Metal-Organic Framework Composites: Volume 2 ZIF-8 Based Materials for Water Decontamination 9783110792591, 9783110792553

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Metal-Organic Framework Composites

Also of interest Metal-Organic Framework Composites. Volume : ZIF- Based Materials for Pharmaceutical Waste Ahmad, Pervaiz, Saeed, Luque, Alsaiari, Harraz (Eds.),  ISBN ----, e-ISBN (PDF) ----

Nanomaterials for Water Remediation Mishra AK, Hussain, Mishra SB (Eds.),  ISBN ----, e-ISBN (PDF) ----

Inorganic and Organometallic Polymers Pal Singh Chauhan, Singh Chundawat,  ISBN ----, e-ISBN (PDF) ----

BioChar. Applications for Bioremediation of Contaminated Systems Thapar Kapoor, Shah (Eds.),  ISBN ----, e-ISBN (PDF) ----

Organometallic Chemistry. Fundamentals and Applications Haiduc, Silaghi-Dumitrescu,  ISBN ----, e-ISBN (PDF) ----

Metal-Organic Framework Composites Volume 2: ZIF-8 Based Materials for Water Decontamination Edited by Awais Ahmad, Muhammad Pervaiz, Umer Younas, Rafael Luque, Mabkhoot Alsaiari and Farid A. Harraz

Editors Awais Ahmed Departamento de Química Orgánica Universidad de Córdoba Campus de Rabanales Carretera Nacional IV-A, Km. 396 14014 Córdoba Spain Umer Younas Department of Chemistry The University of Lahore Lahore 54590 Islamic Republic of Pakistan Mabkhoot Alsaiari Najran University (PCSED) Advanced materials and Nano Research Centre Najran 11001 Kingdom of Saudi Arabia

Muhammad Pervaiz Department of Chemistry Government College University Lahore Punjab 54000 Islamic Republic of Pakistan Rafael Luque Departamento de Química Orgánica Universidad de Córdoba Campus de Rabanales Carretera Nacional IV-A, Km. 396 14014 Córdoba Spain Farid A. Harraz Najran University (PCSED) Advanced materials and Nano Research Centre Najran 11001 Kingdom of Saudi Arabia

ISBN 978-3-11-079255-3 e-ISBN (PDF) 978-3-11-079259-1 e-ISBN (EPUB) 978-3-11-079264-5 Library of Congress Control Number: 2022945052 Bibliographic information published by the Deutsche Nationalbibliothek The Deutsche Nationalbibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data are available on the Internet at http://dnb.dnb.de. © 2023 Walter de Gruyter GmbH, Berlin/Boston Cover image: akinbostanci/E+/Getty Images Typesetting: Integra Software Services Pvt. Ltd. Printing and binding: CPI books GmbH, Leck www.degruyter.com

Acknowledgments The authors/editors would like to acknowledge the support of the deputy for research and innovation-Ministry of Education, Kingdom of Saudi Arabia for this research through grant (NU/IFC/INT/01/003) under the institutional funding committee at Najran University, Kingdom of Saudi Arabia.

https://doi.org/10.1515/9783110792591-202

Contents Acknowledgments List of contributors

V IX

Shumila Shaheen, Anum Fatima, Aqsa, Umer Younas, Rizwan Sikandar, Rana Rashad Mahmood Khan, Muhammad Pervaiz, Zohaib Saeed 1 ZIF-8: An overview 1 Rana Rashad Mahmood Khan, Ramsha Saleem, Mirza Umair Baig, Sadia Yaseen, Muhammad Pervaiz, Zohaib Saeed, Hafiz Muhammad Faizan Haider, Ahmad Adnan 2 ZIF-8 spectacular properties 19 Mushkbar Zahra, Muhammad Pervaiz, Zohaib Saeed, Umer Younas, Rana Rashad Mahmood Khan, Ikram Ahmad, Syed Majid Bukhari, Ayoub Rashid, Ahmad Adnan 3 Heterogeneous catalysis and ZIF-8 33 Talha Mumtaz, Muhammad Pervaiz, Zohaib Saeed, Muhammad Shahzeb, Arooj Ather, Naqeeb Ullah, Rashida Bashir, Muhammad Shahid Cholistani 4 Homogenous catalysis using ZIF-8 51 Mushkbar Zahra, Zohaib Saeed, Muhammad Pervaiz, Rashida Bashir, Talha Mumtaz, Rizwan Sikandar, Umer Younas, Ayoub Rashid, Ahmad Adnan 5 Wastewater treatment: An overview 59 Shumila Shaheen, Muhammad Pervaiz, Syed Majid Bukhari, Zohaib Saeed, Muhammad Imran, Aemin Ali, Ran Rashad Mahmood Khan, Hazqail Umar Khan 6 Removal of heavy metals using ZIF 8 79 Hafiz Amir Nadeem, Zohaib Saeed, Muhammad Pervaiz, Talha Mumtaz, Rizwan Suikandar, Umer Younas, Muhammad Imran 7 Light-driven photocatalysis for dyes using ZIF-8 base composite materials 97

VIII

Contents

Ramsha Saleem, Rana Rashad Mahmood Khan, Hoorish Qamar, Muhammad Pervaiz, Umer Younas, Zohaib Saeed, Hafiz Muhammad Faizan Haider, Ahmad Adnan 8 Recent trends in ZIF-8-based composite materials for the removal of ciprofloxacin 111 Nazia Rasool, Zohaib Saeed, Muhammad Pervaiz, Rashida Bashir, Umer Younas, Hafiz Amir Nadeem, Ayoub Rashid,Ahmad Adnan 9 Future prospects for ZIF-8-based composite material for decontamination of water 137 Index

155

List of contributors Metal Organic Frameworks VOL 2 Chapter 1 Shumila Shaheen Department of Chemistry Government College University Lahore Pakistan

Zohaib Saeed Department of Chemistry Government College University Lahore Pakistan [email protected]

Anum Fatima Department of Chemistry Government College University Lahore Pakistan

Chapter 2 Rana Rashad Mahmood Khan Department of Chemistry Government College University Lahore Pakistan [email protected]

Aqsa Department of Chemistry Government College University Lahore Pakistan Umer Younas Department of Chemistry The University of Lahore Lahore Pakistan Rizwan Sikandar Department of Chemistry Government College University Lahore Pakistan Rana Rashad Mahmood Khan Division of Science and Technology University of Education, Lahore Pakistan Muhammad Pervaiz Department of Chemistry Government College University Lahore Pakistan

https://doi.org/10.1515/9783110792591-204

Ramsha Saleem Department of Chemistry Government College University Lahore Pakistan Mirza Umair Baig Department of Chemistry Government College University Lahore Pakistan Sadia Yaseen Department of Chemistry Government College University Lahore Pakistan Muhammad Pervaiz Department of Chemistry Government College University Lahore Pakistan Zohaib Saeed Department of Chemistry Government College University Lahore Pakistan

X

List of contributors

Hafiz Muhammad Faizan Haider Department of Chemistry Government College University Lahore Pakistan

Syed Majid Bukhari Department of Chemistry University of Sahiwal Sahiwal Pakistan

Ahmad Adnan Department of Chemistry Government College University Lahore Pakistan

Ayoub Rashid Department of Chemistry Government College University Lahore Pakistan

Chapter 3 Mushkbar Zahra Department of Chemistry Government College University Lahore Pakistan

Ahmad Adnan Department of Chemistry Government College University Lahore Pakistan

Muhammad Pervaiza Department of Chemistry Government College University Lahore Pakistan [email protected]

Chapter 4 Talha Mumtaz Department of Chemistry Government College University Lahore Pakistan

Zohaib Saeed Department of Chemistry Government College University Lahore Pakistan

Muhammad Pervaiz Department of Chemistry Government College University Lahore Pakistan [email protected]

Umer Younas Department of Chemistry The University of Lahore Lahore Pakistan

Zohaib Saeed Department of Chemistry Government College University Lahore Pakistan

Rana Rashad Mahmood Khan Department of Chemistry Government College University Lahore Pakistan

Muhammad Shahzeb Department of Chemistry Government College University Lahore Pakistan

Ikram Ahmad Department of Chemistry University of Sahiwal Sahiwal Pakistan

Arooj Ather Department of Chemistry Government College University Lahore Pakistan

List of contributors

Naqeeb Ullah Department of Chemistry Government College University Lahore Pakistan

Rizwan Sikandar Department of Chemistry Government College University Lahore Pakistan

Rashida Bashir Division of Science and Technology University of Education, Lahore Pakistan

Umer Younas Department of Chemistry Government College University Lahore Pakistan

Muhammad Shahid Cholistani Department of Chemistry Government College University Lahore Pakistan

Ayoub Rashid Department of Chemistry Government College University Lahore Pakistan

Chapter 5 Mushkbar Zahra Department of Chemistry Government College University Lahore Pakistan

Ahmad Adnan Department of Chemistry Government College University Lahore Pakistan

Zohaib Saeed Department of Chemistry Government College University Lahore Pakistan [email protected]

Chapter 6 Shumila Shaheen Department of Chemistry Government College University Lahore Pakistan

Muhammad Pervaiz Department of Chemistry Government College University Lahore Pakistan

Muhammad Pervaiz Department of Chemistry Government College University Lahore Pakistan [email protected]

Rashida Bashir Division of Science and Technology University of Education, Lahore Pakistan Talha Mumtaz Department of Chemistry Government College University Lahore Pakistan

XI

Syed Majid Bukhari Department of Chemistry COMSATS University Islamabad Abbottabad Campus Pakistan Zohaib Saeed Department of Chemistry Government College University Lahore Pakistan

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List of contributors

Muhammad Imran Department of Chemistry Government College University Lahore Pakistan

Rizwan Suikandar Department of Chemistry Government College University Lahore Pakistan

Aemin Ali Department of Chemistry Government College University Lahore Pakistan

Umer Younas Department of Chemistry Government College University Lahore Pakistan

Ran Rashad Mahmood Khan Department of Chemistry Government College University Lahore Pakistan

Muhammad Imran Department of Chemistry Government College University Lahore Pakistan

Hazqail Umar Khan Department of Chemistry Government College University Lahore Pakistan

Chapter 8 Ramsha Saleem Department of Chemistry Government College University Lahore Pakistan

Chapter 7 Hafiz Amir Nadeem Department of Chemistry Government College University Lahore Pakistan

Rana Rashad Mahmood Khan Department of Chemistry Government College University Lahore Pakistan [email protected]

Zohaib Saeed Department of Chemistry Government College University Lahore Pakistan [email protected]

Hoorish Qamar Department of Chemistry Government College University Lahore Pakistan

Muhammad Pervaiz Department of Chemistry Government College University Lahore Pakistan

Muhammad Pervaiz Department of Chemistry Government College University Lahore Pakistan

Talha Mumtaz Department of Chemistry Government College University Lahore Pakistan

Umer Younas Department of Chemistry Government College University Lahore Pakistan

List of contributors

Zohaib Saeed Department of Chemistry Government College University Lahore Pakistan Hafiz Muhammad Faizan Haider Department of Chemistry Government College University Lahore Pakistan Ahmad Adnan Department of Chemistry Government College University Lahore Pakistan Chapter 9 Nazia Rasool Department of Chemistry Government College University Lahore Pakistan Zohaib Saeed Department of Chemistry Government College University Lahore Pakistan Muhammad Pervaiz Department of Chemistry Government College University Lahore Pakistan

Rashida Bashir Division of Science and Technology University of Education, Lahore Pakistan Umer Younas Department of Chemistry Government College University Lahore Pakistan Hafiz Amir Nadeem Department of Chemistry Government College University Lahore Pakistan Ayoub Rashid Department of Chemistry Government College University Lahore Pakistan Ahmad Adnan Department of Chemistry Government College University Lahore Pakistan

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Shumila Shaheen, Anum Fatima, Aqsa, Umer Younas, Rizwan Sikandar, Rana Rashad Mahmood Khan, Muhammad Pervaiz, Zohaib Saeed✶

1 ZIF-8: An overview Abstract: Metal-organic frameworks, MOFs, have emerged as a research topic of great interest in the past few decades. MOFs belong to a class of compounds that have porous crystalline polymeric structure. This chapter is a review of ZIF-8 as a representative subclass of MOFs. ZIF-8 is prepared by employing solvothermal, in situ synthesis, sonochemical, and ionothermal methods. ZIF-8 can be integrated with other components such as noble metals, polymers, enzymes, carbon nanotubes, etc., which expands their applications and enhances their mechanical, thermal, and other properties. ZIF-8 has many applications such as removal of heavy metals from aqueous solutions, treatment of wastewater, gas separation, drug delivery and medicinal applications, heterogeneous catalysis, electrochemical sensors, and electrode material for batteries.

1.1 Introduction MOFs are coordination polymers that have a porous crystalline structure. MOFs structural units comprise metal cations as the building units that are coordinated with organic linkers [1]. Recently, the field of metal-organic frameworks has attracted researchers. During the past years, research in the field of MOFs has progressed. The main areas of study related to MOFs are their structure, physical and chemical properties, different methods for synthesis, and different applications. The structure of MOFs is comparable to zeolites, a class of inorganic porous materials. The main factors that account for the stability of MOFs are the composition of the metal, chemical properties of the organic linker, the strength of the coordination bond, and dimensions of the framework [2]. MOFs have applications in the areas of gas storage and separation, storage of energy, delivery of different drugs, and catalysis [3].

✶

Corresponding author: Zohaib Saeed, Department of Chemistry, Government College University, Lahore, Pakistan, e-mail: [email protected] Shumila Shaheen, Anum Fatima, Aqsa, Rizwan Sikandar, Rana Rashad Mahmood Khan, Muhammad Pervaiz, Department of Chemistry, Government College University, Lahore, Pakistan Umer Younas, Department of Chemistry, The University of Lahore, Lahore, Pakistan Division of Science and Technology, University of Education, Lahore, Pakistan

https://doi.org/10.1515/9783110792591-001

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ZIF-8, a representative of the subcategory of MOF, is the zeolitic imidazolate framework. The structure and geometry of the ZIF-8 resemble that of zeolites (inorganic porous materials). ZIF-8 has a six-membered interconnected ring with a 0.34 nm diameter. The pore diameter in ZIF-8 is 1.16 nm. ZIF-8 has the properties of both zeolites and MOFs. Analogous to the structure of zeolites that are composed of silicon and oxygen, ZIF-8 is composed of metal ions bridged to organic ligands. The metal clusters of ZIF-8 are mostly of cobalt or zinc ions. Like zeolites, ZIF-8 possesses a high surface area with more active sites, mechanical stability, and high thermal and chemical stability [4, 5]. In order to broaden the applications of ZIF-8, they have been used in the form of composites with many other active materials. This not only enhances the activities of components of composites but also covers many limitations in them. Till now, many active materials have been used in the formation of composites, and they have been used in a wide variety of applications. Graphene oxide@ZIF-8 composites have increased the CO2 storage capacity [6]. rGO@ZIF-8 and PLA@ZIF-8 composites have been used for water–oil separation, with PLA@ZIF-8 composites being used as a green method in the formation of ZIF-8 composites [7]. Composites of ZIF-8 with noble metals like Pt@ZIF-8 when used along with TiO2 enhance the photo catalytic activity. Composites of ZIF-8 with carbon nanotubes give better thermal, electrical and mechanical properties. Composites of ZIF-8 with enzymes like CAT@ZIF-8 allow their application in pharmaceutical and other industries. Composites of ZIF-8 with quantum dots improve their activities to a significant level.

1.1.1 Metal-organic frameworks (MOFs) MOFs are also known as coordination polymers or porous polymers because of their porous crystalline structure [8]. MOFs, hybrid porous materials, are composed of organic ligands surrounded by positively charged metal ions connected through coordination bonds [9, 10]. MOFs are coordination compounds [11] having a three-dimensional structure with high porosity, crystallinity, high surface areas, and storage volumes. They are highly porous materials with high permeability and selectivity [12]. MOFs are emerging polymers in chemistry because of their applications in various fields. The composites of MOFs have applications as photocatalysts [13], sensors for sensing pollutants in the environment [14], in controlled drug delivery systems [15], in hydrogen storage [16], in catalytic application [17], dye adsorption [18], and many more. MOFs were first introduced in 1995 by Yaghi. Yaghi prepared MOF by using the hydrothermal method of synthesis [19]. Feng et al. successfully used a coating of MOF to protect biological medicinal products, especially antibodies, from environmental factors [20]. MOFs are crystalline in structure, having high surface areas and adjustable pore size. Due to mechanical, thermal, and chemical stability, MOFs have applications in

1 ZIF-8: An overview

3

various fields. Due to their chemical stability, MOFs are generally stable towards chemicals present in their environments like acids, bases, humidity, and coordination ions present in aqueous solutions. As MOFs are mechanically and thermally stable, their structure is not affected by heat or pressure. The strength of the coordination bond between metal and ligand accounts for the thermodynamic stability of MOFs. MOFs are stable when organic ligands having low acid dissociation constant value bind with metal ions of high valency or organic ligands of high acid dissociation constant bind with metal ions of low valency [21, 22].

1.1.2 Zeolite imidazolate framework Zeolite imidazolate framework-8 (ZIF-8) is an MOF. The structure of the ZIF-8 consists of tetrahedral zinc metal ions coordinated with an organic ligand named 2methyl imidazolate [23, 24]. ZIFs have highly ordered and porous structures with geometry just like zeolites. Due to hydrophobic pores present in ZIF-8 and the coordination bond between the metal ion and imidazole ligand, ZIFs are extraordinarily stable chemically and thermally [25]. Under different temperature conditions, using alcoholic or aqueous media, zeolitic imidazole frameworks are synthesized by using different ratios of metal salt and organic linker. The synthesis of ZIF-8 from an aqueous solution at room temperature gives the highest yield of ZIF-8 of 97%. The topology of the ZIF-8 resembles that of zeolites in that the metal-ligand-metal coordination bond in ZIF-8 is 1450, which is similar to the bond angle of Si-O-Si in the zeolites [26].

1.2 Synthesis methods for ZIF-8 1.2.1 In situ synthesis method In situ method is a very efficient method for the synthesis of ZIF-8. In situ method for synthesis requires the properties of the materials to be considered. The basic principle of in situ synthesis is to choose the materials with specific functional groups [27]. The reverse diffusion method is one of the other methods for in situ synthesis of ZIF-8. This method involves the porous matrix on both ends of which are starting reagents. The starting reagents are the source of zinc metal and an organic ligand. The solutions of the starting materials are of different concentrations. The difference in the concentration of both solutions results in the diffusion of the reagent solutions in opposite directions. The porous matrix is an efficient material for the diffusion solutions through the pores of the matrix. When the two solutions come together at the substrate surface, they form a thin layer. The difficulty faced

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by in situ synthesis method is that it is difficult to get thick film by using this method [28]. Li et al. synthesized ZIF-8/ polydimethylsiloxane matrix membrane [29]. Wang et al. used in situ synthesis method for the preparation of ZIF-8 composites on rGO (reduced graphene oxide) [30].

1.2.2 Solvothermal synthesis of ZIF-8 The solvothermal method for the synthesis of ZIF-8 is efficient and commonly used. For the synthesis of ZIF-8, an organic solvent, zinc metal source, and organic ligand source are the starting reagents. A highly diluted solution of zinc metal in an organic solvent is mixed and added to the organic ligand. The solution is heated in an autoclave at a high temperature, to get the product. This method of synthesis takes much time and energy. On the other hand, using the microwave is less timeconsuming. Therefore, the solvothermal process that uses a microwave is preferred. The better yield of ZIF-8 with the small size of the particles is obtained through the microwave solvothermal process [31]. Cravillon et al. successfully prepared ZIF-8 by using the solvothermal method of synthesis. The reagents used were zinc chloride salt as a source of metal and an organic linker [32]. Chen et al. prepared crystals of ZIF-8 hydrangea by using the solvothermal process of synthesis. Dimethylformamide (DMF) solvent, zinc nitrate hexahydrate as the source of zinc metal ion, and a 2-methyl imidazole ligand are the starting materials [33].

1.2.3 Sonochemical synthesis One of the efficient methods used for the synthesis of ZIF-8 and its composites is the sonochemical method, using small amounts of triethylamine and aqueous sodium hydroxide. The sonochemical synthesis method is a pH-controlled synthesis. Therefore, pH is the most crucial factor in sonochemical synthesis. The product yield is 85% at a high concentration of substrate [34]. Bui et al. prepared a ZIF-8 composite with iron oxide by following the sonochemical synthesis method and used the composite for the removal of heavy metal ions [35].

1.2.4 Ionothermal synthesis The ionothermal synthesis method for the synthesis of ZIF-8 is also efficient. Ionic liquids have high thermal stability and low vapor pressure and are excellent microwave absorbers. In solvothermal and other synthesis methods, organic solvents are materials whose wastes are hazardous to the environment, while ionothermal synthesis uses ionic solvents that do not contain neutral molecules. Ionic liquids are efficient

1 ZIF-8: An overview

5

solvents, thermally stable, and easily recyclable. Ionic liquids have a low vapor pressure. Therefore, synthesis is done at standard pressure and in an open container. Besides being used as a solvent in the ionothermal synthesis of ZIF-8, ionic solvents also provide metal cations for the framework. During ionothermal synthesis, microwave heating heats the sample, which is not time-consuming. Experimental studies show that the polar solvents absorb microwave radiations quickly and are heated rapidly, while nonpolar solvents absorb fewer microwave radiations [36].

1.3 ZIF-8 composites In order to expand the applications and functionality of ZIF-8, it is also integrated along with other functional materials, forming composites. These hybrids or composites have an edge over individual components, as they show the collective properties of the components forming them. They keep the original properties of components intact and also make up for any shortcoming present in any single phase during application. This topic is being researched widely. ZIF-8 composites have been integrated with many components such as: – graphene oxide – reduced Graphene oxide – carbon nanotubes – enzymes – aerogels – noble Metals Apart from the components written above, ZIF-8 is also integrated with many other components. ZIF-8 composites are better than micro-porous ZIF-8 in absorption and photo catalytic activity. They also have more applications than micro porous ZIF-8. ZIF-8 composites have varying structures like thin-film particles, core shell particles, etc.

1.3.1 ZIF-8 composites with graphene oxide Kumar et al. reported the formation of GO@ZIF-8 composites. ZG composites were made by using different graphene oxide proportions by weight. Infrared spectroscopy showed that the ZIF-8 and GO original bands shifted to lower frequencies. By studying the intensities of the peaks in the infrared and Raman spectra, it was found that the morphology and size of ZG composites are controlled by the percentage by weight of GO added. The GO sheets act as the location where nanocrystals carry out nucleation and growth. Raman spectra have shown the bonding between

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Reduced Graphene Oxide

Graphene Oxide

improved CO2 storage capacity

Aerogels

ZIF–8

Enzymes

application in industry

water/oil seperation

green water/Oil seperation

Noble Metals

Carbon Nano tubes enhanced catalytic activity

better thermal, electrical and mechanical properties Figure 1.1: Various Composites of ZIF-8.

the zinc metal of the ZIF-8 and GO. Thus, GO sheets can vary the structure and size of nanocrystals [6]. ZG composites have good CO2 storage capacity. It has also been reported that the CO2 storage capacity increases with the increasing GO composition as shown in Figure 1.1 [6].

1.3.2 ZIF-8 composites with reduced graphene oxide Kim et al. suggested producing ZIF-8 composites with reduced graphene oxide on PU foam. PU foam is very flexible. The oxygen groups present on RGO showed great attraction towards ZIF-8 that leads to the production of ZIF-8/RGO, by forming a ZIF-8 layer on RGO sheet. This occurs without significantly disrupting the flexibility of PU foam. The ZIF-8/ RGO showed a combined effect by carrying out oil–water separation. The PU foam coated with ZIF-8/RGO have showed an excellent oil–water separation by absorbing oil to a level of 15–35 g/g without allowing water to pass through [37]. Oil spillage is a big issue in the marine environment. It can cause a serious threat to marine life and water quality and can also result in huge economic loss. Using this composite can help reduce the loss caused by marine oil spillage.

1 ZIF-8: An overview

7

1.3.3 ZIF-8 composites with enzymes Enzymes are biological catalysts. They have long been studied for industrial applications. But due to their low stability, and difficulty in reusability, they are needed to be immobilized in order to use them in industry. MOFs have been used to immobilize enzymes in recent research. There are four different methods of using MOFs in the immobilization of enzymes. These methods are covalent linkages, diffusion into pores, surface absorption, and coprecipitation [38]. Among these methods, surface absorption is the best, as there is no need to consider the dimensions of enzyme in this method. Among MOFs, ZIF-8 is the major candidate used in the immobilization of enzymes as it has good thermal stability, chemical stability, good surface area, and ease of formation [39]. Feng et al. studied the formation of stable catalase enzyme with ZIF-8. Catalase is used widely in the environmental protection and the food industries, but its subunit dissociation poses difficulties in its applications. CAT@ZIF-8 composites which showed great activity and immobilized enzymes and made it possible to use them in industry were formed earlier, but they were not stable in aqueous acidic media. Stable CAT@ZIF-8 with protective nanocoating is also produced by careful selfassembly of coordination complexes or silanes. These composites have better thermostability, reusability, and storability [40]. This has made it possible to use enzymes to get industrial products, by employing natural biocatalysts in the industry.

1.3.4 ZIF-8 composites with quantum dots Quantum dots are luminescent semiconductor nanoparticles. MOFs like ZIF-8 are also being integrated as hosts to quantum dots, in order to yield composites with a wide range of applications. They have been used in many electronic, electrical, bioanalytical, and pharmaceutical applications. Esken prepared composites of quantum dots@ZIF-8 by using gallium nitride quantum dots. GaN quantum dots are dispersed into the porous ZIF-8 structure. This was done by loading ZIF-8 with tri-methyl amine gallane; thus, an inclusion is formed, which gives rise to an intermediate compound. This intermediate compound upon annealing gives GaN@ZIF-8 particles [41]. The supercapacitor is considered excellent for energy storage. SnO2 has been used as an electrode in a supercapacitor, as it has good transparency, electrical and optical properties. It has been studied that SnO2 quantum dots, when combined with ZIF-8, yield a pseudo capacitor. By following the epoxide precipitation route, SnO2 quantum dots get dispersed in the porous ZIF-8 material. This integration of quantum dots into porous MOF ZIF-8 increases the activity of the quantum dot. The specific capacitance of SnO2@ZIF-8 composites reached up to 931 Fg−1. This is much greater than the capacitance shown by only SnO2 quantum dots [42].

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Composites with carbon dots have been made by integrating carbon dots into ZIF-8. This gave rise to the radiometric fluorescent sensors. Also, because of the good absorption ability of MOFs, the absorption of analytes, increased, and the accumulation of target analytes also increased [43]. These are not the only quantum dots that have been integrated into ZIF-8; there are several other quantum dots@ ZIF-8 composites that have been made and are being studied.

1.3.5 ZIF-8 composites with noble metals Fisher and coworkers were the first ones to form the Pd@MOF-5 composite [44]. Noble metals and ZIF-8 combinations are being studied to see their combined effect. These composites have been used in many photo catalytic reactions. They have also been used along with other noble metals in photo catalytic reactions. The Pt@ZIF-8 composite was deposited on TiO2 nanotubes to degrade phenol under visible light. It was then compared with the degradation caused by Pt used with only Ti O2, and the results showed a significant increase in degradation in phenol, when Pt@ZIF-8 composite was used. This showed that the incorporation of ZIF-8 increased the catalytic activity of noble metals [45]. Not only have monometallic composites been formed but work on producing di metallic composites with ZIF-8 has also been done. Liu et al. synthesized Au@Ag and Ag@Au composites and in order to protect them from structure degradation, they used ZIF-8 to immobilize them. Many other noble metals were used in combination with ZIF-8. Rhodamine B was treated by using Ag/AgCl@ZIF-8 [46]. These composites have also been used in removing the water pollutants from water. In a ZIF-8 composite having a core shell structure, with the core being made up of the noble metals, the degradation of water pollutants takes place on the ZIF-8 surface, as it is the outer surface of the composite; and the internal noble metal core has an influence on the properties of the composite, which changes with changing noble metal.

1.3.6 ZIF-8 composites with carbon nanotubes ZIFs have been widely used in a number of applications and are being researched to explore their uses. But ZIFs cannot form isolated particles; also, their crystals show poor conductivity. In order to rule out this limitation, they can be integrated with carbon nanotubes, which are preferred for their excellent mechanical, optical, electrical, and thermal properties. ZIF-8 is mostly used to make a composite with carbon nanotubes because of its vast applications and feasibility. In this way, the properties of both materials can be utilized by the synthesis of these composites.

1 ZIF-8: An overview

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Oxidized carboxylic acid groups were grafted on carbon nanotubes using an acid mixture to attract the linker groups present on MOFs [47]. Another way to produce these composites was to oxidize CNT to form a negatively charged surface on CNT, which can absorb positively charged MOF particles [48].

1.3.7 ZIF-8 composites with aerogels Aerogels are highly porous polymeric networks with very low density and have a high specific surface area. They have high hydrophobicity and also possess high lipophilicity, so they can be helpful in water–oil separation operations. PLA (polylactic acid) is a bio-based aerogel made from lactic acid, and it is a good option for green synthesis of ZIF-8 composites. But they have poor mechanical properties, and low oil absorption capacity limits their use. In order to solve this problem, they have been integrated with ZIF-8 by physical mixing of ZIF-8 nanoparticles in the PLA solution, followed by phase separation. These PLA@ZIF-8 composites have good hydrophobicity and lipophilicity and good durability. This makes them excellent candidates for Table 1.1: Synthesis methods and applications of different composites of ZIF-8. Composite of ZIF-

Synthesis method Applications

References

ZnO@ZIF-

Self-template method

Ethanol gas sensing

[]

SnO @ZIF-

Solvothermal method

NO gas sensing

[]

ZIF-@PAN

In situ synthesis

Cr (VI) removal

[]

ZIF-/TiN/Si/Ti Nanorods

Template method

Anode for Lithium-Ion Batteries (LIBs)

[]

ZIF- @TiO

Hydrothermal method

Photo catalysis and degradation of tetracycline

[]

CQDs@ZIF-

Hydrothermal method

Photocatalysis

[]

PPy@ZIF-/Graphene Aerogels

In situ synthesis

Electrochemical sensing

[]

CuNCs/ZIF-

One-pot synthesis

Detection of HO and estimation of oxidase activity

[]

FeO@ZIF-

Sonochemical synthesis

Removal of Cu+ by adsorption

[]

ZIF-@PLA

In situ synthesis

Oil–water separation

[]

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bio-based water–oil separation agents in case of crude oil leakages of high scale. They also have good reusability as shown in Table 1.1 [7].

1.4 Applications of ZIF-8 1.4.1 Removal of heavy metals from aqueous solutions and treatment of wastewater Industrialization is increasing day by day, resulting in the contamination by industrial wastewater from heavy metals. Heavy metals in water are threatening for living organisms and to the environment. Among the heavy metals, copper and lead are the most toxic [57]. For the treatment of wastewater and for the removal of heavy metal ions from aqueous solutions, ZIFs are used in research, because of their efficiency. ZIFs are used as adsorbents to remove heavy metal ions because of their high porosity, exceptional hydrothermal stability, large surface area, and presence of many active sites [58]. The use of an adsorption mechanism is a cost-efficient and easy method. One of the most efficient adsorbents used is ZIF-8, an MOF, because of its exceptional affinity and chemical and hydrothermal stability [59]. Major common contaminants in water are lead, mercury, antimony, arsenic, copper, chromium, and many more. Wastewater from industrial sites, particularly nuclear industries, includes radioactive nuclear waste, some of which have long half-lives and high solubility. Composites of ZIF-8 are efficient adsorbents for the removal of pollutants from wastewater. By changing the morphology and structure of ZIF-8, its adsorption capacity increases, by increasing the active sites. Composites of ZIF-8 are very efficient in removing pollutants from the wastewater, because they make the separation of adsorbent from the water easy [27]. The exceptional adsorption capacity of ZIF-8 finds its application in removing heavy metal ions from wastewater bodies. The adsorption mechanism involves the interaction between heavy metal ions found in contaminated water and the adsorbent. Heavy metal ions present in aqueous solution and wastewater, on interaction with ZIF-8 (an adsorbent), accumulate on the surface of ZIF-8. The equilibrium adsorption capacity of the ZIF-8 is measured as Qe =

ðCo − Ce Þ × υ m

In solution, Co is adsorbate concentration and Ce is the concentration at equilibrium. The volume of the solution is ʋ, and absorbent mass is m in milligrams [5]. The composite of ZIF-8 with graphene oxide acts as an absorbent and finds its application in eliminating Cu (II) ions from aqueous solutions [60]. Li et al. synthesized an ultrafiltration membrane, PAA/ZIF-8/PVDF, of high adsorption capacity. This ultrafiltration

1 ZIF-8: An overview

11

membrane has application in the efficient removal of heavy metal ions (Nickel-II) from polluted water [61]. Long et al. followed the contra diffusion method of ZIF-8 nanocomposites synthesis and synthesized membrane, PVDF/ZIF-8. The PVDF/ZIF-8 membrane shows high adsorption capacity for iodine ions in an aqueous solution. The adsorption capacity of the ZIF-8 nanocomposite membrane for iodine is 73.33 mg per gram, and the efficiency of iodine removal by PVDF/ZIF-8 membrane is 73.4% [62].

1.4.2 Gas separation Carbon dioxide gas is present in natural gas, which forms acidic compounds and is a greenhouse gas. It is mandatory to separate carbon dioxide gas as it is harmful to the environment. One of the most efficient methods of separating gases is by using membranes, as this method consumes less energy and is a cost-effective method. In the past few years, polymeric membranes are being used for the separation of gases. Carbon dioxide can be separated by using polyethylene oxide, but as polyethylene oxide is not crystalline in structure, it is not mechanically unstable. Amedi et al. successfully prepared polyether amide-based membranes that have zeolite imidazole framework-8-Aminosilane (ZIF-8-APTES) for the efficient separation of gases like carbon dioxide and methane [63].

1.4.3 Drug delivery and medicinal applications ZIF-8, a kind of zeolite, has structural similarities with zeolites and possesses salient characteristics because of which they attracted attention of the medical field. ZIF-8 possesses thermal and chemical stability, degradation based on pH sensitivity, high porosity leading to high loading capacity, and large surface area. All these characteristics make ZIF-8 suitable for controlled drug delivery. High surface area and large pore size make ZIF-8 pH-sensitive and degradable, due to which ZIF-8 finds its best application in drug delivery. Chemical, photodynamic, photo thermal, and chemodynamic drugs can be delivered using ZIF-8 as a nanocarrier [64]. Under acidic conditions, organic ligand of the ZIF-8 protonates. Protonation leads to cleavage of zinc ion and imidazolium ion coordination bond. The bond cleavage decomposes the skeleton of ZIF-8, resulting in the controlled release of the drug. In acetate solutions, ZIF-8 releases drugs faster when delivering the anticancer drug, because the pH of tumor cells ranges from 5.5 to 6.0 [65]. In an aqueous solution of sodium hydroxide and water, ZIF-8 is stable. At acidic pH, ZIF-8 is not stable and decomposes rapidly. This pH-based functionality of ZIF-8 has application in the controlled delivery of drugs. Nowadays, research in biotechnology using nanotechnology is emerging rapidly due to the promising applications in various fields. Porous materials are of

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great importance in academic research and industrial applications. To use ZIF-8 in medicine, it should be nontoxic and biocompatible. The biocompatibility of ZIF-8 is its capability to operate without affecting the environment. Throughout the life of a man, bone tissue continues to remodel. ZIF-8 is used efficiently in bone tissue engineering. For the regeneration of damaged tissues of bones, anti-inflammatory and antibiotic drugs along with the growth factors for the tissues are implanted into the porous framework of ZIF-8 and delivered to the desired area in the body [66].

1.4.4 Heterogeneous catalysis The activity of metal-organic frameworks like ZIF-8 can be increased manyfold by doping with metal ions. For the oxidation of hydrocarbons, copper ions-doped ZIF-8 is used as a catalyst. ZIF-8 is highly stable in water and shows high thermal stability, due to which ZIF-8 finds its use in catalytic reactions [67]. Oxidation–reduction reactions are the most important ones for the conversion and storage of energy. Precious metals like platinum, palladium, and silver-based catalysts are replaced by ZIF-8 that have ferrocene molecules embedded in the pores. ZIF-8 that have ferrocene molecules trapped in the pores are then used as a catalyst for the oxidation–reduction reactions. Ferrocene-embedded ZIF-8 are precursors for the single-atom nitrogen-doped carbon with Fe embedded in it [68]. Yao et al. prepared nanoparticles of ZIF-8 with Co/Zn metals with the property of controllable pore size and used the nanoparticles of ZIF-8 for heterogeneous catalysis for the degradation of a dye named RhB (Rhodamine B). Yao et al. synthesized ZIF-8 nanoparticles by using the ultrasound-assisted synthesis method [69].

1.4.5 Electrochemical sensor PEDOT: PSS (combination of two polymers; polyethylene-dioxythiophene and polystyrene sulfonate) is an electrically conductive combination of polymers [70]. PEDOT: PSS is an electrically conductive, mechanically flexible, and stable polymer. Gao et al. successfully synthesized ZIF-8 composite by using the ultrasonic mixing method and ZIF-8 and PEDOT: PSS as starting material. A cfComposite of ZIF-8 and PEDOT: PSS is used as a sensor for electrochemical detection of pollutants like dichlorophenol [71]. Chen et al. fabricated ZIF-8 with an organic polymer PPy (polypyrrole) and used it as an electrochemical sensor [72].

1 ZIF-8: An overview

13

1.4.6 ZIF-8 in electrodes of batteries ZIF-8 derivatives have improved conductivity as compared to pure MOFs. The cathode in lithium-ion batteries is composed of lithium iron phosphate (LFP). LFP/ CZIF-8 is synthesized by in situ growth of ZIF and coated with carbon having high nitrogen doping that enhances the conductivity of the electrode [4]. The storage capacity of lithium-ion batteries (LIBs) increases by using ZIF-8 composites, titanium/ silicon/TiN as an anode material. By the use of electrodes of ZIF-8 composites, the capacity increases to I650 μAh cm–2, which is 100 folds, as compared to electrodes of ordinary materials used in LIBs [52].

1.5 Conclusion A notable example of MOFs, ZIF-8, has shown applications in different fields of science and even now, ZIF-8 is an important topic in the field of research. This book chapter gives an overview of ZIF-8 as an eminent MOF example. The structure of ZIF8, its chemical, thermal, and mechanical properties, and its applications in different field of electrochemical chemistry, medicine, and sensing and removal of pollutants have been discussed. ZIF-8 forms composites with GO, rGO, enzymes, polymers, quantum dots, noble metals, and carbon nanotubes.

References [1] [2]

[3]

[4]

[5] [6]

Moghadam, P.Z., et al., Structure-mechanical stability relations of metal-organic frameworks via machine learning. Matter, 2019. 1(1): p. 219–234. Kang, I.J., N.A. Khan, E. Haque, and S.H. Jhung, Chemical and thermal stability of isotypic metal–organic frameworks: Effect of metal ions. Chemistry A European Journal, 2011. 17(23): p. 6437–6442. Li, S., X. Liu, H. Chai, and Y. Huang, Recent advances in the construction and analytical applications of metal-organic frameworks-based nanozymes. TrAC Trends in Analytical Chemistry, 2018. 105: p. 391–403. Zou, D., D. Liu, and J. Zhang, From zeolitic imidazolate framework‐8 to metal‐organic frameworks (MOF s): Representative substance for the general study of pioneering MOF applications. Energy Environmental Materials, 2018. 1(4): p. 209–220. Li, K., et al., Sustainable application of ZIF-8 for heavy-metal removal in aqueous solutions. Sustainability, 2021. 13(2): p. 984. Kumar, R., K. Jayaramulu, T.K. Maji, and C.N.R. Rao, Hybrid nanocomposites of ZIF-8 with graphene oxide exhibiting tunable morphology, significant CO2 uptake and other novel properties. Chemical Communications, 2013. 49(43): p. 4947–4949. doi: 10.1039/ C3CC00136A.

14

[7]

[8] [9] [10] [11]

[12]

[13]

[14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]

[27]

Shumila Shaheen et al.

Li, Y., et al., High-hydrophobic ZIF-8@PLA composite aerogel and application for oil-water separation. Separation and Purification Technology, 2021. 270: p. 118794. doi: 10.1016/J. SEPPUR.2021.118794. Devic, T. and C. Serre, High valence 3p and transition metal based MOFs. Chemical Society Reviews, 2014. 43(16): p. 6097–6115. Tu, Y., H. Li, T. Tu, and Q. Zhang, Lamellar enzyme-metal–organic framework composites enable catalysis on large substrates. CCS Chemistry, 2021. 4(3): p. 1198–1205. Lian, X., et al., Enzyme–MOF (metal–organic framework) composites. Chemical Society Reviews, 2017. 46(11): p. 3386–3401. Fonseca, J., T. Gong, L. Jiao, and H.-L. Jiang, Metal–organic frameworks (MOFs) beyond crystallinity: Amorphous MOFs, MOF liquids and MOF glasses. Journal of Materials Chemistry, 2021. 9(17): p. 10562–10611. Younas, M., et al., Recent progress and remaining challenges in post-combustion CO2 capture using metal-organic frameworks (MOFs). Progress in Energy and Combustion Science, 2020. 80: p. 100849. Shi, Y., A.-F. Yang, C.-S. Cao, and B. Zhao, Applications of MOFs: Recent advances in photocatalytic hydrogen production from water. Coordination Chemistry Reviews, 2019. 390: p. 50–75. Yang, G., X. Jiang, H. Xu, and B. Zhao, Applications of MOFs as luminescent sensors for environmental pollutants. Small, 2021. 17(22): p. 2005327. Velásquez-Hernández, M.D.J., et al., Towards applications of bioentities@ MOFs in biomedicine. Coordination Chemistry Reviews, 2021. 429: p. 213651. Basdogan, Y. and S. Keskin, Simulation and modelling of MOFs for hydrogen storage. Crystal Engineering Communications, 2015. 17(2): p. 261–275. He, H., et al., Preparation of MOFs and MOFs derived materials and their catalytic application in air pollution: A review. Catalysis Today, 2021. 375: p. 10–29. Jiang, D., et al., The application of different typological and structural MOFs-based materials for the dyes adsorption. Coordination Chemistry Reviews, 2019. 380: p. 471–483. Furukawa, H., K.E. Cordova, M. O’Keeffe, and O.M. Yaghi, The chemistry and applications of metal-organic frameworks. Science, 2013 80-. 341(6149): p. 1230444. Feng, Y., et al., Antibodies@ MOFs: An in vitro protective coating for preparation and storage of biopharmaceuticals. Advanced Materials, 2019. 31(2): p. 1805148. Yuan, S., et al., Stable metal–organic frameworks: Design, synthesis, and applications. Advanced Materials, 2018. 30(37): p. 1704303. Ding, M., X. Cai, and H.-L. Jiang, Improving MOF stability: Approaches and applications. Chemical Science, 2019. 10(44): p. 10209–10230. Lai, Z., Development of ZIF-8 membranes: Opportunities and challenges for commercial applications. Current Opinion in Chemical Engineering, 2018. 20: p. 78–85. Liang, W., et al., Control of structure topology and spatial distribution of biomacromolecules in protein@ ZIF-8 biocomposites. Chemistry of Materials, 2018. 30(3): p. 1069–1077. James, J.B. and Y.S. Lin, Thermal stability of ZIF-8 membranes for gas separations. Journal of Membrane Science, 2017. 532: p. 9–19. Malekmohammadi, M., S. Fatemi, M. Razavian, and A. Nouralishahi, A comparative study on ZIF-8 synthesis in aqueous and methanolic solutions: Effect of temperature and ligand content. Solid State Sciences, 2019. 91: p. 108–112. Dai, H., et al., Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication, applications and perspective. Coordination Chemistry Reviews, 2021. 441: p. 213985.

1 ZIF-8: An overview

15

[28] Jiang, X., S. Li, Y. Bai, and L. Shao, Ultra-facile aqueous synthesis of nanoporous zeolitic imidazolate framework membranes for hydrogen purification and olefin/paraffin separation. Journal of Materials Chemistry, 2019. 7(18): p. 10898–10904. [29] Li, G., Z. Si, D. Cai, Z. Wang, P. Qin, and T. Tan, The in-situ synthesis of a high-flux ZIF-8/ polydimethylsiloxane mixed matrix membrane for n-butanol pervaporation. Separation and Purification Technology, 2020. 236: p. 116263. [30] Wang, J., L. Gao, J. Zhao, J. Zheng, J. Wang, and J. Huang, A facile in‒situ synthesis of ZIF‑8 nanoparticles anchored on reduced graphene oxide as a sulfur host for Li‑S batteries. Material Research Bulletin, 2021. 133: p. 111061. [31] Nordin, N., A.F. Ismail, A. Mustafa, P.S. Goh, D. Rana, and T. Matsuura, Aqueous room temperature synthesis of zeolitic imidazole framework 8 (ZIF-8) with various concentrations of triethylamine. RSC Advances, 2014. 4(63): p. 33292–33300. [32] Cravillon, J., C.A. Schröder, H. Bux, A. Rothkirch, J. Caro, and M. Wiebcke, Formate modulated solvothermal synthesis of ZIF-8 investigated using time-resolved in situ X-ray diffraction and scanning electron microscopy. Crystal Engineering Communications, 2012. 14(2): p. 492–498. [33] Chen, Y. and S. Tang, Solvothermal synthesis of porous hydrangea-like zeolitic imidazole framework-8 (ZIF-8) crystals. Journal of Solid State Chemistry, 2019. 276: p. 68–74. [34] Cho, H.-Y., J. Kim, S.-N. Kim, and W.-S. Ahn, High yield 1-L scale synthesis of ZIF-8 via a sonochemical route. Microporous Mesoporous Mater, 2013. 169: p. 180–184. [35] Bui, T.T., D.C. Nguyen, S.H. Hua, H. Chun, and Y.S. Kim, Sonochemical preparation of a magnet-responsive Fe3O4@ ZIF-8 adsorbent for efficient Cu2+ removal. Nanomaterials, 2022. 12(5): p. 753. [36] Yang, L. and H. Lu, Microwave‐assisted ionothermal synthesis and characterization of zeolitic imidazolate framework‐8. Chinese Journal of Chemistry, 2012. 30(5): p. 1040–1044. [37] Kim, D.W., et al., Continuous ZIF-8/reduced graphene oxide nanocoating for ultrafast oil/ water separation. Chemical Engineering Journal, 2019. 372: p. 509–515. doi: 10.1016/J. CEJ.2019.04.179. [38] Gkaniatsou, E., C. Sicard, R. Ricoux, J.P. Mahy, N. Steunou, and C. Serre, Metal-organic frameworks: A novel host platform for enzymatic catalysis and detection. Materials Horizons, 2017. 4(1): p. 55–63. doi: 10.1039/C6MH00312E. [39] Wu, Y.-N., et al., Amino acid assisted templating synthesis of hierarchical zeolitic imidazolate framework-8 for efficient arsenate removal, pubs.rsc.org, 2014. doi: 10.1039/c3nr04390h. [40] Feng, Y., et al., Enzymes@ZIF-8 nanocomposites with protection nanocoating: Stability and acid-resistant evaluation. Polymer, 2019. 11(1): p. 27, Dec. 2018, doi: 10.3390/ POLYM11010027. [41] Esken, D., S. Turner, C. Wiktor, S.B. Kalidindi, G. Van Tendeloo, and R.A. Fischer, GaN@ZIF-8: Selective formation of gallium nitride quantum dots inside a zinc methylimidazolate framework. Journal of the American Chemical Society, 2011. 133(41): p. 16370–16373. doi: 10.1021/JA207077U. [42] Gao, Y., J. Wu, W. Zhang, Y. Tan, J. Zhao, and B. Tang, The electrochemical performance of SnO2 quantum dots@zeolitic imidazolate frameworks-8 (ZIF-8) composite material for supercapacitors. Materials Letters, 2014. 128: p. 208–211. doi: 10.1016/J. MATLET.2014.04.175. [43] Ma, Y., et al., A dual-emissive fluorescent sensor fabricated by encapsulating quantum dots and carbon dots into metal–organic frameworks for the ratiometric detection of Cu2+ in tap water. Journal of Materials Chemistry C, 2017. 5(33): p. 8566–8571. doi: 10.1039/C7TC01970J. [44] Hermes, S., et al., Metal@MOF: Loading of highly porous coordination polymers host lattices by metal organic chemical vapor deposition. Angewandte Chemie International Edition, 2005. 44(38): p. 6237–6241. doi: 10.1002/ANIE.200462515.

16

Shumila Shaheen et al.

[45] Rohani, S., T. Isimjan, A. Mohamed, H. Kazemian, M. Salem, and T. Wang, Fabrication, modification and environmental applications of TiO2 nanotube arrays (TNTAs) and nanoparticles. Frontiers of Chemical Science and Engineering, 2012. 6(1): p. 112–122, Dec. 2011. doi: 10.1007/S11705-011-1144-6. [46] Gao, S.T., et al., Integration of a plasmonic semiconductor with a metal–organic framework: A case of Ag/AgCl@ZIF-8 with enhanced visible light photocatalytic activity. RSC Advances, 2014. 4(106): p. 61736–61742. doi: 10.1039/C4RA11364K. [47] Zhang, Y., et al., All-solid-state asymmetric supercapacitors based on ZnO quantum dots/ carbon/CNT and porous N-doped carbon/CNT electrodes derived from a single ZIF-8/CNT. pubs.rsc.org, 2016. 4(26): p. 10282–10293. doi: 10.1039/c6ta03633c. [48] Liu, Y., G. Li, Z. Chen, and X. Peng, CNT-threaded N-doped porous carbon film as binder-free electrode for high-capacity supercapacitor and Li-S battery. Journal of Materials Chemistry, 2017. 5(20): p. 9775–9784. doi: 10.1039/C7TA01526G. [49] Ren, G., et al., ZnO@ ZIF-8 core-shell microspheres for improved ethanol gas sensing. Sensors Actuators B Chemical, 2019. 284: p. 421–427. [50] Zhan, M., et al., Enhanced NO2 gas-sensing performance by core-shell SnO2/ZIF-8 nanospheres. Chemosphere, 2021. 291(3): p. 132842. [51] Yang, X., Y. Zhou, Z. Sun, C. Yang, and D. Tang, Effective strategy to fabricate ZIF-8@ ZIF-8/ polyacrylonitrile nanofibers with high loading efficiency and improved removing of Cr (VI). Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2020. 603: p. 125292. [52] Yu, Y., et al., ZIF-8 cooperating in TiN/Ti/Si nanorods as efficient anodes in micro-lithium-ionbatteries. ACS Applied Materials & Interfaces, 2016. 8(6): p. 3992–3999. [53] Li, R., W. Li, C. Jin, Q. He, and Y. Wang, Fabrication of ZIF-8@ TiO2 micron composite via hydrothermal method with enhanced absorption and photocatalytic activities in tetracycline degradation. Journal of Alloys and Compounds, 2020. 825: p. 154008. [54] Si, Y., X. Li, G. Yang, X. Mie, and L. Ge, Fabrication of a novel core–shell CQDs@ ZIF-8 composite with enhanced photocatalytic activity. Journal of Materials Science, 2020. 55(27): p. 13049–13061. [55] Xie, Y., et al., In-situ synthesis of hierarchically porous polypyrrole@ ZIF-8/graphene aerogels for enhanced electrochemical sensing of 2, 2-methylenebis (4-chlorophenol). Electrochimica Acta, 2019. 311: p. 114–122. [56] Hu, X., X. Liu, X. Zhang, H. Chai, and Y. Huang, One-pot synthesis of the CuNCs/ZIF-8 nanocomposites for sensitively detecting H2O2 and screening of oxidase activity. Biosensors & Bioelectronics, 2018. 105: p. 65–70. [57] Jiang, X., et al., Magnetic metal-organic framework (Fe3O4@ ZIF-8) core-shell composite for the efficient removal of Pb (II) and Cu (II) from water. The Journal of Environmental Chemical Engineering, 2021. 9(5): p. 105959. [58] Wang, C., R. Yang, and H. Wang, Synthesis of ZIF-8/fly ash composite for adsorption of Cu2+, Zn2+ and Ni2+ from aqueous solutions. Materials (Basel), 2020. 13(1): p. 214. [59] Anisi, M., A.A. Ghoreyshi, E. Mehrvarz, and A. Rahimpour, Synthesize optimization, characterization, and application of ZIF-8 adsorbent for elimination of olive oil from aqueous solution. Environmental Science and Pollution Research, 2021. 28(10): p. 12725–12739. [60] Li, D. and F. Xu, Removal of Cu (II) from aqueous solutions using ZIF-8@ GO composites. Journal of Solid State Chemistry, 2021. 302: p. 122406. [61] Li, T., et al., Efficient removal of nickel (II) from high salinity wastewater by a novel PAA/ZIF-8/ PVDF hybrid ultrafiltration membrane. Water Research, 2018. 143: p. 87–98. [62] Long, X., et al., Removal of iodine from aqueous solution by PVDF/ZIF-8 nanocomposite membranes. Separation and Purification Technology, 2020. 238: p. 116488.

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[63] Amedi, H.R. and M. Aghajani, Aminosilane-functionalized ZIF-8/PEBA mixed matrix membrane for gas separation application. Microporous Mesoporous Mater, 2017. 247: p. 124–135. [64] Feng, S., X. Zhang, D. Shi, and Z. Wang, Zeolitic imidazolate framework-8 (ZIF-8) for drug delivery: A critical review. Frontiers of Chemical Science and Engineering, 2021. 15(2): p. 221–237. [65] Wang, Q., Y. Sun, S. Li, P. Zhang, and Q. Yao, Synthesis and modification of ZIF-8 and its application in drug delivery and tumor therapy. RSC Advances, 2020. 10(62): p. 37600–37620. [66] Hoseinpour, V. and Z. Shariatinia, Applications of zeolitic imidazolate framework-8 (ZIF-8) in bone tissue engineering: A review. Tissue & Cell, 2021. 72: p. 101588. [67] Nagarjun, N. and A. Dhakshinamoorthy, A cu-doped ZIF-8 metal organic framework as a heterogeneous solid catalyst for aerobic oxidation of benzylic hydrocarbons. New Journal of Chemistry, 2019. 43(47): p. 18702–18712. [68] Wang, J., et al., ZIF‐8 with ferrocene encapsulated: A promising precursor to single‐atom F-embedded nitrogen‐doped carbon as highly efficient catalyst for oxygen electroreduction. Small, 2018. 14(15): p. 1704282. [69] Yao, B., et al., Rapid ultrasound-assisted synthesis of controllable Zn/Co-based zeolitic imidazolate framework nanoparticles for heterogeneous catalysis. Microporous Mesoporous Mater, 2021. 314: p. 110777. [70] Fu, K., et al., Mixed ion-electron conducting PEO/PEDOT: PSS miscible blends with intense electrochromic response. Polymer (Guildf), 2019. 184: p. 121900. [71] Gao, F., et al., Facile synthesis of ZIF-8@ poly (3, 4-ethylenedioxythiophene): Poly (4-styrenesulfonate) and its application as efficient electrochemical sensor for the determination dichlorophenol. Synthetic Metals, 2021. 277: p. 116769. [72] Chen, Y., W. Huang, K. Chen, T. Zhang, Y. Wang, and J. Wang, Facile fabrication of electrochemical sensor based on novel core-shell PPy@ ZIF-8 structures: Enhanced charge collection for quercetin in human plasma samples. Sensors Actuators B Chemical, 2019. 290: p. 434–442.

Rana Rashad Mahmood Khan✶, Ramsha Saleem, Mirza Umair Baig, Sadia Yaseen, Muhammad Pervaiz, Zohaib Saeed, Hafiz Muhammad Faizan Haider, Ahmad Adnan

2 ZIF-8 spectacular properties Abstract: Zeolitic imidazole framework-8 is a kind of ZIF (a subclass of MOF) that comprises Zn2+ and 2-methylimidazole as center metal and organic linker, respectively. The structure of ZIF-8 resembles inorganic aluminosilicates. This material has gained a lot of attention from researchers due to its spectacular properties, including simple synthetic strategy, exceptional thermal and chemical stabilities, hydrothermal stability, high crystallinity and porosity, and tunable pores. ZIF-8 is one of the very few MOFs that can be synthesized at room temperature using an aqueous solution. ZIF-8 is considered a partially water-stable MOF and various strategies have been developed to improve its hydrothermal stability, such as the incorporation of hydrophobic groups in the ligand, carbonization, and shell-ligand exchange reaction. ZIF-8 is known for its exceptional thermal and chemical stabilities because of the strong interaction between Zn2+ and 2-methylimidazole, while many MOFs suffer from stability issues. ZIF-8 also shows great chemical stability on exposure to various electrolytes and organic solvents. Due to its remarkable properties, ZIF-8 finds use in a wide number of applications as an adsorbent, photocatalyst, sensor, gas separator, etc.

2.1 Introduction Metal-Organic Frameworks (MOFs) are the class of compounds in which a metal coordinates with ligands to form a cage-like porous structure. There are two major components of the MOFs: a metal ion and a ligand [1]. The metal ion is a central part of the MOFs, while ligands are linker molecules. Metal ions form nodes in the structure of MOFs. The connection between metal ions and ligands is through covalent or ionic bonds [2, 3]. The strength of these coordination bonds and the choice of metal and ligand in MOFs dictate the structure of the MOF [4]. Due to the unique structures, MOFs offer diversity in properties, such as high surface area, high and tunable porosity, chemical functionality, uniform structure, enhanced crystallinity, and flexibility in a network [5, 6]. These properties of MOFs make them attractive materials and

✶

Corresponding author: Rana Rashad Mahmood Khan, Department of Chemistry, Government College University, Lahore, Pakistan, e-mail: [email protected] Ramsha Saleem, Mirza Umair Baig, Sadia Yaseen, Muhammad Pervaiz, Zohaib Saeed, Hafiz Muhammad Faizan Haider, Ahmad Adnan, Department of Chemistry, Government College University, Lahore, Pakistan

https://doi.org/10.1515/9783110792591-002

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thus can be applied in numerous applications (as shown in Figure 2.1) including storage of carbon dioxide, catalysis [7, adsorption [8], gas separation [9, gas storage [10], drug delivery [11, 12], energy storage devices [13], ion exchange, water remediation, and purification of gases [14].

1

Catalysis 2

Adsorption

3

Applications of MOFs

Gas separation

4

Gas storage

5 6 7

Drug delivery Sensing

Energy storage

Figure 2.1: Applications of MOFs in different fields.

There are numerous families of MOFs. Figure 2.2 shows the families of MOFs along with its significant members. The distinction in these families is based on the selected metal and organic ligand for the synthesis of MOFs. Additionally, some families of MOFs are common such as HKUST, UiO-66, MIL, MOF-5, and ZIFs [15]. Zeolitic imidazolate framework (ZIF) is a significant subclass of MOFs that offers highly crystalline surface morphology similar to zeolites, characterized by large cavities interconnected via small windows [16]. ZIF offers the structure of the zeolite, comprising Zn or Co as MOFs

HKUST

UIO-66

MIL

MOF-5

ZIF

MIL-101 MIL-125

ZIF-71 ZIF-68 ZIF-11

MIL-53 ZIF-8

Figure 2.2: Some important families of MOFs with their commonly employed members.

2 ZIF-8 spectacular properties

21

the central metal and imidazole or its derivates as organic linkers. Huang et al. and Park et al. introduced ZIFs by synthesizing the first ZIF in the early 2000s [17, 18]. Later, due to their outstanding properties, almost 150 ZIFs of varying structures have been developed by scientists. Among the 150 reported ZIFs’ structures, zeolitic imidazole framework-8 (ZIF-8) has gained a lot of attention from researchers because of its structure and bond angles (145°) [19].

2.1.1 ZIF-8 ZIF-8 is one of the most widely employed ZIF, first introduced as MAF-4 by the Chen group [17]. Later, a systematic study by Yaghi’s group changed its name from MAF-4 to ZIF-8 [18]. ZIF-8, having the chemical formula Zn(Hmim)2, is made up of anions of 2-methylimidazolate (2-mIm) and zinc ions, having the formula [Zn(C4H5N2)2]n [20, 21]. ZIF-8 forms when 2-methylimidazole gets deprotonated and provides a nitrogen atom as an imidazolate, which has coordination ability [22]. The nitrogen of imidazolate then coordinates with Zn2+ to form a ZIF-8 structure [23]. Figure 2.3 illustrates the structure of ZIF-8. The structure of ZIF-8 offers remarkable properties that increase its application in many fields. These properties are due to the presence of MOF and zeolite in the same structure. N

N

N Zn2+ N N N

Zn2+ + HN

N N

N

Figure 2.3: Structure of ZIF-8.

2.2 Spectacular properties of ZIF-8 ZIF-8 offers many spectacular features as shown in Figure 2.4. These characteristics include ease to synthesize, exceptional thermal and hydrothermal stabilities, size stability, unremarkable porosity, alterable pore size, and structure, offering a large

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number of active sites on its surface and high crystallinity [24]. Due to these important features of ZIF-8, they have been applied to many fields. ZIF-8 acts as a promising platform in various applications such as catalysis, adsorption, photocatalytic system, drug delivery, energy storage, gas separation, sensing, etc. (Figure 2.1). Ease to synthesize Tunable Pores

Porosity

Characteristics of ZIF-8 Crystallinity

Size stability

Thermal stability

Hydrothermal stability

Figure 2.4: Spectacular features of ZIF-8.

2.2.1 Simple synthetic strategy of ZIF-8 The synthetic schemes of ZIF-8 were first reported in 2006. At that time, it was synthesized using DMF. In DMF, a portion of 2-mIm undergoes deprotonation and gives up hydrogen ions. The Zn ions then form a linkage with the nitrogen atoms present at the 1,3 positions of deprotonated 2-mIm, subsequently undergoing nucleation, crystal growth, and stationary processes, and ZIF-8 gets synthesized [25]. The kinetics of the reaction is dependent on the deprotonation step, and thus can be altered by varying simple factors, that is, pH of the solution, pKa of the ligand, and the reaction temperature [26]. In comparison to other MOFs, ZIF-8 can be synthesized readily by simple and easy methods. ZIF-8 can even be prepared by just mixing the solutions of its components – Zn2+ precursor and 2-methylimidazole. After the very first development of ZIF-8, many methods have been introduced by researchers to synthesize ZIF-8 that are simple, less time-consuming, and easy. These methods include hydrothermal, microwave, sonochemical, solvothermal, electrochemical, mechanical grinding, and steam-assisted method [27, 28]. The advantages and details of various methods of synthesis of ZIF-8 are illustrated in Table 2.1 and Table 2.2, respectively.

2 ZIF-8 spectacular properties

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Table 2.1: Benefits of the various synthesis methods of ZIF-8 [27–30]. Synthesis method

Advantages

Sonochemical

Small-sized nanocrystals Homogeneous nanoparticles Used for synthesis at a large scale

Microwave-assisted

Facile and inexpensive Reduces synthesis time Controllable size and shape by varying the reaction conditions

Mechanochemical

Green and efficient method Short synthesis time High surface area and pore volume Solvent-free synthesis

Solvothermal

Change in solvent alters the particle size of ZIF-

Microfluidic Reactor

Better mixing of reactant Heat/mass transfer

In the beginning, the solvothermal method was suggested, using DMF for the synthesis of ZIF-8 but now new methods have been optimized by which ZIF-8 can be synthesized at room temperature by using methanol or water as solvent [31, 32]. The use of DMF as a solvent in the solvothermal synthesis of ZIF-8 is limited due to the difficulty faced in the removal of the trapped DMF molecules in the ZIF-8 pores [33]. The rapid synthesis methods have eased the synthetic strategy of ZIF-8 as no special additives or surfactants are required; there is no need for high-cost apparatus; and work can be carried out at room temperature. Wiebcke et al. synthesized ZIF-8 nanocrystal by pouring the Zn solution in methanol into 2-imidazole solution in methanol and stirred at a high speed. In a few minutes, the turbid solution forms, and after 1 h, the ZIF-8 particles are separated from the mixture solution [31]. It is reported that the use of organic solvents in the solvothermal synthesis is costly and not ecofriendly. These limitations are overcome by using deionized water as a substitute for organic solvents. Thus, Pan et al. replaced the methanol with the deionized water. They synthesized the ZIF-8 nanocrystals by a rapid pouring of an aqueous solution of Zn precursor to aqueous solution of 2-mIm, while continuously stirring the aqueous solution [32]. The ratio of metal precursor and 2-mIm contributes significantly to the structural properties of ZIF-8 [33]. A ratio of 20:1 is highly recommended [34]. Studies in literature have shown that the surface area and the pore volume of the ZIF-8 are improved by using microwave irradiation. Microwave irradiation produces ZIF-8 at a relatively low Zn-to-mIm ratio. This technique reduces the time of synthesis, is eco-friendly, and is cost-effective [35].

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Table 2.2: Details of the different methods of the synthesis of ZIF-8. Method used

Solvent

Reaction conditions

Rapid pouring

Methanol

 °C,  h

[]

Deionized water

 °C,  min

[]

Methanol

 °C,  h

[]

DMF

 °C,  h

[]

Deionized water

−

[]

DMF

 °C,  h

[]

DMF

 °C,  h

[]

Methanol

 °C,  h

Mechanochemical

No solvent

 min,  Hz

Microfluidic reactor

Deionized water

 °C,  min

Microwave irradiation

Solvothermal

Reference

[]

2.2.2 Thermal stability Thermal stability is one of the major characteristics of the catalytic material as it is widely employed in industrial reactions that are carried out at a high temperature. So, such materials are preferred whose structure remains stable during the whole process, that is, thermally stable catalysts are preferred. Different studies have been carried out on the structural factors that can control the thermal stability of MOF [38]. Among the wide range of MOFs available, ZIF-8 has shown unmatchable thermal stability. In literature, different temperatures have been mentioned up to which ZIF-8 can remain stable. Zhang et al. synthesized the ZIF-8 by the solvothermal method and found it to be stable up to 600 °C [39]. In other studies, it is reported that ZIF-8 can sustain its structural integrity up to 550 °C [16, 40]. It is mentioned in the literature that the thermal stability of the ZIF-8 depends on the reaction temperature during its synthesis. There is an increase in the thermal stability with the increase in the reaction temperature but up to a certain limit, after which it started to decrease with an increase in the processing temperature. There are high chances of collision between the reactant molecules at high temperatures, and several crystal nuclei instant reactions begin. The activation energy of the reaction reduces and grain growth is completed. But with an increase in temperature above a certain limit, the required activation energy increases and the growth of the crystal remains incomplete. As a result, unstable ZIF-8 is formed [41].

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25

2.2.3 Chemical stability The organic component, 2-methylimidazolate, of ZIF-8 is chemically stable. ZIF-8 retains its crystal lattice structure when exposed to electrolytes such as LiCl, NaOH, LiNO3, and NaCl as well as solvents such as benzene ethanol, and water. ZIF-8 is a chemically stable material and maintains its crystalline structure on exposure to different solvents. ZIF-8 sustains its structural integrity on chemical treatment with benzene and boiling water for 7 days. Also, there was no effect on the ZIF8 crystalline structure when chemically treated with f NaOH solution for 24 h [42–44].

2.2.4 Hydrothermal stability MOFs are a special type of porous material comprising metal ions and organic linkers [45]. They are known for their enhanced porosity, crystallinity, surface areas, and capability to modify surface properties [46]. Thus, they have found many applications in gas separation, adsorption, photocatalysis, catalysis, and other biological fields [47]. But their use is limited due to the structural deterioration under aqueous conditions. Among the large number of MOFs, two classes of MOFs are renowned for their water stability. These two classes are high-valent metal/carboxylate linker (MIL and UiO) and low-valent metal/imidazolate linker (ZIFs) [48]. MIL and UiO maintain their structural integrity in water as water molecules do not get space to form a cluster around the metal (they have crowding around the central metal) and there is a strong metal-ligand bond [49, 50]. The enhanced water stability of ZIF-8 is because of the strong interaction between Zn2+ and imidazole of high pKa values. As a result, a hydrophobic surface appears over the ZIF, which helps it to remain stable under aqueous conditions [51]. There are contradictions found in the results of literature studies regarding the water stability of ZIF-8. Yaghi et al. and Low et al. have declared ZIF-8 as an outstanding hydrothermally stable MOF by proving the retention of crystallinity and surface properties after keeping it in boiling water or steam at 300 °C [18, 51]. However, Leus and his coworkers observed a partial deterioration of its topology on exposure to water [52]. Zhang et al. reported that ZIF-8 undergoes dissociation and as a result, Zn2+ is released into water [53]. Another group of researchers proved Zhang’s statement [54]. Whang et al. mentioned that ZIF-8 changes from highly crystalline to dense crystalline or amorphous MOF [55]. These contradicting results show that there should be more research on the hydrothermal stability of the ZIF-8. ZIF-8 is considered a hydrothermally stable MOF, but up to a certain extent. As a result, different strategies have been reported to enhance the water stability of ZIF-8. The structural integrity of ZIF-8 can be maintained by avoiding the collapse of water molecules with the center metal. For this purpose, there is a need to increase the strength of the Zn2+ and 2-mIm bond. Waltan et al. observed that there is an increase in the hydrothermal stability of ZIF-8 when hydrophobic groups are

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introduced into the structure, and a decrease in the incorporation of hydrophilic groups in the ligand [56]. Yang et al. proposed the shell-ligand exchange reaction (SLER) to make this material stable underwater as shown in Figure 2.5(B). In this reaction, the ligand in the outermost shell of the ZIF-8 is replaced with a hydrophobic ligand that helps to retain its structural morphology and properties when immersed in water [57]. Tanaka et al. proposed a variation in the outermost shell of ZIF-8 by carbonization. Figure 2.5(A) illustrates the methodology to improve the water stability of ZIF-8. As a result of this process, the outer shell gets enriched with carbon atoms, and thus repels water molecules and becomes water-stable [48]. So, it is concluded that small modifications in the synthetic scheme or introducing post-synthetic treatments make ZIF-8 an exceptional hydrothermally stable MOF.

(A)

(B) ZIF-8 without Carbon layer

Carbonization

Dissociated in water

ZIF-8 with Carbon layer

Stable in water

Figure 2.5: Improvement in the water stability of ZIF-8 by (a) development of carbon layer by carbonization [48] and (b) Shell-ligand exchange reaction [57].

2.2.5 Pore size The crystallographic pore aperture of ZIF-8 is 3.4 mm. But the flexibility in its structure improves its pore aperture up to 4.0–4.2 mm pore aperture, which is found to be effective and thus allows ZIF-8 to separate C3H6 (4.0) and C3H8 (4.2) efficiently. Furthermore, the flexibility of ZIF-8 allows it to separate a variety of additional gas pairs, including CO2/N2, H2/CO2, CO2/CH4, and H2/CH4, [58]. The varying pore aperture quality of ZIF-8 makes it a catalyst to separate gas molecules at an industrial level. Recently, mixed matrix membrane (MMM) rather than a separated membrane was developed. It shows advantages such as more selectivity and excellent stability. Zeolitic imidazolate frameworks-8 have been used as filler in the separation of CO2/CH4. The pores in ZIF-8 are quite large. Because of its chemical and thermal stabilities, porous open framework structure, and large surface area, ZIF-8 is a promising option for the separation of CO2/CH4 [59].

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2.2.6 Mechanical stability ZIF-8 is considered a mechanically stable MOF and is thus employed to increase the mechanical strength of various substances. For example, hyaluronic acid (HA) is a naturally occurring polysaccharide that has been demonstrated to aid in the healing of wounds. However, due to its low mechanical strength and instability, it cannot be employed regularly in this field. The use of HA/ZIF-8 for the healing process is another important application of ZIF-8 [60], as synthesized HA/ZIF-8 can overcome the limitation. Mechanical properties of HA/ZIF-8 have improved because of its highstress transfer characteristics and the hydrogen bonding between ZIF-8 and HA. Antibacterial capabilities and cell adhesion are improved on HA-modified films. As a result of the ZIF-8 alterations to HA films, wound healing qualities have improved.

2.3 Applications of ZIF-8 ZIF-8 has a lot of characteristics due to which it is widely employed to a number of applications. Figure 2.6 shows the spectacular features and applications of ZIF-8.

ZIF-8

Surface area

Catalysis High porosity

Properties

Application Drug delivery

Thermal stability Chemical resistance

Mechanical strength

Separation Adsorption

Figure 2.6: Applications of ZIF-8 due to its spectacular properties.

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2.4 Conclusion MOFs are a class of porous materials that have applications in various fields. ZIFs are one of the classes of the MOFs formed by the coordination between Zn ion and the derivates of imidazole. ZIF-8, a member of ZIFs, has some peculiar features that have enhanced its application in various fields. These special properties include easy synthetic strategy, high surface area, porosity, thermal stability, chemical stability, and water resistance.

References [1] [2] [3] [4] [5] [6]

[7] [8] [9] [10] [11] [12] [13]

[14] [15]

Xu, -M.-M., et al., Exchange reactions in metal-organic frameworks: New advances. Coordination Chemistry Reviews, 2020. 421: p. 213421. Lin, Z.-J., et al., Metal–organic frameworks based on flexible ligands (FL-MOFs): Structures and applications. Chemical Society Reviews, 2014. 43(16): p. 5867–5895. Lu, W., et al., Tuning the structure and function of metal–organic frameworks via linker design. Chemical Society Reviews, 2014. 43(16): p. 5561–5593. Farha, O.K., et al., Metal–organic framework materials with ultrahigh surface areas: Is the sky the limit?. Journal of the American Chemical Society, 2012. 134(36): p. 15016–15021. Vashistha, V.K., D.K. Das, and A. Kumar, Metal–organic frameworks-based nanomaterials for nanogenerators: A mini review. International Nano Letters, 2022. p. 1–7. Baumann, A.E., et al., Metal-organic framework functionalization and design strategies for advanced electrochemical energy storage devices. Communications Chemistry, 2019. 2(1): p. 1–14. Furukawa, H., et al., The chemistry and applications of metal-organic frameworks. Science, 2013. 341(6149): p. 1230444. Petit, C., Present and future of MOF research in the field of adsorption and molecular separation. Current Opinion in Chemical Engineering, 2018. 20: p. 132–142. Li, S. and F. Huo, Metal–organic framework composites: From fundamentals to applications. Nanoscale, 2015. 7(17): p. 7482–7501. Li, B., et al., Nanospace within metal–organic frameworks for gas storage and separation. Materials Today Nano, 2018. 2: p. 21–49. Lawson, H.D., S.P. Walton, and C. Chan, Metal–organic frameworks for drug delivery: A design perspective. ACS Applied Materials & Interfaces, 2021. 13(6): p. 7004–7020. Hasan, M.N., et al., Sensitization of nontoxic MOF for their potential drug delivery application against microbial infection. Inorganica Chimica Acta, 2021. 523: p. 120381. Shrivastav, V., et al., Metal-organic frameworks (MOFs) and their composites as electrodes for lithium battery applications: Novel means for alternative energy storage. Coordination Chemistry Reviews, 2019. 393: p. 48–78. Mehtab, T., et al., Metal-organic frameworks for energy storage devices: Batteries and supercapacitors. Journal of Energy Storage, 2019. 21: p. 632–646. Yuan, N., et al., Diverse effects of metal–organic frameworks on microstructure and compressive strength of cement-based composites. Cement and Concrete Composites, 2022. 127: p. 104406.

2 ZIF-8 spectacular properties

29

[16] Troyano, J., et al., Colloidal metal–organic framework particles: The pioneering case of ZIF-8. Chemical Society Reviews, 2019. 48(23): p. 5534–5546. [17] Huang, X.C., et al., Ligand‐directed strategy for zeolite‐type metal–organic frameworks: Zinc (II) imidazolates with unusual zeolitic topologies. Angewandte Chemie International Edition, 2006. 45(10): p. 1557–1559. [18] Park, K.S., et al., Exceptional chemical and thermal stability of zeolitic imidazolate frameworks. Proceedings of the National Academy of Sciences, 2006. 103(27): p. 10186–10191. [19] Phan, A., et al., Synthesis, structure, and carbon dioxide capture properties of zeolitic imidazolate frameworks. 2009. [20] Ortiz, A.U., et al., What makes zeolitic imidazolate frameworks hydrophobic or hydrophilic? The impact of geometry and functionalization on water adsorption. Physical Chemistry Chemical Physics, 2014. 16(21): p. 9940–9949. [21] Phan, A., et al., O, Keeffe, M.; Yaghi, OM. Accounts of Chemical Research, 2010. 43(1): p. 58–67. [22] Tan, P.C., et al., Size control and stability study of zeolitic imidazolate framework-8 to prepare mixed matrix membrane. Journal of Physical Science, 2017. 28: p. 215. [23] Boudjema, L., et al., Confinement-induced electronic excitation limitation of anthracene: the restriction of intramolecular vibrations. The Journal of Physical Chemistry C, 2018. 122(49): p. 28416–28422. [24] Dai, H., et al., Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication, applications and perspective. Coordination Chemistry Reviews, 2021. 441: p. 213985. [25] Venna, S.R., J.B. Jasinski, and M.A. Carreon, Structural evolution of zeolitic imidazolate framework-8. Journal of the American Chemical Society, 2010. 132(51): p. 18030–18033. [26] Song, Y., et al., Structural manipulation of ZIF-8-based membranes for high-efficiency molecular separation. Separation and Purification Technology, 2021. 270: p. 118722. [27] Chen, Y. and S. Tang, Solvothermal synthesis of porous hydrangea-like zeolitic imidazole framework-8 (ZIF-8) crystals. Journal of Solid State Chemistry, 2019. 276: p. 68–74. [28] Lee, Y.-R., et al., ZIF-8: A comparison of synthesis methods. Chemical Engineering Journal, 2015. 271: p. 276–280. [29] Hillman, F., et al., Rapid microwave-assisted synthesis of hybrid zeolitic–imidazolate frameworks with mixed metals and mixed linkers. Journal of Materials Chemistry A, 2017. 5(13): p. 6090–6099. [30] Feng, S., et al., Zeolitic imidazolate framework-8 (ZIF-8) for drug delivery: A critical review. Frontiers of Chemical Science and Engineering, 2021. 15(2): p. 221–237. [31] Cravillon, J., et al., Rapid room-temperature synthesis and characterization of nanocrystals of a prototypical zeolitic imidazolate framework. Chemistry of Materials, 2009. 21(8): p. 1410–1412. [32] Pan, Y., et al., Rapid synthesis of zeolitic imidazolate framework-8 (ZIF-8) nanocrystals in an aqueous system. Chemical Communications, 2011. 47(7): p. 2071–2073. [33] Kida, K., et al., Formation of high crystalline ZIF-8 in an aqueous solution. CrystEngComm, 2013. 15(9): p. 1794–1801. [34] Tanaka, S., et al., Size-controlled synthesis of zeolitic imidazolate framework-8 (ZIF-8) crystals in an aqueous system at room temperature. Chemistry Letters, 2012. 41(10): p. 1337–1339. [35] Bao, Q., et al., Rapid synthesis of zeolitic imidazolate framework-8 (ZIF-8) in aqueous solution via microwave irradiation. Inorganic Chemistry Communications, 2013. 37: p. 170–173.

30

Rana Rashad Mahmood Khan et al.

[36] Awadallah-F, A., et al., On the nanogate-opening pressures of copper-doped zeolitic imidazolate framework ZIF-8 for the adsorption of propane, propylene, isobutane, and nbutane. Journal of Materials Science, 2019. 54(7): p. 5513–5527. [37] Shi, Q., et al., Synthesis of ZIF‐8 and ZIF‐67 by steam‐assisted conversion and an investigation of their tribological behaviors. Angewandte Chemie, 2011. 123(3): p. 698–701. [38] Akçay, A., V. Balci, and A. Uzun, Structural factors controlling thermal stability of imidazolium ionic liquids with 1-n-butyl-3-methylimidazolium cation on γ-Al2O3. Thermochimica Acta, 2014. 589: p. 131–136. [39] Wang, S. and S. Zhang, Study on the structure activity relationship of ZIF-8 synthesis and thermal stability. Journal of Inorganic and Organometallic Polymers and Materials, 2017. 27(5): p. 1317–1322. [40] Banerjee, R., et al., High-throughput synthesis of zeolitic imidazolate frameworks and application to CO2 capture. Science, 2008. 319(5865): p. 939–943. [41] Liu, H., et al., The effect of methyl functionalization on microporous metal‐organic frameworks’ capacity and binding energy for carbon dioxide adsorption. Advanced Functional Materials, 2011. 21(24): p. 4754–4762. [42] Jin, C.-X. and H.-B. Shang, Synthetic methods, properties and controlling roles of synthetic parameters of zeolite imidazole framework-8: A review. Journal of Solid State Chemistry, 2021. 297: p. 122040. [43] Pang, S.H., et al., Facet-specific stability of ZIF-8 in the presence of acid gases dissolved in aqueous solutions. Chemistry of Materials, 2016. 28(19): p. 6960–6967. [44] Wang, Z., et al., Improving ZIF-8 stability in the preparation process of polyimide-based organic solvent nanofiltration membrane. Separation and Purification Technology, 2019. 227: p. 115687. [45] Zhu, Q.-L. and Q. Xu, Metal–organic framework composites. Chemical Society Reviews, 2014. 43(16): p. 5468–5512. [46] Kreno, L.E., et al., Metal–organic framework materials as chemical sensors. Chemical Reviews, 2012. 112(2): p. 1105–1125. [47] Li, H., et al., Design and synthesis of an exceptionally stable and highly porous metal-organic framework. Nature, 1999. 402(6759): p. 276–279. [48] Tanaka, S. and Y. Tanaka, A simple step toward enhancing hydrothermal stability of ZIF-8. ACS Omega, 2019. 4(22): p. 19905–19912. [49] Férey, G., et al., A chromium terephthalate-based solid with unusually large pore volumes and surface area. Science, 2005. 309(5743): p. 2040–2042. [50] Cavka, J.H., et al., A new zirconium inorganic building brick forming metal organic frameworks with exceptional stability. Journal of the American Chemical Society, 2008. 130(42): p. 13850–13851. [51] Low, J.J., et al., Virtual high throughput screening confirmed experimentally: Porous coordination polymer hydration. Journal of the American Chemical Society, 2009. 131(43): p. 15834–15842. [52] Leus, K., et al., Systematic study of the chemical and hydrothermal stability of selected “stable” Metal organic frameworks. Microporous and Mesoporous Materials, 2016. 226: p. 110–116. [53] Zhang, H., M. Zhao, and Y. Lin, Stability of ZIF-8 in water under ambient conditions. Microporous and Mesoporous Materials, 2019. 279: p. 201–210. [54] Duke, M.C., et al., Structural effects on SAPO-34 and ZIF-8 materials exposed to seawater solutions, and their potential as desalination membranes. Desalination, 2016. 377: p. 128–137.

2 ZIF-8 spectacular properties

31

[55] Wang, H., et al., Specific anion effects on the stability of zeolitic imidazolate framework-8 in aqueous solution. Microporous and Mesoporous Materials, 2018. 259: p. 171–177. [56] Jasuja, H., Y.-G. Huang, and K.S. Walton, Adjusting the stability of metal–organic frameworks under humid conditions by ligand functionalization. Langmuir, 2012. 28(49): p. 16874–16880. [57] Liu, X., et al., Improvement of hydrothermal stability of zeolitic imidazolate frameworks. Chemical Communications, 2013. 49(80): p. 9140–9142. [58] Zhao, Y., et al., Flexible polypropylene-supported ZIF-8 membranes for highly efficient propene/propane separation. Journal of the American Chemical Society, 2020. 142(50): p. 20915–20919. [59] Barooah, M., and B. Mandal, Synthesis, characterization and CO2 separation performance of novel PVA/PG/ZIF-8 mixed matrix membrane. Journal of Membrane Science, 2019. 572: p. 198–209. [60] Velásquez-Hernández, M.d.J., et al., Modulation of metal-azolate frameworks for the tunable release of encapsulated glycosaminoglycans. Chemical science, 2020. 11(39): p. 10835–10843.

Mushkbar Zahra, Muhammad Pervaiz✶, Zohaib Saeed, Umer Younas, Rana Rashad Mahmood Khan, Ikram Ahmad, Syed Majid Bukhari, Ayoub Rashid, Ahmad Adnan

3 Heterogeneous catalysis and ZIF-8 Abstract: Swift development in nanoscience has introduced novel opportunities for the fabrication of hybrid metal nanoparticles-based heterogeneous Zeolite Imidazolate Framework-8 (ZIF-8) catalysts. Heterogeneous catalysis by ZIF-8 has now become the center of focus for researchers. Multiple strategies for the synthesis of ZIF-8 as a heterogeneous catalyst have been reviewed in this chapter. This chapter mainly focuses on the multidimensional applications of ZIF-8 heterogeneous catalyst, that is, hydrogenation of carbon-dioxide, oxidation of alcohol, Knoevenagel condensation and biodiesel production, etc. The best heterogenic catalytic efficiency of ZIF-8 has been found to be in Knoevenagel condensation, with 94% product yield. The heterogeneous ZIF-8 catalyst can be re-cycled for 4–5 periods, without momentous loss of catalytic efficiency. This chapter also sheds light on the comparison of common heterogeneous and ZIF-8-based heterogeneous catalysts.

3.1 Introduction A catalyst is the apple of the eye of any chemical reaction. It is the material which assists a chemical reaction in such a way that the speed of chemical reaction is increased and activation energy is minimized. Through catalysts, innovative society and nature pedals the chemical processes. Catalytic activity of catalysts has great impact on our daily lives; it offers us a variety of products – from fertilizers and fuels to pharmaceuticals and plastics. It is also used to separate the emissions from vehicles, energy plants, and industrial processes. Technology is fundamental to economy. It has been expected that 20–30% of processes in the industrial world depend upon the catalysis. The world is facing a number of contests that call for an even more focus on catalysis. The awareness that the technique we used to produce energy may endanger the earth climate points to enhanced investments in alternate energy production ✶

Corresponding author: Muhammad Pervaiz, Department of Chemistry, Government College University, Lahore, Pakistan, e-mail: [email protected] Mushkbar Zahra, Zohaib Saeed, Rana Rashad Mahmood Khan, Ayoub Rashid, Ahmad Adnan, Department of Chemistry, Government College University, Lahore, Pakistan Umer Younas, Department of Chemistry, The University of Lahore, Lahore, Pakistan Department of Chemistry, COMSATS University Islamabad, Abbottabad Campus, Pakistan Ikram Ahmad, Syed Majid Bukhari, Department of Chemistry, University of Sahiwal, Sahiwal, Pakistan

https://doi.org/10.1515/9783110792591-003

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strategies, and catalysis is a fundamental to most processes [1]. Catalysis is an meritorious way to a clean and dominant chemistry. Without being used up, a catalyst is meant to: introduce a new structure, enhance productivity, lessen the raw material and energy consumption, reduce the chance of waste production, and acquire a better environment. Hence, 80% of the industrial chemical reactions use catalysts [2]. A catalyst has the job of swiftly activating the starting feed materials, while decelerating the generation of the most thermodynamically privileged products and, in this manner, permitting the formation of less stable products [3]. Catalyst can be of three types: heterogeneous catalysts, homogeneous catalysts, and enzyme catalysts. Heterogeneous catalysts are present in a state different from that of reactants. Homogeneous catalysts work in the same phase as the reactants, while enzyme catalysts are characteristic proteins [1]. In 1925, Taylor found that on a solid catalyst, there will be all excesses between the cases in which all the atoms in the surface are energetic and those in which comparatively few are so vigorous. Meanwhile, the formulation of the Taylor perception of active sites, the goal for observing, recognizing, transforming and planning active sites of heterogeneous catalysts has been on [4]. Like other heterogeneous catalysts, for example, MgO [3], ZIF can also be used as heterogeneous catalysts. ZIF-8 (zeolite imidazolate framework-8), microporous structure is a kind of metal organic framework (MOF) synthesized by the coordination of 2p orbital of Zinc metal ion and 2-methylimidazole ( 2-mIM), which can be disbursed as a photo-catalyst to break the organic contaminants such as dyes [5]. Metal organic frameworks are presently earning attention for their possible applications in sensors, gas separation and storage, and catalytic reactions. ZIF-8, being categorized as a new sub-branch of MOFs, has appeared as innovative type of highly porous materials. Gathering benefits from both conventional MOFs and zeolites, various reactions have been supported by MOFs as solid acid catalyst; for instance, aldol-condensation, oxidation, hydrogenation, Suzuki cross-coupling, Friedel-craft alkylation, Trans-esterification reaction, etc. are reactions which are carried out using MOFs. A highly spongy ZIF-8 is synthesized through different methods such as solvothermal method and used as an effective catalyst for various reactions such as Knoevenagel reaction (as shown in Figure 3.1), in which Benz aldehyde reacts with malononitrile, in the presence of ZIF-8. O

CN H

BENZALDEHYDE

+

CN Malononitrile

ZIF-8

CN

Toluene, room temperature

CN

1,1-dicyano-2-phenylethene

+

H 2O water

Figure 3.1: Catalytic activity of ZIF-8 for Knoevenagel reaction [6].

The formation of ZIF-8 can be examined by different characterization techniques, that is, scanning electron microscopy, X-ray diffraction, and Fourier transform infra-

3 Heterogeneous catalysis and ZIF-8

35

red microscopy, etc. ZIF-8 can be simply removed from the reaction mixture and reused as significant degrading heterogeneous catalyst [6]. In comparison with pure microporous ZIF-8, ZIF-8 composite material not only improves the adsorption aptitude and photo catalytic activity of ZIF-8, but also extends the applications variety of ZIF-8 [7]. ZIF-8 can be used as heterogeneous catalyst for trans-esterification of vegetable oil. The zinc metal ion as an acid and N-moieties and OH-groups as basic group in ZIF-8 play vital roles in catalytic activity of ZIF-8. The ZIF-8 crystals are coated on PI nanofibers and used as efficient heterogeneous catalyst for the Knoevenagel reaction (as shown in Figure 3.2). ZIF-8 can also be used as an efficient heterogeneous catalyst for hydrogenation of ethylene and cyclohexene [8]. This chapter specifically focuses on the catalytic activity of ZIF-8 and its applications as a heterogeneous catalyst, and it also sheds light on some methods of preparing ZIF-8 heterogeneous catalyst and comparison of general heterogeneous catalysis with ZIF-8 catalysis. Chun et al. developed a simple technology to synthesize yolk-shell-based ZIF-8 nanocrystals. The yolk- shell structure has ability to work as nanoparticle core, microporous shell, and have craters in between, which offer enough potential in heterogeneous catalysis. The synthesis method includes the covering of nanocrystal cores with a layer of Cu2O as the sacrificial pattern, and then, a coating of poly-crystalline ZIF-8. The formation of ZIF-8 coating layer is aided by the clean surface of Cu2O. The yolkshell nanocrystals were analyzed by different characterization techniques, that is, scanning electron microscopy, X-ray diffraction, transmission electron microscopy, and nitrogen adsorption. The Pd/ZIF-8 crystals were used as heterogeneous catalyst for the hydrogenation of cyclo-octene, cyclohexene, and ethylene. The spongy structure of ZIF-8 shell offers admirable molecular magnitude selectivity. The heterogeneous catalytic efficiency of ZIF-8 was high for the hydrogenation of ethylene and cyclohexene but not for the hydrogenation of cyclo-octene [9]. Yebin and his colleagues synthesized monodispersed ZIF-8, by using dimethylsulfoxide as solvent. As a result, the nanoparticles of ZIF-8 of 90–110 nm size were obtained, and it was observed that their dispersion is highly stable, contrary to accumulation. Due to this solvent, the particles were found to have greater porosity and efficient ability to adsorb CO2, in comparison to ZIF-8 particles synthesized with other solvents such as N, N-dimethylformamide, and methanol. The surface chemistry and even size of nanoparticles play a significant role in the Knoevenagel condensation reaction. The higher thermal stability of ZIF-8 nanoparticles, up to 550 °C, has gained much attention in industrial applications [10]. Tuan and his coworkers found the ZIF-8 nanoparticles (PdNPs/ZIF-8) to be an excellent heterogeneous catalyst for the aminocarbonylation of bromoarenes, in the phosphine environment and iodoarenes, in the absence of phosphine. The catalyst remains stable in the presence of air. The palladium coating on ZIF-8 was kept very low as 1% wt and the catalyst prepared was reprocessed many times, showing a minute change in catalytic performance. The catalyst can also be used for the synthesis of ester from alkoxycarbonylation reaction and cyclic and primary amides [11]. Minqi et al. observed the catalytic activity of ZIF-8 in preparing styrene carbonate from carbon dioxide and

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styrene oxide. The ZIF-8 particles exhibited admirable catalytic efficiency at 50 °C, and product yield was 54% at 100 °C. To examine the density and kind of acid sites in fresh and recycled ZIF-8 catalysts, ammonia and pyridine were used as enquiry materials. The existence of Lewis and Bronsted acid sites was exposed by Drift spectroscopy of adsorbed pyridine. But the B-sites vanished in reused ZIF-8 catalyst. The presence of both basic and acid sites in ZIF-8 assisted the adsorption of CO2 and its transformation into cyclic carbonate. The ZIF-8 catalyst does not lose its catalytic activity, even on being reused [12]. Muhammad and his colleagues followed the impregnation approach followed by reduction with sodium borohydride to synthesize hybrid microporous material from distributed anionic sulfonated N-heterocyclic carbene, palladium, and ZIF-8. The negatively charged sulfonated N-heterocyclic carbene was used to stabilize the palladium nanoparticles in the apertures present on the surface of ZIF-8 and found to be an excellent ligand. The resultant product (catalyst) showed efficient catalytic activity in Mizoroki-Heck cross-coupling reaction, even under slight conditions [13]. Mai et al. prepared sodium-hydroxide-doped magnetized Zeolitic imidazolate framework (ZIF-8) catalyst and applied it in production of bio-diesel. The new catalyst was analyzed for the production of biodiesel from ethanolysis of vegetable oil, and it showed 70% conversion of oil. The best conditions in which the catalyst exhibited maximum efficiency was alcohol-to- oil ratio of 21:1, reaction time of one-and-a-half hours, temperature of 75 °C, and reaction catalyst feed of 1% wt. The ethanolysis reaction followed the pseudo second order reaction [14]. Yuan et al. followed facile impregnation method to synthesize palladium nanoparticles incorporated on ZIF-8. The synthesized product was examined by different techniques such as transmission electron microscopy, X-ray diffraction, inductively coupled plasma spectroscopy, and N2 adsorption. The synthesized catalyst showed tremendous activity for the hydrogenation of cinnamaldehyde. It was observed that the solvent used in reaction played a significant role in the catalytic activity of the prepared catalyst. The palladium nanoparticles incorporated on the ZIF-8 had significant impact on the catalytic performance of the prepared catalyst, and it enhanced the catalytic efficiency and hydrocinnamaldehyde selectivity when compared to those impregnated on other MOFs. This catalyst can be recycled a maximum of four times, without loss in selectivity and performance [15].

3.2 General heterogeneous catalysis vs ZIF-8 heterogeneous catalysis: a comparison Heterogeneous catalysis is defined as a catalysis in which the catalyst is not in the same phase as reactants. The mechanism of general heterogeneous catalysts is different from that of ZIF-8 [4]. The heterogeneous catalyst, that is, ZIF-8, can be differentiated from other general catalysts as follows:

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3 Heterogeneous catalysis and ZIF-8

General heterogeneous catalyst vs ZIF- heterogeneous catalyst: a comparison General catalyst

ZIF- catalyst Oxidation

In general catalysis, the general catalysts are used. For example, in the aerobic oxidation of alcohol iron, O, manganese, copper, and ruthenium metals can be used as heterogeneous catalysts []. The reaction is as follows: O4, reaction time 1 hour

OH

In ZIF- catalysis, copper-doped/ZIF- is used as efficient heterogeneous catalyst for the oxidation of aromatic alcohols []. The mechanism of reaction is as followed shown in Figure .: R' CuNO /ZIF-8 (1% molar fraction) 3

CHO

R' O

OH R

R

room temperature, air cinnamyl alcohol

cinnamaldehyde

Figure 3.2: Oxidation of cinnamylalcohol by general catalyst [16].

aromatic alcohol

oxidized into

aromatic ketone

Figure 3.3: Oxidation of aromatic alcohol [17].

Lewis acidity

A general heterogeneous catalyst may or may not be Lewis acid for example: copper, ruthenium, iron metals, etc. are used as heterogeneous catalysts in aerobic oxidation of alcohol [], but they are not Lewis acid; but NbO. nHO has a Lewis acid site on water molecule [].

The ZIF- has reasonable acid-base properties. It has been observed that Zn++ of Zeolitic imidazolate framework- is responsible for the Lewic acidity in it as mentioned in Figure . [].

Zn2+ ZIF-8 Zn+2 responsible for the Lewic acidity of ZIF-8 Figure 3.4: Zn + 2 responsible for the Lewic acidity of ZIF-8 [19].

Surface area

38

Mushkbar Zahra et al.

(continued) General heterogeneous catalyst vs ZIF- heterogeneous catalyst: a comparison General catalyst

ZIF- catalyst

Surface area of the catalyst plays an important role in the catalysis of any chemical reaction. Some catalysts like zinc powder have high surface area due to which it has greater adsorption capacity []. But some heterogeneous catalysts, for example, Tin and zeolite have low surface area. The zeolite has surface area of – m/g [].

The ZIF- and its composites are nanoporous particles that have greater surface area as shown in Figure ., up to  m/g, and higher adsorption capacity for the attachment of heavy metals, dyes, and other contaminants from the waste water; hence, they are used as excellent heterogeneous catalysts [].

ZIF-8

high surface area of ZIF-8

Figure 3.5: Demonstration of high surface area of ZIF-8 [22]. Chemical stability

The chemical stability of general catalysts such as zeolites is high.

Zeolite imidazolate framework- have limited and incompatible stability in some solvents and are unstable during catalytic performance.

Metal sites

A general catalyst, for example, zeolite, has few metal sites.

The ZIF- framework is the combination of metal and organic structures. Hence, it has more metal sites than other catalysts [].

3 Heterogeneous catalysis and ZIF-8

39

3.3 Preparation of different ZIF-8 heterogeneous catalysts The preparation method and composition of catalysts have a great influence on the catalytic activity of the catalyst. Different ZIF-8 heterogeneous catalysts can be prepared as below.

3.3.1 Preparation of ZIF-8: heterogeneous catalyst It has been reported that by following solvothermal method, ZIF-8 can be prepared from 2-methylimidazole and zinc nitrate. In ZIF-8 structure, zinc atoms are joined by nitrogen atoms of 2-methylimidazolate to form a nanosized network of metal and organic molecules. To facilitate the evacuation of the network, solvent exchange is important in the synthesis of spongy MOF-based structures. The prepared ZIF-8 samples are dipped in the dichloromethane at normal temperature for 72 hours. During solvent exchange period, DMF, which are strongly interacting molecules, are exchanged with DCM, weakly interacting molecules, which are simply separated through vacuum in the consequent activation. As a result, white polyhedral crystals of ZIF-8 are obtained, which are dried and weighed later. The total yield of catalyst from this method is 23% [6].

3.3.2 PI/ZIF-8 film: a heterogeneous catalyst In literature, it has been reported that the ZIF-8 coating can be obtained by preparing a mixed solution of zinc nitrate and 2-methylimidazolate in methanol, submerging the PI membrane into it for one day, at room temperature. The influence of ligand/ metal concentration on the growth of film has been examined. It has been examined by scanning electron microscopy that when zinc nitrate concentration is 0.0013 M, very light nanocrystals of 100–200 nm are observed on the PI membrane, whereas when zinc nitrate concentration (hexa-hydrate) is 0.04 M, no crystals are observed. Efficient covering of ZIF-8 (approximately 0.5–2 micrometer) appear for a modest concentration of 0.01 M. As the growth cycles increase, ZIF-8 crystals start casing the surface of substrate and ultimately result in denser MOF layering. Partly hydrolyzed PI membranes have been exposed as a growth substrate. Experiments reveal that hydrolyzed and un-hydrolyzed PI membranes cannot be differentiated on the surface, which proposes that in ZIF-8 growth, there is little contribution of partial hydrolyzation of PI membranes [8].

40

Mushkbar Zahra et al.

3.3.3 Yolk-shell Pd@Cu2O/ZIF-8 polycrystalline crystals: as heterogeneous catalyst To prepare yolk-shell Pd@Cu2O/ZIF-8 nanocrystals, palladium octahedral is coated with Cu2O core shell structure. After copper-oxide layering, palladium@copper-oxide is mixed with zinc nitrate and 2- methylimidazolate in methanol solvent. Due to deprotonation of 2-methylimidazolate on the emergence of ZIF-8, the pH of the mixture gets acidic, and Cu2O is scratched off. A little remainder of Cu2O is observed which is removed by the 3% solution of ammonium hydro-oxide in methanol. The final products obtained are cleaned by methanol and assembled by centrifugation [9].

3.3.4 Monodispersed particles of heterogeneous ZIF-8 catalyst For the preparation of ZIF-8 catalyst as a heterogeneous catalyst, 0.985 gram of 2methylimidazolate and 0.893 gram of zinc nitrate are added in 10 mL of DMSO separately and named as solution A and B, respectively. 2-Methyimidazolate solution in DMSO appears as clear and mixed with zinc solution and stirred for 1800 s in oil bath at 313 K. After magnetic stirring of solutions, a milky colloidal solution is obtained, which is centrifuged three times to obtain white solid particles that are washed with methanol repeatedly. The resultant product is dried for one day at 333 K. The synthesis of ZIF-8 crystals can also be carried out by using DMF and DMSO as solvents, and such ZIF-8 samples are labeled as ZIF-8 (DMF) and ZIF-8 (DMSO) respectively [10].

3.3.5 Crystals of heterogeneous ZIF-8 The ZIF-8 crystals can be synthesized by dissolving 8 mmol zinc nitrate in methanol (1.4 mol), and this solution can be designated as solution. On the other hand, solution of 2-methylimidazolate (64.4 mmol) and methanol (1.4 mmol), which is named as solution B is mixed with the solution A and stirred well for 7–8 h. The resultant solution is centrifuged at 3,000 revolutions per minute and washed with methanol three times, repeatedly. In the result, crystals of ZIF-8 are obtained, which are dried overnight at 100 °C [12].

3.4 Heterogeneous catalysis by ZIF-8: applications ZIF-8, a sub-branch of metal organic framework consists of tetrahedrally ordered metal ions united by imidazolates. Among them, ZIF-8 has currently gained significant attraction due to due to its exclusive structure and characteristics. It has cubic lattice of 143 m, feature cavities of 11.6 Angstrom, and apertures of 3.4 Angstrom. The

41

3 Heterogeneous catalysis and ZIF-8

even sponginess and unique thermal and chemical stability of ZIF-8 grab attention and are popular in broad-spectrum applications such as chemical sensors, waste water treatment, drug delivery agents, gas separation and storage, catalysis, etc. [10]. Applications of ZIF-8 as a heterogeneous catalyst are as follows.

3.4.1 Bifunctional heterogeneous catalyst for biodiesel production Zeolite imidazolate framework-8 can be used as bifunctional catalyst for the transesterification of the rapeseed oil. In a batch reactor, 0.4 gram of ZIF-8 catalyst and 10 gram of rapeseed oil are laden and stirred gently. When the mixture is assorted evenly, a specific amount of methanol is added to it. The constant stirring of the mixture heats up the batch reactor to the temperature of the reaction mixture. Then, the mixture is allowed to hold for two hours at different temperatures, ranging from 80 to 240 °C. When the transesterification of oil by ZIF-8 is completed, the final products are removed from the reaction mixture by filtration, and the heterogeneous catalyst is also separated. The esters obtained as final products are taken out by adding ci-chloromethane into mixture. Then, dichloromethane is also separated from the organic layer by heating it at 70 °C. The esters prepared in this method are dried overnight and weighed. The filtered catalysts are washed and dried for further use [24]. The mechanism of transesterification under base and acid condition, in the presence of ZIF-8 catalyst is as shown in Figure 3.6:

a

O–

O

2

R O

+

H

R1

B R R

R1

O 2

O–

R2

+ BH

-R1O-

O

R

O

O

R2

+

R

H

b

R R

OH

ZIF-8

O O

1

R

C R

O

+

H

-H+/R1OH

+

O

R

O

H

OH

R2

1

+

OR

O

1

R

2

Figure 3.6: Transesterification of rapeseed oil for biodiesel production in acid (b) and base (a) environment by ZIF-8 [24].

3.4.2 Benzyl alcohol oxidation by BiOF/ZIF-8 ZIF-8 particles can also be used to oxidize the aromatic alcohol into aldehyde or ketone. For this purpose, a solution of ethanol and water is prepared by mixing 1.0 mmol

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ethanol in 5 mL of water. After this mixing, the catalyst, that is, BiOF/ZIF-8 (0.02 mmol) and 30% hydrogen peroxide (5 mmol) are mixed with each other, and this solution is added to the ethanol-water solution and stirred at normal conditions. When the reaction is completed, the mixture of catalyst and substrate is allowed to react with 10% sodium hydrogen sulfite solution, so that it can decompose the unreacted hydrogen peroxide present in the mixture. Later, this mixture is treated with 10% sodium hydrooxide, for the same purpose. The final product of oxidation reaction is collected by nbutyl ether. For obtaining pure product, distillation or column chromatography (hexane/ethyl acetate of ratio 10:1) of the reaction mixture is done, so that the oxidized product can be separated easily [25]. The oxidation of benzyl alcohol by BiOF/ZIF-8 is shown in Figure 3.7 below:

O OH

benzylalcohol

BiOF@ZIF-8 H2O2, H2O, room temperature 10 hour

O H

+

95% benzaldehyde

CH3 5% acetophenone

Figure 3.7: Oxidation of benzyl alcohol by BiOF/ZIF-8 [25].

3.4.3 Photocatalytic degradation of methylene blue by ZIF-8 ZIF-8 is not only used as a heterogeneous catalyst, but it can also work as active heterogeneous photo-catalyst for the degradation of methylene blue. For examining the photo-catalytic activity of ZIF-8 under mercury lamp of 500 W in open air and at room temperature, the distance between the lamp and the container holding the reaction mixture is maintained as 5 cm. A 50-mL flask is taken and aqueous solution of methylene blue (50 ml) is prepared. Then, 50 mg ZIF-8 photo-catalyst is taken and added into the above solution and stirred for one hour in darkness. The photodegradation by ZIF-8 as a heterogeneous catalyst happens in darkness to ensure the adsorption/desorption equilibrium and stirring is continued to make the mixture a suspension. From the mixture, 1 mL solution is taken out through a 0.45 micrometer syringe for characterization. The experiment is repeated several times to check the catalytic efficiency of ZIF-8, while concentration of catalyst is kept constant as 0.5 g/L. It has been reported that photocatalytic degradation of dye by ZIF-8 followed pseudo-first order kinetic [26]. The simple and proposed reaction mechanisms of degradation by ZIF-8 are shown in Figures 3.8 and 3.9 below:

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3 Heterogeneous catalysis and ZIF-8

O2

-O-2 e-

LUMO

hv

+

Zn

+

NH2

Zn

e-

HOMO

NH2

H+

H2O Methylene blue

+

-OH

Degradation

Figure 3.8: Simple demonstration of methylene blue degradation by ZIF-8 [26].

N

S H3C

N

NH

CH3

CH3 NH2

H3C

N

N

S H3C

H3C

N

N

CH3

CH3

Cl

CH3

OH

OH

NH2

NH2 HOC

H3C

N H3C

SO3H

N OH

H3C

H

N

SO3H

H3C

Figure 3.9: Proposed catalytic degradation of methylene blue [26].

3.4.4 Metal/ZIF-8-carbide heterogeneous catalyst for CO2 hydrogenation ZIF-8-derived metal carbide/ZIF-8 can also be used for the catalytic hydrogenation of carbon dioxide. Usually, in order to evaluate the catalytic behavior of the M-ZIF-8-C catalyst, a fixed bed reactor is used under atmospheric pressure. The catalyst is first

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treated with hydrogen gas for two hours. 0.2 gram of catalyst is weighed and laden into quartz reactor. The feed gas, that is, 20% volume of carbon dioxide and 80% volume of hydrogen gas, is brought in contact with catalyst at 50 mL/min flow rate. The discharged gas products are examined by an online chromatograph that consists of thermal sensor and two columns. The quantity of carbon dioxide gas converted into product can be estimated from its turnover frequency [27], which is defined as:

Mole of carbon dioxide converted per gram of mole into catalyst in per second is known as turnover frequency of carbon dioxide

The hydrogenation of carbon dioxide by heterogeneous catalyst M/ZIF-8-C has been shown in Figure 3.10 below:

O

O

C Carbon dioxide (CO2)

+

H

H H2

Metal/ZIF-8-carbide

H

H

C

H

O

Methanol CH3OH

Figure 3.10: Hydrogenation of carbon dioxide by metal-carbide-ZIF-8 [27].

H

3 Heterogeneous catalysis and ZIF-8

45

3.4.5 Transesterification of bio-glycerol by ionic-liquid-modified ZIF-8 ZIF can be used as a catalyst for the transesterification of bio-glycerol, under constant stirring and refluxing. For this purpose, a four neck round bottom flask is taken, and the glycerol and dimethyl carbonate are weighed and added in the reactor (round bottom flask) in the ratio of 3:1. The magnetic stirrer is also added to the reaction mixture for constant stirring. Later, the catalyst, that is, [APmim] OH/ZIF-8/LDH is introduced to the reaction mixture to catalyze the substrate under nitrogen environment, and the temperature of the reaction mixture is kept at 75 °C. After constant stirring, the liquid mixture is removed from the catalyst by centrifugation and examined under gaschromatography, which is armed with a flame ionization detector. Automatic temperature is used to segregate the different components of the evaporated mixture in the gas chromatograph. This catalyst displays efficient performance in transesterification of bio-glycerol and can be used 4–5 times, without any significant loss in its catalytic efficiency [28]. The catalytic performance is shown below in Figure 3.11. O

OH HO

OH

+

OCH3 H3CO

GLYCEROL

DI-METHYL CARBONATE

[Apmim]OH/ZIF-8/LDH

CATALYST

OH

glycerol on catalyst surface

OH

HO

O O

+

O

2CH3OH

METHANOL CH2OH

GLYCEROL-CARBONATE Figure 3.11: Glycerol esterification by OH/ZIF-8/LDH [29].

3.4.6 Pd nanoparticles@NHC@ZIF-8 as a heterogeneous catalyst for Mizoroki heck cross-coupling The catalytic behavior of the Pd NPs@NHC@ ZIF-8 can be checked by the Mizoroki heck coupling reaction in DMF-water solvent. For this purpose, 1.2 mmol olefin, 1 mmol aryl halide (bromo-benezene), 2.0 mmol Et3N, and 0.08–1 mol% catalyst are mixed in 2 mL of DMF-water (3:2) and moved to a 10-mL vial, and this reaction solution is stirred at a

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Mushkbar Zahra et al.

temperature between 110 and 130 °C. Later, for aryl chloride, tetrabutylammonium bromide (1.0 mmol) is also introduced to the solution. The reaction progress is checked by thin layer chromatography. After completion of reaction, it is allowed to cool down at normal temperature, and by centrifugation, the catalyst is segregated from the reaction mixture. The solvent is also evaporated in a rotary evaporator. In the remaining mixture, ethyl acetate is introduced to the organic layer, washed by saltwater, and dried on MgSO4. Then, the reaction mixture is sieved in intense in vacuo. The impure product is purified by preparative thin layer chromatography using hexane-ethyl acetate of ratio 1:99 or 10:99 [13]. The cross-coupling reaction by using Pd/NPS/NHC/ZIF-8 as a heterogeneous catalyst has been shown in Figure 3.12 below: X R2

+ H2C R1

aryl-halide

Pd/NPS/NHC/ZIF-8

R2

DMF-WATER SOLVENT, Et3N as base temperature 110-130 C R1 olefins

heck-cross coupling product

Figure 3.12: Mizoroki heck coupling reaction by Pd/Nps/NHC/ZIF-8 catalyst [13].

3.4.7 Polyimide/ZIF-8 as an heterogeneous catalyst for Knoevenagel condensation reaction ZIF-8 crystals are embedded on the polyimide membrane and named as PImembrane/ZIF-8 catalyst. In this catalyst, the weight of ZIF-8 is almost 65%. For Knoevenagel reaction, the first step is catalyst preparation. When the catalyst is prepared, it is used for the condensation reaction. Knoevenagel condensation gives different products; one of those products is 2-benzylidene malononitrile (used as an example). For obtaining 2-benzylidene malononitrile (7A) 0.0531 gram of benzaldehyde, 0.1982 gram of malononitrile and 0.0092 gram of catalyst (ZIF-8) are added in 5.0 mL of toluene solvent, and the reaction mixture is run with continuous bubbling of argon gas and stirred for 12 h. The reaction mixture is purified with silica gel chromatography and white solid particles of product are obtained, which are dried overnight. The product obtained is known as Knoevenagel condensation product [8]. The reaction mechanism by using ZIF-8 catalyst is shown below in Figure 3.13:

3 Heterogeneous catalysis and ZIF-8

CN

CHO PI/ZIF-8

NC

47

CN

CN

+ TOLUENE, ROOM TEMPERATURE

R

Malononitrile

benzaldehyde

2-benzylidene malononitrile 94% yield

Figure 3.13: Knoevenagel condensation by PI/ZIF-8 [8]\.

3.5 Conclusion Zeolitic imidazolate framework-8 is widely used as heterogeneous catalyst for multidimensional applications, such as synthesis, condensation reaction, and hydrogenation, oxidation of organic materials, and photo-catalytic degradation of dyes such as methylene blue. General heterogeneous catalysis of other than ZIF-8 catalyst has been compared with that of ZIF-8, and it has been concluded that ZIF-8 has more attractive characteristics than other catalysts like metals, oxide, zeolites, etc. Preparation of heterogeneous ZIF-8 catalysts through different methods has been reviewed from literature. It has been observed that the microporous nature and greater surface area of 5,000 m2/ gram are the attractive attributes of the ZIF-8, which make it ideal in different broad spectrum applications. Heterogeneous ZIF-8 catalysts have been used for different purposes, and they have been found to be interesting in not only activity, but also in selectivity, as palladium-based ZIF-8 catalyst showed 91% hydrogenation of cinnamaldehyde. The reaction solvent used along with the catalyst also affects the catalytic activity of the ZIF-8 catalyst. A few ZIF-8 heterogeneous catalysts can be reused 4–5 times, with no significant loss in efficiency.

References [1] [2] [3] [4] [5]

Christensen, C.H. and J.K. Nørskov, A molecular view of heterogeneous catalysis. The Journal of Chemical Physics, 2008. 128(18): p. 182503. Barrault, J., et al., Catalysis and fine chemistry. Catalysis Today, 2002. 75(1-4): p. 177–181. Schlögl, R., Heterogeneous catalysis. Angewandte Chemie International Edition, 2015. 54(11): p. 3465–3520. Vojvodic, A. and J.K. Nørskov, New design paradigm for heterogeneous catalysts. National Science Review, 2015. 2(2): p. 140–143. Zheng, H.-B., et al., One-step synthesis of ZIF-8/ZnO composites based on coordination defect strategy and its derivatives for photocatalysis. Journal of Alloys and Compounds, 2020. 838: p. 155219.

48

[6]

[7]

[8] [9]

[10] [11] [12] [13]

[14]

[15]

[16] [17]

[18] [19] [20] [21] [22] [23]

[24]

[25]

Mushkbar Zahra et al.

Tran, U.P., K.K. Le, and N.T. Phan, Expanding applications of metal− organic frameworks: Zeolite imidazolate framework ZIF-8 as an efficient heterogeneous catalyst for the Knoevenagel reaction. Acs Catalysis, 2011. 1(2): p. 120–127. Dai, H., et al., Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication, applications and perspective. Coordination Chemistry Reviews, 2021. 441: p. 213985. Jin, R., et al., ZIF-8 crystal coatings on a polyimide substrate and their catalytic behaviors for the Knoevenagel reaction. Dalton Transactions, 2013. 42(11): p. 3936–3940. Kuo, C.-H., et al., Yolk–shell nanocrystal@ ZIF-8 nanostructures for gas-phase heterogeneous catalysis with selectivity control. Journal of the American Chemical Society, 2012. 134(35): p. 14345–14348. Guan, Y., et al., Monodispersed ZIF-8 particles with enhanced performance for CO2 adsorption and heterogeneous catalysis. Applied Surface Science, 2017. 423: p. 349–353. Dang, T.T., et al., Palladium nanoparticles supported on ZIF-8 as an efficient heterogeneous catalyst for aminocarbonylation. Acs Catalysis, 2013. 3(6): p. 1406–1410. Zhu, M., et al., Catalytic activity of ZIF-8 in the synthesis of styrene carbonate from CO2 and styrene oxide. Catalysis Communications, 2013. 32: p. 36–40. Azad, M., et al., Ultra‐small and highly dispersed Pd nanoparticles inside the pores of ZIF‐8: Sustainable approach to waste‐minimized Mizoroki–Heck cross‐coupling reaction based on reusable heterogeneous catalyst. Applied Organometallic Chemistry, 2019. 33(7): p. e4952. Abdelmigeed, M.O., et al., Magnetized ZIF-8 impregnated with sodium hydroxide as a heterogeneous catalyst for high-quality biodiesel production. Renewable Energy, 2021. 165: p. 405–419. Zhao, Y., et al., Pd nanoparticles supported on ZIF-8 as an efficient heterogeneous catalyst for the selective hydrogenation of cinnamaldehyde. Catalysis Communications, 2014. 57: p. 119–123. Ji, H.-B., et al., Environmentally friendly alcohol oxidation using heterogeneous catalyst in the presence of air at room temperature. Catalysis Communications, 2002. 3(11): p. 511–517. Hou, J., et al., Synthesis of CuII/ZIF-8 metal-organic framework catalyst and its application in the aerobic oxidation of alcohols. Chemical Research in Chinese Universities, 2019. 35(5): p. 860–865. Siddiki, S.H., et al., Lewis acid catalysis of Nb2O5 for reactions of carboxylic acid derivatives in the presence of basic inhibitors. ChemCatChem, 2019. 11(1): p. 383–396. Xiao, J.-D., et al., Modulating acid-base properties of ZIF-8 by thermal-induced structure evolution. Journal of Catalysis, 2022. Burton, P.D., et al., Synthesis of high surface area ZnO (0001) plates as novel oxide supports for heterogeneous catalysts. Catalysis Letters, 2010. 139(1): p. 26–32. Interrante, L., et al., Interesterification of rapeseed oil catalyzed by a low surface area tin (II) oxide heterogeneous catalyst. Fuel Processing Technology, 2018. 177: p. 336–344. Butova, V., et al., Hydrothermal synthesis of high surface area ZIF-8 with minimal use of TEA. Solid State Sciences, 2017. 69: p. 13–21. Dhakshinamoorthy, A., M. Alvaro, and H. Garcia, Metal–organic frameworks as heterogeneous catalysts for oxidation reactions. Catalysis Science & Technology, 2011. 1(6): p. 856–867. Jeon, Y., et al., Core-shell nanostructured heteropoly acid-functionalized metal-organic frameworks: Bifunctional heterogeneous catalyst for efficient biodiesel production. Applied Catalysis. B, Environmental, 2019. 242: p. 51–59. Ghayoumian, N., H. Aliyan, and R. Fazaeli, A novel nano‐cotton‐like bismuth oxyfluoride (NC‐BiOF) and a novel nanosheet heterogeneous compound BiOF@ ZIF‐8 as catalyst for the

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[26] [27] [28] [29]

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selective and green oxidation of benzylic alcohols. Journal of the Chinese Chemical Society, 2019. 66(4): p. 363–370. Jing, H.-P., et al., Photocatalytic degradation of methylene blue in ZIF-8. Rsc Advances, 2014. 4(97): p. 54454–54462. Li, Y., et al., Highly dispersed metal carbide on ZIF‐derived pyridinic‐N‐doped carbon for CO2 enrichment and selective hydrogenation. ChemSusChem, 2018. 11(6): p. 1040–1047. Liu, G., et al., Embedded ionic liquid modified ZIF-8 in CaMgAl hydrotalcites for bio-glycerol transesterification. RSC Advances, 2022. 12(7): p. 4408–4416. Chang, C.-W., et al., MgO nanoparticles confined in ZIF-8 as acid-base bifunctional catalysts for enhanced glycerol carbonate production from transesterification of glycerol and dimethyl carbonate. Catalysis Today, 2020. 351: p. 21–29.

Talha Mumtaz, Muhammad Pervaiz✶, Zohaib Saeed, Muhammad Shahzeb, Arooj Ather, Naqeeb Ullah, Rashida Bashir, Muhammad Shahid Cholistani

4 Homogenous catalysis using ZIF-8 Abstract: The studies about ZIFs indicate that highly commendable porosity and topology are factors that make them feasible for catalytic reactions. ZIF-8 structure can be studied by different analytical techniques. ZIFs have resemblance with topology of Si-O-Si structure present in zeolites. SEM forms various micrographs that had assisted us in characterization of ZIF-8. Afterwards, it had made possible the use of ZIF-8 commercially as a catalyst. ZIF-8 samples were prepared in different solvents like methanol (MeOH), dimethyl formamide (DMF), and dimethylsulfoxide (DMSO). DMSO gave well dispersed frameworks of ZIF with enhanced porosity that was further used for CO2 adsorption. Knoevenagel condensation is also aided by ZIF-8 catalyst, as supported by various characterization techniques such as XRD, SEM, TEM, TGA, etc.

4.1 Introduction ZIF stands for zeolitic imidazolate framework. ZIFs came under light recently; since then, these frameworks have got the attention of researchers and are being used in a number of research projects due their capability to act as an excellent catalyst. ZIFs have resemblance with topology of Si-O-Si structure present in zeolites. Si-O-Si angle is found to be around 145 degrees, very similar to the one present inside the framework of ZIFs. They are unique and that makes them favorable in a number of catalytic reactions. Major frameworks of ZIFs include ZIF-76, ZIF-67, and many others. Not only do they show excellent catalytic activities, but these frameworks have also made it to commercial scale production. Primary focus will be given to ZIF-8 in this particular chapter [1]. The figure demonstrates a clear outlay about formation of a metal organic framework. Primarily, in a metal organic framework, chelates surround the central metal atom resulting in a repeated three dimensional structure. The studies about ✶

Corresponding author: Muhammad Pervaiz, Department of Chemistry, Government College University, Lahore, Pakistan, e-mail: [email protected] Talha Mumtaz, Zohaib Saeed, Muhammad Shahzeb, Arooj Ather, Naqeeb Ullah, Muhammad Shahid Cholistani, Department of Chemistry, Government College University, Lahore, Pakistan Department of Chemistry, The University of Lahore, Lahore, Pakistan Rashida Bashir, Division of Science and Technology, University of Education, Lahore, Pakistan

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1D

2D

+

3D

Figure 4.1: Illustration of metal organic framework in 1D, 2D, and 3D ways.

ZIFs indicate that highly commendable porosity and topology are factors that make them feasible for catalytic reactions. ZIF-8 [2] structure can be studied by different analytical techniques as shown in Figure 4.1.

4.2 Structure of ZIF-8

ZIF-8 with sodalite structure Figure 4.2: Structure of ZIF-8 with sodalite.

The structure clearly depicts high sodalite repeating structure in ZIF-8. Sodalite is a mineral of tectosilicates, accompanying zeolites, and possessing a hexatetrahedral structure. Due to close resemblance with sodalite, ZIF-8 is said to have a sodalite structure. A reaction is carried out between Zinc Nitrate and 2-Methylimidazole ring, and a ZIF-8 framework is formed. ZIF-8 has been used in a number of applications

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like drug delivery after studying Kinetics. Thermal stability and high reactivity are other characteristics of various processes having ZIF-8 as shown in Figure 4.2 [3]. The scanning electron microscope (SEM) can make us visualize images that are under 10 nm size; it helps us to study porosity accompanying the product. SEM forms various micrographs that had assisted us in characterization of ZIF-8 [4]. Afterwards, it had made possible the use of ZIF-8 commercially, as a catalyst. ZIF-8 can be synthesized by a number of methods: some are conventional like solvothermal, but recently, many advanced techniques are being introduced that provide us with better yield and require less time. One such process is Knoevenagel (a condensation reaction aimed at the formation of alpha-beta unsaturated ketone).

4.3 Synthesis methods Table 4.1: Various methods deployed for synthesis of ZIF-8. Synthesis methods Zn+ MeIM Synthesis conditions    

Solvothermal Sonochemical Mechanochemical DGC

  . .

  . 

 °C,  h, DMF as solvent  °C,  h, DMF as solvent  min, no solvent  °C,  h, HO as solvent

The table clearly shows various methods deployed for synthesis of ZIF-8. The top two processes are solvothermal and the rest follow different procedures. It is interesting to note that all these processes have a maximum time limit of 24 h. Nevertheless, using different methods and different conditions and then, comparing them is highly commendable. A comparison shows the method that has to be employed under different conditions. Characterization is, thus, a step that lies ahead as shown in Table 4.1. MeIM stands for (2-methylimidazole), SBET stands for (specific surface area), Vpore stands for (pore volume), and Sext (surface area [external]) in the table. Heterogenous catalysis is that branch of catalysis in which reactants and catalysts are in different phases. In other words, reactants and catalyst show notable disparities. ZIF-8 has proven to be a useful heterocatalyst in processes like CO2 adsorption and Knoevenagel condensation. The data obtained by isotherms clearly depicts that ZIF-8 has proven to be promising in the aforementioned processes. Guan and coworkers have really researched well on these processes and made it easy for us to continue robust research on this particular aspect regarding ZIF-8. ZIF-8 has become a contemporary research topic for a number of leading researchers [5].

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4.4 ZIF-8 as catalyst in CO2 adsorption and Knoevenagel process ZIF-8 samples were prepared in different solvents like methanol (MeOH), dimethyl formamide (DMF), and dimethylsulfoxide (DMSO). DMSO gave well dispersed frameworks of ZIF with enhanced porosity that was further used for CO2 adsorption [6]. Other solvents also showed great results. Using DMSO as a solvent, 12 mmol of 2-methylimidazole and 3 mmol of Zn(NO3)2.6H2O solutions were prepared separately in vials, mixed afterwards, and then subjected to constant magnetic stirring at 313 K of temperature. After 30 min, the white solid amassed in colloidal solution is separated using centrifugation followed by washing with methanol. It is then allowed to dry for a day at 333 K. Afterwards, characterization was done using CO2 isotherm and studying catalytic activity [7]. The study showed very promising results, as you can see in the figure mentioned above comparing SEM, TEM, and particle property. The figure shows that use of MeOH and DMF results in agglomeration of particles, but DMSO, when used as a solvent, resulted in no agglomeration of particles. Thus, these characterizations aid us a lot in opening up different disciplines to study further. For catalytic activity, Knoevenagel condensation was carried on: chemicals used were n-dodecane and benzaldehyde (in the ratio 1:1). The solvent used was tetrahydrofuran (THF). ZIF-8 was added as a catalyst. Afterwards, malonitrile solution was prepared separately with THF as solvent, and then, added to aforementioned mixture. Here, ZIF-8 [8] was present in solid form, so at first, it is dispersed by converting it into a liquid form aided by magnetic stirring and then added to the solution for reaction. The next step after addition of malonitrile is stirring, and it is stirred at 303 K. Results obtained were studied through gas chromatography as shown in Figure 4.3. The XRD pattern suggests, sharper the peak, more the crystallinity. However, here, in this case, it is quite evident that differences are quite small, but DMSO has a slight edge over the others. The yields obtained paint a rosy picture as supported by FTIR and SSNMR The yield for ZIF-8 prepared in MeOH as a solvent was recorded to be 75.4%. The yield for ZIF-8 prepared in DMF as a solvent was recorded to be 46.5%. The yield for ZIF-8 prepared in DMSO as a solvent was recorded to be 32.1%. It was ensured that all solvent was completely dried, and the product obtained was then analyzed. So, yield accuracy and precision is quite good [5]. Thermogravimetric analysis suggests that at higher temperature, that is, at 550 °C, the product disintegrates but at temperatures around 350 °C, it shows that it can prove useful in a number of applications. As depicted in Figures 4.4 and 4.5. One of the most interesting applications in which ZIF-8 could be used is in adsorption of CO2. CO2 emission has increased exponentially in the last few years, and

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Simulated 5

10

15

20 25 25 (degree)

30

35

40

Figure 4.3: XRD patterns of ZIF for methanol (green), DMF (blue), and DMSO (red), respectively.

100

3.5%

Weight Lose (%)

80

60

40

20

10

50

100

200

300

400

500

600

700

Temperature (°C) Figure 4.4: TGA curves of ZIF in different solvents MeOH (black), DMF (blue), and DMSO (red).

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1.6

Adsorbed amount (mmol/g)

1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 0.0

0.4

0.8

0.12

0.16

0.20

P/P0 Figure 4.5: CO2 isotherm of ZIF with MeOH (blue), DMF (red), and DMSO (black) solvents.

it has resulted in a number of health hazards. ZIF-8 has got larger BET surface area when DMSO is used a solvent and it has shown promising results. The conditions are quite favorable: 1 atm pressure and 298 K temperature. Though adsorption of CO2 by using ZIF-8 is not much, as compared to other frameworks, stability at high temperatures favor its use for commercial purposes. The adsorption of CO2 by ZIF-8 when MeOH is used as a solvent is 1.1 mmol/g. The adsorption of CO2 by ZIF-8 when DMF is used as a solvent is 1.27 mmol/g. The adsorption of CO2 by ZIF-8 when DMSO is used as a solvent is 1.48 mmol/g. Knoevenagel condensation finds its application in vegetable oil transesterification. Even at low temperatures, activity is favored by Knoevenagel condensation [9]. Studies showed that the external surface area of ZIF-8 is more important as compared to internal area. As mentioned earlier, reaction of benzaldehyde with malonitrile aided by ZIF-8 showed good results. The reaction time and conversion percentage verify that all such reactions maybe facilitated by ZIF-8. Even among them, DMSO, when used as a solvent, had shown no agglomeration of particles.

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150

Conversion (%)

120

90

60

30

0 0

4

8

12

16

20

Reaction time (h) Figure 4.6: Graph showing Knoevenagel condensation reaction conversion with reaction time.

4.4.1 Future prospects ZIF-8 catalyst is found to be excellent in CO2 adsorption. Researches must be carried out in this particular field to adsorb gases similar to CO2, so that environmentfriendly atmosphere may be possible, with lesser toxic chemicals in air. Not only this, processes like Knoevenagel condensation must be researched thoroughly to get better yield [10]. Other processes must be carried out to check the activity of ZIF-8 on processes resembling Knoevenagel condensation.

4.5 Conclusion Porosity and topology are very important factors in checking MOF feasibility to carry out chemical reactions. Different methods like solvochemical methods are used for ZIF-8 preparation. In CO2 absorption and Knoevenagel condensation for conversion in transesterification, ZIF-8 is used as catalyst. For efficient results and to get batter yield, they should be used. Depending on the solvent medium, results may vary from bad to acceptable.

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References [1]

Venna, S.R., J.B. Jasinski, and M.A.J.J.O.T.A.C.S. Carreon, Structural evolution of zeolitic imidazolate framework-8. National library of medicine. 2010. 132(51): p. 18030–18033. [2] Chen, B., et al., Zeolitic imidazolate framework materials: Recent progress in synthesis and applications. Journal of Materials Chemistry A. 2014. 2(40): p. 16811–16831. [3] Kaur, H., et al., Synthesis and characterization of ZIF-8 nanoparticles for controlled release of 6-mercaptopurine drug. Journal of Drug Delivery Science and Technology, 2017. 41: p. 106–112. [4] Cravillon, J., et al., Formate modulated solvothermal synthesis of ZIF-8 investigated using time-resolved in situ X-ray diffraction and scanning electron microscopy. CrystEngComm. 2012. 14(2): p. 492–498. [5] Lee, Y.-R., et al., ZIF-8: A comparison of synthesis methods. Chemical engineering. 2015. 271: p. 276–280. [6] Feng, X., T. Wu, and M.A.J.J.O.C.G. Carreon, Synthesis of ZIF-67 and ZIF-8 crystals using DMSO (Dimethyl Sulfoxide) as solvent and kinetic transformation studies. Journal of crystal growth. 2016. 455: p. 152–156. [7] Lu, G. and J.T.J.J.O.T.A.C.S. Hupp, Metal− organic frameworks as sensors: A ZIF-8 based Fabry− Pérot device as a selective sensor for chemical vapors and gases. National library of medicine. 2010. 132(23): p. 7832–7833. [8] Fairen-Jimenez, D., et al., Opening the gate: Framework flexibility in ZIF-8 explored by experiments and simulations. National library of medicine. 2011. 133(23): p. 8900–8902. [9] Nguyen, L.T., et al., Metal–organic frameworks for catalysis: The Knoevenagel reaction using zeolite imidazolate framework ZIF-9 as an efficient heterogeneous catalyst. Catalysis Science & Technology. 2012. 2(3): p. 521–528. [10] Xiao, T. and D.J.M.T.E. Liu, Progress in the synthesis, properties and applications of ZIF-7 and its derivatives. Materialstoday Energy. 2019. 14: p. 100357.

Mushkbar Zahra, Zohaib Saeed✶, Muhammad Pervaiz, Rashida Bashir, Talha Mumtaz, Rizwan Sikandar, Umer Younas, Ayoub Rashid, Ahmad Adnan

5 Wastewater treatment: An overview Abstract: With the increasing environmental pollution due to urbanization, industrialization, and the unbalanced use of natural resources, there is a necessity for the introduction of cost effective strategies for environmental remediation. To alleviate water pollution, conventional methods, that is, preliminary, primary, secondary, tertiary, and physiochemical and biological treatments are not sufficient. To combat the alarming levels of wastewater, there is a dire need to use sustainable, effective and low-cost technologies. ZIF-8-based multi-dimensional composites have been proposed to treat wastewater. The exciting attributes of ZIF-8-based composites, such as large surface area and higher adsorption capacity, increase their removal efficiency of noxious substances. A variety of synthesis methods of Zeolite Imidazolate Framework-8-derived composites have been discussed in this chapter. Multi-functional ZIF-8 composites have been used to remove toxic dyes, namely, Rhoda mine b and methylene blue from wastewater. The AgBr/ZIF-8 composites have been found to be the best de-grading material for dyes as their efficiency is 99.5% under visible light. This chapter also sheds light on a number of applications of ZIF-8 for wastewater treatment.

5.1 Introduction Water is the basic need of life and it is impossible to exist without it. Due to the increase in manmade activities, gigantic amount of waste is produced. This waste not only contaminates the soil and atmosphere but also disturbs the purity of ground water. Population has been increasing everyday, which is estimated to reach 9.6 billion by the year 2050 [1]. To meet the requirements of the growing population, economic development is leading to the production of enormous amount of waste. With the increase in urbanization and industrialization, solid and water waste management has become a big challenge for scientists [2, 3]. It has been found that 80% of the wastewater in Pakistan is produced by industries such as petrochemicals, paper and pulp, ✶

Corresponding author: Zohaib Saeed, Department of Chemistry, Government College University, Lahore, Pakistan, e-mail: [email protected] Mushkbar Zahra, Muhammad Pervaiz, Talha Mumtaz, Rizwan Sikandar, Ayoub Rashid, Ahmad Adnan, Department of Chemistry, Government College University, Lahore, Pakistan Umer Younas, Department of Chemistry, The University of Lahore, Lahore, Pakistan Rashida Bashir, Division of Science and Technology, University of Education, Lahore, Pakistan

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cement, polyester yarn, fertilizer, food dispensation, tanneries, processing plant, textile and sugar industries etc.. It has been projected that 2,000 million gallons of wastewater produced by the community is discharged daily to local water bodies. Cities are the major contributors to wastewater production in this country. It is a clear observation that the industrial wastewater produced, which is 0.876 × 109 m3/yr., is directly used for irrigation purpose whereas that discharged into water bodies is almost 0.146 × 109 m3/yr. Pakistan has become a water deficient country now. Hence, there is a dire need to purify the wastewater. Researchers have been following different methods to treat the wastewater, that is, physiochemical treatment, biological treatment, sludge treatment, etc. Recently, modern methods based on zeolite imidazolate framework-8 have been introduced to decontaminate the wastewater [4]. Zeolitic imidazolate framework-8 (a sub-branch of MOF) has a micro porous structure and consists of a 4-joint four-hedral network in which metal ions like zinc and cobalt are connected by nitrogen atoms in ditopic imidazolate anions [5]. Due to the structural elasticity, which permits cogent design of the aperture dimensions and outward functionality, high chemical asset, and thermal constancy, even when temperature is about 500 °C, zeolite imidazolate framework-8 has proved to be a latent substance for hydrogen gas stowage, carbon dioxide attachment, saturated-unsaturated hydrocarbons segregation, and mixed reactions. Among the zeolite imidazolate framework family, zeolite imidazolate framework-8 (zinc 2-mIM) is now most broadly examined for a broad spectrum use [6]. ZIF-8 is prepared by different methods in various organic solvents, that is, dimethylformamide and methanol. Physiochemical properties of the ZIF-8 composites manufactured by different methods have been matched with the properties of ZIF-8 obtained by the electrical chemical method, and difference in their properties was demonstrated in the condensation reaction of Benz aldehyde and malononitrile. The viability of doping of Fe3O4 composites with ZIF-8 was also studied [7]. The contaminated water passes through different stages –prehandling, crucial handling, and auxiliary-handling and third-level handling of wastewater. In pre-handling, the contaminated water undergoes sedimentation (coagulation). In the second step, it passes through coagulation, flocculation, and precipitation. After the precipitation of wastewater, its biodegradation, filtration, and adsorption are carried out whereas in last step, it is passed through oxidation and membrane filtration [8]. However, currently, modern methods based on ZIF-8 composites have been introduced to decontaminate the wastewater, in which the pollutants are removed by adsorptive removal in which mainly organic pollutants, that is, phenol are removed, and photo catalytic removal happens (photo catalytic oxidation of wastewater is carried out). ZIF-8 can be combined with different functional materials such as oxide, metal nanoparticles, fibers, enzymes, and carbon nanotubes graphenes, POMs, QDs (as shown in Figure 5.1) and polymers for better efficiency [9]. This chapter highlights the technologies based on the ZIF-8 composites, which can grab the attention of the reader, and also discusses the old methods of wastewater treatment and the strategies to synthesize ZIF-8 composites.

5 Wastewater treatment: An overview

Oxides

61

Carbon nanotubes Graphenes Metal NP’s

Enzymes ZIF-8

Polymers

QDs

Fibers POMs

Figure 5.1: ZIF-8 combined with functional materials [9].

Tao et al. (2021) synthesized iron-nickel-based ZIF-8 sample to catch contaminants such as MG from the polluted water, which is the result of industrialization and urbanization. The removal efficiency of ZIF-8 for Malachite Green was checked and it was found to be more than 99% when the original Malachite Green weight was 50 mg/L. For analyzing ZIF-8 characteristics, different techniques, such as XRD, FTIR, SEM and GC-MS. X-ray diffraction, revealed that the existence of metals has no effect on the configuration of Zeolite-Imidazolate-Framework-8 and this composite had characteristic peak around 44.8 °. Gas chromatography-mass spectrometry shows that the ZIF-8 Fe/Ni degrades the malachite green into two products successfully. The overall dye-extraction by the catalyst was found to be 92%, which showed that ZIF-8 composite can be a favorable choice for handling of polluted water [10]. Ting et al. (2018) synthesized modern mixed ultra-filtration membrane of ZIF-8. The synthesized Poly Acrylic Acid/ZIF-8/PVDF composite showed comparatively great water fluidity and efficient nickel ion removal from salty wastewater. XPS showed that efficient Nickel (II) removal can be credited to attraction between nickel and the -OH-group of the ZIF-8 and the –COOH group of the poly acrylic acid. Zeolite-imidazolateframework-8 could easily bind nickel metal ion as compared to poly acrylic acid, with a slight effect created by sodium ions present in the wastewater. Percolation study revealed that the small amount of ZIF-8 membrane can efficiently purify salty water and remove the nickel metal ion. Hence, modified ZIF-8 composite membrane exhibited an encouraging capability to decontaminate the wastewater [11]. Zahra and her co-workers (2016) proposed the method of fabrication of microporous carbons by the carbonization of Zeolite Imidazolate Framework-8, which were known as ZIF-8 modified carbon nanoparticles, and characterized them by Scanning and Transmission Electron microscopy. It disclosed that they sustain the original morphology and structure at various temperatures. The carbon nanoparticles fabricated at

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1000 °C showed excellent adsorption capabilities (186.3 mg/g) compared to nanoparticles synthesized at 600 °C (which showed adsorption capacities 49.5 mg/g). The superficial properties of the particles have been examined by different techniques. The zeta potential of samples confirmed that the charge on the surface of the carbon nanoparticles varies from positive (ZIF-8) to negative. The Zeolite Imidazolate Framework-8-modified carbon NPs were known to have excellent absorption capacity for water pollutants due to their acceptable adsorption properties and effectual wet ability [12]. Ming-yue et al. (2021) studied that due to the spongy nature of Zeolitic imidazolate framework-8/polymer composite membrane, they are efficient in gas separation, catalysis, and in biotechnology. The hydro stability of ZIF-8 Nano composites was discovered and under suitable conditions, ZIF-8 composites membranes were set on the dopamine-adapted polysulfone substrates. The doping of DNA molecules meaningfully improved the water attraction of the composite membrane. ZIF-8 composites with DNA-molecules showed greater water fluidity than that of pure ZIF-8 composites supplemented with greater rebuffs for dyes and inorganic salts ions. The DNA-modified ZIF-8 composites exhibited higher water constancy and anti-entangling property during percolation tests. For the stability of ZIF-8 composites, the use of biological macromolecules assists the possible applications for ZIF-8 for pollutant water remedy [13]. J.J et al. [14] fabricated ZIF-8 membranes. It was studied that the stability of the ZIF-8 particles against scattering in water could be maintained by a coating of poly (sodium 4styrenesufonate). It consequently permitted the appropriate development of thin film nanoparticles membrane with equivalent characteristics. The porousness of pure water of thin film nanoparticles membrane improved meaningfully with triethylamine. It is further verified that due to stable ZIF-8 particles, thin film nanoparticles membrane has appreciable inflammation resistance to the produced water than the thin film composites membrane [14].

5.2 Conventional strategies for wastewater treatment Over the last 30 years, water and soil contamination have become a big dilemma for scientists and researchers, but mainly for the industrial world. Along with domestic and agricultural activities, industries are equally responsible for the production of huge amount of water waste, which is discharged into soil and water bodies, due to which soil properties such as structure, porosity, and quality has been disturbed. Hence, constant efforts should be made for the treatment of wastewater and for the protection of water resources. Generally, orthodox wastewater treatment consists of a combination of physical, biological, and chemical methods to remove the toxic effluents from the contaminated wastewater [8]. Some common ways to treat wastewater are as followed shown in Figure 5.2 [15].

5 Wastewater treatment: An overview

Old technologies for waste water treatment

Preliminary treatment – Removes granular solid particles

Primary treatment – Removes organic and inorganic solids

63

Drops of waste/polluted water

Secondary treatment –Removes suspened solids

Figure 5.2: Conventional methods of wastewater treatment [8].

5.2.1 Initial handling Granular and bulky materials are removed in this step. This treatment also aids to minimize the size of large entrained, adjourned, or fluctuating solids particles. The solid materials include pieces of cloth, papers, plastics, trash, wood etc. and some fecal substances. Some removed materials from wastewater in this step also involve heavy inorganic solid stuff such as shingle, grit, metallic, glass. These substances are known as gravel and include undue quantities of lubricants and greases [16].

5.2.2 Basic strategy The first step is proposed in order to remove the large solid particles from wastewater by two methods, sedimentation and flotation. In this treatment, almost 65% of the oil and grease, 50–70% of the suspended solid particles, 25–50% of the incoming biochemical oxygen demand, organic nitrogen, phosphorous is taken out from the wastewater, but colloidal and ionized ingredients are not affected [17].

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5.2.3 Subordinate treatment The solid particles of wastewater that remain untreated in the basic handling are removed in this step. The distribution of the effluents is 65% dissolved solids, 30% suspended solids, and 6% colloidal solids. The objective of the primary treatment is to eliminate the maximum amount of unsettled solids. Settling tanks are used (in basic handling) to take out the relaxed inorganic and organic solid materials from the wastewater. Hence, the waste material obtained from the basic handling of the wastewater mainly consists of dissolved organic and inorganic solid and colloidal substances. The remaining organic solids can be separated by auxiliary handling, which involves the use of micro-organisms in controlled conditions [18].

5.3 Progress in wastewater treatment technologies PROGRESS IN WASTE WATER TREATMENT TECHNOLOGIES

ADVANCED WASTE WATER TREATMENT TECHNOLOGY

SALT REMOVAL TECHNOLOGIES EMERGENCE OF MEMBRANE TREATMENT APPROACH

TERTIARY TREATMENT

PHYSIOCHEMICAL TREATMENT

FREEZE DESALINATION

REVERSE OSMOSIS

COMBINED BIOLOGICAL AND PHYSIOCHEMICAL TREATMENT

ELECTRODIALYSIS

ION EXCHNAGE

Figure 5.3: Progress in wastewater treatment technologies [15].

Primary and secondary treatments largely purify the wastewater from bio-chemical oxygen demand and suspended solids materials. Different treatment technologies have been shown in Figure 5.3 above. However, due to the increase in the number of cases, this type of treatment is inadequate to purify the incoming water and supply reusable water for domestic and industrial reprocessing. Hence, further steps have been designed to remove the additional organic solids and other noxious substances from the wastewater [15].

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5.3.1 Categories of advanced wastewater handling technologies The advanced wastewater handling technologies are of three kinds: – Third-level handling – Physiochemical handling – Mutual handling

5.3.1.1 Third-level handling The handling method that links unit processes to a flow system, such as auxiliary handling, is termed as third-level handling.

5.3.1.2 Physiochemical handling A handling procedure in which physiochemical and biological methods are interlinked to obtain the desired waste is known as physio-chemical handling.

5.3.1.3 Combined biological and physical handling Collective physiochemical and biological handling is distinguished by the required handling objectives. This innovative water handling is applied for the removal of excessive carbon-based and adjourned solid substances, nitrogenous oxygen demand, toxic materials, and nutrients. The old secondary treatment provides biochemical oxygen demand and removes suspended solid substances, but advance wastewater treatment is an efficient method to enhance the domestic water supply [19–21].

5.3.2 Introduction of membrane treatment approach To deal with different treatment situations, chemical and biological treatment technologies have been designed. However, these applications are frequently insufficient for the complete treatment of wastewater; membrane-based physical segregations of water from solids have gained attention nowadays. It is aimed to clean normal and wastewater, and concentrate them into some useful products. It is a FORCE-DRIVEN method and is dependent on the pore-size of the membrane. It separates the solid particles in the incoming feed sample according to the pore size [22].

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5.3.3 Salt removal strategies Desalination is the process of removing liquefied ores (involving brine) from wastewater, ocean water, and saline water. Salt and other solids can be removed from wastewater by four basic strategies, that is, freeze desalination, ion exchange, electro-dialysis distillation, and reverse osmosis. Freezing and distillation involve the elimination of unpolluted water in the form of vapors or frost from saline water. In electro-dialysis and reverse osmosis, membranes are used to isolate the dissolved minerals and salts from wastewater. Over the past few decades, desalination grabbed the attention of scientists and it is extensively used to produce drinking H2O from saline and ground H2O. A detail of the desalination technologies is given below [23].

5.3.3.1 Reverse osmosis In reverse osmosis, salt is removed from the wastewater by pumping it at high pressure through spongy membranes as shown in Figure 5.4. The particles that can block the membranes are first removed from the feed water. The pressure exerted decides the kind of water produced whereas the amount of salt in the feed water sample depends upon the solute [24].

Saline feed water

Pertreatment

High pressure pump

Membrane assembly

Fresh water

Brine discharge Stablized fresh water

Post treatment

Figure 5.4: Flow-sheet diagram of reverse osmosis set-up [15].

5.3.3.2 Electro-dialysis With the help of this method, water is pushed at a minimum pressure between various smooth, parallel, ion-permeable membranes that are arranged in a heap. The cationic permeable membranes are interchanged with the anionic permeable membranes [25].

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At both ends of the membranes, electrodes are set to establish the direct electrical current. The electrical current attracts the ions over the membranes and concentrates them amid alternative duo of membranes. Partly de-salted water is left between the parallel combinations of membranes. Entangling of membranes is not allowed in electro-dialysis. This opposes the flow of ions through the membranes. Irregular devices in the H2O assortment system spontaneously direct the movement of current in the proper track [26].

5.3.3.3 Ion exchange In the ion exchange method, unrequired ions are replaced with required ions as the water passes from IE mastics. For instance, cation interchange mastics have been classically used in domestic and municipal H2O handling plants to eliminate the magnesium and calcium ions from heavy- water, and in factories, to produce extremely clean water [27].

5.3.3.4 Freeze desalination In frozen salt water, ice crystalizes from clean H2O, leaving the liquefied salts and ores in the highly saline-water. The frozen salt energy can concentrate a large amount of water by a smaller consumption of energy. Conventional icing methods consist of the following stages: – Softening of the feed water – Conversion of ice to sludge by crystallization – Ice-saline segregation – Washing of ice – Melting of ice [28].

5.4 Synthesis of ZIF-8 composites for wastewater treatment Though old technologies gained much attention of the scientists and have been successful in purifying wastewater, though not 100%, there is higher need for modern methods of wastewater treatment that can purify the wastewater even more. ZIF-8 and its composites have grabbed the attention nowadays due to their high efficiency in removing pollutants from wastewater. The ZIF-8-based composites for wastewater treatment can be synthesized by different methods given below.

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5.4.1 ZIF-8 synthesis Zeolite Imidazolate Framework-8 is fabricated in the presence of different chemicals, such as zinc nitrate, with six water molecules, 2-methyimidazole, methanol, TiO2 and de-ionized water. For the synthesis of ZIF-8 particles, 0.893 gram (3 mmol) of zinc nitrate and 0.985 gram (12 mmol) of 2-methylimidazolate are taken and dissolved separately in 30 and 20 mL of methanol, respectively, and these solutions are named as A and B, respectively. Next, solution B is gradually added to solution A and the mixture is stirred mechanically. The mixture is then shifted to a Teflonlined autoclave and heated for one day at 140 °C under constant conditions. When the mixture is cooled down in room temperature, it is centrifuged to segregate the precipitates formed from the suspension. The precipitates are washed with methanol many times and white minute particles formed are dried overnight at 60 °C. This sample is titled as S14. By following the same procedure and by changing the concentration of 2-methylimidazolate as 9, 6, 3 mmol, three more samples can also be prepared under the same conditions and named as S13, S12, and S11. By using the above samples, photocatalysts can be prepared as: The S14 sample is calcined for 180 min at 600 °C in a nitrogenous atmosphere. In result, the black particles obtained are marked as s14-n6. S14-n6 is strengthened more at 620 °C for 120 min and the obtained sample is named as S14-N6-N6. The remaining samples are treated the same as S14 [29]. The reaction has been shown below in Figure 5.5. CH3 N

N

2-mIM

+

Zn+2 ZIF-8

Figure 5.5: Formation of ZIF-8 [5].

5.4.2 Fabrication of ZIF-8 nanocrystals The chemicals required for the synthesis of Nano-crystals of ZIF-8 are polysulfone, N-methyl-2-pyrrolidone, Pluronic F127, Puronic P123, and Zn (NO3)2 with six water molecules and 2-methylimidazole. Two hundred mL of methyl alcohol is measured and added to a container, and 2.93 gram of zinc nitrate is added to 200 mL methylalcohol and mixed well. This solution is named as A. Similarly, 6.49 gram of Hmim (2-methylimidazolate) is mixed in 200 mL of methyl alcohol and stirred continuously with a magnetic stirrer. This solution is designated as B. Both A and B solutions are mixed with each other and the resultant mixture appears as a milky suspension after 60 min of stirring. Next, the mixture is centrifuged to obtain crystals, and cleaned with fresh methyl alcohol. The white crystals of Zeolite Imidazolate Framework-8, obtained after centrifugation, are dried at 50 °C overnight.

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5.4.3 ZIF-8 polysulfone composite synthesis: Phase inversion method To prepare ZIF-8 polysulfone composite, polysulfone sphere is prepared, for which, 0.75 g of polysulfone is mixed with 4.25 gram of N-methyl-2-pyrrolidone. This mixture is stirred overnight at room temperature for an efficient mixing. In this mixture, surfactants, that is, P123 and F127 (approximately 0.1-1.0 gram) are added and the entire mixture is stirred again for many hours to obtain a clear/colorless solution. The solution obtained after several hours of stirring is set free for 2–3 h so that all bubbles formed during the reaction may discharge. The above polymer suspension is pumped to a water tank at a speed of 0.2 mL/min by an appropriate stainless steel syringe tip of 18 G size. The air distance is kept approximately at 4 cm. The solid polysulfone spheres are instantly synthesized in water via water /solvent exchange. To remove the remaining N-methyl-2-pyrrolidone, the obtained polymer sphere of polysulfone is placed in water after it is dried for 300 min at 80 °C. ZIF-8 composites are also prepared by the same procedure as followed for the formation of polysulfone sphere but by using F127 surfactant and a syringe tip of 14 G size. Three different samples of ZIF8/Polysulfone can be designed, with weight proportions of 1:1, 2:1, and 4:1. The whole procedure has been mentioned in Figure 5.6 given below:

a

b

o o o oooo ooooo ooooo

Solvent out

water in

Phase inversion to macroporous spheres

Figure 5.6: Schematic diagram of phase inversion method of ZIF-8 by syringe tip a, formation of spongy structure by water/solvent interchange, b [30].

5.4.4 Fabrication of ZIF-8/silica composites The ZIF-8 SiO2 amalgams are synthesized with zinc nitrate, tetraethoxysilane, 2methylimidazolate (2-MeIM), and Pluronic surfactant (P123). A 25 mL of ethanol is taken, and 1.96 gram of surfactant and 0.37 gram of zinc nitrate is added into it. The solution is named as A. Then, 25 mL of deionized water is taken, and 0.81 gram of 2-methylimmidazolate and 1 gram of tetraethoxysilane is added to it. The solution prepared is labeled as B. Next, the A and B solutions are mixed and stirred for half an hour at 40 °C, with a continuous addition of different quantities of tetraethoxysilane, that is, 0, 3, 5, and 7 mmol. A white solution is obtained

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when stirred for a whole one day at 40 °C. This solution is centrifuged to obtain the final product. The centrifuged product is washed with ethanol and desiccated at 50 °C, and designated as ZIF-8/silica composites [31].

5.4.5 Production of ZIF-8 and ZIF-8/TiO2 composites First, 10 mL deionized water is taken, in which 0.3 gram of Zn (NO3)2 is mixed and stirred for 600 s. Similarly, 4.6 gram of 2-mIM is mixed in 71 mL purified water and the solution is mixed for 1200 s. Later, both solutions are mixed and stirred for 240-s and autoclaved at 120 °C for 6 h. The product obtained is centrifuged to get the desired product. Later, the centrifuged product is cleaned with methyl alcohol and water to eliminate the impurities and then dehydrated overnight at 70 °C.

5.4.6 Fabrication of ZIF-8/TiO2 composites 0.1 gram of synthesized ZIF-8 is taken and allowed to react with 40mL of ethyl alcohol. The mixture is stirred for 1200 s at normal temperature. About 0.1 mL tetra butyl titanate is also mixed with the above mixture and stirred for 1200 s again. The solution is moved CH3

+ Zinc nitrate

N

N

2-mIM

120 C, 6 hours

+ ZIF-8

150 C, 12 hours

ZIF-8/TiO2 Figure 5.7: Fabrication of ZIF-8/TiO2 micro-composites [32].

TBOT

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to a 50 mL container. In a 200mL container, 6 mL DI water is mixed and a 50mL Teflon container is set in a 200 mL autoclave. This exclusive set up controls the contact of deionized water and tetra butyl titanate. The autoclave is completely sealed and heated to 150 °C for half-day. With the increase in temperature, hydrolysis of tetra butyl titanate may occur. When the reaction is over, the product is gathered though centrifugation. The centrifuged product is purified by ethyl alcohol and purified water, and then dehydrated at 80 °C for 8 h. The whole process has been explained in Figure 5.7. By following this procedure, nanosphere composites (without ZIF-8 of TiO2) can also prepared [32].

5.4.7 ZIF-8/graphene oxide composites Graphene oxide-modified ZIF-8 composites have been synthesized with nano-sized crystals of zeolite imidazolate framework-8 and highly fluorinated graphene oxide, and identified as highly hydrophobic in nature. The synthesis of graphene oxide and ZIF-8 composites is selected due to the low cost and ease of working. The graphene oxide has various unique properties – structure directing property, coordination modifying, etc. due to which it permits the selective nucleation of ZIF-8 on its surface, which results in localized nucleation, and ZIF-8 nanocrystals of various sizes, interposed in the layers of graphene, are obtained. The micro porous structure of the composites allows fluoride groups to be linked to the graphene oxide. The final composites seem like micro mesoporous. The final hybrid composites have low oil and greater water contact angle as 8 and 1628, respectively, and have rapid kinetics and efficient absorbency for polar/nonpolar organic solvents and oils. Hence, fluorine-rich GO-mediated ZIF-8 composites are successfully utilized in separating oil from water [33]. The formation of fluorine-rich graphene-oxide-based ZIF-8 composites is shown in Figure 5.8 below.

5.5 Modern ZIF-8-based methods of wastewater treatment: ZIF-8 applications Various technologies have been proposed by scientists to treat wastewater in confidence that their harmful effects on the environment can be limited. Some technologies, like biodegradation, coagulation, and flocculation, have been used to purify wastewater from all contaminated pollutants, but they are time-taking, costly and their efficiencies are not idyllic. Certain strategies such as flocculation only minimize the dye-quantity by changing them from one form to another, but in this way, secondary pollutants are formed. Hence, advanced wastewater treatment technologies are needed to be introduced that are cost-effective, environment friendly, and easy to handle. ZIF-8 and its composites are one of the most considered strategies that have been used for the remediation of environment as they have good surface area, which enhances their absorbency

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HF HF HF HF HF HF HF HF HF HF HF HF HF HF HF HF HF HF

CH3

+

Highly fluorinated graphene oxide

N

Zn (II)

N

2-methyl-imidazolate

ZIF-8

Highlty fluorinated graphene oxide/ZIF-8 composites Figure 5.8: Fabrication of fluorine-rich GO/ZIF-8 composites [33].

to remove some dyes from wastewater. It is basically a framework of metal and organic compound, with a tetrahedral structure, which is formed when dimethyl imidazolate cross links with zinc metal ions [10]. ZIF-8-based methods of wastewater treatment are as follows:

5.5.1 Adsorption of ofloxacin on ZIF-8 from wastewater Ofloxacin is successfully removed from wastewater by ZIF-8. Three different experiments are performed to adsorb ofloxacin. A required quantity of zeolite imidazolate framework-8 is taken in to a beaker having a water solution, and constant concentration of ofloxacin is added to it. The mixture is stirred continuously in an orbital shaker at 250 revolutions per min. The solutions sample is then removed and segregated through filtration. The filtered sample is examined by UV-visible spectroscopy, which gives its absorbance peaks against the concentration of ofloxacin solution at 293 nm and 342 nm. The removal efficiency of ofloxacin is 96.3% from a solution of 100 mg/L [34].

5.5.2 Rhodamine B and methyl orange degradation by ZIF-8/silver photocatalyst In a study to examine the degradation rate of ZIF-8/silver-doped photo catalyst, Rhodamine B and methyl orange solution of 100 mL is prepared at a concentration

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of 15 mg//L. In a dye solution, 80 mg/L of hybrid porous composite solution is added. The suspension is formed in darkness and magnetic stirred for half-hour. The stirred mixture is placed under 100 W LED lamps for half-hour. From this suspension, different samples of 5 mL are taken during the reaction time. The spongy photocatalyst, that is, ZIF-8/silver, is separated by the centrifugation at 6000 rmp and the amount of dyes left in the mixture is observed by a spectrophotometer at the maximum adsorption wavelengths of dyes. The confiscation efficacy of Rhodamine B and Methyl Orange has been found to be 93 and 100%, respectively [35].

5.5.3 Hydrocarbon separation by ZIF-8/CF from wastewater ZIF-8/Carbon fiber composites are used to remove the anionic cresol red and cationic methylene blue from wastewater. The removal rate of these two contents is directly proportional to the contact with ZIF-8 surface. The dyes are hydrophilic in nature; so they are soluble in water, whereas ZIF-8 is water-hating in nature. Hence, ZIF-8 cannot take dyes in capillarity tubes. The water-hating nature of ZIF8/CF offers high resistance to water penetration. ZIF-8 shows high hydrophobicity and high removal efficiency of oil than dyes [36].

5.5.4 AgBr/ZIF-8 for purification of wastewater The photo catalytic degradation of dyes is performed in a photochemical reactor in which xenon lamp is also equipped, which is connected with UV and IR cut-off filters, which separates the wavelength between 420–800 nm, respectively. The photo catalytic reactor is brought under Xenon lamp at 15 cm. In each trial, 10 mg/L solution of methylene blue is prepared and 50 mg of catalysts is added to the 100 mL of aqueous solution of methylene blue. To maintain equilibrium of the reaction mixture, it is stirred for one hour in darkness. To remove the catalyst and obtain the final product, centrifugation of 3 mL (approximately) suspension is carried out. The amount of the desired pollutant, that is, methylene blue is examined by ultravioletvisible spectrophotometer at its highest wavelength of 664 nm. Other pollutants, such as methyl orange and Rhodamine B, can also be removed from the wastewater by following the same procedure, as used for methylene blue [37].

5.5.5 ZIF-8/polyvinilidine fluoride for water purification Even stratum of ZIF-8-based PVF membranes is obtained by the contra-diffusion synthesis method. The prepared sample is analyzed by different techniques – XRD, SEM, FTIR, EDX etc. The modified membrane gives maximum H2O flux; approximately

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double that of polyvinylidene fluoride, which shows 65.8 L/m2 hour aqua reflux. The water purifications experiments are performed to examine the best performance and efficiency. The ZIF-8-modified membranes shows efficient performance for removing dyes as they have negative charges in them [38].

5.5.6 Pollutants removal by ZIF-8 Water pollutants can be removed by ZIF-8/wood composites. First, these composites are synthesized by in situ-synthesis. The wood framework in ZIF-8-modified composites allows water transport at a high speed and ZIF-8/wood composites are assimilated in filtration for the treatment of wastewater. About 7.9 wt% ZIF-8 and tri-layered ZIF-8/ wood composites showed an appropriate volume of copper ions solution and also showed excellent reusability and recyclability. The wood-based ZIF-8 composites are low cost, easy to synthesize, and renewable for wastewater remediation purposes [39].

DE = (1-c/c0) ✶ 100% = (1-A/A0) ✶ 100%

5.5.7 ZIF-8 application for methyl orange removal For dye-degradation, 100 mg photocatalyst is taken in a 200 mL beaker, in which 100 mL dye solution is present. To achieve adsorption-desorption equilibrium, the mixture is stirred for half-hour at 25 °C. Next, the mixture is exposed to xenon-lamp radiation. Under continuous mixing, the distance between the xenon lamp and the mixture surface is maintained as 80 cm. To separate the catalyst, the solutions are centrifuged after each half-hour. To compute the amount of methyl orange solution, UV-Visible spectra of solutions are taken. According to Beer Lambert law, the amount of methyl orange is directly proportional to the strength of the adsorption peak. Hence, the efficacy of photo-catalytic degradation is achieved as: In which Co and Ao are the original concentration and absorbance, while C and A are the concentration and absorbance at a certain time, respectively [29].

5.5.8 ZIF-8 derived C-N-ZnO composites for wastewater purification Polluted water has different dues that can be removed by using ZIF-8. The nano-sized ZnO photo catalysts can be formed by the carbonization of ZIF-8 in a nitrogenous atmosphere, which limits the ultra-dispersive zinc into a spongy carbon and by calcination in air, which starts forming ZnO crystals. The photo catalytic degradation of dye is

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examined in sunlight. It was noticed that binary stage synthesis of the photocatalyst and the incorporation of carbon and nitrogen into ZnO crystals enhances the degrading ability of photocatalyst, which gives high removal efficiency of dyes from wastewater [40].

5.6 Conclusion Due to the rapid increase in population, colossal amount of waste is produced as a result of man-made activities, urbanization, industrialization, and the use of natural sources. Waste management has become a big challenge for researchers nowadays as along with soil, water pollution is also increasing day by day. Hence, scientists are struggling to find the best way to exploit or degrade the waste products. Water has a variety of dyes, when it comes to industrial wastewater, and it does not only disturb the water bodies but also spoils the qualities of soil, such as structure, porosity, etc. when discharged into them. Conventional strategies of contaminated water treatment are initial handling, crucial handling, auxiliary handling, and third-level handling but they have not shown 100% efficiency in removing the pollutants. ZIF-8-based modern methods of wastewater treatment are under consideration nowadays as they are less costly, easy to handle, and show high efficiencies in the degradation of toxic dyes. Wood-modified/ZIF-8 composites have been found to be best in removing toxic dyes from wastewater as they are inexpensive and eco-friendly than other ZIF-8based composites.

References [1] [2]

[3]

[4] [5] [6]

Pham, T.P.T., et al., Food waste-to-energy conversion technologies: Current status and future directions. Waste Management, 2015. 38: p. 399–408. Mahajan, S., H. Sadh, and J. Soni, Development of efficient solid waste management system in a town area of Gujarat State: Mahisagar District. International Journal of Advanced Research in Engineering and Technology, 2020. 11(6). Asif, M.B. and Z. Khan, Characterization and treatment of flour mills wastewater for reuse–a case study of al-kausar flour mills, Pakistan. Desalination and Water Treatment, 2016. 57(9): p. 3881–3890. Murtaza, G. and M.H. Zia, Wastewater production, treatment and use in Pakistan. in second regional workshop of the project ‘safe use of wastewater in agriculture. 2012. Lee, Y.-R., et al., ZIF-8: A comparison of synthesis methods. Chemical Engineering Journal, 2015. 271: p. 276–280. Tanaka, S., et al., Size-controlled synthesis of zeolitic imidazolate framework-8 (ZIF-8) crystals in an aqueous system at room temperature. Chemistry Letters, 2012. 41(10): p. 1337–1339.

76

[7]

[8] [9]

[10]

[11] [12]

[13]

[14]

[15] [16] [17]

[18]

[19]

[20] [21]

[22] [23] [24] [25]

Mushkbar Zahra et al.

Park, K.S., et al., Exceptional chemical and thermal stability of zeolitic imidazolate frameworks. Proceedings of the National Academy of Sciences, 2006. 103(27): p. 10186–10191. Crini, G. and E. Lichtfouse, Wastewater treatment: An overview. Green Adsorbents for Pollutant Removal, 2018. p. 1–21. Dai, H., et al., Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication. Applications and Perspective. Coordination Chemistry Reviews, 2021. 441: p. 213985. Zhang, T., et al., Remediation of malachite green in wastewater by ZIF-8@ Fe/Ni nanoparticles based on adsorption and reduction. Journal of Colloid and Interface Science, 2021. 594: p. 398–408. Li, T., et al., Efficient removal of nickel (II) from high salinity wastewater by a novel PAA/ZIF-8/ PVDF hybrid ultrafiltration membrane. Water Research, 2018. 143: p. 87–98. Abbasi, Z., et al., Effect of carbonization temperature on adsorption property of ZIF-8 derived nanoporous carbon for water treatment. Microporous and Mesoporous Materials, 2016. 236: p. 28–37. Zhang, M.-Y., et al., Improving the hydrostability of ZIF-8 membrane by biomolecule towards enhanced nanofiltration performance for dye removal. Journal of Membrane Science, 2021. 618: p. 118630. Beh, J., et al., Development of high water permeability and chemically stable thin film nanocomposite (TFN) forward osmosis (FO) membrane with poly (sodium 4-styrenesulfonate) (PSS)-coated zeolitic imidazolate framework-8 (ZIF-8) for produced water treatment. Journal of Water Process Engineering, 2020. 33: p. 101031. Sonune, A. and R. Ghate, Developments in wastewater treatment methods. Desalination, 2004. 167: p. 55–63. Sivakumar, K. and M. Parvez Ahmed, Impact of water pollution on coconut cultivation in Vellore District, Tamil Nadu, in integrated waste management in India. 2016: Springer, p. 3–11. Pratap, N., et al., The negative and dangerous effects of water pollution and storm water runoff on the environment and the surrounding community. International Journal of Engineering Technologies and Management Research, 2014. 1: p. 185–196. Rusten, B., et al., The innovative moving bed biofilm reactor/solids contact reaeration process for secondary treatment of municipal wastewater. Water Environment Research, 1998. 70(5): p. 1083–1089. Arzate, S., et al., Environmental impacts of an advanced oxidation process as tertiary treatment in a wastewater treatment plant. Science of the Total Environment, 2019. 694: p. 133572. Kurniawan, T.A., et al., Physico–chemical treatment techniques for wastewater laden with heavy metals. Chemical Engineering Journal, 2006. 118(1–2): p. 83–98. Ioannou, L., G.L. Puma, and D. Fatta-Kassinos, Treatment of winery wastewater by physicochemical, biological and advanced processes: A review. Journal of Hazardous Materials, 2015. 286: p. 343–368. Badani, Z., et al., Treatment of textile waste water by membrane bioreactor and reuse. Desalination, 2005. 185(1–3): p. 411–417. Quist-Jensen, C.A., F. Macedonio, and E. Drioli, Membrane technology for water production in agriculture: Desalination and wastewater reuse. Desalination, 2015. 364: p. 17–32. Vourch, M., et al., Treatment of dairy industry wastewater by reverse osmosis for water reuse. Desalination, 2008. 219(1–3): p. 190–202. Al-Amshawee, S., et al., Electrodialysis desalination for water and wastewater: A review. Chemical Engineering Journal, 2020. 380: p. 122231.

5 Wastewater treatment: An overview

77

[26] Mohammadi, T., A. Razmi, and M. Sadrzadeh, Effect of operating parameters on Pb2+ separation from wastewater using electrodialysis. Desalination, 2004. 167: p. 379–385. [27] Da̧browski, A., et al., Selective removal of the heavy metal ions from waters and industrial wastewaters by ion-exchange method. Chemosphere, 2004. 56(2): p. 91–106. [28] Mtombeni, T., et al., Evaluation of the performance of a new freeze desalination technology. International Journal of Environmental Science and Technology, 2013. 10(3): p. 545–550. [29] Zheng, H.-B., et al., One-step synthesis of ZIF-8/ZnO composites based on coordination defect strategy and its derivatives for photocatalysis. Journal of Alloys and Compounds, 2020. 838: p. 155219. [30] Li, L., et al., One-step fabrication of ZIF-8/polymer composite spheres by a phase inversion method for gas adsorption. Colloid and Polymer Science, 2013. 291(11): p. 2711–2717. [31] Hu, X., et al., One-step synthesis of nanostructured mesoporous ZIF-8/silica composites. Microporous and Mesoporous Materials, 2016. 219: p. 311–316. [32] Li, R., et al., Fabrication of ZIF-8@ TiO2 micron composite via hydrothermal method with enhanced absorption and photocatalytic activities in tetracycline degradation. Journal of Alloys and Compounds, 2020. 825: p. 154008. [33] Jayaramulu, K., et al., Biomimetic superhydrophobic/superoleophilic highly fluorinated graphene oxide and ZIF‐8 composites for oil–water separation. Angewandte Chemie International Edition, 2016. 55(3): p. 1178–1182. [34] Yu, R. and Z. Wu, High adsorption for ofloxacin and reusability by the use of ZIF-8 for wastewater treatment. Microporous and Mesoporous Materials, 2020. 308: p. 110494. [35] Abdi, J., Synthesis of Ag-doped ZIF-8 photocatalyst with excellent performance for dye degradation and antibacterial activity. Colloids and Surfaces. A, Physicochemical and Engineering Aspects, 2020. 604: p. 125330. [36] Shahmirzaee, M., et al., Development of a powerful zeolitic imidazolate framework (ZIF-8)/ carbon fiber nanocomposite for separation of hydrocarbons and crude oil from wastewater. Microporous and Mesoporous Materials, 2020. 307: p. 110463. [37] He, Y., et al., Preparation, characterization, and photocatalytic activity of novel AgBr/ZIF-8 composites for water purification. Advanced Powder Technology, 2020. 31(1): p. 439–447. [38] Karimi, A., et al., Contra-diffusion synthesis of ZIF-8 layer on polyvinylidene fluoride ultrafiltration membranes for improved water purification. Journal of Industrial and Engineering Chemistry, 2019. 73: p. 95–105. [39] Zhang, X.-F., et al., In situ growth of ZIF-8 within wood channels for water pollutants removal. Separation and Purification Technology, 2021. 266: p. 118527. [40] Liang, P., et al., Solar photocatalytic water oxidation and purification on ZIF-8-derived C–N–ZnO composites. Energy & Fuels, 2017. 31(3): p. 2138–2143.

Shumila Shaheen, Muhammad Pervaiz✶, Syed Majid Bukhari, Zohaib Saeed, Muhammad Imran, Aemin Ali, Ran Rashad Mahmood Khan, Hazqail Umar Khan

6 Removal of heavy metals using ZIF 8 Abstract: Clean water dictate is growing every day as a consequence of the rapid industrial evolution and population growth. However, due to an insufficient supply of new water sources, there is a requirement for successful, satisfactory wastewater recycling. Many treatment techniques use the reverse osmosis method. Coagulation precipitation and ion exchange methods have been extensively tested, with the ion exchange method being considered the most efficient method. Nevertheless, the existence of heavy metal ions that are non-recyclable, restricts the usage of efficient methods. In this chapter, we evaluate the water-stable metal organic-based framework MOFs, the Zeolite-based imidazolate framework (ZIF-8), associated with the uncomplicated synthesis method for the removal of heavy metals. In this chapter, we discuss the mechanism of heavy metal removal and the factors that influence the percentage efficiency. Applications of ZIF-8-based composites, including drug delivery, catalyst, and electronic devices, are also discussed in detail.

6.1 Introduction With the fast progress of industry, the surroundings have become progressively contaminated with industrial discharge. Among the different synthetic and natural contaminants, heavy metals are extremely noxious and viewed as a key peril for humans. It has become a serious challenge to eradicate these toxic heavy metals from water because of their detrimental ramifications on people. Once ingested by people, heavy metals can usher in lethal obstacles as they cannot be discharged and removed from water. They should, consequently, be eliminated from polluted water to make sure of general health and safety. The major causes of heavy metals are electrification, mining, battery production, smelting, leather, and textile industries. Mercury, arsenic, lead, copper ions, and cadmium are examples of such contaminants must be eliminated

✶

Corresponding author: Muhammad Pervaiz, Department of Chemistry, Government College University, Lahore, Pakistan, e-mail: [email protected] Shumila Shaheen, Zohaib Saeed, Muhammad Imran, Aemin Ali, Ran Rashad Mahmood Khan, Hazqail Umar Khan, Department of Chemistry, Government College University, Lahore, Pakistan Department of Chemistry, The University of Lahore, Lahore, Pakistan Syed Majid Bukhari, Department of Chemistry, COMSATS University Islamabad, Abbottabad Campus, Pakistan

https://doi.org/10.1515/9783110792591-006

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from wastewater. Especially, mercury and lead can destroy the hematopoietic structure and cause damage to the main body parts such as kidneys, liver, and brain, leading to encephalopathy, hepatitis, and hemorrhage, respectively. They also harm the gallbladder and liver, causing cirrhosis and neuritis. Therefore, obliteration of mercury and lead ions from polluted water is an extremely important task [1]. It was determined that the range of copper, cadmium, arsenic, and chromium in the Chinese mitten crab can approach 50.8, 0.262, 0.024, 0.06 mg/kg, approximately [2]. Many techniques have been utilized to eradicate these numerous pollutants, including photocatalytic degradations, adsorption, membrane filtration, chemical precipitation, and biological remediation. Among these techniques, adsorption is considered to be cost-effective because of its cost, general validity for many contaminants, and due to its easy design and operation. Many divergent substances have been viewed as adsorbents, including clay minerals, modified chitosan, activated carbon, and operationalized nanoparticles. Nevertheless, plenty of these materials have drawbacks, such as low selectivity and efficacy, and consequently, empirical implementations of these definite types of substances for adsorbing either antibiotics or metal ions have been restricted as mention in Table 6.1 [3]. Table 6.1: Adsorption capacity of heavy metals by Zif-8 based materials. Zif--based materials

Metals

Adsorption capacity

Surface area

Efficiency

Optimum Reference pH

Zif- and Zif-

Lead (Pb) Mercury (Hg)

. mg/g for (Pb) and . mg/g for Hg

 m/g for Zif- and  m/g for Zif-

.% for Pb and .% for Hg

[]

Chitosan Zif- composite

Cu () Pb ()

. mg/g for Cu and . mg/g for Pb

–

–

–

[]

PAA/Zif-/PVDF

Ni

. mg/g

–

–

.

[]



FeO@Zif-

As ()

–

 m /g

–

–

[]

Zif-/ calcium alginate

Pb ()

. mg/g

–

%



[]

Zif-@Zif-/PAN composite

Cr (V)

. mg/g

 m/g

%

–

[]

Amine-modified Zif-@graphene

Cu+

,. mg/ g

–

–

.

[]

Zif-@PSS

Ni()

. mg/g

–

%

[]

6 Removal of heavy metals using ZIF 8

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Table 6.1 (continued) Zif--based materials

Metals

Adsorption capacity

Surface area

Efficiency

Optimum Reference pH

Magnet responsive-based FeO@Zif-

Cu+

mg/g

–

%

Zif- at Co-Al double layered composite

Cr (V)

 mg/g

 m/g

%



[]

ZnO@ZiF − 

Pb ()

. mg/g

–

–

–

[]

Ni+ Zif@SnO@CoFeO

. mg/g

–

–



[]

ZnS-Zif-

Hg()

. mg/g

–

–

–

[]

Zif-/PET

U(V) . mg/g oxycations

–

–

.

[]

[]

6.1.1 Metal-organic framework MOF has been recognized as an absorptive integrated polymer and is extensively studied as a captivating substance by scientists. MOF consists of ions of metals and peripheral buildings that are part of oxo-clusters uniting organic linkers. The shape of MOF can be modified in a specific range which previously occur and assign potentially for the synergistic meld of effects. ZIFs based materials are involved in diverse fields from the time of their introduction. ZIFs were initially named as MAF-4 and later, properly named as ZIF-8. The chemical notation of ZIF-8 is Zn (Hmim)2 and It compromises 2-methylimidazole with Zn metal. It has a high hydrothermal strength that is appreciably valued as its frame- work is constructed by sturdy links. MOFs have the primacy of polymetallic set and excessive crystallinity in their structure. They have a porous structure, great affinity with polymers, and a higher surface area [17]. Their unique properties and structural heterogeneity make the MOFs as captivating substances for eradicating heavy metals that are toxic. Imidazolate framework has a structure that is similar to zeolite and it is a kind of MOF. It is created in a chemical solution, reacting with Zn, in which imidazolate acts as a natural ligand and zinc acts as an initiator. It is thermally stable within a definite range [18]. The number of publications per year about MOF follow as shown in Figure 6.1.

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3500

number of publications

number of publications

3000 2500 2000 1500 1000 500 0 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019

year Figure 6.1: Number of publications per year for MOF [19].

6.1.2 Synthesis of ZIF-8 Among the different methods of synthesis, including mechanochemical, microwave-assisted method, room-temperature synthesis, and sonochemical, the common method for ZIF-8 synthesis is the solvothermal method.

6.1.2.1 Solvothermal analysis In a solvothermal method, organic solvents act as a reaction medium for the production of IF material. Yaghi et al. were the first ones to prepare ZIF crystals, which were named from ZIF-1 to ZIF-12. These crystals were synthesized in organic solvents like N, N-Dimethylformamide, N, N-di methyl formamide, etc. They also used DMF/DEF/ NMP in the place of previous solvents and made many more ZIF materials of a higher order. Other researchers also prepared ZIF crystals by using these solvents to study the mechanism of formation and other related factors. Yaghi’s method is now been modified. Deprotonating agents such as organic amines were added to DEF or DMF, which assists in material formation. For example, ZIF-78, having a size in the range of microns, is a rod-like hexagonal ZIF and was synthesized with the help of TEA, 30. In the same way, the DMF, with the addition of pyridine at room temperature, formed

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ZIF-90. In the formation of ZIF-76, NaOH was added to DEF and DMF, which enhanced its yield. Methanol is also used in the preparation of ZIF materials. Chen’s group used methanol as the reaction medium to form ZIF crystals, where the layering of 2-methyl imidazole, which contained a reaction medium, was done on aqueous ammonia with five hours of constant stirring. ZIF-8 material can also be prepared on a nanoscale by a simple mixing of methanol solution having Zn(NO3)2 with 2-methyl imidazole at room temperature in a ratio of 1:8 as shown in Figure 6.2 [18]. N CH3 N H + Zn(NO3).6H2O

Complex formation Zn(mim)2(Hmim)2 Zn(mim)2 Zn(Hmim)4+2

ZnN4 formation

ZiF-8 six membered rings

ZiF-8 crystal

Figure 6.2: Synthesis of ZiF-8 by the solvothermal method.

6.2 Heavy metals in wastewater Heavy metals have a definite density around about 5 g/mL or beyond, accompanying greater mass numbers. These elements are considered as extremely dangerous even at the small levels and observed clearly in the crust of earth [20].

6.2.1 Lead Lead is unsurprisingly present in little amounts in the lithosphere and appears as bluish-gray and silver-gray [21, 22]. It is present in canned food, dust, and fossil fuel. Lead pollution in water and environment increases by human activity, for instance, glass making, mining, purifying of metals, and reprocessing of petrol, sand pigments, and paint [23]. Lead is an extremely toxic metal that affects human health as it targets the kidney, brain, and the human nervous system [24].

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6.2.2 Chromium Chromium commonly appears in the lithosphere. Weathering of rocks, biological cycling, and volcanic eruption are the intrinsic causes of chromium in contaminated water [25, 26]. It is present in the ore and not in independent form. It commonly occurs in its hexavalent form in different countries such as Africa, Finland, the USA, India, and the Philippines. Its oxidizing state occurs in the limit of Cr+2 to Cr+6. Nevertheless, the hexavalent state of chromium is more toxic than the trivalent form [27]. A large amount of chromium affects the liver, kidney, and nervous tissue in the human body. It is cancer-causing, resulting in respiratory and stomach cancer [28].

6.2.3 Zinc It is the most important metal in the environment [29]. It is a white-bluish metal and plays a crucial role in the health of humans, even if its large amount produces toxic results. It enters human beings through food and drinking water. Zinc pollution in wastewater takes place usually from phylogenesis sources such as zincfabricating, mining, fertilizers industry, steel production, coal burning, and agricultural. The central nervous system, epidermal, gastrointestinal, reproductive, and skeletal system are the parts of the human body that are mainly attacked medically by zinc deficiency [30]. Surplus zinc causes stomach cramps, vomiting, skin irritation, liver, and kidney failure [31, 32].

6.2.4 Mercury Mercury is a distinct key contaminant registered by USEPA because it can easily enter the endothelial tight junction and affect the fetal brain. A large concentration of mercury Hg (II) triggers disability of the kidney and the pulmonary function, and causes shortness of breath and chest pain. According to the definitive standard, the acceptable range of Hg (II) in surface water is approximately 10 µg/L and in drinking water, it is approximately 1 µg/L [33].

6.3 Methods to remove heavy metals Heavy metal eradication from inorganic sewage can be accomplished by conventional methods. Heavy metals can be eradicated from wastewater through many

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techniques, including coagulation, ion exchange, foam flotation, cementation, chemical precipitation, and electro-deposition.

6.3.1 Precipitation method Heavy metals in inorganic discharge of industries can be extensively removed by the implementation of this method because of its basic framework. These conservative chemical precipitation methods result in indissoluble precipitates of heavy metal ions such as sulfide, phosphate, hydroxide, and carbonate. The mechanism of this method is designed to make indissoluble precipitates by dissolving heavy metals in the given solution. In this method, very small particles are produced, and coagulation, flocculation, and chemical precipitation are employed to enhance their fragment size to separate them as slush. When the metals become solids after precipitation, they can be eliminated, and a small concentration of metal can be removed. The removal efficacy of metals in the target solution may be enhanced to the optimum by adjusting parameters such as initial concentration, temperature, the charge of the ion, pH, etc. The most widely utilized precipitation method is the hydroxide technique due to the reasonable cost of lime, comparative simplicity, and the facility for automated pH control. The solvabilities of the different hydroxides are reduced for pH in the range of 8 to 11 [34].

6.3.2 Coagulation process Electrocoagulation (EC) is a favorable operation attracting the attention of research workers due to its admirable removal efficacy. In EC, reduction takes place at the cathode and oxidation takes place on the galvanic anode in aqueous media when electric current is introduced. Because of the economical availability, iron and aluminum electrodes are frequently utilized. In this method, there is the fabrication of coagulants such as aluminum hydroxide. It is safe and has a high removal efficacy. In EC, solution pH, treatment time, electrode material, and current density play an important part; the amount of space between the electrode and electrolytes also influences the process [35]. Coagulation, integrated with further heavy metals techniques, such as membrane filtration method, flocculation method, and advanced oxidation, is an efficient method to overcome the contaminations produced by heavy metals. Heavy metals can be easily attached with iminodiacetic acid (IDA) and ethylenediaminetetraacetic acid (EDTA) in an aqueous medium. They can also attach to other basic materials that generally reduce the percentage efficacy of heavy metals. Therefore, the oxidation and mineralization of organic matter can be achieved by the Fenton reagent, which is an oxidizing agent. Organic and inorganic

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composites liberate metal ions that change solvated materials into colloidal forms. They accelerate the synchronic transfer of organic matter. Oxidizers are also utilized to alter the valance electrons of heavy metal ions. Natural coagulants such as aluminum and iron-based coagulants partake through the methods of transfer of heavy metals. Coagulants of iron frequently operate a little greater as compared to aluminum-coagulants due to the greater surface area of developing flocculates and extensive pH range. The flocculates created by iron-coagulants are loose, which confirms a high surface area and a three-dimensional framework of adsorbing heavy metal ions. Moreover, the application differs with various heavy metal ions under the same condition of coagulation [2].

6.3.3 Ion exchange method Ion exchange method is the deionization separation method. Anion/cation resin can be interchanged with many unpleasant materials to separate these organic pollutants. This method can irreplaceably function for effluents of industries that hold a small number of heavy metals. Though the eradicating efficacy of the ion exchange method is appreciated, the major disadvantages are sensitivity and high cost, high amount of chloride and pH-of the wastewater [36].

6.3.4 Reverse osmosis method This method involves the separation of heavy metals bypassing via a semi-permeable sheet. This method requires elevated pressure for the eradication of heavy metals. It is mentioned that the elimination efficiencies of arsenic, lead, chromium, and zinc by this method are approximately 95, 93, 92, and 95%, respectively. Even though the percentage of removals of heavy metals is excessive, the major disadvantages of this method are high cost, demands specific chemicals, and persistent membrane fouling. Further, a high quantity of water is also sent out during removal. In addition, together with heavy metal ions, some principal materials are also separated in the reverse osmosis method as depicted in Figure 6.3 [37].

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Precipitation method

Reverse osmosis method

Methods to remove heavy metals

Coagulation process

Ion exchange method

Figure 6.3: Methods to remove heavy metal ions from water.

6.4 The mechanism for removal of heavy metals by ZIF-8 The supportable eradication of heavy metals from an aqueous medium is a topic of great interest. Many techniques are being used to reduce the concentration of heavymetal ions present in wastewater; the reduction targeted at fulfilling the requirements of the EPA- Environmental protection Agency [38]. Nowadays, the MOFs utilization, principally ZIF-8, has captured the attention of many research workers owing to its distinctive properties, which include high adsorption range, large surface area, hydrophobicity, and chemical stability. The priority mechanism fundamental to ZIF-8 efficacy in the removal of heavy metals is its large adsorption capability. Adsorption in wastewater techniques is a physical or chemical method that requires the contaminant collection on the side of an adsorbent when a common interaction between adsorbents and adsorbate is taking place [39]. In the removal of heavy metals, the hydrothermal, adsorption capacity, removal efficiency, and chemical stability are commonly examined by Adsorption capacity: Qc = ðC0 − Ce Þ × v = m

(1)

RE = Ci − Cf =Ci × 100%

(2)

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In equation (1), C0 and Ce represent the initial and equilibrium concentrations, m represents the mass of the given adsorbent in mg, and the value of equilibrium adsorption is given by Qe. Qe is used in the examination of the adsorbent’s adsorption capacity. From equation (2), Ci in mg/L is the initial concentration for the estimation of removal efficacy and the final concentration of ions of heavy metal in wastewater is represented by Cf in mg/L [40, 41]. The efficacy of the adsorbent material is commonly defined by employing kinetic models and adsorption-equilibrium isotherms. The kinetic models relate the adsorption isotherms with the adsorption rate. An example of this is the isotherms given by Langmuir and Freundlich. These isotherms relate the substance adsorbed per unit mass concentration of adsorbent material with the equilibrium concentration [42, 43]. Zhang et al. experimented to determine the adsorption mechanism of ZIF-8 and the efficacy with which copper ions (Cu2+) are removed in aqueous media. An unexpectedly excessive adsorption limit of approximately 800 mg/g of Cu2+, having a fast adsorption time of 30 min, was revealed, resulting in a 97.2% efficacy (removal 97.2%) [44]. ZIF-8 adsorption range is supported by the mechanisms of adsorption, which includes the coordination reaction, surface chemistry, ion-exchange, and hydrophobic interactions [45]. By contrasting X-Ray photoelectron spectroscopy (XPS), Fourier Transform Infra-Red (FTIR) before adsorption, assigned the excessive ZIF-8 Cu2+ sorption owing to the dominant coordination reaction and demineralization joining (N) nitrogen atom on the ZIF-8 junction’s metallic and ionic surface [44]. Liu et al. [46] also worked by the utilization of ZIF-8 in removing arsenite As(III) and arsenate As(V) in the presence of the aqueous medium. The maximum adsorption limit represented by Qmax was calculated to be 49 mg/g for As(V) and 60 mg/g for As(III). This maximum absorption limit is much greater as compared with the other adsorptive materials such as iron laminated zeolite, CuO nana composites, iron chitosan flake, etc. which is differentiated in their study [38, 47]. Zhao et al. [48] organized an experiment for the evaluation of the removal of duplex heavy metal ions (Ni2+, Cd2+, and Co2+), which are four in number, from an aqueous medium by using ZIF-8 for the chemisorptions on these nanoparticles. They utilized ZIF-8, the couple, as basic nanoparticles and in the development of nanoparticles to eliminate duplex heavy metal ions. In his experiment, even if ZIF-8 exhibited characteristics like Cu2+, a surprisingly high ZIF-8 adsorption range was found in the eradication of the duplex heavy metals. ZIF-8 nanocrystal membrane was used with graphene oxide and magnesium hydroxide (Mg (OH) 2) [40]. They evaluated the maximum removal efficacy of Cr(VI) as 98%. There may be different mechanisms that account for the excessive experiences of ZIF, including hydrogen bonding, diffusion, and electrostatic attraction. It was determined that a positively charged superficial of ZIF-8 was present due to the presence of − NH2, = N- groups that are present in imidazolate ligand. It showed protonation when in the aqueous medium, showing that the adsorption of Cr(VI) has electrostatic interaction. The hydroxyl groups, combining with zinc and the formation of Mg(OH)2 along with GO, made the electrostatic interactions with Cr VI) stronger and also reduced it, forming Cr(III). Positively charged

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magnesium interrelated with oxyanion activating chemisorptions and accelerated a basic adsorption root. Zhou et al. studied the utilization of ZIF-8 in synchronic elimination for different pollutants, such as norfloxacin and copper from an aqueous medium. They noticed a large removal efficacy of 80% and 95% for norfloxacin and copper, respectively. However, they observed that the adsorptive mechanism for the complex pollutants was commonly due to the demineralization in the adsorption of Cu(II), while π-π assembling between the benzene loop of norfloxacin and imidazole loop of ZIF-8 was accountable for the adsorption of norfloxacin [49]. Consequently, surface charge, functional groups, or many mechanisms may be employed in removal mechanisms. It was examined that arsenic absorbance in the presence of an aqueous medium is dependent upon the interparticle diffusion close to the previous result. An important point to highlight is that these mechanisms have potency, which is judged and controlled by optimum conditions, including temperature, contact time, pH, and adsorbent features [49].

6.5 Factors affecting the removal efficiency of ZIF-8 6.5.1 PH of solution The pH of the solvent is the principal environmental factor that will affect the chemical properties and surface structure of the ZIF-8 composite, along with the distribution of pollutants in an aqueous medium. For optimum pH, it is examined by different factors, including the kinds of pollutants, reaction processes, and the structure of ZIF-8. When the ZIF-8 composite is utilized to adsorbate pollutants, the solution pH should be correlated with the isoelectric point (pI) of the nanocomposite, which is favorable to the adsorptive reaction. When the overall charge on the interfacial surface of the ZIF-8 is zero, then pH of the solution at that point is called the isoelectric point. When the pH is greater than a point of zero, the interfacial surface charge of ZIF-8 is negative. When the pH is less than the point of zero, the surface charge is positive. According to records, ZIF-8 is positively charged at many ranges of pH. The zeta potential of ZIF-8 begins to decrease when the pH is greater than 8, and it becomes negative at pH 11. The pH can influence the elimination of pollutants by effacing the active sites and the changeability of the adsorptive material. In photocatalytic reactions, it is important to determine the optimum pH that is applicable for the generation of free radicals [17, 50].

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6.5.2 Effect of temperature The efficiency of composites is influenced by temperature, as the optimum temperature is a crucial parameter that affects its efficacy. The diffusion rate of contaminants will increase by the rise in temperature within the optimum range of temperatures. It will induce a high initial dose of adsorption rate. It is an endothermic reaction according to a viewpoint of chemisorptions as it requires a high temperature. If a reaction is exothermic, then a low temperature will be favorable to speed up the reaction. In an experiment by Wang for the adsorption of U (VI) with ZIF-8-based polyacrylonitrile composite ZIF-8/PAN, the method of adsorption was the endothermic process. The collision frequency of ZIF-8/PAN and U(VI) ions was promoted when the temperature increased. The result showed that high temperature is considered beneficial for the removal range of ZIF-8/PAN for U (VI) [51].

6.5.3 Ionic strength The influence on ionic concentration was commonly examined, after the development of ZIF-8 composite, for the management of pollutants, including differently charged particles; K+, NO3, etc. generally interact for the elimination of different contaminants. Fluctuations in this method will alter the electrical and chemical strength of water at the interfacial surface of the adsorptive material. It was important to examine the effect of synchronizing charged particles; mostly it was adsorptive contrast of target pollutants and foreign ions. The coexisting ions will engage the adsorption place, which guides the destruction of the adsorption amount, and its amount will cause modifications, following the different adsorptive mechanisms [52].

6.5.4 Initial concentration and photocatalytic dose Generally, the equilibrium time fluctuates relative to the number of pollutants. Many research workers have deduced that a greater amount of pollutants will affect the removal efficacy. This is the reason that at small concentrations, the active sites of ZIF8 composite are more accessible to pollutants. The pollutants decrease the coherence length of the light quantum into the solution if the absorption of pollutants is high. As a result, it decreases the absorption efficacy of light by the interfacial plane of the photocatalyst [53]. It evaluated the outcome of the ZIF-8-based PTA@AuNP application and an initial amount of tetracycline (TC) for the removal of TC. The high amount of ZIF-8-based PTA@AuNP accelerated the photodegradation of TC and approached the highest for an amount of approximately 0.6. it was observed that the high concentration is not applicable for the efficiency of photodegradation because the high concentration of TC will be absorbed on the photocatalytic surface, thereby inhibiting

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the immediate contact between the TC molecules and the oxygen species. It could be concluded from the reflection time that the photodegradation efficacy for it accelerated the first time and approached the adsorption equilibrium after ten minutes [54].

6.6 Applications 6.6.1 Catalyst As ZIFs are porous materials, just like other porous materials such as aluminosilicate zeolites, almost 181 ZIF and materials based on ZIFs are being used as catalysts. ZIF crystal substances can also be used as mobile catalysts for several reactions, including monoglyceride synthesis, Friedel- craft acylation, knoevenagel reaction, transesterification, epoxidation, hydrogen production, and oxidation. ZIFs are also used in heterogeneous catalysts. ZIFs used as heterogeneous catalysts for the reaction known as Knoevenagel of malononitrile with benzaldehyde are ZIF-8, ZIF-9 and ZIF-10, forming benzylidene malononitrile [55].

6.6.2 Sensing and electronic device Due to the attractive properties of ZIFs such as adjustable pore size, good textural properties, and ease of function, they have been used in electronic devices and sensors. ZIFs have outstanding selective absorption qualities due to which they are used in chemical sensing. Their high microporosity and hydrophobicity make them a good candidate for their employment in applications with low dielectric constants. The use of ZIF-8 as a sensor was first done by Hupp and co-workers during the construction of the Fabry- Perot-based device, which acted as a careful devise sensor for gases. When this ZIF-8 was exposed to the vapor of water-ethanol mixtures having different ethanol concentrations, it showed chemical selectivity. ZIFs are also used in biosensor construction as matrices. For example, electrochemical biosensors that are ZIF-based have been synthesized for the measurement of in vivo electrochemicals such as glucose. ZIFs are also used as the matrix in co-immobilization electrocatalysts and dehydrogenases. ZIF-67, ZIF-68, ZIF-7, and also ZIF-8 have been used for this purpose [56].

6.6.3 Drug delivery Due to the good thermal properties, chemical stability, tunable properties, and pHsensitive releasing properties, ZIFs are being used widely in drug delivery or in the control of drug molecule release. ZIF-8 is being used in the drug delivery of anti-

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cancerous agents. As ZIF-8 does not decompose in water and NaOH but decomposes in acids, Sun et al. found that because of the unstable pH properties of ZIF-8, it can also be used for drug deliveries. Due to its good textural properties and porous structure, ZIF-8 also has a very good loading capacity for anti-cancerous drugs [57].

6.7 Conclusion ZIF-8 exhibits versatile potential for the transfer of heavy metals from aqueous media. This chapter shows that different heavy metals can be moved from an aqueous medium using ZIF-8-based materials. However, there is a necessity to survey other kinds of heavy metals like iron, thallium, and mercury, which are dangerous to humans even at minor concentrations. This book chapter shows the mechanism of ZIF-8-based materials and identifies factors such as pH, temperature, and ionic concentrations that affect the mechanism.

References [1]

Ahmad, K., et al., Effect of metal atom in zeolitic imidazolate frameworks (ZIF-8 & 67) for removal of Pb2+ & Hg2+ from water. Food and Chemical Toxicology, 2021. 149: p. 112008. [2] Tang, X., et al., Chemical coagulation process for the removal of heavy metals from water: A review. Desalination and Water Treatment, 2016. 57(4): 1733–1748. [3] Zhou, L., et al., Simultaneous removal of mixed contaminants, copper and norfloxacin, from aqueous solution by ZIF-8. Chemical Engineering Journal, 2019. 362: p. 628–637. [4] Wang, C., et al., Efficient Removal of Cu (Ii) and Pb (Ii) from Water by in Situ Synthesis of CsZif-8 Composite Microspheres. Available at SSRN 4058887. [5] Li, T., et al., Efficient removal of nickel (II) from high salinity wastewater by a novel PAA/ZIF-8/ PVDF hybrid ultrafiltration membrane. Water Research, 2018. 143: p. 87–98. [6] Huo, J.-B., et al., Magnetic responsive Fe3O4-ZIF-8 core-shell composites for efficient removal of As (III) from water. Colloids and Surfaces. A, Physicochemical and Engineering Aspects, 2018. 539: p. 59–68. [7] Song, Y., et al., Facile fabrication of ZIF-8/calcium alginate microparticles for highly efficient adsorption of Pb (II) from aqueous solutions. Industrial & Engineering Chemistry Research, 2019. 58(16): 6394–6401. [8] Yang, X., et al., Effective strategy to fabricate ZIF-8@ ZIF-8/polyacrylonitrile nanofibers with high loading efficiency and improved removing of Cr (VI). Colloids and Surfaces. A, Physicochemical and Engineering Aspects, 2020. 603: p. 125292. [9] Wei, N., et al., Fabrication of an amine-modified ZIF-8@ GO membrane for high-efficiency adsorption of copper ions. New Journal of Chemistry, 2019. 43(14): 5603–5610. [10] Ji, C., et al., Sorption enhancement of nickel (II) from wastewater by ZIF-8 modified with poly (sodium 4-styrenesulfonate): mechanism and kinetic study. Chemical Engineering Journal, 2021. 414: p. 128812.

6 Removal of heavy metals using ZIF 8

[11] [12]

[13]

[14]

[15] [16] [17]

[18] [19] [20]

[21] [22] [23] [24]

[25]

[26] [27]

[28] [29] [30]

93

Bui, T.T., et al., Sonochemical preparation of a magnet-responsive Fe3O4@ ZIF-8 adsorbent for efficient Cu2+ removal. Nanomaterials, 2022. 12(5): 753. Wang, F. and Z. Guo, Insitu growth of ZIF-8 on CoAl layered double hydroxide/carbon fiber composites for highly efficient absorptive removal of hexavalent chromium from aqueous solutions. Applied Clay Science, 2019. 175: p. 115–123. Liu, J., et al., A novel metal-organic framework-derived ZnO@ ZIF-8 adsorbent with high efficiency for Pb (II) from solution: Performance and mechanisms. Journal of Molecular Liquids, 2022. 356: p. 119057. Roudbari, R., N. Keramati, and M. Ghorbani, Porous nanocomposite based on metal-organic framework: Antibacterial activity and efficient removal of Ni (II) heavy metal ion. Journal of Molecular Liquids, 2021. 322: p. 114524. Liu, F., et al., A novel monolith ZnS-ZIF-8 adsorption material for ultraeffective Hg (II) capture from wastewater. Journal of Hazardous Materials, 2019. 367: p. 381–389. Li, J., et al., Simultaneous removal of U (VI) and Re (VII) by highly efficient functionalized ZIF-8 nanosheets adsorbent. Journal of Hazardous Materials, 2020. 393: p. 122398. Dai, H., et al., Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication. Applications and Perspective. Coordination Chemistry Reviews, 2021. 441: p. 213985. Chen, B., et al., Zeolitic imidazolate framework materials: Recent progress in synthesis and applications. Journal of Materials Chemistry A, 2014. 2(40): 16811–16831. Meng, J., et al., Advances in metal–organic framework coatings: Versatile synthesis and broad applications. Chemical Society Reviews, 2020. 49(10): 3142–3186. Rani, L., et al., A critical review on recent developments in MOF adsorbents for the elimination of toxic heavy metals from aqueous solutions. Environmental Science and Pollution Research, 2020. 27(36): 44771–44796. Tangahu, B.V., et al. A review on heavy metals (As, Pb, and Hg) uptake by plants through phytoremediation. International Journal of Chemical Engineering, 2011. p. 2011. Tchounwou, P.B., et al. Heavy metal toxicity and the environment. Molecular, Clinical and Environmental Toxicology, 2012. 101: p. 133–164. Needleman, H.L. and D. Bellinger, The health effects of low level exposure to lead. Annual Review of Public Health, 1991. 12(1): p. 111–140. Tong, S., Y.E.V. Schirnding, and T. Prapamontol, Environmental lead exposure: A public health problem of global dimensions. Bulletin of the World Health Organization, 2000. 78(9): p. 1068–1077. Fishbein, L., Sources, transport and alterations of metal compounds: An overview. I. Arsenic, beryllium, cadmium, chromium, and nickel. Environmental Health Perspectives, 1981. 40: p. 43–64. Gonnelli, C. and G. Renella, Chromium and nickel. Heavy Metals in Soils, 2013. 22: p. 313–333. Dhal, B., et al., Chemical and microbial remediation of hexavalent chromium from contaminated soil and mining/metallurgical solid waste: A review. Journal of Hazardous Materials, 2013. 250: p. 272–291. Jacobs, J.A. and S.M. Testa, Overview of chromium (VI) in the environment: Background and history. Chromium (VI) Handbook, 2005. p. 1–21. Jaishankar, M., et al., Toxicity, mechanism and health effects of some heavy metals. Interdisciplinary Toxicology, 2014. 7(2): 60–72. Machado, I., G. Bergmann, and M. Pistón, A simple and fast ultrasound-assisted extraction procedure for Fe and Zn determination in milk-based infant formulas using flame atomic absorption spectrometry (FAAS). Food Chemistry, 2016. 194: p. 373–376.

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Shumila Shaheen et al.

[31] Duruibe, J.O., M. Ogwuegbu, and J. Egwurugwu, Heavy metal pollution and human biotoxic effects. International Journal of Physical Sciences, 2007. 2(5): p. 112–118. [32] Ali, H., E. Khan, and M.A. Sajad, Phytoremediation of heavy metals – concepts and applications. Chemosphere, 2013. 91(7): p. 869–881. [33] Zabihi, M., A. Ahmadpour, and A.H. Asl, Removal of mercury from water by carbonaceous sorbents derived from walnut shell. Journal of Hazardous Materials, 2009. 167(1–3): p. 230–236. [34] Gunatilake, S., Methods of removing heavy metals from industrial wastewater. Methods, 2015. 1(1): p. 14. [35] Hakizimana, J.N., et al., Electrocoagulation process in water treatment: A review of electrocoagulation modeling approaches. Desalination, 2017. 404: p. 1–21. [36] Patidar, K., A. Chouhan, and L.S. Thakur, Removal of heavy metals from water and waste water by electrocoagulation process – a review. Int Res J Eng Technol, 2017. 4(11): p. 16–25. [37] Wimalawansa, S.J., Purification of contaminated water with reverse osmosis: Effective solution of providing clean water for human needs in developing countries. International Journal of Emerging Technology and Advanced Engineering, 2013. 3(12): p. 75–89. [38] Shomar, B., G. Müller, and A. Yahya, Potential use of treated wastewater and sludge in the agricultural sector of the Gaza strip. Clean Technologies and Environmental Policy, 2004. 6 (2): p. 128–137. [39] Li, J., et al., Metal–organic framework-based materials: Superior adsorbents for the capture of toxic and radioactive metal ions. Chemical Society Reviews, 2018. 47(7): 2322–2356. [40] Begum, J., Z. Hussain, and T. Noor, Adsorption and kinetic study of Cr (VI) on ZIF-8 based composites. Materials Research Express, 2020. 7(1): p. 015083. [41] Abdi, J. and H. Abedini, MOF-based polymeric nanocomposite beads as an efficient adsorbent for wastewater treatment in batch and continuous systems: Modelling and experiment. Chemical Engineering Journal, 2020. 400: p. 125862. [42] Kobielska, P.A., et al., Metal–organic frameworks for heavy metal removal from water. Coordination Chemistry Reviews, 2018. 358: p. 92–107. [43] Huang, Y., et al., Heavy metal ion removal of wastewater by zeolite-imidazolate frameworks. Separation and Purification Technology, 2018. 194: p. 462–469. [44] Zhang, Y., et al., Unveiling the adsorption mechanism of zeolitic imidazolate framework-8 with high efficiency for removal of copper ions from aqueous solutions. Dalton Transactions, 2016. 45(32): 12653–12660. [45] Simonin, J.-P., On the comparison of pseudo-first order and pseudo-second order rate laws in the modeling of adsorption kinetics. Chemical Engineering Journal, 2016. 300: p. 254–263. [46] Zou, D., D. Liu, and J. Zhang, From zeolitic imidazolate framework‐8 to metal‐organic frameworks (MOF s): Representative substance for the general study of pioneering MOF applications. Energy & Environmental Materials, 2018. 1(4): p. 209–220. [47] Abbasi, Z., et al., Metal–organic frameworks (MOFs) and MOF-derived porous carbon materials for sustainable adsorptive wastewater treatment, in sustainable nanoscale engineering. 2020: Elsevier, p. 163–194. [48] Zhao, Y., et al., Removal of heavy metal ions from aqueous solutions by adsorption onto ZIF-8 nanocrystals. Chemistry Letters, 2015. 44(6): 758–760. [49] Jung, B.K., et al., Adsorptive removal of p-arsanilic acid from water using mesoporous zeolitic imidazolate framework-8. Chemical Engineering Journal, 2015. 267: p. 9–15. [50] Hassan, N., et al., Synthesis and characterization of ZnO nanoparticles via zeolitic imidazolate framework-8 and its application for removal of dyes. Journal of Molecular Structure, 2020. 1210: p. 128029.

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[51] Wang, C., et al., In situ growth of ZIF-8 on PAN fibrous filters for highly efficient U (VI) removal. ACS Applied Materials & Interfaces, 2018. 10(28): 24164–24171. [52] Xiong, T., et al., Highly efficient removal of diclofenac sodium from medical wastewater by Mg/Al layered double hydroxide-poly (m-phenylenediamine) composite. Chemical Engineering Journal, 2019. 366: p. 83–91. [53] Yuan, Y., et al., Preparation of konjac glucomannan-based zeolitic imidazolate framework-8 composite aerogels with high adsorptive capacity of ciprofloxacin from water. Colloids and Surfaces A Physicochemical and Engineering Aspects, 2018. 544: p. 187–195. [54] Beni, F.A., et al., UV-switchable phosphotungstic acid sandwiched between ZIF-8 and Au nanoparticles to improve simultaneous adsorption and UV light photocatalysis toward tetracycline degradation. Microporous and Mesoporous Materials, 2020. 303: p. 110275. [55] Li, Q. and H. Kim, Hydrogen production from NaBH4 hydrolysis via Co-ZIF-9 catalyst. Fuel Processing Technology, 2012. 100: p. 43–48. [56] Lu, G. and J.T. Hupp, Metal− organic frameworks as sensors: A ZIF-8 based Fabry− Pérot device as a selective sensor for chemical vapors and gases. Journal of the American Chemical Society, 2010. 132(23): p. 7832–7833. [57] Sun, C.-Y., et al., Zeolitic imidazolate framework-8 as efficient pH-sensitive drug delivery vehicle. Dalton Transactions, 2012. 41(23): 6906–6909.

Hafiz Amir Nadeem, Zohaib Saeed✶, Muhammad Pervaiz, Talha Mumtaz, Rizwan Suikandar, Umer Younas, Muhammad Imran

7 Light-driven photocatalysis for dyes using ZIF-8 base composite materials Abstract: Zinc metal and 2-methylimidazole are part of zeolite imidazolate framework-8 (a typical metal-organic framework material). ZIF-8 finds wide application in photocatalytic materials. ZIF-8 composite materials are of significant importance. Specific surface area decreases if ZIF-8 material heaps together. When we remove pollutants from the ZIF-8 materials, it isn’t easy to separate them from water. Hence, ZIF-8 material has weak recyclability. Modern ZIF-8 composite materials are available for wastewater treatment. This chapter elaborates on preparing and designing new methods for the ZIF-8 composite. Nowadays, we use ZIF-8 composite as an adsorbent and photocatalyst. The primary purpose of further research on ZIF8 material is wastewater treatment. Several factors that affect the efficiency and the mechanism of ZIF-8 material in removing pollutants have been discussed in this chapter. This chapter discusses how we make efficient ZIF-8 composites that can be used to remove dyes from water. We also propose future research direction and current challenges of ZIF-8 composite materials.

7.1 Introduction Coordination compounds are formed with the assistance of metal ions and organic/ inorganic ligands with the help of coordination bonds. Due to their diverse and adjustable structure functionality, these compounds are widely studied. Based on coordination polymers, a huge variety of these compounds were synthesized. MOFs are used as coordination frame materials formed due to the coordination of organic ligands, metal clusters, or metal ions. Compared to porous carbon materials and pure sieves of inorganic molecules, MOFs have various advantages: they have a massive area of surface porosity, and the MOFs gain a certain degree of flexibility due to the single sigma bond and structures; MOFs are easy to design. MOFs have

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Corresponding author: Zohaib Saeed, Department of Chemistry, Government College University, Lahore, Pakistan, e-mail: [email protected] Hafiz Amir Nadeem, Muhammad Pervaiz, Talha Mumtaz, Rizwan Suikandar, Umer Younas, Muhammad Imran, Department of Chemistry, Government College University, Lahore, Pakistan Department of Chemistry, The University of Lahore, Lahore, Pakistan https://doi.org/10.1515/9783110792591-007

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broad applications and excellent performance prospects in catalysis, sensing, drug delivery, separation, and adsorption [1]. Great attention can be gained by those MOFs that possess some photocatalytic activity. These photocatalytic MOFs are specially used in the degradation of organic pollutants and dyes [2, 3]. ZIF-8, a flexible MOF based on an imidazolate ligand, was chosen as a photocatalyst to decompose the dye (methylene blue) under UV light irradiation. Pollution due to water is one of the serious problems that are endangering the health of human beings [4, 5]. Thus, controlling and treating water pollution is necessary, due to excessive consumption of dyes and other harmful toxic substances. Thousands of EOCs (emerging organic contaminants) have been discovered – pharmaceuticals, industrial pollutants, dyes, and personal care products that play a crucial role in polluting water [6, 7]. The last name of ZIF-8 was MAF-4 [8, 9]. Compared to other MOFs, manufacturing of ZIF-8 was easy. It has higher hydrothermal and chemical stability, enhancing robustness towards other compounds with a cage-like structure. ZIF-8 has enough ability to maintain its structural stability up to 500 °C and maintain its porosity and crystallinity after being inserted into various solvents like organic and water [10, 11]. Due to its porous structure, ZIF-8 is easily tailorable, which gives immense benefits in its modification. On the surface of ZIF-8, there is the facial separation of charge, and it has several active sites. ZIF-8 and its composites are widely used in different forms, including membranes, powders, or thin films, to treat wastewater dyes and other essential fields [12]. The unique chemical and physical properties of ZIF-8 give a good platform for photocatalytic systems, adsorptions, and treatment of water pollutants from wastewater. The controlled integration of the ZIF-8 and different functional groups results in new multifunctional hybrids or composites; these multifunctional hybrids demonstrate higher and better properties than all other individual components because it exhibits combined behavior; these hybrids have grabbed immense attention. Many ZIF-8 composites combined with active species like metals, oxides, fibers, polyoxometalates (PMOs), graphene, polymers, CNTs (carbon nanotubes), and many more (Figure 7.1) have been prepared efficiently. The original functions and properties of each phase can also be maintained, and in the application, the limitations of any single phase can also be made up for [46]. Compared to pure microporous ZIF-8, ZIF-8 hybrid composites can also increase the photocatalytic activity and adsorption capacity and broaden the applications of ZIF-8. Several previous types of research have proved the importance of this incorporation. For example, the solution to the limitation of processability and maintaining the extraordinary catalytic activity of the ZIF-8 and the stability of the matrix was done by fixing the ZIF-8 in the formed matrix. MoO3@ZIF-8 was prepared by Zhang et al. to decrease the Cr (VI) in visible light. MoO3@ZIF-8 demonstrated better photocatalytic activity than pure ZIF-8 and MoO3 nanowires. Separation from any liquid could quickly be done after the adsorption and they

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ZIF-8@PTA@AuNP

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Figure 7.1: The schematic diagram elaborates different shapes of ZIF-8 composites: (a) ZIF8@SiO2@Fe3O4; (b) Ag/AgCl@ZIF-8; (c) ZIF-8@PTA@Au; (d) MoO3@ZIF-8; (e) CF@LDH@ZIF-8; (f) TiO2@ZIF-8; (g) PPy@ZIF-8. PTA indicates polyoxometalate, CF indicates carbon fiber, LDH elaborates Co-Al layered double hydroxide. Reprinted with permission from [14], copyright 2021 Elsevier.

also possess good flexibility and structural forming prosperities. Based on synthesis methods, ZIF-8 composites can be divided into various types. The types include bottom-up and post-synthetic approaches for the ZIF-8 composites that have single particles. Based on structures, there are several additional classes, which are ZIF-8 core-shell particles, ZIF-8 thin film or membrane, and so on. Mn2+, Co2+, and Zn2+ ions (especially the first series of transition metals) that are divalent metal ions are primarily employed to manufacture metal-organic frameworks (MOFs) and play a crucial role in carrying drugs. According to SHAB

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(soft and hard acid-base concept), these metals have suitable hardness and softness and form coordination with nitrogen and oxygen, which are common donors and have moderate reversibility of coordination. The coordination reversibility between organic ligands and divalent metal cations gives the MOFs unique benefits in the delivery of drugs and photocatalysis [13]. The manufacturing of new ZIF-8 composites has been promoted with advanced synthesis methods and characterization techniques. Many monographs and articles have discussed the leading theory of the MOF-based composites. The researchers described synthesis strategies and many physiochemical properties of the composites. The primary purpose of the ZIF-8-based composite is their use in several kinds of wastewater treatment. This chapter firstly introduces different types of synthesis of composites. Then, a few different examples are analyzed in detail to discuss the adsorption and photocatalytic degradation of pollutants in different forms of wastewater to highlight the recent and advanced applications of ZIF-8 composites. Other detailed topics discussed are removal mechanism, factors affecting removal efficiency, challenges, and prospects.

7.1.1 Shortcomings (i) ZIF-8 NPs tend to form clusters in universal solvent (water), which enhances the size of particles, promotes resistance, and reduces the performance of adsorption and interfacial surface area. (ii) ZIF-8 Nanocomposites are not easy to separate from an aqueous medium, and their reuse and regeneration are immensely restricted. (iii) Due to the sizeable immense bandgap, ZIF-8 and its composites show weak response towards visible light. With the enhancing demand for functional materials, the application of monomer ZIF-8 is limited [15].

7.2 ZIF-8 composites strategies With the synergistic property of host and guest, using ZIF-8 nanocomposites is a practical and convenient approach. It is found that the control over the manufacturing of ZIF-8 nanocomposites is crucial, as only the ZIF-8 structure gives surety for the replication of nucleation. At the same time, manufacturing composites by any other technique are unattainable by surface adsorption, guest infiltration, and covalent linkages [16]. A couple of single-particle ZIF-8 composites synthesis categories have been reported, with the assistance of functional materials post-synthetic hybridization of pre-manufactured ZIF-8 [17].

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For the encapsulation of nanoparticles in ZIF-8, there are a couple of ways: first is a “ship-in-a-bottle” technique, which includes the inserting of precursors into the shells of ZIF-8, which are pre-synthesized. In the process of manufacturing, ZIF-8 acts as a self-sacrificial template, and then the decomposition of precursor is done to produce cavities for the deposition of particles. This approach of encapsulation provides simplicity for the production interface between ZIF-8 and particles, due to the production of nanosized particle cavities in the ZIF-8 nanocomposite material. ZIF-8 frameworks can be damaged due to the overloading of particles. Due to the “ship-in-a-bottle” technique, successful synthesis of ZIF-8@Au was done [18]. The de novo or the “bottle-around-ship” is the other approach in loading ZIF-8 on the nanoparticles. The caves do not limit the area of pre-synthesized ZIF-8 particles. While this method successfully controls the composition and shape of the NPs, many aspects should be considered, for example, the interaction between ZIF8 and particles or capping agents [19]. It is impossible to achieve proper size distribution in the cavities when the NPs are in liquid form. The “bottle-a round-ship” method was successfully employed by Liu et al. who encapsulated the droplets of EGaIn into the cavities of ZIF-8 [20].

7.3 Applications of light-driven photocatalysis for dyes using ZIF-8 base composite materials 7.3.1 ZIF-8 composites used to treat wastewater ZIF-8 composites, owing to their excellent adsorbent and photocatalytic properties, are among the modern and excellent base composites that have immeasurable applications in the field of wastewater regeneration. ZIF-8 works on the phenomenon of adsorption for efficient removal of dyes (methylene blue) [21] from wastewater [14].

7.3.2 ZIF-8 composites for the adsorptive sewage treatment One of the most famous techniques used to treat wastewater is adsorption, as it is economical due to its facial operations and low levels of litter byproducts. The major reservations are selecting efficient sorbent and modifications in the adsorbent’s properties and morphology to enhance its ability. ZIF-8 can adsorb molecules larger than its pore size due to its properties: large surface area to volume ratio, high porosity rate, and rotating door effect. A series of experimental work done by the Yaghi group on ZIF-8 has proven that its synthesis, modification, and integration with other materials easily make it a promising and efficient adsorbent [9]. When comparing single

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ZIF-8 and ZIF-8 composite, the composite has the following benefits: (i) decreases the accretion of adsorbent; (ii) makes removal of adsorbent easy; and (iii) increases the ability of the adsorbent [22]. Compared to all the conventional or commercial materials, the ZIF-8 composite is more efficient, with the active groups present at the surface allowing better adsorption [23]. 1500–2500 m2/g being the surface area of ZIF-8 nanoparticles [24].

7.3.3 Removal of inorganic materials and dyes from wastewater Inorganic pollutants include radioactive material and ions of heavy metal halogens [25]. Heavy metal ions like As, Cu, Hg, Cr, Pb, and Ni are all responsible for environmental pollution [26]. With the development of nuclear energy, there has been an increase in nuclear waste production, a significant water pollutant. Due to high solubility and long half-life, some radioactive materials are more harmful than others. Events like Chornobyl and Fukushima’s Daiichi Nuclear Power Plant are two famous examples of radioactive leaks [27]. These inorganic materials are highly toxic, carcinogenic, and non-biodegradable. Selective adsorption is the most efficient technique used to eliminate these harmful pollutants. ZIF-8 composite, due to its synthesis, characterization, and ability to be modified, is a useful adsorbent [28]. For example, arsenic, a heavy metal, has been declared by WHO (World Health Organization) as one of the most toxic heavy metals. Its allowed maximum levels in water are 10 ug L-1 [29]. Arsenic is present in water in neutral arsenate ions [30]. As (III), as compared to As (V), is more toxic, mobile, and has a lower affinity to adsorbents; thus, an additional step of pre-oxidation to As (V) is required before using the phenomenon of adsorption [31]. The first step of removing As in case of the presence of As3+ involves preoxidation of As3+ to As4+. Jian and coworkers effectively synthesized nanocomposites b-MnO2@ZIF-8 [32]. The former research of Jian and coworkers successfully proved that ZIF-8 had a high pHIEP of 9.6, so Adsorption of As4+ is easier on ZIF-8 via electrostatic attraction. MnO2 can oxidize As (III), which increases the affinity of As towards the adsorbent. Cr (Chromium) is another toxic heavy metal that exists as CrO42- or Cr2O72-, with the tanning industry being its primary source and water, its main sink [33]. Some articles have reported that ZIF-8 is an effective adsorbent used to eliminate Cr from water [34]. Zhu developed a microsphere MP@ZIF-8 to eliminate Cr from water. Zhu’s MP@ZIF-8 consists of a polydopamine inner shell, magnetic core, and an outer shell of ZIF-8 (Figure 7.2). MP@ZIF-8 is easy to recycle, which makes manufacturing economical. Cr interacts with the active sites of the sphere, leading to adsorption [26].

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Zn(NO3)2.6H2O 2-methylimidazole

pH = 8.5 tris-buffer Fe3O4

CH3OH MP

MP@ZIF-8

Figure 7.2: Formation of the MP@ZIF-8 composites. Reproduced with permission from Ref [26]. Copyright 2017, the American Chemical Society.

7.3.3.1 Photolytic removal of pollutants using ZIF-8 composites The most modern method used for wastewater treatment is catalytic, including Fenton catalytic oxidation, photocatalytic oxidation, electrochemical catalytic methods, and ozone oxidation. Photocatalysis, being economical and eco-friendly, has a better impact on removing pollutants [35]. It is better at degrading the organic pollutant than the adsorption technique. Though this technique produces a range of harmful byproducts, it is best for degrading the component entirely [35]. Thus, scientists found the need to synthesize a better photocatalyst. The most widely used photocatalysts are semiconductor materials [36]. Many components have been used since then, like TiO2, CdS, ZnO, and Zn4O (CO2)(MOF-5) [37]. Advanced ZIF-8 showed excellent catalytic properties [38]. Nanocrystals of ZIF-8 have been used to date. However, due to limitations in its activity, modifications have been made, like the addition of metal oxides [39].

7.4 Methods for the synthesis of ZIF-8-based composites There are many novel strategies for manufacturing ZIF-8 nanocomposites: sonochemical, micro-reactor synthesis, stepwise growth, and deposition reduction processes, excluding main synthesis methods. The sonochemical method is used to prepare Ti02/ZIF-8. Zeng et al. prepared Ti02/ZIF-8 by this method [41]. There are many advantages of micro-reactor synthesis, which are given below: i) After connecting with different reactants, the surface area is kept more prominent. ii) Thermal conductivity can heat up or cool down the micro-reactor in a short time. iii) If we increase the mass transfer rate, mixing between reactants becomes fast. iv) We can easily adjust synthesis conditions under the micro-reactor method.

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(a) Cd2+, Zn2+, S2– Cd0.5Zn0.5S

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Figure 7.3: (a) The manufacturing diagram of Cd0.5Zn0.5S@ ZIF-8 photo catalyst. (b) XPS spectra of various samples: S 2p. (c) The photocatalytic capability of different samples (d) Schematic explanation of TC detection, adsorption, and photodegradation by CBO@ZIF-8, reprinted with permission from refs [14, 40]. Copyright 2018 the Elsevier. Copyright 2020 the American Chemical Society.

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We can easily adjust experimental conditions like temperature, residence time, and pressure in the micro-reactor method because we use fewer reactants in this method. MOF was fabricated on other materials using the LPE strategy, in the past. Designing the ZIF-8 layer on powder substrate by LPE strategy has not been thoroughly investigated [42]. It isn’t easy to grow MOFs. Shekhinah et al. successfully deposited MOF layers on a modified bulk substrate, using an LPE strategy [43]. Mesoscopic channels are operated by MOFs layer, using this strategy. ZIF-8 layers are deposited on SiO2 nanopowders by Peng et al. ZIF-8 grows around the substrate surface by applying the LPE strategy, and ZIF-8 is also protected from the nucleation by using this strategy. Non-monotonic synthesis strategies practically produce ZIF-8 composites [44]. Fe3O4@ZIF-8 and polystyrene sulfonate are fabricated by surface modification and solvothermal method, using the example of Wu et al.. Both Fe3O4@ZIF-8 and polystyrene sulfonate can modify the Fe3O4 particles. After medication, nucleation and growth of ZIF-8 increase on the surface of Fe3O4 [45]. Synthesized composites can be stable in water and contain a high surface area. If we use different synthesis methods synergistically during the synthesis process, we can obtain optimum properties of the ZIF-8 composite as shown in Figure 7.3. A series of methods are summarized, for example., surface modification, in situ growth, template synthesis method, sol-gel, etc. These strategies give us a natural way to synthesize organic and inorganic ZIF-8-based nanocomposites for the removal of dyes. Various sorts of inorganic (ZIF-8 Fe3O4@ZIF-8, MnO2@ZIF-8, and CF/LDH@ZIF-8)composites could be synthesized by advanced methods that can be use to adsorb harmful substances (dyes). The iron and manganese ZIF-8 composites can adsorb As(III) and can be synthesized by micro fluid and template method, while the CF/LDH-ZIF-8 nanocomposite has the ability to adsorb chromium(VI) and its synthesis was done by in situ method. Most organic ZIF-8 materials can be synthesized by using the in situ method and can adsorb U (VI), Hg (II), 2-naphthol, Pb (II), Cd (II), etc. from different materials.

7.5 Conclusion and future prospects ZIF-8-based composites show enhanced performance due to synergic functions – instead of serving as a single material, they have numerous applications in industrial wastewater treatment. Here are some future directions of ZIF-8 composites based on application in wastewater treatment. 1. ZIF-8 composites can be synthesized by various methods such as NPs encapsulation, the introduction of the NPs to the surface of ZIF-8, polymerization of ZIF-8, ZIF-8 fibers, and so on, to enhance the potential application of composites. Despite all these methods and the increasing number of composites, we

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are still unable to obtain an ideal ZIF-8 composite that has the composition, proper size, and properties of spatial orientation and dispersion. Hence, there is a need to explore and explain the reaction mechanism between matrix and reinforcement. Moreover, scientists are working on innovative methods for synthesis, like the sonochemical method, microfluidic method, and so on. They are also looking forward to combining two synthesis methods to maximize the performance of composites. 2. As the ZIF-8 composite synthesis is very sensitive, a minor change in the synthesis condition leads to a massive change in the diverging properties of the composites. To reduce this, future research will look at analyzing the synergic mechanism of the ZIF-8 composites with the help of the characterization techniques such as FTIR, XPS, SEM, and TEM. 3. The removal efficiency of the composites is influenced by many reaction conditions like pH, temperature, ionic strength, and so on. In the future, it is important to find the relationship between these factors and the ZIF-8 composites. With the help of this, we shall be able to remove certain specific and targeted pollutants. The competitive pollutants should also be removed simultaneously by experimentation using further studies. 4. The essential purpose of any research is to expand it to an industrial scale from a laboratory scale. The recyclability of the ZIF-8 composites should also be considered besides the degradation capacity, selective adsorption, and photodegradation of the pollutants. Further research is also needed to enhance the adsorption capacity of the solar energy of the composite to minimize the rate of recombination of light photogenerated electron-hole pair. 5. The manufacturing of environment-friendly ZIF-8-based composites is a costly procedure and utilizes human resources. Due to its high cost, it is challenging to scale up. To make it useful, a lot of work is still needed to make it costeffective. 6. ZIF-8 composites can also be attached to the organic polymers to serve as a polymer membrane for wastewater treatment. With the help of this, we should be able to remove organic pollutants from industrial waste, such as paints, oils, organic acids, etc. ZIF-8-based composites also have an excellent storage capacity for gases, so they can also be used for such purposes. ZIF-8-based composites is a very vast topic that has several applications as they are very efficient in wastewater treatment and water regeneration. Furthermore, advanced treatment and characterization techniques should promote the production of new ZIF-8-based composite materials that would be more useful in various fields.

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References [1]

[2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]

[15] [16] [17] [18]

[19] [20] [21] [22]

Montes-Hernandez, G., et al., Removal of oxyanions from synthetic wastewater via carbonation process of calcium hydroxide: Applied and fundamental aspects. 2009. 166(2-3): p. 788–795. Imran, M., et al., Enhanced visible light photocatalytic activity of TiO2 co-doped with Fe, Co, and S for degradation of Cango red. 2021. 255: p. 119644. Joseph, L., et al., Removal of contaminants of emerging concern by metal-organic framework nanoadsorbents: A review. 2019. 369: p. 928–946. Shannon, M.A., et al., Science and technology for water purification in the coming decades. 2010. p. 337–346. Vorosmarty, C.J., et al., Global water resources: Vulnerability from climate change and population growth. 2000. 289(5477): p. 284–288. Lapworth, D., et al., Emerging organic contaminants in groundwater: A review of sources, fate and occurrence. 2012. 163: p. 287–303. Liang, W., et al., 3D, eco-friendly metal-organic frameworks@ carbon nanotube aerogels composite materials for removal of pesticides in water. 2021. 401: p. 123718. Huang, X.C., et al., Ligand‐directed strategy for zeolite‐type metal–organic frameworks: Zinc (II) imidazolates with unusual zeolitic topologies. 2006. 45(10): p. 1557–1559. Park, K.S., et al., Exceptional chemical and thermal stability of zeolitic imidazolate frameworks. 2006. 103(27): p. 10186–10191. Banerjee, R., et al., High-throughput synthesis of zeolitic imidazolate frameworks and application to CO2 capture. 2008. 319(5865): p. 939–943. Troyano, J., et al., Colloidal metal–organic framework particles: The pioneering case of ZIF-8. 2019. 48(23): p. 5534–5546. Musarurwa, H. and N.T.J.C.P. Tavengwa, Application of polysaccharide-based metal organic framework membranes in separation science. 2022. 275: p. 118743. Wang, Q., et al., Synthesis and modification of ZIF-8 and its application in drug delivery and tumor therapy. 2020. 10(62): p. 37600–37620. Dai, H., et al., Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication, applications and perspective. Coordination Chemistry Reviews, 2021. 441: p. 213985. Dicker, M.P., et al., Green composites: A review of material attributes and complementary applications. 2014. 56: p. 280–289. Li, S., et al., Template‐directed synthesis of porous and protective core–shell bionanoparticles. 2016. 128(36): p. 10849–10854. Tsuruoka, T., et al., Controlled self-assembly of metal–organic frameworks on metal nanoparticles for efficient synthesis of hybrid nanostructures. 2011. 3(10): p. 3788–3791. Li, Z. and H.C.J.C.O.M. Zeng, Surface and bulk integrations of single-layered Au or Ag nanoparticles onto designated crystal planes {110} or {100} of ZIF-8. 2013. 25(9): p. 1761–1768. Hu, P., et al., Core–shell catalysts of metal nanoparticle core and metal–organic framework shell. 2014. 4(12): p. 4409–4419. Liu, Y., et al., A liquid metal composite by ZIF-8 encapsulation. 2020. 56(12): p. 1851–1854. He, Y., et al., Preparation, characterization, and photocatalytic activity of novel AgBr/ZIF-8 composites for water purification. 2020. 31(1): p. 439–447. Dong, W., et al., Facile synthesis of In2S3/UiO-66 composite with enhanced adsorption performance and photocatalytic activity for the removal of tetracycline under visible light irradiation. 2019. 535: p. 444–457.

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[23] Li, J., et al., Metal–organic framework-based materials: Superior adsorbents for the capture of toxic and radioactive metal ions. 2018. 47(7): p. 2322–2356. [24] Barnes, K.K., et al., A national reconnaissance of pharmaceuticals and other organic wastewater contaminants in the United States—I) Groundwater. 2008. 402(2-3): p. 192–200. [25] Mohan, D., et al., Organic and inorganic contaminants removal from water with biochar, a renewable, low cost and sustainable adsorbent–a critical review. 2014. 160: p. 191–202. [26] Zhu, K., et al., Cr (VI) reduction and immobilization by core-double-shell structured magnetic polydopamine@ zeolitic idazolate frameworks-8 microspheres. 2017. 5(8): p. 6795–6802. [27] Hobbs, D., et al., Development of an improved titanate-based sorbent for strontium and actinide separations under strongly alkaline conditions. 2010. 46(1): p. 119–129. [28] Xu, G.-R., et al., Metal organic framework (MOF)-based micro/nanoscaled materials for heavy metal ions removal: The cutting-edge study on designs, synthesis, and applications. 2021. 427: p. 213554. [29] Chen, W.-R. and C.-H.J.J.O.H.M. Huang, Surface adsorption of organoarsenic roxarsone and arsanilic acid on iron and aluminum oxides. 2012. 227: p. 378–385. [30] Ma, L. and S.J.E.C.L. Tu, Removal of arsenic from aqueous solution by two types of nano TiO2 crystals. 2011. 9(4): p. 465–472. [31] Tresintsi, S., et al., Kilogram-scale synthesis of iron oxy-hydroxides with improved arsenic removal capacity: Study of Fe (II) oxidation–precipitation parameters. 2012. 46(16): p. 5255–5267. [32] Jian, M., et al., Self-assembled one-dimensional MnO 2@ zeolitic imidazolate framework-8 nanostructures for highly efficient arsenite removal. 2016. 3(5): p. 1186–1194. [33] El-Sherif, I.Y., et al., Polymeric nanofibers for the removal of Cr (III) from tannery waste water. 2013. 129: p. 410–413. [34] Ding, Y., et al., Structure induced selective adsorption performance of ZIF-8 nanocrystals in water. 2017. 520: p. 661–667. [35] Jiang, L., et al., A facile band alignment of polymeric carbon nitride isotype heterojunctions for enhanced photocatalytic tetracycline degradation. 2018. 5(11): p. 2604–2617. [36] Fujishima, A. and K.J.N. Honda, Electrochemical photolysis of water at a semiconductor electrode. 1972. 238(5358): p. 37–38. [37] Yuan, X., et al., Highly efficient visible-light-induced photoactivity of Z-scheme Ag 2 CO 3/Ag/ WO 3 photocatalysts for organic pollutant degradation. 2017. 4(11): p. 2175–2185. [38] Long, J., et al., Amine-functionalized zirconium metal–organic framework as efficient visiblelight photocatalyst for aerobic organic transformations. 2012. 48(95): p. 11656–11658. [39] Beni, F.A., et al., UV-switchable phosphotungstic acid sandwiched between ZIF-8 and Au nanoparticles to improve simultaneous adsorption and UV light photocatalysis toward tetracycline degradation. 2020. 303: p. 110275. [40] Gao, Y., et al., A novel multifunctional p-type semiconductor@ MOFs nanoporous platform for simultaneous sensing and photodegradation of tetracycline. ACS Applied Materials & Interfaces, 2020. 12(9): p. 11036–11044. [41] Zeng, X., et al., Sonocrystallization of ZIF-8 on electrostatic spinning TiO2 nanofibers surface with enhanced photocatalysis property through synergistic effect. 2016. 8(31): p. 20274–20282. [42] Jia, Z., et al., The BiOCl/diatomite composites for rapid photocatalytic degradation of ciprofloxacin: Efficiency, toxicity evaluation, mechanisms and pathways. 2020. 380: p. 122422.

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[43] Shekhah, O., et al., Step-by-step route for the synthesis of metal− organic frameworks. 2007. 129(49): p. 15118–15119. [44] Lei, Z., et al., Multiphase surface growth of hydrophobic ZIF-8 on melamine sponge for excellent oil/water separation and effective catalysis in a Knoevenagel reaction. 2018. 6(7): p. 3258–3263. [45] Wu, Y., et al., Magnetic metal-organic frameworks (Fe3O4@ ZIF-8) composites for U (VI) and Eu (III) elimination: Simultaneously achieve favorable stability and functionality. 2019. 378: p. 122105.

Ramsha Saleem, Rana Rashad Mahmood Khan✶, Hoorish Qamar, Muhammad Pervaiz, Umer Younas, Zohaib Saeed, Hafiz Muhammad Faizan Haider, Ahmad Adnan

8 Recent trends in ZIF-8-based composite materials for the removal of ciprofloxacin Abstract: Ciprofloxacin (CIP) is one of the fluoroquinolones developed to fight several bacterial infections. CIP abuse and its low biodegradability cause water contamination that leads to the production of CIP-resistant bacteria. A high concentration of CIP, including other quinolones, causes harmful effects on fish, humans, bacteria, algae, and protozoa. Adsorption has been preferred over other removal methods. The superior properties of ZIF-8 over other MOFs have made it a promising adsorbent for the removal of CIP from an aquatic environment. However, ZIF-8 suffers from its inability to recover from an aqueous environment and the related mass transfer problems. These limitations have been overcome by the synthesis of ZIF-8-based composites. ZIF8 composites have been proved as efficient catalysts for the adsorption of CIP from water. They offer a higher number of adsorption sites for CIP than ZIF-8. The adsorption of CIP over ZIF-8-based composites occurs via the interaction between the adsorbent and CIP. They interact through hydrogen bonding, electrostatic interaction, complexation, pi-pi interaction, and hydrophobic interaction. The pH of the solution contributes significantly to the type of interaction taking place between the composite and CIP. These composites can be used in the practical application of decontamination of wastewater because of their high regeneration and recycling ability.

8.1 Introduction Antibiotics are natural, synthetic, and semi-synthetic chemotherapeutic compounds with antimicrobial activity against living organisms [1]. Since 1929, when the first antibiotic (penicillin) was discovered, a large number of antibiotics have been synthesized. These antibiotics have become the most employed antibacterial drugs for plants, animals, and humans due to their high efficacy and low cost [2]. It is estimated

✶ Corresponding author: Rana Rashad Mahmood Khan, Department of Chemistry, Government College University, Lahore, Pakistan, e-mail: [email protected] Ramsha Saleem, Rana Rashad Mahmood Khan, Hoorish Qamar, Muhammad Pervaiz, Zohaib Saeed, Hafiz Muhammad Faizan Haider, Ahmad Adnan, Department of Chemistry, Government College, University Lahore, Pakistan Umer Younas, Department of Chemistry, The University of University, Lahore, Pakistan

https://doi.org/10.1515/9783110792591-008

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that almost 100,000–200,000 tons of antibiotics are consumed worldwide per annum [3]. In addition to their uses as antimicrobial drugs, antibiotics also contribute significantly to accelerating the growth of farm animals as well as aquaculture [4]. Antibiotics comprise 6% of the total drugs and more than 70% of the antibiotics are used in veterinary care [5]. However, these antibiotics are not completely degraded by the digestive system of living organisms. Thus, the residues are directly or indirectly released into the terrestrial or aquatic environment. The residues of antibiotics have been identified in various environments, which present grave threats to the ecosystem and human health [6–11]. Antibiotics are generally classified into two groups based on their mode of action – bacteriostatic and bactericidal. Bactericidal antibiotics kill bacteria whereas bacteriostatic antibiotics resist the growth of bacteria. Antibiotics can also be categorized into different classes depending on their structural formulas [12]. Figure 8.1 shows the classification of antibiotics in various groups based on their structural formulas.

ANTIBIOTICS QUINOLONES – Ciprofloxacin – norfloxacin – Enrofloxacin – Ofloxacin

SULFONAMIDES – Sulfadizine – Sulfapyridine – Sulfamethazine – Sulfathiazole – Sulfamerazine

TETRACYCLINES – Tetracycline – Oxytetracycline – Doxycycline

MACROLIDES – Erythromycin – Clarithromycin – Azithromycin

NITROIMIDAZOLE – Metronidazole

PENICILLIN – Amoxillin – Ampicillin

LINOCOSAMIDES – Linomycin – Clindamycin – Pirlimycin

Figure 8.1: Classification of antibiotics based on their structure.

Quinolones are one of the classes of antibiotics that are widely employed to treat a broad-spectrum of bacterial infections [13]. Table 8.1 shows the attributive features of CIP, including its structural formula. CIP is a second-generation fluoroquinolone used to treat bacterial infections in animals and humans, especially respiratory, intraabdominal, skin, and urinary tract infections [14–17]. CIP contains fluorine that enables it to target gram-negative bacteria on a large scale and some gram-positive bacteria [18]. It is a bactericidal antibiotic that kills bacteria by inhibiting DNA replication in bacteria [1, 19]. It is also used to treat infectious diseases in fish in aquaculture. Fluoroquinolones comprise the major portion of veterinary drugs. They are widely employed in swine, poultry, and cattle farming, and this leads to their contamination of water bodies [20]. Due to the extensive applications and the non-biodegradable nature of CIP, it contributes significantly to the waste caused by pharmaceutical products in the

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Table 8.1: Salient features of CIP [19, 21–23]. Appearance

Light yellow crystalline powder

Molecular formula

CHFNO

Structural formula HN N

N OH

O O

O

Molar Mass

. g/mol

log Kow

.

pH (.% aqueous solution)

.–.

pKa

., ., ., .

Solubility in water (at  °C)

 mg/mL

Mode of action

Bactericidal

Target

Inhibits DNA replication

water bodies. Many studies have shown that CIP is found in surface water, rivers, lakes, and drinking water in many parts of the world. Table 8.2 shows the occurrence of CIP in various waterbodies worldwide. Table 8.2: Occurrence of CIP in aquatic bodies in the different regions of the world. Country

Region

Sample type

Max. concentration (ng/L)

Reference

China

Yangtze River delta

Drinking water

.

[]

Beijing-Tianjin-Hebei

Surface water

.

[]

Yellow River

Sediments

.

[]



Hai River



Liao River

. .

[]

.

[]

Chaohu Lake

Freshwater

Aquaculture Pond Guilin

Water Sediments

.

Yangtze River

Real water

.

[]

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Table 8.2 (continued) Country

Region

Sample type

Dingzi Bay

Aquaculture pond water

Mariculture Pond

Coastal region

Xiong’an New Area

Max. concentration (ng/L)

Reference

.

Non-aquaculture pond water

.

Aquaculture natural water

.

Non-aquaculture natural water

.

Aquaculture sediments

.

Non-aquaculture sediments

.

Aquaculture sediments

.

Non-aquaculture sediments

.

Groundwater

.

Surface water

.

Sediments

.

[]

[]

South Africa

Msunduzi River

Water

.

[]

Kenya

Juja Drain

Drain water

.

[]

Drain Sediments

.

Australia India

Chennai Dumpsite

China

Beijing Greenhouse

Austria India 1

Queensland River

River water Soil Soil

. 

.





[] [] []



Beijing Open field

Soil

.

−

Soil fertilized with manure



[]

.

[]

Ganges River

River water

μg/kg, μg/L, ng/kg, and μg/g. 2

3

4

8.1.1 Possible routes of CIP to enter the environment There are many ways through which CIP becomes a part of our aquatic and terrestrial environment, including excretory products that contain residues, wastewater from pharmaceutical industries and hospitals, and improper disposal of unused and expired drugs [38]. Figure 8.2 shows the route and the fate of CIP in the environment.

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115

ARM ARM

Surface water

Hospital Wastewater Aquaculture

Crops Wa Trea stewate tme nt p r lant

Domestic Wastewater

Sludge

Fields

Figure 8.2: Route of entry and fate of CIP in the environment.

CIP enters the aquatic bodies via the wastewater containing residues coming from the production unit of the pharmaceutical industries [39]. The concentration of CIP in pharmaceutical industrial wastewater is estimated to be approximately 31 mg/L [40]. The wastewater of hospitals also makes a considerable contribution to the contamination of water bodies. Approximately 150 μg/L of CIP has been detected in the effluents of hospital wastewater [40]. CIP is used as human and veterinary drugs to treat bacterial infections. When CIP is used as medicine, only a small amount of it is metabolized by the liver in the body of an organism and the unmetabolized form is excreted via urine and feces [41]. Approximately 65% of the unmetabolized CIP is removed through urine and about 25% via feces [42]. In this way, CIP residues enter the sewerage system from the body of the CIP consumers. The sewerage water that contains the domestic waste then reaches the conventional wastewater treatment plant. Several studies have revealed that wastewater treatment plants are not highly efficient for the removal of CIP due to their mobility and high water solubility [43]. Only 62.25% of the CIP gets removed by traditional wastewater treatment plants [44]. As a result, treated water comprising CIP residues is released to the nearby surface water bodies. The sludge produced from WWTPs contains almost 70% CIP residues [45]. The second most common route of entry of CIP into our ecosystem is the use of animal waste, comprising CIP residues, as manure to fertilize the land. The contaminated manure leads to antibiotic pollution in the soil, which then results in aquatic pollution due to the flow of water from the soil to the surrounding water bodies [46].

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One of the major ways is the direct application of CIP in aquaculture for the growth of fish or the protection of species from bacterial infections [20]. There are some unconventional means of causing CIP pollution in the environment; that is, the lack of a proper system to dispose of the unused or expired drugs containing CIP as an active pharmaceutical ingredient (API). The best solution to avoid the entry of CIP into the natural environment via this route is to recycle the active pharmaceutical ingredient, as the expired or unused medications comprise almost more than 90% API [46].

8.1.2 Ecotoxicity of CIP The accumulation of antibiotics in the water bodies gives rise to the production of antibiotic-resistant bacteria by the development of resistant genes in them. These resistant bacteria enter the drinking water and the vegetables growing in the contaminated soil. Then, the transfer of these bacteria to humans and animals causes acute and chronic illnesses [47]. A high concentration of CIP has bad effects on fish, humans, and algae. Figure 8.3 illustrates the impact of high concentration of CIP on health of different organisms. Exposure to high concentrations of FQs (CIP, norfloxacin, and ofloxacin) in humans and animals causes fetal variations in the development of bone, cartilages, and tendons [34, 48]. They also cause harmful effects on algae, bacteria, and crustaceans [49]. Wastewater Plant

CIF

Low Removal Efficiency

Algae

Protozoa

Oxidative Stress

Abnormal Heart

Neonatal Changes in Development of Bone, Cartilage, and Tendon

Less Sperm Mobility

Mitochondrial damage

Death Rate

Figure 8.3: Effects of CIP on different organisms on their exposure to a high concentration.

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Literature studies have shown that a high concentration of CIP in water bodies causes abnormalities at early developmental stages in fish [50]. CIP (10 μg/L) along with other pharmaceuticals leads to mortality in fish [51]. The presence of FQs (CIP, norfloxacin, and ofloxacin) of more than 37.5 mg/L affects the normal development of zebrafish larvae and their hatching period [52]. CIP, along with other FQs, is found to be involved in the variation of cardiac tissue in zebrafish, which in turn irregulates its heartbeat [53]. The combined action of CIP also plays a significant role in the transcriptional and translational changes in the fish. They also contribute to the increased production of some enzymes in fish, such as creatinine kinase. The elevated levels of creatinine kinase damage its mitochondria and reduce its sperm movement, and ultimately increase the death rate in fish [54].

8.2 Strategies for the removal of CIP from an aquatic environment To date, various strategies have been developed and used to eliminate CIP from the sewerage system to lessen the stress of its high concentration on our ecosystem. Various methods developed to remove CIP from waterbodies are shown in Figure 8.4. These include biochemical [55–57], coagulation-flocculation [58], physicochemical [41, 59], membrane treatment [60, 61], ion-exchange [62], adsorption [63], and photocatalytic methods [64–66]. However, these traditional and conventional ways suffer from some limitations. There are high chances of the production of toxic byproducts in ozonation, whereas advanced oxidation processes and UV irradiation require special reactors and storage tanks for oxidizing agents such as hydrogen peroxide [67]. Among all the removal strategies, adsorption is of particular interest due to its high efficiency, low cost, ability to recycle and recover, and ease of operation [68]. Along with adsorption, photocatalysis has also become an emerging strategy, as it is eco-friendly and costeffective [69]. Till now, many different adsorbents have been used for the removal of CIP from aquatic bodies, such as iron-based [70], clay-based [71], metallic oxides [72–74], carbonaceous materials [75, 76], biochar [77, 78], and metal-organic frameworks (MOFs) [79, 80]. It is necessary for an adsorbent to have a large surface area and high porosity [81]. In this regard, MOFs have gained high attention as adsorbents due to their exciting features. MOFs are the crystalline porous coordination polymers synthesized by selfassemblage of metal ions or clusters with ligands [82]. MOFs have various advantages over other adsorbents, such as easy and simple synthetic methods, high crystallinity, large surface area, high porosity, tunable pore size, abundant active sites, and reusability [83]. Therefore, MOFs have been applied for the removal of contaminants from water and fuels on a large scale [84, 85]. A variety of MOFs have been applied for the

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Coagulation Sedimentation Filtration

PHYSICOCHEMICAL

CO2 + H2O

Antibiotics Byproducts

BIOCHEMICAL

Removal of CIP from water

ADSORPTION

Antibiotics Byproducts

MEMBRANE TREATMENT

ION-ECHANGE ADVANCED OXIDATION

Figure 8.4: Ways to eliminate CIP from an aquatic environment.

removal of CIP from wastewater. Rathod et al. developed and used MOF-5 for the adsorption of CIP from water [86]. Similarly, Ma et al. prepared HDC-1100 (HKUST-1Derived Cu@Cu(I)@Cu(II)/Carbon) and used it for the removal of CIP with a maximum adsorption of 529 mg/g [79]. However, the use of these MOFs is limited by their low thermal and mechanical stability. To overcome the limitation of these MOFs, researchers have started the use of ZIF-8 due to its high thermal stability.

8.2.1 Physicochemical properties of ZIF-8 ZIF-8 has a wide number of applications in different fields, such as drug delivery, tumor therapy, water decontamination, electrochemical applications, heterogeneous catalysis, etc. due to its outstanding behavior[87–90]. ZIF-8 is a small-pore MOF, with the chemical formula Zn(Hmim)2, comprising Zn2+ and 2-methylimidazole as a metal center and organic ligand, respectively [91]. Figure 8.5 depicts many advantages of ZIF-8 over other MOFs. The most important characteristic of ZIF-8 is its simple synthetic method. There is no need for costly autoclaves as they can be easily prepared at 25°C or at a temperature below the boiling point of the solvent in a very short time [89]. It is one of the few MOFs that can be prepared in an aqueous solution [92]. One of the peculiar features of ZIF-8 is its exceptional chemical, hydrothermal, and thermal strength [93]. It can sustain its structural integrity up to 500°C, which is much better than other MOFs. It can also maintain its structural properties in aqueous solutions [94, 95]. Moreover,

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ZIF-8 has unique characteristics of high porosity, crystallinity, structural flexibility, easy functional alteration, small and tailorable pore size, large surface area, and small particle size [93]. The ease of modification in its pore size and structure enables obtaining mesoporous and multistage porous ZIF-8, which offers more reaction sites [96].

Porous and Crystalline Tunable Pores

Simple Synthesis ZIF-8 High Surface Area

Easy to modify Thermal and Chemical stability

Figure 8.5: Peculiar characteristics of ZIF-8.

The excellent physicochemical characteristics of ZIF-8 make it an important catalyst for the decontamination of water. While it has some exceptional properties, it has a few limitations, namely, (i) its adsorption ability gets reduced in the aqueous system due to the agglomeration of particles, which leads to a decreased surface area; (ii) difficulty in the separation of ZIF-8 from an aqueous system, which restricts its reuse and causes mass transfer problem; and (iii) it has a wide bandgap of almost 5 eV, making it unable to absorb the visible region of sunlight. These limitations restrict its applications as an adsorbent and as a photocatalyst on a large scale [96]. To overcome these limitations, ZIF-8-based composites have been developed. Various ZIF-8 composites with graphene, metals, metal oxides, carbon, polymers, fibers, and biological molecules have been formed to improve its adsorptive and photocatalytic properties [97–104].

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8.3 Applications of ZIF-8-based composites for the removal of CIP ZIF-8-based composites have emerged as a new material to treat sewage water and a lot of research has been carried out on using them for the removal of harmful materials from waterbodies. CIP is one of the pharmaceutical wastes that cause various problems for human beings, fish, and other organisms in high concentrations. However, the use of ZIF-8-based composites to eliminate CIP from water bodies is not extensive now. Only a few composites of ZIF-8 have been synthesized to adsorb CIP efficiently from water [105–109]. ZIF-8-based composites used for the elimination of CIP can be categorized into three types: carbon-based, iron-based, and biopolymerbased composites. Table 8.3 shows the surface area and adsorption capacity of various ZIF-8-based composites. Table 8.3: Adsorption capacity of ZIF-8-based composites reported in the literature for CIP. ZIF--based composite

NPC- ZPC- C@silica Fe doped ZIF- KGM/ZIF- 1

Initial CIP concentration

Adsorption capacity

mg/L

mg/g  –   

. . .  .

Reference

[] [] [] [] []

mg/g

8.3.1 Carbon-based ZIF-8 composites Several carbonaceous catalysts have been found in literature for the removal of waste from water, including graphene, graphene oxide, graphene hydrogels, carbon nanotubes, modified carbon, etc. However, these materials show less affinity for CIP; thus making its removal difficult using these catalysts. For example, Peng et al. demonstrated the removal of CIP using nitrogen-containing functional groups, functionalized by ordered mesoporous carbon CMK-3, at the rate of 329.9 mg/g [110]. Baylon et al. reported 1.7446 mg/g of CIP removal using multiwalled carbon nanotubes (MWCNT) [111]. Along with the porosity and crystallinity of the adsorbent, the functional groups present on it also contribute significantly to the adsorption performance. Thus, carbon-based ZIF-8 composites have been synthesized. These include ZIF-8-derived C@silica core-shell nanoparticles and N-doped nanoporous carbon [106, 108, 109]. Huang et al. synthesized ZIF-8 derived nanoporous carbon (NPC) by the carbonization of ZIF-8 and used it for CIP removal. Figure 8.6(A)

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8 Recent trends in ZIF-8-based composite materials for the removal of ciprofloxacin

shows the synthetic scheme of the NPC. The synthesized NPC-700 showed pristine rhombic dodecahedral morphology, with average particle sizes of 140–150 nm. The pore volume and the surface area of NPC-700 have been estimated as 0.65 cm3/g and 750 m2/g, respectively. As a result, NPC-700 showed outstanding adsorption capacity for CIP; that is, 416.7 mg/g. The removal of CIP by NPC-700 is basically due to the electrostatic and hydrophobic interactions [109]. CH3 (A)

NH

ZIF-8

r Ca

+ N

ni

2-Methylimidazole

n F

OH

N

OH O

O

Recycle

O

1.89 g Zn(NO3)2.6H2O 1.64g 2-Methylimidazole

N

io

N

NPC

F

(B)

N

t za

HN

N Et 3 F/ DM

(C) HN

bo

Zn2+

H H H HH H N N N ZIF-8

T = 140 °C t = 15 min 450 W

O

N2 - Flow

ZPC

ZPC-800

600, 800, 1000 °C 4 h, 3 °C/min

Figure 8.6: Synthetic scheme of (a) NPC-700 [109] and (b) ZPC [108]; (c) Interaction between functional groups on ZPC-800 and CIP [108].

ZIF-8-derived NPC shows exceptional adsorption capacity of CIP along with a high possibility of regeneration and reuse of catalyst, but the synthetic method is timeconsuming [108]. Therefore, Tran et al. proposed the new fabrication scheme for ZIF-8 derived NPC (ZPC), microwave synthesis. Figure 8.6(B) illustrates the fabrication scheme of ZPC. Microwave synthesis plays an important role in the reduction of the time required for synthesis [112]. It is reported that ZPC-800 exhibits a surface area of 268 m2/g and the adsorption capacity for CIP of 905.5 mg/g. Electrostatic interaction between the N-H functional group of ZPC-800 and CIP makes it a good adsorbent. The mechanism by which ZPC-800 removes CIP from waterbodies is shown in Figure 8.6(C). [108], but CIP is a zwitterion, forming anion and cation at pH > 9 and < 6, respectively. CIP becomes both positively and negatively charged at pH 6 to 9, whereas carbon becomes anionic at pH 6. So, the adsorption of CIP over such catalysts gets reduced due to the less electrostatic interaction between them [109]. It is observed in literature that silica coating over nanoparticles increases the anionic character of these particles [113]. So, Zhang et al. coated the ZIF-8-derived carbon catalyst with silica to evaluate the effect of silica on their adsorption behavior. Silica-based ZIF-8-derived carbon (C@silica) has been prepared by the carbonization

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of silica-coated ZIF-8 nanoparticles. The core-shell morphology of these nanoparticles has been observed with a thick shell of almost 13–28 nm. It has been found that silica enhances the adsorption capacity of the catalyst [106].

8.3.2 Iron-based ZIF-8 composites Doping of transition metal to ZIF-8 is one of the best tools to enhance the adsorption capacity of ZIF-8 as the doped metal provides more active sites for adsorption. Iron is a cheap, abundantly available, and non-toxic element and acts as a good adsorbent for various antibiotics. It adsorbs antibiotics through a cation bridge with nucleophilic groups of antibiotics [114]. Therefore, Jiang et al. synthesized an iron-doped ZIF-8 for the removal of CIP by the precipitation method. Fe-doped ZIF-8 showed exceptional CIP adsorption – 1484 mg/g. Fe-doped ZIF-8 is found to be more efficient than ZIF-8. ZIF-8 contains Zn2+, a 4-coordination ion whereas Fe2+ is a 6-coordination ion. On doping ZIF-8 with Fe2+, some of the Zn ions are replaced with Fe ions, which remain unsaturated, and its two empty coordination sites increase the number of active sites and coordinate with the nucleophilic groups of CIP [115]. Fe-doped ZIF-8 has been more selective for CIP and CTC than TC, AMX, and MNZ [107]. The difference in selectivity for antibiotics could be attributed to the type of functional group and the occurrence of aromatic rings in the structure of antibiotics [116].

8.3.3 Polymer-based ZIF-8 composites ZIF-8 has many advantages over other adsorbents but the very small size of ZIF-8 restricts its regain and reusability. Therefore, there must be a carrier for ZIF-8. Aerogels, as a carrier, make the catalyst recyclable because they are less dense and float over water [117]. Yan et al. used konjac glucomannan (KGM)-based aerogel as a carrier for ZIF-8 [105]. KGM is a lightweight, less dense, highly abundant, biodegradable, and cheap polymer that can form aerogel easily. Therefore, KGM-based aerogels have been used to immobilize nanoparticles [118]. The maximum adsorption capacity has been estimated to be 811.03 mg/g at 303 K and 7.0 pH when CIP concentration was 1500 mg/g [105].

8.4 Mechanism of adsorption A proper understanding of adsorption could be possible by knowing its mechanism. Several functional groups are present on the surface of ZIF-8 – that is, N atom, low coordinated Zn atoms, and imidazole [96]. These functional groups contribute

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significantly to the development of interaction between ZIF-8 and CIP. Adsorption takes place as a result of an interaction between CIP and ZIF-8 composite, depending on their physicochemical properties [83]. The interaction involved in the adsorptive removal of antibiotics from wastewater is π-π interaction, hydrogen bonding, electrostatic interaction, pore filling, and chemical coordination. Figure 8.7 shows the ways of interaction developed between CIF and ZIF-8 composites for the removal of CIP from wastewater. [119]. The type of interaction involved in adsorption depends on the type of adsorbent and the adsorbate.

HydrogenBonding Complexation Electrostatic Interaction

π-π Interaction

ZIF-8 based composites

Ciprofloxacin

CIP adsorbed on ZIF-8 based composites

Figure 8.7: Schematic illustration of the plausible mechanism of adsorption of CIP using ZIF-8 composites.

8.4.1 Electrostatic interaction Electrostatic interaction is the attractive force between oppositely charged ions [96]. Various ZIF-8 composites have been found to be involved in the removal of harmful waste products (including antibiotics, organic pollutants, inorganic metals, and other pharmaceutical products) via interaction between anions and cations of the adsorbate and the adsorbent [116, 120–122]. Electrostatic interaction plays a crucial role in the removal of CIP using carbon-based ZIF-8 catalysts [106, 107]. The solution pH contributes significantly to the electrostatic interaction as the nature of the charges on the surface of ZIF-8-based composites can be varied by changing the pH [116]. Researchers modify the zeta potential of composites to allow

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a favorable electrostatic interaction between the composites and CIP. Zhang et al. synthesized silica-coated ZIF-8 to reduce the zeta potential of the surface of the adsorbent and thus improve the efficiency of CIP removal [106]. CIP occurs as the anion, cation, and zwitterion in aqueous media. When using carbon-based ZIF-8 composites, electrostatic interaction occurs when CIP is in zwitterionic form; hydrophobic interaction when in cationic form; and electrostatic repulsion in the anionic form [123].

8.4.2 π–π Interaction It is a weak interactive force that arises between aromatic groups and frequently occurs between nucleophilic and electrophilic centers of a molecule [96]. The high adsorption efficiency of the composite for antibiotics is due to the π–π interaction. ZIF-8 contains Zn2+ and an imidazolate ring, which further forms π–π interaction with the aromatic ring of CIP, thus increasing the chances of CIP adsorption [91].

8.4.3 Hydrogen bonding Hydrogen bonding is one of the common interactions utilized for efficient adsorption [124]. This phenomenon is not limited to the purification of water but also finds application in fuel purification [125–127]. The surface functional groups of the adsorbent play a key role in the development of the H-bond with the adsorbate. For the adsorption via H-bonding, the adsorbent must have free groups (such as carboxyl, lactonic, phenolic, pyridine, pyroline, and amine) that are capable of forming H-bonds with an adsorbate. Ionic liquid-derived ZIF-8 composite with nitrogendoped carbon (IMDC) has several exposed free functional groups that result in the efficient removal of herbicides from an aqueous solution [67]. In the case of ZPC800, N-H is found, which can form an H-bond with the highly electronegative atom of CIP. Figure 8.6(C) shows the formation of H-bond between the catalyst and CIF for its efficient removal. [108].

8.5 Factors affecting the adsorption capacity of ZIF-8-based composites to remove CIP ZIF-8-based composites have been identified as a promising strategy to remove CIP from water bodies. ZIF-8 removes CIP from water by adsorption. The adsorption capacity of the composites is greatly influenced by factors such as pH, initial concentration of adsorbate, and dosage of adsorbent.

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8.5.1 pH pH is one of the prominent factors that influences the adsorption capacity of ZIF-8 based composites by producing variation in the surface charges of the adsorbent and affecting the extent of ionization of the adsorbate [116]. Figure 8.8 shows the effect of pH on the adsorption capacity of CIP by ZIF-8 based composites. It has been observed that the adsorption capacity of these composites shows a remarkable increase with the increase in pH from 3 to 6. It then starts to decrease when the pH becomes more than 6. The reason behind this change in adsorption capacity is the change in the behavior of electrostatic and hydrophobic interaction between the CIP and the carbon surface. CIP is an amphiphilic molecule and hence exists as a cation at pH below 6, a zwitterion between 6 and 9, and an anion above 9 [113]. The carbon surface becomes anionic when the pH is 6.0. Electrostatic interaction occurs between the oppositely charged ions. So, there is maximum adsorption at 6.0 due to the favorable electrostatic interaction between the zwitterion of CIP and the negatively charged carbon surface. When pH exceeds 6.0, the presence of several anions makes the electrostatic interaction unfavorable, thus restricting the efficient adsorption of CIP. When pH < 6.0, there is a decrease in the zwitterions of CIP, which leads to the hydrophobic interaction.

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Max qe ZIF-8 based composite

Figure 8.8: Effect of pH on the adsorption capacity of CIP by ZIF-8-based composites.

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The optimum pH for the removal of CIP from waterbodies using various ZIF-8based composites is reported as 6.0 [106, 109] or 7.0 [105, 107]. Figure 8.9 illustrates the effect of pH on the adsorption of CIP by various ZIF-8-based composites. (B)

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Fe doped ZIF–8 Optimum pH = 7.0

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Figure 8.9: Effect of pH on adsorption capacity of CIP by (a) Fe-doped ZIF-8 [107]; (b) KGM/ZIF-8 [105]; and (c) NPC-700 [109] and C@silica [106].

8.5.2 Dosage of adsorbent It is evaluated that there is no effective adsorption of CIP when the adsorbent is added in high concentrations. The addition of an excess adsorbent causes variation in the physical properties of the liquid/solid [108]. The adsorption capacity reduces with an increase in the dosage of the adsorbent. This is because there is much exposure of active sites at the low amount of adsorbent and thus saturation of adsorption sites occurs at a high rate, leading to the exceptional adsorption capacity [107, 109]. Figure 8.10 shows the impact of the concentration of adsorbent on the adsorption capacity.

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8.5.3 Initial concentration of CIP Literature studies have revealed that there is a direct relation between the initial concentration of the adsorbate and the adsorption efficiency (Figure 8.11) [108, 128, 129]. (A)

(B) 170 Adsorption Capacity (mg/g)

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Figure 8.10: Influence of adsorbent dosage on the adsorption capacity of CIP by (a) NPC-700 [109] and (b) Fe-doped ZIF-8 [107].

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(B) NPC-700

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Figure 8.11: Effect of initial concentration of CIP on the efficiency of adsorption of CIP by (a) NPC700 [109]; (b) ZPC-800 [108]; and (c) Fe-doped ZIF-8 [107].

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The high efficiency is due to the high concentration gradient between the adsorbate in water and the adsorbent. This concentration gradient acts as a driving force that pushes the CIP towards the adsorbent [109].

8.6 Regeneration and reusability of ZIF-8-based composites ZIF-8 has proved to be an efficient catalyst for the adsorptive removal of waste from the aquatic environment, but the regeneration of the catalyst is difficult due to its small size. To improve the reusability of ZIF-8, its composites have been synthesized [107, 123]. Regeneration and reusability are the important features of adsorbents for practical applications, and these two factors have made the ZIF-8 composites a promising candidate for the adsorption of pollutants from wastewater. The increase in the number of repetitions of the cycle causes a small change in the adsorption efficiency. Yang et al. used the Fe-doped ZIF-8 for the adsorption of CIP five times but the adsorption capacity remained almost unchanged [107]. The effect of reusability of Fedoped ZIF-8 on the efficiency of removal of ZIF-8 is shown in Figure 8.12(A). [107]. The results of the recyclability test of NPC-700 also proved that it is a stable adsorbent [109]. Figure 8.12(B) illustrates the impact of number of cycles of CIP removal by NPC-700 on the adsorption capacity of CIP. (A)

(B) Adsorption capacity (mg/g)

Adsorption capacity (mg/g)

1600 1400 1200 1000 800 600

400 200

100 80 60 40 20 0

0 1

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4 3 No. of cycle

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Figure 8.12: Reusability of (a) Fe-doped ZIF-8 [107] and (b) NPC-700 [109].

8.7 Conclusion CIP is a second-generation fluoroquinolone used to treat human and animal infections. Residues of CIP have been found in soil and water in different regions of the

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world. A high concentration of CIP in the aquatic environment acts as a threat to living organisms and the ecosystem, therefore there is a necessity to remove CIP from water bodies. Adsorption is found to be a cheap, effective, and simple method to eliminate CIP from water. MOFs are found to be emerging adsorbents due to their high porosity, crystallinity, and simple synthetic methods, but their low thermal and hydrothermal stabilities limit their uses. ZIF-8 has been proved as one of the thermostable MOFs. ZIF-8 composites are attractive as important adsorbents for CIP due to their recyclability. ZIF-8 composites sustain their adsorptive properties for several cycles. Therefore, they can be used in practical applications for the removal of CIP.

References [1] [2]

[3]

[4]

[5] [6]

[7] [8] [9] [10] [11]

[12] [13]

Kumar, M., et al., Antibiotics bioremediation: Perspectives on its ecotoxicity and resistance. Environment International, 2019. 124: p. 448–461. Rigos, G., K. Bitchava, and I. Nengas, Antibacterial drugs in products originating from aquaculture: assessing the risks to public welfare. Mediterranean marine science, 2010. 11(1): p. 33–42. Saini, R., et al., Screening of microbial enzymes and their potential applications in the bioremediation process, in microbial products for health, environment and agriculture. 2021: Springer, p. 359–378. Cowieson, A. and A. Kluenter, Contribution of exogenous enzymes to potentiate the removal of antibiotic growth promoters in poultry production. Animal Feed Science and Technology, 2019. 250: p. 81–92. He, Z., et al., Pharmaceuticals pollution of aquaculture and its management in China. Journal of Molecular Liquids, 2016. 223: p. 781–789. Hu, F.-Y., et al., Determination of 26 veterinary antibiotics residues in water matrices by lyophilization in combination with LC–MS/MS. Journal of Chromatography B, 2014. 949: p. 79–86. Matongo, S., et al., Pharmaceutical residues in water and sediment of Msunduzi River, kwazulu-natal, South Africa. Chemosphere, 2015. 134: p. 133–140. Christian, T., et al., Determination of antibiotic residues in manure, soil, and surface waters. Acta Hydrochimica Et Hydrobiologica, 2003. 31(1): p. 36–44. Wei, R., et al., Occurrence of veterinary antibiotics in animal wastewater and surface water around farms in Jiangsu Province, China. Chemosphere, 2011. 82(10): p. 1408–1414. Pan, L., et al., Determination and distribution of pesticides and antibiotics in agricultural soils from northern China. RSC Advances, 2019. 9(28): p. 15686–15693. Wei, R., et al., Occurrence of seventeen veterinary antibiotics and resistant bacterias in manure-fertilized vegetable farm soil in four provinces of China. Chemosphere, 2019. 215: p. 234–240. Kovalakova, P., et al., Occurrence and toxicity of antibiotics in the aquatic environment: A review. Chemosphere, 2020. 251: p. 126351. Jia, A., et al., Occurrence and fate of quinolone and fluoroquinolone antibiotics in a municipal sewage treatment plant. Water Research, 2012. 46(2): p. 387–394.

130

[14]

[15] [16]

[17]

[18]

[19]

[20] [21] [22]

[23]

[24]

[25]

[26]

[27] [28] [29]

[30]

[31]

Ramsha Saleem et al.

Xing, X., et al., Removal of ciprofloxacin from water by nitrogen doped TiO2 immobilized on glass spheres: Rapid screening of degradation products. Journal of Photochemistry and Photobiology. A, Chemistry, 2018. 359: p. 23–32. Jiang, W.-T., et al., Removal of ciprofloxacin from water by birnessite. Journal of Hazardous Materials, 2013. 250: p. 362–369. Ahmadi, S., et al., Efficacy of persulfate-based advanced oxidation process (US/PS/Fe 3 O 4) for ciprofloxacin removal from aqueous solutions. Applied Water Science, 2020. 10(8): p. 1–6. Liang, C., et al., ZIF-67 derived hollow cobalt sulfide as superior adsorbent for effective adsorption removal of ciprofloxacin antibiotics. Chemical Engineering Journal, 2018. 344: p. 95–104. Robinson, A.A., J.B. Belden, and M.J. Lydy, Toxicity of fluoroquinolone antibiotics to aquatic organisms. Environmental Toxicology and Chemistry: An International Journal, 2005. 24(2): p.423–430. Sosa-Hernández, J.E., et al., Sources of antibiotics pollutants in the aquatic environment under SARS-CoV-2 pandemic situation. Case Studies in Chemical and Environmental Engineering, 2021. 4: p. 100127. Bojarski, B., B. Kot, and M. Witeska, Antibacterials in aquatic environment and their toxicity to fish. Pharmaceuticals, 2020. 13(8): p.189. Al-Omar, M.A., Ciprofloxacin: Physical profile. Profiles of Drug Substances, Excipients and Related Methodology, 2005. 31: p. 163–178. Liu, J., et al., A granular adsorbent-supported Fe/Ni nanoparticles activating persulfate system for simultaneous adsorption and degradation of ciprofloxacin. Chinese Journal of Chemical Engineering, 2020. 28(4): p. 1077–1084. Fu, C., et al., Occurrence and distribution of antibiotics in groundwater, surface water, and sediment in Xiong’an New Area, China, and their relationship with antibiotic resistance genes. Science of the Total Environment, 2022. 807: p. 151011. Cui, C., et al., Occurrence, distribution, and seasonal variation of antibiotics in an artificial water source reservoir in the Yangtze River delta, East China. Environmental Science and Pollution Research, 2018. 25(20): p. 19393–19402. Cheng, J., et al., Occurrence, seasonal variation and risk assessment of antibiotics in the surface water of North China. Archives of Environmental Contamination and Toxicology, 2019. 77(1): p. 88–97. Zhou, L.-J., et al., Trends in the occurrence of human and veterinary antibiotics in the sediments of the Yellow River, Hai River and Liao River in northern China. Environmental Pollution, 2011. 159(7): p. 1877–1885. Zhou, Q., et al., Occurrence and risk assessment of antibiotics in the surface water of Chaohu Lake and its tributaries in China. Science of the Total Environment, 2022. 807: p. 151040. Chen, J., et al., Antibiotics in aquaculture ponds from Guilin, South of China: Occurrence, distribution, and health risk assessment. Environmental Research, 2022. 204: p. 112084. Zhang, D., et al., Risk assessments of emerging contaminants in various waters and changes of microbial diversity in sediments from Yangtze River chemical contiguous zone, Eastern China. Science of the Total Environment, 2022. 803: p. 149982. Zhang, J., et al., Occurrence, distribution and risk assessment of antibiotics at various aquaculture stages in typical aquaculture areas surrounding the Yellow Sea. Journal of Environmental Sciences, 2023. 126: p. 621–632. Agunbiade, F.O. and B. Moodley, Occurrence and distribution pattern of acidic pharmaceuticals in surface water, wastewater, and sediment of the Msunduzi River, Kwazulu‐ Natal, South Africa. Environmental Toxicology and Chemistry, 2016. 35(1): p.36–46.

8 Recent trends in ZIF-8-based composite materials for the removal of ciprofloxacin

131

[32] Muriuki, C.W., et al., Occurrence, distribution, and risk assessment of pharmaceuticals in wastewater and open surface drains of peri-urban areas: Case study of Juja town, Kenya. Environmental Pollution, 2020. 267: p. 115503. [33] Watkinson, A., et al., The occurrence of antibiotics in an urban watershed: From wastewater to drinking water. Science of the Total Environment, 2009. 407(8): p. 2711–2723. [34] Arun, S., et al., Occurrence, sources and risk assessment of fluoroquinolones in dumpsite soil and sewage sludge from Chennai, India. Environmental Toxicology and Pharmacology, 2020. 79: p. 103410. [35] Li, C., et al., Occurrence of antibiotics in soils and manures from greenhouse vegetable production bases of Beijing, China and an associated risk assessment. Science of the Total Environment, 2015. 521: p. 101–107. [36] Martínez-Carballo, E., et al., Environmental monitoring study of selected veterinary antibiotics in animal manure and soils in Austria. Environmental Pollution, 2007. 148(2): p. 570–579. [37] Singh, V. and S. Suthar, Occurrence, seasonal variations, and ecological risk of pharmaceuticals and personal care products in River Ganges at two holy cities of India. Chemosphere, 2021. 268: p. 129331. [38] Afonso-Olivares, C., Z. Sosa-Ferrera, and J.J. Santana-Rodríguez, Analysis of antiinflammatory, analgesic, stimulant and antidepressant drugs in purified water from wastewater treatment plants using SPE-LC tandem mass spectrometry. Journal of Environmental Science and Health, Part A, 2012. 47(6): p.887–895. [39] Chen, H., et al., Characterization of antibiotics in a large-scale river system of China: Occurrence pattern, spatiotemporal distribution and environmental risks. Science of the Total Environment, 2018. 618: p. 409–418. [40] Khan, N.A., et al., Development of Mn-PBA on GO sheets for adsorptive removal of ciprofloxacin from water: Kinetics, isothermal, thermodynamic and mechanistic studies. Materials Chemistry and Physics, 2020. 245: p. 122737. [41] Batt, A.L., S. Kim, and D.S. Aga, Comparison of the occurrence of antibiotics in four full-scale wastewater treatment plants with varying designs and operations. Chemosphere, 2007. 68(3): p.428–435. [42] Sodhi, K.K. and D.K. Singh, Insight into the fluoroquinolone resistance, sources, ecotoxicity, and degradation with special emphasis on ciprofloxacin. Journal of Water Process Engineering, 2021. 43: p. 102218. [43] Dehghan, A., et al., Enhanced kinetic removal of ciprofloxacin onto metal-organic frameworks by sonication, process optimization and metal leaching study. Nanomaterials, 2019. 9(10): p. 1422. [44] Rojas, S. and P. Horcajada, Metal–organic frameworks for the removal of emerging organic contaminants in water. Chemical Reviews, 2020. 120(16): p.8378–8415. [45] Lindberg, R.H., et al., Behavior of fluoroquinolones and trimethoprim during mechanical, chemical, and active sludge treatment of sewage water and digestion of sludge. Environmental Science & Technology, 2006. 40(3): p. 1042–1048. [46] de Ilurdoz, M.S., J.J. Sadhwani, and J.V. Reboso, Antibiotic removal processes from water & wastewater for the protection of the aquatic environment-a review. Journal of Water Process Engineering, 2022. 45: p. 102474. [47] Mangla, D., A. Sharma, and S. Ikram, Critical review on adsorptive removal of antibiotics: Present situation, challenges and future perspective. Journal of Hazardous Materials, 2022. 425: p. 127946. [48] Menschik, M., et al., Effects of ciprofloxacin and ofloxacin on adult human cartilage in vitro. Antimicrobial Agents and Chemotherapy, 1997. 41(11): p. 2562–2565.

132

Ramsha Saleem et al.

[49] An, T., et al., Mechanistic considerations for the advanced oxidation treatment of fluoroquinolone pharmaceutical compounds using TiO2 heterogeneous catalysis. The Journal of Physical Chemistry A, 2010. 114(7): p. 2569–2575. [50] Liu, J., X. Li, and X. Wang, Toxicological effects of ciprofloxacin exposure to Drosophila melanogaster. Chemosphere, 2019. 237: p. 124542. [51] Yang, C., G. Song, and W. Lim, A review of the toxicity in fish exposed to antibiotics. Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology, 2020. 237: p. 108840. [52] Wang, H., et al., Toxicity evaluation of β‐diketone antibiotics on the development of embryo‐ larval zebrafish (Danio rerio). Environmental Toxicology, 2014. 29(10): p. 1134–1146. [53] Yin, X., et al., Toxicological assessment of trace β-diketone antibiotic mixtures on zebrafish (Danio rerio) by proteomic analysis. PLoS One, 2014. 9(7): p. e102731. [54] Ding, L., et al., Joint toxicity of fluoroquinolone and tetracycline antibiotics to zebrafish (Danio rerio) based on biochemical biomarkers and histopathological observation. The Journal of Toxicological Sciences, 2017. 42(3): p. 267–280. [55] Cuprys, A., et al., Potential of agro-industrial produced laccase to remove ciprofloxacin. Environmental Science and Pollution Research, 2022. 29(7): p. 10112–10121. [56] Hassan, M., et al., Removal of antibiotics from wastewater and its problematic effects on microbial communities by bioelectrochemical technology: Current knowledge and future perspectives. Environmental Engineering Research, 2021. 26(1): p. 16–30. [57] Do, M.T. and D.C. Stuckey, Fate and removal of Ciprofloxacin in an anaerobic membrane bioreactor (AnMBR). Bioresource Technology, 2019. 289: p. 121683. [58] Ahmadzadeh, S., et al., Removal of ciprofloxacin from hospital wastewater using electrocoagulation technique by aluminum electrode: Optimization and modelling through response surface methodology. Process Safety and Environmental Protection, 2017. 109: p. 538–547. [59] Behera, S.K., et al., Occurrence and removal of antibiotics, hormones and several other pharmaceuticals in wastewater treatment plants of the largest industrial city of Korea. Science of the Total Environment, 2011. 409(20): p. 4351–4360. [60] Košutić, K., et al., Removal of antibiotics from a model wastewater by RO/NF membranes. Separation and Purification Technology, 2007. 53(3): p. 244–249. [61] Xu, Z., et al., Removal of antibiotics by sequencing-batch membrane bioreactor for swine wastewater treatment. Science of the Total Environment, 2019. 684: p. 23–30. [62] Wang, T., et al., Adsorptive removal of antibiotics from water using magnetic ion exchange resin. Journal of Environmental Sciences, 2017. 52: p. 111–117. [63] Ahmed, M.B., et al., Adsorptive removal of antibiotics from water and wastewater: Progress and challenges. Science of the Total Environment, 2015. 532: p. 112–126. [64] Khoshnamvand, N., et al., Response surface methodology (RSM) modeling to improve removal of ciprofloxacin from aqueous solutions in photocatalytic process using copper oxide nanoparticles (CuO/UV). AMB Express, 2018. 8(1): p. 1–9. [65] Malakootian, M., et al., Photocatalytic ozonation degradation of ciprofloxacin using ZnO nanoparticles immobilized on the surface of stones. Journal of Dispersion Science and Technology, 2019. 40(6): p. 846–854. [66] Shehu Imam, S., R. Adnan, and N.H. Mohd Kaus, Photocatalytic degradation of ciprofloxacin in aqueous media: A short review. Toxicological and Environmental Chemistry, 2018. 100 (5–7): p.518–539. [67] Sarker, M., I. Ahmed, and S.H. Jhung, Adsorptive removal of herbicides from water over nitrogen-doped carbon obtained from ionic liquid@ ZIF-8. Chemical Engineering Journal, 2017. 323: p. 203–211.

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[68] Rafatullah, M., et al., Adsorption of methylene blue on low-cost adsorbents: A review. Journal of Hazardous Materials, 2010. 177(1–3): p. 70–80. [69] Lee, K.M., et al., Recent developments of zinc oxide based photocatalyst in water treatment technology: A review. Water Research, 2016. 88: p. 428–448. [70] Maggio, A.A., et al., Fe-and SiFe-pillared clays from a mineralogical waste as adsorbents of ciprofloxacin from water. Applied Clay Science, 2022. 220: p. 106458. [71] Arif, M., et al., Carbon dioxide activated biochar-clay mineral composite efficiently removes ciprofloxacin from contaminated water-Reveals an incubation study. Journal of Cleaner Production, 2022. 332: p. 130079. [72] Falyouna, O., et al., Synthesis of hybrid magnesium hydroxide/magnesium oxide nanorods [Mg (OH) 2/MgO] for prompt and efficient adsorption of ciprofloxacin from aqueous solutions. Journal of Cleaner Production, 2022. 342: p. 130949. [73] Tang, J., et al., A mechanistic study of ciprofloxacin adsorption by goethite in the presence of silver and titanium dioxide nanoparticles. Journal of Environmental Sciences, 2022. 118: p. 46–56. [74] Magesh, N., et al., Adsorption behavior of fluoroquinolone (ciprofloxacin) using zinc oxide impregnated activated carbon prepared from jack fruit peel: Kinetics and isotherm studies. Chemosphere, 2022. 290: p. 133227. [75] Fu, H., et al., Activated carbon adsorption of quinolone antibiotics in water: Performance, mechanism, and modeling. Journal of Environmental Sciences, 2017. 56: p. 145–152. [76] Li, X., et al., Adsorption of ciprofloxacin, bisphenol and 2-chlorophenol on electrospun carbon nanofibers: In comparison with powder activated carbon. Journal of Colloid and Interface Science, 2015. 447: p. 120–127. [77] Dou, S., et al., Fish scale-based biochar with defined pore size and ultrahigh specific surface area for highly efficient adsorption of ciprofloxacin. Chemosphere, 2022. 287: p. 131962. [78] Hamadeen, H.M. and E.A. Elkhatib, New nanostructured activated biochar for effective removal of antibiotic ciprofloxacin from wastewater: Adsorption dynamics and mechanisms. Environmental Research, 2022. 210: p. 112929. [79] Yu, F., et al., HKUST-1-derived Cu@ Cu (I)@ Cu (II)/Carbon adsorbents for ciprofloxacin removal with high adsorption performance. Separation and Purification Technology, 2022. 288: p. 120647. [80] Huang, S., et al., In-situ fabrication from MOFs derived MnxCo3-x@ C modified graphite felt cathode for efficient electro-Fenton degradation of ciprofloxacin. Applied Surface Science, 2022. 586: p. 152804. [81] Ibrahim, A.O., et al., Adsorptive removal of different pollutants using metal-organic framework adsorbents. Journal of Molecular Liquids, 2021. 333: p. 115593. [82] Chung, Y.G., et al., Computation-ready, experimental metal–organic frameworks: A tool to enable high-throughput screening of nanoporous crystals. Chemistry of Materials, 2014. 26(21): p. 6185–6192. [83] Du, C., et al., A review of metal organic framework (MOFs)-based materials for antibiotics removal via adsorption and photocatalysis. Chemosphere, 2021. 272: p. 129501. [84] Li, S., et al., Water purification: Adsorption over metal‐organic frameworks. Chinese Journal of Chemistry, 2016. 34(2): p. 175–185. [85] Mon, M., et al., Metal–organic framework technologies for water remediation: Towards a sustainable ecosystem. Journal of Materials Chemistry A, 2018. 6(12): p. 4912–4947. [86] Gadipelly, C.R., K.V. Marathe, and V.K. Rathod, Effective adsorption of ciprofloxacin hydrochloride from aqueous solutions using metal-organic framework. Separation Science and Technology, 2018. 53(17): p.2826–2832.

134

Ramsha Saleem et al.

[87] Jiang, M., et al., Hierarchically porous N-doped carbon derived from ZIF-8 nanocomposites for electrochemical applications. Electrochimica Acta, 2016. 196: p. 699–707. [88] Tran, U.P., K.K. Le, and N.T. Phan, Expanding applications of metal− organic frameworks: Zeolite imidazolate framework ZIF-8 as an efficient heterogeneous catalyst for the knoevenagel reaction. Acs Catalysis, 2011. 1(2): p.120–127. [89] Lai, Z., Development of ZIF-8 membranes: Opportunities and challenges for commercial applications. Current Opinion in Chemical Engineering, 2018. 20: p. 78–85. [90] Abdelhamid, H.N., Zeolitic imidazolate frameworks (ZIF-8) for biomedical applications: A review. Current Medicinal Chemistry, 2021. 28(34): p.7023–7075. [91] Liu, X., et al., A facile approach for the synthesis of Z-scheme photocatalyst ZIF-8/gC 3 N 4 with highly enhanced photocatalytic activity under simulated sunlight. New Journal of Chemistry, 2018. 42(14): p. 12180–12187. [92] Pan, Y., et al., Rapid synthesis of zeolitic imidazolate framework-8 (ZIF-8) nanocrystals in an aqueous system. Chemical Communications, 2011. 47(7): p. 2071–2073. [93] Pattengale, B., et al., Exceptionally long-lived charge separated state in zeolitic imidazolate framework: Implication for photocatalytic applications. Journal of the American Chemical Society, 2016. 138(26): p. 8072–8075. [94] Banerjee, R., et al., High-throughput synthesis of zeolitic imidazolate frameworks and application to CO2 capture. Science, 2008. 319(5865): p. 939–943. [95] Troyano, J., et al., Colloidal metal–organic framework particles: The pioneering case of ZIF-8. Chemical Society Reviews, 2019. 48(23): p. 5534–5546. [96] Dai, H., et al., Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication, applications and perspective. Coordination Chemistry Reviews, 2021. 441: p. 213985. [97] Dong, R., et al., Removal of phenol from aqueous solution using acid-modified Pseudomonas putida-sepiolite/ZIF-8 bio-nanocomposites. Chemosphere, 2020. 239: p. 124708. [98] Feng, Y., et al., Enzymes@ ZIF-8 nanocomposites with protection nanocoating: Stability and acid-resistant evaluation. Polymers, 2019. 11(1): p. 27. [99] Guo, Y., et al., ZIF-8 coated polyvinylidenefluoride (PVDF) hollow fiber for highly efficient separation of small dye molecules. Applied Materials Today, 2016. 5: p. 103–110. [100] He, Y., et al., ZIF-8-derived photocatalyst membrane for water decontamination: From static adsorption-degradation to dynamic flow removal. Science of the Total Environment, 2022. 824: p. 153865. [101] Arabkhani, P., et al., Decorating graphene oxide with zeolitic imidazolate framework (ZIF-8) and pseudo-boehmite offers ultra-high adsorption capacity of diclofenac in hospital effluents. Chemosphere, 2021. 271: p. 129610. [102] Liu, G., et al., Adsorption and removal of organophosphorus pesticides from environmental water and soil samples by using magnetic multi-walled carbon nanotubes@ organic framework ZIF-8. Journal of Materials Science, 2018. 53(15): p. 10772–10783. [103] Ding, Y., et al., Structure induced selective adsorption performance of ZIF-8 nanocrystals in water. Colloids and Surfaces A Physicochemical and Engineering Aspects, 2017. 520: p. 661–667. [104] Abdi, J., Synthesis of Ag-doped ZIF-8 photocatalyst with excellent performance for dye degradation and antibacterial activity. Colloids and Surfaces A Physicochemical and Engineering Aspects, 2020. 604: p. 125330. [105] Yuan, Y., et al., Preparation of konjac glucomannan-based zeolitic imidazolate framework-8 composite aerogels with high adsorptive capacity of ciprofloxacin from water. Colloids and Surfaces A Physicochemical and Engineering Aspects, 2018. 544: p. 187–195.

8 Recent trends in ZIF-8-based composite materials for the removal of ciprofloxacin

135

[106] Li, Y., et al., Preparation of C@ silica core/shell nanoparticles from ZIF-8 for efficient ciprofloxacin adsorption. Chemical Engineering Journal, 2018. 343: p. 645–653. [107] Yang, H., et al., Fe-doped zeolitic imidazolate framework-8 as superior adsorbent for enhanced ciprofloxacin removal from aqueous solution. Applied Surface Science, 2022. 586. [108] Dang, H.H., et al., Zeolitic-imidazolate framework-derived N-self-doped porous carbons with ultrahigh theoretical adsorption capacities for tetracycline and ciprofloxacin. Journal of Environmental Chemical Engineering, 2021. 9(1): p. 104938. [109] Li, S., X. Zhang, and Y. Huang, Zeolitic imidazolate framework-8 derived nanoporous carbon as an effective and recyclable adsorbent for removal of ciprofloxacin antibiotics from water. Journal of Hazardous Materials, 2017. 321: p. 711–719. [110] Peng, X., et al., Adsorption behavior and mechanisms of ciprofloxacin from aqueous solution by ordered mesoporous carbon and bamboo-based carbon. Journal of Colloid and Interface Science, 2015. 460: p. 349–360. [111] Avcı, A., İ. İnci, and N. Baylan, Adsorption of ciprofloxacin hydrochloride on multiwall carbon nanotube. Journal of Molecular Structure, 2020. 1206: p. 127711. [112] Van Tran, T., et al., Microwave-assisted solvothermal fabrication of hybrid zeolitic–imidazolate framework (ZIF-8) for optimizing dyes adsorption efficiency using response surface methodology. Journal of Environmental Chemical Engineering, 2020. 8(4): p. 104189. [113] Kandula, S. and P. Jeevanandam, Synthesis of Silica@ Ni‐Co mixed metal oxide core–shell nanorattles and their potential use as effective adsorbents for waste water treatment. European Journal of Inorganic Chemistry, 2015. 2015(25): p.4260–4274. [114] Wu, Y., et al., The correlation of adsorption behavior between ciprofloxacin hydrochloride and the active sites of Fe-doped MCM-41. Frontiers in Chemistry, 2018. 6: p. 17. [115] Liang, G., et al., Relying on the non-radical pathways for selective degradation organic pollutants in Fe and Cu co-doped biochar/peroxymonosulfate system: The roles of Cu, Fe, defect sites and ketonic group. Separation and Purification Technology, 2021. 279: p. 119697. [116] Yang, H., et al., High-performance Fe-doped ZIF-8 adsorbent for capturing tetracycline from aqueous solution. Journal of Hazardous Materials, 2021. 416: p. 126046. [117] Yu, M., et al., Magnetic carbon aerogel pyrolysis from sodium carboxymethyl cellulose/ sodium montmorillonite composite aerogel for removal of organic contamination. Journal of Porous Materials, 2018. 25(3): p. 657–664. [118] Xiao, M., et al., Carboxymethyl modification of konjac glucomannan affects water binding properties. Carbohydrate Polymers, 2015. 130: p. 1–8. [119] Hasan, Z. and S.H. Jhung, Removal of hazardous organics from water using metal-organic frameworks (MOFs): Plausible mechanisms for selective adsorptions. Journal of Hazardous Materials, 2015. 283: p. 329–339. [120] Zhou, L., et al., A new nFe@ ZIF-8 for the removal of Pb (II) from wastewater by selective adsorption and reduction. Journal of Colloid and Interface Science, 2020. 565: p. 167–176. [121] Peng, J., et al., Hierarchically porous ZIF-8 for tetracycline hydrochloride elimination. Journal of Sol-Gel Science and Technology, 2021. 99(2): p. 339–353. [122] Wang, Y., et al., In situ growth of ZIF-8 nanoparticles on chitosan to form the hybrid nanocomposites for high-efficiency removal of Congo Red. International Journal of Biological Macromolecules, 2019. 137: p. 77–86. [123] Qiu, J., et al., Acid-promoted synthesis of UiO-66 for highly selective adsorption of anionic dyes: Adsorption performance and mechanisms. Journal of Colloid and Interface Science, 2017. 499: p. 151–158.

136

Ramsha Saleem et al.

[124] Ahmed, I. and S.H. Jhung, Applications of metal-organic frameworks in adsorption/ separation processes via hydrogen bonding interactions. Chemical Engineering Journal, 2017. 310: p. 197–215. [125] Seo, P.W., I. Ahmed, and S.H. Jhung, Adsorptive removal of nitrogen-containing compounds from a model fuel using a metal–organic framework having a free carboxylic acid group. Chemical Engineering Journal, 2016. 299: p. 236–243. [126] Abdelhameed, R.M., et al., Cu-BTC metal-organic framework natural fabric composites for fuel purification. Fuel Processing Technology, 2017. 159: p. 306–312. [127] Seo, P.W., et al., Adsorptive removal of pharmaceuticals and personal care products from water with functionalized metal-organic frameworks: Remarkable adsorbents with hydrogenbonding abilities. Scientific Reports, 2016. 6(1): p. 1–11. [128] Alghamdi, A.A., et al., Efficient adsorption of lead (II) from aqueous phase solutions using polypyrrole-based activated carbon. Materials, 2019. 12(12): p. 2020. [129] Sahnoun, S., et al., Adsorption of tartrazine from an aqueous solution by octadecyltrimethylammonium bromide-modified bentonite: Kinetics and isotherm modeling. Comptes Rendus Chimie, 2018. 21(3–4): p. 391–398.

Nazia Rasool, Zohaib Saeed✶, Muhammad Pervaiz, Rashida Bashir, Umer Younas, Hafiz Amir Nadeem, Ayoub Rashid, Ahmad Adnan

9 Future prospects for ZIF-8-based composite material for decontamination of water Abstract: Zeolitic imidazolate framework-8 (ZIF-8), is a metal organic framework, which consists of two atoms of Zn metal and 2-methylimidazole and is a popular MOF material. ZIF-8 contains the quirky properties and these properties grant it higher-level absorption capacity and fine host capacity for the photocatalytic material, making it an excellent outline material for the decontamination of wastewater. Nevertheless, decline in surface results when ZIF-8 is collected together, and due to these properties, ZIF-8 is used widely for decontamination of wastewater. It is very difficult to detach them from wastewater after the removal of pollutants because they show weak recyclability. A novel ZIF-8 material that is currently being used has solved the above problem and is being successfully used in the treatment of wastewater or decontamination of water. There has been ongoing research on ZIF-8 composites as adsorbents and photocatalysts to drag out the pollutants from wastewater.

9.1 Introduction As one of the major environmental problems, the pollutants in the wastewater endanger human health [1, 2]. Therefore, it is immensely crucial and important to manage and control water pollution. There are vast ranges of sources that contain the different kind of complex components, which cause pollution of water. Many emerging organic contaminants (EOCs) cause the water pollution, as do pharmaceutical, some industrial pollutants and care products, and so forth. Due to their chemical and physical properties such as highly water solubility and high grade, most of EOCs can be barely removed from the wastewater after the treatment even at very low concentration. Apart from EOCs, inorganic pollutants are the cause of several crucial issues of human health due to their carcinogenicity, mutagenicity, toxicity, and teratogenicity ✶ Corresponding author: Zohaib Saeed, Department of Chemistry, Government College University, Lahore, Pakistan, e-mail: [email protected] Nazia Rasool, Zohaib Saeed, Muhammad Pervaiz, Hafiz Amir Nadeem, Ayoub Rashid, Ahmad Adnan, Department of Chemistry, Government College University, Lahore, Pakistan Umer Younas, Department of Chemistry, The University of Lahore, Lahore, Pakistan Rashida Bashir, Division of Science and Technology, University of Education, Lahore, Pakistan

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as also environment complaints that effect the environment badly [3]. Many strategies and techniques have been followed to purify the wastewater, like coagulation, filtration, and others. Anyhow, owing to large facilities and along with high costs of exorbitant maintenance all these methods and techniques are not very good for wastewater treatment. Furthermore, it is a huge problem to separate the pollutants or concentrate them to make them nonpoisonous It is more economical to treat water pollutants by using adsorption and photocatalytic reaction. In order to acquire good efficiency in removal of pollutants for the preparation of photocatalyst and adsorbents, researchers are trying to produce a novel material [4].

9.1.1 What is MOF in terms of ZIF-8? MOF is an arduously investigated material for engineers and researchers because of its porous properties, and it is popular as a porous coordination polymer and also a kind of porous inorganic/organic hybrid material. MOF has high surface area, ordered pore structure, polymetal sites, high crystallinity and capabilities of polymer. Its novel distinct properties and diversity in structure make it a fascinating material for removal of pollutants, toxic material, and a few EOCs from wastewater [5]. Zeolite is a type of MOF that contains zeolites structure, which is carried by reaction in solvents with source of metal of Co or Zn atoms and by the derivatives of imidazole derivates, which act as organic ligands. After the discovery of ZIF-8 in 2006, it has played a vital role in many fields due to its novel properties or applications. ZIF-8 is considered as an archetypal material. A group, namely Chen, initially prepared it and named it as MAF-4. Thereafter, a new group, namely Yaghi research team, studied it methodically, and then named it ZIF-8, which has then become its official name. The chemical formula of ZIF-8 is Zn (Hmim) 2, and it consists of 2-methylimdazole and a metal atom of Zn. When compared to other MOFs, the synthesis plans or strategies are easy for ZIF-8 [6].

9.1.2 Use of ZIF-8 in different fields due to its novel properties When the temperature is high, such as above 500 °C, ZIF exhibits structure stability and thermal stability. Also, ZIF-8 has novel properties such as retaining its crystallinity and porosity when it is introduced in various solutions, for example, in organic solutions [3]. ZIF-8 has effortlessly tailorable structure and pore size, which play an advantageous role in its modification. Furthermore, there is amplification in the applications range of traditional ZIF-8, because the formation is mesoporous and multi-stage porous in ZIF-8 [7]. Since ZIF-8 material is used extensively in many other forms like colloid, membrane, thin film, and powder form, it is used in a wide variety of fields.

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9.1.3 Use of ZIF-8-based composites in decontamination of wastewater or removal of pollutants from water The quirky physical and chemical properties of ZIF-8 offer a very excellent stage for research and designs in the field of adsorption and photocatalyst system and help remove the pollutants. However, ZIF-8 has the following shortcomings: (i) ZIF-8 nanoparticles aggregate in water, which results in decline of interfacial area, transfer of resistance, and increase in particle size, thereby resulting in a decrease in its adsorption performance; (ii) because of the large band gap, ZIF-8 displays asthenic response to visible light, and this affects its efficiency of solar irradiation [8]. Nowadays, ZIF-8 material is successfully synthesized with the help of active species, for example, metals, oxides, fibers, graphene, polyoxometalates (POMs), carbon nanotubes, and many others (Figure 9.1). When compared to the sterling microporous ZIF-8, ZIF-8 composites increase not only the photocatalyst activity and adsorption capacity but also the range of applications range [2, 4, 6]. For instance, when ZIF-8 is fixed on erected matrix, it controls the common shortcoming of ZIF-8, namely limited processability, and this also maintains the stability of matrix and catalytic activity of ZIF-8. MoO3@ZIF-8 was prepared by Zang et al., in order to decrease the Cr(VI) beneath visible light. MoO3@ZIF shows good photocatalytic activity as compared to the nanowires of ZIF-8 and MoO3 [9]. The good structure making and flexibility property of ZIF-8/PDA/PAN composite fiber make it easy to separate them from liquid after

POMs CNTs graphene

Enzymes

ZIF-8 QDs Polymers

Metal Fibers

Nano-particles Oxides

Figure 9.1: Functional groups consolidated with ZIF-8.

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adsorption [10]. In the synthesis strategies, ZIF-8 composites are classified into disparate forms like bottom-up approach and postsynthetic approach. The bottom-up approach is for single particles of ZIF-8 nanocomposites. In postsynthetic approach, single particle ZIF-8 composites are formed. On the basis of expatiate structure, ZIF-8 composites are divided into three categories: ZIF-8 membrane or thin film, ZIF-8 core shell particles, and some other distinct structures [9, 11]. The MOF-based composites synthesis strategies and major physicochemical properties are described in many articles [12, 13]. This chapter will describe about the different forms of ZIF-8 composites and also throw light on the latest progress or advancement of ZIF-8 composites in the degradation of wastewater by using adsorption or photocatalytic activity.

9.2 Synthesis designs for ZIF-8-based composites There are many effective approaches of making ZIF-8 composite materials with the help of synergistic properties of host and guest components and the making of nanocomposite [14, 15]. When synthesizing ZIF-8 nanoparticles it is critical and difficult to achieve proper control, because the localization of nucleation and its ensuing growth around the functional guest can be proved by optical structure of ZIF-8. Thus, generating composites is not possible with other techniques, for instance covalent linkage or surface-adsorption and guest infiltration [16]. Single-particle-ZIF-8 composite are of two categories, encapsulation of guest material into ZIF-8 and postsynthetic hybridization of pre-synthesized ZIF-8 with the aid of functional material [17, 18]. The encapsulation of ZIF-8 nanoparticles is done by two methods. The first is SIABA (ship-in-a-bottle approach) in which precursors are introduced into the pre-prepared ZIF-8 shells. In order to decrease or decompose the precursors to produce the particles which deposit in the cavity, usually ZIF-8 works as a superlative self-sacrificial template (Figure 9.2). Generally, when nanoparticles are present in the form of liquid nanodroplets, it is very difficult to attain pore size distribution inside the cavity. In the bottle-around-ship method which was used by Liu et al. EGaIn nanodroplets were successfully encapsulated into ZIF-8 cavities. Numerous ethylene-moieties and carbonyl groups on polyvinylpyrrolidone (PVP) cause the promotion of ZIF-8 all over EGaIn, when the EGaIn nanoparticles are treated with polyvinylpyrrolidone (PVP) [19]. A few creative and new ideas were given by the advanced studies of liquid particle-based ZIF-8 composites by Liu et al. [20]. With the help of previous studies, it is considered that by using the above mentioned encapsulation strategies, ZIF-8 could also be buried through many molecules in order to make the ZIF-8 composites, by low cost photochemical process (Figure 9.3a). There have been many methods discussed in order to prepare the ZIF-8 composites, which are in situ method, template method,

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and surface modification method. The wastewater treatment on the basis of disparate ZIF-8 composites is described in Table 9.1.

D Enc rugs aps tion ula-

s ug dr

Ino r mo ganic l enc ecules aps tion ula

mo Bio l Enc ecule aps s -tio ula n poly mer s

biomoleculeS

Zn+2 +

Inorganic molecules encapsulation

Inorganic s5 Nanoparticle

ds -ro no Na

Sph ere s

es Cub

ars St

Figure 9.2: Encapsulation of inorganic molecules and bio molecules is described in a schematic way.

Table 9.1: Pollutants which are decontaminated from wastewater by ZIF-8 composites. Ref [5, 21–29]. Types

Absorbates

Composites

Synthesis methods

Cr(VI) As(III) As(III) MG RhB RhB Pb(II) and -naphthylamine

CF/LDG@ZIF- Fe@ZIF- MnO@ZIF- ZIF-@CNT MnO@ZIF- Tio@ZIF- ZIF-@GO

In situ method Microfluidic method Template method Surface modification method Solvothermal method Sonochemical method In situ method

Pb(II) and Cd(II) Hg(II) CR

BC@ZIF- HRP@ZIF- ZIF-@CS

In situ method In situ method In situ method

ZIF- Inorganic

ZIF- Organic

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Table 9.1 (continued) Types

Absorbates

Composites

Synthesis methods

CIP Tc -napthol

KGM/ZIF- ZIF-@PTA/Au ZIF-@wool

Sol gel method Hydrothermal method In situ method

9.2.1 Synthesis of ZIF-8-based composite by in situ method This method is a very simple method because of the higher requirements of the properties of material. The basic principle is that in order to make disparate groups, dispense biochemical reaction or interaction to attain binding without treatment by the utilization of some definite functional groups or surface distinctness of the components of material [30]. PS@ZIF core shell particles were prepared by Lee and Hwang et al. by in situ method [31]. They incorporated ZIF-8 with the affinity of hydroxyl group on the surface of polystyrene microsphere to ZIF-8 by using polystyrene as carrier as shown in Figure 9.2. In this process, the core bears negative charge and Zn + 2 absorbs it, and then, ZIF-8 is formed around the core. The control of shell thickness is done during the stepwise process [32]. The in situ method was used by Ma et al. They tried to use cellulose of bacteria as carrier and made BC@ZIF core shell with the help of fragile interaction between ZIF-8 groups and BC. The structural integrity with compressive strain of BC@ZIF is more than 80%. TiO2/ZIF8 was used by Ran group in the in situ method. In their experiment, they pretreated the cotton fiber with poly-dopamine; thus, Zn + 2 could chelate with phenolic hydroxyl function group of poly-domine. Therefore, in situ growth of TiO2/ZIF-8 on CF happens. There are some other methods like reverse diffusion method in which on both ends of the matrix, two precursors (of ZIF-8) are used and due to difference in the concentrations, the two solutions will diffuse in different directions throughout the pore of substrate. A film is made when they nucleate [33].

9.2.2 Synthesis of ZIF-8-based composite by surface modification method In this process, the adsorption and binding force got strong among some nanoparticles and ZIF-8, by using the surface of nuclear particles with few numbers of surfactants, crystal seed or coupling agent, in order to attain their close combination. This method is very easy and applied widely [34, 35]. In 2012, a variety of inorganic nanoparticles were encapsulated in ZIF-8. Lu et al. used the encapsulation by in situ

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A ZIF-8

Metals Molecules Inorganic NP

B

ZIF-8 growth MeOH heat Carboxylate-terminated polystyrene ZIF-8 precursors

Polystyrene@ZIF-8 core shell microshpere

C seeding process

2h

[H

R 2O T M eO

gr ow th

H]

Seeded MSS RT 5min[H20]

ZI F-8

MSS

MSS-ZIF-8

Figure 9.3: (a) ZIF-8 with inorganic nanoparticles (left), polymer metal coating (right), (b) preparation scheme. and (c) preparation of MSS-ZIF-8.

method of the functional guest into ZIF-8 crystal, and then, they used the PVP in order to work in NPs [36]. They encapsulated many nanoparticles in the form of sphere and cube (Figure 9.4), because of the interaction of NPs@ZIF-8 between two nonpolar denominators among some organic ligands in order to endure the combination of NPs and ZIF-8 material. PT/ZIF8, Pd/ZIF-8 and Au/ZIF-8 show great catalytic

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activity. To show the surface modification method, all these are taken as instances for the future studies of making of ZIF-8 composites by this method. In seed crystal by secondary growth method, there is use of nanoscale ZIF-8 seed particles instead of chemical reagent, in order to speed up the growth of ZIF-8 crystal and modify the surface of the carrier particles, with the help of speed crystal, and in the end, it formed ZIF-8 crystals (Figure 9.3c). Sorribas et al. used mesoporous silica ZIF-8 in the form of sphere; here, ZIF-8 grew around the MMS with the help of seeding process and they used mesoporous MMS as core and also as a template [37]. Zn + 2 chelates with MSS and results in the nucleation of ZIF-8 crystal. By thermo gravimetric analysis, it has been reported that MSS-Z8 was stable when temperature is above 400 °C.

9.2.3 Synthesis of ZIF-8-based composite by template synthesis method There are two types of template synthesis: the first is soft template method and other one is hard template method. Soft or hard template method is used for the material in which molecules have stiff structure. However, the material has molecules which have no fixed structure and which have the threshold limiting ability in a space, it affects the growth of nuclear particles; then template synthesis [38, 39] method is used. In this process, nanoparticles are coated with the ZIF-8. Before coating the nanoparticles with the ZIF-8, in order to stabilize the nanoparticles, capping agents or ions or surfactants are used. Then, this nanocomposite is used for the treatment of contaminated water. Soft template method is also called micro emulsion; in this method we took two solvents in the presence of surfactants; after that, reactants are placed between superficial walls or between microbubbles. Later, the amalgam formed core shell [39, 40]. A researcher named Yang made the core shell of Pd@ZIF-8 in the presence of a stabilizer, PVP [41]. There is another process, Pickering g emulsion or hard template method, in which interfacial growth of ZIF-8 is done in the presence of the stabilizer, graphene that forms the composite ZIF-8/GO for the decontamination of water. A scientist named as Lin, formed the core of Pd/ZnO. He made it by placing the nanoparticles of Pd on the surface of ZnO. In order to achieve ZIF-8 growth through this method, he coated Pd/ZnO with the ZIF-8 film; as a result, Pd/ZnO/ZIF-8 composites are formed, which are used in the treatment of water [42].

9.2.4 Other methods for synthesis of ZIF-8-based composite Instead of these methods which are mentioned above, there are many other methods which are: (i) microreactor synthesis method, (ii) sono chemical method, (iii) stepwise growth, and (iv) decomposition reduction method. These methods are also

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used for making the ZIF-8 composites [27]. In microreactor synthesis, the ZIF-8 composites are prepared in a reactor, while in sono chemical method, ZIF-8 composites are made by the utilization of ultrasonic waves, that is, high-frequency sound waves. The next is decomposition reduction method in which ZIF-8 composites are prepared by the decomposition of material. In stepwise growth, different kinds of core shell are used step by step, and then formation of ZIF-8 composites results, which are used for decontamination of wastewater [43, 44].

9.3 Future prospective applications of ZIF-based composites for decontamination or removal of pollutants from wastewater Owing to their outstanding properties, ZIF-8-based composites are used enormously as absorbent or photocatalyst for the removal of pollutants from wastewater or for decontamination of water. Owing to their novel properties, the composites are used for decontamination of waste or pollutants from water. ZIF-8 composites are ecofriendly, and therefore are widely used in the decontamination process.

9.3.1 The use of ZIF-8 composites for the adsorptive removing of pollutants in wastewater Nowadays, ZIF-8 is used for the decontamination of water in adsorptive ways. Adsorptive ways are popular in the decontamination of wastewater. The crystal form of ZIF, or MOF, in general, is known for its porosity, but is difficult to mass-produce and incorporate in actual applications due to unavoidable inter crystalline defects. ZIFs have recently been used for several purposes, such as: membrane constituents, gas exchange and storage, biosensor, catalysis agents, and drug carriers for the development of DDS 20, 21, 22, 23, 24, and adsorptive removing of organic pollutant by use of ZIF-8 Composites [21]. ZIF-8 exhibits the following properties: (i) decline of the aggregation of adsorbent; (ii) ease in directing adsorbents from water; and (iii) adsorbents with good stability and by rise of active sites displayed fine recyclability and adsorption ability [45] ZIF-8 glass retains its porous structure in its crystalline state, allowing it to be used in gas separation and storage applications. The glassy form would also provide one-of-a-kind processing and mass-production opportunities. Last but not the least, composites made from ZIF glass have the distinct advantage of a broad design space, due to the composition and structure tuning. Carbon capture applications and carbon capture and storage (CCS) are the main topics of this article. ZIFs exhibit some properties relevant to

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Modification of ZIF-8 is easy

The stability of adsorbent which demonstrates good recyclability and adsorption ability and good recyclability by rise of active sites

Decline of the aggregation of adsorbent

Ease in discrete of absorbent from water

Stability of adsorbent which demonstrates better adsorption ability by raise of active sites.

Figure 9.4: Amplification, the easy way modification of ZIF-8.

carbon dioxide capture, while commercial technology still centers on amine solvent. Zeolites have tunable pores that range from 3 to 12 Angstroms, allowing them to separate carbon dioxide [46].

9.3.1.1 Absorptive decontamination of inorganic pollutants in waste waster by use of ZIF-8 composites Inorganic pollutants include the radioactive material, surfeit halides ions, and heavy metal ions. Arsenic is very toxic and people get health problems by drinking water polluted by arsenic. A group of scientists found that Arsenic could be removed by ZIF-8 through electronic attraction [47]. As described in Table 9.2, these inorganic pollutants are very dangerous to human health and cause cancer by entering the food chain. ZIFs exhibit properties relevant to carbon dioxide capture, while commercial technology still centers on amine solvent. Zeolites have tunable pores that range from 3 to 12 Angstroms, allowing them to separate carbon dioxide. Because a CO2 molecule is around 5.4 Angstroms in length, zeolites with pore sizes of 4–5 Angstroms can be effective in capturing carbon dioxide. Other factors, however, must be taken into account when determining how effective zeolites will be in capturing carbon dioxide. The first is basicity, which is achieved by exchanging alkali metal cations. The second factor affecting cation exchange capacity is the Si/Al ratio to earn a better grade [48].

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Table 9.2: A few general contaminants in drinking water [49, 50]. Contaminants

Conc. MCL Major sources of pollutants (mg/L)

Health dangers

Copper

.

Corrosion of natural deposit and pumping system

Liver and kidney damages

Cyanide

.

Release of contaminants from metal/steel

Problems of nerve damage and thyroid gland

Lead

.

Erosion of natural deposit and pumping system

Risk of sight disease

Mercury

. Corrosion of natural deposit and discharge Kidney damage from refineries and problem

Barium



Coal burning and defense industries

Blood pressure complaints

Arsenic

.

Corrosion of glass and electric products

Risk of cancer and blood pressure

Antimony

. Ceramic, solder, electronic

Elevating of blood cholesterol and decline of sugar

Chromium

.

Corrosion of natural deposit

Allergic disease

Dalaphone

.

Herbicides

Kidney disease

Benzene

. Release of leaching from gas storage tank

Decline in blood platelets

Antrazine

. Herbicides

kidney, liver, and adrenal disease

Hexachlorobenzene

. Use of pesticides

Risk of cancer and liver, kidney problems

Diquat

.

Cataracts

Radioactive contaminants

Use of herbicides

9.3.1.2 Absorptive removing of organic pollutants from wastewater by use of ZIF-8 composites Organic pollutants are more abundant than inorganic ones. Dyes present in wastewater because of contamination of water and other kinds of pollutants can be removed by encapsulation of Fe3O4 with ZIF-8 and form the composite of Fe3 O4/ZIF based

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composite for the removal of dyes from wastewater. Because a well-studied ZIF, ZIF8, has a relatively high separation factor for hydrogen and carbon dioxide mixtures, much ZIF research focuses on separation of hydrogen and carbon dioxide. It is also great for separating hydrocarbon mixtures like the ones as follows: Ethane-propane is equal to 80% ethane, 10 ethylene-propylene, propane-ethylene = 167. ZIF-8 had the highest selectivity of all the ZIFs that have been evaluated. ZIFs have also showed promise in separating other alcohols from water, such as propanol and butanol. Distillation is commonly used to separate water and ethanol (or other alcohols); however, ZIFs may offer a lower energy separation option. ZIF has wide range of applications due to its properties. It has applications in gas separation due to its porous nature by adsorption or in membranes in sensing. ZIF nanocatalysts have excellent stability and have long-term operation. ZIF derivatives have very stable structure and play an important role as a promising membrane for gas separation process [51]. Further studies are continuing on ZIF and its derivatives due to its robustness and greater separation ability. Because of unavoidable intercrystalline defects, the crystal form of ZIF or MOF, in general, is difficult to mass-produce and incorporate in actual applications. There are a number of intriguing characters in ZIF glasses and researchers are addressing those challenges in order to make promised applications a reality [52]. The first is that after the melt-quench process, ZIF glass retains its porous structure in its crystalline state, allowing it to be used in gas separation and storage applications. The glassy form would also provide one-of-a-kind processing and mass-production opportunities. Last but not the least, composites made from ZIF glass have the distinct advantage of a broad design space due to the composition and structure tuning [53].

9.3.2 Photochemical exclusion of pollutants by ZIF-8-based composites We use catalytic method for the treatment of water pollutants. These catalytic methods are photochemical oxidation, ozone oxidation, and photocatalytic oxidation. Nowadays, “green technology” is used to decontaminate organic pollutants and other pollutants from wastewater. The disadvantage of photocatalytic oxidation is that it produces unwanted by-products when degradation of metal ion is done. Organic pollutants that are present in water and water into carbon dioxide are also completely degraded with photocatalytic oxidation [54]. We can make inorganic pollutants risk-free by use of photocatalytic oxidation. CdS, ZnS, and ZnO are the photocatalytic materials. They are used for manufacture of semiconductors. The main function of photocatalytic materials is to make MOF-based composites [55]. Demeaning of phenol was done initially done by the Indian Professor, Garcia, in the University of Valencia by using ZnO4 (CO2)6(MOF-5) because ZnO4 (CO) 6(MOF5) has a photocatalytic-activity. But ZIF-8 has higher potential with photocatalytic activity because it contains organic functional groups and large porous volume.

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Active catalytic particles are mingled with ZIF-8 when we use ZIF-8 with catalyst, because ZIF-8 functions as a mass diffusion of active particles. When UV light is applied, ZIF-8 shows properties of a semiconductor. This is the first step of photocatalysis because of holes, and electrons are produced [56].

9.3.2.1 ZIF-8 coalesce with noble metal Pd@MOF-5 is a noble metal supported by MOF discovered by Fisher and his coworkers. They are applicable in photocatalysis due to localized plasmon effect for Ag, Au, and Pt (noble metal nanoparticles). But it has limited function because Pd@MOF5 agglomerates in water. The main reasons for using ZIF-8 to functionalize the pores are its thermal stability and three dimensional structures. Combination efficiency of noble metals increases due to two properties (thermal stability and three-dimensional structures) of ZIF-8. Noble metals have the ability to clean up the electrons as well as enhancing the transmission of electrons. ZIF-8 contains conduction band where transmission of electrons take place [57]. Photocatalytic activity, which is responsible for pollutants removal, increases when electrons and hydronium ions react with water. Surface structure has limited application on noble metals. There is a no need of surfactants for making the required scale of zeolitic imidazolate-framework-8 composite. ZIF-8 composite, with core shell composite of Pd@ZIF-8, is a high-efficiency photocatalyst, which contains ZIF-8 composite. This ligand ZIF-8 composite can absorb maximum light energy. In photocatalytic process, ZIF-8 functionalize synergistically with catalytic activity by adjusting its pore size. We should make porous size of ZIF-8 to mesoporous. Phenol action is suppressed in visible light if we dispatch Pt/ ZIF-8 on TiO2 nanotubes. This process was first discovered by Isimjan et al. Degradation efficiency increased six times by Pt/TiO2 nanotube [58].

9.3.2.2 ZIF-8 coalesce with semiconductor Semiconductor combination with ZIF-8 is used to increase or improve the photocatalytic properties of ZIF-8. The semiconductors which are combined with ZIF-8 for decontamination of water are of two types. The first is the n-type which has a large number of electrons and they are CdS, TiO2, ZnO, and ZnS; the other is p-type and has large number of holes. The p-type semiconductors are Cu2O, PbS, CoO3, and PbS [59, 60]. The combinations of semiconductors with ZIF-8 increases the photocatalytic effectiveness of ZIF-8 because the composite of ZIF-8, which coalesce with the ZIF-8, has excellent physical and chemical properties. A scientist, Chandra, encapsulated the TiO2, which is a p-type semiconductor in order to remove the dye from wastewater, into the ZIF-8. It is considered that degradation rate of composite TiO3/ZIF-8 for the degradation of methylene blue is 87.5% [61].

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9.3.2.3 ZIF-8 coalesce with other nanoparticles Instead of semiconductors, nanoparticles are also used for the decontamination of water due to its good shape and fine crystallinity [62]. The metal oxides that have semiconducting or magnetic properties are coalesced with ZIF-8 through the template synthesis method. ZIF-8 acts as a template and provides space to metal oxides. This combination of ZIF-8 with nanoparticles is used for the decontamination of water, like MoO3@ZIF-8, which is composite of ZIF-8 is used to degrade the Cr(VI). Furthermore, Fe3o4@ZIF-8 and Mn3O4@ZIF-8 are also used to remove many kinds of pollutants from the wastewater [63]. When we use ZnO@ZIF-8, this composite of ZIF-8 degrades Cr(VI) from the dye wastewater after about 240 min, with the help of photocatalysis. Later, after about 80 min, 50% of Cr(VI) is degraded by ZnO@ZIF-8 [64].

9.4 Conclusion ZIF-8 has been successful in the removal of pollutants from the wastewater. The future prospective applications of ZIF-8-based composites have been increasing day by day, due to presence of active sites on it, for the treatment of wastewater. This chapter discussed the synthesis methods for the preparing of composites of ZIF-8 and their future prospective applications for the treatment of wastewater. The recent research tells us that the preparation of ZIF-8 composites for the treatment of wastewater is economical and eco-friendly. The shortcoming in the research of ZIF8 for wastewater treatment or decontamination of water is of the high cost of ZIF-8 composite material. Aside of decontamination of water, it also plays a good role in other fields like separation, therapy, storage, and catalysis. This chapter also tells us about the encapsulated method for ZIF-8. It is still a big challenge to achieve proper pore size, size, dispersion properties, and composition. There is need for modification in the synthesis methods of ZIF-8 composites. Furthermore, selective adsorption, photo degradation, adsorption, and degradation capacity are in consideration for decontamination of water.

References [1] [2] [3]

Vorosmarty, C.J., et al., Global water resources: Vulnerability from climate change and population growth. 2000. 289(5477): p. 284–288. Shannon, M.A., et al., Science and technology for water purification in the coming decades. Nature, 2008. 452(7185): p. 301–310. Savage, N. and M.S. Diallo. Nanomaterials and water purification: Opportunities and challenges. Journal of Nanoparticle Research, 2005. 7(4): p. 331–342.

9 Future prospects for ZIF-8-based composite material for decontamination of water

[4] [5]

[6]

[7] [8]

[9] [10]

[11] [12]

[13]

[14] [15] [16] [17]

[18] [19]

[20] [21]

[22]

151

Bolto, B. and J. Gregory. Organic polyelectrolytes in water treatment. Water Research, 2007. 41(11): p. 2301–2324. Dai, H., et al., Recent advances on ZIF-8 composites for adsorption and photocatalytic wastewater pollutant removal: Fabrication, applications and perspective. 2021. 441: p. 213985. Verma, A.K., R.R. Dash, and P. Bhunia. A review on chemical coagulation/flocculation technologies for removal of colour from textile wastewaters. Journal of Environmental Management, 2012. 93(1): p. 154–168. Jiang, J.-Q., et al., Laboratory study of electro-coagulation–flotation for water treatment. Water Research, 2002. 36(16): p. 4064–4078. Liang, W., et al., 3D, eco-friendly metal-organic frameworks@carbon nanotube aerogels composite materials for removal of pesticides in water. Journal of Hazardous Materials, 2021. 401: p. 123718. Zhang, Y. and S.-J. Park, Facile construction of MoO3@ZIF-8 core-shell nanorods for efficient photoreduction of aqueous Cr (VI). Applied Catalysis. B, Environmental, 2019. 240: p. 92–101. Chao, S., et al., Preparation of polydopamine-modified zeolitic imidazolate framework-8 functionalized electrospun fibers for efficient removal of tetracycline. Journal of Colloid and Interface Science, 2019. 552: p. 506–516. Stock, N. and S. Biswas. Synthesis of metal-organic frameworks (MOFs): Routes to various MOF topologies, morphologies, and composites. Chemical Reviews, 2012. 112(2): p. 933–969. Zheng, H., et al., Transcriptome analysis of maize inbred lines differing in drought tolerance provides novel insights into the molecular mechanisms of drought responses in roots. Plant Physiology and Biochemistry, 2020. 149: p. 11–26. Zhang, M., et al., Self-template synthesis of double-shell TiO2@ZIF-8 hollow nanospheres via sonocrystallization with enhanced photocatalytic activities in hydrogen generation. Applied Catalysis. B, Environmental, 2019. 241: p. 149–158. Venter, J.C., et al., The sequence of the human genome. 2001. 291(5507): p. 1304–1351. Wee, L.H., et al., Local transformation of ZIF-8 powders and coatings into ZnO nanorods for photocatalytic application. Nanoscale, 2014. 6(4): p. 2056–2060. Li, S., et al., Template-directed synthesis of porous and protective core–shell bionanoparticles. Angewandte Chemie International Edition, 2016. 55(36): p. 10691–10696. Hermes, S., et al., Metal@MOF: Loading of highly porous coordination polymers host lattices by metal organic chemical vapor deposition. Angewandte Chemie International Edition, 2005. 44(38): p. 6237–6241. Houk, R.J.T., et al., Silver cluster formation, dynamics, and chemistry in metal−organic frameworks. Nano Letters, 2009. 9(10): p. 3413–3418. Li, Z. and H.C. Zeng. Surface and bulk integrations of single-layered Au or Ag nanoparticles onto designated crystal planes {110} or {100} of ZIF-8. Chemistry of Materials, 2013. 25(9): p. 1761–1768. Liu, Y., et al., A liquid metal composite by ZIF-8 encapsulation. Chemical Communications, 2020. 56(12): p. 1851–1854. Beni, F.A., et al., UV-switchable phosphotungstic acid sandwiched between ZIF-8 and Au nanoparticles to improve simultaneous adsorption and UV light photocatalysis toward tetracycline degradation. 2020. 303: p. 110275. Faustini, M., et al., Microfluidic approach toward continuous and ultrafast synthesis of metal–organic framework crystals and hetero structures in confined microdroplets. Journal of the American Chemical Society, 2013. 135(39): p. 14619–14626.

152

Nazia Rasool et al.

[23] Hu, L., et al., Peroxymonosulfate activation by Mn3O4/metal-organic framework for degradation of refractory aqueous organic pollutant rhodamine B. Chinese Journal of Catalysis, 2017. 38(8): p. 1360–1372. [24] Jian, M., et al., Self-assembled one-dimensional MnO2@zeolitic imidazolate framework-8 nanostructures for highly efficient arsenite removal. Environmental Science: Nano, 2016. 3(5): p. 1186–1194. [25] Qiu, J., et al., Constructing Cd0.5Zn0.5S@ZIF-8 nanocomposites through self-assembly strategy to enhance Cr(VI) photocatalytic reduction. Journal of Hazardous Materials, 2018. 349: p. 234–241. [26] Wang, F. and Z. Guo, In situ growth of ZIF-8 on CoAl layered double hydroxide/carbon fiber composites for highly efficient absorptive removal of hexavalent chromium from aqueous solutions. Applied Clay Science, 2019. 175: p. 115–123. [27] Zeng, X., et al., Sonocrystallization of ZIF-8 on electrostatic spinning TiO2 nanofibers surface with enhanced photocatalysis property through synergistic effect. ACS Applied Materials & Interfaces, 2016. 8(31): p. 20274–20282. [28] Zhuang, J., et al., Optimized metal–organic-framework nanospheres for drug delivery: evaluation of small-molecule encapsulation. ACS Nano, 2014. 8(3): p. 2812–2819. [29] Zheng, G., et al., Encapsulation of single plasmonic nanoparticles within ZIF-8 and SERS analysis of the MOF flexibility. Small, 2016. 12(29): p. 3935–3943. [30] Sharsheeva, A., et al., Light-controllable systems based on TiO2-ZIF-8 composites for targeted drug release: Communicating with tumour cells. Journal of Materials Chemistry B, 2019. 7(43): p. 6810–6821. [31] Hwang, S., et al., Hollow ZIF-8 nanoparticles improve the permeability of mixed matrix membranes for CO2/CH4 gas separation. Journal of Membrane Science, 2015. 480: p. 11–19. [32] Ma, X., et al., Multifunctional flexible composite aerogels constructed through in-situ growth of metal-organic framework nanoparticles on bacterial cellulose. Chemical Engineering Journal, 2019. 356: p. 227–235. [33] Jiang, X., et al., Ultra-facile aqueous synthesis of nanoporous zeolitic imidazolate framework membranes for hydrogen purification and olefin/paraffin separation. Journal of Materials Chemistry A, 2019. 7(18): p. 10898–10904. [34] Li, L., et al., Accelerating chemo- and regioselective hydrogenation of alkynes over bimetallic nanoparticles in a metal–organic framework. ACS Catalysis, 2020. 10(14): p. 7753–7762. [35] Yang, Y., et al., Nanoporous gold embedded ZIF composite for enhanced electrochemical nitrogen fixation. Angewandte Chemie International Edition, 2019. 58(43): p. 15362–15366. [36] Lu, G., et al., Imparting functionality to a metal–organic framework material by controlled nanoparticle encapsulation. Nature Chemistry, 2012. 4(4): p. 310–316. [37] Sorribas, S., et al., Ordered mesoporous silica–(ZIF-8) core–shell spheres. Chemical Communications, 2012. 48(75): p. 9388–9390. [38] Cai, G., et al., Encapsulating soluble active species into hollow crystalline porous capsules beyond integration of homogeneous and heterogeneous catalysis. National Science Review, 2019. 7(1): p. 37–45. [39] Dai, C., et al., Synthesis of yolk–shell HPW@Hollow silicalite-1 for esterification reaction. Chemical Communications, 2014. 50(37): p. 4846–4848. [40] Bian, Z., et al., In situ interfacial growth of zeolitic imidazolate framework (ZIF-8) nanoparticles induced by a graphene oxide pickering emulsion. RSC Advances, 2015. 5(40): p. 31502–31505. [41] Lin, L., et al., In situ fabrication of a perfect Pd/ZnO@ZIF-8 core–shell microsphere as an efficient catalyst by a ZnO support-induced ZIF-8 growth strategy. Nanoscale, 2015. 7(17): p. 7615–7623.

9 Future prospects for ZIF-8-based composite material for decontamination of water

153

[42] Liu, Y., et al., In situ synthesis of MOF membranes on ZnAl-CO3 LDH buffer layer-modified substrates. Journal of the American Chemical Society, 2014. 136(41): p. 14353–14356. [43] So, M.C., et al., Post-assembly transformations of porphyrin-containing metal–organic framework (MOF) films fabricated via automated layer-by-layer coordination. Chemical Communications, 2015. 51(1): p. 85–88. [44] Liu, J., et al., Harnessing Ag nanofilm as an electrons transfer mediator for enhanced visible light photocatalytic performance of Ag@AgCl/Ag nanofilm/ZIF-8 photocatalyst. Applied Catalysis. B, Environmental, 2017. 202: p. 64–71. [45] Rowsell, J.L.C. and O.M. Yaghi. Effects of functionalization, catenation, and variation of the metal oxide and organic linking units on the low-pressure hydrogen adsorption properties of metal−organic frameworks. Journal of the American Chemical Society, 2006. 128(4): p. 1304–1315. [46] Khan, S., et al., Health risks of heavy metals in contaminated soils and food crops irrigated with wastewater in Beijing, China. Environmental Pollution, 2008. 152(3): p. 686–692. [47] Mohan, D., et al., Organic and inorganic contaminants removal from water with biochar, a renewable, low cost and sustainable adsorbent – A critical review. Bioresource Technology, 2014. 160: p. 191–202. [48] Zhu, K., et al., Cr(VI) reduction and immobilization by core-double-shell structured magnetic polydopamine@zeolitic idazolate frameworks-8 microspheres. ACS Sustainable Chemistry & Engineering, 2017. 5(8): p. 6795–6802. [49] Chen, W.-R. and C.-H. Huang, Surface adsorption of organoarsenic roxarsone and arsanilic acid on iron and aluminum oxides. Journal of Hazardous Materials, 2012. 227–228: p. 378–385. [50] Xu, G.-R., et al., Metal organic framework (MOF)-based micro/nanoscaled materials for heavy metal ions removal: The cutting-edge study on designs, synthesis, and applications. 2021. 427: p. 213554. [51] Ulrich, G., R. Ziessel, and A. Harriman. The chemistry of fluorescent bodipy dyes: Versatility unsurpassed. Angewandte Chemie International Edition, 2008. 47(7): p. 1184–1201. [52] Xiong, T., et al., Highly efficient removal of diclofenac sodium from medical wastewater by Mg/Al layered double hydroxide-poly(m-phenylenediamine) composite. Chemical Engineering Journal, 2019. 366: p. 83–91. [53] Sharma, B., A.K. Dangi, and P. Shukla, Contemporary enzyme based technologies for bioremediation: A review. Journal of Environmental Management, 2018. 210: p. 10–22. [54] Jiang, L., et al., A facile band alignment of polymeric carbon nitride isotype heterojunctions for enhanced photocatalytic tetracycline degradation. Environmental Science: Nano, 2018. 5 (11): p. 2604–2617. [55] Ade, P.A., et al., Planck 2013 results. XVI. Cosmological parameters. 2014. 571: p. A16. [56] Yuan, X., et al., Highly efficient visible-light-induced photoactivity of Z-scheme Ag2CO3/Ag/ WO3 photocatalysts for organic pollutant degradation. Environmental Science: Nano, 2017. 4 (11): p. 2175–2185. [57] Ding, M., et al., Carbon capture and conversion using metal–organic frameworks and MOFbased materials. 2019. 48(10): p. 2783–2828. [58] Rohani, S., et al., Fabrication, modification and environmental applications of TiO2 nanotube arrays (TNTAs) and nanoparticles. Frontiers of Chemical Science and Engineering, 2012. 6(1): p. 112–122. [59] Zhang, Y. and S.-J. Park, Stabilization of dispersed CuPd bimetallic alloy nanoparticles on ZIF8 for photoreduction of Cr(VI) in aqueous solution. Chemical Engineering Journal, 2019. 369: p. 353–362.

154

Nazia Rasool et al.

[60] Gao, Y., et al., A novel multifunctional p-type semiconductor@MOFs nanoporous platform for simultaneous sensing and photodegradation of tetracycline. ACS Applied Materials & Interfaces, 2020. 12(9): p. 11036–11044. [61] Malik, A., et al., Multifunctional CdSNPs@ZIF-8: Potential antibacterial agent against GFPexpressing escherichia coli and staphylococcus aureus and efficient photocatalyst for degradation of methylene blue. ACS Omega, 2018. 3(7): p. 8288–8308. [62] Hall, A.S., et al., Microporous brookite-phase titania made by replication of a metal–organic framework. Journal of the American Chemical Society, 2013. 135(44): p. 16276–16279. [63] Redfern, J., et al., Toxicity and antimicrobial properties of ZnO@ZIF-8 embedded silicone against planktonic and biofilm catheter-associated pathogens. ACS Applied Nano Materials, 2018. 1(4): p. 1657–1665. [64] Ma, J., et al., In-situ preparation of hollow cellulose nanocrystals/zeolitic imidazolate framework hybrid microspheres derived from pickering emulsion. Journal of Colloid and Interface Science, 2020. 572: p. 160–169.

Index accounts 3, 88–89, 146 active 2, 10, 22, 34, 42, 89–90, 98, 102, 116–117, 122, 126, 139, 145–146, 149–150 activities 2, 51, 59, 62,75 advantages 22, 26, 86, 97, 103, 117–118, 122, 138, 145, 148 amount 4, 41, 59, 61–62, 64, 66–67, 73–75, 83–86, 90, 115, 126 applications 1–3, 5, 7–8, 10–13, 19, 21–22, 25, 27–28, 33–35, 40–41, 47, 52, 54, 56, 59, 62, 65, 71, 74, 79, 86, 90–91, 97–98, 100–101, 105–106, 111–112, 116, 118–120, 124, 128–129, 138–139, 145, 148–150 attention 11, 19, 21, 34–35, 41, 51, 60, 65–67, 85, 87, 98, 117 biodegradability 60, 71, 102, 111–112, 122 biological 2, 7, 25, 59–60, 62, 65, 80, 84, 119 capacity 2, 6, 9–11, 13, 38, 59, 62, 80–81, 87, 92, 98, 120–122, 124–128, 137, 139, 146, 150 carbonization 19, 26, 61, 74, 120, 121 chemical 1–3, 7, 10–11, 13, 19, 21, 25–28, 33–34, 38, 41, 54, 57, 60, 62, 65, 68, 80–81, 85–87, 89, 90–91, 98, 103–104, 118–119, 123, 137–139, 144 classified 67, 112, 140 conditions 3, 11, 23–25, 36, 41–42, 53, 56, 62, 64, 68, 86, 89, 103, 105–106 consideration 3, 7, 19, 25, 27, 71, 75, 79–80, 83, 90, 101, 106, 115, 138, 140, 149–150 conventional 34, 53, 59, 62–63, 67, 75, 84, 102, 115–117 coordination 1–3, 7, 11, 19, 21, 28, 34, 71, 88, 97, 100, 117, 122–123, 138 degradation 8–9, 11–12, 42–43, 47, 60, 71–75, 80, 98, 100, 106, 140, 148–150 devices 20, 67, 79, 91 differentiated 36, 39, 88 diffusion 3, 7, 11, 88–90, 142, 149 discharged 44, 60, 62, 66, 69, 75, 79, 85, 147 disparate 140–142 dopamine 62 drugs 1–2, 11–12, 20, 22, 27, 41, 53, 79, 91–92, 98–100, 111–112, 114–116, 118, 141, 145 https://doi.org/10.1515/9783110792591-010

economical 85, 101–103, 138, 150 emerging 1–2, 11, 40, 64, 98, 117, 120, 129, 137 encephalopathy 80 excellent 4, 6–9, 26, 35–36, 38, 51, 57, 62, 74, 98, 101, 103, 106, 119, 137, 139, 148–149 factors 1–2, 4, 12, 22, 24, 51–52, 57, 67, 79, 82, 89, 92, 97, 100, 106, 124–125, 128, 146, 148 favorable 51, 56, 61, 85, 89–90, 124–125 formation 2, 5, 7, 34–36, 51, 53, 68–69, 71, 82–83, 88, 103, 124, 138, 145 frameworks 1–3, 5, 11–13, 19–21, 26, 33–34, 36–38, 40–41, 47, 51–52, 54, 56, 59–62, 68, 71–72, 74, 79, 81, 85–86, 92, 97, 99, 101, 117, 137, 149 functional 3, 5, 11, 19, 41, 59–61, 84, 86, 89, 91, 97–98, 100, 105, 119–122, 124, 139–140, 142–143, 148, 149 further 41, 51, 54, 62, 64, 85–86, 97, 106, 124, 148 generation 34, 89 heavy metal 1, 4, 10–11, 38, 79–81, 83–88, 92, 102, 142, 146 hexagonal 82 infiltration 109, 140 innovative 33–34, 65, 106 imitation 2, 8, 23, 27, 98, 103, 111, 117–119 lithosphere 83–84 magnetic 40, 45, 54, 68, 73, 102, 150 metal 1–6, 8, 10–13, 19–21, 23, 24–25, 33–35, 37–40, 43–44, 47, 51–52, 60–61, 72, 79–81, 83–88, 92, 97–100, 102–103, 117–119, 122–123, 137–139, 143, 146, 148–150 methanol 23–24, 35, 39–41, 44–45, 51, 54–55, 60, 68, 83 method 1–4, 7, 9–12, 22–24, 26, 34–36, 39, 41, 47, 53, 57, 59–63, 65–67, 69, 71–73, 75, 79, 82–87, 90, 97, 99–101, 103, 105–106, 111, 117–118, 121–122, 129, 138, 140–145, 148, 150 methylene 42–43, 47, 59, 73, 98, 101, 149 microscopy 34–36, 39, 61

156

Index

modification 26, 90, 98, 101, 103, 105, 119, 138, 141–142, 144, 146, 150 mutagenicity 137 notable 13, 53 opposite 3, 123, 125 organic 1–4, 11–12, 19–21, 23, 25, 34, 38–41, 46, 51–52, 60, 62–65, 71–72, 81–82, 85–86, 97–98, 100, 103, 105–106, 118, 123, 137–138, 141, 143, 145, 147–148 photo catalytic 2, 5, 8, 35, 42, 47, 60, 73–74 polyvinylpyrrolidone 140 processability 98, 139 processes 22, 33–34, 53, 57, 65, 89, 103, 117 reacts 8, 12, 19, 22–24, 26, 33–37, 41–42, 45–47, 51–54, 56–57, 60, 68–71, 73, 82–83, 88–91, 106, 119, 138, 142, 144, 149 reduces 4–6, 23–24, 34, 85, 87–88, 100, 106, 117, 119, 121, 124, 126 respiratory 84, 112 resultant 36, 40, 68 separation 1–2, 6, 9–11, 20, 22–23, 25–26, 33–34, 39–42, 54, 62, 64–65, 71, 73–74, 85–86, 97–98, 100, 119, 138–139, 145–146, 148, 150 sieves 46, 97

stability 1–4, 7, 10–12, 19, 21, 22, 24–28, 35–36, 38, 41, 53, 56, 62, 87, 91, 98, 118–119, 129, 138–139, 144–146, 148–149 steam 25 strategy 19, 22–23, 28, 63, 105, 117, 124 synchronic 86, 89 tailorable 98, 119, 138 tanks 64, 69, 117, 147 tanneries 60 temperature 3–4, 19, 22–25, 34, 36–37, 39, 41–42, 45–47, 54–56, 60–61, 68–71, 82–83, 85, 89–90, 92, 105–106, 118, 138, 144 terrestrial 112, 114 transcriptional 117 ultra-filtration 61 uniqueness 19, 41, 51, 71, 81, 98, 100, 119 veterinary 112, 115 widely 2, 5, 7–8, 19, 21, 24, 27, 47, 85, 91, 97–98, 103, 112, 118–119, 137–138, 142, 145, 148 ZIF 1–13, 19–28, 33–47, 51–57, 59–75, 79–92, 97–107, 111–129, 137–150