010 Elsevier.

3.2 CHEMOTHERAPY Chemotherapy term denotes the use of anticancer drug which can halt the cancerous cells from dividing. It averts the disease by cell killing as they divide. It can cause some serious side effects to the patient, and hence extensive care is needed. Depending upon the individual and on cancer’s stage, chemotherapy can remove the cancer cells and will suspend the symptoms on a long-term basis. Chemotherapy is one of the most widely used treatments for cancer. Though it provides satisfactory results, it affects

32

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both cancerous and normal tissue causing unwanted side effects. In fact, due to the differences in genetic makeup, all the patients cannot respond to the treatment to a similar extent [12]. One example is an expression of single nucleotide polymorphism in enzymes requires for the metabolism of drugs and it can influence the target drug’s affinity constant and drug metabolism rate. Thus, there is a change in the effective half-lives and rate of the elimination of drugs in the body. In this regard, there is a need to advance new techniques to identify and deliver the drugs at their specific target for the efficacious killing of cancerous cells and nanomaterials-based drug carriers play an important role in this direction [12]. Some of the Food and Drug Administration (FDA) approved anticancer drugs are tabulated in Table 3.1. 3.3 DRUG TARGETING: ADVANTAGE AND DISADVANTAGE There are different advantages of targeted drug delivery like simplified methods for the administration of drug, decrease in the quantity of drug as well as the price of therapy. The concentration of the drug will increase at the targeted sites in comparison to other region thereby, side effects can be decreased. In the same line, there are some disadvantages too, such as rapid clearance of targeting carriers if not properly surface-modified, immune reactions from the immune system for carriers which are administered intravenously, inadequate localization of carriers into tumor cells, etc. [15] Conventional intravascular or oral approaches led to the distribution of drugs throughout the body and only a minimal quantity of the therapeu­ tics reaching the tumor location. Drug targeting towards the tumor will increase the amount of drugs in the tumors instead of the healthy tissues resulting in the increase of the treatment efficiency and minimizing the side effects [14, 15]. 3.4 IDEAL CHARACTERISTICS OF TARGETED DRUG DELIVERY SYSTEM Nanocarriers utilized for targeting should be biocompatible or non-toxic to the normal healthy tissues. It should be chemically and physically stable both in in-vitro and in-vivo. It ensures the distribution of drug only towards the target cells or tissues or organs, and its capillary distribution should be uniform. Drug release rate should be controlled and predictable. The action

Some of the Anticancer Drugs Approved by FDA

Drug

Therapeutic Class

Target gene

Methotrexate

Leukemia, head, and neck cancer, bone cancer, gestational trophoblastic disease, lymphoma, lung cancer, breast cancer

DHFR

Chlorambucil

Leukemia, lymphoma

DNA synthesis

Vincristine sulfate

Leukemia

TUBB, TUBA4A

Fluorouracil

Breast cancer, stomach cancer, pancreatic cancer, colorectal cancer

DNA synthesis

Doxorubicin hydrochloride (DOX)

Breast cancer, ovarian cancer, lung cancer, sarcoma, thyroid cancer, kidney cancer, brain cancer, leukemia, lymphoma, bladder cancer, stomach cancer

DNA synthesis, TOP2A

Cisplatin

Bladder cancer, ovarian cancer, testicular cancer

DNA synthesis

Carboplatin

Ovarian cancer

DNA synthesis

Paclitaxel

Breast cancer, pancreatic cancer, sarcoma, lung cancer, ovarian cancer

TUBB1, TUBA4A

Docetaxel

Breast cancer, head and neck cancer, stomach cancer, brain cancer, prostate cancer, lung cancer

TUBB1, TUBA4A,

Gemcitabine

Pancreatic cancer, breast cancer, lung cancer, ovarian cancer

RRM1, DNA synthesis, TYMS

Nanomaterial Aspect of Drug Delivery

TABLE 3.1

Source: http://creativecommons.org/licenses/by/4.0/. Data from Ref. [13]; (Open access).

33

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Nanostructured Smart Materials

of the drug should not be affected by drug release, and it should release the optimum amount of drug. The drug leakage should be least during movement. Further, the nanocarriers should be biodegradable or get rapidly cleared from the body without any disturbance after the therapeutic function. For example, kidney filtration is an advantageous pathway to get the NPs cleared as the health hazards emerging due to decomposition and extended accumulation of NPs in the body can be reduced [16, 17]. But the passage of the NPs through the kidney relies heavily on its surface charge, size, and shape due to the distinctive glomerular capillary wall structure [17, 18]. The glomerular capillary wall consists of three different layers. Due to the effects of all the layers, a globular NPs having a hydrodynamic diameter (HD) less than 6 nm is able to pass easily through the glomerular capillary wall. However, it is tough for the larger one having HD more than 8 nm [17, 18]. Since the charge of the glomerular capillary wall is negative, a NP having HD 6–8 nm with a positive charge and little larger than kidney filtration threshold (KFT) is able to pass the kidney filtration barrier because of suitable charge interactions while it is difficult for the neutral or negative charged NPs having same HD [17, 19]. Shape of the NPs also plays an important role in the filtration process by kidney because the shape of the glomerular basement membrane (GBM) slit is rectangular [17, 20]. Hence larger NPs which are linear in structure having width lesser than KFT can be filtered by kidney [17]. The nanocarrier system should be simple and easy to manufacture in a cost-effective and reproducible way. In a report, a biodegradable novel drug delivery system (CM) is designed based on selfassembly of delaminated CoAl-layered double hydroxides (LDHs) which acts as a basic positive charged unit and manganese dioxide (MnO2) as a negative charged unit. For better targeting folic acid (FA) was attached to CM by covalent bond, thus forming FA-CM [21]. Results show that this FA-CM have dual stimuli-responsive drug release based on pH and glutathione (GSH) and it can well degrade into Mn2+, Al3+ and Co2+ in cancerous cells. Co is an important trace element of human body. The human body can easily excrete Al, and it is non-toxic if consumed not more than 40 mg/day/kg of body mass. Mn is crucial for metabolism, development, and antioxidant system. This system can load both positive and negative charged drugs such as DOX and sulforhodamine B optionally. Hydrophilic DOX and hydrophobic paclitaxel (PTX) were used as model drugs to load on FA-CM to obtain synergistic combination therapy. Drug release profiles of FA-CM@DOX show higher release rate either in pH 5.8 or in the presence of GSH, because it mimics the tumor’s acidic environment, due to the reduction of MnO2 and

Nanomaterial Aspect of Drug Delivery

35

degradation of CoAl-LDHs. A further increment was observed when merged with low pH and GSH. About no release of drug has been observed at pH 7.4 [21]. In another report poly(vinylcaprolactam) termed as PVCL-based microgels were prepared by precipitation polymerization method by addition of disulfide-bonded cross-linker N,N-bis(acryloyl) cystamine (BAC) for the formation of a biodegradable, biocompatible, robust, and smart drug delivery system which can release drugs due to redox potential, pH, and temperature. Microgel consists of an interior network of BAC cross-linked polymer consist of temperature-sensitive PVCL and pH-sensitive poly(methacrylic acid) and the PEG-rich corona which stabilizes the particles. Microgel is stable under physiological conditions but undergoes volume phase transition temperature with change of pH and mass of methacrylic acid (MAA) and degrades quickly due to the breaking of disulfide bonds in reductive environment. After degradation of polymer, it will be easily excreted out by the excretory pathway. DOX encapsulation efficiency was 53.6% [22]. 3.5 TYPES OF DRUG TARGETING 3.5.1 PASSIVE TARGETING Passive targeting utilizes the characteristics of the tumor biology, which makes the NPs release the anticancer drugs into the tumor cells by enhanced permeability and retention (EPR) effect. Leaky blood vessels and abnormal lymphatic drainage are the two common characteristics of the tumor cells. Tumor vascular leakiness is caused by increased cytokines, angiogenesis, and some other vascular active factors which can cause enhanced permeability. Angiogenesis in tumor means irregular size and shape or structure of vasculature organs like arteries, venules, and capillaries [23]. NPs which are utilized in the drug delivery system must be larger enough in size to avert their outflow into capillaries, and they should be smaller enough so that they cannot be captured by macrophages present in RESs like spleen and liver. Sinusoid’s size in spleen and fenestra in liver’s endothelial lining is 150–200 nm and gap junction size between endothelial cells of the leaky tumor vasculature is in the range of 100–600 nm. Therefore, NPs size must be up to 100 nm so that it can reach the tumor by crossing these two kinds of vasculatures [24, 25]. EPR effect would be effective if the NPs are capable to evade the immune system and circulate in the blood for a longer duration. Thus, a high concentration of drug loaded NPs can be attained at

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the tumor location, which is 10 to 50 times more as compared to normal tissue within 1 to 2 days [26]. Ideally NPs size must be in between 10–100 nm and its surface charge must be either neutral or anionic to escape from the elimination through the renal system. It should not get captured from RES otherwise opsonization and then phagocytosis will occur [11, 27]. 3.5.2 ACTIVE TARGETING Active targeting are the particular interactions present in between the target cells and the drug or drug carrier system, normally due to particular ligand­ receptor interactions [28–30]. Such kind of interactions happens only when the two entities are very close to each other (less than 0.5 nm). Active targeting, as suggested by the name is a way of guiding drug/drug carrier towards a target similar to a cruise missile [28]. In this kind of targeting, NPs are functionalized with targeting ligands so that it can be attached to the specific receptor expressed at the tumor tissue particularly [11]. Prolong circulation time is needed for the efficacious transport of NPs to the tumor tissue by EPR effect and increment of the endocytosis of NPs by the targeting molecule. The therapeutic effect increases due to internalization of NPs-based drug delivery system [31–33]. Ligands which are grafted to the NPs surface for targeting may act as a homing device, thus improves the drug delivery to the particular cells and tissues [34, 35]. Few examples of targeting moieties are FA and folate grafted NPs or folate drug conjugates, which binds to the folate receptor and carry the bounded molecules inside the cells by receptor-mediated endocytosis [36]. A serum glycoprotein transferrin binds to the transferrin receptor and carry iron via blood and into cells, and is further internalized by receptor-mediated endocytosis. There is a high level of expression of the transferrin receptor in the cancerous cells up to 100 times more in comparison to the normal cells with average expression [11, 24, 37]. 3.6 DIFFERENT NANOPARTICULATE SYSTEMS FOR DRUG DELIVERY Different types of inorganic and organic nanomaterials are available for utilization in drug delivery. Each of them is having their own properties and can be modified accordingly for biological purposes.

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3.6.1 ORGANIC NPS FOR DRUG DELIVERY 3.6.1.1 LIPOSOMES Liposomes are phospholipid vesicles that consist of single or multiple concentric lipid bilayers that enclose the distinct aqueous space. They have a unique capability to store hydrophilic and lipophilic compounds as a result, a broad range of drugs can be stored in these materials. Hydrophobic substances can be stored in the bilayer, and hydrophilic substances can be stored in the aqueous center [38, 39] as shown in Figure 3.2. Loading of the drug into liposome can be done either by synthesis of the liposome in aqueous solution which is saturated with the dissolved drug or by the usage of organic solvents and solvent exchange techniques or by usage of lipophilic drugs or pH gradient methods [40, 41]. Nanoliposomes reach their specific target both by active and passive targeting [42, 43]. Liposomes can do active targeting by utilization of antibody-based approach. A pendant type immunoliposome was designed in which antibodies were conjugated to the PEG chain at its distal end. This pendant type immunoliposome showed better targeting ability to the target site of solid tumor tissue and lung endothelial cells in comparison to ordinary liposome mainly because of free PEG chains which helped to avoid uptake of immunoliposome by RES, results in more blood concentration and increment in the immunoliposomes target binding [44]. Lee et al. reported the co-delivery of cisplatin and DOX by a single polymer caged nanobin (PCN). This PCN composed of liposomal core which encapsulate DOX and protected by a polymer shell (with tunable drug ratios) loaded with cisplatin prodrug and is pH-responsive. Cytotoxicity analysis shows an enhanced therapeutic efficiency of each drug at low doses in a synergistic way in comparison to the combinations of free drugs or separately nanopackaged drugs [45]. One of the major developments in the area of the drug delivery is the ability of liposomes to counter the rising issue of multidrug resistance (MDR) of cancer which extremely reduces the efficiency of chemotherapeutics. Suggested mechanisms for the MDR at the cellular level are related to increment in the drug metabolism due to the increment of the expression of enzyme mainly of glutathione S-transferase, transporters of drugs and efflux proteins [41, 46], proteins acquired point mutation which is the drug or therapeutic targets [41]. Nanoliposome releases the entrapped drug slowly thus get sustained subjection towards the target with increased efficiency.

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FIGURE 3.2 Various kinds of liposomal drug delivery system (A) Conventional liposome: It contains lipid bilayer which consists of anionic, cationic or neutral (phospho)lipids and cholesterol which encloses the aqueous core. Aqueous space and lipid bilayer both can store hydrophilic and hydrophobic drugs, respectively. (B) PEGylated liposome: To sterically stabilize the liposome. (C) Ligand targeted liposome: By attaching ligands like peptide, antibody, and carbohydrates, liposome can be used as a targeting agent. (D) Theranostic liposome: System consists of NPs, targeting part, imaging part, and therapeutic part. Source: Reprinted from Ref. [39]. Creative Commons Attribution License (CC BY); (Open access).

3.6.1.2 CHITOSAN NPS Chitosan (CS) is a very commonly used biopolymer for the synthesis of NPs due to its distinctive structural features. It stimulates cross-linking with different types of cross-linkers like sodium tripolyphosphate (TPP), glutaraldehyde, geneipin, etc., to make a well-organized network to attach the drugs in the NPs [47]. Since these CS NPs possess relatively good blood survival time and little RES uptake because of its small size, it can be used to target the tumor area through the abnormal vasculature of the tumor tissue known as the EPR effect [42]. Common procedures used for the synthesis of CS NPs are coacervation/precipitation based methods, self-assembly,

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ionic gelation, reverse micellar methods, and emulsion-based methods [48]. Different formulations of CS in the delivery of drug and other biomedical applications together with the method of preparation are represented in Figure 3.3. CS exhibits antitumor property itself due to its positive charge that has the ability to neutralize the charge of tumor cell surface, which is negative and helps in selective absorption [49]. DOX incorporated Carboxymethyl CS NPs grafted with methoxyPEG possess high cellular toxicity and can stop the cancer cell proliferation [50]. CS NPs loaded with paclitaxel at different ratio with encapsulation efficiency ranging from 32.2 ± 8.21% to 94.0 ± 16.73% shows sustained drug release effect [51]. Cytotoxicity analysis proves that paclitaxel- CS NPs have greater toxicity compared to that of paclitaxel itself along with more cellular uptake efficiency [51]. Chitosan NPs and its ammonium quaternary derivative (O-HTCC) can be loaded with DOX, and results showed that DOX release doesn’t depend upon molecular weight of polymer instead depends upon pH. Encapsulation efficiency was above 70% for CS NPs and around 50% for O-HTCC [52].

FIGURE 3.3 Various types of drug delivery systems based on chitosan (oval-shaped) and their various methods of preparation (rectangle-shaped). Source: Reprinted with permission from Ref. [60]. © 2018 Elsevier.

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A system made up of CS/poly(ethylene glycol)-glycyrrhetinic acid (CTS/ PEG-GA) NPs was manufactured by ionic gelation with glycyrrhetinic acid as a targeting agent. Results showed a high level of accumulation (~ 50%) in the rat liver due to the presence of a targeting agent. CTS/PEG-GA NPs loaded with DOX manifests extraordinary cytotoxicity in QGY-7703 cells and can inhibit tumor growth effectively in mice bearing H22 cells [53]. CS manifests different features which increase its usefulness as a drug delivery cargo such as mucoadhesive nature and capability to temporarily open tight epithelial junctions. Aforementioned ability of CS has been used in drug delivery for different kinds of epithelia like nasal [54], intestinal [55, 56], ocular [57], buccal [58], and pulmonary [59]. 3.6.1.3 SOLID LIPID NPS (SNPS) Solid lipid NPs (SLNPs) were made as a substitute lipid-based nano-system like micelles, emulsions, liposomes, and polymeric NPs. Compared to synthetic non-biodegradable polymeric NPs, the lipids which are biocompatible, e.g., cetyl palmitate, cetyl alcohol compritol®888 ATO, tristearin/Dynasan®118, precirol®ATO5, glyceryl monostearate, trimyristin/Dynasan®114, imwitor ®900, stearic acid, etc., are used in the formation of SLNPs that can be easily tolerated physiologically during in vivo administration. They can also be formed without using organic solvents which are toxic [61, 62]. SLNPs containing lipids remains solid at both room and body temperature. Several procedures have been devised for the formation of SLNPs using biocompatible lipid or molecules of lipids having a safe use history in the field of medicine [63]. They can be prepared by using different solid lipids like waxes, steroids, fatty acids, mono-, di-, and triglycerides, etc., [64, 65]. Various surfactants such as poloxamer, phospholipid, and polysorbates which can sterically stabilize the NPs can be used for the formulation [64]. Different strategies have been adopted to utilize SLNPs as a drug delivery carrier. It is combined with iron oxide magnetic nanoparticles (IONPs) to use it as heating elements for control therapeutic efficacy. Solid lipid matrices are melted using magnetic heating to release the entrapped drug [66], and the rising of temperature is called hyperthermia [67]. This can elevate the immune response for nonspecific immunotherapy of particular diseases. Another strategy for drug delivery is the use of pH-sensitive SLNPs. DOX loaded SLNPs was prepared by Subedi and co-workers by solvent emulsification diffusion method [68]. The lipid core used was Glycerylcaprate (Capmul®MCM C10) and shell material was curdlan. To dissolve both lipid and drug, dimethyl

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sulfoxide was used. The entrapment efficiency and drug loading capacity was 67.5 ± 2.4% and 2.8 ± 0.1%. At lower pH high release rate of DOX was achieved [68]. Camptothecin (CPT) prodrug loaded to SLNPs for oral drug delivery [69]. First, CPT-palmitic acid conjugate was made via a breakable disulfide bond linker (CPT-SS-PA) and encapsulated on SLNPs that gives association efficiency of around 93.0 ± 2.6% [69]. It is a redox responsive system which releases CPT after CPT-SS-PA SLNPs internalization because of elevated GSH expression which produce reducing environment in tumor (suggested). CPT-SS-PA SLNPs redox-sensitive property was studied in a reducing medium containing DL-dithiothreitol (DTT) [69]. 3.6.1.4 ALBUMIN-BASED NPS Albumin-based NPs cargo presents a fascinating approach as the noteworthy quantity of drug can be loaded into the matrix of the particle because albumin molecule have various drug binding sites [70]. Albumin NPs provides various advantages such as they are biodegradable, reproducible, and easy to prepare. Its matrix is potentially used for attachment of drugs due to elevated protein binding of different drugs [71]. With the EPR effect, albumin NPs have the capability to target passively based on the leaky vasculature (Which is still debatable). For example, inflammatory rheumatoid arthritis in which plasma proteins is more permeable to the blood joint barrier having six times more increment in permeability for albumin [72]. Abraxane, also called nab-paclitaxel is an albumin NPs based drug and first to get approval for human use from FDA. Anticancer drug paclitaxel bound to human albumin NPs of size ~130 nm [73]. Compared to free paclitaxel, bound one is having more circulation half-life and the absence of Cremophor EL® solvent which induces hypersensitivity [41, 73]. Kim et al. have prepared curcumin-loaded human serum albumin NPs by using albumin-bound technology. The particles were in a size range of 130–150 nm having greater water solubility (300 fold) compared to free curcumin with insignificant activity loss upon storage [74]. In recent research, Bovine serum albumin (BSA) molecules were self-assembled with DOX, which a typical hydrophobic drug to form DOX@BSA NPs. Then aptamer AS1411 was conjugated on the DOX@ BSA NPs surface to form DOX@Apt-BSA. The NPs modified with aptamer show increased cellular uptake and cytotoxicity against MCF-7 cells in comparison to the NPs with no aptamer modification [75]. Recent research reports theranostics use of albumin-based NPs. It is reported that addition of suitable near-infrared absorbing dyes, e.g., croconine and administering

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intravenously, the albumin-dye NPs get accumulated in the tumor location and functions both as photoacoustic pH imaging and pH-responsive photothermal ablation for the treatment of big tumors [76]. 3.6.1.5 GELATIN NPS Gelatin is a denatured protein processed through hydrolysis of animal collagen either in acidic or alkaline solution. The FDA recognized it as a generally recog­ nized as safe (GRAS) material due to its long history of safe use in cosmetics, food products, and pharmaceuticals [77, 78]. Upon degradation by the enzyme, gelatin doesn’t give any harmful by-product as it is obtained from collagen [78, 79]. Gelatin NPs are widely used for specific drug targeting and controlled release along with minimal cytotoxicity [80]. It has the ability to do passive targeting due to the EPR effect, and thus, the NPs have enough time to be at the tumor site to release the loaded drugs even with lower frequency and dose [78, 80]. Gelatin NPs conjugated with epidermal growth factor (EGF) were used to target lung cancer that showed overexpression of the EGF receptor. EGF conjugated gelatin NPs loaded with DOX can be inhaled to enhance the efficacy of the drug and to lower its side effects [81]. Gelatin NPs are capable of crossing blood-brain barrier. Hence they can be loaded with cardamom extract to utilize it as a drug delivery system to treat glioblastoma [82]. 3.6.2 INORGANIC NPS FOR DRUG DELIVERY 3.6.2.1 IRON OXIDE NPS Iron oxides have different crystalline forms such as hematite (α-Fe2O3), maghemite (γ-Fe2O3), wustite (Fe-O), magnetite (Fe3O4) and some other different high pressure stabilized amorphous forms [83]. Among them, maghemite and magnetite are widely used for the biological applications [84]. Superparamagnetic iron oxide nanoparticles (SPION) provide a wide area of applications like magnetic resonance imaging (MRI), drug delivery, magnetofection, and hyperthermia [85] (Figure 3.4). SPION can be functionalized with amino acids, silica, polymers, and some organic compound to obtain optimum physical and chemical properties. Different FDA approved polymers such as PEG, polycaprolactone, polylactic-co-glycolic acid, polylactic acid, CS, dextran, etc., can be used to integrate with the SPION [86]. Several artificial biocompatible polymers are also used for coating, e.g., PEG copolymer with various unique

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formulations. This provides elucidated properties for delivery of drug in terms of stability, functionalization, and drug release. PEG-diacid, a functionalized PEG was used to coat mesoporous MgFe2O4 with high specific surface area and magnetization for chemo-thermal therapy. Up to 90% of the cancer cell death was reported when cells were treated with drug-loaded conjugate along with magnetic hyperthermia due to synergistic effect [87]. SPION can also assist in the generation of reactive oxygen species (ROS) for cancer treatment [88, 89]. Due to acidic environment of tumor, SPION releases Fe ions that can catalyze H2O2 by Fenton reaction which generate ROS such as hydroxyl and hydroperoxyl radicals. These radicals can oxidize cell membrane, lipids, proteins, etc. [90].

FIGURE 3.4 Use of magnetic nanoparticles for cancer: diagnosis and therapy. Source: Reprinted with permission from Ref. [91]. © 2015 Elsevier.

3.6.2.2 GOLD NPS Gold NP possesses many features in terms of physical, chemical, optical, and electronic properties and is used in various fields of nanomedicine

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[92–94]. Generally, gold NPs are prepared by reducing chloroauric acid chemically [95]. Gold NPs can be loaded with anticancer drugs either by covalent or non-covalent bonds. Paclitaxel can be conjugated to gold NPs by covalent bond [96]. Gold NPs can be cross-linked with pH-responsive systems such as DOX is conjugated to gold NPs by a hydrazone linker, and the drug delivery can be on-demand [97]. Toxicity of gold NPs vary with its surface charge, e.g., positively charged gold NPs at lower concentration causes cell death while neutrally charged particles can cause cell death only at remarkably higher concentrations [98]. Gold NPs stabilized with poly (bis(carboxyphenoxy) phosphazene) was synthesized as a charge reversal nanohybrid system triggered by pH. It was loaded with CPT and tested against the MDA-MB-231 breast cancer cell line. Results showed that it can potentially decrease the drug loss in normal tissue, and drug gets released intracellularly in cancer cells [99]. In another strategy, gold NPs was capped with fucoidan, which is a sulfated polysaccharide that occurs naturally and is a magnificent drug candidate. Fucoidan was used as capping agent and reducing agent as well. It is then conjugated with DOX (Figure 3.5) [100]. 3.6.2.3 MESOPOROUS SILICA NPS Among different inorganic nanomaterials, mesoporous silica NPs (MSN) are a potential material for biomedical applications. MSN are utilized for MRI, optical imaging, photodynamic therapy, and drug delivery [101–104]. Due to its high pore volume and surface area, it can carry high payloads of the drug [105]. MSN can be functionalized with various organic moieties such as PEG [106], polyethylenimine [107], CS [108] p(NIPAM-co-MA) [109] and used for drug delivery and release. Surface tailoring can be utilized to avoid unnecessary biological interactions, enhance bioavailability and cellular uptake, and diverting the system from the immune scrutiny [105]. MSN possesses a high specific surface area (600–1000 m2/g) and pore volume (0.6–1.0 ml/g) and is suitable for high drugs payload [105]. The drug loading can be done through physical adsorption and solvent evaporation [110]. It is reported that MSN soaked in a solution-containing drug till the equilibrium when all drug molecules physically adsorbed into the pore channel [111]. In solvent evaporation, the drug is loaded by amalgamation of physical adsorp­ tion followed by rapid evaporation of solvent [112]. A hydrophobic drug CPT loaded on mesoporous silica NPs and tested on different cancer cell lines. Results proves inhibitory effect on the growth of three pancreatic cell lines (Capan-1, PANC-1, AsPc-1), one stomach cancer cell line (MKN45) and one

Nanomaterial Aspect of Drug Delivery 45

FIGURE 3.5 Scheme for the synthesis of fucoidan capped gold NPs and then DOX loading. Source: Reprinted with permission from Ref. [100]. © 2016 Elsevier.

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colon cancer cell line (SW 480) [113]. In another report, a dual responsive targeted drug delivery system was designed based on smart polymer coated mesoporous silica for laryngeal carcinoma therapy. Poly(N-isopropylacryl­ amide), a widely used temperature-sensitive polymer brushes was used to graft on the channel and outer shell of mesoporous silica. Incorporation of co-monomer units, such as MAA, the low critical solution temperature (LCST) of the copolymer can be adjusted above the body temperature up to 39 °C. The copolymer is extended and have hydrophilic properties below LCST thus, the pores will be closed, and the loaded material will be inside the mesoporous silica. Above the LCST, there is a phase transition of the copolymer to hydrophobic state and shrunken conformation, thus releases the loaded material. The addition of MAA imparts the copolymer chain with pH-sensitive properties. At lower pH value, the LCST of copolymer brushes also become low. FA is attached to impart the system with targeting abilities to Hep2 cells which contains folate receptors [109]. 3.6.2.4 ZINC OXIDE (ZNO) NANOMATERIALS Zinc oxide (ZnO) which manifests with various types of nanostructures consist of distinctive piezoelectric, semiconducting, and optical properties [114, 115]. ZnO NPs is one of the most significant metal oxide NPs used in different fields due to its unusual physical and chemical properties [116]. FDA approved ZnO as GRAS material [117]; however, when reduced to the nanoscale range, these materials can develop toxicity, and thorough toxicity assessment is required both in vivo and in vitro [117]. In comparison to other metal oxides, ZnO NPs is comparatively less toxic and cost-effective for biomedical applications such as anticancer drug delivery and bioimaging [118, 119]. PEG-600 modified ZnO NPs was prepared by co-precipitation technique and subsequently loaded with DOX. This DOX-ZnO/PEG nanocomposite [120] doesn’t only increase the concentration of DOX intracellularly but also hinder the proliferation of cervical cancer HeLa cells depends upon concentration [120]. DOX was adsorbed on ZnO NPs, and cytotoxicity was studied on MCF-7 cells, and it was reported that DOX loaded ZnO NPs exhibited better anti-cancerous activity in comparison to its individual analogs due to more retention and better targeting towards tumor cells [121]. Inherent blue fluorescent ZnO quantum dots (QDs) coated with folate-conjugated CS by electrostatic interaction and can be loaded with DOX with an efficiency of 75% [122]. DOX get trapped due to the interactions with the surface of ZnO QDs and/or folate via hydrogen bonding.

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An external layer of CS provides increased aqueous stability to ZnO QDs due to its hydrophilic nature and cationic charge. It is reported that DOX gets released faster at normal physiological pH of 7.4, which requires to be improved for further studies [122]. In another report, a biodegradable ZnO@ polymer-DOX nanocomposite was prepared to have a high loading capacity. Due to the decomposition of the ZnO@polymer-DOX nanocomposite, approx 90 wt.% of DOX got released within the duration of 10 hours at pH 5.0, and approximately 15 wt.% DOX released after 10 hours at pH 7.0. At a suitable concentration, the ZnO@polymer-DOX shows higher cytotoxicity against human brain cancer cells (U251 cells) [123]. 3.6.2.5 CARBON-BASED MATERIAL Different types of carbon materials can be tailored through surface chemistry, such as nanographene. It can be formed with a very high surface area, which facilitates drug loading and have distinctive optical and electrical properties [124]. Nanographene oxide (NGO) bounded with PEG possess magnificent physiological stability and restricted toxicity on the tested cells. SN38, a water-insoluble aromatic drug can be successfully loaded on the NGO-PEG surface by p-p stacking and hydrophobic interactions. The resultant NGO­ PEG-SN38 shows better cytoxicity in comparison to its FDA approved water-soluble prodrug (CPT11, irinotecan) [125]. Carbon nanotubes (CNTs) have been on the other hand utilized for diverse applications of sensing, electronics, optics, biomedicine, and gas storage. Single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs) are the two supreme structures widely used for drugs and biomolecules delivery [126]. CNTs get inside tumors passively without the help of antibodies or any other big molecules. Such EPR effect is used for the delivery of several kinds of anticancer drugs [127, 128]. Liu and co-workers used p-p stacking for DOX loading on branched PEG functionalized SWCNT and studied its pharmacokinetics and biodistribution. Results were showing an increment in circulation halflife, for SWNT-DOX (around 2.22 hours) in comparison to free DOX (0.21 hours) [129]. With organic molecules, carbon nanotube can interact by p-p stacking interactions. Supramolecular complexes can be formed by interaction of DOX with the surface of CNT by p-p stacking [130, 131] and about 50–60 wt % (w/w) of DOX can be conjugated to the CNT surface. Surface modified CNTs can bind DOX molecule non-covalently with the help of hydrophobic and p-p stacking interactions. Due to its aromatic

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nature and having less aqueous solubility of DOX in deprotonated form in basic conditions will help it to attach with nanotubes. More aromatic substances can also bind or get wrapped along with the backbone of CNT and get released at the target [130]. In another report, a dual-targeted drug delivery system was developed in which MWCNT was difunctionalized with FA and iron (FA-MWCNT@Fe) for the transportation of DOX in HeLa cells. The motive of this system is to escort it towards tumor location with the help of an external magnetic field afterwards FA moiety present on CNT will target the FA receptors which is overexpressed on the tumor. It shows a release of 23% of DOX within 24 hours, which increases to 59% in the presence of near-infrared radiation (NIR). This system possesses prolong as well as NIR dependent release [132]. 3.7 PHARMACOLOGICAL STUDIES NPs-based drug delivery system is successful only when its drug loading capacity is high, so that quantity of material to be administered gets reduced. Loading of the drug can be achieved by two techniques. One is by incorporating drug during the formation of NPs (incorporation method), and the other one is drug absorption after the synthesis of NPs, which is attained by shaking the NPs with the drug solution (adsorption/absorption technique) [133]. The drug can be released from the NPs by various stimuli such as pH, temperature, mechanical force, electromagnetic field, etc. The tumor area is having little acidic pH and hence useful for the pH-responsive release of drugs. It is reported that SPION coated with biodegradable and a pH-sensitive copolymer of poly (beta-amino ester) loaded with DOX, exhibit a pH-sensitive drug release profile. The drug release is quick at a pH of 5.5 and 6.4, which mimics the endosomal environment, and slower at 7.4 pH, which is the physiological environment [134]. Drug release can also be thermoresponsive when NPs are coated with different thermorespon­ sive polymer [135]. No premature release was revealed at physiological temperature, and efficient release of drug is obtained by raising the tempera­ ture through NIR irradiation [136]. Many different kinds of drug release models have been formulated to analyze the data for the release rate of drug dissolution [137, 138]. One of the most famous drug release models is the Higuchi drug release model. It is based on the hypothesis that (a) matrix drug concentration initially is higher than drug solubility, (b) drug diffusion happens only in a single dimension (negligible edge effect), (c) particles of drugs are very small in comparison to the system’s thickness, (d) matrix

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swelling and dissolution is insignificant, (e) diffusivity of drug is constant, in the release environment, (f) sink conditions are perfectly maintained [137]. Higuchi model equation is represented as: C = [D (2qt – Cs) Cst]½

(1)

where, C = total amount of released drug per unit area of matrix (mg/cm2); D = diffusion coefficient of drug present in matrix (cm2/hr); qt = total quantity of drug present in unit volume of matrix (mg/cm3); Cs = dimensional solubility of drug in polymer matrix (mg/cm3); and t = time (hr). Another drug release model is the zero-order release model [139]. Here the release kinetics, follow a constant release of drug from the drug delivery vehicles like transdermal system, oral osmotic tablets, etc. It is represented as: Q = Q0 + K0t

(2)

where Q is the quantity of released or dissolved drug (assumes as drug get released quickly after it dissolves); Q0 is the quantity of drug present initially in solution (assumes as zero); and K0 is zero-order release constant. 3.8 THE HARMFUL EFFECT OF NPS The toxicity of the NPs should be evaluated to make sure that the NPs system does not affect the patient after post-injection. NPs supports the production of pro-oxidants, mainly under the subjection of light, and thus disturbs the equilibrium between the formation of ROS and the ability of the biological system to nullify it [140, 141]. Metallic NPs are one of the most commonly used kinds of nanomaterial, but about its environmental effects, not much information is available. Although bulk gold is said to be safe but gold NPs possess some unusual properties which attracts many groups attention to check their cellular uptake and cytotoxicity [142, 143]. IONPs produce toxicity generally by producing ROS in the cells. More chemical reactivity of NPs results in the formation of more ROS [144, 145]. Substantial generation of ROS leads to damage to the cells by disrupting DNA, peroxidizing lipids, gene transcription modulation, and protein alteration, which results in reduced physiological function and cell death/apoptosis [90]. Oxidative stress generated by the NPs can increase the inflammation by upregulation of redox-sensitive transcription factors like activating protein 1 (AP-1), extracellular signal-regulated kinases (ERK) c-Jun, N-terminal kinases, JNK, nuclear factor kappa B (NFkB), and p38 mitogen-activated protein kinases pathways [140, 141].

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50 3.9 CONCLUSION

NPs mediated drug delivery provides a way for the betterment of medical treatment of tumors by reducing the side effect of the anti-cancerous drugs on the healthy tissues. They can successfully replace the limitations of the old traditional methods. However, it has its own limitations too. To overcome it, numerous researches still have been going on for the use of NPs to treat cancer as well as its utilization as imaging and diagnostic agent. Overall, these can be potent medicine for the treatment of cancer. KEYWORDS • • • • • •

active and passive targeting chemotherapy drug delivery nanoparticles single nucleotide polymorphism toxicity

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GRAPHICAL ABSTRACT

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CHAPTER 4

Polymer Functionalized Reduced Graphene Oxide-Based Nickel Nanoparticles as Highly Efficient Dye Catalyst for Water Remediation V. RAMALAKSHMI and J. BALAVIJAYALAKSHMI Department of Physics, PSGR Krishnammal College for Women, Coimbatore, Tamil Nadu, India, E-mails: [email protected] (V. Ramalakshmi), [email protected] (J. Balavijayalakshmi)

ABSTRACT The present work describes the synthesis and characterization of reduced graphene oxide (RGO) based nickel nanoparticles containing beta­ cyclodextrin composite and its application for removal of a textile dye from an aqueous medium. For this purpose, GO is produced by modified Hummer’s method, then after, GO-CD and GO-CD-Ni nanocomposites were synthesized via the wet chemical method. The synthesized adsorbents (GO, GO-CD, and GO-CD-Ni) were characterized using different characterization techniques such as Fourier transform infrared spectroscopy, x-ray diffraction (XRD) analysis, and field emission scanning electron microscopy (FE-SEM) analysis. Also, the various parameters which affecting dye removal like pH, contact time, amount of adsorbents, and initial dye concentrations were investigated. The synthesized adsorbents exhibit excellent adsorption performance for the removal of textile dyes. The adsorption process is pH-dependent, and the adsorption capacity is increased with the increase in contact time and with that of adsorbent dosage.

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4.1 INTRODUCTION In recent years, water pollution with harmful chemical dyes and heavy metal ions has become the main cause of environmental problems. Many industrial processes like art, paper, pulp manufacturing, plastic, dyeing of cloth, textiles, leather treatment, printing, food products, etc., are involved in a variety of synthetic chemical dyes for various uses [1]. Exoneration of these hazardous dyes and chemicals into water bodies are disconcerting for both toxicological and esthetical reasons [2]. Dyes have complex aromatic molecular structure and thus reduce penetration of light into the water bodies and photosynthesis [3]. This characteristic feature makes dyes to degrade and produce toxic products like carcinogens and sometimes explosives leading to severe diseases and disorders [2]. These dyes in water bodies produce some dissolved anionic substances, namely sulfates, nitrates, and phosphates. These anionic substances accord some changes in pH of the dyes, which affects chemical and biological processes in the water medium. Because of these reasons, a desirable treatment is required to remove these compounds from the environment. Various techniques such as physical, chemical, and biological treatments include adsorption, coagulation, photo-catalytic decolonization, ozonation, microbial decomposition, wet-air oxidation, sono-chemical, and electrochemical methods are espoused for the removal of dyes and hazardous chemical from environment [4]. Among these techniques, adsorption is considered to be the most effective, because of its unique features that provide promising results [2]. The variety of adsorbents was widely employed in the adsorption procedure for the removal of colored dye pollutants from paper, textile, and cosmetic industries wastewaters [5–9]. Recently, graphene and GO-based nanomaterials received much attention for adsorption of dye pollutants because of its unique and outstanding electrical, mechanical, and thermal properties [5]. Graphene is defined as a few layers of two-dimensional sp2 hybridized carbon atoms, arranged tightly into a honeycomb lattice [5, 10]. It has various outstanding properties such as a flat surface and great surface area, which makes graphene as a suitable adsorbent [11–13]. However, it also has a hydrophobic surface property which makes graphene insoluble in water. Hence, GO polymer has been used as an adsorbent in the described work. GO has all the outstanding properties of graphene, except it has hydrophilic surface property. The hydrophilic surface property is may be due to the distribution of oxygenated functional groups such as epoxide, carboxyl, and carbonyl groups on the surface of graphene [14]. These oxygenated functional groups are responsible for the formation of

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stable aqueous colloid suspension with various dyes, heavy metal ions, and phenols. Another advantage of GO as an adsorbent is that it has a high negative charge density so that it can interact with positively charged species such as cationic dyes, polymers, and heavy metal ions. To improve the adsorption property of GO, it was further modified with cyclodextrin polymer and nickel nanoparticles [15, 16]. Cyclodextrins (CDs) are natural polymer molecules produced from starch and are commercially available at low cost. Cyclodextrin have a hydrophilic exterior cavity and a hydrophobic interior cavity. The most outstanding property of cyclodextrin molecules was that they are highly capable of forming stable host-guest inclusion complex with a variety of aromatic molecules through virtue of a serious of weak intermolecular forces. Cyclodextrin is a building block to improve the adsorption capacity of many adsorbents. In addition to the biocompatibility and renewability, cyclodextrin molecules functionalized magnetic nanoparticles decorated GO nanocomposite can greatly contribute to simultaneous enhancement of the adsorption capacity of dye pollutant and reduction of the environmental toxicity of magnetic graphene hybrids [17–20]. Here, Nickel magnetic nanoparticles were used to modify the surface of cyclodextrin functionalized GO. The magnetic properties of nickel nanoparticles were quite different from their bulk counterparts. It has remarkable properties in the field of hydrogen storage and as a catalyst. Nowadays, nanoparticles are widely employed as an efficient adsorbent for the removal of dye pollutants because of its large specific surface area and small diffusion resistance. The use of nanomaterials based dye adsorbent for the treatment of wastewater produces an alternate or complementary method to the conventional treatment methods [21–25]. Hence, in the described work, the nickel nanoparticles decorated cyclodextrin functionalized GO nanocomposites were synthesized and employed for the removal of textile dyes from water. The synthesized nickel nanoparticles decorated cyclodextrin functionalized GO nanocomposites were finely characterized using Fourier transform infrared (FT-IR), Field emission scanning electron microscopy (FE-SEM), and x-ray diffraction (XRD) analysis. 4.2 PREPARATION OF GRAPHENE OXIDE (GO)/CYCLODEXTRIN/ NI NANOCOMPOSITE In a typical synthesis procedure, GO is prepared from graphite powder via modified Hummer’s method [26–28]. The powder of natural graphite (2.0 g)

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and sodium nitrate (1.0 g) were taken in a flask containing concentrated H2SO4. The reaction suspension is then kept under ice bath condition at the temperature of 20°C with continuous magnetic stirring for 1 hour. Then, potassium permanganate (KMnO4) as a reducing agent was added slowly into the reaction mixture. The rate of addition of KMnO4 was carefully controlled to keep the reaction mixture temperature lower than 20°C. The reaction suspension is then allowed to stir for 12 hours at 35°C. Then the reaction suspension was treated with 500 mL of deionized followed by the addition of 5 mL of hydrogen peroxide solution to remove the presence of unreacted reducing agents in the reaction suspension. Finally, the reaction mixture is centrifuged using concentrated HCl followed by deionized water and dried for 12 hours at 60°C [29, 30]. The GO-CD nanocomposite was synthesized by the wet chemical method. Each 50 mL of an aqueous solution containing 0.1 g of GO and 0.8 g of β-CD is stirred for 2 hours. Then, the aqueous solution of CD is added dropwise into GO solution with 300 μL of ammonia solution and 50μ L of Hydrazine hydrate as a reducing agent. The reaction mixture was stirred for 4 hrs at 60°C. The obtained GO-CD nanocomposite is centrifuged for 10 min and then dissolved in 50 mL of distilled water. About 50 mL of 0.002 M of nickel chloride and 0.5 M of NaBH4 is taken and stirred for an hour. The well-dissolved nickel chloride solution was then added dropwise into the GO-CD reaction mixture, followed by the addition of NaBH4 solution with pH maintained at 9–10. Then, the reac­ tion mixture was stirred at 60°C for 4 hours and then centrifuged and dried under vacuum overnight [31]. 4.3 RESULTS AND DISCUSSION 4.3.1 FT-IR SPECTRAL ANALYSIS FT-IR measurement is utilized to examine the bonding interactions in graphene before and after the oxidation reaction. The FT-IR spectra of synthesized GO, GO/β-CD, and GO/β-CD/Ni nanocomposites are shown in Figure 4.1(a–c). The FT-IR spectrum of synthesized GO (Figure 4.1(a)) shows the characteristic bands at 3122 cm–1, 1712 cm–1, 1606 cm–1, 1412 cm–1, 1181 cm–1 and 1052 cm–1, which may be attributed to the stretching vibrations of hydroxyl O-H group, carboxyl C = O groups, aromatic C = C group, C-OH stretching vibrations, epoxy C-O and alkoxy C-O group respectively. The

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presence of oxygen functional groups such as C = O and C-O confirms the oxidation of graphite powder into GO prepared using modified Hummer’s method [27].

FIGURE 4.1

FT-IR spectra of (a) GO, (b) GO/β-CD, (c) GO/β-CD/Ni nanocomposite.

In Figure 4.1(b), carbon-oxygen functional groups of GO are existing, and their characteristic peaks are found to be very weak. This remarkable decrease in the intensity of the characteristic band may be due to the reduction of graphene into reduced GO after the addition of hydrazine. The presence of CD molecules on the surface of rGO is confirmed by observing the bands at 1034 cm–1, 1126 cm–1, 1375 cm–1, 2928 cm–1, 3510 cm–1 [32]. The bands obtained at 1034 cm–1 and 1126 cm–1 confirms the presence of coupled C-O stretching and C-C stretching vibrations, respectively. The typical FT-IR bands of β-CD are observed at 2928 cm–1 and 3510 cm–1 may be attributed to asymmetric stretching vibrations of CH2 group and the bending vibrations of C-H / O-H groups are observed at 1375 cm–1. It is further confirmed from

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the FT-IR results that CD molecules are functionalized to the surface of rGO [32, 33]. Figure 4.1(c) shows the characteristic bands of β-cyclodextrin functionalized GO nanosheets with the additional bands at 664 cm–1 and 462 cm–1 which may correspond to the Ni-O vibration and Ni-OH stretching bond [33]. 4.3.2 XRD ANALYSIS XRD analysis is used to investigate the crystal structure and to measure the average spacing between layers or rows of atoms [26]. Figure 4.2(a–c) illustrates the XRD patterns of pure GO, cyclodextrin functionalized GO and Nickel nanoparticles doped cyclodextrin functionalized GO. As shown in Figure 4.2(a), the diffraction peak at 11.12° with the d spacing value of 0.79 nm is very typical for GO which confirms the successful synthesis of GO by modified Hummers method using graphite powder [27]. There is a very weak diffraction peak at 42.440 with the d spacing value of 0.21 nm, which is believed due to the incomplete oxidation of graphite powder [27].

FIGURE 4.2

XRD pattern of (a) GO, (b) GO/β-CD, (c) GO/β-CD/Ni nanocomposite.

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In Figure 4.2(b), a very weak and broad diffraction peak can be observed for rGO-CD nanocomposites at 19.10° and 24.6°. The rGO exhibits a broad diffraction peak at 24.6° corresponding to the d-spacing of 0.36 nm along the (002) orientation as presented in Figure 4.2(b) [28, 34]. This may be due to the assembly of graphene layers and removal of oxygen functional groups, bringing into decrease in d-spacing. In addition, the desertion of the peak at 11.12° from the XRD pattern also evidenced that the oxygen functional groups or the oxygenated molecules are entirely removed from the rGO composite. The diffraction peaks observed at 19.1° confirms the presence of cyclodextrin molecules bounded to the reduced graphene surface [29]. There is also a weak diffraction peak at 42.44° with (001) orientation of graphene evidence the amorphous nature of disordered carbon materials [28]. These results are related to the exfoliation and reduction processes of GO and also the functionalization of CD molecules with the reduced GO. The broad diffraction peaks are observed at 9.8°, 19.7°, 37.8°, 44.2° and 60.4° as shown in Figure 4.2(c). The diffraction peaks obtained at 23.5° and 19.7° suggests the successful formation of rGO by the reduc­ tion of GO nanocomposite and functionalization of CD molecules on the surface of rGO sheets. The other diffraction peaks obtained at 37.8°, 44.2° and 60.4° are corresponding to the (111), (200) and (220) planes of nickel oxide nanoparticles doped on the surface of GO-CD, respectively [35]. The obtained diffraction peaks are well matched to those of the standard JCPDS card of nickel nanoparticles (JCPDS-47–1049) [35–37]. The XRD results clearly revealed that the nickel nanoparticles are crystalline in nature with a face-centered cubic structure. Furthermore, the successful incorporation and uniform distribution of nickel nanoparticles and cyclodextrin into the GO are confirmed by the presence of major characteristic peaks of reduced GO with decreased intensity. The XRD results also indicated that the Ni nanoparticles and cyclodextrin molecules are well anchored onto the GO surface. The average crystalline sizes of the Ni nanoparticles are determined using the Debye-Scherrer equation for the (111), (200), and (220) planes and it is found to be approximately 18 nm in size. 4.3.3 FE-SEM ANALYSIS The FE-SEM images are utilized to examine the morphologies of the synthesized samples. Figure 4.3(a–c) shows the FE-SEM images of the pure GO, cyclodextrin functionalized reduced GO and nickel nanoparticles

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deposited cyclodextrin functionalized reduced GO nanocomposite. As shown in Figure 4.3(a), the morphology of GO is like transparent sheet form [31]. The surface of the GO is observed to be rough and it is clearly display the aggregation of GO. In Figure 4.3(b), a thin white layer is observed on the as-synthesized graphene surface, which confirms the coating of cyclodextrin on the surface of GO. When modified with CD, the aggregation of GO disappear and homogeneous film is formed [32]. It is further confirmed from Figure 4.3(c), that the synthesized nickel nanoparticles are uniformly deposited on the surface of the CD functionalized reduced GO surface. The presence of bright white spots on the surface of CD functionalized reduced GO surface indicates the presence of nickel nanoparticles [31].

(a)

(b)

(c) FIGURE 4.3

FE-SEM image of (a) GO, (b) GO/CD, (c) GO/CD/Ni nanocomposite.

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4.3.4 MEASUREMENT OF DYE UPTAKE 4.3.4.1 EFFECT OF PH ON DYE REMOVAL The effect of pH on the removal of textile dye from aqueous solution is shown in Figure 4.4. The pH of the system enforces an important role in controlling textile dye removal via surface charge properties of adsorbents and adsorbate surface properties, including charge, ionic structure, and adsorption capacity [38]. The adsorption experiment of anionic textile dye is performed in 2–6 pH for 1 hour. The impact of pH on the textile dye adsorption at initial dye concentration of 25 mg L–1 is examined and is shown in Figure 4.4. It is confirmed that the maximum adsorption takes place at pH is equal to 2, and the adsorption capacity is found to be lower at pH 6. As a result of the high electrostatic force of attraction between anionic dye and positively charged surface of adsorbents, higher dye adsorption takes place at lower pH (2) values. At higher pH (6) values, OH– ions compete effectively with anionic dye molecule causing the decrease in dye removal efficiency from aqueous medium. However, with the increase of pH from pH 2 to pH 4, both dye

FIGURE 4.4

UV-Vis spectra of (a) pH-2, (b) pH-4 (c) pH-6 dye.

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and adsorbent surface get negatively charged and the removal percentage significantly decreased due to the electrostatic repulsive force [38, 39]. 4.3.4.2 EFFECT OF CONTACT TIME Adsorption time is the most significant parameter in the removal of dye from aqueous solution. To determine and evaluate the adsorption equilibrium time, the adsorption of textile dye onto pure GO, cyclodextrin functionalized GO and Ni-CD-GO nanocomposites are investigated. Figure 4.5 shows the adsorption time for the maximum removal of dye from water by using nano­ composites. The influence of contact time in the range of 5 min to 1 hour at 25 mg L–1 of textile dye at room temperature (RT) is studied for 25 mg of adsorbent. It is evidenced from Figure 4.5 that with the emerging of contact time from 5 to 30 min at 300 rpm stirring rate, the removal percentage is considerably increased; this confirms that the removal of dye is rapid in initial stages. This may be due to the availability of vacant surface sites during the preliminary stage of adsorption. The accomplishment of reaction takes place after agitating the reaction solutions for up to 45 minutes, and once equilibrium is attained, the percentage of adsorption of dye have not shown any noticeable changes with time. This suggests that after equilibrium is attained, further treatment has not provided any more removal. This may be due to the vacant sites get occupied by dye molecules, which leads to create a repulsive force between the adsorbate on the adsorbent surface and saturation of adsorbents [38, 40]. 4.3.4.3 EFFECT OF ADSORBENT DOSAGE Another important parameter that controls the capacity of adsorbent is the amount of adsorbent used for the removal of dye from an aqueous medium. Effects of the mass of adsorbent used for the removal of textile dye with an initial concentration of 25 mg L–1 are investigated. Figure 4.6 shows the amount of adsorbent needed for the removal of dye from an aqueous medium. It is found that the efficiency of textile dye removal is increased to 100% by increasing adsorbent dosage from 5 mg to 25 mg L–1. Further addition of adsorbent dose to 30 mg L–1, the dye removal efficiency has not significantly influenced. An increase in the adsorption efficiency with an increase in adsorbent mass can be attributed to greater surface area and the availability of more adsorption sites [39, 40].

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FIGURE 4.5 UV-Vis spectra of (a) pure dye, (b–f) 5–60 mints of dye with GO/CD/Ni nanocomposite.

4.4 CONCLUSION CDs loaded GO nanomaterials, and nickel nanoparticles were synthesized and characterized using various techniques. The prepared nickel nanoparti­ cles were then loaded with CD/GO nanocomposites and used for the removal of dye from an aqueous medium. The adsorbents were characterized with FT-IR, XRD, and SEM analysis. Effects of various operating parameters, including solution pH and the effect of contact time and concentration of nanocomposites on the extent of dye adsorption were studied, and the results were analyzed. It is seen that the as-synthesized GO/CD/Ni nanocomposites were effective adsorbents for the removal of dye from aqueous solution. Therefore, we can surely conclude that the synthesized GO-CD-Ni nano­ composites are efficient for the quantitative removal of textile dyes from an aqueous medium.

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FIGURE 4.6 UV-Vis spectra of (i) 5 mg, (ii) 10 mg, (iii) 15 mg, (iv) 20 mg, (v) 25 mg of GO/CD/Ni nanocomposites with dye.

KEYWORDS • • • • • •

cyclodextrin polymer field emission scanning electron microscopy Fourier transform infrared spectroscopy graphene oxide nickel nanoparticles textile dye adsorption

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CHAPTER 5

Fabrication of Interdigitated Electrodes (IDEs) by Screen Printing Technology and Their Structural Studies A. AKSHAYA KUMAR, S. K. NAVEEN KUMAR, and ALMAW AYELE ANILEY Department of Electronics, Mangalore University, Mangalagangothri–574199, Mangalore, Karnataka, India, E-mail: [email protected] (A. A. Kumar)

ABSTRACT The sensitive layer’s unique nanostructures with interdigitated electrodes (IDEs) platforms have a great significant interest in miniaturized electrochemical sensor applications. Herein, we report the zinc oxide (ZnO) nanorods (NRs) modified IDEs structure was designed and screen printed on the fiber epoxybased printed circuit board (PCB) for electrochemical pH and nutrients sensor applications. The spacing between the four parallel IDEs structure was 1 mm, and it has modeled and tested using CIRCAD software tool. The copper (Cu) metal is the electrode material and screen printed on the fiber epoxy substrate. The ZnO NRs are used as the active layer for the electrochemical sensor platforms. The manufactured ZnO seed particle solution was deposited on the IDEs structure by using a spin coating method. The structural, chemical composition and morphological properties of the ZnO NRs modified IDEs platform examined and it has been studied with field emission scanning electron microscopy (FE-SEM), energy-dispersive x-ray spectroscopy (EDS) and atomic force microscopy (AFM). The FeSEM results proved that ZnO NRs based sensitive layers formed on the top of the IDEs structure and the average length and diameters of the grown ZnO NRs found to be 1 μm and ≈ 40 ± 10 nm. The root means square surface roughness of the layer was detected in the average range of 200 nm.

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5.1 INTRODUCTION The nanomaterial-based sensing technology has renovated the soil condi­ tion detection sensor system in agriculture because of the continuous increase in the world population has brought up the need for improvement of the agriculture production system. The ultra-high sensitivity, selectivity, label-free detection, simplicity, and fast response are key parameters of the nanomaterial-based sensing devices in the agricultural land. Additionally, the researcher trying to utilize interdigitated electrodes (IDEs) structures for the fabrication of electrochemical sensors. The IDEs play the predominant role in sensing operations and applications, where electrical signs produced by the nanomaterial-based layer have to be noticed and transmitted via IDEs to the processing systems. The IDEs based sensors are cost-effective due to low material cost, high accuracy, and precision, enhanced detection limit, and resolution. Varieties of techniques are used for designing and fabrication of IDEs structures to detect the sensing signals. The most widely used IDEs fabrication method is the photolithography process, which is used to formulate the micro-gap capacitive transducer for bio-substance recognition [1]. The miniature IDE arrays fabricated from the micro and nanofabrication method using nanoimprint lithography and subsequent photolithography techniques [2]. The photolithography process gives high accuracy but has numerous fabrication phases and requires sophisticated instruments. The zinc oxide (ZnO) nanomaterial-based thick film layers were fabricated and used for the capacitive sensing device [3]. In recent years efforts are made to simplify the fabrication process for IDEs fabrication, using techniques such as stamp and laser printing on the glass substrate from silver ink material [4, 5]. The screenprinting is another technique amended to develop IDEs for pH detection appli­ cations. The IDEs electrodes consist of a comb-like structure with a micro gap size below 10 microns or less. Further RuO2 nanomaterial-based active layers were developed on the IDEs surface for sensing applications [6–8]. The metal oxide materials such as TiO, TiO2, Ta2O5, SnO, SnO2, and insulating oxides such as Nb2O5 and Bi2O3, and their mixtures in different proportions are being examined in conjunction with an IDEs pattern to produce a conductimetric/ capacitive pH sensor [9, 10]. A variety of materials are tested over a wide range of frequency levels, and changes in their electrical parameters are used to calibrate the device [11, 12]. The IDEs are also developed on the flexible substrates for biomedical applications [13, 14]. The IDEs combined with nanostructure oriented active layers fascinated the researchers due to their beneficial features like small size, easy to operate, great sensitivity, fast response, and lower cost of fabrication [6, 10, 15, 16]. In

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addition, metal oxides based materials are offering a large surface to volume ratio and thereby increase the electrochemical performance to detect the signal. Among metal oxides, ZnO has multiple properties and is the widely studied material due to easiness and low-cost production process. Various approaches were adopted to synthesize the ZnO nanostructures, among them hydrothermal growth of ZnO nanostructures is one of the widely explored methods [17–20]. This research work elaborates the development of ZnO NRs modified IDEs structure on the 20 x 25 mm2 fiber epoxy-based printed circuit board (PCB) using screen-printing technology. The spacing between the four parallel IDEs structure was 1 mm and it was modeled and tested using CIRCAD software tool. The sol-gel method is used to prepare ZnO seed solution by using Zinc acetate as the precursor material. The spin coating unit method was used to deposit the ZnO solution over the IDEs surface. The fabricated IDEs structure characterized and studied using FeSEM, EDS, and AFM for analyzing structural and chemical compositional belongings of the ZnO nanostructured sensitive layer on the IDEs sensor platforms. 5.2 MATERIALS AND FABRICATION METHODS 5.2.1 CHEMICALS AND EQUIPMENT’S USED Zinc acetate dehydrates, zinc nitrate hexahydrate, monoethanolamine (MEA) and hexamethylenetetramine (HMT) was used as precursor material for the ZnO NRs. The combination of conducting copper (Cu) metal and non-conducting fiber epoxy-based materials used to develop the IDEs. The benchtop screenprinting and spin coating unit has used to the fabrication IDEs structure sensors platforms. The field emission scanning electron microscopy (FE-SEM) and atomic force microscopy (AFM), energy-dispersive x-ray spectroscopy (EDS) are used to study the structural and chemical compositions of the fabricated IDEs modified ZnO NRs active structure. 5.2.2 EXPERIMENTAL METHODS 5.2.2.1 IDES STRUCTURE FABRICATION The IDEs consists of fiber epoxy material-based PCB with dimension 25 × 20 mm, which served as a non-conductive substrate withstand up to

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200°C temperature. An IDEs electrode platforms have fabricated on the PCB. Initially, the IDEs structure designed and tested using the CIRCAD software tool. The 1 mm finger gaped IDEs design and fabricated structure is shown in Figures 5.1 and 5.2, respectively.

FIGURE 5.1

The IDEs design.

FIGURE 5.2

The fabricated IDEs structure.

The comb-like structured eight electrodes with the thickness of 159 to 709 nm and 1 mm finger gaped IDEs are fabricated. The length of the indi­ vidual electrode is 20 mm and the width is 16 mm. the fabricated sensor will provide the sensing area of about 20 × 16 mm2.

Fabrication of Interdigitated Electrodes (IDEs)

81

5.2.2.2 ZnO SEED SOLUTION AND LAYER PREPARATION The ZnO seed solution was obtained using zinc acetate dehydrate as parent material, MEA as stabilizer materials for the particle solution. ZnO seed particle solution was obtained by mixing 2.2 grams of zinc acetate dehydrate with 50 ml of ethanol. The mixed solution was stirred at 65°C for 20 minutes. To obtain a uniform and clear solution, 0.6 ml of MEA was mixed with the ZnO particle solution, while in the stirring continuously at 65°C for 2 Hours. The white color solution was then converted into a clear ZnO particle solution. The solution was kept for 12 hours to age at room temperature (RT). The spin coating unit was used to develop the ZnO seed layer on the IDEs with the spinning speed of 3,000 RPM for 30 s with the three-step programming process and it will provide 18 × 16 mm2 detecting area on top of the IDEs structure. The drying process performed on a muffle furnace at 150°C for 10 minutes. The same coating process repeated four times to obtain thicker and uniform ZnO thin films on the IDEs. The ZnO nanostructures were obtained through a simple hydrothermal growth process. The hydrothermal growing solution contained of an assorted solution of zinc nitrate hexahydrate and HMT. The 4.4 gm of zinc nitrate hexahydrate added with the 3.25 gm of the HMT in deionized water. The ZnO nanostructures were grown-up by dipping the IDEs. During this process, the solution was heated at 93°C for 6 hours in a laboratory muffle furnace. The samples were precisely cleaned with deionized water to remove the uncommon pollutants from the surface of the samples. 5.3 RESULTS AND DISCUSSION FESEM with energy dispersive spectroscopy (EDS) was used for the struc­ tural, morphological, and chemical compositional analysis of the samples. The structural morphology and roughness of the IDEs were also examined by using AFM instrument. 5.3.1 FESEM CHARACTERIZATION The topmost view of the interdigitated electrode structure and ZnO thin film FESEM images are shown in Figure 5.3(a). The screen-printed IDEs patterns designed for a 1 mm finger gap in between the two electrodes. The edge of each electrode is non-uniformly arranged on the substrate due to

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the high-temperature treatment during the particle deposition process. The FESEM images of the ZnO seed layers shown in Figure 5.3(b). The topmost view of the ZnO NRs sensitive layer pictures is shown in Figures 5.4(a) and (b) in the resolution of 1 micrometer and 100 nm, respectively. The length and diameters of the grown ZnO NRs are found to be 1 μm and ≈ 40 ± 10 nm. The majority of ZnO shows the hexagonal faceted nanorods (NRs) surface morphology and also the grown ZnO NRs homogeneously scattered throughout the IDEs surface.

FIGURE 5.3

FeSEM image of the IDEs structure (a) and ZnO seed layer (b).

FIGURE 5.4

FeSEM images of the ZnO NRs on the IDEs.

5.3.2 EDS CHARACTERIZATION EDS is an investigative technique to know the chemical composition of the materials. Figure 5.5(a) and (b) illustrates the EDS composition spectra for ZnO NRs. It is confirmed from the EDS analysis; grown ZnO NRs on the IDEs is composed of Zinc and Oxygen elements. The weight percentage of

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83

Zinc (Zn) and Oxygen (O) in ZnO NRs are 610.53 and 168.97, respectively. This again confirms the grown ZnO NRs contain only, pure (Zinc) Zn, and oxygen (O) elements.

FIGURE 5.5

The EDS chemical composition spectra of ZnO NRs modified IDEs.

5.3.3 AFM CHARACTERIZATION The surface morphology of IDEs modified with IDEs completed by using AFM. The ambient contact mode AFM imaging was accomplished using multimode nanoscope with IIIa controller (Bruker, Germany). The surface roughness of the screen-printed IDEs modified ZnO thin films controls the detection speed. During the calibration of the electrochemical sensors, a definite collection of voltage is applied through the electrodes; the electrical field was produced on each digit makes in the micro gap electrodes, variations in the electrical parameters of the ZnO active layer. While varying the concentration of the target groups, the polarity of the charged surface groups of the layer disturbed and movement of ions will take place in the surface of the ZnO NRs layer and finally which leads to change in the electrical properties of the active layer [10]. Figure 5.6 shows the 2-dimensional and 3-dimensional view of the AFM images. 5.4 CONCLUSION The IDEs structure was designed and screen printed on the PCB and further decorated with the ZnO NRs. The comb-like IDEs pattern was designed and tested using the CIRCAD software tool. The copper (Cu) metal is the electrode material and screen printed on the fiber epoxy substrate. The

84

The 2D and 3D AFM images AFM image of the IDE pattern modified by the ZnO nanostructured layer [21].

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FIGURE 5.6

Fabrication of Interdigitated Electrodes (IDEs)

85

ZnO seed solution was coated on the IDEs structure by using a three-step spin coating method. The ZnO NRs grew on the top of the IDEs using the hydrothermal growth process. The structural and chemical properties of the IDEs structure and nanostructured ZnO NRs layer have been studied. The average length and diameters of the grown ZnO NRs are 1 μm and ≈ 40 ± 10 nm. The EDS composition spectrum confirms the occurrence of Zinc (Zn) and Oxygen (O) elements in the active layer of ZnO NRs. The root means square surface roughness of the layer was detected in the average range of 200 nm. The invented ZnO NRs altered IDEs electrode platforms could be used as the capacitive pH and nutrient measurement sensors in micro solu­ tion applications. ACKNOWLEDGMENTS We would like to thank the Department of Science and Technology (DST), for the INSPIRE FELLOWSHIP (Registration Number: IF170544) and University Grant Commission (194-3/2016(IC)) sponsored the Indo-US Bilateral Research project for funding and instruments facilities provided to this research. KEYWORDS • • • • • • •

atomic force microscopy energy dispersive spectroscopy fiber epoxy field emission scanning electron microscopy hexamethylenetetramine interdigitated electrodes screen printing

REFERENCES 1. Lin, T. K., (2014). Fabrication of Interdigitated Electrodes (IDE’s) by Conventional Photo­ lithography Technique for pH Measurement Using Micro-Gap Structure, 1570016883(8), 8, 9.

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2. Delle, L. E., et al., (2018). Scalable fabrication and application of nanoscale IDE-arrays as multi-electrode platform for label-free biosensing. Sensors Actuators, B Chem., 265, 115–125. 3. Foo, K. L., Hashim, U., Prasad, H., & Kashif, M., (2012). Study of ZnO micro-gap on SiO2/Si substrate by conventional lithography method for pH measurement. 10th IEEE Int. Conf. Semicond. Electron. ICSE 2012-Proc. (pp. 191–194). 4. Kim, H., Auyeung, R. C. Y., Lee, S. H., Huston, A. L., & Piqué, A., (2010). Laserprinted interdigitated Ag electrodes for organic thin-film transistors. J. Phys. D. Appl. Phys., 43(8). 5. Sen, C. K., & Lee, C. H., (2014). Fabrication of silver interdigitated electrode by a stamp method. Adv. Mater. Sci. Eng., 2014. 6. Manjakkal, L., Cvejin, K., Kulawik, J., Zaraska, K., & Szwagierczak, D., (2014). Electrochemical interdigitated conductimetric ph sensor based on RuO2 thick film sensitive layer. EPE 2014-Proc. 2014 Int. Conf. Expo. Electr. Power Eng., No. Epe. (pp. 797–800). 7. Farehanim, M. A., Hashim, U., Azizah, N., Fatin, M. F., & Azman, A. H., (2017). Fabrication of interdigitated electrodes (IDEs) using basic conventional lithography for pH measurement. AIP Conf. Proc., 1808. 8. Simic, M., Manjakkal, L., Zaraska, K., Stojanovic, G. M., & Dahiya, R., (2017). TiO2­ based thick film pH sensor. IEEE Sens. J., 17(2), 248–255. 9. Gill, E., Arshak, K., Arshak, A., & Korostynska, O., (2008). Mixed metal oxide films as pH sensing materials. Microsyst. Technol., 14(4/5), 499–507. 10. Manjakkal, L., Cvejin, K., Kulawik, J., Zaraska, K., Socha, R. P., & Szwagierczak, D., (2016). X-ray photoelectron spectroscopic and electrochemical impedance spectroscopic analysis of RuO2-Ta2O5 thick film pH sensors. Anal. Chim. Acta, 931, 47–56. 11. Arshak, K., Gill, E., Arshak, A., & Korostynska, O., (2007). Investigation of tin oxides as sensing layers in conductimetric interdigitated pH sensors. Sensors Actuators, B. Chem., 127(1), 42–53. 12. Yogeswaran, U., & Chen, S., (2008). A Review on the Electrochemical Sensors and Biosensors Composed of Nanowires as Sensing Material, 12(9), 290–313. 13. Oberländer, J., et al., (2015). Study of interdigitated electrode arrays using experiments and finite element models for the evaluation of sterilization processes. Sensors (Switzerland), 15(10), 26115–26127. 14. Adzhri, R., et al., (2016). Titanium dioxide interdigitated electrode (IDE) for detection of cardiac troponin biomarker. ARPN J. Eng. Appl. Sci., 11(14), 8817–8821. 15. Manjakkal, L., Sakthivel, B., Gopalakrishnan, N., & Dahiya, R., (2018). Printed flexible electrochemical pH sensors based on CuO nanorods. Sensors Actuators, B. Chem., 263, 50–58. 16. Zhong, M. L., Zeng, D. C., Liu, Z. W., Yu, H. Y., Zhong, X. C., & Qiu, W. Q., (2010). Synthesis, growth mechanism and gas-sensing properties of large-scale CuO nanowires. Acta Mater., 58(18), 5926–5932. 17. Ahmad, R., Ahn, M. S., & Hahn, Y. B., (2017). ZnO nanorods array-based field-effect transistor biosensor for phosphate detection. J. Colloid Interface Sci., 498, 292–297. 18. Fan, J., Li, T., & Heng, H., (2016). Hydrothermal growth of ZnO nanoflowers and their photocatalyst application. Bull. Mater. Sci., 39(1), 19–26. 19. Akshaya, K. A., Naveen, K. S. K., Aniley, A. A., Bhansali, S., & Fernandez, R. E., (2019). In: Naveen, K. S. K., (ed.), Hydrothermal Growth of Zinc Oxide (ZnO) Nanorods

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(NRs), Structural, and Chemical Composition Studies for pH Measurement Sensor Applications (Vol. 88, No. 1, pp. 437–447). ECS Trans. 20. Akshaya, K. A., & Naveen, K. S. K., (2019). Comprehensive review on pH and nutrients detection sensitive materials and methods for agriculture applications. Sensor Letters, 17(19), 663–670, 21. Akshaya, K. A., Naveen, K. S. K., Aniley, A. A., Bhansali, S., & Fernandez, R. E., (2019). Hydrothermal growth of zinc oxide (ZnO) nanorods (NRs) on screen-printed IDEs for pH measurement application. J. of the Electrochem. Soc., 166(9), B3264–B3270.

CHAPTER 6

Photocatalytic Effect of Tin Oxide-Zinc Oxide Nanocomposites Prepared by the Solvothermal Method K. J. ABHIRAMA and K. U. MADHU Physics Research Centre, S. T. Hindu College, Nagercoil–629002, Tamil Nadu, India, E-mail: [email protected] (K. J. Abhirama)

ABSTRACT In the present work, a simple microwave-assisted solvothermal technique has been adopted for the synthesis of tin oxide-zinc oxide (ZnO) nanocomposite. The prepared nanocomposites were characterized using scanning electron microscopy, energy dispersive spectrum analysis. The prepared samples were agglomerated and spherical in shape. The degradation mechanism of malachite green dye at different interval of time under UV light irradiation was evaluated using the prepared nanocomposites as the catalysts. Degradation efficiency with respect to irradiation time was calculated for the prepared samples. The higher photocatalytic activity was observed for ZnO nanoparticles as a catalyst. 6.1 INTRODUCTION Nanomaterials can be used to overcome some of the social issues such as energy crisis and wastewater treatment to some extent. The nanocomposite is an area of nanoscale research that led to the design and manufacture of commercial products. Nanocomposites can be synthesized via hydro­ thermal method [1, 2], sol-gel method [3], co-precipitation technique, [4], and spray pyrolysis technique [5]. Zinc/iron oxide nanocomposite was synthesized by Tamar Gordon et al. [6] via hydrolysis of Fe3+ and Zn2+ ions

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of varying ratios on gelatin/Zn/Fe nuclei. They observed high antibacterial activity for nanocomposites with a higher weight ratio. SnO2 nanoparticles, ZnO micro rods, and their nanocomposites were synthesized by Wen-Hui Zhang et al. [7] for the fabrication of a gas sensor to detect trimethylamine (TMA). The nanocomposites show high sensitivity towards TMA, and hence it is used to detect the freshness of dead fish. SnO2-ZnO composite was used as a photoanode in the fabrication of dye-sensitized solar cells by Supphadate et al. [8]. Research is going on in these fields, and many of the researchers synthesized nanomaterials, which were used in making solar cells [9], lithium-ion batteries [10] as catalyst [11], as antibacterial and antifungal agents [12], and as sensors [13]. Catalysis is a process where the rate of a chemical transformation of the reactants is modified by a substance without being altered or consumed in the end. The substance used is known as catalyst, and it has the capability to increase the rate of a reaction, thereby reducing the activation energy. Photocatalysis is a process in which light is used to activate the substance, which modifies the rate of a chemical reaction. The substance used to modify the rate of a chemical reaction by irradiating with light is known as photocatalyst. Malachite green dye was used in the textile industry [14], as a food additive and coloring agent, also as a biocide in the aquaculture industry [15], in the paper and leather industry [16]. The discharge of wastewater containing malachite green dye into the water bodies causes water pollution, which in turn causes diseases such as carcinogenesis, mutagenesis, chromosomal fractures, teratogenicity, and respiratory toxicity [17]. Therefore, it is necessary and important to remove malachite green dye from wastewater before discharging it into water bodies [18]. Removal of toxic substances generated from dyes can be done through physical and chemical processes such as precipitation, flocculation, adsorption, ultra-filtration, reverse osmosis, and advanced oxidation processes (AOP) [19]. Photocatalysis is an AOP and it has attracted many scientists in the field of environmental protection because it has super oxidation ability [20]. In the present work, tin oxide-ZnO nanocomposites were synthesized via a simple microwave-assisted solvothermal technique. The prepared nanocomposites were characterized by XRD, SEM, and EDS analysis. Then the prepared nanocomposites were used as a catalyst for the degradation of malachite green dye under UV light irradiation.

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6.2 EXPERIMENTAL 6.2.1 MATERIALS AND METHODS All the chemicals used in the preparation of (SnO2)1–x(ZnO)x nanocomposites were analytical reagent (AR) grade. The solvent used in the preparation of nanomaterials was ethylene glycol. Double distilled water was used for washing the as-prepared nanopowders. Acetone was also used to wash the as-prepared nanopowders in order to remove the organic impurities if present. (SnO2)1–x (ZnO)x nanocomposites (with x values 0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0) was synthesized using simple microwave-assisted solvothermal technique and it was explained in detail in our earlier work [21]. The as prepared samples were calcinated at 500°C for 1 hr. The calcinated samples were used to carry out further characterizations. 6.2.2 CHARACTERIZATION OF NANOCOMPOSITES In the present work, the morphology and the chemical composition of (SnO2)1–x(ZnO)x nanocomposites were studied using SEM and EDS analyses. The photocatalytic activity of prepared samples was explained in detail. Here 50 ml of 10 ppm aqueous malachite green solution was taken in a 100 ml beaker. 100 mg of prepared nanocomposite powder was added and stirred well using a magnetic stirrer for about 10 min. To achieve adsorption-desorption equilibrium, the dye solution containing the dispersed nanocomposite powder was kept in the dark for about half an hour. Then the solution was kept under UV light and was irradiated for up to 6 hours. After every 1 hour interval, 5 ml of malachite green solution was taken out, and it was centrifuged to remove the catalyst. Then it was characterized by UV-Vis spectral analysis. Systronics 2201 UV-Visible double beam spectrophotometer in the wave­ length range 200–800 nm was used to observe the photocatalytic application studies of (SnO2)1–x (ZnO)x (with x values 0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0) nanocomposites. The photocatalytic activities of undoped (SnO2)1–x (ZnO)x nanocomposites were evaluated by observing the degradation of malachite green dye under UV light irradiation. For UV irradiation 18 W UV-AB fluorescent lamp was used. From the UV-Vis absorption spectra of malachite green solution, the degradation of malachite green could be observed. The degradation efficiency was calculated using the formula [18, 22].

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D=

100× (Ci − Ce) Ci

where, D is the degradation efficiency, Ci is the initial dye concentration and Ce is the dye concentration at definite interval of time. 6.3 RESULT AND DISCUSSION 6.3.1 SEM AND EDS ANALYSIS The morphology and the chemical composition of (SnO2)1–x (ZnO)x nanocom­ posites were studied using SEM and EDS analyzes. The SEM micrographs recorded with 30,000x magnification were shown in Figures 6.1–6.7. The SEM micrographs show that the morphology of all the samples were spherical in shape and agglomerated. The relative rate of nucleation, growth process, and agglomeration influence the particle size and distribution of nanoparticles [23].

FIGURE 6.1

SEM micrograph of SnO2 nanoparticles.

The presence of spherical morphology was reported by Simin et al. [24] and Thenmozhi et al. [25] in SnO2 nanoparticles. Agglomeration of particles along with spherical morphology was reported by Priya et al. [26] in tin oxide nanoparticles synthesized via the sol-gel method. Gajendiran et al. [27] reported that Zn doped SnO2 nanoparticles possess spherical morphology. Rana et al. [28] reported the presence of homogeneous and agglomerated ZnO nanoparticles with a grain size of 80 nm. Swati et al. [29] observed ZnO nanoparticles with spherical morphology along with agglomeration. They added that the aging of samples could cause agglomeration.

Photocatalytic Effect of Tin Oxide-Zinc Oxide

FIGURE 6.2

SEM micrograph of (SnO2)0.8(ZnO)0.2 nanocomposite.

FIGURE 6.3

SEM micrograph of (SnO2)0.6(ZnO)0.4 nanocomposite.

FIGURE 6.4

SEM micrograph of (SnO2)0.5(ZnO)0.5 nanocomposite.

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FIGURE 6.5

SEM micrograph of (SnO2)0.4(ZnO)0.6 nanocomposite.

FIGURE 6.6

SEM micrograph of SnO2(0.2)ZnO(0.8) nanocomposite.

FIGURE 6.7

SEM micrograph of ZnO nanoparticle.

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The EDS patterns observed were shown in Figures 6.8–6.14. In all the EDS patterns occurrence of peaks at 0.27 and 2.12 keV show the presence of carbon and gold and it was due to the carbon tape substrate used for holding the sample while taking the measurement and also the presence of gold peak was due to the use of gold for coating the sample [3]. The peak positions showing the presence of Sn, Zn, and O atoms for (SnO2)1–x(ZnO)x nanocom­ posites were tabulated and shown in Table 6.1.

FIGURE 6.8

EDS pattern of SnO2 nanoparticles.

FIGURE 6.9

EDS pattern of (SnO2)0.8(ZnO)0.2 nanocomposite.

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FIGURE 6.10

EDS pattern of (SnO2)0.6(ZnO)0.4 nanocomposite.

FIGURE 6.11

EDS pattern of (SnO2)0.5(ZnO)0.5 nanocomposite.

Photocatalytic Effect of Tin Oxide-Zinc Oxide

FIGURE 6.12

EDS pattern of (SnO2)0.4(ZnO)0.6 nanocomposite.

FIGURE 6.13

EDS pattern of (SnO2)0.2(ZnO)0.8 nanocomposite.

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FIGURE 6.14

EDS pattern of ZnO nanoparticles.

TABLE 6.1 Peak Positions of Elements Present in (SnO2)1–x(ZnO)x Nanocomposites Obtained from EDS Analysis System(with expected composition) SnO2

(SnO2)0.8(ZnO)0.2

(SnO2)0.6(ZnO)0.4

Tin 3.05 3.40 3.60 3.90 4.13 3.05 3.40 3.60 3.90 4.13 3.05 3.40 3.60 3.90 4.13

Peak positions of elements in keV Zinc Oxygen 0.52

1.00 8.60 9.50

0.52

1.00 8.60 9.50

0.52

Photocatalytic Effect of Tin Oxide-Zinc Oxide TABLE 6.1

(Continued)

System(with expected composition) (SnO2)0.5(ZnO)0.5

(SnO2)0.4(ZnO)0.6

(SnO2)0.2(ZnO)0.8

ZnO

99

Peak positions of elements in keV Tin Zinc Oxygen 3.05 1.00 0.52 3.40 8.60 3.60 9.50 3.90 4.13 3.05 1.00 0.52 3.40 8.60 3.60 9.50 3.90 4.13 3.05 1.00 0.52 3.40 8.60 3.60 9.50 3.90 4.13 1.00 0.52 8.60 9.50

(SnO2)1–x(ZnO)x nanocomposites contain only Sn, Zn, and O and was free from impurities and it indicates that the obtained (SnO2)1–x(ZnO)x nano­ composites have high purity. An increase in the intensity of Zn peaks was observed in Figures 6.12 and 6.13; and it may be due to an increase in the concentration of zinc. Meanwhile, the decrease in the intensity of Sn peaks was noted, and it may be due to the decrease in the concentration of tin. The elemental compositions (atomic %) present in the prepared samples were shown in Table 6.2. It was observed that the atomic weight percentage of Zinc increases as the x values increases from (0.2–1.0). 6.3.2 PHOTOCATALYTIC ACTIVITY The UV-Vis absorption spectra of malachite green dye at different intervals of time under the UV light irradiation observed for (SnO2)1–x(ZnO)x nano­ composites were shown in Figures 6.15–6.21. Degradation occurs in two phases: one is by absorption in dark, and the other is by photocatalysis under

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light illumination [30]. In oxide semiconductors, the incident photons having energies greater than the bandgap energy of the semiconductor has the ability to transfer electron from valence band to the conduction band resulting in the formation of electron-hole pairs. The holes in the valence band are capable of generating hydroxyl radicals at the surface, and they react with adsorbed dye molecules while the electron in the conduction band has the ability to reduce the oxygen molecules present in the solution. The hydroxyl radical thus formed is strong enough to carry out the degradation process [31]. The photocatalytic activity depends on calcinations temperature, photocatalyst load, initial concentration of dye and capping ligand [32]. Dye cationic radical is formed when electron transfer occurs from the dye to the positive holes of SnO2 [33]. TABLE 6.2 Elemental Composition (Atomic %) of (SnO2)1–x(ZnO)x Nanocomposites Obtained from EDS Analysis System (with Expected Composition)

Elemental Composition (Atomic %) Tin

Zinc

Oxygen

SnO2

20.32

–

79.68

(SnO2)0.8(ZnO)0.2

19.43

0.20

80.37

(SnO2)0.6(ZnO)0.4

17.18

3.70

79.12

(SnO2)0.5(ZnO)0.5

17.36

8.05

74.59

(SnO2)0.4(ZnO)0.6

12.11

13.09

74.80

(SnO2)0.2(ZnO)0.8

5.13

31.26

63.62

ZnO

–

46.02

53.98

FIGURE 6.15 UV-Vis absorption spectra of malachite green dye at different intervals under UV light irradiation for SnO2 nanoparticles.

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FIGURE 6.16 UV-Vis absorption spectra of malachite green dye at different intervals under UV light irradiation for (SnO2)0.8(ZnO)0.2 nanocomposite.

FIGURE 6.17 UV-Vis absorption spectra of malachite green dye at different intervals under UV light irradiation for (SnO2)0.6(ZnO)0.4 nanocomposite.

FIGURE 6.18 UV-Vis absorption spectra of malachite green dye at different intervals under UV light irradiation for (SnO2)0.5(ZnO)0.5 nanocomposite.

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FIGURE 6.19 UV-Vis absorption spectra of malachite green dye at different intervals under UV light irradiation for (SnO2)0.4(ZnO)0.6 nanocomposite.

FIGURE 6.20 UV-Vis absorption spectra of malachite green dye at different intervals under UV light irradiation for (SnO2)0.2(ZnO)0.8 nanocomposite.

FIGURE 6.21 UV-Vis absorption spectra of malachite green dye at different intervals under UV light irradiation for ZnO nanoparticles.

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The degradation efficiency of (SnO2)1–x (ZnO)x nanocomposites with respect to irradiation time was shown in Figure 6.22. It was observed that almost 55% of degradation of dye occurs in solution containing ZnO as catalyst. This is because ZnO nanoparticles take part in degradation during the first phase. ZnO catalyst shows 90% of degradation after an interval of 4 hrs. Undoped (SnO2)1–x (ZnO)x (with x values 0.2, 0.4, 0.5, 0.6 and 0.8) nanocomposites shows lower activity when compared to ZnO. In addition, it shows higher activity when compared to SnO2 nanoparticles. A similar result was reported by Kowsari et al. [34], and it was due to the difference in the surface area of the particles. In ZnO nanoparticles, the recombinations of photogenerated electron-hole pairs are suppressed, hence it shows higher photocatalytic activity [35]. ZnO is capable of absorbing large quanta of visible light, and it promotes more electrons to higher energy states. That is why ZnO shows higher photocatalytic activity. The degradation efficiencies of undoped (SnO2)1–x (ZnO)x nanocomposites are provided in Table 6.3.

FIGURE 6.22

Degradation efficiency of (SnO2)1–x (ZnO)x nanocomposites.

6.4 CONCLUSION Tin oxide-ZnO nanocomposites were synthesized using a simple microwaveassisted solvothermal technique. SEM and EDS analysis of the prepared nano­ composites shows spherical morphology and agglomeration of particles. The

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prepared nanocomposites was used as a catalyst to evaluate the degradation mechanism of malachite green dye. The degradation efficiencies of (SnO2)1–x (ZnO)x nanocomposites was calculated, and it was observed that almost 55% of degradation of dye occurs in a solution containing ZnO as a catalyst. This occurs because in ZnO nanoparticles, the degradation takes place during the first phase. Undoped (SnO2)1–x (ZnO)x (with x values 0.2, 0.4, 0.5, 0.6 and 0.8) nanocomposites shows lower photocatalytic activity when compared to ZnO. In addition, it shows higher activity when compared to SnO2 nanopar­ ticles. In ZnO nanoparticles, the recombinations of photogenerated electronhole pairs are suppressed; hence it shows higher photocatalytic activity. TABLE 6.3

Degradation Efficiency of Undoped (SnO2)1–x (ZnO)x Nanocomposites

System (with Expected Composition)

Degradation (%)

SnO2

90

(SnO2)0.8(ZnO)0.2

91

(SnO2)0.6(ZnO)0.4

93

(SnO2)0.5(ZnO)0.5

94

(SnO2)0.4(ZnO)0.6

95

(SnO2)0.2(ZnO)0.8

97

ZnO

97

KEYWORDS • • • • • •

malachite green nanocomposite photocatalytic degradation tin oxide UV irradiation zinc oxide

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17. Xueyan, L., Shuai, A., Wen, S., Qi, Y., & Lei, Z., (2014). Microwave-induced catalytic oxidation of malachite green under magnetic Cu-ferrites: New insight into the degradation mechanism and pathway. Journal of Molecular Catalysis A: Chemical, 395, 243–250. 18. Xian-Jiao, Z., Wan-Qian, G., Shan-Shan, Y., He-Shan, Z., & Nan-Qi, R., (2013). Ultrasonic-assisted ozone oxidation process of triphenylmethane dye degradation: Evidence for the promotion effects of ultrasonic on malachite green decolorization and degradation mechanism. Bioresource Technology, 128, 827–830. 19. Gao, G., Zhang, A., Zhang, M., Chen, J., & Zhang, Q., (2008). Photocatalytic degradation mechanism of malachite green under visible light irradiation over novel biomimetic photocatalyst HMS-FePcs. Chinese Journal of Catalysis, 29(5), 426–430. 20. Manish, M., Manoj, S., & Pandey, O. P., (2014). UV–Visible light-induced photocatalytic studies of Cu doped ZnO nanoparticles prepared by co-precipitation method. Solar Energy, 110, 386–397. 21. Abhirama, K. J., & Madhu, K. U., (2017). Electrical parameters of (SnO2)1-x (ZnO)x nanocomposites prepared by solvothermal method. International Journal of Advanced Engineering and Research Development, 4(09), 511–518. 22. Hadi, F. M., Abdollah, F. S., & Mohammad, A. Z., (2011). Semiconductor-assisted self-cleaning polymeric fibers based on zinc oxide nanoparticles. Journal of Applied Polymer Science, 121, 3641–3650. 23. Virender, S. K., Dhiman, R. L., Davender, S., Maan, A. S., & Susheel, A., (2013). Synthesis and characterization of tin oxide nanoparticles via sol-gel method using ethanol as solvent. International Journal of Advanced Research in Science and Engineering, 2(1), 5. 24. Simin, T., Amir, A., Amin, T., & Emad, T., (2014). Synthesis and characterization of tin oxide nanoparticles via the co-precipitation method. Materials Science-Poland, 32(1), 98–101. 25. Thenmozhi, C., Manivannan, V., Kumar, E., & Veera, R. M. S., (2015). Synthesis and characterization of SnO2 and PANI doped SnO2 nanoparticles by microwave-assisted solution method. International Research Journal of Engineering and Technology (IRJET), 02(09), 2634–2640. 26. Subramaniam, M. P., Geetha, A., & Ramamurthi, K., (2016). Structural, morphological and optical properties of tin oxide nanoparticles synthesized by sol-gel method adding hydrochloric acid. J. Sol-Gel Sci. Technol., 8. 27. Gajendiran, J., & Rajendran, V., (2011). Size controlled and optical properties of Zn-doped SnO2 nanoparticles via sol-gel process. Optoelectronics and Advanced Materials-Rapid Communications, 5(1), 44–48. 28. Rana, S. B., Singh, P., Sharma, A. K., Carbonari, A. W., & Dogra, R., (2010). Synthesis and characterization of pure and doped ZnO nanoparticles. Journal of Optoelectronics and Advanced Materials, 12(2), 257–261. 29. Swati, K. S., & Mahendra, S. D., (2015). Optical and structural properties of zinc oxide nanoparticles. International Journal of Advanced Research in Physical Science (IJARPS), 2(1), 14–18. 30. Ramesh, R., Caroline, A., Sampa, C., & Pratim, B., (2017). Photocatalytic degradation of methyl orange dye by pristine titanium dioxide, zinc oxide, and graphene oxide nanostructures and their composites under visible light irradiation. Appl. Nanosci., 7, 253–259.

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31. Sajjad, K., & Hosakere, D. R., (2013). Photocatalytic degradation of acid yellow 36 using zinc oxide photocatalyst in aqueous media. Journal of Catalysts, 6. 32. Abebe, B., Om, P. Y., & Tania, D., (2016). Photocatalytic degradation of methylene blue dye by zinc oxide nanoparticles obtained from precipitation and sol-gel methods. Environ. Sci. Pollut. Res., 9. 33. Bekir, E., Tugrul, Y., Ali, S., & Tugba, Y., (2011). Investigation of photocatalytic effect of SnO2 nanoparticles synthesized by hydrothermal method on the decolorization of two organic dyes. Photochemistry and Photobiology, 87, 267–274. 34. Elaheh, K., & Mohammad, R. G., (2012). Ionic liquid-assisted, facile synthesis of ZnO/ SnO2 nanocomposites, and investigation of their photocatalytic activity. Materials Letters, 68, 17–20. 35. Wang, C., Zhao, J., Wang, X., Mai, B., Sheng, G., Peng, P., & Fu, J., (2002). Preparation, characterization and photocatalytic activity of nano-sized ZnO/SnO2 coupled photocata­ lysts. Applied Catalysis B: Environmental, 39, 269–279.

CHAPTER 7

MMT Intercalated Pd Nanocatalyst for Heck (Mizoroki-Heck) Reaction PRASHANT GAUTAM and VIVEK SRIVASTAVA Basic Sciences, Chemistry, NIIT University, NH-8 Jaipur/Delhi Highway, Neemrana, Rajasthan –301705, India, Phone: +91-1494660623, E-mail: [email protected] (V. Srivastava)

ABSTRACT The Heck reaction is one of the most studied coupling reactions and is recognized with the Nobel Prize in Chemistry. Several research articles, reviews, and books have been published on Heck’s reaction. Most of the book chapters and reviews are describing the various features of the Heck reaction. Industrial catalysts with broad applicability need a continuous catalyst development process through modification of ligand design, geometry, and functionality. Recently, catalysts have been synthesized by anchoring active palladium species on the surface of polymer support, particularly insoluble in a reaction medium. An appropriate mixture of palladium salt and ligand is also used as an important modification in some cases to get better results. Considering the same, we successfully synthesized and further characterized Pd-MMT clay before going to test them as a catalyst for the Mizoroki-Heck reaction. The highest yield of the Mizoroki-Heck reaction product was recovered using thermally stable and highly reactive Pd-MMT-1 clay catalyst in the functionalized reaction medium. Seven times catalyst recycling is the added advantage of this proposed protocol. 7.1 INTRODUCTION The coupling reactions have started a new era of chemical transformation and become an important transformation for carbon-carbon bond-forming

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reactions. Heck, Suzuki, Sonogoshira, Negishi, Kumada, Stille, Tsuji-Trost, etc., have played an important role to shape chemical synthesis [1–4]. Among different types of the coupling reaction, the Heck reaction is extensively applied in the synthesis of agrochemical, pharmaceutical, and fine chemical, etc., [2, 3]. Heck procedure is striking from a synthetic point of view as it offers a high degree of chemoselectivity and easy reaction settings. This reaction was first coined by Mizoroki-Heck independently and in small time gained much attention due to high efficiency and simplicity [5–7]. The Heck reaction is mainly defined as a vinylation or arylation of olefins (where a large variety of olefins like derivatives of styrenes, acrylates) [1–9]. The aryl halide variants developed in addition to typical aryl bromides and iodides are aromatic triflates, aroyl chlorides, aryl sulfonyl chlorides, aromatic diazonium salts, aroyl anhydrides, acyl chlorides, and arylsilanols [7–14]. The catalyst is an essential part of a reaction where a variety of metals along with a huge range of ligands is studied. Significant progress for the preparation and characterization of a variety of ligands and catalysts has been made for avoiding protection and deprotection procedures, therefore allowing for syntheses to be carried out in fewer steps [10–15]. Development, novel catalytic properties, and extensive mechanistic studies are summarized in several reviews based on the seminal work of many researchers and reviewers as described in the following sections. Palladium is usually the preferred metal as it tolerates a wide variety of functional groups, and it has a remarkable ability to assemble C-C bonds between appropriately functionalized substrates. Most palladium-based methodologies proceed with stereo- and regioselectivity and with excellent yields [15–20]. Generally, the less crowded structure is preferred during the Heck reaction and often favors a trans product. Few mechanisms are also supported by the discussion on the regioselectivity and stereoselectivity of the Heck reaction. Sometimes compounds such as TBAB (tetra butyl ammonium bromide) are added in the reaction mixture along with organic or inorganic bases needed for the sequestration of acid generated. Typical solvents for the Heck reaction are dipolar aprotic solvents like DMF (dimethylformamide) and NMP (N-methyl-2-pyrrolidone); however, the reaction is also performed in many other different solvents, and in fact, there are large numbers of reviews dedicated to the use of various solvents [20–23]. Besides these, many manuscripts describe the reaction in the absence of one of the components (other than substrates) such as ligand-free, organic solvent-free, and so on. Recent publications also describe how to recover used catalysts, especially using an aqueous medium, which implies the potential for a greener approach for organic reactions.

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Top-down and bottom-up approaches are conceivable for the synthesis of nanoparticle catalysts. Numerous methods were developed, including rather conventional techniques like mechanical grinding or chemical breakdown of bulk material or electrochemical or solvothermal processing of precursor solutions [24–26]. Further selected examples and innovative alternatives, such as microwave irradiation processing, resulted in catalysts with more defined size and shape. Nanocatalysis is considered a vital catalytic system of all types of sustainable organic transformations. Magnetic, metal oxides, core-shell, and supported types of Pd nanocatalyst have been utilized in several catalytic applications [27]. Supported nanocatalysts are considered as a unique population of reusable nanocatalysts due to their cheap preparation cost, exceptional activity, good selectivity, high stability, efficient/easy retrieval, and virtuous recyclability. The synergy of significant organic reaction with unique features of nanocatalysts is highly demanding to achieve significant products [24, 25, 28–33]. These supported heterogeneous nanocatalysts with high surface area provide an effective alternative over conventional catalysts in terms of good catalytic activity, selectivity, and stability by tuning their shape, size, composition, and nature of nanocatalyst structure. In some of the reports, it is well mentioned that the catalytic activity of nanocatalysts is mainly increasing while decreasing the size of nanostructures [27]. However, while reducing the size of the active site to nanoscale dimensions, the surface free energy increases to its initial value such change in nanoscale structure initiates the aggregation of the nanoparticles into small clusters. Such change in nanoscale structure drops the catalytic performance of nanocatalyst. The tedious isolation of nanocatalysts becomes difficult due to their nanoscale dimensions, which can be simplified by supporting them on an organic/ inorganic support. A notable modification has been made to achieve the best performance of nanocatalysts in terms of reaction condition, activity, selectivity, and reusability, but still metal leaching in nanocatalysis under harsh conditions or continuous flow reactions in flow reactor remains a major concern yet to be solved. The design and development of new, more robust, and advanced multifunctional nanomaterials and imperative protocols for the decoration of homogeneous metals, organic ligands, or catalysts entities are still required to overcome these difficulties [33–38]. Pd nanoparticles (Pd NPs) have an extremely small size and high surface-to-volume ratios and have received great attention in the past decades [35–37]. Pd NPs have demonstrated outstanding effectiveness as catalysts for catalytic properties in different organic reactions on chemical and pharmaceutical industries, including hydrogenation and C–C coupling reactions like Suzuki, Mizoroki-Heck, and Sonogashira reaction. Although,

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Pd NPs appeared as an important form of Pd catalyst, unfortunately, they also suffer from some unique problems of nanoparticles like size, shape, activity, stability, and agglomeration [36–49]. Pd NPs were supported on different organic/inorganic supports like polymer, ionic liquid, activated carbon, silica, MCM-41, clays, Al2O3, and Zeolite get agglomeration free, active, and stable Pd NPs, but the curse of costly starting material, tedious synthetic protocol, and most important reproducibility of synthetic protocol collectively hurt the supported synthesis of Pd NPs [40–49]. Na-Montmorillonite clay (MMT) is one of the important materials which are used as a support for various transition metals, mainly because of its exceptional physicochemical properties like large chemically active surface area, high cation exchange capacity (CEC), and variation of internal chemical composition, variation in types of exchangeable ions and surface charge, and interactions with inorganic and organic liquids [50–52]. MMT supported metal nanoparticles: An update on syntheses and applications. Additionally, MMT supported catalytic system also offer, a high degree of thermal stability, provides protection to metal against air/moisture, easy catalyst isolation, and recycling. The interlayer spacing of aluminosilicates in MMT is filled with several Na+, K+, and Ca2+ ions, these ions are considered as exchangeable cations in MMT, which are mainly responsible for the metal ion-exchange reaction. MMT supported metal has been tested as a catalyst for several reactions like oxidation, reduction, transesterification, and coupling reactions, but to achieve maximum metal exchange as well as high catalyst loading are still a challenge [50–56]. Ionic liquids (ILs) are organic salts that are liquid below 100˚C, have received considerable attention as substitutes for volatile organic solvents. Due to their remarkable properties, such as outstanding solvating potential, thermal stability, and their tunable properties by suitable choices of cations and anions, they are considered as a favorable reaction medium over conventional solvent systems for chemical synthesis [57–62]. ILs is mainly made up of cationic and anionic components can be arranged to achieve a specific set of properties. In this context, the term “designer solvents” has been used to establish the potential of this environment-benign ILs in chemical transformations. Being designer solvents, they can be modified to as per the specific requirement of the reaction conditions; therefore they also name “task-specific ILs (TSILs).” Since these liquids can dissolve numerous transition metal complexes, they have been working regularly as an alternative solvent system many catalytic organic transformations to enhance reaction rates and selectivity [63, 64]. ILs is very much gifted to limit several undesirable properties of the conventional organic solvents and have successfully been applied in several catalytic

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application areas affording high catalytic activity. The present study is aimed at exploring the application of ionic liquid as TSIL to avoid the use of a toxic base in the Mizoroki-Heck reaction. In this chapter, we are presenting the controlled synthesis of Pd NPs within the interlayer spacing of MMT followed by cation exchange method. We utilized Pd-MMT clay as a catalyst for the Mizoroki-Heck reaction in TSILs (1,3-di(N,N-dimethylaminoethyl)-2-methylimidazolium trifluoromethane sulfonate ([DAMI] [TFO]) [65] to synthesize 2-aryl and 2,2-diary vinylphohonates. 7.2 EXPERIMENTAL PART All the reagent grade chemicals were purchased from Sigma Aldrich and SD Fine chemicals. All the 1H and 13C NMR spectra were recorded with 400 MHz Bruker spectrometer with the CDCl3 solvent system. The internal standard for 1H and 13C NMR spectra were kept at 7.26 and 7.36 ppm, respectively (supporting information). 31P NMR spectra of all the unknown compounds were recorded Varian 400 NMR spectrometer (85% H3PO4 as an external standard) (supporting information). The Na MMT was supplied from Southern Clay Product, Texas-USA with the registered product name Cloisiite Na and it was used for tetraamminepalladium(II) chloride monohydrate intercalation with going to any further purification of pretreatment process. The CEC of Na-MMT was 92.6 mequiv/100 g. Philips X’Pert MPD instruments were used to record all small and wide-angle X-ray powder diffraction (XRD) data. The Pd-MMT clay material was characterized by TEM (Hitachi S-3700N) and energy-dispersive x-ray spectroscopy (EDX) (Perkin Elmer, PHI 1600 spectrometer). The specific surface area (BET) of the catalyst was determined on a micro metrics Flowsorb III 2310 instru­ ment. Fourier transforms infrared spectrophotometer (FTIR) analysis of all the samples were studied with Bruker Tensor-27. Elemental analysis was conducted in a Perkin Elmer Optima 3300 XL. ICP-OES (inductively coupled plasma atomic emission spectroscopy) was applied to determine the metal Pd and phosphorus content. 7.2.1 SYNTHESIS OF PD-MMT CLAY Perfectly cleaned and dried 250 mL round bottom flask was charged with the suspension of Na MMT clay (10 g) with 100 mL water. The aqueous solution

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of 150 mL of palladium acetate (10 mM) solution was added in a dropwise manner into the homogeneous slurry of Na MMT clay within 3 hours by maintaining the pH of the solution at 5.5 (using 0.1N HCl). The combined reaction was stirred at 25–30°C for the next 24 hours to obtain a uniform dispersion. Further, Pd exchanged clay was washed with double distilled water using centrifugation. Washing was stopped as soon as we got chloridefree supernatant (monitored with silver nitrate solution). Finally, chloride and acetate-free Pd exchanged MMT clay was dried using lyophilizer 12 hours. At last, we obtained free-flowing black colored powder as Pd-MMT-1 clay (9.5 g, 2.5 w/w % Pd). In the same pattern, we also prepared Pd-MMT-2 clay (9.6 g.5 w/w % Pd) using palladium acetate solution (10 mM) with 10 g Na MMT clay. pH of the above-mentioned reaction mass was also controlled by the addition of 0.1 N HCl. 7.2.2 EXPERIMENTAL PROCEDURE OF MIZOROKI-HECK REACTION 50 mL glass-made reaction vessel was charged with aryl halides and vinyl phosphonate with Pd-MMT clay- 1 or 2 catalysts in a solvent system with or without a base as per Tables 7.2 and 7.3. The combined reaction mass was heated at 80°C for one hour. After the completion of the reaction, the reaction product was then recovered with diethyl ether (5 x 2 mL) and further purified by column chromatography. Isolated ionic liquid immobilized Pd-MMT-1 clay was further dried in a high vacuum at 50°C for 0.5 hours to evaporate all the volatile impurities. After the vacuum treatment, all the reactants were added as per the above-mentioned protocol with ionic liquid immobilized Pd-MMT-1 clay to recycle the catalytic system. 7.3 RESULTS AND DISCUSSION Task-specific [DAMI][TFO] ionic liquid was synthesized as per our previously reported procedure [65]. We synthesized two different types of Pd-MMT clay 1 and 2, followed by mixing the neat Na-MMT clay with aqueous solution tetraamminepalladium(II) chloride monohydrate in acidic medium for 24 hours at room temperature (RT) to ensure complete exchange of palladium metal ion with the exchangeable cation of MMT clay. After the exchange, the Pd-MMT clay was washed several times deionized water and dried under lyophilizer. We obtained Pd-MMT clay-1 while mixing MMT clay with 6 mM aqueous solution of tetraamminepalladium(II) chloride

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115

monohydrate. Pd loading on MMT clay was determined by calculating the change between the concentrations of palladium metal ion in initial palladium acetate solution with respect to the mother liquor recovered after the filtration of Pd-MMT clay followed by inductively coupled plasma emission spectroscopy (ICP-OES). We obtained good palladium metal ion loading over Pd-MMT-1 clay (2.5% w/w Pd metal) in comparison with Pd-MMT-2 clay (0.5% w/w Pd metal, obtained by mixing 3 mM aqueous solution of palladium acetate with MMT clay). The change in the basal spacing of Pd @MMT clay with respect to neat MMT clay was studied using small to medium angle x-ray scattering (SAXS) analysis (Figure 7.1). In SAXS study, an increase in the basal spacing of neat MMT clay was (d001 = 12.95 Å) recorded after the intercalation of palladium metal ion within the interlayer spacing of MMT clay. After the intercalation, the basal spacing of Pd-MMT-1 clay was increased up to d001 = 15.25 Å. Such a significant increase in d001 spacing of MMT clay confirms the presence of palladium metal ion between the interlayer spaces of MMT clay. Sharp 001 XRD peaks gave a clear indication of parallel arrangements of clay sheets and the uniform addition of Pd NPs (Figure 7.1).

FIGURE 7.1

SAXS analysis and XRD data of Na-MMT and Pd-MMT clays.

Therefore, we can conclude the presence of an ordered lamellar structure of Pd metal loaded MMT with the face-to-face arrangement of MMT clay sheets. We obtained a small characteristic signal as a peak in XRD data of Pd-MMT clay; this confirms the presence of Pd NPs in MMT clay. The XRD signals of Pd NPs appeared as sharp peaks near to 40, 46, and

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68°, respectively, representing the (111), (200) and (220) Bragg reflection (Figure 7.1). The XRD pattern of Pd metal was found in good agreement of JCPDS standard (#05-0681) and confirmed the synthesis of Pd NPs within the interlayer spacing of MMT clay. Face-centered cubic (fcc) crystal structure was used to calculate the size of Pd NPs using peak broadening profile of (111) signal at 40˚ using Scherrer equation. The calculated crystallite size of the Pd NPs was found in 5.5 nm size for Pd-MMT-1 clay and 9.5 nm sizes for Pd-MMT-2 clay. We also studied the effect of the ionic liquid on the basal spacing of MMT clay. The sign of an increase in basal spacing of Pd-MMT-2 clay was also noticed and it was found near to d001 = 14.25 Å (Figure 7.1) [66, 67]. The morphology of MMT clay with and without Pd metal exchange, the particle size of Pd NPs as well as the presence of Pd NPs within the interlayer spacing was further confirmed by performing the high-resolution transmission electron microscopy (HRTEM) (Figure 7.2). We obtained the agglomeration free uniform distribution of Pd NPs within the interlayer spacing of MMT clay. In Pd-MMT-1 clay, the particle size of Pd was recorded near to 5.5 nm with a standard deviation of ±0.25 nm, while some increase in the particle size of Pd metal was observed near to 9.5 nm with a standard deviation of ±0.25 nm with Pd-MMT-2 clay. During the reaction, Pd-MMT clay was used as a catalyst, and functionalized ionic liquid was used as a reaction medium as well as an effective substitute of amine. The presence of functionalized ionic liquid with Pd-MMT clay creates a chance of cation exchange between the cationic parts of ionic liquid with remaining unexchanged Na+ ions in the Pd-MMT clay. This type of exchange was confirmed by further SAXS analysis and FT IR analysis. The presence of characteristic bands near to 1650, 1543, 843 cm–1 both in [DAMI][TFO] ionic liquid and [DAMI]+ ion-exchanged Pd-MMT clay confirmed the exchange of remaining Na+ ions with cations of [DAMI][TFO] ionic liquid (Figure 7.3). This exchange was also supported by SAXS analysis and d001 spacing was reaching up to 17.20 Å from 15.25 Å in Pd-MMT-1 clay (Figure 7.2). The same change in Pd-MMT-2 clay was also recorded where the basal spacing has increased from 14.25 Å to 16.75 Å [66]. The textural properties of Na-MMT clay and Pd-MMT clays represented them as mesoporous solid (Table 7.1 and Figure 7.3). The nitrogen adsorp­ tion-desorption isotherm of neat MMT, Pd-MMT clay 1 and Pd-MMT clay 2 gave typical type IV with hysteresis loop at P/P0 ̴ 0.4 to 0.8 (Figure 7.3). This data reveals no change in the porous structure of Na-MMT clay even after

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the insertion of Pd NPs. Drop in the BET surface area and total pore volume after the intercalation Pd NPs was recorded mainly due to the capping of some pores with metal NPs. It shows the development of adsorbent multi­ pliers’ and weak adsorbate-adsorbent connections. The different shapes of the adsorption-desorption isotherms were due to the configuration and size distribution of Pd NPS. Absenteeism of any unexpected changes in the surface area and pore volume supported the no sign of agglomeration.

FIGURE 7.2 HRTEM images (100 nm scale) of Na-MMT clay and Pd-MMT clays (before and after catalysis).

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118 TABLE 7.1

Textural Properties of Na-MMT Clay and Pd-MMT Clays

Samples

BET Surface Area (m2/g)

Average Pore Size (nm)

Pore Volume (cm3/g)

Na-MMT

385

3.47

0.361

Pd-MMT clay-1

372

3.34

0.217

Pd-MMT clay-2

381

3.40

0.210

Energy dispersive x-ray spectroscopy (EDS) was applied to understand the chemical composition of Pd-MMT clay to know better the structure and homogeneity of prepared materials (Figure 7.3). The presence of character­ istic signals of Pd metal in EDS spectra confirmed the presence of Pd NPs.

FIGURE 7.3 Textural properties of Na-MMT clay and Pd-MMT clays (with or without ionic liquid).

After the completion of the careful physiochemical analysis of Pd-MMT clay, we further used them as a catalyst for two very important reactions, namely the Mizoroki-Heck reaction. 7.3.1 MIZOROKI-HECK REACTION WITH PD-MMT CLAY AS CATALYST Alkenylphosphonates are considered an important chemical in medical science, material science, and polymer additives. Various protocols such

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119

as the Suzuki-Miyaura coupling of boronic acids with vinyl phosphonate, a Mizoroki-Heck reaction using vinyl phosphonate with different aryl derivatives, aldehyde insertion into zirconacycle phosphonates and Olefin cross-metathesis has been reported using numerous transition metal catalytic systems under a toxic conventional solvent system. The reaction is mainly suffering from catalyst recycling and the requirement of the toxic base for the successful completion of the reaction. In this report, we are using our well-characterized Pd-MMT clay catalysts to improve the reaction kinetics of vinyl phosphonates synthesis followed by Mizoroki-Heck reaction. Initially, we allowed Pd @MMT clay 1 to catalyze a model MizorokiHeck reaction between iodobenzene and diethyl vinyl phosphonate under functionalized ionic liquid medium (instead of using the toxic conventional solvent system and toxic base) at 80°C for 1 hour (Scheme 7.1, Table 7.2). We successfully obtained the corresponding reaction product with good yield. The same reaction condition was also tested with Pd-MMT clay-2 catalyst unfortunately; lower yield was recorded due to low Pd metal loading (Table 7.2; Entry: 2).

SCHEME 7.1

Model Mizoroki-Heck reaction.

No sign of drastic change in the yield of Mizoroki-Heck reaction while elevating the reaction temperature or time and quantity of ionic liquid or catalyst, but of course, while lowering the reaction condition, a clear drop in reaction yield was recorded. Replacement of functionalized ionic liquid with series of base and non-functionalized [bmim][NTf2] ionic liquid shoed the importance of [DAMI][TFO] ionic liquid, which works as active bases (due to the presence of two-NH functional group) and effective reaction medium. We also received lower catalytic activity of conventional Pd catalysts over our developed Pd-MMT clay catalytic system in ionic liquid medium (Table 7.2, entry 20 and 21). No sign of reaction product was recorded in the absence of Pd-MMT clay 1 catalyst. After completion of the reaction, the product was effortlessly isolated via diethyl ether extraction and further purified using column chromatography. We successfully recycled our ionic liquid immobilized Pd-MMT-1 clay

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120 TABLE 7.2

Reaction Optimization of Mizoroki Heck Reaction

Entry Catalyst (0.01 g) Solvent (0.150 g)

Base (1 mmol)

Time (h)

Temperature Yield (°C) (%)

1.

Pd-MMT clay-1

[DAMI][TFO] –

1h

80°C

93%

2.

Pd-MMT clay-2

[DAMI][TFO] –

1h

80°C

56%

3.

Pd-MMT clay-1 (0.02 g)

[DAMI][TFO] –

1h

80°C

93%

4.

Pd-MMT clay-1 (0.005 g)

[DAMI][TFO] –

1h

80°C

53%

5.

Pd-MMT clay-1

[DAMI][TFO] – (0.200 g)

1h

80°C

92%

6.

Pd-MMT clay-1

[DAMI][TFO] – (0.100 g)

1h

80°C

73%

7.

Pd-MMT clay-1

[DAMI][TFO] KOH

1h

80°C

91%

8.

Pd-MMT clay-1

[DAMI][TFO] K2CO3

1h

80°C

88%

9.

Pd-MMT clay-1

[DAMI][TFO]

1h

80°C

92%

10.

Pd-MMT clay-1

[DAMI][TFO] Et3N

1h

80°C

91%

11.

Pd-MMT clay-1

[bmim][NTf2]

1h

80°C

36%

12.

Pd-MMT clay-1

[bmim][NTf2]

1h

80°C

74%

13.

Pd-MMT clay-1

[DAMI][TFO] –

1h

50°C

35%

14.

Pd-MMT clay-1

[DAMI][TFO] –

1h

100°C

92%

15.

Pd-MMT clay-1

[DAMI][TFO] –

2h

100°C

92%

16.

Pd-MMT clay-1

[DAMI][TFO] –

30 h

100°C

43%

17.

Pd-MMT clay-1

DMF

i

Pr2NH

1h

80°C

67%

18.

Pd-MMT clay-1

THF

i

Pr2NH

1h

80°C

60%

19.

Pd-MMT clay-1

CH3CN

i

Pr2NH

1h

80°C

46%

20.

Pd(NH3)4Cl2·H2O [DAMI][TFO] –

1h

80°C

66%

21.

Pd(OAc)2

[DAMI][TFO] –

1h

80°C

62%

22.

–

[DAMI][TFO] –

1h

80C

–

Pr2NH

i

Pr2NH

i

up 8 cycles without showing any significant loss in catalytic activity in terms of reaction yield. Surprisingly, no signature of catalyst leaching was recorded while performing filtration test during recycling experiments. All the solid material was isolated with 0.45 mm polytetrafluoroethylene (PTFE) filter, and recovered liquid was mixed with the reactants of the

MMT Intercalated Pd Nanocatalyst for Heck

121

model Mizoroki-Heck reaction. No product formation was recorded during this reaction which confirmed the zero leaching of Pd metal from MMT clay. These filtration experiments were also supported by ICP-OES analysis of above-mentioned filtrate, where no signal from Pd metal was received. A sign of agglomeration and low reaction yield was recorded in TEM image analysis after seven times recycling of Pd-MMT clay-1 catalyst (Figure 7.4). Due to agglomeration increase on the particle size of Pd NPs was observed from 6.5 nm to 39.5 nm (with a standard deviation of ±0.75 nm). In some of the reports, the formation of palladium black was reported due to the high reaction temperature. In our case, no such observation was found mainly due to the extended thermal stability of Pd NPs because of thermally stable MMT clay.

FIGURE 7.4

Catalyst recycling experiment data.

We applied the optimized reaction condition for the variance of aryl halides and with different types of dialkylvinylphophonates. All the results were summarized in Table 7.3 and Scheme 7.2.

SCHEME 7.2

Mono Mizoroki-Heck reaction.

Nanostructured Smart Materials

122 TABLE 7.3 Entry

Pd-MMT-1 Clay Catalyzed the Mono Mizoroki-Heck Reaction Aryl Halide (1 mmol)

Phosphonate (2 mmol)

Yield (%)

1.

90

2.

84

3.

87

4.

82

5.

93

6.

92

7.

92

8.

94

9.

85

10.

87

11.

88

12.

92

13.

93

14.

92

MMT Intercalated Pd Nanocatalyst for Heck TABLE 7.3 Entry

123

(Continued) Aryl Halide (1 mmol)

Phosphonate (2 mmol)

Yield (%)

15.

87

16.

89

17.

86

18.

84

19.

67

20.

68

21.

60

22.

56

23.

71

24.

70

25.

71

26.

77

27.

77

28.

78

Nanostructured Smart Materials

124 TABLE 7.3 Entry

(Continued) Aryl Halide (1 mmol)

Phosphonate (2 mmol)

Yield (%)

29.

74

30.

81

31.

75

32.

76

33.

63

34.

64

We tested a variety of aryl iodide (electron-rich and electron-poor) with two different types of vinyl phosphonate derivatives. We obtained good to excellent yield in all cases. Surprisingly, lowering in reaction yield was not reported with sterically hindered aryl halides (Table 7.3; Entries 15–18). We easily performed typical oxidative addition of aryl bromide derivatives with MMT supported Pd metal without increasing the reaction temperature, reaction time, and catalyst loading (Table 7.3; Entries 19–30). This outcome represented the high catalytic performance of the Pd-MMT-1 clay catalyst in the ionic liquid medium. We obtain the slow reaction rate with electron-rich aryl bromide derivatives than electron-deficient composition. The presence of steric effect on aryl bromide derivatives as low reaction yield was recorded in their corresponding reaction products (Table 7.3; Entries 31–34.). 7.4 CONCLUSIONS We successfully developed two MMT supported Pd nana catalytic systems with different loading. The cation exchanged method was used to prepare the above-mentioned catalytic systems. Various sophisticated analytical techniques such as FTIR, ICP-OES, SAXS, XRD, FTIR, N2 physisorption,

MMT Intercalated Pd Nanocatalyst for Heck

125

EDS, and TEM were used to understand the physiochemical behavior of Pd nanoparticle exchanged MMT clay. All the analytical results were found in good agreement with each other, and most importantly, no change properties of MMT clay was observed after the exchange of Pd NPs into it. ICP-OES method further confirmed the high Pd NPs loading within the interlayer spacing of clay. TEM and XRD analysis confirmed the presence of agglom­ eration free and narrow size distributed Pd NPs within the basal spacing MMT clay. We also prepared two types of functional and nonfunctional ILs to use them as an active solvent system in our reaction. The ionic liquid was also found responsible for the highly selective Mizoroki-Heck reaction. Pd-MMT clay under catalyst recycling experiments was found highly active under thermal heating and successfully recycled the Pd-MMT-1 clay catalyst up to 7 runs. KEYWORDS • • • • • • •

C-C coupling reaction ionic liquids Mizoroki-Heck reaction Na-MMT clay nanoparticles palladium nano metal Pd nanoparticles

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CHAPTER 8

A Novel Approach for Production and Characterization of Al-Mg Eutectic Alloy Nanopowder by Electrical Explosion of Thin Plates C. MOHAMMED IQBAL,1 S. R. CHAKRAVARTHY,1 R. JAYAGANTHAN,2 R. SARATHI,3 and A. SRINIVASAN4 Department of Aerospace Engineering, IIT Madras, Chennai–600036, India, E-mails: [email protected] (C. M. Iqbal), [email protected] (S. R. Chakravarthy)

1

Department of Engineering Design, IIT Madras, Chennai–600036, India, E-mail: [email protected]

2

Department of Electrical Engineering, IIT Madras, Chennai–600036, India, E-mail: [email protected]

3

Division of Material Science and Technology (NIIST) Trivandrum, Kerala, India, E-mail: [email protected]

4

ABSTRACT Electrical explosion technique of thin wire is one of the most efficient methods to produce metal nanopowders with higher level of purity. Nanopowder of Al-Mg alloy was synthesized using electrical explosion of thin plates in the present work. Thin plates of Al-Mg eutectic alloy were cut from the thin casting by low-speed diamond cutter and thickness is further reduced by polishing using emery sheets of coarse and finer grades. A voltage doubler circuit is used to charge the capacitor to elevated voltage and is discharged through the metal plate in a wire explosion chamber filled with argon gas at 100 kPa pressure. The nanopowder obtained is examined using scanning

132

Nanostructured Smart Materials

electron microscope (SEM) and transmission electron microscope (TEM). X-ray diffraction (XRD) analysis confirms peaks corresponding to inter­ metallics. SEM and TEM images substantiate the spherical structure of the nanoparticles and diameter of particles ranges from 20 nm to 95 nm. The results corroborate the method of explosion of thin plates as a potential alternative for production of nanopowder of metal alloys and inter-metallics. 8.1 INTRODUCTION Particles show elevated reactivity, chemical, and physical properties when brought to smaller size owing to the fact of the presence of higher surface to volume atoms than the bulk, and it becomes significant when the size of particles is reduced to the nano level. The higher reactivity of the atoms makes them preferable for a high-energy application like solid propellants, underwater propulsion systems, powder metallurgy, explosive formulations, military pyrotechnics, etc. [1–3]. Nanoparticles are produced by two approaches, viz. top to bottom and bottom to top approach. A top (bigger) particle is brought down to bottom (small) particles by different means is more convenient in the production of nanoparticles. Macrograins of bulk material will be crushed down to the nano level. The electrical explosion of thin wire (WEP) is one of the most efficient methods to produce nanopowder of metals with a higher level of purity. A thin metal wire is heated and evaporated by discharging high voltage through it by a capacitor charged by a voltage doubling circuit [1, 2, 4–6]. Aluminum nanopowder of high purity level is produced by WEP, and thermodynamic approach was extended to predict size-dependent melting and enthalpy of fusion [7, 8]. The oxide layer surrounding Al particles has a higher melting temperature, which hinders the pure Al particles to take part in the combustion reaction, which in turn is driven to ignition delay [9, 10]. Magnesium shows better features in terms of melting point, ignition temperature, etc. Al-Mg alloys are desirable in energetic formulations and fuel additives, which can be attributed to higher combustion enthalpy offered by aluminum while magnesium augmenting ignition [11]. The unavailability of wires of the preferred cross-sectional area limits the application of the electrical wire explosion method to produce nanopowder of metal alloys and inter-metallics. Aluminum-based alloys find application as an energetic additive in propellant formulations, explosives pyrotechnics, etc., owing to the fact of reduced ignition delay, tailored density, high enthalpy, etc. Electrodeposition of alloying elements in pure metal wire and exploding the wire to produce nanopowder is one of the methods to produce nanopowder

A Novel Approach for Production and Characterization

133

of metal alloys and inter-metallics. Al-Cu, Cu-Ni alloy nanopowders were fabricated by electrical explosion of Cu deposited Al and Ni wires [12]. Finding the right combination of electrolyte and metals again constrains the application of electrolytic deposition and the further explosion of the wire. Multi-stepped milling of elemental Al and Mg powder to produce Al-Mg alloy powder yielded micron-scale particles [13]. Nanopowder of Al-Mg alloy was synthesized using electrical explosion of thin plates. A voltage doubler circuit is used to charge the capacitor to elevated voltage and is discharged through the metal plate. Transmission electron microscope (TEM) and scanning electron microscope (SEM) images confirm the nanoparticles of diameter ranging from 20 nm to 95 nm. 8.2 EXPERIMENTAL DETAILS Thin plates of Al-Mg eutectic alloy were cut by low speed (Buehler isoMet low speed) diamond cutter and thickness is further reduced by polishing using emery sheets of coarse and finer grades. The thickness is brought to less than 0.5 mm (Table 8.1). TABLE 8.1

Sample Parameters

Length of the Plate

55 mm

Chamber Pressure

100 kPa

Thickness of the Plate

0.5 mm

Ambiance

Argon

Width of the Plate

5 mm

The basic schematic diagram of the wire explosion setup is shown in Figure 8.1. The source charges the capacitor, which is then discharged through the thin wire. A voltage-double circuit is used to charge the capacitor to the required magnitude of voltage. The circuit functions like an RLC circuit, whose maximum delivered energy in a time period t is: W=V×I×t

(1)

where V is the voltage across the electrodes to which the thin plates/metal strips are connected and I is the current flow through it at the time of the explosion. The stored energy in the capacitor is: W = (1/2)CV2

(2)

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134

where, C is the capacitance. The stored energy is discharged through the plate. Energy needed for vaporizing the alloy plate could be estimated as: Ws = Cs * ΔTm + hm + Cl * ΔTg + hg

(3)

where, Cs is heat capacity of the alloy, Tm is the melting temperature of the alloy: ΔTm = Tm − To (4) where, To is the initial temperature of the plate, hm is latent heat of melting, Cl is heat capacity of molten metal: ΔTg = Tb − Tm

(5)

where Tb is the boiling point of molten alloy and hg is latent heat of vaporization.

FIGURE 8.1

Schematic diagram of the WEP experimental setup.

8.2.1 MECHANISM OF NANOPARTICLE FORMATION The switch S is a high voltage trigatron gap, R is the electrical resistance of the plate, and L is the contribution by the internal inductance of the capacitor and the lead inductance. The characteristic voltage across the resistance R and the current flowing through it were measured using the voltage probe (EP-50 k, PEEC. A Japan) and the current probe (Pearson Electronics USA Current transformer Model No-101), respectively as shown in Figure 8.2. The magnitude of current flow in the circuit depends on the resistance and the inductance in the circuit [14]. In the present work, the circuit parameters match with the condition for the RLC under-damped circuit, where: R2 1 < 2 LC L

(6)

A Novel Approach for Production and Characterization

FIGURE 8.2

135

Characteristic voltage and current waveform.

The voltage appears across the thin plates on closing the switch S and the current increases, which ultimately melts the thin plate by Joule heating and forms a supersaturated vapor in the inert gas atmosphere. Due to high energy density, the plate melts and evaporates momentarily to form plasma. The high temperature plasma collides with inert gas in the chamber, which is at a low temperature and initiates nucleation process. The supersaturated vapor transforms to Al-Mg alloy nanoparticles on reactive collision with the inert Argon gas and nucleation of Al and Mg nuclei further aided by the low chamber pressure. Classical theory on grain nucleation and growth suggests that the final grain structure of polycrystalline materials is determined by the nucleation and growth conditions prevailing during phase transformations (PTs) [15]. The large temperature difference between the inert gas and the supersaturated vapor enhances the nucleation rate initially, which results in a reduction in the size of nuclei leading to the formation of the finer-sized particles (Figure 8.3). 8.3 RESULT AND DISCUSSIONS Figures 8.4 and 8.5 show XRD patterns of bulk Al-Mg alloy and the nano Al-Mg alloy powder produced by WEP. Peaks at 35.90°, 37.46° and

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Nanostructured Smart Materials

43.62° values of diffraction angle (2θ in the XRD pattern of nanopowder corresponds to Al3Mg2 and 2θ value of 76.49° corresponds to AlMg, which confirms the presence of intermetallic compounds in the nanopowder. Peaks corresponding to Al2MgO4 and MgO are also found in the pattern, which could be due to oxidation of the constituent alloy metals in vapor form. Similar peaks are present in the XRD pattern of the bulk Al-Mg alloy used as the base of WEP.

FIGURE 8.3 High voltage electrical explosion chamber with thin metal plate connected between the electrodes (color image).

FIGURE 8.4

XRD of Al-Mg eutectic alloy (bulk material).

A Novel Approach for Production and Characterization

FIGURE 8.5

137

XRD of Al-Mg eutectic alloy (nanopowder).

The size of the powder particles produced depends mainly on the degree of superheating of the metal vapor, which in turn depends on energy deposited in the plate. Figure 8.6 shows SEM analysis of the powder, which confirms spherical morphology of particles TEM images of the powder shown in Figure 8.7 substantiate the expected spherical structure and size distribution of particles. The diameter of the particles ranges from 10 nm to 90 nm, with the majority of the particles falling below 40 nm of diameter. Figure 8.8 shows the selected area electron diffraction (SAED) pattern. Distinct dots and ring pattern affirm the crystalline structure of the nanoparticles produced. 8.4 CONCLUSION Thin plates are prepared by cutting Al-Mg alloy cast using a low-speed diamond cutter and polished further to reduce the thickness. Nanopowders of Al-Mg eutectic alloy are synthesized by WEP of the plates in the inert ambiance of Argon gas at a chamber pressure of 100 kPa. The powder is characterized by different crystallographic analysis methods. XRD analysis confirms the presence of a major inter-metallic phase as in the parent bulk

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FIGURE 8.6

SEM image of nanopowders.

FIGURE 8.7

TEM image of nanopowders.

FIGURE 8.8

SAED pattern of nanopowders.

A Novel Approach for Production and Characterization

139

Al-Mg alloy. SEM images establish the expected spherical morphology of the powder particles. The diameter of the particles is measured from TEM images of the particles, which are in accordance with the proposed size distribution with the size of the particles ranging from 10 to 95 nm. The results indicate that WEP of thin plates could be a potential alternative for the production of complex intermetallic alloy combinations with a higher level of brittleness. ACKNOWLEDGMENTS This work has been supported by the National Centre for Combus­ tion Research and Development (NCCRD), Department of Aerospace Engineering, Department of Engineering Design and High Voltage Lab– Department of Electrical Engineering Indian Institute of Technology (IIT) Madras, Chennai, India. KEYWORDS • • • • • •

Al-Mg eutectic nanopowder electrical explosion explosion of thin plates nanopowders scanning electron microscope transmission electron microscope

REFERENCES 1. Yanan, G., & Li, Q., (2011). Effects of addition of energetic nanoparticles on fuel droplet combustion at dilute and dense particle loading. 23rd ICDERS, 46. 2. Sindhu, T. K., Sarathi, R., & Chakravarthy, S. R., (2007). Generation of nano aluminum powder through wire explosion process and its characterization. Materials Characterization, 58(2), 148–155. 3. Gregory, Y., Haiyang, W., & Michael, Z. R., (2010). Application of nano aluminum/ nitrocellulose mesoparticles in composite solid rocket propellants. Propellants Explosives Pyrotechnics, 40(3), 35.

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4. Sindhu, T. K., Sarathi, R., & Chakravarthy, S. R., (2008). Understanding nanoparticle formation by a wire explosion process through experimental and modeling studies. Nanotechnology, 19. 5. Nazarenko, O., (2007). Nanopowders produced by electrical explosion of wires. Proceedings of European Congress of Chemical Engineering, 6. 6. Zenin, A. A., Kuznetsov, G. P., & Kolesnikov, V. I., (2011). Combustion of aluminummagnesium alloy particles under microgravity conditions. Russian Journal of Physical Chemistry B., 5, 84–96. 7. Mingxia, Z., Xuewen, L., Zhenye, M., Lixiong, Z., Fengqi, Z., Siyu, X., & Huixiang, X., (2015). Effect of particle size on reactivity and combustion characteristics of aluminum nanoparticles. Combustion Science and Technology, 187, 1036–1043. 8. Santhosh, K. L., Chakravarthi, S. R., Sarathi, R., & Jayaganthan, R., (2017). Thermo­ dynamic modeling and characterizations of Al nanoparticles produced by electrical wire explosion process. Journal of Materials Research, 32(4). 9. Heesung, Y., & Woongsup, Y., (2010). Modeling of aluminum particle combustion with emphasis on the oxide effects and variable transport properties. Journal of Mechanical Science and Technology, 24(4), 909–921. 10. Cho, C., Choi, Y. W., Kang, C., & Lee, G. W., (2007). Effects of the medium on synthesis of nanopowders by wire explosion process. Applied Physics Letter, 91, 141501. 11. Yasmine, A., & Edward, L. D., (2015). Ignition and combustion of Al-Mg alloy powders prepared by different techniques. Combustion and Flame, 162, 1440–1447. 12. Wonbaek, K., Je-Shin, P., Chang-Yul, S., Hankwon, C., & Jae-Chun, L., (2007). Fabrication of alloy nanopowders by the electrical explosion of electrodeposited wires. Materials Letters, 61, 4259–4261. 13. Yasmine, A., Mirko, S., & Edward, D. L., (2013). Ignition and combustion of mechanically alloyed Al-Mg powders with customized particle sizes. Combustion and Flame, 160, 835–842. 14. Hayt, W. H., Kemmerly, J. E., & Durbin, S. M., (2006). Engineering Circuit Analysis (6th edn.). New Delhi, India: Tata Mcgraw-Hill. 15. Lu, L., Dahle, A. K., & St. John, D. H., (2006). Heterogeneous nucleation of Mg-Al alloys. Scripta Materialia, 54, 2197–2201.

CHAPTER 9

Investigation on Wear and Corrosion Behavior of Ti2N Thin Films J. MENGHANI,1 K. B. PAI,2 M. K. TOTLANI,3 and N. JALGOANKAR4 Mechanical Engineering Department, SVNIT Surat, Gujarat, India, E-mail: [email protected] 1

2

ITM Universe, Vadodara, Gujarat, India

Associated with BARC, Mumbai and Later on was Independent Consultant, Mumbai, Maharashtra, India

3

4

Multi-Arc India Ltd., Umargoan, Gujarat, India

ABSTRACT Metal nitride thin films deposited by physical vapor deposition (PVD) have received great interest as wear and corrosion-resistant coating. When the deposition parameters are changed during TiN deposition, a Ti2N coating with interesting properties of corrosion and wear resistance can be deposited. Cathode arc evaporation technique in reactive nitrogen atmosphere was adopted to deposit Ti-N coatings of varying thickness (1.5 µ, 2.0 µ, 2.5 µ, 3.0 µ and 4.0 μm) on 316 stainless steel substrates. In the present study corrosion resistance, wear resistance, and microstructure of thin films of different thickness is investigated. The coefficient of steady-state friction (COF) of the films ranged from 0.284 to 0.6. The results in the case of pin on disc testing indicate that even if COF of 2.0μ Ti-N (0.235) thin film is lower than 4.0μ Ti-N (0.284) thin film, the wear resistance of 4.0 TiN is better because of large steady-state sliding. Corrosion resistance in 0.1 NHCl solution using potentiodynamic test indicates that the highest corrosion resistance is observed in 2μ Ti-N thin films. Thus corrosion and wear properties of the films were dependent on lamellae thicknesses and film structure.

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In many tribological applications, hard coatings of metal nitrides are now commonly used [1, 2]. Metal nitride coatings are usually relatively inert, but there are many factors influencing corrosion behavior. The corrosion and wear resistance of ceramic coating-substrate system depends on the specific properties of coating, its chemical composition, and its structure and physical defects of the coating [3]. Owing to the exceptional abrasion resistance, favorable hardness and higher corrosion resistance, wear resistance, and high melting temperature, TiN coatings have been widely used in practical applications to achieve surface protection of metal materials [4–9]. The cathode arc deposition is one of the most frequently used deposi­ tion techniques. Since it normally yields coating a dense structure and good adhesion to substrate. Cathodic arc is high current, low voltage electrical discharge in which highly ionized plasma coating of electron and ions of background gas and cathode material generated from cathode surface. For coating such as TiN, nitrogen gas is introduced during the arc process, and ionization of N2 can occur during its interaction with electron and ion flux. Therefore, nitrogen-containing compound is deposited on the substrate [10–12]. Environments of deposition and the percentage of reagents in the plane of substrate determines the composition of coating in accordance with the formulas: Ti + N2 = TiN + 0.5N2 2Ti + N2 = 2TiN 3Ti + N2 = Ti2N + TiN 4Ti + N2 = Ti2N + TiN + Ti

(1) (2) (3) (4)

The variables affecting composition of final coating are the degree of ioniza­ tion, condensation of titanium and partial pressure of nitrogen [13]. From the Ti-N phase diagram [14], in addition to δTiN a second Ti2N phase can be formed. Due to more negative formation enthalpy formation of δ-TiN nitride is more thermodynamically favored than the formation of ε-Ti2N nitride. According to the Ti-N equilibrium diagram, δ-TiN formation occurs where there is a local increase in concentration above the solubility limit of nitrogen [15]. Ti2N thin films have much lower residual stresses hence can be depos­ ited with thickness up to tens of micrometers. Most depositions consist of multiphase coatings (Ti-TiN-Ti2N) in which Ti2N are the most abundant phase [16–20].

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143

The present work aims to evaluate the corrosion and sliding wear resistance of Ti-N thin films of varying thickness. For this purpose, elec­ trochemical measurements were performed in 0.1NHCl and wear test were carried out in pin on disk apparatus. Microstructure characterization was done using XRD and SEM. 9.2 EXPERIMENTAL PART 9.2.1 FILM DEPOSITION Titanium nitride thin films were deposited with cathodic arc evaporation (CAE) system at Multi-Arc (I) Ltd, Umargaon. Cathode Ti (99.95%) of 60 mm diameter was used as target. Substrate consists of Stainless Samples of 50 mm in diameter and 2 mm in thickness. Before coating deposition, the samples were chemically degreased, ultrasonically cleaned in acetone for 5 minutes and ethanol for 5 minutes, and then dried in warm air. Lastly, samples were dried in an oven for 30 minutes. After that, they were placed at a distance of 170 mm from the cathode in the vacuum. The chamber was evacuated to a pressure of 5 × 10–5 Pa. Substrates were ion etched with Titanium ion bombardment. The arc current was 60 A. To improve adhesion of Ti-N, a pure titanium layer (about 0.1 μm thick) was deposited on the substrate at a bias voltage of −150 V. Nitrogen at a pressure of 0.007–0.008 MPa was used as a reactive gas. The deposition process was performed at a substrate bias voltage of −150 V for 45 min for varying the time. 9.2.2 WEAR TESTING: PIN ON DISK TESTER The wear tests of the thin films were performed under dry sliding conditions using a pin on disc tribometer (Model TR-20, DUCOM-Bangalore) the procedure followed was as per ASTM G99-17 with continuous rotation. The coefficient of friction (COF) was recorded simultaneously during the tests. The parameters used were load of 4 kg, rotating speed of 200 rpm and a time was 20 minutes. The test procedure involves attachment of the coating to standard 6 mm cylinder pin using adhesive. The counterface disk consists of SAE 52100 steel having a hardness of Rc55 and diameter of 60 cm and rotated at a constant velocity. The configuration ensures that a point (Hertzian) contact is established initially for the wear test, regardless of any small misalignment

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of the pin. From Hertzian contact theory, the contact pressure was calculated to be in the range of 700–800 MPa, which is similar to the contact pressures that industrial coatings are normally subjected to in-service (Figure 9.1) [20].

FIGURE 9.1

Wear testing geometry.

9.2.3 CORROSION TESTING The potentiodynamic polarization was performed in 1000 ml solutions of 0.1NHCl solution using a PARSTAT 273 electrochemical workstation. The Ti-N films acted as a working electrode and the exposed area of all samples was 1 cm2. The platinum electrode and saturated calomel electrode (SCE) were used as counter electrode and reference electrode, respectively. During potentiodynamic polarization measurements, all the tests were performed after stabilizing the open circuit potential. The potential was swept from −1000 mV to 600 mV versus SCE at a scan rate of 0.5 mV/s. 9.2.4 SEM AND XRD CHARACTERIZATION The coating phase composition and average grain size was evaluated by X-ray diffractometer (XRD:PHILIPS PANalyticaX’Per PRO MRD). The Cu Kα line at 0.15405 nm was used as the source for diffraction pattern analysis. All spectra were recorded under the same conditions. The results were interpreted using the JCPDS database. Hitachi 3400S scanning electron microscope (SEM) along with EDS facility was used to evaluate coating morphology, wear, and corroded surface topography.

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145

9.3 RESULTS AND DISCUSSION 9.3.1 MICROSTRUCTURE CHARACTERIZATION Macroparticles are formed at cathode spots together with electrons and ions. The reason for its formation is the increase in pressure of plasma on cathode resulting information of liquid surface which on rapidly quenching forms macroparticles. These macro particles increase surface roughness. Figure 9.2 shows SEM and EDX analysis of 1.5 μm TiN coating. EDX point analysis confirms the presence of macro-particle composed of Ti [21]. 15TN(12) 64915

16193

1

10 μm

15TN(12)_pt1

Full Scale counts: 2462

Ti

2500 2000 1500 1000

Ti

500 0

0 klm - 8 - 0

FIGURE 9.2

2

4

keV

Fe 6

8

10

SEM and EDX analysis of as deposited 1.5 μm TiN thin film.

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The protective efficiency, Pi (%), which is opposite of porosity of the films can be calculated by using electrochemical techniques, by Eqn. (1) [22]. ⎡ ⎛ i ⎞⎤ Pi (%) = ⎢1 − ⎜ corr ⎟ ⎥ × 100 0 ⎣⎢ ⎝ icorr ⎠ ⎥⎦

where; icorr and i0corr represent the corrosion current density in the pres­ ence and absence of coating, respectively. 9.3.2 XRD ANALYSIS When N is added to Ti, Figure 9.3 shows combined diffraction patterns of Ti-N at different thickness (1.5, 2.0, 2.5, 3.0 and 4.0μ). Peaks corresponding to the Ti2N and γ Fe are observed. All the peaks corresponding to Ti2N formation showed the greatest intensity and it was predominant. This means that the phases in the coating did not alter with the coating thickness. The peak corresponding to γ Fe (Peak 2 and Peak 3) are from the stainless steel substrate, the height of Fe diffraction peaks rapidly decreases with the increase of the thickness of TiN coating, indicating the complete coverage of the coating. As per Ti-N phase diagram nitrogen stabilizes α Ti to higher temperature. Several crystallographic phases of TiN exist depending on temperature and nitrogen atomic percentage. The primary nitride phases TiN crystallizing in rock salt structure (fm3m) with lattice parameter of 4.24 A° for stoichiometric TiN (N/Ti = 1) sub-stoichiometric Ti2N (N/ Ti = 0.5) the other major Ti-N compound has two known phases e-Ti2N and δ-TiN. The δ-Ti2N phase is metastable and transforms by aging into thermodynamically active e-Ti2N. The e-TiNx transition metal nitride has a tetragonal structure which is related to bcc β-Ti and to hcp α-Ti [10, 23, 24]. However, in the present case (Figure 9.3), we have obtained Ti2N for all the coatings. The average grain size can be estimated from the full-width at halfmaximum (FWHM) of peak by Sherrer’s relation [25]: D=

kλ β cos θ

where, λ, θ, and B are the x-ray wavelength, Bragg diffraction angle and FWHM in radians, respectively. The average grain size, COF, and electro­ chemical results are, as listed in Table 9.1.

Investigation on Wear and Corrosion Behavior of Ti2N Thin Films

FIGURE 9.3 TABLE 9.1

147

Combined XRD spectra of Ti-Nx films of varying thickness. Characteristics of the Ti-N Coatings of Varying Thickness

Sr. Sample No.

Grain Size COF (nm)

Ecorr (mV) Icorr (µA/cm2) Protective Efficiency P (%)

1.

S. S

-

-

–408 mV

31.05 µA/cm2 ­

2.

1.5 μm Ti-N

6.775 nm

0.6

–422.2 mV

696.7 µA/cm2

97.75%

3.

2.0 μm Ti-N

7.996 nm

0.325

–421.4 mV

1.540 µA/cm

99.99%

4.

2.5 μm Ti-N

6.44 nm

0.30

–427.3 mV

2

454.8 µA/cm

98.54%

5.

3.0 μm Ti-N

5.732 nm

0.321

–417.6 mV

123.2 µA/cm2

99.61%

6.

4.0 μm Ti-N

4.318 nm

0.284

–420.6 mV

102.0 µA/cm

99.68%

2

2

9.3.3 TRIBOLOGICAL PERFORMANCE 9.3.3.1 WEAR DEBRIS Figure 9.4(a) for 1.5μ Ti-N thin films shows the shallow plowing grooves on the surface of the specimen. Some pores corresponding to the removal of Ti rich macroparticles are observed. EDX analysis (ii) indicates the intense peak of iron and small peak of Ti and oxygen. SEM analysis at high magnification Microgrooves are formed which are associated with crack nucleation on surface, subsequent crack propagation and finally loose particles of large size are trapped and dragged along resulting in formation of macrogrooves [19]. The plate-shaped particles are observed in the wear residues, indicating plow

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wear, nucleation, and propagation of subsurface cracks or plastic cutting in asperity contact [26]. Figure 9.4(b) for 2.0μ Ti-N thin films, the damage pattern indicates that plastic deformation occurred to some extent via plowing and wedge forma­ tion. The results are similar as obtained by Ref. [27] within the wear track shows compact and very fine-grained submicron-sized wear debris particles. EDX analysis at high magnification indicates intense peak of iron and the weak peak of Ti, indicating removal of Ti-N coating. Very less quantity of small spherical shape particles are observed in wear track, the reason being, wear particles may not escape from interface to become loose debris and some remain trapped and appear as spherical. The damage pattern indicates that plastic deformation occurred via adhesive wear [26, 28]. For (c) 2.5μ Ti-N thin films indicate that the film worn off only at some locations. Delamination may have originated from either a surface crack or a macroparticle. Similar behavior is observed by Chatterjee et al. [29] EDX analysis Figure 9.4(d) at high magnification indicates intense peak of iron and less intense peak of Ti. Slight reduction in intensity of Ti peak at high magnifi­ cation (within wear track) compared to that at low magnification large coverage area, indicating incomplete removal of coating. Eccentrically shaped particles are observed within the wear track designating wear debris are engendered by detachment of transferred fragments in adhesive wear and brittle fracture [26]. For (d) 3.0μ Ti-N thin films, (i) grooves are observed on the wear track; (ii) indicates the intense peak of Ti and weak peak of iron and oxygen indicating that Ti-N coating is intact. SEM analysis at high magnification indicates the formation of a continuous, thick layer of debris-covered at the center of the wear scar, which was formed during the tribo-oxidation process by repeatedly grinding and rubbing similar behavior is observed by Moa et al. [28] for TiAlN coatings were deposited on cemented carbide by the arc-physical vapor deposition. Irregular shaped particles are observed within the wear track indicating wear debris are produced by detachment of transferred fragments in adhesive wear and brittle fracture [26]. For (e) 4.0μ Ti-N thin films, (i) shallow grooves are observed. There is crack perpendicular to sliding direction within the coating is observed on the wear track. The explanation for this is when the plastic deformation of substrate is exceeded material causes the formation of micro-cracks, where the intersection of these cracks results in material removal after repeated sliding contacts. The deep degradation results from a crack propagation perpendicular to the substrate plane, leading to the formation of large debris [30]. (ii) indicates the intense peak of Ti and weak peak of iron and oxygen, indicating that Ti-N coating is intact. SEM analysis at high magnification.

Investigation on Wear and Corrosion Behavior of Ti2N Thin Films

(a) 1.5μ Ti-N Thin Films (Continued)

(c) 2.5.0μ Ti-N Thin Films

149

FIGURE 9.4

(b) 2.0μ Ti-N Thin Films

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150

(d) 3.0μ Ti-N Thin Film

(e) 4.0μ Ti-N Thin Film

FIGURE 9.4 SEM micrograph and EDX analysis of TiN coating of varying thickness (a) 1.5 μm Ti-N thin films, (b) 2.0 μm Ti-N thin films, (c) 2.5 μm Ti-N thin films, (d) 3.0 μm Ti-N thin films, and (e) 4.0 μm Ti-N thin films.

9.3.3.2 COEFFICIENT OF FRICTION (COF) The changes in wear resistance due to the increase in thickness is due to the difference in hardness of resultant coating and the adhesive strength between film and substrate (Figure 9.5) [31]. The initial wear was related to the surface state of the specimen [2] and microstructure [32, 33]. The macroparticles existing on the sample surface played an important role in this stage. All the coatings except 1.5μ TiN had similar run-in friction coefficient values. The friction coefficient of 1.5μ TiN coating increase rapidly due to the presence of titanium-rich particles of rounded morphology, and these particles have a different distribution over the coatings surface. Metallic titanium adheres to the steel ball, and therefore notably contributes to the increase in the friction coefficient value [34].

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151

FIGURE 9.5 Variation in coefficient of friction (COF) with time for Ti-N of varying thickness during wear testing.

During sliding, changes in the conditions of mating surfaces occur which affect friction and wear properties. After some period, the so-called “run-in,” “break-in” or “wearing-in” period, the friction force generally stabilizes into what is called steady-state sliding [26]. This wearing period is usually taken as the criterion for evaluating the wear resistance of materials. The wider this period, the better the wear resistance [35]. In general, friction is believed to result from three components: adhesion, plowing, and asperity deformation. The increase in COF can be attributed to two effects which play in a synergetic way. From one side, consumption of the protective layer leaves the surface more weak against wear and on the other hand, debris produced increases COF [26]. The 1.5 and 2.5μ TiN coating exhibited a different debris abstracting morphology from the 3μ TiN coating at the edge of the wear track. The initial increase in COF is associated with plowing because of roughening and trapped wear particles remaining in the wear track. Although COF of 2.0μ Ti-N (0.235) thin film is lower than 4.0μ TiN (0.284) thin film, the wear resistance of 4.0 TiN is better because of large steady-state sliding. 9.3.4 ELECTROCHEMICAL PROPERTIES For comparison, the polarization behavior of the substrate is plotted. In the anodic region, the current density of all the coatings is higher than

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the substrate. The corrosion current density is often used as an important parameter to evaluate the kinetics of corrosion reactions. Corrosion protec­ tion is normally inversely proportional to the corrosion current density (io) measured via polarization [36]. In this case, where PVD coatings are chemically not reactive, the corrosion current density indicates pores in the coatings, where the electrochemical reaction of the substrate takes place. Although icorr value is low, the current in the anodic region for all the thick­ ness is higher than stainless steel (Figure 9.6). 600.0 3TI2N

400.0 200.0

1.5TI2N

E (nU)

0.0 2.5TI2N

-200.0

2TI2N

-400.0 -600.0 4TI2N

-800.0 -1000.0

-8

-7

-6

-5

-4

I/area (A/cmẐ)

-3

-2

-1 10n

FIGURE 9.6 An overlap of the potentiodynamic polarization curves representative of the behavior of the samples prepared with the variation thickness is presented.

For all the coated samples, the icorr is two or three orders of magnitude lower than that of the substrate, revealing an improved corrosion resistance of the film. From the corresponding curve, the anodic current density for 2μ Ti-N and 4μ Ti-N changes a little with potential increasing from –200 mV to the breakthrough potential +150 mV. In this interval, the passive layer protects the specimen surface from dissolving. While, anodic current density increases dramatically with potential over 200 mV, probably due to a pitting corrosion mechanism initiated at the local defects of the film [37]. The formation of the pit can be further confirmed by considering the curve in the cathodic region. In cathodic polarization, one can see that the coated samples starts at a current lower than the stainless steel, but near the corro­ sion potential, the coated sample current increases until it becomes almost equal to that of stainless steel. This phenomenon can be explained by pitting of the coatings at defect sites [38].

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153

The compositional analysis of coatings after potentiodynamic test was done using EDX attached to SEM. Figure 9.7 indicates the large peak of Ti, and small peaks of Fe, and Mn indicating less intense corrosive attack. The coating system shows few very small and shallow pits.

Electron Image 1

400μm

Cl

Sun Spectrum

Ti

O Ti Cr Mn Fe Ca Si K Na Al Mg

S Cl

K

Ca K Ca

4 0 1 3 2 Full Scale 2123 cts Cursor: 0.000 keV FIGURE 9.7 0.1N HCl.

Ti

5

Mn Cr Cr 6

Fe Mn Fe 7

8

9

10 keV

The EDX analysis of 1.5μ Ti-N thin film subjected to potentiodynamic test in

9.4 CONCLUSIONS 1. Effect of lamelle thickness on composition, wear, and corrosion behavior of Ti-N. The coatings deposited by cathodic arc plasma evaporation were achieved.

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2. Number and size of pinholes determines corrosion resistance of thin films. Diffusion of electrolyte occurs through pinholes and attack underneath substrate and causes corrosion. Highest corrosion resis­ tance was observed in 2μ Ti-N. This may be due to less number of porosity and dense structure. 3. Higher internal stresses and high porosity and the presence of macro Ti particles within 1.5 μm Ti-N is reflected in terms of low corrosion resistance. 4. The 1.5 and 2.5μ TiN coating exhibited different debris removing morphology from the 3μTiN coating at the edge of the wear scar. The debris (tribo-chemical products) of the 2.0μ and 2.5μ TiN coating was ejected out and accumulated around the edge, while the debris of the 3μ TiN coating was difficult to be ejected out of the wear scars. 5. Friction and wear are believed to result from three components: adhesion, plowing, and asperity deformation, which are different in the coating of different thickness. ACKNOWLEDGMENTS This research has been supported by AICTE research promotion scheme (RPS) entitled “Nano Composite Zirconium-Based Thin Films for Functional application,” F.No.: 8023/RID/BOR/RPS-134/2005–2006. I am especially thankful to Prof. S. N Pathak, Head, Materials Engineering Department VNIT Nagpur and Dr. D. R. Peshwe for their valuable guidance. Its characteristic is micro-abrasion (micro-cutting), i.e., a continued formation of asperities on the contact body generates grooves in the wear track. KEYWORDS • • • • • •

cathodic arc evaporation coefficient of friction full-width at half-maximum saturated calomel electrode scanning electron microscope x-ray diffractometer

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18. Ljungcrantz, H., Hultman, L., Sundgren, J. E., Håkansson, G., & Karlsson, L., (1994). Microstructural investigation of droplets in arc-evaporated TiN films. Surface and Coatings Technology, 63(1/2), 123–128. 19. Perry, A. J., Treglio, J. R., & Tian, A. F., (1995). Low-temperature Deposition of titanium nitride. Surface and Coatings Technology, 76, 815–820. 20. Yang, S. M., Chang, Y. Y., Wang, D. Y., Lin, D. Y., & Wu, W., (2007). Mechanical properties of nano-structured Ti-Si-N films synthesized by cathodic arc evaporation. Journal of Alloys and Compounds, 440(1/2), 375–379. 21. André, A., (2008). Cathodic Arcs: From Fractal Spots to Energetic Condensation. ISSN: 1615-5653, ISBN: 978-0-387-79107-4, e-ISBN: 978-0-387-79108-1. doi: 10.1007/978-0-387-79108-1. 22. Wagner, J., Mitterer, C., Penoy, M., Michotte, C., Wallgram, W., & Kathrein, M., (2008). The effect of deposition temperature on microstructure and properties of thermal CVD TiN coatings. International Journal of Refractory Metals and Hard Materials, 26(2), 120–126. 23. PalDey, S., & Deevi, S. C., (2003). Properties of single layer and gradient (Ti, Al) N coatings. Materials Science and Engineering: A, 361(1/2), 1–8. 24. Logothetidis, S. B., Alexandrou, I. B., & Kokkou, S. B., (1996). Optimization of TiN thin film growth with in situ monitoring: The effect of bias voltage and nitrogen flow rate. Surface and Coatings Technology, 80(1/2), 66–71. 25. Lee, Y. C., Hu, S. Y., Water, W., Tiong, K. K., Feng, Z. C., Chen, Y. T., Huang, J. C., et al., (2009). Rapid thermal annealing effects on the structural and optical properties of ZnO films deposited on Si substrates. Journal of Luminescence, 129(2), 148–152. 26. Bhushan, B., (2013). Introduction to Tribology. John Wiley & Sons. 27. Boxman, R. L., Zhitomirsky, V., Alterkop, B., Gidalevich, E., Beilis, I., Keidar, M., & Goldsmith, S., (1996). Recent progress in filtered vacuum arc deposition. Surface and Coatings Technology, 86, 243–253. 28. Mo, J. L., Zhu, M. H., Lei, B., Leng, Y. X., & Huang, N., (2007). Comparison of tribological behaviors of AlCrN and TiAlN coatings—Deposited by physical vapor deposition. Wear, 263(7–12), 1423–1429. 29. Chatterjee, A., Jayaraman, S., Gerbi, J. E., Kumar, N., Abelson, J. R., Bellon, P., Polycarpou, A. A., & Chevalier, J. P., (2006). Tribological behavior of hafnium diboride thin films. Surface and Coatings Technology, 201(7), 4317–4322. 30. Steyer, P., Mege, A., Pech, D., Mendibide, C., Fontaine, J., Pierson, J. F., Esnouf, C., & Goudeau, P., (2008). Influence of the nano structuration of PVD hard TiN-based films on the durability of coated steel. Surface and Coatings Technology, 202(11), 2268–2277. 31. Nolan, D., Huang, S. W., Leskovsek, V., & Braun, S., (2006). Sliding wear of titanium nitride thin films deposited on Ti-6Al-4V alloy by PVD and plasma nitriding processes. Surface and Coatings Technology, 200(20/21), 5698–5705. 32. Savisalo, T., Lewis, D. B., Luo, Q., Bolton, M., & Hovsepian, P., (2008). Structure of duplex CrN/NbN coatings and their performance against corrosion and wear. Surface and Coatings Technology, 202(9), 1661–1667. 33. Jiménez, H., Restrepo, E., & Devia, A., (2006). Effect of the substrate temperature in ZrN coatings grown by the pulsed arc technique studied by XRD. Surface and Coatings Technology, 201(3/4), 1594–1601. 34. Bull, S. J., Bhat, D. G., & Staia, M. H., (2003). Properties and performance of commercial TiCN coatings. Part 1, coating architecture and hardness Modeling. Surface and Coatings Technology, 163, 499–506.

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35. Lang, F., & Yu, Z., (2001). The corrosion resistance and wear resistance of thick TiN coatings deposited by arc ion plating. Surface and Coatings Technology, 145(1–3), 80–87. 36. Darja, K. M., Peter, P., Miha, Č., & Marijan, M., (2004). The corrosion behavior of Cr-(C,N) PVD hard coatings deposited on various substrates. Electrochimica Acta, 49(9/10), 1371–1698. 37. Li, L., Erwu, N., Guohua, L., Xianhui, Z., Huan, C., Songhua, F., Chizi, L., & Si-Ze, Y., (2007). Synthesis and electrochemical synthesis of Ta-N thin films fabricated by cathode arc deposition. Applied Surface Science, 253(16), 6811–6816. 38. Flores, M., Blanco, O., Muhl, S., Piña, C., & Heiras, J., (1998). Corrosion of a Zn-Al-Cu alloy coated with TiN/Ti films. Surface and Coating Technology, 108, 109, 449–453.

CHAPTER 10

Structural Study of Ethylene GlycolAssisted Solution Combustion Synthesis of Strontium Doped LaMnO3 P. V. JITHIN and JOJI KURIAN Department of Physics, Nirmalagiri College, Nirmalagiri P. O., Kannur–670701, Kerala, India, E-mail: [email protected] (J. Kurian)

ABSTRACT Single-phase LaMnO3 (lanthanum manganite) and Sr (strontium)-doped LaMnO3 samples are prepared by ethylene glycol assisted solution combustion method. The samples are sintered at 650°C and 850°C and studied for their structural properties. Thermogravimetric-differential scanning calorimetric (TG-DSC) measurements give the information about the perovskite phase formation temperature, which is around 600°C. The structural phase formation of the samples is confirmed using the x-ray diffraction (XRD) studies. From the Rietveld refined XRD data, it is clear that Sr doping allows the orthorhombic phase to evolve at the expense of the rhombohedral phase. The Fourier transform infrared (FT-IR) spectro­ scopic studies confirmed that the method of preparation employed gives only the perovskite structure of the sample, with no impurity/secondary phases being formed. The absorption intensities of the FTIR spectra diminished with an increase in the dopant concentration, probably because of the transition into the metallic phase of the samples. Similarly, this can be attributed to the strain induced by the ionic mismatch of the substituted divalent strontium cation at the A-site of lanthanum manganite.

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10.1 INTRODUCTION The compounds with chemical formula ABO3, where ‘A’ represents rare earth or alkaline earth element and B stands for transition metal ion are oxide compounds which can crystallize in the perovskite structure. Crystallization of these compounds occurs in the perovskite structure. In this class of mate­ rials, lanthanum-based manganite perovskites are of materials in this class of perovskite oxides, La-based manganites have been extensively studied for their various properties [1]. The property of colossal magnetoresistance (CMR) exhibited in hole-doped LaMnO3 (LMO) renewed interest in the study on these materials [2]. This renewed interest of research in such mate­ rials arose from their possible applications in magneto-electronic devices, spin-polarized transport devices, magnetic recording heads, etc., [3]. Doped La-based manganites show a wide range of magnetic and electrical transport properties, depending on the nature of the characteristic to the nature of dopant, the site of the dopant and its concentration. A multifold variation in the magnetoresistance in Ca doped LaMnO3 (LCMO) films were reported by Jin et al., making this a potential candidate for various applications. This finding makes LCMO an important material for various applications [4]. Incorporation of a divalent cation at the A-site, results in mixed valance manganites. This can lead to Mn3+/Mn4+ electrons hopping through the Mn3+-O-Mn4+ network, thereby possibly increasing the conductivity in such samples [5]. This type of electron transfer mechanism introduces metallic and ferromagnetic (FM) nature in LaMnO3 [which is an antiferromagnetic (AFM) type mott insulator] when elements like Sr, Ca, etc., are doped at the La site [6]. A metal to insulator (M-I) transition as well as paramagnetic to ferromagnetic (PM-FM) at the Curie temperature (TC) are phenomena observed in La-based manganite samples, with the introduction of a dopant at the La or Mn site [7]. Use of dopants can also lead to super-exchange (SE) interactions ensuing in the AFM nature of pristine LaMnO3 [2, 8]. The simultaneous occurrence of electrical and magnetic phase transitions makes perovskite manganites a class of interesting materials to be studied for their various properties. Research groups around the world working on La-based manganites have adopted conventional sample processing techniques for the preparation of the samples, like co-precipitation [9, 10], solid-state reaction [11, 12], hydrothermal method [13, 14], sol-gel process [15–17], microwave synthesis [18], with these samples exhibiting M-I and PM-FM transitions. These studies reveal that in perovskite La-manganites, the experimental parameters

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chosen can affect the observed properties of the samples, some of which are not completely understood to date, making studies on these materials very challenging. All the above-mentioned preparation techniques need high temperature and long durations of sintering for the single-phase formation of the LSMO samples. Ghosh et al. reported that Sr-doped LaMnO3 (LSMO) material needs temperature higher than 1000°C for the single-phase formation of samples prepared using co-precipitation techniques [8]. At the same time, various other research groups have argued that the sol-gel method can be used to synthesize LSMO samples at relatively lower sintering temperature compared with the solid-state reaction and co-precipitation method [19–22]. In this work, we report the synthesis of La1–xSrxMnO3 (x = 0, 0.1. 0.2, 0.3) (LSMO) via the ethylene glycol assisted solution combustion method. This is in view of the possibility of manipulating the properties of the samples by minutely altering the sample synthesis method. To the best of our knowledge, no report has been made on the study of La-manganites prepared using this sample synthesis technique. This study highlights the structural evolution of the samples as a function of Sr content. 10.2 EXPERIMENTAL PART Strontium (Sr) doped polycrystalline LaMnO3 samples (LSMO) are prepared for this study by ethylene glycol assisted solution combustion method. Stoi­ chiometric amounts of analytical grade lanthanum nitrate (LaN3O9.6H2O), strontium nitrate (Sr(NO3)2), and manganese acetate (C4H6MnO4.4H2O) are dissolved in ample amounts of distilled water and stirred on a preheated magnetic stirrer. Then ethylene glycol (C2H6O2) is added to this solution, maintaining the metal nitrate to ethylene glycol ratio at 1:21. The heated solu­ tion slowly evaporates, turning the resultant solution brown in color, which then suddenly gets ignited. The whole combustion process is completed within few seconds, resulting in a black-colored fluffy pile of ash. The collected samples were finely ground and calcined at two different temperatures, 650°C and 850°C, for 6 hours. The amount of Sr content varies from 0 to 30% and the prepared samples are named as LMO, LS1MO, LS2MO and LS3MO, respectively, S1, S2, and S3 being used to signal 10, 20 and 30% of Sr doping. The calcined samples are characterized using thermogravimetric-differential scanning calorimetric (TG-DSC), XRD (Rigaku MiniFlex-600), and Fourier transform infrared spectrometric (FTIR) (Agilent Cary-630 with KBr pellet) studies. The TGA-DSC studies are carried out using a NETZSCH simulta­ neous thermal analyzer F3 Jupiter system, heating the as-prepared sample

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from room temperature (RT) up to 850°C, with a heating rate of 10 K/min, in the nitrogen atmosphere. 10.3 RESULTS AND DISCUSSION Figure 10.1 depicts the various stages of the LSMO sample preparation process. The dried solutions are ignited spewing huge flames and produce black colored fluffy ashes. During this exothermic reaction large amount of heat energy is released. This energy is used for the phase formation of the LSMO samples.

FIGURE 10.1

Combustion reaction of LSMO sample.

The structural properties of the as-prepared samples are studied using the XRD patterns. From the XRD measurements, it is clear that the as-prepared samples crystallize in the perovskite phase with very small content of impurity phases. The samples are then used for the TG-DSC analysis, which gives information on the evolution of the crystalline phase of the LSMO sample. From the TG studies, it is evident that there is very little weight loss in the prepared samples with temperature. This means that the chemical reaction is almost complete during the initial combustion reaction. The broad exothermic peak in the DSC curve in the range of 200 to 600 indicates the decomposition of the un-reacted part of the starting precursor. Only a slight weight loss is observed for temperatures higher than 600°C. This is indica­ tive of the perovskite phase formation, beginning at ~ 600°C prolonged sintering above this temperature may result in the bulk form of the material (Figure 10.2). The XRD patterns of the pristine LSMO system and those of samples sintered at higher temperatures are depicted in Figure 10.3. The sintering process is done to confirm the temperatures at which the samples must be

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heated to obtained good phase formations. The XRD patterns of the samples have been recorded for Bragg angles ranging from 20° to 80° using Cu-Kα radiation (λ = 1.54Å). The XRD data are Rietveld refined using MAUD program to extract the structural information; the refined patterns are depicted in Figure 10.4. This corroborates guaranteed single-phase formation on utilizing higher sintering temperature [23]. The diffraction peaks observed in the diffraction patterns of each of the polycrystalline samples depicts the highly crystalline nature of the samples. No other additional impurity peaks were detected within in the resolution capacity of the XRD instrument.

FIGURE 10.2

TG-DSC curve of La0.9Sr0.1MnO3 sample.

From the refinement process (Figure 10.4), it is apparent that the rhombohedral (R3c) geometry is the dominant crystalline phase for LMO samples. Substitution of La by Sr increases the relative weight percentage of orthorhombic (Pbnm) crystalline phase as observed from the tabulated values in Table 10.1. This slow structural evolution of the samples is evident only on closer inspection of the XRD data between the 2θ range of 31° and 34°, which is shown in the inset of Figure 10.5. Accordingly, it is found that with an increase in the Sr content, the doublet peak around 32.5° completely disappeared and merged into a single peak, which is an indication of the phase transformation (PT). A slight decrease in the lattice parameters of the two phases is observed. This indicates that more Mn3+ ions convert to Mn4+ ions, maintaining the electrical neutrality almost stable. This points to the possibility of increased conductivity of the samples, which may be due to double exchange interaction via the Mn3+-O-Mn4+ network thus being

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formed. It can be positively speculated that in either of the magnetic phases (PM or FM phase) the magnetic moments may be higher in these samples. This diminishing cell volume of the two phases is another indication of this change. This is because, the variation in the ionic radii of the Mn3+ (0.645Å) and Mn4+ (0.53Å) [5]. From the table, it is also observed that the average crystallite size of the sample decreases with an increase in the doping concentration. A graphical representation of the effect of dopant concentra­ tion on the crystallite size and lattice parameter of the rhombohedral phase of the sintered sample is shown in Figure 10.5.

FIGURE 10.3

XRD pattern of La1–xSrxMnO3 (0 ≤ x ≤ 0.3) sample.

FIGURE 10.4

Rietveld refined XRD pattern of La1–xSrxMnO3 (0 ≤ x ≤ 0.3) heated at 850°C.

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FIGURE 10.5

Effect of dopant on the lattice parameter and crystallite size of the sample.

TABLE 10.1

Refined Structural Parameters of La1–xSrxMnO3 (0 ≤ x ≤ 0.3) Heated at 850°C*

Sample

Space Group

Wt. Percent a (Å) (%) (±0.01)

b (Å) (±0.01)

c (Å) (±0.01)

V (Å)

D (nm) (±2)

LMO

R-3c

98.1%

5.522

–

13.369

352.9

73

Pbnm

1.9%

5.707

5.585

7.729

246.3

R-3c

90.0%

5.524

–

13.371

353.2

Pbnm

10.0%

5.497

5.547

R-3c

84.7%

5.513

Pbnm

15.3%

5.467

LS1MO LS2MO LS3MO *

R-3c

70.6%

5.509

Pbnm

29.4%

5.463

5.529 5.523

7.766

236.8

13.369

351.7

7.740

233.9

13.374

351.5

7.726

233.1

97 79 65

Values of the lattice parameters (a, b, c), cell volume (V) and crystallite size (D) are tabulated.

Figure 10.6 shows the bonding characteristics of the sintered samples (850°C). The full range spectra are shown in the inset of the figure. There are 20 vibrational modes, in which only eight modes are IR active. It is known that 15 normal modes of vibrations are observed in ideal perovskite struc­ tures. Of these, only three vibrational modes are present in the wavenumber region between 200 to 800 cm–1 [24]. In the present study, the main absorp­ tion band at ~ 600 cm–1 corresponds to the stretching vibration (ʋs). The major absorption feature at ~ 600 cm–1 represents the stretching vibration (ʋs) of Mn-O bond in the perovskite, which involves the change in Mn-O-Mn bond length in the MnO6 octahedron. The band near 400 cm–1 indicates the vibration of Mn-O-Mn bond in the bending mode (ʋb) [25]. The bands near 920 cm–1 correspond to the existence of carbonate in the undoped sample,

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which probably due to the residual phase from the starting materials used. From the bending and stretching vibrations, it is evident that the prepared samples are single phase formed, and the XRD results are in good agreement with the theoretical studies.

FIGURE 10.6

FTIR spectrum of La1–xSrxMnO3 (0 ≤ x ≤ 0.3) sintered at 850°C.

From the figure, it is clear that the stretching absorption intensity of the sample decreases with an increase in the dopant concentration. According to the dopant concentration, the stretching absorption intensity of the sample decreases. Thus, this is an indication of the possibilities of the inherent metallic nature of the sample. It is also observed that the absorp­ tion feature pertaining to the bending mode of vibration decreases with an increase in the concentration of strontium to 30 wt%. This can be attributed to the strain being induced in the material due to ionic size mismatch, on increasing the content of Sr in the samples. The decrease of the size of the sample crystallites is the result of the strain arising due to the increase in the Sr content [26]. 10.4 CONCLUSION The current work highlights variation in the structural properties of Sr-doped LaMnO3 nanoparticles synthesized via the ethylene glycol assisted solution combustion method. TG-DSC data gives information about the perovskite phase formation temperature, and data shows that this occurs at 600°C.

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The Rietveld refined XRD data showed better phase formation in samples sintered at a higher temperature. The addition of Sr increases the concentra­ tion of the orthorhombic phase. The cell volume and average crystallite size of the samples decrease with an increase in the Sr content. The spectroscopic studies affirm that perovskite structured LMO and LSMO systems can be obtained via the synthesis methods opted for in this study, in spite of using such low sintering temperatures and for such short durations. The inherent metallic nature of the material can be clearly observed from the decrease of absorption intensities of the stretching and bending vibration modes of the samples. This also gives information about the incorporation of strain in the host material due to the ionic radii mismatch of the dopant and parent A-site cation. KEYWORDS • • • • • •

colossal magnetoresistance combustion magnetic phases phase transformation refinement super-exchange

REFERENCES 1. Julien, V., Manuel, B., & Zunger, A., (2019). Origin of band gaps in 3 d perovskite oxides. Nat. Commun., 10(1658), 1–11. 2. Endoh, Y., Hirota, K., Ishihara, S., Okamoto, S., Murakami, Y., Nishizawa, A., Fukuda, T., et al., (1999). Transition between two ferromagnetic states driven by orbital ordering in La0.88 Sr0.12 MnO3. Phys. Rev. Lett., 82(21), 4328–4331. 3. Nogués, J., & Schuller, I. K., (1999). Exchange bias. J. Magn. Magn. Mater., 192(2), 203–232. 4. Jin, S., Tiefel, T. H., Mccormack, M., Fastnacht, R. A., Ramesh, R., & Chen, L. H., (1994). Thousandfold change in resistivity films magnetoresistive. Science, 264, 413–415. 5. Li, L., Wang, C. B., Shen, Y. J., Shen, Q., & Zhang, L. M., (2015). Influence of annealing on structure and thermochromic property of spark plasma sintered La1-xSrxMnO3 compounds. J. Mater. Sci. Mater. Electron, 26(4), 2508–2513.

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6. Kansara, S. B., et al., (2017). Structural, transport and magnetic properties of monovalent doped La1-xNaxMnO3 manganites. Ceram. Int., 41(5), 7162–7173. 7. Tola, P. S., Kim, D. H., Liu, C., Phan, T. L., & Lee, B. W., (2016). Ferromagnetism in LaMnO3 nanoparticles prepared by sol-gel method combined with polyvinyl alcohol. J. Electron. Mater., 45(7), 3501–3508. 8. Paraskevopoulos, M., Mayr, F., Hemberger, J., Loidl, A., Heichele, R., Maurer, D., Muller, V., Mukhin, A. A., & Balbashov, A. M., (2000). Magnetic properties and the phase diagram of La1-xSrxMnO3 for x≤0.2. J. Phys. Condens. Matter, 12(17), 3993–4011. 9. Ghosh, A., Sahu, A. K., Gulnar, A. K., & Suri, A. K., (2005). Synthesis and characterization of lanthanum strontium manganite. Scr. Mater., 52(12), 1305–1309. 10. Mahmood, A., Warsi, M. F., Ashiq, M. N., & Sher, M., (2012). Improvements in electrical and dielectric properties of substituted multiferroic LaMnO3 based nanostructures synthesized by co-precipitation method. Mater. Res. Bull., 47(12), 4197–4202. 11. Grossin, D., & Noudem, J. G., (2004). Synthesis of fine La0.8Sr0.2MnO3 powder by different ways. Solid State Sci., 6(9), 939–944. 12. Shu, Q., Zhang, J., Yan, B., & Liu, J., (2009). Phase formation mechanism and kinetics in solid-state synthesis of undoped and calcium-doped lanthanum manganite. Mater. Res. Bull., 44(3), 649–653. 13. Ngida, R. E. A., Zawrah, M. F., Khattab, R. M., & Heikal, E., (2018). Hydrothermal synthesis, sintering and characterization of nano La-manganite perovskite doped with Ca or Sr ceram. Int., 45(4), 4894–4901. 14. Spooren, J., Walton, I., & Millange, F., (2005). A study of the manganites La0.5M0.5MnO3 (M=Ca, Sr, Ba) prepared by hydrothermal synthesis. J. Mater. Chem., 15(15), 1542–1551. 15. Pandya, D. D., Asokan, K., Shah, N. A., & Solanki, P. S., (2018). Studies on transport properties of manganite-based nano-micro particles-matrix composites. J. Alloys Compd. 16. Yin, X., Liu, X., Yan, Y., & Chen, Q., (2014). Preparation of La0.67Ca0.33MnO3,Ag x polycrystalline by sol-gel method. J. Sol-Gel Sci. Technol., 70(3), 361–365. 17. Ravi, S., & Karthikeyan, A., (2014). Effect of calcination temperature on La0.7Sr0.3MnO3 nanoparticles synthesized with modified sol-gel route. Phys. Procedia., 54(2004), 45–54. 18. Chen, W., Li, F., Liu, L., & Liu, Y., (2006). One-step synthesis of nanocrystalline perovskite LaMnO3powders via microwave-induced solution combustion route. J. Rare Earths, 24(6), 782–787. 19. Bishnu, D. R., Kyle, S., Megan, A. M., Ronald, T. J., Yung, H., & Parashu, K., (2018). Near-room-temperature magnetocaloric properties of La1-xSrxMnO3 (x = 0.11, 0.17, and 0.19) nanoparticles. Mater. Res. Express, 5(10), 106103. 20. Belkahla, A., Cherif, K., Belmabrouk, H., Bajahzar, A., Dhahri, J., & Hlil, E. K., (2019). Influence of non-magnetic ion In3+ on the magneto-transport properties in La0.7Bi0.05Sr0.15Ca0.1Mn1-xInxO3 (0 ≤x≤0.3) perovskite. Solid State Commun., 294, 16–22. 21. Kaman, O., Jirák, Z., Hejtmánek, J., Ndayishimiye, A., Prakasam, M., & Goglio, G., (2019). Tunneling magnetoresistance of hydrothermally sintered La1-xSrxMnO3-silica nanocomposites. J. Magn. Magn. Mater., 479, 135–143. 22. Navin, K., & Kurchania, R., (2019). Influence of BaTiO3 on magnetic and transport properties of La0.7Sr0.3MnO3-BaTiO3 nanocomposite. J. Supercond Nov. Magn., 32(3), 539–547.

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23. Lutterotti, L., Matthies, S., Wenk, H. R., Schultz, A. S., & Richardson, J. W., (1997). Combined texture and structure analysis of deformed limestone from time-of-flight neutron diffraction spectra. J. Appl. Phys., 81(2), 594–600. 24. Kumar, N., Kishan, H., Rao, A., & Awana, V. P. S., (2010). La0.7Ca0. 3Mn1− xCrxO3 (0 ≤ x ≤ 1) manganites. J. Appl. Phys., 107(8), 083905-0-6. 25. Gao, F., Lewis, R. A., Wang, X. L., & Dou, S. X., (2002). Far-infrared reflection and transmission of La1-xCaxMnO3. J. Alloys Compd., 347(1/2), 314–318. 26. Roy, C., & Budhani, R. C., (1999). Raman, infrared and x-ray diffraction study of phase stability in La1-xBaxMnO3 doped manganites. J. Appl. Phys., 85(6), 3124–3131.

CHAPTER 11

Molecular Dynamics Study of Single Crystal Metallic Nanowires JIT SARKAR Boldink Technologies Private Limited, Howrah, West Bengal–711110, India, E-mail: [email protected]

ABSTRACT Nanowires are usually defined as nanostructured materials having a constrained diameter in the scale of few nanometers and an unconstrained length with a much higher length to diameter ratio. During atomistic studies of nanowires using molecular dynamics (MD) simulations, generally, periodic boundary conditions are considered along the axial direction to simulate the unconstrained or infinite length condition over a finite length considered in the simulation. The present study investigates the mechanical properties and deformation behavior of single-crystal FCC metallic (silver and aluminum) nanowires under periodic boundary conditions. The generated nanowires were subjected to thermal equilibration and relaxation, followed by their tensile testing, in analogous to real experiment. Both the FCC metallic nanowires contain high amount of local atomic stresses even after thermal equilibration, which can be attributed to the effect of free surface, higher surface to volume ratio and large lattice mismatch in FCC nanowires at atomic level. The mechanical properties like yield strength, Young's modulus and percentage elongation, along with the deformation behavior of these single-crystal nanowires were investigated from the corresponding engineering stress-strain curves. The results show ultra-high-strength and Young’s modulus with higher ductility in both the nanowires. The ultra-high mechanical properties can also be attributed to the consideration of single defect-free crystals, higher surface to volume ratio, and ultra-high strain rate of loading. The mode of fracture in both the nanowires was found to be in a ductile cup and cone manner. Thus these FCC metallic nanowires can

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find use as probable reinforcing agent to develop advanced materials with ultra-high-strength and mechanical properties. 11.1 INTRODUCTION Different types of nanomaterials have drawn much attention among the materials research communities due to their excellent mechanical, thermal, chemical, electrical, and optical properties with respect to their bulk counterparts. The excellent material properties exhibited by different types of nanomaterials can be attributed to their dominatingly large specific surface and/or interface areas at atomistic scale. Moreover, very less defects are present in materials at the nanoscale, which also in turn enhance their properties. Thus different types of nanomaterials are widely synthesized and characterized by several researchers around the world for advanced industrial and technological applications like solar cells, gas sensors, electronic devices, catalysts, inkjet printing, coating, etc., to cite a few examples. In this regard, different single-crystal nanomaterials have shown much enhanced material properties in respect to their polycrystalline counterparts. This can be attributed to the absence of grain boundaries and/or interfaces, which act as the source of different types of defects at the atomic level. Thus the fundamental knowledge and understanding of the behavior of materials at nanoscale is a pre-requisite for further studies and investigations of the properties of different types of nanomaterials, for their possible application in the development of advanced and smart materials. However, the extensive characterization of different properties of nano­ structured materials at the atomic scale is restricted by the limitations in proper experimental setups and facilities. Currently available modern experimental setups and facilities cannot evaluate the mechanical properties of single-crystal nanostructured materials from tensile testing. But the idea of the mechanical properties of single-crystal nanostructured materials are otherwise required during nanoscale engineering using those materials, by reinforcing certain nanostructured materials to develop advanced high strength nanocomposites for defense and aerospace applications. However, the recent developments of different mathematical and computational tools have overcome certain limita­ tions and allow us to perform electronic and atomic level calculations with much precision and accuracy. Some of the efficient and accurate mathematical and computational tools are first principles, ab-initio, Monte Carlo, molecular dynamics (MD), etc., are some examples to cite a few. MD have proven to be one such efficient and effective tool which can perform atomic-level calcula­ tions of different single crystal nanostructured materials.

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Nanowires are one of the important classes of nanostructured materials with unique properties owing to their constrained diameter in the scale of few nanometers and unconstrained length. The unique mechanical, thermal, electrical, chemical, and optical properties of nanowires have drawn much attention of researchers with vast worldwide researches going on in the field of different nanowires. Silver and aluminum nanowires have been moderately studied with several scopes for detailed investigations of the unusual mechanical properties exhibited by these nanowires. All experimentally synthesized silver and aluminum nanowires have constrained length [1–6], yet maintaining a higher length to diameter ratio and thus giving an unconstrained length condition in nanoscale. Due to experimental limitations, it is not always possible to characterize the different properties of nanowires at atomistic scale, and these limitations are overcome by different simulation studies. MD simulation proved to be an efficient simulation tool for the study of material behavior at the atomic level. Few MD studies have been carried out to estimate the mechanical properties and deformation behavior of silver and aluminum nanowires at atomic scale [6–12]. MD has proved to be an accurate and efficient simulation tool for studying the mechanical properties of nanowires, as it can effectively simulate the infinite length condition of the nanowires. Computational limitations do not allow us to simulate infinite length size nanowires and so periodic boundary conditions are applied along the longitudinal boundaries to simulate the infinite length condition. When any atom leaves the simulation box from one side, it again re-enters from another side. The present study investigates the mechanical properties and deformation behavior of cylindrical single crystal silver and aluminum nanowires under periodic boundary conditions using MD simulation technique. All the testing parameters and procedures were kept constant in either case. The mechanical properties and deformation behavior of these single-crystal metallic nanowires were investigated by tensile testing simulations in analogous to real tensile testing experiments. The nanowires were subjected to thermal equilibration and relaxation at room temperature (RT) (298 K) for a good amount of time to ensure complete thermal stability of the nanowires. A part of the nanowires comprising of few atoms were fixed from both ends, the lower end is kept fixed while the upper end is moved along the axial direction with a constant ultra-high strain velocity. The engineering stress and strain were calculated from the load-displacement data, and the mechanical properties were estimated from the engineering stress-strain curves.

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174 11.2 COMPUTATIONAL METHODS

The thermal equilibration/relaxation and tensile testing simulations of the nanowires were carried out using an open-source large-scale atomic/molecular massively parallel simulator (LAMMPS) software package [13] and the atomistic simulation data were visualized using an open-source software package ‘OVITO’ [14]. Single crystal of cylindrical silver and aluminum nanowires having volume equivalent to spherical volume of diameter 10 nm and length four times the diameter were generated using the crystal structure generation algorithm already present in LAMMPS. The nanowires were generated in such a way that the (001) plane was perpendicular to the axis of the cylinder and the (001) direction was parallel to the axis of the cylinder. Though silver and aluminum nanowires exposing (111) facets are most stable, so that their axis is in the (110) direction. But in the present study (001) is considered as the axial direction in order to carry out the tensile simulations in analogous to real tensile testing experiment, where (001) is the axis and direction of loading for any material under test. Using the MaxwellBoltzmann energy distribution function [15], the nanowires were assigned an initial velocity, and after initial assignment of position and velocity of atoms, the nanowires were thermally equilibrated at RT (298 K) using a canonical NVT ensemble by using Nosé-Hoover thermostat [16]. The accuracy of any simulation results depends on the potential used to define the interatomic and pairwise interactions. The interatomic and pairwise interactions in silver and aluminum nanowires were defined using an alloy type ‘Embedded Atom Method’ potential [17, 18], which defines the total energy of the ith atom as: ⎛ ⎞ 1 Ei = Fα ⎜ ∑ ρβ ( rij ) ⎟ + ∑ φαβ ( rij ) ⎝ j ≠i ⎠ 2 j ≠i

(1)

where, F is the embedding energy and a function of the atomic electron density ρ, φ is a pair potential interaction, α and β are the element types of atoms i and j, and the embedding energy term attributed to the multi-body nature of this potential. The thermal equilibration of the single crystal silver and aluminum nanowires was carried out for a total time of 20 ps with a time step of 1 fs to ensure complete thermal stability of the nanowires at RT along its length. To generate the trajectories of the atoms, time integration were done using Velocity-Verlet algorithm [19]. Periodic boundary conditions were used in both simulations and the simu­ lation boxes were kept large enough to eliminate end effects and interaction between atoms through boundaries, thus exhibiting infinite length condition of nanowires. The thermally equilibrated nanowires were subjected to RT

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tensile loading along the length of the nanowires in the axial (001) direction to simulate real tensile testing experiment. One-sixth portion of the nanow­ ires were fixed from their both ends to use as grips for firmly holding the nanowires at both ends during tensile loading. The lower grips were kept fixed while the upper grips were pulled along the (001) direction with a constant ultra-high strain velocity of 2 Å/ps, thus applying tensile forces on the remaining two-third portion of the nanowires. The engineering strain at any instant was calculated from the displacement of the center of mass of upper or movable end of the nanowires with respect to their initial position of center of mass during undeformed condition, divided by the position of the center of mass during undeformed condition. The engineering stress at any instant was calculated by the summation of total load acting along the axial direction on fixed or lower end divided by the initial cross-sectional area of the nanowires in undeformed condition. The change in temperature of the nanowires at any instant was measured from the overall temperature of the middle portions of the nanowires undergoing the tensile deformation. The engineering stress versus engineering strain curves were plotted for both the silver and aluminum nanowires, and the mechanical properties like yield stress, Young’s modulus and percent elongation were calculated from the respective engineering stress-strain curves. The deformation behavior at different stages of tensile testing and the final mode of fracture (ductile or brittle) were visually studied using Ovito. 11.3 RESULTS AND DISCUSSION 11.3.1 LOCAL ATOMIC STRESSES IN FCC METALLIC NANOWIRES The variation of temperature during the entire thermal equilibration process for both the FCC metallic nanowires is shown in Figure 11.1. With the initiation of thermal equilibration, the temperature initially shows some wide fluctuations up to few time steps, and then the fluctuations gradually decrease. The temperature gradually attains the desired stable value, which indicates the completion of thermal equilibration and complete thermal stability of the nanowires. The slight fluctuations or noises over the entire thermal equilibration process can be attributed to the vibration of the atoms at the nanoscale. The nanowires even after thermal equilibration and relaxation for 20 ps, contain some amount of local atomic stresses. This can be attributed to the combined effect of consideration of single crystal, effect of free surface and large lattice mismatch in FCC metallic nanowires [20, 21] at the atomic

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FIGURE 11.1

Variation of temperature with time during thermal equilibration.

scale. The existing local atomic stresses ranges in the order of GPa and are much higher in nanowires of smaller dimension due to their high surface to volume ratio. To get clear visualization of this small amount of stress distribution along different zones of nanowires and to identify which zones are experiencing relatively greater forces, atomic pressure analysis seems to be an interesting way of study. For any atom i, the local atomic stress (Pi) can be calculated by [20]: Pi = −

dEi 1 =− 3Vi dVi

∑r j≠ i

ij

⎡ dϕij ⎤ dψ ij −ψ ij D ( i )⎥ ⎢ drij ⎢⎣ drij ⎥⎦

(2)

where, Ei is the atomic energy, Vi is the atomic volume in the nanowire, rij is the relative distance between atoms i and j: ⎡

⎛ rij ⎞⎤ −1⎟⎥ ⎜r ⎟ ⎝ 0ij ⎠ ⎥⎦

ϕij ( rij ) = Aij exp ⎢- pij ⎜ ⎣⎢

r0ij =

r0ii + r0jj 2 ⎡

( i ≠ j) ⎛r

(3) (4)

⎞⎤

ψ ij ( rij ) = ξij exp ⎢-qij ⎜ ij −1⎟ ⎥ ⎜r ⎟ ⎝ 0ij ⎠ ⎦⎥ ⎣⎢

(5)

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and D (i ) =

177

1

∑ψ ( r ) j≠ i

2 ij

ij

(6)

The existing local atomic stresses, in turn, create volumetric strain within these FCC metallic nanowires even after thermal equilibration. The distribution of the volumetric strain within the thermally equilibrated single crystal silver and aluminum nanowires are shown in Figure 11.2.

FIGURE 11.2 Distribution of volumetric strain along the thermally equilibrated (a) silver and (b) aluminum nanowires.

11.3.2 STRESS-STRAIN CURVES AND DEFORMATION BEHAVIOR The calculated values of engineering stress and engineering strain during the entire tensile deformation process were plotted to obtain the engineering stress-strain curves of both single crystal silver and aluminum nanowires under periodic boundary conditions as shown in Figure 11.3. Both the engi­ neering stress-strain curves initially show some high fluctuations of stresses, which can be attributed to the local atomic stresses still existing in these FCC metallic nanowires at atomic level even after thermal equilibration

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and relaxation for sufficient time, due to the several factors as discussed in earlier Section 11.3.1. After the initial stress fluctuations, the engi­ neering stress linearly increases with strain, which can be attributed to the elastic deformation-taking place in these single-crystal FCC nanowires in the absence of dislocations. The nanowires reach their yield strength and thereafter-small number of dislocations is generated in the nanowires which indicate the initiation of plastic deformation behavior with gradual drop in engineering stress. Both the FCC nanowires show a good amount of plastic deformation during the subsequent deformation process and the stress gradu­ ally decreases up to the final failure of the nanowires. The higher elongation due to sufficient plastic deformation can be attributed to the movement of a small number of dislocations without any tangling and barrier as the defor­ mation process continues until nanovoids start generating. These nanovoids coalesce to form relatively bigger voids causing the initiation of necking and the nanowires finally fail in a ductile cup and cone manner. The elastic defor­ mation behavior primarily dominates in both the FCC nanowires during the initial stages of tensile loading until the nanowires reach their yield stress. The plastic deformation behavior then dominates in the subsequent stages of deformation until leading to the final rupture of the nanowires. It was also observed that the temperature of the nanowires initially increase as a natural consequence of any deformation process, and the deformation occurs at a higher temperature with some fluctuations as a result of atomic vibrations. The temperature then suddenly drops when the nanowires finally rupture. It was found that both the FCC metallic nanowires show similar deformation and fracture behavior. The different stages of tensile testing are shown in Figure 11.4, starting from initial thermally equilibrated sample to initiation of necking and growth of the neck leading to final failure. It was also found that very low equilibration temperature and/or very high strain velocity of loading alter the deformation behavior and changes the mode of fracture from ductile to catastrophic brittle manner during the tensile testing. 11.3.3 MECHANICAL PROPERTIES OF THE FCC NANOWIRES FCC is among the most widely studied crystal structure using MD simula­ tions as it is the common crystal structure of several metals. Moreover, the interatomic and pairwise interaction potentials of metals with FCC crystal structure are well developed. Therefore, the present study has focused on the mechanical properties of FCC nanowires under periodic boundary condi­ tions. The mechanical properties like yield strength, Young’s modulus and

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179

percentage elongation in both the single crystal FCC metallic nanowires under periodic boundary conditions are listed in Table 11.1.

FIGURE 11.3 Engineering stress-strain curves of silver and aluminum nanowires.

FIGURE 11.4

Different stages of tensile testing of aluminum nanowire.

Both the nanowires show ultra-high yield strength and Young’s modulus, which can be attributed to the factors like consideration of single defect-free crystals, higher surface to volume ratio, and ultra-high strain rate of loading.

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The existing local atomic stresses in these FCC nanowires are also reflected from the initial high fluctuation of stress in the engineering stress-strain curves. The silver nanowire shows much-enhanced strength and Young’s modulus than aluminum nanowires, which can be also be attributed to the presence of less number of point defects like vacancies and interstitials in silver nanowire during the entire tensile deformation process. However, the aluminum nanowire shows higher total elongation indicating the occurrence of more amount of localized plastic deformation within it, even after the presence of a large number of point defects in comparison to silver nanow­ ires. On the other hand, the silver nanowire shows higher uniform elongation in comparison to the aluminum nanowire. The point defects start generating within the nanowires as soon as they are subjected to the tensile loading and the variation of a total number of point defects like vacancies and interstitials in both the FCC metallic nanowires during the continuous tensile loading until rupture is shown in Figure 11.5. TABLE 11.1

Mechanical Properties of the Single Crystal FCC Metallic Nanowires

Nanowire Type

Yield Strength (GPa)

Young’s Modulus (GPa)

Percentage Elongation

Silver

7.5 GPa

389.3 GPa

35.2%

Aluminum

3.4 GPa

239.2 GPa

36.4%

The total number of point defects gradually increases with the progress of the tensile deformation process, followed by some initial fluctuations, which may be attributed to the presence of the local atomic stresses which gradually relieve during the initial stages. The fluctuations at the later stage can be attributed to the annihilation and generation of point defects during the plastic deformation process. The plastic deformation in both the nanow­ ires is governed by the nature and type of dislocations motion as the tensile deformation progresses. The movement of the 1/6 Shockley partial dislocations primarily contributes to the plastic deformation process, and there is continuous annihilation and generation of dislocations as the plastic deformation process continues. Some localized plastic deformation has been observed in both the FCC nanowires just above the neck region, which is also primarily contributed by the movement of 1/6 Shockley partial dislocations. Besides the 1/6 Shockley partial dislocations, the move­ ment of few number of 1/3 Hirth and 1/6 Stair-rod dislocations also contribute to the plastic deformation occurring at and above the neck region, respectively. A change in the crystal structure of some of the atoms

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181

from FCC to HCP in both the nanowires have also been observed in the portions of atoms above and below the necking region. After the completion of elastic deformation and at the point of initiation of plastic deformation process, there is a change in the crystal structure of some of the atoms from FCC to HCP, which generates dislocations and the movement of these dislo­ cations governed the plastic deformation process. As the tensile deformation continues, more atoms are undergoing transition from FCC to HCP crystal structures around the neck region and also in the region of localized plastic deformation. This generates more number of dislocations, and an increase in dislocations motion contributes further to the plastic deformation occurring in both the FCC nanowires. Thus both the FCC metallic nanowires under­ study show an excellent combination of strength and ductility with the silver nanowire showing much superior combination of mechanical properties in comparison to the aluminum nanowire.

FIGURE 11.5

Variation of point defects with tensile deformation in both the nanowires.

11.4 CONCLUSION Therefore, the present study has thoroughly investigated the mechanical prop­ erties and deformation behavior of single-crystal FCC metallic nanowires, by

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considering the tensile testing of silver and aluminum nanowires under peri­ odic boundary condition. Both the nanowires exhibit ultra-high-strength and Young’s modulus with an excellent combination of elongation or ductility. The ultra-high mechanical properties of these nanowires can be attributed to the consideration of a single-crystal under ideal conditions and free from all types of internal defects. Moreover, ultra-high strain rate of tensile simulations in comparison to conventional strain rate of tensile experiments further contributed to the ultra-high mechanical properties exhibited by these nanowires. Due to their ultra-high-strength and ductility at nanoscale, single-crystal FCC metallic nanowires can be potential candidates that can be used as reinforcement to develop different advanced materials with excel­ lent mechanical properties and better durability for defense and aerospace applications. KEYWORDS • • • • • •

deformation behavior FCC nanowires mechanical properties molecular dynamics periodic boundary tensile testing

REFERENCES 1. Sun, Y., Yin, Y., Mayers, B. T., Herricks, T., & Xia, Y., (2002). Uniform silver nanowires synthesis by reducing AgNO3 with ethylene glycol in the presence of seeds and poly(vinyl pyrrolidone). Chem. Mater., 14(11), 4736–4745. 2. Liu, B., Yan, H., Chen, S., Guan, Y., Wu, G., Jin, R., & Li, L., (2017). Stable and controllable synthesis of silver nanowires for transparent conducting film. Nanoscale Res. Lett., 12, 212. 3. Gebeyehu, M. B., Chala, T. F., Chang, S. Y., Wu, C. M., & Lee, J. Y., (2017). Synthesis and highly effective purification of silver nanowires to enhance transmittance at low sheet resistance with simple polyol and scalable selective precipitation method. RSC Adv., 7, 16139–16148. 4. Hwang, S., Baik, C. W., & Whang, D., (2012). Synthesized aluminum nanowires for future interconnects. IEEE Nanotechnol. Mag., 6(3), 24–26.

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5. Benson, J., Boukhalfa, S., Magasinski, A., Kvit, A., & Yushin, G., (2011). Chemical vapor deposition of aluminum nanowires on metal substrates for electrical energy storage applications. ACS Nano., 6(1), 118–125. 6. Lee, J. W., Kang, M. G., Kim, B. S., Hong, B. H., Whang, D., & Hwang, S. W., (2010). Single crystalline aluminum nanowires with ideal resistivity. Scr. Mater., 63(10), 1009–1012. 7. Lin, Y., Peng, J., Hua, L. Y., Hai, X. Z., Bin, S. D., & Bin, G., (2014). Molecular dynamics simulation of polycrystal silver nanowires under tensile deformation. Acta Phys. Sin., 63, 016201. 8. McDowell, M. T., Leach, A. M., & Gall, K., (2008). Bending and tensile deformation of metallic nanowires. Model. Simul. Mater. Sci. Eng., 16, 045003. 9. Gao, Y., Sun, Y., Yang, X., Sun, Q., & Zhao, J., (2016). Investigation on the mechanical behavior of faceted Ag nanowires. Mol. Simul., 42(3), 220–228. 10. Sung, P. H., Wu, C. D., & Fang, T. H., (2012). Effects of temperature, loading rate, and nanowire length on torsional deformation and mechanical properties of aluminum nanowires investigated using molecular dynamics simulation. J. Phys. D: Appl. Phys., 45, 215303. 11. Sen, F. G., Alpas, A. T., Van, D. A. C. T., & Qi, Y., (2014). Oxidation-assisted ductility of aluminum nanowires. Nat. Comm., 5(3), 959. 12. Liang, W., & Zhou, M., (2006). Atomistic simulations reveal shape memory of fcc metal nanowires. Phys. Rev. B., 73, 115409. 13. Plimpton, S., (1995). Fast parallel algorithms for short-range molecular dynamics. J. Comp. Phys., 117, 1–19. 14. Stukowski, A., (2010). Visualization and analysis of atomistic simulation data with OVITO-the open visualization tool. Model. Simul. Mater. Sci. Eng., 18, 015012. 15. Rowlinson, J. S., (2005). The Maxwell-Boltzmann distribution. Mol. Phys., 103, 2821–2828. 16. Evans, D. J., & Holian, B. L., (1985). The Nose-Hoover thermostat. J. Chem. Phys., 83, 4069–4074. 17. Williams, P. L., Mishin, Y., & Hamilton, J. C., (2006). An embedded-atom potential for the Cu-Ag system. Modeling Simul. Mater. Sci. Eng., 14, 817–833. 18. Cai, J., & Ye, Y. Y., (1996). Simple analytical embedded-atom-potential model including a long-range force for fcc metals and their alloys. Phys. Rev. B., 54, 8398–8410. 19. Li, J., (2005). Basic molecular dynamics. In: Yip, S., (ed.), Handbook of Materials Modeling (Part A, pp. 565–588). Springer. The Netherlands. 20. Sarkar, J., & Das, D. K., (2018). Study of the effect of varying core diameter, shell thickness, and strain velocity on the tensile properties of single crystals of Cu-Ag coreshell nanowire using molecular dynamics simulations. J. Nanopart. Res., 20, 9. 21. Sarkar, J., (2018). Investigation of mechanical properties and deformation behavior of single-crystal Al-Cu core-shell nanowire generated using non-equilibrium molecular dynamics simulation. J. Nanopart. Res., 20, 153.

CHAPTER 12

Low-Temperature Gas Sensing Properties of Reduced Graphene Oxide Incorporated Perovskite Nanocomposite N. VIDYARAJAN and L. K. ALEXANDER Department of Physics, University of Calicut, Kerala–673635, India, E-mail: [email protected] (N. Vidyarajan)

ABSTRACT Perovskite LaFe0.8Al0.2O3 (LFAL) with Pbnm crystal structure has been synthesized by a citric acid-mediated solution method. It is incorporated with reduced graphene oxide (RGO) to enable low-temperature gas sensing properties. X-ray diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) analysis shows the successful functionalization of perovskite with reduced GO. The sensing activity studies of the composite under 3 ppm NO2 gas shows a variation with respect to substrate temperature.

186

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12.1 INTRODUCTION Gas sensing has been extensively used in various fields, which include industry, agriculture, and electronics. Metal oxide with size in nanoregim is considered to be an important variant in sensors, and widely captivating in gas sensing applications. Increased surface to volume ratio, near the surface with high chemiresistive variation, more surface active sites, etc., makes metal oxides a good candidate for gas sensing application [1]. Because of the multiple functionality as well as chemical, mechanical, and thermal stability, perovskite-a complex oxide-with ABO3 structures are well known for their high-temperature applications [2]. Retaining the structural stability at elevated temperature enables perovskite to use in gas sensing applications. Different elemental combinations at A and B sites of the perovskite provide a unique way to design high-performance gas sensors [3]. LaFeO3 (LFO) is one of the promising materials among ABO3 perovskite with profuse functionalities and use widely in electrochemical applications such as electrocatalysis, electrode in solid oxide fuel cells, electrochemical sensing, etc. Furthermore, due to the physical and chemical properties, LFO, and its related compounds have potential in detecting pollutant gases [4–6]. The P-type semiconductor LFO retains its properties at high temperature and extensively used as an effective gas sensor [7–9]. However, the selectivity and response of the LFO are very poor [10]. To activate the perovskite at low temperature, different strategies have to be employed. Doping at A and B sites of the compound changes the physical and chemical properties of the parent compound. Another mechanism is to functionalize the metal oxide with the highly reactive carbonaceous material. Reduced graphene oxide (RGO) is effectively utilizing its surface properties for the functionaliza­ tion. The functional groups on the surface of RGO adsorb the gases and present excellent sensitivities to gas molecules [11]. However, in order to meet the requirements of a practical sensor for higher sensitivity and selec­ tivity, further improvements have to be made on RGO [12]. Here we are reducing the temperature dependence of B-site doped perovskite compound by combining it with RGO. 12.2 MATERIALS AND METHODS Hummer’s method was used for the preparation of graphene oxide (GO), and it is used as the precursor for the preparation of RGO. Al-doped Lanthanum

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187

iron oxide was prepared from the citric acid-mediated solution method using 1:1:2 ratios of metal nitrates to citric acid. A combined reduction and ex-situ functionalization of GO with Al-doped lanthanum orthoferrite (GLFAL) were made in the ratio of 1:10 (GO to LFAL) by one-pot hydrothermal method at 180°C for 6 hours. X-ray diffraction (XRD, Rigaku MiniFlux) has been taken for structural analysis and FESEM for morphological analysis. 12.3 RESULT AND DISCUSSION Figure 12.1(a) shows the XRD pattern of RGO incorporated LaFe0.8Al0.2O3 crystalline perovskite compound. The patterns are well-matched and indexed with the JCPDS of Pbnm structure. The addition of Al into the B site would not produce any extra phase in the sample. FESEM images were used to reveal the morphology of the sample (Figure 12.1(b)). It shows the presence of both LFAL and RGO in the nanocomposite. The wrinkled like structure shows the presence of RGO in the composite.

(a) FIGURE 12.1

(b)

(a) XRD pattern and (b) FESEM images of GLFAL.

The gas sensing property of the compound has been carried out in the presence of nitrous oxide as the testing gas. Figure 12.2(a) shows the gassensing response of the synthesized nanocomposite. When the gas flow was changed between air and 3 ppm NO2 in the air at different temperatures, the resistance of the element decreases sharply upon NO2 exposure but did not return to the initial value when airflow was restored. Nature of the graph emphasizes the P-type behavior of grapheme-perovskite nanocomposite.

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Being an electronegative gas, when NO2 approaches the sensing material, it withdraws electrons from the composite and increases the holes concentra­ tion. Thus the majority carriers through the material increases and hence decrease the resistance.

(a)

(b) FIGURE 12.2 (a) Gas sensing properties of GLFAL nanocomposite at RT, 50°C, 100°C, and 150°C (b) Response curve of GLFAL-100°C.

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189

By varying the substrate temperature, the sensing action of the compound has been studied. Figure 12.2(a) shows the gas response of the compound at room temperature (RT), 50°C, 100°C, and 150°C. At lower temperature, it is noticed that the desorption is slower than gas adsorption, so the recovery time is higher in this case. When the temperature increases from RT to 100°C composite shows an improved response and sensitivity. It can be seen that at 100°C the desorption process is more or less complete, and the resistance reaches to its original level upon airflow. It is also noted that when the temperature increases, the value of base resistance decreases. Humidity is one of the major interfering factors for gas sensors. It especially affects the gas sensing properties of reduced GO [13]. This might be the reason for the slow desorption of NO2 gas from the surface of the graphene-incorporated nanocomposite at a lower temperature. At higher temperature, the influence of humidity becomes less and here we can see that the response at 100°C is higher compared to all other temperature range. When the temperature is higher than 100°, the response level decrease. At 200°C, the compound does not show any sensing action. This might be due to the decomposition of reduced GO. The response curve of the composite GLFAL at 100°C is shown in Figure 12.2(b). Response and recovery time calculated for GLFAL-100°C is 12.16 minutes and 17 minutes, respectively. 12.4 CONCLUSION Perovskite LaFe0.8 Al0.2O3 has been prepared by citric acid-mediated solution method. To enable the low-temperature activity of the perovskite compound, the surface properties of reduced GO is effectively utilized. Sensing proper­ ties of the composite show an increase in sensitivity while increasing the temperature. At lower temperature, the influence of humidity slows down the desorption of gas molecule from the surface of GLFAL composite, whereas, at a higher temperature, the decomposition of RGO reduces the sensitivity of the composite. At an optimum temperature of 100°C, the sample shows a complete recovery of adsorbed gas on the surface. The recovery time and response time of the GLFAL composite at 100°C is 12.16 minutes and 17 minutes, respectively. ACKNOWLEDGMENT Authors acknowledge INUP, IISC Bangalore for the characterization of FESEM and gas sensing.

Nanostructured Smart Materials

190 KEYWORDS • • • • • •

Al-doped lanthanum orthoferrite citric acid desorption electronegative gas nanocomposite reduced graphene oxide

REFERENCES 1. Dai, Z., Lee, C. S., Kim, B. Y., Kwak, C. H., Yoon, J. W., Jeong, H. M., & Lee, J. H., (2014). Honeycomb-like periodic porous LaFeO3 thin-film chemiresistors with enhanced gas-sensing performances. ACS Applied Materials and Interfaces, 6, 16217–16226. doi: 10.1021/am504386q. 2. Rondinelli, J. M., May, S. J., & Freeland, J. W., (2012). Control of octahedral connectivity in perovskite oxide heterostructures: An emerging route to multifunctional materials discovery. MRS Bulletin, 37, 261–270. doi: 10.1557/mrs.2012.49. 3. Giang, H. T., Duy, H. T., Ngan, P. Q., Thai, G. H., Anh, T. D. T., Thu, D. T., & Toan, N. N., (2013). Effect of 3d transition metals on gas sensing characteristics of perovskite oxides LaFe1-xCoxO3. Analytical Methods, 5, 4252. doi: 10.1039/c3ay26533a. 4. Doroftei, C., Popa, P. D., & Iacomi, F., (2012). Synthesis of nanocrystalline La-Pb-Fe-O perovskite and methanol-sensing characteristics. Sensors and Actuators B: Chemical, 161, 977–981. doi: 10.1016/j.snb.2011.11.078. 5. Toan, N. N., Saukko, S., & Lantto, V., (2003). Gas sensing with semiconducting perovskite oxide LaFeO3. Physica B: Condensed Matter, 327, 279–282. doi: 10.1016/ S0921-4526(02)01764-7. 6. Wang, X., Qin, H., Sun, L., & Hu, J., (2013). CO2 sensing properties and mechanism of nanocrystalline LaFeO3 sensor. Sensors and Actuators B: Chemical, 188, 965–971. doi: 10.1016/j.snb.2013.07.100. 7. Chen, J., Xu, L., Li, W., & Gou, X., (2005). Fe2O3 nanotubes in gas sensor and lithium-ion battery applications. Advanced Materials, 17, 582–586. doi: 10.1002/adma.200401101. 8. Zhu, Q., Zhang, Y. M., Zhang, J., Zhu, Z. Q., & Liu, Q. J., (2015). A new and high response gas sensor for methanol using molecularly imprinted technique. Sensors and Actuators B: Chemical, 207, 398–403. doi: 10.1016/j.snb.2014.10.027. 9. Zhang, Y., Liu, Q., Zhang, J., Zhu, Q., & Zhu, Z., (2014). A highly sensitive and selective formaldehyde gas sensor using a molecular imprinting technique based on Ag–LaFeO3. J. Mater. Chem. C., 2, 10067–10072. doi: 10.1039/C4TC01972E. 10. Rong, Q., Zhang, Y., Hu, J., Li, K., Wang, H., Chen, M., Lv, T., Zhu, Z., Zhang, J., & Liu, Q., (2018). Design of ultrasensitive Ag-LaFeO3 methanol gas sensor based

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191

on quasi molecular imprinting technology. Scientific Reports, 8. doi: 10.1038/ s41598-018-32113-x. 11. Mao, S., Cui, S., Lu, G., Yu, K., Wen, Z., & Chen, J., (2012). Tuning gas-sensing properties of reduced graphene oxide using tin oxide nanocrystals. Journal of Materials Chemistry, 22, 11009. doi: 10.1039/c2jm30378g. 12. Yuan, W., & Shi, G., (2013). Graphene-based gas sensors. Journal of Materials Chemistry A., 1, 10078. doi: 10.1039/c3ta11774j. 13. Some, S., Xu, Y., Kim, Y., Yoon, Y., Qin, H., Kulkarni, A., Kim, T., & Lee, H., (2013). Highly sensitive and selective gas sensor using hydrophilic and hydrophobic graphenes. Scientific Reports, 3. doi: 10.1038/srep01868.

CHAPTER 13

Synthesis and Characterization of LFOBFO Multiferroic Nanocomposites AYEKPAM KIRANJIT SINGH,1 T. H. DAVID SINGH,2 and IBETOMBI SOIBAM1 Department of Physics, NIT Manipur, Imphal–795004, Manipur, India, E-mail: [email protected] (I. Soibam) 1

2

Department of Chemistry, NIT Manipur, Imphal–795004, Manipur, India

ABSTRACT Stoichiometric weight proportions of pure phase Li0.5Fe2.5O4 (LFO) and BiFeO3 (BFO) were mixed by solid-state reaction method to form nanocomposites. The compositional formula being (1–x)BFO-xLFO (x = 0, 0.25, 0.50, 0.75, 1.0). LFO was prepared by the citrate precursor method while BFO was prepared by sol-gel method independently. Characterization of the pure and biphase mixture were carried out by using XRD analysis, FTIR studies, and complex dielectric. Lattice constants and theoretical density of all the samples were obtained from the Rietveld refinement (Fullprof software) of the XRD data. A decreasing trend in density with increasing LFO was observed. FTIR studies show the presence of different bonds. Complex dielectric comprising of dielectric constant (έ) and dielectric loss were studied as a function of the applied external electric field and composition. A dispersive behavior in both the parameter, i.e., dielectric constant and dielectric loss subjected to frequency was observed. The frequency range under consideration is 20 Hz–2 MHz. Variation of dielectric constant (έ) and dielectric loss with increase in LFO concentration were also studied at a particular frequency. It shows a decreasing trend. Explanations for the observed results were being discussed.

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13.1 INTRODUCTION In recent times, nanocomposites have emerged as one of the new technological solutions for improving device application characteristics. Intense research has been carried out on these materials, particularly for its applications in making supercapacitors, high-density memory devices, photocatalytic, and photovoltaic devices [1–9]. One of the important aspects of making nanocomposites is to check the compatibility of mixing different structure materials for improving particular device application characteristics. Various researchers have contributed a lot of different strategies and methods for making composites. Available literature survey reports the synthesis of different composites by choosing suitable ferroelectric and ferromagnetic components. Various nanocomposites such asBiFeO3/Bi0.95Mn0.05FeO3­ Ni0.5Zn0.5Fe2O4 [2], xCrFe2O4-(1–x)BiFeO3 [3], CrFe2O4-BiFeO3 [4], xNi0.75Co0.25Fe2O4-(1–x)BiFeO3 [5], xBi0.95Mn0.05FeO3-(1–x)Ni0.5Zn0.5Fe2O4 [6], Ni0.8Zn0.2Fe2O4-Ba0.6Sr0.4TiO3 [7], CoFe2O4-BaTiO3 [8], (1–x)BiFeO3­ xNi0.8Zn0.2Fe2O4 [9] have been prepared by different workers using varied methods. Several experiments were performed to study their structural, electrical, magnetic, and optical properties. However, the reports on synthesis and investigation of the nanocomposites consisting of perovskite phase BFO and spinel phase LFO were very few. Therefore, as a novel approach, nanocomposites may be synthesized at low temperature by choosing pure phase BFO as ferroelectric part and LFO as ferromagnetic part. The present work aims in synthesizing the nanocomposites of BFO-LFO and to further study their structural and dielectric properties of the synthesized samples. 13.2 EXPERIMENT BFO ceramics were prepared using sol-gel technique by taking the stoichiometric amount of bismuth nitrate and iron nitrate as its starting precursors. First, stoichiometric amount of bismuth nitrate and iron nitrate were taken separately with 2-methoxyethanol as the solvent. The two solutions were stirred using a magnetic stirrer and after 30 minutes, they were mixed together and heated for 45 minutes with continuous stirring. Nitric acid and citric acid were added to help remove impurities and as a chelating agent, respectively. After 30 minutes of stirring and slow heating, the solution was then heated at 120°C for 2 hours to obtain a gel. The gel so formed was dried at 110°C for about 3 hours in a Petri dish. The flakes were then crushed to fine powders and calcined at 550°C in a microwave furnace

Synthesis and Characterization of LFO-BFO

195

for 30 minutes, which is further leached with 1M HNO3 acid to obtain BFO ceramic. Lithium ferrites were synthesized by auto combustion method using citrate precursor technique. A stoichiometric amount of lithium nitrate and iron nitrate was taken with citric acid in a water medium. The solution was stirred for 30 minutes using a magnetic stirrer, and ammonia solution was added dropwise until the solution just became neutral. The solution was stirred for 30 minutes and then heated at 100°C. Afterward, the process of auto-combustion occurs yielding fine grey ash powder. This powder was then calcined at 600°C in a microwave furnace to obtain lithium ferrites. The nanocomposites having the compositional formula (1–x)BFO-xLFO with x = 0, 0.25, 0.50, 0.75, 1.0 were prepared by mixing the required proportions of BFO and LFO for 2 hours with acetone as its mixing medium. The composite formed was then pressed to pellets and sintered at 600°C for 30 minutes in a microwave furnace. Characterization were carried out using XRD (BRUKER D8 Advance Eco), FTIR (Perkin Elmer, spectrum two), and LCR meter (Agilent E4980). For dielectric measurement LCR meter was used. Prior to the measurement, silver paste were applied on both sides of the pellets, thereby acting as capacitors with the nanocomposites as the dielectric medium sandwiched between the two silver surfaces. 13.3 RESULTS AND DISCUSSIONS Figure 13.1 shows the XRD diffraction pattern of (1–x)BFO-xLFO nano­ composite with x = 0, 0.25, 0.50, 0.75, 1.0 measured at room temperature (RT). All the major peaks of x = 0 were indexed to rhombohedrally distorted perovskite BFO and all the major peaks of x = 1 were indexed to cubic spinel structured LFO. The XRD pattern of the three composites viz. x = 0.25, 0.5 and 0.75 show the presence of both the BFO and LFO phases with no impurity peaks present in it. Table 13.1 shows the data obtained from the Rietveld refinement (FullProf software) of the XRD pattern. The crystallite sizes were calculated using Scherrer’s formula. There is an increase in crystallite size with the increase in the concentration of lithium ferrite. The average crystallite size of the nanocomposites ranges between that of pure phase bismuth ferrite and pure phase lithium ferrite in the range 16 nm–41 nm. This increase in average crystallite size can be explained by the increasing concentration of the lithium ferrite possessing higher crystallite size as compared to that of BFO. The theoretical (XRD) and the bulk density are in agreement with

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each other in which the densities of the samples decrease with the increase in concentration of lithium ferrite. This can be explained by the increase in concentration of the less dense lithium ferrite. The porosity of the samples also increases with increase in the concentration of lithium ferrite.

FIGURE 13.1 XRD pattern of (1–x)BFO-xLFO (*) corresponds to BFO phase and (#) corresponds to LFO phase. TABLE 13.1 Crystallite Size, Lattice Constant, Density (XRD and Bulk) and Porosity of (1–x)BFO-xLFO with x = 0, 0.25, 0.50, 0.75, 1.0 Concentration Crystallite Size (nm)

Lattice constant (Ǻ) Perovskite

Spinel

a=b

c

a

ρBulk ρXRD (g/c.c.) (g/c.c.)

Porosity (%)

0

16

5.576

13.86

0

8.38

5.749

31

0.25

34

5.575

13.86

8.443

7.838

4.807

39

0.5

37

5.578

13.87

8.449

7.296

4.093

44

0.75

40

5.842

13.62

8.316

6.753

3.693

45

1

41

0

0

8.315

6.211

2.847

54

Synthesis and Characterization of LFO-BFO

197

A typical FTIR spectra of (1–x)BFO-xLFO nanocomposites with x = 0, 0.25, 0.50, 0.75, 1.0 is shown in Figure 13.2. It exhibit two distinct absorption bands corresponding to the stretching vibrations of the tetrahedral site complexes (510–800 cm–1) and octahedral site complexes (300–510 cm–1) in which the tetrahedral ions vibrate along the line joining the cation and neighboring oxygen ions and the octahedral cations vibrate in a direction perpendicular to the axis joining the tetrahedral metal ion and oxygen ion [10–13].

FIGURE 13.2

FTIR spectra of (1–x)BFO-xLFO with x = 0, 0.25, 0.50, 0.75, 1.0.

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In the present study, the presence of a strong absorption band (575–710) nm is attributed to the stretching of Fe3+ and O at the tetrahedral sites. It got split into three bands, which occur due to the presence of the small amount of Fe2+ in the synthesized lithium ferrite, according to Potakawa. This effect (Jahn teller distortion) produced by the presence of Fe2+ causes local deformation in the lattice due to non-cubic component of the crystal field potential and hence produces the splitting of the band. The absorption band observed at 815–825 cm–1 in the nanocomposites is attributed to the presence of trapped nitrate ion, NO3– from the samples. The observation is in agreement with the earlier report and hence supports the phase formation of XRD studies [14]. Figures 13.3 and 13.4 show the variation of dielectric constant (έ) and dielectric loss as a function of frequency, respectively. Frequency range under investigation being 20 Hz to 2 MHz. The variation of dielectric constant (έ) and dielectric loss shows a dispersive behavior in the whole frequency range. The high value of dielectric constant at low frequency could be explained on the basis of space charge polarization and Koop’s two-layer model [15].

FIGURE 13.3

Variation of dielectric constant (έ) with frequency.

Synthesis and Characterization of LFO-BFO

FIGURE 13.4

199

Variation of dielectric loss with frequency.

Figure 13.5 shows the variation of dielectric constant and dielectric loss as a function of LFO concentration at 500 Hz external electric field. The elec­ trical conduction in ferrites is usually explained by the Verwey mechanism of electron hopping [16, 17]. With the increase in LFO concentration, the value of dielectric constant decreases. This may be due to the high porosity, which increases the non-conductive behavior. As the porosity increases, the charge carrier faces more pores on their way, leading to increase resistivity. Ulti­ mately it reduces the hopping process, and hence the value of the dielectric constant decreases. The porosity shows an increasing trend with increasing LFO concentration. The dielectric loss increases as we increase the concentration of lithium ferrite. This may be attributed to the decreasing dielectric constant as we increase the concentration of lithium ferrite [9]. Lower dielectric constant corresponds to increase resistivity. Since the resistivity is high the conducting electron faces difficulty to move within the sample and a large amount of energy is consumed in hopping process between Fe3+↔Fe2+ which result in higher dielectric loss.

Nanostructured Smart Materials

200 40

30

0.4 0.3

20

0.2 10

Dielectric loss

Dielectric Constant (έ)

0.5

0.1 0

x=0

x=0.25

x=0.50

x=0.75

x=1.0

0.0

Concentration FIGURE 13.5

Variation of dielectric constant (έ) and dielectric loss with concentration.

13.4 CONCLUSION Nanocomposites having the compositional formula (1–x)BFO-xLFO with x = (0, 0.25, 0.50, 0.75, 1.0) were successfully prepared by mixing stoichio­ metric proportion of BFO and LFO which were independently prepared by sol-gel and citrate precursor method. The phase formation was confirmed from XRD. FTIR spectra reveal the presence of tetrahedral and octahedral bonds present in the nanocomposites. The value of the dielectric constant is observed to decrease with increasing LFO concentration. Dispersion is observed in both the dielectric constant and dielectric loss as a function of applied frequency. ACKNOWLEDGMENT The authors would like to thank NIT, Manipur for the XRD measurement, and DST GoI (EMR)/2016/001348) for their financial support.

Synthesis and Characterization of LFO-BFO

201

KEYWORDS • • • • • •

dielectric constant dielectric loss high-performance liquid chromatography lithium ferrite nanocomposites Rietveld refinement

REFERENCES 1. Catalan, G., & Scott, J. F., (2009). Physics and applications of bismuth ferrite. Adv. Matter., 21, 2463–2485. 2. Dhanalakhsmi, B., & Pratap, K., (2015). Impedance spectroscopy and dielectric properties of multiferroic BiFeO3/Bi0.95Mn0.05FeO3-Ni0.5Zn0.5Fe2O4composites. Ceram. Int., 42, 2186–2197. 3. Kumar, A., & Yadav, K. L., (2011). A systematic study on magnetic, dielectric and magnetocapacitance properties of Ni-doped bismuth ferrite. J. Phys. Chem., 72, 1189–1194. 4. Ratnakar, P., (2014). CrFe2O4-BiFeO3 perovskite multiferroic nanocomposites: A review. Mat. Sci. Res. India, 11,128–145. 5. Nidhi, A., & Yadav, K. L., (2014). Structural, dielectric, magnetic, and optical properties of Ni0.75Zn0.25Fe2O4-BiFeO3 composites. J. Mater. Sci., 49, 4423–4438. 6. Dhanalaxmi, B., Caltun, O. F., Dumitru, I., et al., (2015). Bi0.95Mn0.05FeO3-Ni0.5Zn0.5Fe2O4 nanocomposites with multiferroic properties. Mater. Today Proc., 2, 3806–3812. 7. Yang, H., Wang, H., He, L., et al., (2010). Polarization relaxation mechanism of Ba0.6Sr0.4 TiO3/Ni0.8Zn0.2Fe2O4 composite with giant dielectric constant and high permeability. J. Appl. Phys., 108, 074105–074110. 8. Liu, X. M., Fua, S. Y., & Huanga, C., (2005). Synthesis and magnetic characterization of novel CoFe2O4-BiFeO3 nanocomposites. Mater. Sci. Eng. B, 121, 255–260. 9. Mani, A. D., & Soibam, I., (2017). Comparative studies of the dielectric properties of (1−x)BiFeO3-xNi0.8Zn 0.2Fe2O4 (x = 0.0, 0.2, 0.5, 0.8, 1.0) multiferroic nanocomposite with their single phase BiFeO3 and Ni0.8Zn 0.2Fe2O4. Physica. B, 507, 21–26. 10. Sagar, E. S., Kadam, R. H., Anil, S. G., Ali, G., & Akimitsu, M., (2011). Effect of sintering temperature and the particle size on the structural and magnetic properties of nanocrystalline Li0.5Fe2.5O4. J. of Magnetism and Magnetic Materials, 323, 3104–3108. 11. Waldron, R. D., (1955). Infrared spectra of ferrites. Phys. Rev., 99, 1727–1735. 12. Angadi, J. V., et al., (2017). Composition dependent structural and morphological modifications in nanocrystalline Mn-Zn ferrites induced by high energy gammairradiation. Mat. Chem. Phys., 199, 313–321.

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13. Watawe, S. C., Sutar, B. D., Sarwade, B. D., & Chougule, B. K., (2001). IR studies of some mixed Li-Co ferrites. Intl. J. Inorg. Mater., 3, 819–823. 14. Hafner, S., (1961). Order/disorder and ultrared absorption IV. The absorption of some metal oxides with spinel structure. Zeitschrift Für Kristallographie–Crystalline Materials, 115(5, 6), 331–358. 15. Agrawal, D. K., (1998). Microwave processing of ceramics. Curr. Opin. Solid State Mater. Sci., 3, 480–486. 16. Dzunuzovic, A. S., et al., (2016). J. Magn. Matter., 374, 245–251. 17. Verwey, E. J. W., & De Boer, J. H., (1936). Recl. Trav. Pays. Bass, 55, 331. 18. Verwey, E. J. W., Haayman, P. W., & Romeijn, F. C., (1947). J. Chem. Phys., 5, 181.

CHAPTER 14

Mycobacterium tuberculosis Diagnosis with Conventional, Molecular Probe, and Nanobiosensing Techniques DEEPAK V. SAWANT1 and SHIVAJI H. PAWAR1,2 Center for Interdisciplinary Research, D. Y. Patil Education Society, Kolhapur–416006, Maharashtra, India, E-mail: [email protected] (D. V. Sawant) 1

Center for Innovative and Applied Research, Anekant Education Society, TC College Complex, Baramati, Maharashtra, India

2

ABSTRACT Tuberculosis (TB) is a transmissible disease caused by Mycobacterium tuberculosis. TB infection affects mainly upper respiratory organs such as the lungs, so-called pulmonary TB. They can also affect multiple organs like bones, joints, skin, and genital organs, etc., are extrapulmonary TB infection. However, the vast majority of TB cases include pulmonary TB. The prevalence of TB is very high in developing nations, where diagnosing of latent TB, drug-resistant TB, and HIV co-infected, pediatric TB remains still a challenge. There are so many low sensitive conventional TB diagnosis methods are available which are responsible for delay in early-stage TB diagnosis. There is an urgent demand for precise and early-stage TB detection techniques. TB diagnostic tools used nowadays need a great deal of time, and it requires a big laboratory infrastructure and skilled medical laboratory technologist. Owing to this, the urgent necessity for, portable device for single-step TB diagnosis as a real point-of-care (POC) analytical device which is greatly increasing with an importance with low cost. Emerging of nanotechnology in detecting TB has speeded with more specific and ultrasensitive TB test. This article reviews several traditional and molecular probe methods available for TB detection methods and focus the necessity of new

204

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development in TB nanodiagnosis. Further, we focus on several analytical modalities such as magnetic, optical, and colorimetric nanobiosensor for TB diagnosis. 14.1 INTRODUCTION According to World Health Organization Report (WHO) 2017, 10 million people (range, 9.0–11.1 million) developed TB disease in which 5.8 million were men, 3.2 million women, and 1.0 million children [1]. Morphologi­ cally, mycobacterium species is slow-growing, thereby causing a delay in diagnosis by traditional methods. Nanotechnology has given fast result with sensitivity and specificity of the test has considerable potential for early diagnosis, treatment, and prevention of TB [1, 2]. In India, 15 million suffer from TB, of which over 3 million are highly contagious open cases. Every year half a millions of TB patients expire, and every two minutes, one TB patient died. Tuberculosis (TB) is a chronic disease, projected to be one-third of the worldwide inhabitants ill with TB. The WHO recommended stopping TB strategy; approximately 22 million people were saved through a direct observation treatment short-course (DOTS) [3, 4]. India is a high burden for TB patients. The Indian government has stated in the year 2025, and the country is free from TB. This can be possible only by adopting innovative technologies for identification, prohibition, and TB management. One of the leading technologies today, which will meet these requirements is the nanomaterial-based devices for early diagnosis of TB [4, 5]. Mycobacteria is morphologically, rod-shaped, small, thin, slightly curved acid-fast (AF) bacilli. Mycobacterium are classified into two classes for their identification and treatment, such as M. tuberculosis bacilli complex (MTBC), which is pathogenic to humans and M. bovis is infected to animal, and M. leprosy is a source of leprosy [6]. Accurate TB detection methods contributed to the early-stage identification of MTB and associated infections. Identification of resourceful mycobacteria is made by repetitive segregation and recognition of infection consistent compatible medical and radiology appearance. The conventional microscopic AF diagnosis method cannot differentiate between pathogenic M. tuberculosis and Nontuber­ culosis mycobacteria (NTM). The conventional diagnosis of TB infection confirmed by the gold standard culture method. Several big corporate labs were mostly established by using DNA amplification to detect MTB targets. The upper respiratory, pulmonary mycobacterium infection with early detection technique requires smear microscopy and radiological evidence

Mycobacterium tuberculosis Diagnosis

205

by chest x-rays (CXR). These methods depend on the skill of the technician and Microbiologist [7]. The arrival of the nanomaterial-based device has given successful results in the early detection of TB within hours [8]. In this review, TB diagnosis with conventional and molecular probe-based methods of the various types of biomarkers and nanomaterials that have been used in TB diagnosis, which include nano-biosensor, focuses the need for point-of­ care (POC) device in early-stage TB diagnosis [9]. 14.2 TRADITIONAL TB DIAGNOSIS METHODS The traditional TB diagnosis methods are based on culture, biochemical tests, microscopy staining methods, and radiological diagnosis. The culture methods are a gold standard method for diagnosis of TB, but it requires 2 to 6 weeks [10]. All traditional TB diagnosis methods are low sensitive and require skilled medical technologist for screening MTB. The traditional MTB detection techniques were shown in Figure 14.1.

FIGURE 14.1

TB diagnosis methods.

14.2.1 MICROSCOPIC AFB The conventional microscopic smear observation of the MTB detection method is simple, rapid, and inexpensive. This method is routinely used in underdeveloped and developing countries. The AF smears microscopy examination is mostly used for anti-tuberculosis chemotherapy. Nevertheless, this method requires the correct sample collection technique. The lowest

206

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limit of this technique requires at least 5000 bacteria/ml for microscopic observation of AF bacilli [11]. At the list, three early morning sputum samples were collected for each chest symptomatic patient for the diagnosis of TB. The major investigative method for smear microscopy trusts on the staining of the AF bacilli using Ziehl-Neelsen (ZN) stain. This conventional AF smear microscopy observation is suggested for TB detection. 14.2.2 DIGITAL CHEST X-RAY (CXR) Acute pulmonary TB infection can be easily diagnosed with radiological CXR. The CXR permits the diagnosis of TB in resources limited settings, and it is endorsed by the WHO. CXR normally uses to find TB infection, but it is done in conjunction with TST (tuberculin skin test). The latest study results have proven that chest radiographs are the ideal methodology for finding in pediatric TB patients [12]. 14.2.3 CULTURE AND BIOCHEMICAL CHARACTERIZATION Isolation of MTB from clinical sputum samples is a challenging and tedious process [13]. There are so many traditional methods for the diagnosis of MTB, like a diagnosis of biochemical markers for the identification of different myco­ bacteria, including MTB identification [14]. Various types of the biochemical test also used for confirmation of MTB tests, which include niacin produc­ tion, nitrate reduction, tween-80 hydrolysis, aryl-sulfatase, urea hydrolysis, tellurite reduction, TCH sensitivity, catalase (qualitative and quantitative), growth on MacConkey agar and L J media, sodium chloride tolerance, etc., for identification of MTB [15]. The traditional TB diagnosis methods are usually preliminarily identified by traits such as rate of growth, pigmentation, and colony morphology and biochemical profiles [16, 17]. The traditional methods are well established, standardized, and relatively inexpensive but are slow in providing clinically relevant information and are limited in scope to the species for which a large number of strains have been studied. 14.2.4 ISOLATION AND IDENTIFICATION The clinical sputum samples were distributed into a sterile container, for sample pre-treatment and processing [18]. Using WHO-approved NALC

Mycobacterium tuberculosis Diagnosis

207

(N-acetyl-L-cysteine), 2% sodium hydroxide is used for digestion and decontamination of pulmonary sputum samples [19, 20]. After 3 to 4 weeks, the microbial growth is seen on the LJ media [21]. AF bacilli were subcul­ tured on Middlebrooks 7H10 agar at 35°C. The growth and rough and buff yellow-colored colony shown in Figure 14.2.

FIGURE 14.2

MTB growth on the Lowenstein-Jensen slopes.

14.3 NEWER LABORATORY DIAGNOSIS METHODS FOR TB The molecular diagnostic is an assembly of systems used to analyze molec­ ular markers in the genome. The person’s genetic code and how their cells express their genes as proteins application in molecular biology to health analysis [22]. However, conventional methods are slow and require multi­ step for assay procedure. Some new methods are now including for genetic investigations through the use of nucleic acid probes (Gen-Probe from Hain Life science Germany), nucleic acid amplification (NAAT), and nucleic acid sequencing [23–25]. The analysis of mycobacterial fatty acids by gas chromatography with these advanced new replacements for conventional TB detection methods. The favorable distinctive features of new molecular TB diagnosis methods summarize in Figure 14.3.

208

FIGURE 14.3

Nanostructured Smart Materials

Favorable distinctive features of new molecular TB diagnosis methods.

14.3.1 HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY (HPLC) The recognition of MTBC species in pulmonary sputum samples by chromatographic profile analysis can be performed once visible growth is obtained in solid media [26, 27]. The study of mycobacterial cell wall contains fatty acid [28]. The fatty acid contain with the specific chemical composition of MTB is identify by HPLC [29]. The strong mycolic acids are usually high-molecular-weight oily fatty acids that are present in the cell walls of a limited number of bacterial genera [30]. The MTB cell wall is chemically composed with 20 to 30 carbon atoms present in mycolic acid, where the genus Mycobacterium tuberculosis contains 60 to 90 carbon atoms. After several preparation steps, a gradient of methanol and dichloromethane (methylene chloride) is used to separate the mycolic acid esters, which are detected by UV spectrophotometry [31]. HPLC of mycolic acids is a rapid technique; but the basic format requires bacterial colonies grown in culture. HPLC has been shown to discriminate between species better than biochemical methods and gas chromatography-mass spectrometry.

Mycobacterium tuberculosis Diagnosis

209

14.3.2 MOLECULAR PROBE TECHNIQUES Molecular detection method mainly used in vitro biological assays such as real-time PCR (polymer chain reaction) or Fluorescence in situ hybridization [32]. The test identifies a molecule, often in low concentrations, that is a marker of infection in a clinical sample taken from a patient. It is a molecular genetic assay for identification of the clinically most relevant mycobacterial species from cultured material [33]. The molecular detection methods based on DNA (deoxyribonucleic acid) recognition by PCR to increase the number of nucleic acid molecules, thereby amplifying the target sequence in the patient clinical sample. Molecular methods are used to identify infective diseases such as TB with specific strains such as IS6110. The genetic identification can be swift; for example, a loop-mediated isothermal amplification test (LAMP) for TB. The common mycobacterium may be tested by using DNA strip technology and permits the identification of the M. avium, M. scrofulaceum, M. chelonae, M. fortuitum, M. gordonae, M. abscessus, M. intracellulare, M. interjected, M. kansasii, M. malmoense, M. peregrinum, M. marinum, and M. ulcerans, the M. tuberculosis complex and M. xenopi species [34]. Another DNA hybridization method used for MTB diagnosis by using nitrocellulose strip, the probe which is attach with streptavidin-biotin bound enzyme. The change in color effect and results were quantitatively analyzed by PCR software [35]. The DNA label PCR products are hybridized with oligo-probes and immobilized on a nitrocellulose strip. The identification of mutations binding to wild-type probes or by binding to oligo-probes specific for MTB mutations. The commercial products based on PCR hybridization on nitrocellulose strips can detect multi-resistance TB from a clinical sample or culture with good specificity and sensitivity [35]. 14.3.3 POLYMERASE CHAIN REACTION (PCR) A perfect analytical technique used to detect and identify MTB from pulmo­ nary sputum samples and other biological samples, thereby avoiding the rela­ tively lengthy time required for culturing. Since specimens usually contain only a few number of TB bacilli, direct detection requires either an extremely sensitive and specific assay or a process by which a diagnostically useful component of the target organism can be amplified to a detectable level. The real time PCR assays for the quick recognition of MTBC species with specific target in rpoB (rifampicin resistance) by Lee et al. and 16S rDNA. The internal transcribed spacer (ITS) 16S-23S rDNA genes for species identification by

210

Nanostructured Smart Materials

these assays. The PCR amplification is either followed by restriction endo­ nuclease assay, sequencing, or both [36]. Favorable distinctive features of new molecular TB diagnosis methods are shown in Figure 14.3. 14.3.4 SEQUENCING (16S RRNA) The presence of 16S and 23S rRNA genes in all organisms, except for viruses, renders it a suitable target for identifying microorganisms down to the species level. The ribosomal nucleic acids are measured to be genotypic significant molecules and have events of evolution engraved in the sequences of rRNA. This leads to the difficult in the expansion of simple sequence analysis method as restriction length polymorphism analysis (RFLP) or hybridization with probes. IS6110 insert sequence is the Mycobacterium tuberculosis-specific fragment, which is considered as the gold standard for identification for multiple copies in most MTB strains [36]. 14.3.5 GENE XPERT Gene Xpert is a compact, fully automated machine industrialized in the United States (US) and manufactured by Cepheid, which is maintained by the American National Institutes of Health. This test endorsed by WHO and the mechanism is based on DNA amplification to recognize early detection of MTB. New molecular-based identification of pulmonary and extrapul­ monary TB diagnosis done by rapid diagnostic methods produces results within 2 hrs. A NAAT test for the analysis of TB infection. The amplified Mycobacterium tuberculosis direct Gene-Probe test with the amplicons of MTB (Roche Diagnostics) were allowed for use with respiratory tract specimens that confirmed positive for AFB on smear [36]. Gene Xpert test is real and precise instrument for early detection TB, making it better quality as compared to AF smear microscopy [37]. Early diagnosis of MTB with Gene Xpert is a new potential tool in resource-limited settings, resulting in a progress of TB patient’s supervision and gives better outcome for early diag­ nosis. Gene Xpert had an advanced authentication as compared to AF smear microscopy. The accuracy of gene Xpert shows 98% sensitivity and 97% specificity endorsed through WHO specific for TB recognition. The major outcome of this instrument is to identify rifampicin-resistant and hence, finding the patients with multidrug-resistant (MDR) TB [38]. Gene Xpert can assist as a fast and precise analytical instrument gives more accurate

Mycobacterium tuberculosis Diagnosis

211

results as compare to conventional AF smear microscopy. The Gene Xpert with cartridge is shown in Figure 14.4.

FIGURE 14.4

Gene Xpert with cartridge.

14.4 NANOTECHNOLOGY-BASED TB DIAGNOSIS The arrival of nanotechnology for the early-stage detection of TB with association of chemistry, physics, and biology, included with bioengineering nanoscale. The synthesis of nanoparticles for making portable nano biosensor for various types of infectious disease for spot diagnosis. Nanoparticles less than 100 nm dimension with various properties of the nanoparticles which includes magnetic, optical, and electronic used for diagnosis of TB. The applications of nanotechnology have a great potential in the diagnosis, prevention, and treatment of pulmonary sputum samples. Nanotechnology has an enormous power on the early diagnosis and treatment of disease. Along with other technology used in drug, radionuclide, and cancer therapy. The nanoscale size-dependent properties make this technique superior and indispensable in multi-field of human activity [39]. Nanotechnology is promising in disease diagnosis, especially in identifying bacterial and viral infection, enzymes markers, cancerous cell, and specific protein derivatives. The main focus for the preparation of medical nanodiagnostic devices for application of early-stage TB diagnosis and to increase the sensitivity and

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specificity of the test results for both in vivo and in vitro identification for TB. Most of the infectious disease-causing agents like bacteria thus, the arrival of nanotechnology in clinical diagnosis of TB. All the above-said limitations have been overcome in the nanodiagnostic technique by producing results within hours with increased sensitivity and specificity [40]. 14.4.1 DIAGNOSIS OF TB BY GOLD NANOPARTICLES Recently scientists contribute their energies closer to the development of economical TB nanodevice with robust and reproducible. As such, nanopar­ ticle-based methods are expected to evolve incrementally through the years, permitting to satisfy the needs tackled in the area. Various types of nanomaterial used for development of nanodevice. Mirkin and his team members developed gold nanoparticle capped with thiol modified oligonucleotides (Au-Nano­ probes) were considerably apply for early-stage recognition infections such as Mycobacterium tuberculosis. Mirkin strategy was used to diagnosis TB complex which is naked eye colorimetric spot diagnosis [41]. By tailoring AuNps with GP-1 and GP-2 oligonucleotide probe in colloidal suspension. The colorimetric change effects from the differential aggregation outlines of Au-nano probes induced by improved ion power in the absence/presence MTB target-specific sequence. The existence of the complementary target sequence no change in color of gold nanoparticle (red color) due to localized SPR (525 nm), while no precise target sequence indicate GNPs clumping when addition of salt and color of GNPs change red to purple (redshift at 650 nm of the LSPR). The GNPs were broadly recycled owing to their property (SPR) which results from the collective oscillation of the electrons of the conduction band [42]. This gives the red color solution and absorption peak is at 520 nm for 20 nm AuNPs [43]. In addition, GNPs are biocompatible, so they are suitable for biological application. Early-stage identification of MTB with precise DNA sequence is extremely sensitive assay by Costa et al. [44] and his co-worker group fabricates DNA electrochemical biosensor to increase the sensitivity of assay. The schematic representation of fabrications of colorimetric gold sensor is shown in Figure 14.5. 14.4.2 MAGNETIC NANOPARTICLE FOR TB DIAGNOSIS Iron oxide nanoparticles represent an ideal material for trying to know the effect of surfaces on magnetism, for studying dipolar coupling, and for

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probing catalytic processes. Superparamagnetic iron oxide nanoparticles (SPIONs) were commonly used MRI further they also find its application in cell tracking [45], drug delivery and cancer therapy [46], and DNA biosensor [47]. Functionalization of magnetic nanoparticle is done with a wide range of ligands, making them available for detecting target DNA/ RNA, bacteria, and viruses. SPIONs (Superpara iron oxide nanoparticles) have been commercialized as MRI contrast enhancers, and offer additional benefits outside their stronger magnetizations. The MNPs tailored with various types of capping agent’s to provide very specific interactions with biological samples. In magnetic separations, SPIONs are typically inserted in a matrix material, which is then functionalized with a biologically active species (Figure 14.6) [48].

hybridization

Bare Gold nanoparticle red colour FIGURE 14.5

Agregated Gold nanoparticle purple colour

Design and fabrication of Au nanoprobe for colorimetric detection.

The bioconjugation with SPIONs (superparamagnetic nanoparticles) with different diagnostic methods has opened a new path for mycobacteria, protein, and cell sensing, and quantitative analysis [49]. The scope of SPIONs at many industrial uses like biosensing applications, MNP storage media, and medical applications [50]. Non-appearance of outer magnetic waves, the magnetic interactions between every two NPs in the dispersion, building the

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dispersion stable in physiological solutions and helping NPs coupling with biological agents. Owing to this exclusive property of MNPs, the innova­ tive systems for MTB detection in clinical samples is improved beside with manipulation of these clinical samples with an external magnetic field [51].

FIGURE 14.6

Magnetic method for TB diagnosis.

14.4.3 QUANTUM DOT FOR TB DIAGNOSIS Quantum dots (QDs) are very tiny nanoparticles normally size is less than 10 nanometers. The small size and shape renders their electronic and optical features. The light radiate ability of QDs nanoparticles has precise wavelength with high absorption of light, more photostability, and narrow equal transmission bands with control of 3 D responses [52]. The physical and optical property making them biocompatible. Functionalization of QDs with a wide range of biomolecules made them eligible for imaging, diagnostic, and therapeutic purpose by Gao et al. and Liandris et al. formulated a methodology to detect pathogenic TB using functionalized QDs with immune magnetic separation [53]. In this study, QDs is functionalized with streptavidin and coupled with Cadmium Selenide (CdSe) to detect the

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surface antigen of mycobacterium species [54]. In aspect, QDs have now been used in a large number of medical applications, including studies of protein trafficking, DNA biosensor assay, and dynamic studies of cell mobility by Zrazhevskiy et al. [55]. Rotem and his co-workers reported the use of QDs for the revealing of infectious bacteria. Newly QDs have been used for the recognition and imaging of respiratory infectious diseases for pulmonary TB. Ghazali and co-workers established and assessed a detection to analyze specific DNA sequences combining fluorescent semiconductor QDs with MNp beads allowing for a firm diagnosis of Mycobacterium tuberculosis complex [56]. 14.4.4 SILICA NANOPARTICLE FOR TB DIAGNOSIS Dye-doped silica NPs contain large amounts of dye (fluorophores) molecules inside a silica matrix, amplifying the fluorescence of every contact incident. Ekrami et al. through their study proved that bioconjugated silica nanoparticle gives the best result in detecting TB compared with conventional methods in analyzing TB from sputum sample [57]. The test results show 97.1% sensitivity and 91.35% specificity in 152 sputum samples analyzed [58]. This result is far superior to the AFB test results (86% sensitivity and 84.9% specificity) and nested PCR which gives only 86.9% sensitivity and 88.6% specificity [59, 60]. 14.4.5 POINT OF CARE TEST (POC) FOR TB The Au-nano probe assay efficiently prolonged near the real-time identification of pathogen of interest with a functionalized Au-nano probe classifies one-step assay with the presence or absence of pathogens [61, 62]. To enhance the detection perspective of this approach for TB. This idea covers spot colorimetric observation for rapid detection technique for early detection of TB [63]. Here, we try to present an advanced thiol-linked ssDNA altered gold nanoprobe for TB recognition [64]. The attempts has been completed to encompass these devices to permit for additional layers of proof for one-step analysis, also through realizing the difference in direction of agglomeration and hybrid productivities or counting on the use of more Plasmon signatures of NPs [65, 66]. Whereas these methods simplified the detection of MTB PCR products, they still required amplification of MTB DNA by PCR, which remains challenging at the POC assay [67]. To overcome

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this experiment, sensitivity of the test can be improved by scaling down the sensors to nanoscale [68]. Point of care assay is feasible for TB diagnosis by integrating microfluidics and nanotechnology along with lab-on-a-chip [69]. The linear range of TB, detection limit, and type of nanobiosensor was shown in Table 14.1. TABLE 14.1

Nanomaterial-Based Detection System of MTB

Sr. Nanomaterial No. Use

Applications Detection Limit

Descriptions References

1.

Magnetic (MNP) MTB

106 cells/ml Fluorescence Dunin-Borkowski et al. 1998 [59]

2.

Silica NPs

MTB

102 cells/ml Fluorescence Qin et al. 2007 [63]

3.

Quantum dots

MTB

104 cells/ml SYBER

Gazouli et al. 2010 [64]

4.

SPION

MTB

103 cells/ml SYBER

Sawant et al. 2018 [53]

5.

AuNps

MTB

10 ng/µL

DNA

Liandris et al. 2009 [69]

6.

Ag NPs

MTB

0.03 f M

DNA

Victor V. et al. 2018 [39]

7.

Chitosan-ZrO2

MTB

0.00078 μM DNA

Dilan, Qin et al. 2007 [63]

8.

ZrO2-MWCNT

MTB

0.01 nM

Gazouli et al. 2010 [64]

9.

ZrO2

MTB

0.065 ng/μL DNA

4

DNA

Gupta et al. 2007 [67]

14.5 CONCLUSIONS Most of the conventional methods available for TB detection are just an improvisation of older techniques, which is an half a century ancient system. The optimization of culture techniques is increasing the detection rate, but they failed to prove during clinical trials in large scale. However, nanotechnology-based TB diagnosis platforms have been converted to the medical setting for molecular diagnostics. The unlimited energies put into the expansion of proof-of-concept methodologies; most of the period absence the robustness. Future innovative developments in nanodiagnosis will stay through miniaturization of biochip technology to the nanoscale series for POC diagnostics with a sample-in answer-out style that hinders user-error, thus permitting their use by non-technical persons. New genera­ tion molecular nanotechnology are helpful for novel diagnostic method, but more work is to remain as a TB point of care (POC) device.

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KEYWORDS • • • • • •

aging temperature carbon nanotubes glass transition temperature Kohlrausch-Williams-Watts polymer nanocomposites polystyrene

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CHAPTER 15

Physical Aging in PS-MWCNT Composite: An Enthalpy Relaxation Study MD. AMIR SOHEL, ABHIJIT MONDAL, and ASMITA SENGUPTA Department of Physics, Visva-Bharati Central University, Santiniketan, West Bengal–731235, India, E-mail: [email protected] (A. Sengupta)

ABSTRACT Physical aging behavior of pure polystyrene (PS) film and PS-multi wall carbon nanotube (MWCNT) composite film has been studied by moni­ toring enthalpy relaxation using differential scanning calorimeter (DSC). The PS-MWCNT film with 2.5 wt % MWCNT was prepared via the solution casting method. In this work, we have studied the physical aging behavior of pure PS and PS-MWCNT composite film. The glass transition temperature (Tg) for PS and PS-MWCNT composite as obtained from DSC are 98.2°C and 95.3°C, respectively. To study the physical aging behavior, both the samples were isothermally annealed at an aging temperature (Ta) 84°C for various aging time (ta) from 1 hour to 48 hours. The Tg for both the samples increases with aging time. This ascending trend of Tg for the aged sample is due to the relaxation of molecular chain mobility. The kinetics of enthalpy relaxation due to physical aging has been studied using Kolrausch-Williams-Watt (KWW) model. By applying this model to the experimental results, we calculate the values of relaxation time (τkww). The values of relaxation time (τkww) as obtained from KWW model are 13.45 ± 0.16 hours and 10.82 ± 0.95 hours for PS and PS-MWCNT, respectively. This shows that the relaxation due to aging in PS is slower than that in PS-MWCNT composite.

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15.1 INTRODUCTION The introduction of nanomaterials into polymers generates polymer nanocomposites (PNCs). Recently, PNCs have attracted great attention to researchers and industries due to their improvements in various properties such as mechanical strength, thermal stability, electrical properties, etc. Incorporation of carbon nanotubes (CNTs) as fillers into polymers provides composite materials with superior material properties such as strength, modulus, electrical conductivity, unlike that is provided by carbon fibers, carbon black, graphite. Though CNT-based polymer composite has a large field of applications such as aerospace [1], automotive [2], and microelec­ tronics [3], there are a number of factors which constraint the engineering applications of CNT-based PNC’s and out of them, dimensional instability is of most concerned which results from the physical aging of PNC’s. It is well known that the physical aging is a natural phenomenon which usually takes place in amorphous glassy materials and originates from the fact that they are generally out-of-equilibrium in their glassy state, having excess values of thermodynamic quantities such as volume, enthalpy, or entropy [4]. The term excess is with reference to the equilibrium state. In nature, all thermodynamic non-equilibrium state evolves to achieve equilibrium and hence the out of equilibrium glassy material moves towards the equilibrium by reducing the excess thermodynamic quantities. This structural relaxation of glassy material towards an equilibrium state is called ‘physical aging,’ and it causes volume contraction and densification of the material. Thus, physical aging causes an alternation of the dimension of the glassy material and has an intense effect on the properties (i.e., physical, mechanical, electrical, etc.), which depend on the structure of the material [4–6]. Thus, to design stable PNC materials detailed knowledge of physical aging for these materials is required for their long-term applications, especially the role of nanostructure on the behavior of physical aging in PNCs. The study of physical aging of polymer composite is important not only because of their long-term performances but also for the inconsistency in the physical aging behavior of different polymer composites which reflects in the literatures [7–14], and these inconsistencies may have assumed to be due to the complex interac­ tions between the host polymer matrix and the nanoparticles. In this work, we have studied the physical aging of pure polystyrene (PS) and PS-MWCNT (2.5 wt %) composite film prepared via solution casting method and tried to understand the interaction between PS and MWCNT in the composite film. We have studied enthalpy relaxation due to physical aging for aging time (ta) up to 48 hours and employed Kohlrausch-Williams-Watts

Physical Aging in PS-MWCNT Composite

225

(KWW) model [15] to describe the enthalpy relaxation kinetics and to esti­ mate the mean relaxation time (τkww). 15.2 EXPERIMENTAL PROCEDURE 15.2.1 MATERIALS AND SAMPLE PREPARATION Polystyrene (PS, Mw = 394 kg mol–1, Mn = 175 kg mol–1) was obtained from BASF AG Ludwigshafen, Germany. Multiwall carbon nanotube (MWCNT, purity >90%, diameter-10–15 nm, length~5 µm) were purchased from Ad Nano Technologies, Karnataka, India. All the materials were used as received. The solution casting method was used to fabricate the composite since it has the advantage through low viscosity which accelerates the mixing and dispersion of MWCNT. At first, a solution of PS and toluene was obtained by dissolving 1 gm of PS into 10 ml of toluene and 25 mg of MWCNT were ultrasonically dispersed into another 10 ml of toluene for 90 minutes to have a stable suspension of MWCNTs in toluene. Then the two solutions were mixed and again ultrasonicated for 45 minutes to obtain a uniform dispersion of MWCNTs in PS. The resulted solution was then poured in a glass Petri dish and was allowed normal evaporation of the solvent for several days. Finally, they were placed in a hot air oven at 100°C for 24 hours to completely remove the traces of the solvent. The pure PS film was also prepared using the same method. The film obtained has an average thickness of 220–230 µm. 15.2.2 ENTHALPY RELAXATION EXPERIMENT Enthalpy relaxation measurement was carried out by differential scanning calorimetry (200F3, NETZSCH). Samples were cut into small pieces to have weight between 10–15 mg and sealed in DSC aluminum pans. They were first heated to 150°C and remained there for 5 minutes to erase previous thermal history and then the sample pans were placed at an aging temperature (Ta) 84°C in a hot air oven having temperature accuracy ±0.5°C for aging up to a maximum of 48 hours. Having aged for different aging times in the hot air oven, samples were heated in DSC from 20°C to 150°C at the rate of 10°C/ min after each aging, respectively. Measurements for unaged samples were taken by reheating the samples from 20°C to 150°C after the first heating to 150°C and subsequent cooling to 20°C. Temperature variation of specific

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226

heat capacity (Cp) of the samples is obtained using the ratio method where sapphire is taken as the standard sample. 15.3 RESULTS AND DISCUSSIONS The normalized DSC curve of pure PS and PS-MWCNT (2.5 wt%) composite for unaged and aged up to 48 hours are shown in Figures 15.1 and 15.2, respectively. In the study of physical aging, glass transition temperature (Tg) is an important parameter, since the deviation Tg-Ta determines the restoring force required to the relaxation during physical aging [16]. The Tg is deter­ mined from the DSC heating curve and the point of inflection is taken as the Tg. The Tg of the unaged pure PS and PS-MWCNT films are found at 98.2°C and 95.7°C, respectively. A previous study [17] on PS shows that the Tg of bulk PS is 100°C.

FIGURE 15.1

Normalized DSC heating scans of unaged and aged PS film.

Therefore, the Tg value of the pure PS film is slightly (~2°C) less than that of bulk PS. Such depression in Tg of PS film is reported in literature [18]. Again, we see that the Tg is depressed in PS-MWCNT composite by 2.5°C compared to that of pure PS. This depression of Tg in PS-MWCNT composite is in agreement with the results obtained for PMMA/silica and PS/gold composite by Boucher et al. [7, 8, 19] and may suggest that in the

Physical Aging in PS-MWCNT Composite

FIGURE 15.2 film.

227

Normalized DSC heating scans of unaged and aged PS-MWCNT composite

PS-MWCNT composite MWCNT acts as a plasticizer. For the aged sample, we have seen the usual behavior of glassy polymers, i.e., the Tg, area of the endothermic peak and the peak value of the endotherm associated with the glass transition increase with increase in aging time for both pure PS and PS-MWCNT composite film. The variation of Tg of PS and PS-MWCNT film with aging time is shown in Figure 15.3. When polymeric materials are quenched from their melt state to below the Tg, the materials have a larger free volume. With the aging of the material, relaxation of free volume takes place resulting to a reduction in the free volume which causes reduction of segmental mobility in the aged sample compared to that of the unaged sample. When the aged sample reheated, it takes more energy to complete the glass transition resulting in an increase in area of the endothermic peak associated with the glass transition. Moreover, due to the reduction of segmental mobility in the aged sample, it is necessary to heat up a sample to a higher temperature to complete the structural rearrangement which occurs during glass transition and hence the Tg as well as the peak value of the endotherm increases with aging time. The enthalpy required to complete the glass transition is obtained by integrating the endothermic peak associated with the glass transition. Relaxation in enthalpy for aged sample is obtained using the equation: ΔH relax = ∫

To

T1

(C

p , aged

− C p , ref ) dT

(1)

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228

where, Cp,aged and Cp,ref are the specific heat capacities of the aged and unaged sample; To and T1 are the reference temperatures above Tg and below the Ta, respectively. The KWW equation for enthalpy relaxation is given as follows: and

ΔH relax = ΔH ∞ (1− ∅ ( t ) )

(2)

∅ ( t ) = exp ( −t / τ kww )

(3)

β

where, t, τkww and β are the aging time, characteristics enthalpy relaxation time, non-exponential parameter, respectively. The non-exponential param­ eter β is usually considered as the distribution of enthalpy relaxation time having a value between 0 and 1. Both τkww and β are adjustable parameters which are determined by fitting the experimental data to the Eqn. (3). ∆H∞ is the equilibrium enthalpy relaxation which can be calculated using the following equation: ΔH ∞ = ΔC p (Tg − Ta )

(4)

where, ∆Cp is the change in heat capacity at Tg and Ta is the aging temperature. In the KWW Eqn. (2), the relaxation function ϕ(t) is related to the amount of enthalpy relaxation ΔHrelax by the following relation: ∅ ( t ) =1 − ΔH relax / ΔH ∞

FIGURE 15.3

Variation of glass transition temperature (Tg) with aging time (ta).

(5)

Physical Aging in PS-MWCNT Composite

229

Using the Eqn. (5) we calculate the values for relaxation function ϕ(t) for aging time up to 48 hours. Figures 15.4 and 15.5 represent the plot of ϕ(t) with aging time for PS and PS-MWCNT composite, respectively. The points in the graph show the experimental values of ϕ(t), and the solid

FIGURE 15.4

Variation of relaxation function ϕ(t) with aging time for PS.

FIGURE 15.5 Variation of relaxation function ϕ(t) with aging time for PS-MWCNT composite.

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lines represent the best-fitted curve to Eqn. (3) for ϕ(t). The fitting program is done by Origin software through a non-linear curve fitting method and gives satisfactory results since the R-square value is approximately 0.98. This suggests that the enthalpy relaxation in PS and PS-MWCNT composite takes place in accordance with the KWW model, and hence using this model, we can predict the long-term enthalpy relaxation process from the short-term data. From the fitting results, β have the values 0.57 ± 0.04 and 0.59 ± 0.05 for PS and PS-MWCNT composite whereas τkww has the values 13.45 ± 1.17 hour and 10.82 ± 0.95 hours for PS and PS-MWCNT composite, respectively. In our previous study on PLA, we have shown the parameters β and τkww have the values 0.50 and 1454 ± 1.34 × 102 minutes, respectively [20]. In the present study, the relaxation time τkww of PS-MWCNT composite have a lower value than that for pure PS and signifies that the presence of MWCNT in PS enhances or acceler­ ates the relaxation process during physical aging, which again suggests that the MWCNT in the PS-MWCNT composite acts as a plasticizer. Out of the various model, free volume hole diffusion model is well accepted to describe quantitatively the physical aging phenomenon in polymer composite. In PS-MWCNT composite, MWCNTs increase the free volume by acting as plasticizer and consequently enhance the relaxation rate during aging. Thus, depending on the above discussions, we may conclude that the MWCNT in the PS-MWCNT composite acts as plasticizer. 15.4 CONCLUSIONS On the basis of DSC analysis, the kinetic parameters of enthalpy relax­ ation in PS and PS-MWCNT composite are successfully determined using KWW model. The relaxation time (τkww) for PS and PS-MWCNT composite are 13.45 ± 1.17 hours and 10.82 ± 0.95 hours. From these values of τkww, we can conclude that the presence of MWCNT enhances the relaxation in PS-MWCNT and MWCNT in PS-MWCNT composite acts as a plasticizer. ACKNOWLEDGMENT Md. Amir Sohel wishes to acknowledge CSIR, Govt of India, for providing SRF-direct fellowship.

Physical Aging in PS-MWCNT Composite

231

KEYWORDS • • • • • •

differential scanning calorimetry enthalpy relaxation glass transition physical aging polystyrene PS-MWCNT composite

REFERENCES 1. Bellucci, S., Balasubramanian, C., Micciulla, F., & Rinaldi, G., (2007). CNT composites for aerospace applications. J. Exp. Nanosci., 2, 193–206. 2. Kaushar, A., Rafique, I., & Muhammad, B., (2016). A review of applications of polymer/ carbon nanotubes and epoxy/CNT composites. Polym. Plast. Technol. Eng., 55, 1167–1191. 3. Aryasomayajula, L., & Wolter, K. J., (2013). Carbon nanotube composites for electronic packaging applications: A review. Journal of Nanotechnology, 6. Article Id: 296517. http://dx.doi.org/10.1155/2013/296517. 4. Struik, L. C. E., (1977). Physical aging in plastics and other glassy materials. Polym. Eng. Sci., 17, 165–173. 5. Hodge, I. M., (1995). Physical aging in polymer glasses. Science, 267, 1945–1947. 6. Hutchinson, J. M., (1995). Physical aging of polymers. Prog. Polym. Sci., 20, 703–760. 7. Boucher, V. M., Cangialosi, D., Alegra, A., Colmenero, J., Gonzalez-Irun, J., & Liz-Marzan, L. M., (2010). Accelerated physical aging in PMMA/silica nanocomposites. Soft Matter., 6, 3306–3317. 8. Boucher, V. M., Cangialosi, D., Alegra, A., & Colmenero, J., (2010). Enthalpy recovery in PMMA/silica nanocomposites. Macromol., 43, 7594–7607. 9. Amanuel, S., Gaudette, A. N., & Sternstein, S. S., (2008). Enthalpic relaxation of silicapolyvinyl acetate nanocomposite. J. Polym. Sci. Part B Polym. Phys., 46, 2733–2740. 10. D’Amore, A., Caprino, G., & Nicolais, L., (1999). Long-term behavior of PEI and PEI-based composites subjected to physical aging. Compos. Sci. Technol., 59, 1993–2003. 11. Lu, H. B., & Nutt, S., (2003). Enthalpy relaxation of layered silicate-epoxy nanocom­ posites. Macromol. Chem. Phys., 204, 1832–1841. 12. Lizundia, E., Oleaga, A., Salazar, A., & Sarasua, J. R., (2012). Nano- and microstructural effects on thermal properties of poly(l-lactide)/multiwall carbon nanotube composites. Polymer, 53, 2412–2421. 13. Lin, Y., Liu, L., Cheng, J., Shangguan, Y., Yu, W., Qiu, B., & Zheng, Q., (2014). Segmental dynamics and physical aging of polystyrene/ silver nanocomposite. RSC Adv., 4, 20086–20093.

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14. Amanuel, S., Gaudette, A. N., & Sternstein, S. S., (2008). Enthalpic relaxation of silicapolyvinyl acetate. J. Polym. Sci. B., 46, 2733–2740. 15. Williams, G., & Watts, D. C., (1970). Non-symmetrical dielectric relaxation behavior arising from a simple empirical decay function. Trans. Faraday Soc., 66, 80–85. 16. Cangialosi, D., Boucher, V. M., Alegra, A., & Colmenero, J., (2013). Physical aging in polymers and polymer nanocomposites: Recent results and open questions. Soft Matter., 9, 8619–8630. 17. Sohel, M. A., Mandal, A., Mondal, A., Pan, S., & Sengupta, A., (2018). Calorimetric analysis of uncompatibilized polypropylene/polystyrene blend using DSC. Macromol. Symp., 379, 1700032. 18. Cangialosi, D., Alegria, A., & Colmenero, J., (2016). Effect of nanostructure on the thermal glass transition and physical aging in polymer materials. Prog. Polym. Sci., 54, 128–147. 19. Boucher, V. M., Cangialosi, D., Alegra, A., Colmenero, J., Santos, I. P., & Liz-Marzan, L. M., (2011). Physical aging of polystyrene/gold nanocomposites and its relation to the calorimetric Tg depression. Soft Matter., 7, 3607–3620. 20. Sohel, M. A., Mondal, A., & Sengupta, A., (2018). In Mangalore University. In: Narayana, Y., (ed.), Proceedings of International Conference RAMSB. Mangalore (India), Mangalore, Karnataka.

CHAPTER 16

Dual Probe Heat Pulse (DPHP) Method Soil Moisture Sensor Using Advanced Materials-Based Thermistor and Fluorine Doped Tin Oxide (FTO) Thin Film Electric Heater ALMAW AYELE ANILEY,1,2 S. K. NAVEEN KUMAR,1 and A. AKSHAYA KUMAR1 Department of Electronics, Mangalore University, Mangalagangothri–574199, Mangalore, Karnataka, India

1

Department of Electrical and Computer Engineering, Debre Markos University, Debre Markos, Ethiopia

2

ABSTRACT Dual probe heat pulse (DPHP) soil moisture and temperature sensor is a cheap and precise technique of determining volumetric soil moisture content (θv) for a representative agricultural soil. Here, heat pulse method soil moisture content estimation using thin-film heater as a heat source and nanoceramic powder-based thermistor as temperature sensor has been designed, fabricated, calibrated, and tested. The thermistor is fabricated from NiMn2O4 nanoceramic powder. The NiMn2O4 nanoceramic powder, in turn, fabricated from acetates of Nickel and manganese using the wet chemical method. The heater is Fluorine doped tin oxide (FTO) coated thin-film heater with a dimension of 2.6 cm × 2.6 cm and 1 mm thickness. The heater and the temperature sensor are fixed at a distance of 6 mm from each other. The pulse duration is set to 5 minutes. The 5V DC power source is used as a power source for the developed sensor. The result indicated that in a soil sample with a known amount of θv, the temperature first rises to some time and finally, it stabilizes as the time goes up. It also confirmed that the change

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in temperature of the soil is inversely proportional to the change in soil moisture content. The measured and the laboratory tested soil volumetric moisture contents have been checked and they are found to be agreed. The system can also measure the soil temperature in two- or three-digit precision. 16.1 INTRODUCTION There are numerous definitions for soil based on the discipline defining it. Some of the definitions are geologic definition, old-style definition, constituent definition, and soil classification definition. Soil constituent definition says that soil is consists of inorganic matter, carbon-based matter, air, and water. The details are found somewhere else [1, 2]. The deepness of soil outline, which is vital for plant development is 100–200 cm [3]. The extreme distance of most crops root is 1 m [1]. Few crops root will reach up to 1.20 m [1] depth in the soil. The soil moisture is the quantity of water in the soil in a different context. It can be defined in two different ways [4] as soil water content and soil water potential. Soil water content is the quantity of water that can be dignified in mass or volume. It is usually measured by the standard method called the thermogravimetric method. The thermogravimetric method measures the quantity of water in grams found in the specific soil sample. The experiment typically has been performed in the test center. It is done by drying a known mass of soil sample on heater usually at 105 °C for 1 day or until we get constant mass. The change in mass of the dried soil sample and the original soil sample is the mass of the water which is available for plants in agriculture. This method is correct, easy but it is not repeatable for the second time, time taking, destructs the soil, and requires more manpower. It is also called a direct (laboratory) method of soil moisture content measurement. There have been numerous volumetric soil water content quantifying approaches. The concept of θv is related to defining the soil moisture content in units of volume. Essentially it is very hard to get θv directly. Rather it can be calculated from a thermogravimetric (θg) method using some features which are calibration methods. The percentage of θv is the product of gravimetric water content (θg) and bulk density (Pb) of the soil sample divided by the density of water (Pw). There are other indirect (field) θv methods such as neutron moderation method (NM), time-domain reflectometry (TDR) method, frequency domain reflectometry (FDR) method, amplitude domain reflectometry (ADR) method, phase transformation (PT) method and

Dual Probe Heat Pulse (DPHP) Method Soil Moisture Sensor

235

noncontact method (microwave method, ground penetration radar, x-ray tomography and nuclear magnetic resonance imaging (NMRI) technique) [5]. To mention some of the advantages of these methods are direct volume measuring capacity and good accuracy and some of the disadvantages are small coverage area, low precision, and soil-specific calibration. The percentage (%) range of θv is from 0–100% [3, 6] but a representative agri­ cultural θv is in the range of 5%–35% [7]. Potential soil water is the degree of energy that the plant root should provide to draw water from the soil. It predicts a certain agricultural soil’s water status. It is measured with regard to units of stress. Tensiometer, heat dissipation method, psychrometer, strength block, and granular matrix are some of the current soil water potential gauging techniques [8]. All of these measure pressure so that there is a need for converting this pressure in terms of water content. This is one of the biggest disadvantages of this kind of soil moisture content measurement methods. Other disadvantages of these methods are inaccurate measurement, limited soil suction range, temperature-dependent, soil type dependent, and high cost. Tables 16.1 and 16.2 discuss the working principle, advantages, and drawbacks (disad­ vantages) of each type of in-situ (field) soil moisture content estimation methods [8–16]. Heat pulse-based soil moisture estimation method is one type that may be constructed by some distance separated or contacted heater and tempera­ ture sensor without porous block or contact temperature sensor and heater with the porous block. A number of works have been done for soil moisture content quantifying using heat pulse method using ordinary heaters and thermometers [3, 14, 17–19]. Here, the ordinary heaters and thermometers affect the overall performance of the sensor. The heater affects the sensor by increasing the energy consumption or by degrading itself in a short period and shortening the lifespan of the sensor. The heater also determines the size and miniaturization ability of the sensor. The bulk temperature sensors possess low accuracy, precision, high energy consumption, large in weight and dimension, contain poison materials, long response and recovery time [12, 15, 16]. Due to these component factors, the heat pulse method soil moisture content measurement is suffering from high cost, high-energy requirement, long response time, inaccuracy, and low precision. In this chapter, DPHP method soil moisture meter has been designed, fabricated using advanced materials, calibrated, and used to estimate θv. Nanomate­ rial components of the resulting sensor improve power consumption, size, weight, accuracy, precision, and cost.

2.

Neutron Moderation (NM)

1.

Name

Working Principle

Advantages

Disadvantages

A radioactive source releases highspeed neutrons. When they collide with particles of the same mass as a neutron (i.e., protons, H+), they drastically retard and form a “cloud” of “thermalized” (slowed) neutrons.

• Robust and accurate (±0.5%).

• Unsafe.

• Can be implemented in many soil depths.

• Requires soil-specific calibration.

• Large size coverage.

• Slow response.

• Not pretentious by salinity/air gaps. • Stable

• Weighty and clumsy. • Inefficient and hard near soil surface. • Cannot be automated. • Costly.

The soil bulk dielectric constant (εab) is obtained by using the time it needs for an electromagnetic wave (emw) to propagate via a transmission line (TL) in soil medium. Since the moving speed (V) is a function of εab, εab is proportional to the square of the transit duration out and back along the Tl: εab = (c/v) = [(c × t)/(2 × L)] 2

2

C: velocity of electromagnetic waves in a vacuum. L: the length of Tl embedded in the soil

• Accurate (±1%).

• Comparatively costly.

• Simple calibration.

• Potentially restricted applicability in heavily saline or in highly conductive heavy clay soils.

• Easily extended. • Many ways of probe patterns. • Small soil disturbance. • Comparatively insensitive soil salinity. • Can also be used soil electrical conductivity measurement.

• Soil-specific (complex) calibration required for soils having huge amounts of bound water. • Comparatively small sensing volume.

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Time Domain Reflectometry (TDR)

No.

Summary of Volumetric Methods of Soil Moisture Content Measurement

236

TABLE 16.1

Advantages

Disadvantages

The capacitance of a capacitor using soil as a dielectric material depends on soil moisture content. When the capacitor is connected to a source to form a circuit, variations in soil water content can be detected by fluctuations in the circuit operating frequency.

• Accurate (±1%). • Can be used in highly saline soil. • Improved resolution with the comparison of TDR. • Able to use with conventional data loggers. • Flexibility in probe design. • Cheaper than TDR

• Narrow coverage area (about 4 cm). • Require nice contact with the soil. • Affected by temperature, pb, clay content, and air gaps than TDR. • Requires soil-specific calibration.

Phase Transmission (PT)

Name

After traveling a known distance, a periodic signal shows a phase shift relative to the original. This phase shift is influenced by the velocity of propagation. Because propagation speed is related to soil water content, soil moisture content can be determined by the phase shift for a given frequency and traveled distance.

• Accurate in soil-specific calibration (±1%). • Sensing volume (1.2–1.5 m3). • Can be connected to conventional data loggers. • Low-cost.

• • • • •

When an electromagnetic wave (em) • Accurate (±1%–±5%). moves along a transmission line (TL) to • Negligible soil disturbance. a region with dissimilar impedance, part • Possible to connect to conventional of the transferred energy is reflected data loggers. back to the source. • Low-cost. • Temperate independent. • Field estimation of soil bulk density possible

Frequency Domain (FD)

3.

4.

5.

Soil disturbance during installation. Requires soil-specific calibration. Vulnerable to salinity levels > 3 dS/m Low precise. Everlastingly installed in the field

• Soil-specific calibration. • Influenced by air gaps, stones or channeling water directly onto the probe rods. • Small sensing volume

237

Working Principle

ADR

No.

(Continued)

Dual Probe Heat Pulse (DPHP) Method Soil Moisture Sensor

TABLE 16.1

Disadvantages

It measures the time taken to travel one-way for an electromagnetic wave (beat) along the transmission line. It works as indistinguishable as TDR; no coordinated contact is required between the soil and the sensor in any case.

• Accurate (±1–2%).

• Reduced precision.

• Large sensing soil volume.

• Soil is disturbed.

• Conventional data logger.

• Permanent installation requirement

It works in the same manner as TDR but does not need direct contact between the soil and the sensor

• Small.

• Low-cost

• Compact.

• Not widely used because it is in the research and development phase

• Low-cost.

• Only measures soil moisture and • No contact between the soil and the Use two antennae to transmit and electrical conductivity of the receive EM signals that are reflected by sensor probe. surrounding surface soil. the soil, whereas the passive microwave Key: just receives signals naturally emitted A & P EMI methods: active and passive • Could not directly measure water by the soil surface. content electromagnetic induction

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8.

Advantages

Time Domain Transmission (TDT)

7.

Working Principle

Ground Penetrating Radar (GPR)

6.

Name

A & P EMI Methods

No.

(Continued)

238

TABLE 16.1

No.

Name Working Principle

Gypsum (Bouyoucos) Block (GB)

Tensiometer

1.

2.

Summary of Tensiometric Methods of Soil Moisture Estimation

Granular Matrix Sensors (GMS)

3.

Disadvantages

• Simple to read the data. • Large coverage area (Up to 10 cm sphere radius). • Can read continuously. • Might not require power. • Nicely-suited for high-frequency sampling. • Little maintenance skill

• Limited soil suction range (