Overview of Inorganic Compounds 9781774695555, 9781774694312

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An Overview of Inorganic Compounds

AN OVERVIEW OF INORGANIC COMPOUNDS

Rose Marie O. Mendoza

ARCLER

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An Overview of Inorganic Compounds Rose Marie O. Mendoza

Arcler Press 224 Shoreacres Road Burlington, ON L7L 2H2 Canada www.arclerpress.com Email: [email protected]

e-book Edition 2023 ISBN: 978-1-77469-555-5 (e-book)

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ABOUT THE AUTHOR

Dr. Rose obtained her PhD in Chemical Engineering from the University of the Philippines-Diliman in 2013, while her Masters in Chemical Engineering and BS Chemical Engineering degree was obtained from Adamson University. She is also a Professor in the Graduate School Department under the Master of Engineering Program at Adamson University since 2006. In 2017, she obtained her Post Doctorate Degree in Green Power: Hydrogen Generation and Fuel Cell Development from the University of California Merced, USA (in collaboration with the Energy Storage and Conversion Materials Laboratory of the University of the Philippines, Diliman). She is a visiting scientist to several universities abroad such as the University of California Merced in USA, Kindai University in Japan, National Taiwan University and Chia Nan University of Pharmacy and Science in Taiwan. She has published more than 20 research papers in water treatment and remediation, green technology, fuel cells, electrodialysis, nanomaterials, high voltage spatial electricity, batteries in peer-reviewed journals, and have more than 15 textbooks published in chemical engineering and processes. As an educator, she is very active in publishing her research to local peer reviewed journals. An advocate of Climate Action, a Climate Reality Leader Corp Member and a budding Sustainability and Circularity talent, Dr. Mendoza is also presently actively engaged in several local and international Green Federation as Board Member and Officer such as the Green Party of the Philippines, and Treasurer of the Asian Pacific Federation of Green Women’s Network. She is also one of the Board of Directors of the Philippine Society of Engineering Educators, Mark Energy Revolution Corporation and one of the pioneering members of the Philippine Institute of Chemical Engineers, CaMaNaVa Chapter, and an Associate Member of the National Research Council of the Philippines (NRCP).

TABLE OF CONTENTS



List of Figures.................................................................................................xi



List of Tables..................................................................................................xv



List of Abbreviations.................................................................................... xvii

Preface..................................................................................................... ....xxi Chapter 1

Introduction to Inorganic Compounds....................................................... 1 1.1. Introduction......................................................................................... 2 1.2. Inorganic Chemistry and Inorganic Compounds.................................. 4 1.3. Classification of Inorganic Compounds................................................ 6 1.4. Some Subdivisions of Inorganic Chemistry......................................... 14 1.5. Types of Reactions and Examples of Inorganic Compounds............... 16 1.6. Inorganic Chemistry’s Applications.................................................... 16 References................................................................................................ 17

Chapter 2

Nomenclature of Inorganic Compounds.................................................. 21 2.1. Introduction....................................................................................... 22 2.2. Naming Binary Ionic Compounds...................................................... 23 2.3. Naming Covalent Compounds........................................................... 28 2.4. Polyatomic Ions................................................................................. 29 2.5. Hydrates............................................................................................ 30 2.6. Binary Covalent Compounds............................................................. 31 2.7. Acids................................................................................................. 34 2.8. Bases................................................................................................. 36 2.9. Summary........................................................................................... 38 References................................................................................................ 39

Chapter 3

Porous Inorganic Materials...................................................................... 45 3.1. Introduction....................................................................................... 46 3.2. Microporous Materials....................................................................... 47

3.3. Mesoporous Materials........................................................................ 51 3.4. Macroporous Materials...................................................................... 74 3.5. Hierarchical Porous Structures........................................................... 77 References................................................................................................ 80 Chapter 4

Magnetic Inorganic Compounds for Functional Applications................... 91 4.1. Introduction....................................................................................... 92 4.2. Magnetocaloric Materials.................................................................. 96 4.3. Magnetic Nanoparticles..................................................................... 99 4.4. Applications of Functional Magnetic Nanoparticles......................... 101 4.5. Technology of Magnetic Recording.................................................. 105 4.6. Perspectives and Summary............................................................... 106 References.............................................................................................. 108

Chapter 5

Metal Oxide Nanoparticles for Anti-Bacterial and Wastewater Applications........................................................................................... 115 5.1. Introduction..................................................................................... 116 5.2. Wastewater...................................................................................... 118 5.3. Importance of Nanoparticles............................................................ 122 5.4. Metal Oxide Nanoparticles (MONPS).............................................. 125 References.............................................................................................. 150

Chapter 6

Multifunctional Inorganic Compounds for Energy Applications............. 163 6.1. Introduction..................................................................................... 164 6.2. Energy Generation Applications....................................................... 169 6.3. Energy-Conversion Applications...................................................... 177 6.4. Energy Storage Applications............................................................. 184 References.............................................................................................. 190

Chapter 7

Applications of Inorganic Semiconducting Materials in Electronics....... 199 7.1. Introduction..................................................................................... 200 7.2. Bottom-Up Techniques.................................................................... 201 7.3. Top-Down Approaches.................................................................... 204 7.4. Mechanics....................................................................................... 208 7.5. Epidermal Electronics...................................................................... 209 References.............................................................................................. 218

viii

Chapter 8

Inorganic Nanoparticles for Biomedical Applications............................ 225 8.1. Introduction..................................................................................... 226 8.2. Unguided Drug Delivery Systems.................................................... 228 8.3. Magnetically-Guided Drug Delivery Systems................................... 230 8.4. Optically-Triggered Drug Delivery Systems...................................... 234 References.............................................................................................. 238

Index...................................................................................................... 243

ix

LIST OF FIGURES Figure 1.1. Ionic bonding in sodium chloride Figure 1.2. Oxidation-reduction reactions in sodium chloride Figure 1.3. Coordination compound formation from transition metal Figure 2.1. Naming an ionic compound Figure 2.2. Metals that form more than one cation and their locations in the periodic table Figure 2.3. The relationship between the names of oxoanions and the number of oxygen atoms present Figure 2.4. Loss of water from a hydrate with heating (left); when blue CuSO4⋅5H2OCuSO4·5H2O is heated, two molecules of water are lost at 30°C, two more at 110°C, and the last at 250°C to give white “anhydrous” CuSO4CuSO4 (right) Figure 2.5. Naming a covalent inorganic compound

Figure 2.6. The structures of some covalent inorganic compounds and the locations of the “central atoms” in the periodic table Figure 2.7. The relationship between the names of the oxoacids and the names of the parent oxoanions Figure 2.8. Methylamine structure Figure 3.1. The international union of pure and applied chemistry (IUPAC) categorization of porous materials depends on pore diameter Figure 3.2. MCM-41 might be formed by one of two probable processes, (1) or (2), according to the presented models Figure 3.3. Graphic of the interaction among inorganic and surfactants substances in a schematic diagram Figure 3.4. TEM images of MCM-41 with various pore sizes up to 100A Figure 3.5. Organometallic and organic bridging groups that have been integrated into PMOs Figure 3.6. A diagram illustrating the overall technique for producing ordered macroporous materials via colloidal crystal templating is shown Figure 3.7. A diagram depicting the technique for applying emulsion droplets as templates to macroporous materials

Figure 3.8. The manufacturing of hierarchically ordered oxides is depicted in this diagram Figure 4.1. Magnetic characteristic lengths in permanent magnets, as well as an illustration of typical microstructures, are provided Figure 4.2. Hard magnetic materials’ maximum energy density (BH) max at room temperature has increased steadily since the beginning of the 20th century, and there are now several distinct types of materials with equivalent energy density Figure 4.3. Roadmap for the development of an ultralow-loss nanocrystalline alloy Figure 4.4. Diagram of a magnetic refrigeration cycle, which moves heat from the heat load to the surrounding environment. Materials in high and low magnetic fields are depicted in yellow and green boxes, respectively, by the color of the box Figure 4.5. (A) Paramagnetically charged particles in the presence of a magnetic field. There is no evidence of change in magnetization; and (B) superparamagnetic particles that are subjected to a magnetic field or that are at a low temperature Figure 4.6. In biology the use of multifunctional magnetic nanoparticles has a wide range of possible applications Figure 5.1. Different sources of wastewater Figure 5.2. Various pollutants found in water Figure 5.3. Commonly used types of nanoparticles Figure 5.4. Wastewater treatment by nanoparticles Figure 5.5. Metal oxide nanoparticles are used in a variety of applications Figure 5.6. Metal oxide nanoparticles come in five different varieties Figure 5.7. ZnO nanoparticles were synthesized using a variety of approaches Figure 5.8. Main synthetic methods employed with Ag2O nanoparticles Figure 5.9. Major synthetic techniques used for Ti2O nanoparticles Figure 5.10. Major synthetic techniques used for iron oxide nanoparticles Figure 6.1. Different energy uses, such as storage, conversion, energy generation, saving, and transmission, are highly reliant on the various functionalities of different types of materials. Nanomaterials such as piezoelectric, thermoelectric, photovoltaic, triboelectric, catalytic, and electrochromic materials have made significant contributions to a wide range of energy-related fields Figure 6.2. (a) The free-energy landscape for the production and interactions that determine the usual condition of nanomaterials in the environment is depicted in this conceptual representation. (b) Representation of the band model for chemical bonding among metal atoms in a schematic diagram. (c) According to the extent of delocalization of valence electrons in the metal cluster, there are corresponding energies levels of the valence electrons Figure 6.3. (a) Schematic representation of a TE module constructed from a thermocouple with n-type thermoelectric legs. (b) Schematic depicting the interaction xii

of the different TE characteristics with the carrier density, illustrative of the difficulty in attempting to optimize the material ZT density. Single-walled carbon nanotube systems have been studied in detail, and the forms of the individual curves have been derived from this research. (c) The optimum ZT values for various standard TE materials have increased over time Figure 6.4. (a) Atomic model of the wurtzite-structured ZnO. (b) The piezoelectric characteristics of the material, as well as the various piezo potentials in the tension and compression modes of the material, were investigated. (c) The piezoelectric potential distribution in a ZnO nanowire subjected to axial strain was calculated using numerical methods Figure 6.5. TENG theoretical models are presented here. (a) Schematic depiction of the first TENG and the cycle of operation that it goes through. (b) The displaced current model of a TENG operating in the contact separation mode. (c) The electrical circuit model of a TENG that is equivalent to the real thing Figure 6.6. Schematic depicting the construction of certain common inorganic halide perovskite crystal structures (ABX3), their transformation into diverse nanostructures, and finally their integration into numerous applications Figure 6.7. The ErCl3 pseudo capacitor’s electrochemical performance and construction technique Figure 7.1. Stretchable and flexible electronic devices that usage monocrystalline semiconductor nanomaterials formed expending synthetic, bottom-up methods Figure 7.2. Single crystalline inorganic nanoribbons and nanomembranes, created utilizing lithographically controlled, top-down techniques, are being investigated further Figure 7.3. Design methods for stretchable and flexible electronics Figure 7.4. Skin-like or epidermal electronic system Figure 7.5. Wirelessly operated epidermal electronic systems Figure 7.6. Implantable wireless optogenetic system Figure 8.1. Surface functionalization of inorganic nanoparticles as seen in a schematic Figure 8.2. (a) 7 nm; (b) 11 nm; and (c) 13 nm J-Fe2O3 nanoparticles produced employing thermal decomposition of organometallic precursors Figure 8.3. The transmission electron micrograph and associated electron diffraction pattern of J-Fe2O3 particles coated with polymethyl acrylic acid are shown (Yu and Chow, 2004) Figure 8.4. Representation of the different interaction regions of a single particle with a single layer of oleic acid coating Figure 8.5. Au-Au2S nanoparticles with a cisplatin-loaded surface modification (Ren and Chow, 2003) Figure 8.6. The biodistribution of Au-Au2S nanoparticles in KM mice treated with intra-tumor injection at various time periods was investigated xiii

LIST OF TABLES Table 1.1. Periodic table showing inorganic compounds Table 1.2. Rules of nomenclature for binary ionic compounds Table 1.3. Common simple anions and cations Table 1.4. General ions that form multiple cations Table 1.5. Nitrogen and oxygen compounds and their nomenclature Table 1.6. Prefixes employed in chemical nomenclature Table 1.7. Common polyatomic ions Table 1.8. Chlorine-containing oxyanions Table 1.9. Terms of common acids Table 2.1. Common cations of metals that form more than one ion Table 2.2. Common polyatomic ions and their names Table 2.3. Prefixes for indicating the number of atoms in chemical names Table 2.4. Some common acids that do not contain oxygen Table 2.5. Nomenclature and chemical formulae of Oxides Table 3.1. Inorganic precursors and surfactants interact with each other in a variety of ways, which is depicted in this diagram Table 3.2. Various g values and associated mesophases Table 3.3. A summation of several silicate mesophases Table 5.1. Wastewater treatment procedures that have been employed in the past Table 5.2. Traditional water purifying systems have limitations Table 5.3. Existing ZnO nanoparticles technologies and their use in wastewater treatment Table 5.4. Methods for making ZnO nanoparticles in a variety of sizes Table 5.5. Methods for dealing with CuO nanoparticles that are now available, as well as their application in wastewater treatment (Fathima et al., 2008) Table 5.6. Existing Ag2O nanoparticle production technologies and their application in wastewater treatment are discussed (Naseem and Durrani, 2021) Table 5.7. Existing TiO2 nanoparticle production technologies and their usage in wastewater treatment are discussed (Naseem and Durrani, 2021)

LIST OF ABBREVIATIONS 0D

zero-dimensional

2D

two-dimensional

AOP

advanced oxidation processes

BaTiO3

barium titanate

BPM

bit patterned media

CD

carbon dots

CFCs

chlorofluorocarbons

CH3NH2

methylamine

Cs

cadmium

CVD

chemical vapor deposition

ECGs

electrocardiograms

EDA

ethylenediamine

EISA

evaporation-induced self-assembly

ETM

electron-transporting materials

FCC

face-centered cubic

GC

gas chromatography

H2SO4

sulfuric acid

H3PO4

phosphoric acid

HCl

hydrogen chloride

HCN

hydrogen cyanide

HFCs

hydrofluorocarbons

HMS

hexagonal molecular sieves

IUPAC

International Union of Pure and Applied Chemistry

LAT

ligand-assisted templating

MA

methylammonium

MB

methylene blue

MGO

malachite green oxalate

MIC

minimum inhibitory concentration

MO

methyl orange

MONPs

metal oxide nanoparticles

MRI

magnetic resonance imaging

NFC

near-field communication

NG

nanogenerator

NH3

ammonia

NH

ammonium

NH4NO3

ammonium nitrate

NH4OH

ammonium hydroxide

NIR

near-infrared

NO2

nitrite

NO

nitrate

NWs

nanostructured materials

OH

hydroxide ion

ORR

oxygen reduction reaction

PAHs

polycyclic aromatic hydrocarbons

PCE

power conversion efficiency

PDMS

polydimethylsiloxane

PEO

polyethylene oxide

PO4

phosphate ion

PSCs

perovskite solar cells

PSCs

photonic crystals

PV

photovoltaic

PZT

lead zirconate titanate

RHCP

randomly stacked hexagonal close-packed planes

SDS

sodium dodecyl sulfate

SEM

scanning electron microscopy

SFM

super ferromagnetic

SO42−

sulfate

t.o.e.

ton oil equivalents

TE

textile effluent

TENG

triboelectric nanogenerators

TMB

1,3,5-trimethylbenzene

TMD

transition-metal dichalcogenides

+ 4

− 3

−

3−

TMOS

tetramethyl orthosilicate

TMR

tunneling magnetoresistance

TOAB

tetraethylammonium bromide

UV

ultraviolet

ZPN

ZnO polyurethane nanocomposite

xix

PREFACE

The majority of the Earth’s crust is made up of inorganic materials, however, the contents of the deep mantle are still being studied. Simple carbon compounds are frequently referred to be inorganic. Carbon monoxide, CO2, carbides, and the salts of inorganic cations carbonates, cyanides, thiocyanates, and cyanates are only a few examples. Many of these are common components of predominantly organic systems, such as organisms; simply because a chemical is inorganic does not mean it does not exist in living things. Since antiquity, inorganic compounds have been recognized and employed; the deep blue pigment Prussian blue (KFe2(CN)6) is perhaps the earliest. However, until the late nineteenth and early 20th centuries, when the current subject of coordination chemistry formed, the chemical composition of these molecules remained unknown. Much of what we know about inorganic chemistry comes from the work of Sophus Mads Jorgensen (1837–1914) and Alfred Werner (1866–1919) [Nobel Prize in Chemistry in 1913], as well as their disagreements. Following Werner’s victory in these disputes, inorganic chemistry fell out of favor until the mid-20th century, when the Second World War reignited interest. Several notable discoveries and hypotheses were established during the postwar era. Important bonding theories in coordination compounds, for example, have been established. These are two essential and complementary theories that explain the spectroscopic, chemical, and structural features of inorganic coordination compounds; CFT is more straightforward, while LFT is more precise. The Haber-Bosch process was discovered in the 1950s when organometallic catalysts were identified to catalyze crucial organic processes. The Haber-Bosch process is one of the most significant industrial processes in the world, and it is catalyzed by an inorganic oxide catalyst. It allows for the direct production of ammonia from nitrogen (N2) and hydrogen (H2). N2(g)+3H2(g) ⇌ 2NH3 (g)

Since its invention in the early 20th century, it has resulted in the creation of a massive amount of fertilizer, resulting in a massive increase in world food production. As a result, it is thought that this mechanism is responsible for a considerable portion of the nitrogen in the average human body. While the reaction in the industrial environment must be carried out at high pressure and temperature, the nitrogenase enzyme found on the plant’s roots can carry out this reaction in the gentle circumstances found in soil.

The goal of further research was to enhance inorganic catalysts by better understanding metal cofactors in enzyme. The connection between the Haber-Bosche manufacturing processes and the nitrogenase enzyme was an early link between organometallic and biology sciences. This book contains eight chapters. Chapters 1 and 2 deal with the introduction of inorganic compounds and their nomenclature. Chapter 3 focusses on the classification, properties, and applications of porous inorganic materials. Chapter 4 discusses the applications and properties of magnetic inorganic compounds. Chapter 5 focuses on the applications of metallic nanoparticles for wastewater treatment and anti-bacterial applications. Chapter 6 contains information about multifunctional inorganic compounds and their applications in energy sector. Chapter 7 introduces the readers with semiconducting inorganic materials and their applications in electronics industry. Finally, Chapter 8 deals with the applications of inorganic compounds in biomedical applications. This book is equally beneficial for students from the fields of chemistry, chemical engineering, and catalysis. Moreover, professionals from different synthesis industries can also benefit from this book of inorganic compounds.

CHAPTER

1

INTRODUCTION TO INORGANIC COMPOUNDS

CONTENTS 1.1. Introduction......................................................................................... 2 1.2. Inorganic Chemistry and Inorganic Compounds.................................. 4 1.3. Classification of Inorganic Compounds................................................ 6 1.4. Some Subdivisions of Inorganic Chemistry......................................... 14 1.5. Types of Reactions and Examples of Inorganic Compounds............... 16 1.6. Inorganic Chemistry’s Applications.................................................... 16 References................................................................................................ 17

2

An Overview of Inorganic Compounds

1.1. INTRODUCTION When two or more chemical elements combine (except Carbon to Hydrogen) to form another substance in nearly definite and whole number proportions, the term “inorganic compound” is the thing in mind. Though this universal definition was not so strict since carbon compounds as carbides, carbonates, cyanides as well as graphite, carbon dioxide and carbon monoxide are classified inorganic, there are some exceptions to rules in chemistry that are considered (which will be discussed in the following chapters) as a result of techniques and processes employed to realize the criteria and implement the protocol. One popular technique depends on the presence of specific components. For instance, halides are composed of more than halogen atoms, hydrides are composed of more than one hydrogen atom, and oxides are composed of more than one oxygen atom (Hasenknopf, 2005). Organic complexes are defined as those that contain carbon atoms in their backbone, while all other compounds are categorized as inorganic. As the term implies, organometallic complexes are organic molecules that are covalently linked to metal atoms (Figure 1.1).

Figure 1.1. Ionic bonding in sodium chloride. Source: https://www.britannica.com/science/chemical-compound/Classification-of-compounds. Note: In a chemical process, an atom of Na gives one of its electrons to an atom of Cl, and the resultant negative ion (Cl) and positive ion (Na+) combine to create a stable ionic compound.

Introduction to Inorganic Compounds

3

Another approach for classifying chemical compounds depends on the bond type in the molecule. Ionic compounds are comprised of ions and are kept together by the attraction of oppositely charged ions. The famous ionic substance is sodium chloride (common salt). Molecular compounds are made up of molecules that are kept together due to electron sharing. Water, for example, is composed of H2O molecules; methane is composed of CH4 molecules, and hydrofluoric acid is composed of HF molecules (Allmann and Hinek, 2007). Water (H2O) and HF are inorganic while CH4 is organic by classification. It is therefore modest to say the organic molecules occur when carbon is bonded to hydrogen, or when hydrogen is substituted by any other group in an electron-sharing mechanism (covalent bonds). The 3rd strategy depends on reactivity—more precisely, the complex chemical reactions are expected to go through. For instance, acids are chemicals that, when dissolved in water, form H+ ions (protons). As a result, acids are classified as proton donors. Very often, acids are in their aqueous form such as that of nitric acid (HNO3), sulfuric acid (H2SO4), hydrochloric acid (HCl), and phosphoric acid (H3PO4). By contrast, bases are proton acceptors (Stull, 1947; Smith, 2014). The most typical base is the hydroxide ion (OH), which forms a water molecule when combined with an H+ ion (usually written H2O).

Another significant category of chemical processes is oxidation-reduction reactions. Oxidation results to the loss of electron, whereas reduction results in the gain of electrons. For instance, in the reaction of sodium metal with chlorine gas to generate NaCl, 2 Na+ + Cl2 → 2 NaCl

electrons (e) are moved from sodium atoms to chlorine atoms, resulting in the creation of sodium chloride as illustrated in Figure 1.2 (Yamase, 2005).

Figure 1.2. Oxidation-reduction reactions in sodium chloride. Source: https://www.shutterstock.com/search/sodium+chloride+ions.

4

An Overview of Inorganic Compounds

This process results in every sodium atom releasing an electron. When an atom releases and electron, it is oxidized. As shown in Figure 1.2, every chlorine atom acquires an electron and once it’s requirement of electrons are supplied, it becomes more negative. When an atom gains an electron, it is then reduced. In this reaction, sodium serves as the reducing agent (it provides electrons), while chlorine serves as the oxidizing agent. Sodium is the reason why chlorine is reduced, while chlorine is the reason why sodium is oxidized. Metals are the most often used reducing agents because they tend to lose electrons during their interactions with nonmetals. Reacting agents include halogens like bromine (Br2), chlorine (Cl2), and fluorine (F2), as well as some oxyanions such as Cr2O72 (the dichromate ion) and the MnO4 (permanganate ion) (Prudent et al., 2008).

1.2. INORGANIC CHEMISTRY AND INORGANIC COMPOUNDS The term “organic” refers to compounds containing carbon atoms. As a result, the branch of chemistry that studies complexes that do not contain carbon-hydrogen bonds are known as ‘Inorganic Chemistry.’ Metals, salts, and chemical substances are all examples of substances that lack carbonhydrogen bonding (Prudent et al., 2008). On this planet, around 100,000 inorganic substances are known to exist. Inorganic chemistry is concerned with the behavior of these substances and their properties, including their chemical and physical aspects. Except for carbon and hydrogen, all elements of the periodic table are included in the types of inorganic compounds (Sadler, 1991). Numerous elements are employed in research and technology: copper, nickel, iron, and titanium, for instance, are used in structural and electrical applications. The transition metals combine with one another and other metallic elements to generate a variety of useful alloys. For example, gold in jewelries will never be that hard and molded if it is not mixed with other metals like silver, copper, or zinc at several percentages. Say, yellow gold is approximately 92% gold, 5% silver, 2% copper and 1% zinc while rose gold is actually 75% gold, 22% copper and 3% silver. This is because pure gold is relatively soft and easily melted. The other metals harden it, making it ideal for jewelries. As mentioned in the previous section of this book, carbonates and cyanides are composed of carbon, but are classified as inorganic compound

Introduction to Inorganic Compounds

5

because they lack long carbon-carbon bonds that are uniquely found among organic substances. Typically, inorganic compounds are classified according to the components or groupings of elements they have. For instance, oxides can be molecular or ionic. Ionic oxides results in oxygen (O2) combining with metals. In contrast, molecular oxides are composed of molecules in which O (oxygen) is covalently bonded to another nonmetal, for example, nitrogen (N) or sulfur (S) (Brown, 1978). When ionic oxides are dissolved in water, the O2 ions create OH (hydroxide ions), resulting in a basic solution. When molecular oxides combine with oxyacids, water, including nitric acid (HNO3) and H2SO4, are formed. Inorganic compounds also contain hydrides (which include H ions or hydrogen atoms), nitrides (which contain N3 ions), sulfides (which contain S2 ions) and phosphides (which comprise P3 ions). Transition metals can be used to synthesize a wide range of inorganic chemicals. The most significant are coordination compounds, which contain between two and six ligands around the metal atom or ion. Ligands are neutral compounds or ions with pairs of electrons that can be donated to the metal atom to create a covalent coordination connection (Cariati et al., 2016).

Figure 1.3. Coordination compound formation from transition metal. Source: https://www.britannica.com/science/chemical-compound/Classification-of-compounds.

The ensuing covalent bond is given a unique term since just one item (the ligand) supplies both electrons shared in the bond (see Figure 1.3). Hexaaminecobalt (III) chloride, [Co(NH3)6]Cl3 is an example of a coordination compound . It comprises a cobalt ion (Co3+), a Co(NH3)63+ ion, with six ammonia molecules (NH3) connected as ligands (Bartel et al., 2016). There was no structured method to naming compounds in the initial years of the science of chemistry. Chemists invented lead sugar, quicklime,

An Overview of Inorganic Compounds

6

magnesia milk, Epsom salts, and laughing gas to characterize well-known chemicals. These are referred to as trivial or common names. As chemistry progressed, it became clear that using common names for all common compounds, which is more than a million, would create enormous confusion. Memorizing trivial terms for such a huge number of compounds would be impossible. As a result, a systematic nomenclature (the process of naming) has been devised. On the other hand, the systematic terms for NH3 and H2O are never employed because it makes the substance harder to remember; these important compounds are simply called ammonia and water (Kumar et al., 2016). It will be too boring to call water as hydrogen dioxide or ammonia as nitrogen trihydride. Binary complexes—those composed of two elements—are the simplest chemical compounds. Binary ionic chemicals and binary molecular compounds are classified differently and discussed separately.

1.3. CLASSIFICATION OF INORGANIC COMPOUNDS The inorganic compounds are categorized in the following text (Wilding et al., 1984). In this classification, it is always noteworthy to consider that all compounds listed below have their organic counterparts. •

Acids: These dissolves in water and produce hydrogen ions. Examples of acids include sulfuric acid or H2SO4, , or hydrochloric acid, HCl. Below is an illustration of an inorganic acid reaction. HCl(aq)+ H2O(l)→ H3O+(aq)+ Cl−(aq) •

Bases: are substances that produced OH- ions when mixed with water. When dissolved in water, ammonia, calcium hydroxide, potassium hydroxide, and sodium hydroxide release OH– ions. See the sample dissociation of potassium hydroxide, KOH below: KOH(s) → K⁺(aq) + OH⁻(aq) •

•

Salts: are the products of the reaction between a base and an acid. Table salt, sodium hydroxide or NaCl, is a typical example of a salt. Oxides: These are substances that contain oxygen atom bonded to a metal. Binary oxides like NaO usually decompose by the action of heat, while a classic example of an oxyacids nitric acid (HNO3) and sulfuric acid (H2SO4).

Introduction to Inorganic Compounds

7

Table 1.1. Periodic Table Showing Inorganic Compounds

1.3.1. Binary Compounds 1.3.1.1. Binary Ionic Compounds The nomenclature of binary ionic compounds is simple: the ions are named according to the following principles (Nowrouzi et al., 2018): The positive ion (referred to as a cation) is first, followed by the -ion (anion). • Simple cations are named for their parental element. For instance, Li+ is referred to as lithium in the names of the compounds that contain this ion. Also, Na+ is referred to as Mg2+, and sodium is referred to as magnesium, etc. • A simple anion is named by changing the ending or the original name to -ide. Therefore, the F ion is referred to as fluoride, the Br ion as bromide, the S2 ion as sulfide, and so forth. The subsequent instances demonstrate the principles for binary ionic compound nomenclature (Table 1.2). •

8

An Overview of Inorganic Compounds

Table 1.2. Rules of Nomenclature for Binary Ionic Compounds Name

Ions Present

Compound

Sodium chloride

Na , Cl

NaCl

Calcium sulfide

Ca2+, S2–

CaS

Potassium iodide

K ,I

KI

Magnesium oxide

Mg2–, O2–

MgO

Cesium bromide

Cs , Br

CsBr

+

+

+

–

–

–

Simple ions are denoted in the formulations of ionic compounds by the element’s chemical symbol: Na denotes Na+, Cl denotes Cl, and so on. Nevertheless, when specific ions are displayed, their charge is always included. Therefore, potassium bromide is denoted by the formula KBr, but when the bromide and potassium ions are displayed separately, they are denoted by the symbols Br and K+ (Zhou et al., 2011). When a single metal atom may create many cations, the charge on the specific cation should be indicated in the compound’s name. For instance, Pb (lead) can occur in ionic compounds as Pb4+ or Pb2+ ions. Additionally, iron (Fe) may be converted to Fe3+ or Fe2+ ions, and tin (Sn) can be converted to Sn4+ or Sn2+ ions, while Au (gold) can be converted to Au3+ or Au+ ions, etc. Another method of representing these binary compounds that includes metals is by the use of a Roman number to indicate the ion’s charge. For instance, Fe3+ iron (III) chloride is the iron cation involved in the formation of the molecule FeCl3, thus can be named as Iron (III) Chloride aside from its name ferric chloride On the other hand, iron (III) chloride in the chemical FeCl2, or ferrous chloride includes Fe2+ and its name is written as Iron (II) chloride. The Roman number as illustrated in Table 1.3, in the name indicates the metal ion charge present in each case (Chamel and Fantina, 2016). Table 1.3. Common Simple Anions and Cations Name

Cation

Name

Anion

Potassium

K

+

Bromide

Br–

Lithium

Li+

Fluoride

F–

Hydrogen

H

Hydride

H–

Sodium

Na+

Chloride

Cl–

Beryllium

Be

Oxide

O2–

Cesium

Cs+

Iodide

I–

Magnesium

Mg

Sulfide

S2–

+

2+

2+

Introduction to Inorganic Compounds Barium

Ba2+

Calcium

Ca2+

Silver

Ag+

Aluminum

Al3+

9

Occasionally, an alternate method for identifying compounds including metals that form just two ions is seen, particularly in ancient works. The ion with the greater charge is designated by the suffix -ic, whereas the ion with the fewer charge is designated by the postfix -ous. For instance, Fe3+ is the ferric ion, whereas Fe2+ is the ferrous ion. FeCl2 and FeCl3 are thus referred to as ferrous chloride and ferric chloride (Table 1.4) (Sarmiento et al., 2013). Table 1.4. General Ions That Form Multiple Cations Systematic Name Iron(II) Iron(III) Copper(I) Copper(II) Cobalt(II) Cobalt(III) Tin(II) Tin(IV) Lead(II) Lead(IV) Mercury(I) Mercury(II)

Ion Fe2+ Fe3+ Cu+ Cu2+ Co2+ Co3+ Sn2+ Sn4+ Pb2+ Pb4+ Hg22+(*) Hg2+

Alternate Name Ferrous Ferric Cuprous Cupric Cobaltous Cobaltic Stannous Stannic Plumbous Plumbic Mercurous Mercuric

*Mercury(I) ions constantly appear bound together to form Hg22+.

1.3.1.2. Binary Molecular (Covalent) Compounds Binary molecular compounds are generated when two nonmetals react. While these compounds lack ions, they are termed likewise binary ionic complexes. These principles govern the naming of binary covalent compounds (Ossi and Pastorelli, 1998): • •

The formula’s first element is specified first, followed by the element’s entire name. The 2nd element is referred to as an anion.

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10

•

Prefixes specify the number of atoms present. The prefix monois dropped if the initial element occurs as a single atom. For instance, carbon monoxide is called carbon monoxide instead of mono carbon monoxide. These illustrations demonstrate how the principles are employed in nitrogen-oxygen covalent molecules (Table 1.5). Table 1.5. Nitrogen and Oxygen Compounds and Their Nomenclature Systematic Name

Compound

Dinitrogen monoxide (nitrous oxide – laughing gas) N2O Dinitrogen pentoxide

N2O5

Dinitrogen trioxide

N2O3

Nitrogen dioxide

NO2

Dinitrogen tetroxide

N2O4

Nitrogen monoxide (nitric oxide)

NO

As illustrated in Table 1.6, when the element’s name starts with a vowel, the last o or an of the prefix is frequently omitted to prevent problematic pronunciations. For instance, N2O4 is mentioned as dinitrogen tetroxide rather than dinitrogen tetraoxide, whereas CO is known as carbon monoxide rather than carbon monooxide (Table 1.6) (Guo et al., 2008). Table 1.6. Prefixes Employed in Chemical Nomenclature Number of Atoms 8 7 6 5 4 3 2 1

Prefix octaheptaHexapentatetratridimono-

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1.3.2. Nonbinary (Ternary) Compounds 1.3.2.1. Ionic Compounds Containing Polyatomic Ions Ammonium nitrate (NH4NO3) is a unique ionic molecule because it comprises NO3 and NH4+, and polyatomic ions. As the name implies, a polyatomic ion is a charged particle formed by the union of many atoms. Polyatomic ions (see Table 1.7) are given unique names in the terminology of the compounds that include them (Ryan et al., 2014). Table 1.7. Common Polyatomic Ions Ion NH4+ NO3– SO42– SO32– OH– NO2– HSO4–

Name Ammonium Nitrate Sulfate Sulfite Hydroxide Nitrite

H2PO4 CN– PO43– HPO42–

–

O22– CrO42– Cr2O72– MnO4– C2H3O2– ClO4– ClO3– ClO2– ClO– HCO3– CO3

2–

Hydrogen sulfate* Dihydrogen phosphate Cyanide Phosphate Hydrogen phosphate Peroxide Chromate Dichromate Permanganate Acetate Perchlorate Chlorate Chlorite Hypochlorite Hydrogen carbonate** Carbonate

**Bicarbonate and *bisulfate are extensively used colloquial terms for hydrogen sulfate and hydrogen carbonate.

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An Overview of Inorganic Compounds

Many polyatomic anions include an atom of a certain element in conjunction with varying amounts of oxygen. These anions are referred to as oxyanions. When the sequence comprises just two members, the ion with fewer oxygen atoms is designated by the suffix -ite, while the suffix that is used to designates the other ion is -ate. For instance, SO32 is referred to as sulfite, whereas SO42 is referred to as sulfate. When a series has more than two oxyanions, the prefixes hypo- (less than) and per- (greater than) denote the series members having the fewest and greatest amount of oxygen atoms and ended with suffix -ate. The chlorinated oxyanions offer as an illustration in Table 1.8 (Naah and Sanger, 2012): Table 1.8. Chlorine-Containing Oxyanions Name Perchlorate Chlorate Chlorite Hypochlorite

Ion ClO4– ClO3– ClO2– ClO–

Naming polyatomic ionic compounds are analogous to nomenclature binary ionic complexes. For instance, the chemical NaOH is sodium hydroxide due to both the OH (hydroxide) anion and the Na+ (sodium) cation. As with binary ionic compounds, when a metal capable of forming several cations(or what is called a multivalent metal), the charge on the cation is indicated using a Roman number. For instance, the molecule FeSO4 is referred to as iron(II) sulfate due to the presence of Fe2+ (Wirtz et al., 2006).

1.3.2.2. Acids Consider an acid as a molecule that contains one H+ (hydrogen ion) bound to an anion. The terminology of acids is determined by oxygen in the anion. If the anion is oxygen-free, the acid is named by the use of a prefix hydro-. Hydrochloric acid, for instance, is HCl dissolved in water. Likewise, H2S and HCN are hydrosulfuric (or dihydrogen sulfide) and hydrocyanic acids (or hydrogen cyanide) when dissolved in water (Chen et al., 2009). As the acid’s anion contains oxygen, the suffix -ic or -ous are used as the basis name of the anion. If the anion’s term ends in -ate, ir is changed to -ic then the word “acid” is added. For instance, H2SO4 is sulfuric acid because it comprises the SO42- (sulfate anion); H3PO4 is phosphoric acid (H3PO4)

Introduction to Inorganic Compounds

13

because it covers the PO43+ (phosphate anion), and HC2H3O2 is acetic acid because it includes the C2H3O2- (acetate ion). For anions ending in -ite, the -ite is substituted by -ous then the word acid. For instance, H2SO3, which includes SO32 (sulfite), is called sulfurous acid, and HNO2, which comprises nitrite (NO2), is called nitrous acid. In Table 1.9, the acids of chlorine’s oxyanions are employed to demonstrate the conventions for naming acids based on the number of oxygen atoms (Chizhik et al., 2002). Table 1.9. Terms of Common Acids Formula

Name

H5P3O10

Triphosphoric acid

H2SO5

Peroxymonoosulfuric acid

H3PO4

Orthophosphoric acid**

H3BO3

Orthoboric acid*

H2CO3

Carbonic acid

H3PO3

Phosphorous acid

H4P2O7

Pyrophosphoric acid

(HPO3)3

Trimetaphosphoric acid

HPO3

Metaphosphoric acid

H2S2O6

Dithionic acid

H3PO2

Hypophosphorous acid

HMnO4

Permanganic acid

H2S2O3

Thiosulfuric acid

HF

Hydrofluoric acid

HCl

Hydrochloric acid

HC2H3O2

Acetic acid

H2SO3

Sulfurous acid

H2SO4

Sulfuric acid

HNO2

Nitrous acid

14

An Overview of Inorganic Compounds HNO3

Nitric acid

H2S

Hydrosulfuric acid

HCN

Hydrocyanic acid

HI

Hydroiodic acid

HClO4

Perchloric acid

HBr

Hydrobromic acid

HClO3

Chloric acid

HClO

Hypochlorous acid

HClO2

Chlorous acid

*Often called boric acid. **Often called phosphoric acid.

1.3.3. Compounds with Complexions A coordination compound comprises one or more complicated structural components; everyone contains a core atom directly linked to a group called ligands. Coordination compound nomenclature depends on these structural interactions (Dai et al., 2009).

1.4. SOME SUBDIVISIONS OF INORGANIC CHEMISTRY 1.4.1. Organometallic Chemistry Organometallic Chemistry has expanded at a breakneck rate over the last three to four decades as an interdisciplinary field within Inorganic Chemistry. On an academic level, attempts to explicate the kind of bonds in an evergrowing list of fascinating organometallic compounds have resulted in incomplete knowledge of the nature and range of chemical bonds (Schröder et al., 2000). Compounds of organometallic are largely employed in industries as homogeneous catalysis agents. The themes discussed in this book provide readers with new perspectives on organometallic chemistry. Organometallic chemistry involves the investigation of organometallic compounds. Since several compounds not including these bonds are

Introduction to Inorganic Compounds

15

chemically similar, an alternate may be molecules with mostly covalent metallic bonds. Organometallic chemistry combines inorganic and organic chemistry (Pregosin et al., 2005).

1.4.2. Transition Elements Transition elements have incompletely filled d-orbitals in their second to the last shell. This conceptual description is advantageous because it identifies a transition element based on its electrical configuration alone. Mercury, cadmium, and zinc are not considered transition elements because they lack a partly packed d-orbital. They are, nevertheless, transition elements as well, as their characteristics are an addition of the transition elements’ features in inorganic chemistry. Indeed, the zinc group acts as connective tissue among the representative and transition elements (Connelly and Geiger, 1996). The 24 elements in question have the following features: they are all metals, the majority of which are lustrous, solid, and hard, have high boiling and melting temperatures, and are excellent conductors of electricity and heat. Due to the wide variety of these qualities, the assertions are analogous to the generic properties of all other components (Audrieth and Daniels, 1951).

1.4.3. Coordination Chemistry Coordination chemicals were used long before inorganic chemistry was established. Tassaert initiated a logical examination of bonding and structure in coordination chemistry, which was continued till the end of the 19th century by eminent chemists such as Alfred Werner, Jorgensen, and Wilhelm Blomstrand. Werner’s coordination theory evolved into the foundation of current coordination chemistry (Bailar, 1989).

1.4.4. p-Block Elements The p-block comprises the elements in groups 13 to 18 of the periodic table. Inorganic chemistry p block elements, similar to additional block elements, have significant characteristics due to their ionization enthalpy, atomic size, electronegativity, and electron gain enthalpy. The lack of d-orbitals in the 2nd period and the existence of d- or f-orbitals in bulky elements substantially influence their characteristics. Hence, bulky p-block elements vary from their light congeners (Ugo, 1975).

An Overview of Inorganic Compounds

16

1.5. TYPES OF REACTIONS AND EXAMPLES OF INORGANIC COMPOUNDS Inorganic chemistry consists of four chemical reactions: decomposition, combination, double displacement, and single displacement processes (Hoigné and Bader, 1983): •

• •

•

Combination Reactions: As implied by the term ‘Combination,’ two or more substances join to produce a result, referred to as a Combination reaction. For instance: Barium + F2 → BaF2 Decomposition Reaction: It is a reaction in which a single atom breaks up into two products. For instance: FeS → Fe + S Single Displacement Reactions: A reaction in which one atom of one element is substituted for another atom of another element. For instance: Zn (s) + CuSO4 (aq) → Cu (s) + ZnSO4 (aq) Double Displacement Reactions: Additionally, this sort of reaction is referred to as ‘metathesis reactions.’ Two components from two distinct compounds combine to produce two novel complexes. For instance: CaCl2 (aq) + 2AgNO3 (aq) → Ca(NO3)2 (aq) + 2 AgCl (s)

1.6. INORGANIC CHEMISTRY’S APPLICATIONS Inorganic chemistry has numerous applications in several areas, for example, Engineering, chemical, biology, etc. (Farrell, 2002): • • • • •

It is used in medicine and healthcare institutions; The most typical application is in our daily life, where we utilize table salt or the chemical muriatic acid; Baking soda is a common ingredient in making cakes and other baked goods; Numerous inorganic chemicals are used in the ceramic industry; It is used in the electrical area to create electric circuits such as silicon in computers, and so on.

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REFERENCES 1.

Allmann, R., & Hinek, R., (2007). The introduction of structure types into the inorganic crystal structure database ICSD. Acta Crystallographica Section A: Foundations of Crystallography, 63(5), 412–417. 2. Audrieth, L. F., & Daniels, F., (1951). Physical and inorganic chemistry. Industrial & Engineering Chemistry, 43(2), 269–288. 3. Bailar, J. C., (1989). A history of the division of inorganic chemistry, American chemical society. Journal of Chemical Education, 66(7), 537. 4. Bartel, C. J., Clary, J. M., Sutton, C., Vigil-Fowler, D., Goldsmith, B. R., Holder, A. M., & Musgrave, C. B., (2020). Inorganic halide double perovskites with optoelectronic properties modulated by sublattice mixing. Journal of the American Chemical Society, 142(11), 5135– 5145. 5. Brown, I. D., (1978). Bond valences—A simple structural model for inorganic chemistry. Chemical Society Reviews, 7(3), 359–376. 6. Cariati, E., Lucenti, E., Botta, C., Giovanella, U., Marinotto, D., & Righetto, S., (2016). Cu (I) hybrid inorganic–organic materials with intriguing stimuli responsive and optoelectronic properties. Coordination Chemistry Reviews, 306, 566–614. 7. Chamel, N., & Fantina, A. F., (2016). Binary and ternary ionic compounds in the outer crust of a cold nonaccreting neutron star. Physical Review C, 94(6), 065802. 8. Chattopadhyay, J., Kim, C., Kim, R., & Pak, D., (2009). Thermogravimetric study on pyrolysis of biomass with Cu/Al2O3 catalysts. Journal of Industrial and Engineering Chemistry, 15(1), 72–76. 9. Chen, Z., He, W., Beer, M., Megharaj, M., & Naidu, R., (2009). Speciation of glyphosate, phosphate and aminomethylphosphonic acid in soil extracts by ion chromatography with inductively coupled plasma mass spectrometry with an octopole reaction system. Talanta, 78(3), 852–856. 10. Chizhik, V. I., Egorov, A. V., Komolkin, A. V., & Vorontsova, A. A., (2002). Microstructure and dynamics of electrolyte solutions containing polyatomic ions by NMR relaxation and molecular dynamics simulation. Journal of Molecular Liquids, 98, 173–182.

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11. Clark, R. J., & Stewart, B., (1979). The resonance Raman effect— Review of the theory and of applications in inorganic chemistry. Inorganic Chemistry and Spectroscopy, 2, 1–80. 12. Connelly, N. G., & Geiger, W. E., (1996). Chemical redox agents for organometallic chemistry. Chemical Reviews, 96(2), 877–910. 13. Dai, R., Liu, J., Yu, C., Sun, R., Lan, Y., & Mao, J. D., (2009). A comparative study of oxidation of Cr (III) in aqueous ions, complex ions and insoluble compounds by manganese-bearing mineral (birnessite). Chemosphere, 76(4), 536–541. 14. Farrell, N., (2002). Biomedical uses and applications of inorganic chemistry: An overview. Coordination Chemistry Reviews, 232(1, 2), 1–4. 15. Gordon, S., & Campbell, C., (1955). Differential thermal analysis of inorganic compounds. Analytical Chemistry, 27(7), 1102–1109. 16. Guo, X., Li, L., Liu, Z., Yu, D., He, J., Liu, R., & Wang, H. T., (2008). Hardness of covalent compounds: Roles of metallic component and d valence electrons. Journal of Applied Physics, 104(2), 023503. 17. Hasenknopf, B., (2005). Polyoxometalates: Introduction to a class of inorganic compounds and their biomedical applications. Front. Biosci., 10(275), 10–2741. 18. Hoigné, J. H. W. R. J., Bader, H., Haag, W. R., & Staehelin, J., (1985). Rate constants of reactions of ozone with organic and inorganic compounds in water—III. Inorganic compounds and radicals. Water Research, 19(8), 993–1004. 19. Hoigné, J., & Bader, H. J. W. R., (1983). Rate constants of reactions of ozone with organic and inorganic compounds in water—I: Nondissociating organic compounds. Water Research, 17(2), 173–183. 20. Hoigné, J., & Bader, H., (1983). Rate constants of reactions of ozone with organic and inorganic compounds in water—II: Dissociating organic compounds. Water Research, 17(2), 185–194. 21. Kumar, A., Balasubramaniam, K. R., Kangsabanik, J., & Alam, A., (2016). Crystal structure, stability, and optoelectronic properties of the organic-inorganic wide-band-gap perovskite CH3 NH3 BaI3: Candidate for transparent conductor applications. Physical Review B, 94(18), 180105.

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22. Naah, B. M., & Sanger, M. J., (2012). Student misconceptions in writing balanced equations for dissolving ionic compounds in water. Chemistry Education Research and Practice, 13(3), 186–194. 23. Nowrouzi, I., Manshad, A. K., & Mohammadi, A. H., (2018). Effects of dissolved binary ionic compounds and different densities of brine on interfacial tension (IFT), wettability alteration, and contact angle in smart water and carbonated smart water injection processes in carbonate oil reservoirs. Journal of Molecular Liquids, 254, 83–92. 24. Orpen, A. G., (2002). Applications of the Cambridge structural database to molecular inorganic chemistry. Acta Crystallographica Section B: Structural Science, 58(3), 398–406. 25. Ossi, P. M., & Pastorelli, R., (1998). Modeling the structural stability of irradiated covalent compounds. Surface and Coatings Technology, 103, 9–15. 26. Pregosin, P. S., Kumar, P. A., & Fernández, I., (2005). Pulsed gradient spin− echo (PGSE) diffusion and 1H, 19F heteronuclear over Hauser spectroscopy (HOESY) NMR methods in inorganic and organometallic chemistry: Something old and something new. Chemical Reviews, 105(8), 2977–2998. 27. Prudent, R., Moucadel, V., Laudet, B., Barette, C., Lafanechère, L., Hasenknopf, B., & Cochet, C., (2008). Identification of polyoxometalates as nanomolar noncompetitive inhibitors of protein kinase CK2. Chemistry & Biology, 15(7), 683–692. 28. Ronconi, L., & Sadler, P. J., (2008). Applications of heteronuclear NMR spectroscopy in biological and medicinal inorganic chemistry. Coordination Chemistry Reviews, 252(21, 22), 2239–2277. 29. Ryan, S., & Herrington, D. G., (2014). Sticky ions: A student-centered activity using magnetic models to explore the dissolving of ionic compounds. Journal of Chemical Education, 91(6), 860–863. 30. Sadler, P. J., (1991). Inorganic chemistry and drug design. Advances in Inorganic Chemistry, 36, 1–48. 31. Sarmiento-Perez, R., Cerqueira, T. F. T., Valencia-Jaime, I., Amsler, M., Goedecker, S., Botti, S., & Romero, A. H., (2013). Sodium–gold binaries: Novel structures for ionic compounds from an ab initio structural search. New Journal of Physics, 15(11), 115007. 32. Schröder, D., Shaik, S., & Schwarz, H., (2000). Two-state reactivity as a new concept in organometallic chemistry. Accounts of Chemical Research, 33(3), 139–145.

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33. Stull, D. R., (1947). Inorganic compounds. Industrial & Engineering Chemistry, 39(4), 540–550. 34. Ugo, R., (1975). The contribution of organometallic chemistry and homogeneous catalysis to the understanding of surface reactions. Catalysis Reviews Science and Engineering, 11(1), 225–297. 35. Wang, J., Wang, G., Zhang, M., Chen, M., Li, D., Min, F., & Yan, Y., (2006). A comparative study of thermolysis characteristics and kinetics of seaweeds and fir wood. Process Biochemistry, 41(8), 1883–1886. 36. Wang, J., Zhang, M., Chen, M., Min, F., Zhang, S., Ren, Z., & Yan, Y., (2006). Catalytic effects of six inorganic compounds on pyrolysis of three kinds of biomass. Thermochimica Acta, 444(1), 110–114. 37. Wilding, C. R., Walter, A., & Double, D. D., (1984). A classification of inorganic and organic admixtures by conduction calorimetry. Cement and Concrete Research, 14(2), 185–194. 38. Wirtz, M. C., Kaufmann, J., & Hawley, G., (2006). Nomenclature made practical: Student discovery of the nomenclature rules. Journal of Chemical Education, 83(4), 595. 39. Yamase, T., (2005). Anti-tumor,-viral, and-bacterial activities of polyoxometalates for realizing an inorganic drug. Journal of Materials Chemistry, 15(45), 4773–4782. 40. Zhou, X. W., Doty, F. P., & Yang, P., (2011). Atomistic simulation study of atomic size effects on B1 (NaCl), B2 (CsCl), and B3 (zinc-blende) crystal stability of binary ionic compounds. Computational Materials Science, 50(8), 2470–2481.

CHAPTER

2

NOMENCLATURE OF INORGANIC COMPOUNDS

CONTENTS 2.1. Introduction....................................................................................... 22 2.2. Naming Binary Ionic Compounds...................................................... 23 2.3. Naming Covalent Compounds........................................................... 28 2.4. Polyatomic Ions................................................................................. 29 2.5. Hydrates............................................................................................ 30 2.6. Binary Covalent Compounds............................................................. 31 2.7. Acids................................................................................................. 34 2.8. Bases................................................................................................. 36 2.9. Summary........................................................................................... 38 References................................................................................................ 39

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An Overview of Inorganic Compounds

2.1. INTRODUCTION Generally, there are two types of inorganic compounds that can be formed: ionic compounds and molecular compounds. Nomenclature is the process of naming chemical compounds with different names so that they can be easily identified as separate chemicals. Inorganic compounds are compounds that do not deal with the formation of carbohydrates, or simply all other compounds that do not fit into the description of an organic compound. For example, organic compounds include molecules with carbon rings and/or chains with hydrogen atoms. Inorganic compounds, the topic of this chapter, are every other molecule that does not include these distinctive carbon and hydrogen structures (Bassett et al., 1960). The universal adoption of an agreed chemical nomenclature is a key tool for communication in the chemical sciences, for computer-based searching in databases, and for regulatory purposes, such as those associated with health and safety or commercial activity. The International Union of Pure and Applied Chemistry (IUPAC) provides recommendations on the nature and use of chemical nomenclature. It should be noted that many compounds may have non-systematic or semi-systematic names (some of which are not accepted by IUPAC for several reasons, for example, because they are ambiguous) and IUPAC rules allow for more than one systematic name in many cases. IUPAC is working towards identification of single names which are to be preferred for regulatory purposes (Preferred IUPAC Names, or PINs) (Hartshorn et al., 2015). The boundaries between ‘organic’ and ‘inorganic’ compounds are blurred. The nomenclature types described in this chapter are applicable to compounds, molecules, and ions that do not contain carbon, but also to many structures that do contain carbon, notably those containing elements of Groups 1–12. Most boron-containing compounds are treated using a special nomenclature (Lima et al., 1990). The empirical and molecular formulas discussed in the preceding section are precise and informative, but they have some disadvantages. First, they are inconvenient for routine verbal communication. For example, saying “C-A-three-P-O-four-two” for Ca3(PO4)2 is much more difficult than saying “calcium phosphate.” In addition, many compounds have the same empirical and molecular formulas but different arrangements of atoms, which differences result in very different chemical and physical properties. In such cases, it is necessary for the compounds to have different names that distinguish among the possible arrangements (Adams, 1972).

Nomenclature of Inorganic Compounds

23

Many compounds, particularly those that have been known for a relatively long time, have more than one name: a common name (sometimes several), and a systematic name, which is the name assigned by adhering to specific rules. Like the names of most elements, the common names of chemical compounds generally have historical origins, although they often appear to be unrelated to the compounds of interest. For example, the systematic name for KNO3 is potassium nitrate, but its common name is saltpeter (Hidayah and Lutfi, 2018). In this text, a systematic nomenclature is used to assign meaningful names to the millions of known substances. Unfortunately, some chemicals that are widely used in commerce and industry are still known almost exclusively by their common names; in such cases, familiarity with the common name as well as the systematic one is required. The objective of this and the next two sections is to teach how to write the formula for a simple inorganic compound from its name—and vice versa—and introduce some frequentlyencountered common names (Hartshorn and House, 1998).

2.2. NAMING BINARY IONIC COMPOUNDS Binary ionic compounds contain only two elements. The procedure for naming such compounds is outlined in Figure 2.1.

Figure 2.1. Naming an ionic compound. Source: http://webmis.highland.cc.il.us/~jsullivan/principles-of-general-chemistry-v1.0/s06-04-naming-covalent-compounds.html.

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The steps for naming binary ionic compounds are: • • i.

Place the ions in their proper order: cation and then anion; Name the cation: Metals That Form Only One Cation: As noted previously, these metals are usually in Groups 1–3, 12, and 13. The name of the cation of a metal that forms only one cation is the same as the name of the metal (with the word ion added if the cation is by itself). For example, Na+ is the sodium ion, Ca2+ is the calcium ion, and Al3+ is the aluminum ion (Wirtz et al., 1006). ii. Metals That Form More Than One Cation: As shown in Figure 2.2, many metals can form more than one cation. This behavior is observed for most transition metals, many actinides, and the heaviest elements of Groups 13–15. In such cases, the positive charge on the metal is indicated by a roman numeral in parentheses immediately following the name of the metal. Thus Cu+ is copper(I) (read as “copper one”), Fe2+ is iron(II), Fe3+ is iron(III), Sn2+ is tin(II), and Sn4+ is tin(IV) (Baker and Ollis, 1957). An older system of nomenclature for such cations is still widely used, however. The name of the cation with the higher charge is formed from the root of the element’s Latin name with the suffix -ic attached, and the name of the cation with the lower charge has the same root with the suffix -ous. The names of Fe3+, Fe2+, Sn4+, and Sn2+ are therefore ferric, ferrous, stannic, and stannous, respectively. Even though this text uses the systematic names with roman numerals, it is important to recognize these common names because they are still often used. For example, on the label of dental fluoride rinse, the compound chemists call tin (II) fluoride, is usually listed as stannous fluoride (Bactong et al., 2021). Some examples of metals that form more than one cation are listed in Table 2.1, along with the names of the ions. Note that the simple Hg+ cation does not occur in chemical compounds. Instead, all compounds of mercury (I) contain a dimeric cation, Hg22+, in which the two Hg atoms are bonded together (Gorter, 1970).

Nomenclature of Inorganic Compounds

25

Table 2.1. Common Cations of Metals That Form More Than One Ion Cation

Systematic Name

Common Name

Cation

Systematic Name

Common Name

Co2+

Cobalt(II)

Cobaltous*

Pb4+

Lead(IV)

Plumbic*

Co3+

Cobalt(III)

Cobaltic*

Pb2+

Lead(II)

Plumbous*

Cr

Chromium(II)

Chromous

Cu

Copper(II)

Cupric

Cr

Chromium(III)

Chromic

Cu

Copper(I)

Cuprous

Fe2+

Iron(II)

Ferrous

Sn4+

Tin(IV)

Stannic

Fe

Iron(III)

Ferric

Sn

Tin(II)

Stannous

Mn2+

Manganese(II)

Manganous*

Hg2+

Mercury(II)

Mercuric

Mn3+

Manganese(III)

Manganic* Hg22+

Mercury(I)

Mercurous†

2+ 3+

3+

2+ +

2+

*Not widely used. †The isolated mercury (I) ion exists only as the gaseous ion. Polyatomic Cations: The names of the common polyatomic cations that are relatively important in ionic compounds (such as, the ammonium ion) are in Table 2.2 (Schippers et al., 1973). 1. Name the anion. i. Monatomic Anions: These are named by adding the suffix -ide to the root of the name of the parent element; thus, Cl– is chloride, O2– is oxide, P3– is phosphide, N3– is nitride (also called azide), and C4– is carbide. Because the charges on these ions can be predicted from their position in the periodic table, it is not necessary to specify the charge in the name. Examples of monatomic anions are in Table 2.2 (Mackay and Shevchenko, 2008). ii. Polyatomic Anions: These typically have common names that must be memorized; some examples are in Table 2.2. Polyatomic anions that contain a single metal or nonmetal atom plus one or more oxygen atoms are called oxoanions (or oxyanions). In cases where only two oxoanions are known for an element, the name of the oxoanion with more oxygen atoms ends in -ate, and the name of the oxoanion with fewer oxygen atoms ends in -ite. For example, NO3– is nitrate and NO2– is nitrite (Grant, 1972). The halogens and some of the transition metals form more extensive series of oxoanions with as many as four members. In the names of these iii.

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26

oxoanions, the prefix per- is used to identify the oxoanion with the most oxygen (so that ClO4– is perchlorate and ClO3– is chlorate), and the prefix hypo- is used to identify the anion with the fewest oxygen (ClO2– is chlorite and ClO– is hypochlorite). The relationship between the names of oxoanions and the number of oxygen atoms present is diagrammed in Figure 2.3 “The Relationship between the Names of Oxoanions and the Number of Oxygen Atoms Present.” Differentiating the oxoanions in such a series is no trivial matter; for example, the hypochlorite ion is the active ingredient in laundry bleach and swimming pool disinfectant, but compounds that contain the perchlorate ion can explode if they come into contact with organic substances (Tsushima and Yamaguchi, 1973). 2.

Write the name of the compound as the name of the cation followed by the name of the anion.

Figure 2.2. Metals that form more than one cation and their locations in the periodic table. Source: https://saylordotorg.github.io/text_general-chemistry-principles-patterns-and-applications-v1.0/s06-03-naming-ionic-compounds.html.

It is not necessary to indicate the number of cations or anions present per formula unit in the name of an ionic compound because this information is implied by the charges on the ions. The charge of the ions must be considered when writing the formula for an ionic compound from its name, however. Because the charge on the chloride ion is –1 and the charge on the calcium ion is +2, for example, consistent with their positions in the

Nomenclature of Inorganic Compounds

27

periodic table, arithmetic indicates that calcium chloride must contain twice as many chloride ions as calcium ions to maintain electrical neutrality. Thus, the formula is CaCl2. Similarly, calcium phosphate must be Ca3(PO4)2 because the cation and the anion have charges of +2 and –3, respectively. The best way to learn how to name ionic compounds is to work through a few examples (Katayev et al., 2007). With only a few exceptions, these metals are usually transition metals or actinides.

Figure 2.3. The relationship between the names of oxoanions and the number of oxygen atoms present. Source: https://chem.libretexts.org/Bookshelves/General_Chemistry/ Map%3A_General_Chemistry_%28Petrucci_et_al.%29/03%3A_Chemical_ Compounds/3.6%3A_Names_and_Formulas_of_Inorganic_Compounds. Note: Cations are always named before anions.

Most transition metals, many actinides, and the heaviest elements of groups 13–15 can form more than one cation (Finke and Özkar, 2004). There is a systematic method used to name ionic compounds. Ionic compounds are named according to systematic procedures, although common names are widely used. Systematic nomenclature enables chemists to write the structure of any compound from its name and vice versa. Ionic compounds are named by writing the cation first, followed by the anion. If a metal can form cations with more than one charge, the charge is indicated by

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roman numerals in parentheses following the name of the metal. Oxoanions are polyatomic anions that contain a single metal or nonmetal atom and one or more oxygen atoms (Boiocchi et al., 2004).

2.3. NAMING COVALENT COMPOUNDS As with ionic compounds, the system for naming covalent compounds enables chemists to write the molecular formula from the name and vice versa. This and the following section describe the rules for naming simple covalent compounds, beginning with inorganic compounds, and then turning to simple organic compounds that contain only carbon and hydrogen (Morris, 2011). When chemists synthesize a new compound, they may not yet know its molecular or structural formula. In such cases, they usually begin by determining its empirical formula, the relative numbers of atoms of the elements in a compound, reduced to the smallest whole numbers. Because the empirical formula is based on experimental measurements of the numbers of atoms in a sample of the compound, it shows only the ratios of the numbers of the elements present. The difference between empirical and molecular formulas can be illustrated with butane, a covalent compound used as the fuel in disposable lighters. The molecular formula for butane is C4H10. The ratio of carbon atoms to hydrogen atoms in butane is 4:10, which can be reduced to 2:5. The empirical formula for butane is therefore C2H5. The formula unit is the absolute grouping of atoms or ions represented by the empirical formula of a compound, either ionic or covalent. Butane has the empirical formula C2H5, but it contains two C2H5 formula units, giving a molecular formula of C4H10 (Lind, 1992). Because ionic compounds do not contain discrete molecules, empirical formulas are used to indicate their compositions. All compounds, whether ionic or covalent, must be electrically neutral. Consequently, the positive and negative charges in a formula unit must exactly cancel each other. If the cation and the anion have charges of equal magnitude, such as Na+ and Cl–, then the compound must have a 1:1 ratio of cations to anions, and the empirical formula must be NaCl. If the charges are not the same magnitude, then a cation:anion ratio other than 1:1 is needed to produce a neutral compound. In the case of Mg2+ and Cl–, for example, two Cl– ions are needed to balance the two positive charges on each Mg2+ ion, giving an empirical formula of MgCl2. Similarly, the formula for the ionic compound that contains Na+ and O2– ions is Na2O (Celikler, 2010).

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29

Ionic compounds do not contain discrete molecules, so empirical formulas are used to indicate their compositions.

2.4. POLYATOMIC IONS Polyatomic ions are groups of atoms that bear net electrical charges, although the atoms in a polyatomic ion are held together by the same covalent bonds that hold atoms together in molecules. Just as there are many more kinds of molecules than simple elements, there are many more kinds of polyatomic ions than monatomic ions. Two examples of polyatomic cations are the ammonium (NH4+) and the methylammonium (CH3NH3+) ions. Polyatomic anions are much more numerous than polyatomic cations; some common examples are in Table 2.2 (Robson, 1983). Table 2.2. Common Polyatomic Ions and Their Names Formula

Name of Ion

Formula

Name of Ion

NH4

Ammonium

HPO4

Hydrogen phosphate

CH3NH3+

Methylammonium

H2PO4–

Dihydrogen phosphate

OH

Hydroxide

ClO

Hypochlorite

+

O2

–

2–

CN– SCN

2–

–

Peroxide

ClO2

–

Chlorite

Cyanide

ClO3–

Chlorate

Thiocyanate

ClO4

NO2

–

Nitrite

MnO4

NO3–

Nitrate

CrO42–

Chromate

CO

Carbonate

Cr2O

Dichromate

–

2– 3

HCO3

–

Hydrogen carbonate, or bicarbonate C2O

Perchlorate

–

Permanganate

–

2– 7

Oxalate

2– 4

SO3

Sulfite

HCO2

SO4

Sulfate

CH3CO2

HSO4–

Hydrogen sulfate, or bisulfate

C6H5CO2–

PO43–

Phosphate

2– 2–

Formate

– –

Acetate Benzoate

The method used to predict the empirical formulas for ionic compounds that contain monatomic ions can also be used for compounds that contain polyatomic ions. The overall charge on the cations must balance the overall charge on the anions in the formula unit. Thus, K+ and NO3– ions combine in a 1:1 ratio to form KNO3 (potassium nitrate or saltpeter), a major ingredient in black gunpowder. Similarly, Ca2+ and SO42– form CaSO4 (calcium sulfate), which combines with varying amounts of water to form gypsum and plaster

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of Paris. The polyatomic ions NH4+ and NO3– form NH4NO3 (ammonium nitrate), a widely used fertilizer and, in the wrong hands, an explosive (Jarrold and Shvartsburg, 1996). One example of a compound in which the ions have charges of different magnitudes is calcium phosphate, which is composed of Ca2+ and PO43– ions; it is a major component of bones. The compound is electrically neutral because the ions combine in a ratio of three Ca2+ ions [3(+2) = +6] for every two ions [2(–3) = –6], giving an empirical formula of Ca3(PO4)2; the parentheses around PO4 in the empirical formula indicate that it is a polyatomic ion. Writing the formula for calcium phosphate as Ca3P2O8 gives the correct number of each atom in the formula unit, but it obscures the fact that the compound contains readily identifiable PO43– ions (Bates, 1986).

2.5. HYDRATES Many ionic compounds occur as hydrates, compounds that contain specific ratios of loosely bound water molecules, called waters of hydration. Waters of hydration can often be removed simply by heating. For example, calcium dihydrogen phosphate can form a solid that contains one molecule of water per Ca(H2PO4)2 unit and is used as a leavening agent in the food industry to cause baked goods to rise. The empirical formula for the solid is Ca(H2PO4)2·H2O. In contrast, copper sulfate usually forms a blue solid that contains five waters of hydration per formula unit, with the empirical formula CuSO4·5H2O. When heated, all five water molecules are lost, giving a white solid with the empirical formula CuSO4 (Figure 2.4) (Grant and Khankari, 1995).

Figure 2.4. Loss of water from a hydrate with heating (left); when blue CuSO4⋅5H2OCuSO4·5H2O is heated, two molecules of water are lost at 30°C, two more at 110°C, and the last at 250°C to give white “anhydrous” CuSOCuSO4 (right). 4 Source: https://www.quora.com/What-happens-when-you-heat-CaSO4-5H2O.

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31

Compounds that differ only in the numbers of waters of hydration can have very different properties. For example, CaSO4·½H2O is plaster of Paris, which was often used to make sturdy casts for broken arms or legs, whereas CaSO4·2H2O is the less dense, flakier gypsum, a mineral used in drywall panels for home construction. When a cast would set, a mixture of plaster of Paris and water crystallized to give solid CaSO4·2H2O. Similar processes are used in the setting of cement and concrete (Sloan, 2003).

2.6. BINARY COVALENT COMPOUNDS Binary covalent compounds are covalent compounds that contain only two elements—are named using a procedure similar to that used for simple ionic compounds, but prefixes are added as needed to indicate the number of atoms of each kind. The procedure, diagrammed in Figure 2.5 consists of the following steps (Guo et al., 2008):

Figure 2.5. Naming a covalent inorganic compound. Source: https://saylordotorg.github.io/text_general-chemistry-principles-patterns-and-applications-v1.0/s06-04-naming-covalent-compounds.html.

• •

•

Place the elements in their proper order. The element farthest to the left in the periodic table is usually named first. If both elements are in the same group, the element closer to the bottom of the column is named first. The second element is named as if it were a monatomic anion in an ionic compound (even though it is not), with the suffix -ide attached to the root of the element name.

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32

• •

Identify the number of each type of atom present. Prefixes derived from Greek stems are used to indicate the number of each type of atom in the formula unit (Table 2.3). The prefix mono- (“one”) is used only when absolutely necessary to avoid confusion, just as the subscript 1 is omitted when writing molecular formulas. To demonstrate steps 1 and 2a, HCl is named hydrogen chloride (because hydrogen is to the left of chlorine in the periodic table), and PCl5 is phosphorus pentachloride. The order of the elements in the name of BrF3, bromine trifluoride, is determined by the fact that bromine lies below fluorine in Group 17. Table 2.3. Prefixes for Indicating the Number of Atoms in Chemical Names Prefix monoditritetrapentahexa-

•

Number 1 2 3 4 5 6

Prefix heptaoctanonadecaundecadodeca-

Number 7 8 9 10 11 12

If a molecule contains more than one atom of both elements, then prefixes are used for both. Thus, N2O3 is dinitrogen trioxide, as shown in Figure 2.5. • In some names, the final a or o of the prefix is dropped to avoid awkward pronunciation. Thus, OsO4 is osmium tetroxide rather than osmium tetraoxide. • Write the name of the compound. • Binary compounds of the elements with oxygen are generally named as “element oxide,” with prefixes that indicate the number of atoms of each element per formula unit. For example, CO is carbon monoxide. The only exception is binary compounds of oxygen with fluorine, which are named as oxygen fluorides. Certain compounds are always called by the common names that were assigned before formulas were used. For example, H2O is water (not dihydrogen oxide); NH3 is ammonia; PH3 is phosphine; SiH4 is silane; and B2H6, a dimer of BH3, is diborane. For many compounds, the systematic name and the common name are both used frequently, requiring familiarity

Nomenclature of Inorganic Compounds

33

with both. For example, the systematic name for NO is nitrogen monoxide, but it is much more commonly called nitric oxide. Similarly, N2O is usually called nitrous oxide rather than dinitrogen monoxide. Notice that the suffixes -ic and -ous are the same ones used for ionic compounds (Tang and Yip, 1995). Start with the element at the far left in the periodic table and work to the right. If two or more elements are in the same group, start with the bottom element and work up. The structures of some of the compounds are shown in Figure 2.6 along with the location of the “central atom” of each compound in the periodic table. It may seem that the compositions and structures of such compounds are entirely random, but this is not true. After mastering the material discussed later on this course, one is able to predict the compositions and structures of compounds of this type with a high degree of accuracy (Gutowsky and Hoffman, 1951).

Figure 2.6. The structures of some covalent inorganic compounds and the locations of the “central atoms” in the periodic table. Source: https://chem.libretexts.org/Bookshelves/General_Chemistry/ Map%3A_General_Chemistry_(Petrucci_et_al.)/03%3A_Chemical_ Compounds/3.6%3A_Names_and_Formulas_of_Inorganic_Compounds. Note: The compositions and structures of covalent inorganic compounds are not random and can be predicted from the locations of the component atoms in the periodic table (Alyea et al., 1971).

The learning objective of this module is to identify and name some common acids and bases. For our purposes at this point in the text, we can define an acid as a substance with at least one hydrogen atom that can

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dissociate to form an anion and an H+ ion (a proton) in an aqueous solution, thereby forming an acidic solution. We can define bases as compounds that produce hydroxide ions (OH–) and a cation when dissolved in water, thus forming a basic solution. Solutions that are neither basic nor acidic are neutral. We will discuss the chemistry of acids and bases in more detail later, but in this section, we describe the nomenclature of common acids and identify some important bases so that you can recognize them in future discussions. Pure acids and bases and their concentrated aqueous solutions are commonly encountered in the laboratory. They are usually highly corrosive, so they must be handled with care (Munby and Ross, 1991).

2.7. ACIDS The names of acids differentiate between (1) acids in which the H+ ion is attached to an oxygen atom of a polyatomic anion (these are called oxoacids, or occasionally oxyacids) and (2) acids in which the H+ ion is attached to some other element. In the latter case, the name of the acid begins with hydro- and ends in -ic, with the root of the name of the other element or ion in between. Recall that the name of the anion derived from this kind of acid always ends in -ide. Thus, hydrogen chloride (HCl) gas dissolves in water to form hydrochloric acid (which contains H+ and Cl– ions), hydrogen cyanide (HCN) gas forms hydrocyanic acid (which contains H+ and CN– ions), and so forth (Table 2.4). Examples of this kind of acid are commonly encountered and very important. For instance, your stomach contains a dilute solution of hydrochloric acid to help digest food. When the mechanisms that prevent the stomach from digesting itself malfunction, the acid destroys the lining of the stomach and an ulcer form (Lin et al., 2007). Acids are distinguished by whether the H+ ion is attached to an oxygen atom of a polyatomic anion or some other element. Table 2.4. Some Common Acids That Do Not Contain Oxygen Formula

Name in Aqueous Solution

Name of Gaseous Species

HF

Hydrofluoric acid

Hydrogen fluoride

HCl

Hydrochloric acid

Hydrogen chloride

HBr

Hydrobromic acid

Hydrogen bromide

HI

Hydroiodic acid

Hydrogen iodide

HCN

Hydrocyanic acid

Hydrogen cyanide

H 2S

Hydrosulfuric acid

Hydrogen sulfide

Nomenclature of Inorganic Compounds

35

If an acid contains one or more H+ ions attached to oxygen, it is a derivative of one of the common oxoanions, such as sulfate (SO42–) or nitrate (NO3–). These acids contain as many H+ ions as are necessary to balance the negative charge on the anion, resulting in a neutral species such as H2SO4 and HNO3 (Bradley and Mosimege, 1998).

The names of acids are derived from the names of anions according to the following rules (Lin and Chiu, 2010): •

If the name of the anion ends in -ate, then the name of the acid ends in -ic. For example, because NO3– is the nitrate ion, HNO3 is nitric acid. Similarly, ClO4– is the perchlorate ion, so HClO4 is perchloric acid. Two important acids are sulfuric acid (H2SO4) from the sulfate ion (SO42–) and phosphoric acid (H3PO4) from the phosphate ion (PO43–). These two names use a slight variant of the root of the anion name: sulfate becomes sulfuric and phosphate becomes phosphoric (Sesen and Tarhan, 2011). • If the name of the anion ends in -ite, then the name of the acid ends in -ous. For example, OCl– is the hypochlorite ion, and HOCl is hypochlorous acid; NO2– is the nitrite ion, and HNO2 is nitrous acid; and SO32– is the sulfite ion, and H2SO3 is sulfurous acid. The same roots are used whether the acid name ends in -ic or -ous; thus, sulfite becomes sulfurous. The relationship between the names of the oxoacids and the parent oxoanions is illustrated in Figure 2.7, and some common oxoacids are in Table 2.5. Table 2.5. Nomenclature and chemical formulae of common oxoacids Formula

Name

HNO2

Nitrous acid

HNO3

Nitric acid

H2SO3

Sulfurous acid

H2SO4

Sulfuric acid

H3PO4

Phosphoric acid

H2CO3

Carbonic acid

36

An Overview of Inorganic Compounds

HClO

Hypochlorous acid

HClO2

Chlorous acid

HClO3

Chloric acid

HClO4

Perchloric acid

Figure 2.7. The relationship between the names of the oxoacids and the names of the parent oxoanions. Source: https://chem.libretexts.org/Bookshelves/General_Chemistry/ Map%3A_General_Chemistry_(Petrucci_et_al.)/03%3A_Chemical_ Compounds/3.6%3A_Names_and_Formulas_of_Inorganic_Compounds.

2.8. BASES We will present more comprehensive definitions of bases in later chapters, but virtually every base you encounter in the meantime will be an ionic compound, such as sodium hydroxide (NaOH) and barium hydroxide [Ba(OH)2], that contains the hydroxide ion and a metal cation. These have the general formula M(OH)n. It is important to recognize that alcohols, with the general formula ROH, are covalent compounds, not ionic compounds; consequently, they do not dissociate in water to form a basic solution (containing OH– ions) (Clarridge, 2004). When a base reacts with any of the acids we have discussed, it accepts a proton (H+). For example, the hydroxide ion (OH–) accepts a proton to form H2O. Thus, bases are also referred to as proton acceptors (Figure 2.8).

Nomenclature of Inorganic Compounds

37

Figure 2.8. Methylamine structure. Source: https://www.researchgate.net/figure/Geometric-structure-of-methylamine-molecule_fig1_266616298.

Concentrated aqueous solutions of ammonia (NH3) contain significant amounts of the hydroxide ion, even though the dissolved substance is not primarily ammonium hydroxide (NH4OH) as is often stated on the label. Thus, aqueous ammonia solution is also a common base. Replacing a hydrogen atom of NH3 with an alkyl group results in an amine (RNH2), which is also a base. Amines have pungent odors—for example, methylamine (CH3NH2) is one of the compounds responsible for the foul odor associated with spoiled fish. The physiological importance of amines is suggested in the word vitamin, which is derived from the phrase vital amines. The word was coined to describe dietary substances that were effective at preventing scurvy, rickets, and other diseases because these substances were assumed to be amines. Subsequently, some vitamins have indeed been confirmed to be amines (Lin and Chiu, 2010). Metal hydroxides (MOH) yield OH– ions and are bases, alcohols (ROH) do not yield OH– or H+ ions and are neutral, and carboxylic acids (RCO2H) yield H+ ions and are acids. Common acids and the polyatomic anions derived from them have their own names and rules for nomenclature. The nomenclature of acids differentiates between oxoacids, in which the H+ ion is attached to an oxygen atom of a polyatomic ion, and acids, in which the H+ ion is attached to another element. Carboxylic acids are an important class of organic acids. Ammonia is an important base, as are its organic derivatives, the amines (Lin and Chiu, 2010).

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38

2.9. SUMMARY •

The composition of a compound is represented by an empirical or molecular formula, each consisting of at least one formula unit. • Covalent inorganic compounds are named using a procedure similar to that used for ionic compounds, whereas hydrocarbons use a system based on the number of bonds between carbon atoms. Covalent inorganic compounds are named by a procedure similar to that used for ionic compounds, using prefixes to indicate the numbers of atoms in the molecular formula. An empirical formula gives the relative numbers of atoms of the elements in a compound, reduced to the lowest whole numbers. The formula unit is the absolute grouping represented by the empirical formula of a compound, either ionic or covalent. Empirical formulas are particularly useful for describing the composition of ionic compounds, which do not contain readily identifiable molecules. Some ionic compounds occur as hydrates, which contain specific ratios of loosely bound water molecules called waters of hydration (Salzer, 1999).

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39

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46. Salzer, A., (1999). Nomenclature of organometallic compounds of the transition elements (IUPAC Recommendations 1999). Pure and Applied Chemistry, 71(8), 1557–1585. 47. Schippers, A. B. A., Brandwijk, V., & Gorter, E. W., (1973). Derivation and discussion of crystal structures of compounds ABX3 and A2BX6: Part I. Derivation of the structures. Journal of Solid State Chemistry, 6(4), 479–492. 48. Scott, J. D., (1943). The need for reform in inorganic chemical nomenclature. Chemical Reviews, 32(1), 73–97. 49. Sesen, B. A., & Tarhan, L., (2011). Active-learning versus teachercentered instruction for learning acids and bases. Research in Science & Technological Education, 29(2), 205–226. 50. Shevchenko, V. Y., & Mackay, A. L., (2008). Geometrical principles of the self-assembly of nanoparticles. Glass Physics and Chemistry, 34(1), 1–8. 51. Shvartsburg, A. A., & Jarrold, M. F., (1996). An exact hard-spheres scattering model for the mobilities of polyatomic ions. Chemical Physics Letters, 261(1, 2), 86–91. 52. Sloan, E. D., (2003). Fundamental principles and applications of natural gas hydrates. Nature, 426(6964), 353–359. 53. Speijer, D., (2011). Oxygen radicals shaping evolution: Why fatty acid catabolism leads to peroxisomes while neurons do without it: FADH2/ NADH flux ratios determining mitochondrial radical formation were crucial for the eukaryotic invention of peroxisomes and catabolic tissue differentiation. Bioessays, 33(2), 88–94. 54. Stoyanov, E. S., Kim, K. C., & Reed, C. A., (2006). An infrared νNH scale for weakly basic anions. Implications for single-molecule acidity and super acidity. Journal of the American Chemical Society, 128(26), 8500–8508. 55. Tang, M., & Yip, S., (1995). Atomic size effects in pressure-induced amorphization of a binary covalent lattice. Physical Review Letters, 75(14), 2738. 56. Van, W. J. R., (1964). Nomenclature of phosphorus compounds. Journal of Chemical Documentation, 4(2), 84–90.

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57. Wirtz, M. C., Kaufmann, J., & Hawley, G., (2006). Nomenclature made practical: Student discovery of the nomenclature rules. Journal of Chemical Education, 83(4), 595. 58. Yamaguchi, T., & Tsushima, K., (1973). Spin reorientation in rareearth orthochromites and orthoferrites. Bussei, 14, 483–494.

CHAPTER

3

POROUS INORGANIC MATERIALS

CONTENTS 3.1. Introduction....................................................................................... 46 3.2. Microporous Materials....................................................................... 47 3.3. Mesoporous Materials........................................................................ 51 3.4. Macroporous Materials...................................................................... 74 3.5. Hierarchical Porous Structures........................................................... 77 References................................................................................................ 80

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An Overview of Inorganic Compounds

3.1. INTRODUCTION Porous materials are of considerable economic significance due to their extensive range of uses as catalysts, adsorbents, and ion exchangers. Porous materials come in a range of chemical compositions, pore shape and degree of crystallinity, and size. As per IUPAC definition, porous materials are categorized into three categories based on their pore size: microporous materials have pores smaller than 2 nm, mesoporous materials have pores between 2 and 50 nm, and macroporous materials have pores greater than 50 nm (Sing et al., 1985). Pores of varying diameters have distinct effects of physical adsorption, as described in the isotherm. The isotherm plots the quantity of a particular gas that a solid absorbs or releases with relation to the pressure of the gas at a fixed temperature. The type-I isotherm exhibits a sharp increase in pressure at extremely low pressures and a lengthy saturation phase, which is typical of microporous materials. At high relative pressure, the type-IV isotherm displays a sharp rise and, in several situations, a hysteresis loop, which in mesopores is related to capillary condensation (Gimblett et al., 1988). Researchers pioneered the creation of microporous materials in the late 1940s with the production of synthetic zeolites. They developed numerous commercially significant microporous materials over the first five years of their work, including zeolites Y, X, and A. Over the next three decades, zeolites with a variety of chemical and topologies compositions were synthesized, ending in the 1970s with the production of ZSM-5 and its aluminum-free pure silica form. In 1982, researchers announced the synthesis of aluminophosphate molecular sieves, paving the way for the development of crystalline microporous materials to non-silicates. Ever since the 1980s and early 1990s, there has been an increase in several additional compositions of crystalline microporous materials have been synthesized, such as metalorganic structures and chalcogenides (Foresi et al., 1997). Before the 1990s, materials having pore sizes in the meso range, like activated carbons and silica gels, had a disordered pore structure with a wide range of pore sizes. In 1992, Mobil scientists developed a series of mesoporous silicas (designated M41S) with cubic and hexagonal symmetry and very regular pore diameters ranging from 2 to 10 nm utilizing cationic surfactants as a template (Figure 3.1).

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Figure 3.1. The international union of pure and applied chemistry (IUPAC) categorization of porous materials depends on pore diameter. Source: https://www.researchgate.net/figure/IUPAC-classification-of-porousmaterials_fig1_309816564.

Since the discovery of M41S, there has been a surge of concern in ordered mesoporous materials. The templated technique was also used to synthesize ordered macroporous materials following the discovery of ordered mesoporous materials. Macroporous materials with homogeneous pore diameters are projected to possess advantageous optical characteristics and may find utility as photonic crystals (PSCs) along with optical band gaps (Zheng et al., 2003). This chapter discusses ordered mesoporous materials, which have grown in popularity during the last decade. To be thorough, the contemporaneous advances in the fields of ordered macroporous and crystalline microporous materials are summarized.

3.2. MICROPOROUS MATERIALS Microporous materials are generated by the presence of hydrated organic species or inorganic cations inside the cavities of inorganic-organic hybrid host framework or an extended inorganic. Organic entities that exist outside the framework are often protonated amines, neutral solvent molecules, or quaternary ammonium cations. Calcination and dehydration are two commonly employed procedures for removing non-structure species and generating microporosity (Cotton, 2018). While crystalline microporous materials contain those with pore sizes ranging from 10 to 20A, very few of them have pore sizes in this range.

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As a result, microporous materials are limited to applications involving tiny molecules. There has always been a need to expand the pore size of a crystalline material beyond 10A while preserving the essential hydrothermal or thermal stability for a variety of applications. Latest breakthroughs in metal-organic framework and chalcogenide materials have demonstrated significant potential for the fabrication of materials with extra-large pores. Along with the goal to enhance the pore size, there has been considerable significance in developing multifunctional materials that include crystalline microporosity with other desirable features like semi conductivity, ferromagnetism, framework chirality, or ion conductivity (Cotton, 2018).

3.2.1. Germanates and Microporous Silicates Natural and manmade zeolites are examples of microporous materials. Zeolites are crystalline 3D alumino-silicates with open cages or channels. Zeolites’ structural and synthetic principles have affected the progress of microporous materials significantly during the last 50 years. For instance, the employment of organic structure-directing reagents in the production of high silica zeolites and their all-silica polymorphs aided in the invention of alumino-phosphate molecular sieves later in life. Researcher provided an exhaustive study on the structure and creation of zeolites and associated minerals, which will not be reproduced here (O’keeffe and Yaghi, 1999). Due to zeolites’ commercial relevance, several efforts have been made to synthesize novel microporous materials. One strategy that is frequently employed is to replace framework cations (e.g., Si4+ or Al3+) in zeolites with alternative cations like Ge4+, Ga3+, or P5+. Gallo silicates and Gallo(or alumino-) germanates were among the first non-zeolite microporous materials developed due to their similar resemblance to zeolites. Generally, Gallo silicates and Gallo- (or alumino-) germanates lack previously observed framework network topology in zeolites. Nevertheless, the recent application of organic structure-managing agents in the synthesis of germanates has led to the development of a variety of materials with hitherto unheard-of structure topologies (Bu et al., 1998). By and large, every compositional system has a distinct variety of T–O bond lengths and T–O–Tangles and a distinct affinity for forms of framework topology. For example, germanates are more likely to arise in structures with strained double four-ring units. A second instance is the synthesis of UCSB-7. It can be made as a gallogermanate or an alumino germanate under a range of experimental settings (Corma et al., 2002). It

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has not, however, been made as a silicate. Thus, it is unsurprising that novel microporous materials may be created by integrating the germanium source into the silicate synthesis mixture (Cheetham et al., 1999).

3.2.2. Microporous Arsenates and Phosphates In the 1980s, the manufacturing of alumino-phosphate molecular sieves marked a watershed moment in the progress of microporous materials. After that, most global synthetic attempts have been concentrated on nonsilicate microporous materials. Several unique structure topologies may be discovered using phosphates, and numerous more elements can be added into phosphates to generate additional novel framework compositions or topologies (Gier and Stucky, 1991). As originally constructed, aluminum-phosphate molecular sieves have a neutral framework and often need alkyl ammonium cations or organic amines as extra-structure types. Nevertheless, it was quickly found that Si4+ and a variety of metal cations could be integrated into the alumino-phosphate framework, resulting in a negative framework like that of high-silica zeolites when Al3+ sites are completely replaced by divalent cations like Be2+ or Zn2+, a series of beryllo- or zinco-phosphates like low-silica zeolites results. Although the negative structure charge and related extra-framework chargebalancing cations are advantageous for a variety of microporous material applications, the constancy of microporous materials often declines as the negative framework charge increases (Feng et al., 2001). The production of an extra-large pore microporous material in the alumino-phosphate composition is significant. VPI-5, a hydrated aluminophosphate, contains a single-dimensional network with a window size defined by 18 tetrahedral cations. At the time of their finding, zeolites had a maximum window size of just 12. Consequently, the invention of VPI-5 sparked new efforts to the synthesis of microporous materials with extralarge pores. Since then, several phosphates and silicates with extra-large pores have been synthesized. The discovery of metal-organic framework and chalcogenide materials hold fresh potential for the creation of materials with extra-large pores. In comparison to microporous phosphates, microporous arsenates are uncommon. When divalent metal cations like Be2+ and Zn2+ are used as framework tetrahedral atoms, the structures and syntheses of arsenates are like those of phosphates. However, the Gallo- (or alumino-) arsenates and their equivalent phosphates bear little resemblance. Some parallels between

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An Overview of Inorganic Compounds

arsenates and phosphates have been noticed in the middle stage, where both trivalent and divalent metal cations are there (Feng and Stucky, 1997).

3.2.3. Microporous Sulfides and Selenides The substitution of chalcogens (e.g., S2) for framework anions (i.e., O2) is a more contemporary method for creating microporous materials. The first attempts to synthesize microporous chalcogenides used tin sulfides or germanium. Nevertheless, tin and germanium sulfides do not create microporous materials in the same way as all-silica zeolites do. It was later discovered that adding low-valent cations like Mn2+ to the Ge–S structure aided in the formation of three-dimensional frameworks. Gallium and indium chalcogenide compositions have also been used to fabricate three-dimensional selenide and sulfide structures. Additionally, the introduction of monovalent or divalent cations into gallium or indium chalcogenide structures has resulted in the formation of several novel framework chalcogenides, which are frequently dependent on the structure of chalcogenide clusters (Zheng et al., 2002). In chalcogenides combining tetravalent (M4+) trivalent (M3+) and cations has resulted in the formation of a sequence of framework chalcogenides, one of which exhibits microporous performance. However, the M3+ to M4+ ratio in these chalcogenides can be significantly lower than that in zeolites and has been shown to lie inside the range of around 0.21 to 0. Despite the low M3+ to M4+ ratio, several of the sulfides in this family exhibit sufficient resistance to ion exchange and heat treatment. UCR-20GaGeSTAEA (TAEA = tris(2aminoethyl) amine) exchanged with Cs+ displays the type-I isotherm and has a pore size of up to 9.5A. Chalcogenides, like zeolites, may be produced using either organic or inorganic cations as extra-structure species. Recently, a group of selenides and hydrated sulfides was synthesized. ICF-m materials were synthesized in aqueous solutions from regular inorganic salts. Fast ion conductivity at ambient temperature and medium to high humidity is one of the most intriguing features of these inorganic chalcogenides. The ionic conductivity of lithium compounds, for instance, ICF-26 and ICF-22, is much larger than that of previously identified crystalline lithium compounds (Yaghi et al., 2003)

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3.3. MESOPOROUS MATERIALS 3.3.1. Formation Mechanisms and Synthesis Pathways 3.3.1.1. Base Synthesis In the last decade, the ordered mesoporous materials synthesis has significantly enlarged the variety of ordered porous materials and created several new prospects for material design and application. The synthetic process employed to prepare these compounds is critical. Prior to this, porous materials were typically synthesized using single molecules or hydrated clusters of simple ions. Nevertheless, it is the assembling of surfactant molecules that drives the concentration of inorganic precursors during the creation of ordered mesoporous materials. Mobil scientists identified two broad paths based on the similarities among water/surfactant and M41S liquid crystal phases (Figure 3.2). According to the first model, the structure-directing ingredient is the water-surfactant liquid crystal phase. This model cannot account for the discovery that silicate-surfactant mesophases can emerge at surfactant concentrations as low as 1%, which is extremely low for the development of a liquid crystal phase (Badamali et al., 2013). According to the 2nd concept, the existence of silicate facilitates the ordering of surfactant micelles into a hexagonal configuration. Monnier et al. (1993) further extended this concept into a very comprehensive cooperative assembly method.

Figure 3.2. MCM-41 might be formed by one of two probable processes, (1) or (2), according to the presented models. Source: https://www.researchgate.net/figure/Proposed-LCT-liquid-crystal-templating-synthetic-mechanism-to-form-MCM-41-ref-21-and_fig2_342121663.

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An Overview of Inorganic Compounds

Monnier et al. (1993) concepts provided a complete explanation for how silicate species might initiate the creation of inorganic-organic compound mesophases. This method implies the binding of cationic surfactants directly to negatively charged silicate oligomers by the use of cooperative multidentate binding, charge-density matching crosswise the silicate surfactant boundary, and the special polymerization of silicates at the boundary are all critical factors in the development of mesophases.

3.3.1.2. Acid Synthesis It was later shown that direct contact between inorganic precursors and surfactants is not the only avenue to produce mesophases. Following Mobil’s work, a significant finding was the creation of mesophases in acidic solutions by combining cationic inorganic species. In this chapter, it is proposed that halide anions mediate the interaction among cationic surfactant head groups and cationic silica species. Huo et al. (1994) proposed a comprehensive mechanism for the creation of mesostructured organic/inorganic composites based on their synthetic outcomes under both acidic and basic environments. Electrostatic interactions among the inorganic precursor I and the surfactant head group S are involved in this pathway (Figure 3.3). Among charged surfactant head groups (anionic S, cationic S+) and charged inorganic precursors (anionic I, cationic I+), both mediated and direct modes are conceivable, resultant in four synthetic ways: (S+I), (SI+), (S+XI+), and (SM+I). When base situations are applied, the (S+I) and (SM+I) pathways occur, whereas the (SI+) and (S+XI+) routes occur during acid synthesis. The development of the acid synthesis technique and the four hypothesized routes influenced the subsequent progress of mesoporous materials significantly. Zhao et al. (1998) significantly increased the applicability of the acid synthesis process by using amphiphilic triblock copolymers to synthesize a sequence of periodic ordered mesoporous silicas, SBA-n, with consistent pore diameters exceeding 100A.

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Figure 3.3. Graphic of the interaction among inorganic and surfactants substances in a schematic diagram. Source: https://home.csulb.edu/~xbu/publications0/B2.pdf.

Previously, mesoporous materials with pore sizes in this spectrum also did not be present or had far less ordering than SBA-n. SBA-n was hypothesized to be formed from block copolymers through the (S0H+) (XI+) route in acidic conditions by a mix of hydrogen-bonding and electrostatic interactions. The use of acidic media distinguishes this study from Pinnavaia et al. (2004) priors work. Zhao et al. (1998) demonstrated that by progressively increasing the quantity of the swelling agent, a structural shift from hexagonally organized mesophases to MCFs occurred.

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An Overview of Inorganic Compounds

MCFs were synthesized using aqueous hydrochloric acid (HCl), 1,3,5-trimethylbenzene (TMB), triblock copolymer P123, and ethanol. The organic-inorganic boundary at the surface of P123-coated TMB droplets was hydrolyzed in aqueous HCl to generate hydrophilic cationic silica types that reduced around the organic assemblies. MCFs have homogenous spherical cells with a diameter tunable between 24 and 42 nm, dependent on the quantity of TMB and the aging temperature (Zhang et al., 1996).

3.3.1.3. Neutral Synthesis Pinnavaia et al. (2004) employed neutral alkyl amines as precursors to synthesize disturbed mesoporous silica, which they dubbed HMS (hexagonal molecular sieves). The creation of S0I0 has been postulated because of the interaction of S0 (neutral amine micelles) with (I0 neutral inorganic precursors). Hydrogen bonding was the mode of interaction between S0 and I0. In comparison to M41S, the resultant HMS exhibits a ‘worm-like’ pore structure with thicker formation walls and smaller X-ray scattering domain sizes. Mesoporous silica may also be produced utilizing N0 with a hydrophilic head group of polyethylene oxide (PEO, EOn). Triblock copolymers or PEO surfactants that are nonionic are used. Worm-like disordered amorphous silica or mesoporous silica is generated through the postulated neutral N0I0 assembly route. The lack of structural order might be a result of insufficient electrostatic or hydrogen-bonding interactions. Pinnavaia et al. (2004) changed the N0I0 method by including tiny metal cations into the assembly process, resulting in more ordered mesoporous silica. This procedure is referred to as (N0Mn+) I0, and it involves the formation of hydrogen bonds among cationic metal complexes comprising neutral inorganic precursors (I0) and nonionic R(EO)nH surfactants (N0). The electrostatic forces were increased by complexing tiny Mn+ cations with the EO groups of N0. As concise in Table 3.1, a variety of connections among the inorganic precursors and the organic surfactants, such as electrostatic charge matching (S+I, SI+, S+XI+, and SM+I), H-bonding (N0I0 and S0I0), covalent connections, or their combination (N0Mn+) I0), ((S0H+) (XI+) and may all play a significant role in the development of mesostructured.

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3.3.1.4. Ligand-Assisted Templating (LAT) Mechanism Ying and Antonelli (1995) synthesized hexagonally mesoporous niobium oxide utilizing alkyl amines as the structure-directing agent. A novel method known as ‘ligand-assisted templating’ (LAT) has been proposed. Prior to condensation and hydrolysis of the preformed alkoxide-surfactant precursor, the suggested process includes direct covalent contacts among the amine ligand and the Nb alkoxide precursor via the N–Nb link. After extraction of the surfactant, mesostructured remain maintained. This technique enables easy manipulation of the metal/surfactant ratio to regulate the mesostructured phases, giving in a group of mesoporous transition metal oxides (Pm3n NbTMS3, lamellar Nb-TMS4 cubic, and ‘P63/mmc’ hexagonal Nb-TMS2). Table 3.1. Inorganic Precursors and Surfactants Interact with Each Other in a Variety of Ways, which is Depicted in This Diagram

Mn+= metal cations; I = inorganic species; aS = surfactants; N = nonionic surfactants; X– = halide anions.

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3.3.1.5. Direct Liquid Crystal Templating Method Thus far, mesoporous materials have been synthesized at surfactant concentrations that are often insufficient to induce the formation of longrange organized lyotropic liquid crystal phases in a water/surfactant system. Co-organization of organic and inorganic species is induced by a variety of different types of interfacial contacts, and the tougher the bond the more ordered the ensuing mesophases (Brinker et al., 1999). Additionally, mesoporous materials may be formed at high surfactant absorptions, allowing for the formation of long-range liquid crystals in the lack of inorganic precursors. Attard et al. (1995) showed this strategy by employing nonionic surfactant liquid crystal phases as templates, like octaethylene glycol monohexadecyl ether (C16EO8) or octaethylene glycol monododecyl ether (C12EO8). This manufacturing strategy is like route 1 of Mobil scientists’ initial liquid crystal templating process for MCM-41. Attard’s (1995) method involved hydrolyzing and condensing tetramethyl orthosilicate (TMOS) in the aqueous sphere of the liquid crystal phase at a pH of roughly 2, resulting in mesostructured hexagonal, lamellar, or cubic silica. Methanol produced during the hydrolysis of TMOS disrupts the liquid crystal’s long-range order; however, when the methanol is removed, the lyotropic liquid crystal is refurbished and acts as a template phase for subsequent silicate condensation. Because the resultant pore system is shaped like the lyotropic mesophase, this technique is often referred to as ‘nano casting.’ Feng et al. (2000) synthesized a sequence of periodic ordered mesoporous silica by employing high concentrations of triblock copolymers in quaternary and multi-component ternary systems. One distinguishing characteristic of Feng’s technique is the removal of methanol below vacuum before combining silicate precursors and surfactants. As a result, once created, the lyotropic liquid crystal phase retains its long-range ordering through the silicate condensation method. It is also beneficial to remove methanol before combining it with surfactant/cosurfactant/oil since the existence of cosurfactant, surfactant, or oil may make efficient methanol removal problematic. The inclusion of cosurfactants and oils allows for greater control over a variety of structural properties of the resultant mesophases, such as wall thickness and pore size. Inorganic precursors’ condensation happens in the aqueous sphere of prepared lyotropic liquid crystals during direct liquid crystal templating.

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This technique minimizes the contact surfactant headgroups among and inorganic precursors, which might disturb the long-range order of liquid crystals—for silicates, executing reactions at a pH of around 2, the silicates’ isoelectric idea aids in minimizing such contact.

3.3.1.6. EISA (Evaporation-Induced Self-Assembly) Brinker et al. (1999) established a straightforward EISA (evaporation-induced self-assembly) approach for the quick fabrication of nanocomposite materials or patterned porous in the form of spheres, fibers, or films. Evaporation of ethanol raised the concentration of surfactant in a homogenous solution of surfactant and soluble silica under the crucial micellar concentration, resulting in the self-assembly of silica surfactant micelles and their subsequent organization. By varying the primary surfactant/water/ alcohol molar ratio cubic, two-dimensional (2D) hexagonal, lamellar silica-surfactant mesophases, three-dimensional hexagonal and may be synthesized.

3.3.2. Structure The pore structure of mesoporous materials, like the pore size and pore geometry, is a critical parameter for practical applications, particularly those that require shape and size selectivity and easy access to porosity. Controlling the pore structure of mesoporous materials has been a major focus of research.

3.3.2.1. Pore Geometry Control Pore geometry is related to mesophase symmetry and can be imprecise when the ordering of the mesophases is very low. Highly organized mesophases, on the other hand, maybe generated under a wide variety of experimental settings. It is feasible to modify the topological properties of emerging mesophases by tweaking synthetic parameters (Raman et al., 1996). Mobil’s first study resulted in the synthesis of a 2D ordered hexagonal phase in conjunction with unidimensional channels (p6m) and a three-dimensional ordered cubic phase with three-dimensional bicontinuous channels (Ia3d). Huo et al. (1994) discovered a novel Pm3n (cubic phase), SBA-1, by utilizing an acidic medium and C16H33N(C2H5) (C5H10)+ (cetyl-ethyl piperidinium) or the surfactant C16H33N(C2H5)3+. Additionally, SBA-739 (base synthesis) and SBA-238 (acid synthesis) with earlier unknown pore structures were synthesized employing divalent quaternary ammonium surfactants with the common formula CnH2n+1N(CH3)2(CH2)sN(CH3)32+. Zhao et al. (1998)

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An Overview of Inorganic Compounds

synthesized two novel cubic mesoporous silicas, SBA-16 (Im-3m) and SBA11 (Pm-3m), from EO106PO70EO106 and C16EO10, along with SBA-12, which is structurally identical to SBA-2 (Prouzet and Pinnavaia, 1997). Controlling the structure of mesophases is facilitated by the employment of surfactant molecules with varying geometrical characteristics and charges. At the interface, inorganic species intermingle with surfactant micelles via electrostatic contact or hydrogen bonding, as per the cooperative self-assembly creation process. Thus, phase transitions are likely to be accompanied by changes in the interface’s curvature. Micelle organization is connected to the local operational surfactant packing parameter g = V/a0l in classical micelle chemistry, where a0 is the effective head group area at the micelle surface, V is the total volume of the hydrophobic chains, and l is the kinetic surfactant tail length. The anticipated mesophase is determined by the value of g. Huo et al. (1994) pioneered the use of this approach to describe and forecast the structure and phase transition of products. Additionally, the concentration ratio of surfactants to inorganic precursors affects the shape of mesophases. MCM-41, for example, was synthesized with a C16H33(CH3)3N+/Si ratio of < 1. When the ratio of C16H33(CH3)3N+ to Si exceeds one, the Ia3d can be formed. Comparably, Nb-TMS4 (p2), NbTMS2 (P63/MMC), Nb-TMS1 (p6m) and were synthesized at a variety of surfactant to Nb ratios (Huo et al., 1994).

3.3.2.2. Pore Size Engineering Length of the Surfactant Chain. Beneath analogous reaction circumstances, the pore size of surfactants typically rises with chain length. While quaternary ammonium surfactants with various alkyl tails (n = 8, 9, 10, 12, 14, and 16) were utilized, the pore size of the resultant materials rose from 18 to 37A as the chain length increased (Table 3.2). Table 3.2. Various g Values and Associated Mesophases Mesophase

Space Group

g

Examples

Lamellar

p2

>1

MCM-50

Cubic

Pm3n

1/3

SBA-1

3D hexagonal

P63/MMC

SBA-15 (TEOS) > FSM-16 (layered silicate), PCH (layered silicate) > MCM-41 (TEOS), MCM-48 (TEOS), HMS (layered silicate) (TEOS).

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Hydrothermal stability is primarily determined by the thickness of the wall and the degree of polymerization. Owing to its highly polymerized and thicker walls, SBA-15 and KIT-1 are very resistant to hydrothermal treatment. Below mild steaming circumstances, the pore structure of materials with equal wall thickness may result in a difference in hydrothermal stability. Cubic MCM-48 degrades more slowly than hexagonal mesoporous materials. Weller et al. (1983) reported the following hydrothermal stability order: PCH > FSM-16, MCM-41 (fumed silica and TEOS), HMS. KIT-1 > SBA-15 > MCM-48 (TEOS and fumed silica) (Yaghi et al., 2003). Distinct hydrothermal and thermal stability, mechanical stability appears to be less reliant on the mesoporous material’s composition. With increasing pressure, all materials eventually compress, resulting in a reduction in pore volume and surface area. The latest research indicates that cubic mesoporous materials such as MCM-48 and SBA-1 are very hexagonal mesoporous materials are more mechanically strong than hexagonal mesoporous materials like SBA-15 and MCM-41. The primary reason for mechanical instability was shown to be the hydrolysis of Si–O–Si bonds through water adsorbed on silanol groups during compression. Materials that have been organically functionalized are further hydrophobic than their untreated equivalents, resulting in increased mechanical stability (Galarneau et al., 2003).

3.3.6. Application Since the finding of ordered mesoporous materials, scholars have investigated a variety of potential applications that make use of the mesoporous materials’ distinctive compositional or structural properties. Along with traditional applications like ion exchange, separation, and catalysis, novel applications for mesoporous materials often in HPLC contain stationary phases, macromolecular, and bio separations, enzyme immobilization, optical host materials, low dielectric constant materials, templates for porous carbon fabrication, and reactions in limited environments (Zhao et al., 1998).

3.3.6.1. Catalysis One of the most significant uses for ordered mesoporous materials in catalysis. Mesoporous materials can be employed in either redox or acid catalysis as catalysts. Trivalent cations including B and Al are frequently added into siliceous mesoporous frameworks to help produce additional acid sites. Additionally, acidity can be produced by spreading heteropoly acids

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or grafting the inorganic surface of mesoporous materials with functional groups. Numerous altered MCM-41 materials have been discovered to be catalytically active in a variety of acid-catalyzed reactions, yet mesoporous materials have a low acidity because of their disordered architecture. As a result, their use in petroleum processing and precision chemical synthesis is limited (Zhang et al., 1996). Attempts have been made to produce mesoporous materials with transition metal modifications for redox catalysis. These materials enable catalytic oxidation chemistry to be extended to big molecules. Additionally, In the oxidation of aromatic complexes, specific catalytic activity has been demonstrated employing titanium-containing mesoporous silica (Ti-HMS and Ti-MCM-41) (Pauly and Pinnavaia, 1999). Apart from their direct application as catalysts, mesoporous materials are particularly advantageous as catalyst supports due to their great thermal stability, surface area, and inexpensive cost. The production and catalytic activity of metal (e.g., Pd, Pt, Cu, Ru) and oxides metals (such as. ZrO2, VOx, TiO2, Fe2O3) based on ordered mesoporous materials have been extensively studied. Mesoporous materials have also had an influence on organometallic chemistry, as demonstrated by a novel sequence of composites formed by functionalizing mesoporous materials in conjunction with organometallic complexes (Antonelli et al., 1996).

3.3.6.2. Environmental Separation and Remediation Heavy metal ion removal has been a primary focus of environmental rehabilitation and cleaning. As adsorbents, a variety of materials have been utilized, including activated silica gels, clays, charcoal, and ion-exchange resins. Recently, mesoporous silicas that are functionalized have been demonstrated to offer a viable, if not a superior, substitute. Antonelli et al. (1996) synthesized a great efficient Hg2+ adsorbent by grafting thiol moieties to the context walls of mesoporous silica, abbreviated MPHMS. MP-HMS demonstrated an enhanced approach of guest varieties to binding sites, as well as a high loading capacity of 310 mg g1 (1.5 mmol g1) when compared to porous materials having a disordered structure, such as silica gel. Simultaneously, Feng et al. (1997) produced a comparable heavy-metal ion adsorbent by cross-linking a monolayer of mercaptopropyl-silane containing thiol terminal groups to large-pore MCM-41. The adsorbent that resulted, on mesoporous supports (FMMS) the functionalized monolayers, was

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particularly efficient in removing Hg2+ and further heavy metal ions. Due to the high relative surface exposure (up to 76%) of monolayers, a remarkable adsorption capacity of 505 mg g1 for Hg2+ was obtained. Antonelli et al. (1996) discovered a one-step technique to produce TEOS by co-condensing it through 3-mercaptopropyltrimethoxysilane in the existence of surfactants. In comparison to the previously investigated thiourea ligands, the mercaptopropyl ligand should have a weaker binding to mercury ions than the thiol group, facilitating adsorbent renewal. An excellent example is MCM-41, with large pores that have been grafted with 1-allyl-3-propylthiourea, which may be easily renewed under moderate circumstances.

3.3.6.3. Chromatography Viable SiO2 stationary phases for chromatography were created using the PICA process, resulting in an inter-particle (textural) pore structure through a modest surface area (100–550 m2 g-1) and a wide pore-size range. Ordered mesoporous silicas have a large surface area of up to 1,600 m2 g-1 and a tunable and uniform pore size due to intra-particle (structural) porosity and therefore are predicted to function better as stationary phases. MCM-41 was initially evaluated as a chromatographic matrix for normal-phase HPLC and size exclusion chromatography (Huo et al., 1995). The most noteworthy feature of MCM-41 is its capacity to efficiently separate several types of analytes within realistic analytical timeframes. Researchers employed APMS to extract ferrocene after acetylferrocene using normal-phase flash liquid chromatography, demonstrating superior separation capabilities (such as extended retention time, greater selectivity) compared to commercial silicas. Like findings have been achieved with APMS and spherical MCM48 in chiral HPLC, reversed-phase, and normal-phase. Yao et al. (2014) separated polycyclic aromatic hydrocarbons (PAHs) using MSU-1 spheres and normal-phase HPLC. On spherical SBA-15, biomolecules were separated using reversed-phase HPLC. In contrast to its uses in high-performance liquid chromatography, there are very some attempts to employ mesoporous silicas in GC (gas chromatography) (Yao et al., 2014).

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3.4. MACROPOROUS MATERIALS 3.4.1. Synthesis Emulsion’s crystals are colloidal or can be used to template ordered macroporous materials. In contrast to microporous and macroporous materials, mesoporous materials have a comparatively straightforward synthesis technique.

3.4.1.1. Colloidal Crystal Templating Figure 3.6 illustrates a typical three-step process to produce macroporous materials via colloidal crystal templating. To begin, monodispersed colloidal spheres form ordered 3-dimensional or occasionally 2D arrays to act as templates. Second, colloidal crystals’ spaces are occupied through precursors that harden to create composites. Eventually, the original spheres are eliminated, leaving behind a sturdy structure of unified voids that faithfully mimic the template arrays. Due to their high monodispersity and commercial availability, silica spheres and latex are the very often employed templates for colloidal crystal assemblage. Numerous crystallization techniques, such as filtration, centrifugation, sedimentation, pressing, slit filling, and convective deposition have been utilized to generate densely packed structures. All these approaches produce polycrystalline fields, often with RHCP (randomly stacked hexagonal close-packed planes) or FCC (face-centered cubic) packing, with a void space content of 26 volume percent. Occasionally, sintered or annealed colloidal crystals are used to strengthen their stability and assure connectivity (Reddy and Sayari, 1996). The structure of the interstices, their packing with suitable media, and subsequent fluid-solid transition are critical components of the whole synthesis. Through sol-gel hydrolysis and polymerization, fluid precursors in the gaps of crystal arrays can coagulate. Numerous methods, with chemical conversion and salt precipitation, spraying techniques, CVD (chemical vapor deposition), nanocrystal deposition and salt reduction, oxide, and sintering, electroless, and electrodeposition deposition, have been developed in recent years (Cabrera et al., 1999).

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Figure 3.6. A diagram illustrating the overall technique for producing ordered macroporous materials via colloidal crystal templating is shown. Source: https://www.sciencedirect.com/science/article/abs/pii/ S135902940000039X. Note: (1) Colloidal particles are arranged in a pattern to generate a colloidal crystal template.; (2) using precursors to fill up the gaps and holes in order to build composites; and (3) elimination of templates.

To get porous structures, it is necessary to remove the templates from the composites. In contrast, silicas may be separated through calcination, dissolving with suitable solvents, or UV degradation, whilst polymer templates can be eliminated by dissolution in NaOH or HF solution.

3.4.1.2. Emulsion Templating Feng and Pine (2000) explained that a very homogeneous emulsion droplets’ dispersion might be used as templates for the creation of macroporous titania, silica, and zirconia materials. Their study demonstrated that shearing

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and/or fractionating polydisperse emulsions result in homogenous emulsion droplets round that alkoxide precursors are formed using a sol-gel technique. Following heat treatment and drying, solid materials having spherical pores left through the globules of emulsion were obtained (see Figure 3.7). Through emulsion droplets, the macroporous materials templated have very homogeneous holes ranging in size from 50 nm to 10 m, in contrast to colloidal crystal templated materials, which have pores ranging in size from 100 to 1,000 nm. The materials may be modified to have a porosity of up to 90%.

Figure 3.7. A diagram depicting the technique for applying emulsion droplets as templates to macroporous materials. Source: https://pubs.acs.org/doi/10.1021/ja059849b.

3.4.2. Wall Structures and Composition Previously, an overview of ordered macroporous materials with varying compositions was provided. Numerous compositions, extending from and

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carbons to semiconductors, metals, polymers, and oxides, have been created. Macroporous materials can have amorphous or crystalline wall structures, micropores or mesopores, obtained through organic modification, or surface catalysts (Prouzet and Pinnavaia, 1997).

3.4.3. Applications Since macroporous materials exhibit three-dimensional periodicity on a length scale equivalent to that of evident light, 3DOM materials may be used as PSCs. Additionally, catalysts, bio-glasses, substrates, and sensors for surface-improved Raman scattering spectroscopy are probable uses.

3.5. HIERARCHICAL POROUS STRUCTURES Hierarchical porous materials are organized solids with varying length scales. Multiple porosity materials are of relevance for separation and catalysis applications since these applications can benefit from the diversity of pore structures. Microporous–mesoporous composites, for example, have demonstrated higher catalytic activity due to the combined effect of strong acidity from zeolites and a high reactant or product mobility because of large homogeneous mesopores. Numerous techniques for the synthesis and design of porous hierarchy materials have been described, as detailed below (Huang et al., 2016).

3.5.1. Multiple Templating As earlier noted, supramolecular micelles, organic molecules, and colloidal crystals serve as templates for the fabrication of macroporous, mesoporous, and microporous materials. Combining many templates in a single synthesis should result in the formation of hierarchically porous materials. Yang et al. (1998) established a straightforward method for fabricating hierarchically ordered oxides (titania, niobium, and silica) by merging cooperative assembly, micro-molding, and latex sphere templating employing PDMS (polydimethylsiloxane) stamps simultaneously or sequentially (Figure 3.8(a)). In their study, they put a PDMS mold with micrometer-scale shapes on a substrate, forming accessible passageways among the mold and the substrate via which liquid spheres are organized into a dense array (Zheng et al., 2002). A solution containing a sol-gel block copolymer precursor was used to fill the array’s gaps. After enough time had passed for polymerization and cross-linking, the mold was detached, and the organic templates were destroyed through calcination. The resultant materials displayed mesoporous

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walls with macroporous structures on their surfaces (Figure 3.8(b–e)). Huang et al. (2016) synthesized a composite of MCM-41/ZSM-5 with linked micropore and mesopore.

Figure 3.8. The manufacturing of hierarchically ordered oxides is depicted in this diagram. Source: https://www.science.org/doi/abs/10.1126/science.282.5397.2244. Note: TEM images of hierarchical ordered mesoporous silica (a) and SEM (scanning electron microscopy) images (b, c, and d), taken at different magnifications, show a high-quality surface pattern (1,000 nm), which is composed of a macroporous (100 nm) framework of cubic mesoporous silica (11 nm), as shown in TEM image (e).

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3.5.2. Assembly from Building Blocks Colloidal zeolites have been utilized to construct hierarchical porous materials as building blocks. By infiltrating zeolite nanoparticles in ethanol sol into such an ordered array of macroporous zeolites, polystyrene spheres were formed by a self-assembly method. Following ethanol evaporation, capillary forces aggregated zeolite nanoparticles (Huo et al., 1996). After calcination, a high concentration of peripheral silanol groups encouraged the development of hydrogen bonds among particles and ultimately Si–O–Si interactions. The technology has been improved to create translucent, selfstanding zeolite membranes with regulated mesoporosity. Simultaneously, premade zeolite-coated polystyrene domains have been employed as building blocks for the construction of hierarchical materials with ordered macroporosity, meso, and nano. The core-shell building components were synthesized using a ‘layer-by-layer’ process, in which positively charged macromolecules and zeolite nanoparticles were alternately adsorbed against latex spheres. This enables the layer numbers to be used to fine-tune the wall thickness of the final macroporous monoliths (Inagaki et al., 1996).

3.5.3. Structural Rearrangement and Bulk Dissolution The goal behind this technology is to incorporate new pore systems into the natural porosity of heavy substrates to form hierarchical structures. Diatoms are unicellular algae with silica walls and internal pore diameters ranging from micron to submicron. Zeolitization of diatoms, which involves dispersing diatoms, have nanoparticles of zeolite on their surfaces and then converting a portion of the diatom silicas to zeolites by hydrothermal conversion, resulting in the production of a meso/microporous composite material (Liu and Pinnavaia, 2002). Also, wood has been employed as a substrate for the manufacture of meso/macroporous composites and zeolites. Calcination is used to eliminate wood after synthesis.

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97. Zhang, Z., Hicks, R. W., Pauly, T. R., & Pinnavaia, T. J., (2002). Mesostructured forms of γ-Al2O3. Journal of the American Chemical Society, 124(8), 1592–1593. 98. Zhao, D., Feng, J., Huo, Q., Melosh, N., Fredrickson, G. H., Chmelka, B. F., & Stucky, G. D., (1998). Triblock copolymer syntheses of mesoporous silica with periodic 50 to 300 angstrom pores. Science, 279(5350), 548–552. 99. Zhao, D., Huo, Q., Feng, J., Chmelka, B. F., & Stucky, G. D., (1998). Nonionic triblock and star diblock copolymer and oligomeric surfactant syntheses of highly ordered, hydrothermally stable, mesoporous silica structures. Journal of the American Chemical Society, 120(24), 6024– 6036. 100. Zhao, D., Luan, Z., & Kevan, L., (1997). Electron spin resonance and electron spin echo modulation spectroscopy of aluminophosphatebased mesoporous molecular sieve containing framework manganese. The Journal of Physical Chemistry B, 101(35), 6943–6948. 101. Zheng, N., Bu, X., & Feng, P., (2003). Synthetic design of crystalline inorganic chalcogenides exhibiting fast-ion conductivity. Nature, 426(6965), 428–432. 102. Zheng, N., Bu, X., Wang, B., & Feng, P., (2002). Microporous and photoluminescent chalcogenide zeolite analogs. Science, 298(5602), 2366–2369. 103. Zhou, H., Zhu, S., Hibino, M., Honma, I., & Ichihara, M., (2003). Lithium storage in ordered mesoporous carbon (CMK‐3) with high reversible specific energy capacity and good cycling performance. Advanced Materials, 15(24), 2107–2111. 104. Zhu, H., Jones, D. J., Zajac, J., Dutartre, R., Rhomari, M., & Rozière, J., (2002). Synthesis of periodic large mesoporous organosilicas and functionalization by incorporation of ligands into the framework wall. Chemistry of Materials, 14(12), 4886–4894.

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CONTENTS 4.1. Introduction....................................................................................... 92 4.2. Magnetocaloric Materials.................................................................. 96 4.3. Magnetic Nanoparticles..................................................................... 99 4.4. Applications of Functional Magnetic Nanoparticles......................... 101 4.5. Technology of Magnetic Recording.................................................. 105 4.6. Perspectives and Summary............................................................... 106 References.............................................................................................. 108

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4.1. INTRODUCTION It is also known as the smart materials of the future. Functional magnetic materials are a class of materials that have crucial and fascinating physical characteristics that may be altered when a magnetic field is present. Models are fascinating and have a significant influence on the advancement of many technologies. Their magnetic reaction to an outdoor magnetic field can be classified as diamagnetic, paramagnetic, antiferromagnetic, or ferromagnetic, depending on the nature of the external magnetic field. Due to their interface/surface impacts, electronic charge transport, and magnetic interfaces, they exhibit exceptional magnetic behavior compared to bulk materials. It is possible to employ them in various critical applications, such as data storage systems, refrigerators, medical research, and magnetic recording. The fundamental attractive magnetic characteristics appropriate to an extensive range of applications will be discussed in detail in this chapter (Chen et al., 2004). Magnetic materials are critical to the development of scientific advancement and industrial development. In various applications such as power production and electronic, transmission devices, digital data storage and analog, medical devices, magnetic treatment and sensors, scientific equipment, and medication delivery, they are continually in use. Functional magnetic materials have different physical characteristics that may be altered when subjected to an applied excitation, for example, a magnetic field, and are used in a variety of applications. According to some, they are regarded as the “smart materials” of the future (Gutfleisch et al., 2006). In magnetic freezers, when an increase or decrease in the entropy throughout the material’s magnetic ordering temperature happens, the material may be employed. As an alternate cooling technology, this functionality of magnetic materials has a significant potential for application. It is founded on the MCE, which is a rescindable temperature variation in a magnetic material that occurs when an adjustable magnetic field is functional to the magnetic material. This feature also opens the door to the possibility of a small, highly efficient, and environmentally friendly substitute to the most widely employed vapor-compression-based freezing technology now available. The primary obstacles are the access to high magnetocaloric materials in sufficient numbers that display big MCE at room temperature in an acceptable magnetic field, along with the capacity to produce materials with minimal hysteretic losses (Hirosawa et al., 2017).

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As a result of their intriguing properties, magnetic nanoparticles have been the emphasis of study. They will undoubtedly find applications in data processing and storage, spintronics, and catalysis, environmental studies, MRI (magnetic resonance imaging), drug delivery, and other fields. When compared to bulk materials, these materials exhibit unusual magnetic behavior, which is mostly due to their magnetic interactions, electronic charge transfer, and surface/interface effects, among other things. Specifically, as seen in Figure 4.1, local magnetic characteristics with a size scale of nanometers or smaller perform a critical role in the interaction between microstructure and magnetic properties in perpetual magnets. When it comes to nanoscale structures, the most common phenomena to see are the increasing importance of surface effects, flaws, and the appearance of novel phases. Because of this, these phenomena may be used in the development of novel magnetic nanoparticles (Holmes et al., 2005).

4.1.1. Hard Magnetic Materials Several new permanent magnet materials have been found in the last century, including Techniques for manufacturing these magnets that have been demonstrated to be successful (Gutfleisch, 2000). Various device designs, including such magnets, have been successfully used in a variety of active and passive applications. Permanent magnets have seen an increase in their energy produced during the last few years, starting with steels, and growing to 3 MGOe for hexagonal ferrites and ultimately reaching a peak of 56 MGOe for neodymium-iron-boron magnets through the last few years. As a result, commercially manufactured sintered Nd-Fe-B grades may achieve around 90% of the maximum energy density (BH)max, which is the theoretical limit for energy density. As seen in Figure 4.2, permanent magnets have undergone significant progress over a period of around 100 years (Raisigel et al., 2006; Abdelbasir and Shalan, 2019). In contrast, the hunt for new hard magnetic compounds with greater remainder magnetization has, to a large degree, come to a halt, with no significant breakthroughs being observed recently. As for ternary and quadrilateral systems, only a small number of them have been investigated thus far. In the current state of affairs, the method of nanocomposites is the most actively pursued, along with exchange-besides a soft magnetic phase, which has an inherent upper limit of 0Ms = 2.43 T for a Fe65Co35 alloy, where Ms is the saturation magnetization, and 0 is the permeability of free space (Das et al., 2005).

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Figure 4.1. Magnetic characteristic lengths in permanent magnets, as well as an illustration of typical microstructures, are provided. Source: https://iopscience.iop.org/article/10.1088/2043-6254/aa597c.

Figure 4.2. Hard magnetic materials’ maximum energy density (BH)max at room temperature has increased steadily since the beginning of the 20th century, and there are now several distinct types of materials with equivalent energy density. Source: http://power.eee.metu.edu.tr.

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Recently, there has been a resurgence of interest in several forms of elevated permanent magnets centered on rare-earth intermetallic complexes, which are becoming increasingly popular. Among the driving forces behind this are, for instance, the growing need for energy-efficient technology, in which these magnets frequently play a critical part (Azzerboni et al., 2007; Sugimoto, 2011). For the development of rare-earth permanent magnets, the primary driving force has been the requirement for increased energy densities at a variety of operating temperatures (RPMs).

4.1.2. Soft Magnetic Materials The easiest magnetization reversal, which is followed by a short region of the low coercivity, and the hysteresis loop of soft magnetic materials are the characteristics that distinguish them the most. Soft magnetic materials are comparable to hard magnetic materials in that they must have their key magnetic characteristics and microstructure tuned in order to be produced. Permanent magnets, instead, an extremely low magnetocrystalline anisotropy is required as well as weak to nearly nil contact among grain boundaries and magnetic domain walls, which is the polar opposing of the parameters necessary for perpetual magnets (Hinz et al., 2004). In electrical power applications, for example, distribution transformers, generators, and a wide variety of motors, in addition to in electronics, where a large number of inductive mechanisms are essential, as depicted in the road chart of ultra-low-loss nanocrystalline alloy as depicted in Figure 4.3, soft magnetic materials are extremely important (Contreras et al., 2017). The absorbency of material is quite likely to be the most significant concern in the choosing of material for DC applications. When a material is used to generate a magnetic field or to generate a force, the saturation magnetization of the material may also be crucial to consider. When it comes to alternating current applications, the essential consideration is how much energy is wasted in the system when the material cycles beyond its hysteresis loop. In a magnetic material, energy loss can be caused by three different types of phenomena: (1) hysteresis loss, which is proportional to the area contained inside the hysteresis loop; (2) eddy current loss, which is proportional to the generation of electric currents in the magnetic material as well as the interconnected resistive losses; and (3) irregular loss, which is proportional to the movement of domain walls within the material (Dempsey et al., 2007).

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Figure 4.3. Roadmap for the development of an ultra-low-loss nanocrystalline alloy. Source: http://nanoc.imr.tohoku.ac.jp/eng/research.html.

4.2. MAGNETOCALORIC MATERIALS Current society is reliant on easily accessible refrigeration for the preservation of food and the provision of suitable living conditions. The cooling capacity of conventional refrigerators is provided by ozone, which is used to reduce hazardous substances like chlorofluorocarbons (CFCs) and hydrofluorocarbons (HFCs) as well as NH3 (ammonia) in a vapor compression cycle. Regular refrigerators are often cumbersome, heavy, and inefficient, despite the fact that they are capable of meeting cooling requirements. Recently, a new refrigeration technology based on the MCE has been researched as a potential solution to the shortcomings of vaporcompression refrigeration by addressing their shortcomings (Johannesen et al., 1968). When comparing magnetic refrigeration to gas compressing refrigeration, there are three significant benefits to consider. First and first, magnetic refrigerators emit no toxic gases; second, they can be constructed in a compact manner since their primary working material is solid; and 3rd, they are almost noiseless. Aside from that, when using gadolinium, the cooling efficiency can approach 60% of the theoretical efficiency perimeter (Zimm et al., 1998), whereas the best gas-compressing refrigerators only achieve 45% of the theoretical efficiency limit. While commercial freezers of this

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kind are still in the early phases of development, research efforts to produce novel materials with enhanced MCE are aimed at optimizing the chilling capabilities and energy efficiency of this emerging technology, which is still in its infancy. This section compares and contrasts the various materials, with a particular emphasis on transition metal-containing compounds. An applied magnetic field causes a change in the magnetic order of material. This change in magnetic order results in a change in the entropy associated with the magnetic degrees of freedom of the material (magnetic entropy, Sm). Sm must be covered by an equal and opposite change in the entropy connected with the lattice under adiabatic circumstances, which results in a change in the temperature of the material under adiabatic conditions. This temperature shift, denoted by the letter Tad, is commonly referred to as the MCE. Because of the thermodynamic Maxwell connection, it is associated with the magnetic characteristics of the material (Tishin and Spichkin, 2016; Abdelbasir and Shalan, 2019).

(1) It is possible to determine Sm using magnetization data obtained at different temperatures throughout time intervals. These magnetization measurements should be carried out with caution in materials that exhibit a first-order phase transition with significant hysteresis in order to avoid overestimating the rates of the entropy change in these materials (Caron et al., 2009). The magnetic entropy change can also be obtained directly from a calorimetric amount of the field dependency of the high-temperature capacity, c, and then combining the results. Validation has been performed to ensure that the values of Sm (B, T) generated from magnetization measurements are consistent with the values determined from calorimetric measurements (Gschneidner et al., 1999). Statistical incorporation of the adiabatic temperature change can then be performed employing the magnetization and heat content values that have been empirically or theoretically predicted. With little doubt, the MCE will be big when c (T, B) is small and(M/T)B is large when both of these parameters are held constant. For effects at elevated temperatures, the Dulong-Petit law states that the heat capacity on the order of the Dulong-Petit law equals 3 NR, where N is the number of molecules and R is the molar gas constant. As a result, we should concentrate on identifying a significant variation in magnetization at the proper temperature (Hornick et al., 2010).

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Because the order factor of the phase transition B fluctuates intensively within a short temperature region, a substantial MCE is expected to occur not far from crests at the magnetic-ordering temperature (Figure 4.4).

Figure 4.4. Diagram of a magnetic refrigeration cycle, which moves heat from the heat load to the surrounding environment. Materials in high and low magnetic fields are depicted in yellow and green boxes, respectively, by the color of the box. Source: https://iopscience.iop.org/article/10.1088/0022-3727/38/23/R01/.

The refrigeration-magnetic cycle shows how initially random-oriented magnetic properties are ordered through a magnetic field, leading to heating of the magnetocaloric material and then heat transfer from the magnetocaloric material to the adjacent environment (Tegus et al., 2002; Brück, 2005). When the field is removed, the magnetic instants become disordered, subsequent to the material being cooled below its ambient temperature. The heat from the system may then be removed by the use of a heat-transfer medium, which can be either helium, air, or water, varying on the operating temperature of the system. As a result, magnetic refrigeration is regarded as an environmentally benign cooling method (Rueff et al., 2004).

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4.3. MAGNETIC NANOPARTICLES Nanotechnology has permeated all fields of science, including physics and chemistry, as well as biomedical study and allied sectors, over the course of many decades. Nanoparticles are described as materials with particle sizes ranging from 1 to 100 nanometers in broad terms (Gleiter et al., 2001). Physical properties of bulk materials are well-defined; but, when they are reduced to nanoparticles, their qualities are changed depending on the ultimate size of the particles. In comparison to bulk material, one of the most significant changes in the characteristics of nanoparticles is the significant rise in the number of molecules/atoms on the particle’s surface, resulting in the obtainability of an essentially higher surface area than in bulk material (Han et al., 2018). Because of the high surface area of particles, ligands, and/ or capping agents may be attached to them, making them more appropriate for the effective labeling of tracer/drug molecules than other materials. Because of the change in physicochemical characteristics that occurs during the alteration of bulk material to nanoparticles, they are more appropriate for delivering therapeutic agents to the sick location due to their improved diffusion capacity. A wide range of nanoparticles, especially MNs (magnetic nanoparticles), have been produced and described for use in a variety of industrial, biological, and therapeutic applications, among other things (Cullity and Graham, 2011). MNs are nanoparticles that are manufactured from magnetic elements such as cobalt, nickel, and iron or their chemical products and are used in a variety of applications. There are numerous domains in every particle of bulk magnetic materials that are removed by walls, and every domain represents an area where the magnetism is directed in a certain direction (Miller, 2006; Koji et al., 2011). When bulk material is transformed into MN, every particle can reach a single sphere. Because the surrounding thermal energy is much lower in larger particles (micrometer size) than in smaller particles, the magnetic moment’s orientation does not alter with the passage of time. Because of the reduction in particle size (to sub-micron size), the particle energy diminishes, and the magnetic moment’s direction changes in relation to the original direction or with angle. However, if the particle size decreases further, the direction of the magnetic moment shifts to the opposite direction (180°), which is referred to as the superparamagnetic behavior of magnetic nanoparticles (Ohno et al., 2002; Dui et al., 2015). Unlike superparamagnetism, which is created by particle size, paramagnetism is an inherent feature of the material produced by the atomic constitution of the substance (e.g., Na). As a result of the large magnetic moment of B,

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superparamagnetic particles are distinguished from ordinary paramagnetic particles in that they exhibit paramagnetic behavior in the nonexistence of a magnetic field, and no magnetization is preserved when the magnetic field is removed (De Greef et al., 2010). It is possible to convert ferromagnetic particles into superparamagnetic particles by reducing particle size under the critical size limit. Paramagnetic materials do not have magnetic relations among their atoms; as a result, the net magnetic moment of a particle is equal to the number of atoms contained within the particle. In superparamagnetic or ferromagnetic materials, on the other hand, the interatomic magnetic interaction results in the generation of the net magnetic moment of the particle. Because of the growing amount of the composition of spins in MN, there is a potential of transitioning from ferromagnetic to superparamagnetic (Figure 4.5) with either lowering temperature or rising magnetic field (Gajbhiye et al., 2008; Ningthoujam and Gajbhiye, 2010).

Figure 4.5. (A) Paramagnetically charged particles in the presence of a magnetic field. There is no evidence of change in magnetization; and (B) superparamagnetic particles that are subjected to a magnetic field or that are at a low temperature. Source: https://aip.scitation.org/doi/10.1063/1.3311611.

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These MNs have been used for a variety of applications, including the separation of cells/biological materials and the administration of drugs, due to their unique ability to attract and interact under magnetic field circumstances. The capacity of MNs to function as distinguish agents in MRI for diagnostic purposes has drawn the attention of researchers. Considering their decreased biocompatibility, toxicity, and considerable deposits of MNs at the sick site, it may be appropriate to point out that they are well-suited for restorative treatments (Fan et al., 2006). When these MNs are subjected to magnetic field properties, a phase gap between the direction of the magnetic moments and the direction of the applied magnetic field causes thermal losses to occur. Heat causes the alignment of magnetic moment to fluctuate thermally, and there are two main mechanisms at work: I Magnetic moment fluctuations caused by Neel’s fluctuations in relation to the crystal lattice; and (2) The Brownian variations of the particle itself in relation to the medium in which it has been put are described here as follows. These are impacted by the viscosity of the medium, as well as other factors that might have an impact on the mobility of the particle. These internally and externally frictions formed on MN below the influence of an external magnetic lead in “foci” of heat generation, which may be capable of killing the cell if the cell is not protected. In this way, targeted heat creation by MN at the tumor location has the considerable benefit of destroying tumor cells while causing little damage to normal tissues and surrounding tissues (Goya et al., 2003; Barbeta et al., 2010).

4.4. APPLICATIONS OF FUNCTIONAL MAGNETIC NANOPARTICLES As a result of the exceptional ability to regulate coercivity in magnetic nanoparticles, a few major technological applications, notably in the area of information storage, have been developed. In order to further enhance the density of magnetic storage devices approaching 100 Gbit/inch2 and even some Tbit/inch2, small magnetic particles appear to be the most viable options (Muetterties and Phillips, 1959; Moser et al., 2002). Apart from data storage, magnetic nanoparticles have a wide range of other uses, some of which include high-performance permanent magnets, high-frequency electronics, ferrofluids, and magnetic refrigeration. There are several biological and medical uses for magnetic particles, including drug-targeting and cancer treatment, as well as lymph node imaging and hyperthermia (Berry and Curtis, 2003; Tartaj et al., 2003). Recently, scientists have been successful in producing MN that is multifunctional. Magnetic nanoparticles

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may be functionalized in a variety of ways, including connecting them to antibodies, proteins, dyes, and other molecules (Euliss et al., 2003; Andrä et al., 2007). They can also be blended with another functional nanoparticle, for example, metallic nanoparticles or quantum dots, which can improve their performance. Magnetic nanoparticles, for example, might be employed as seeds for the growth of semiconducting chalcogenides, as one illustration. This results in the formation of hetero or core-shell nanostructures with both magnetic and fluorescence features as a final product in this example (Reinoso et al., 2005). This culminates in the demonstration of intracellular use of nanoparticles, which has the potential to be used for dual-functional molecular imaging. MNs may be utilized to increase MRI contrast because the signal arising from proton magnetic moments surrounding magnetic nanoparticles can be captured by echoing absorption, which can be used to improve contrast in MRI scans. These multifunctional MNs have the potential to be employed in a variety of biological applications, including protein purification, therapeutic elimination of toxins, and bacterium detection. Figure 4.6 depicts these two ways for fabricating multifunctional MNs, as well as their diverse biological uses in the context of the human body (Shiroishi et al., 2009). During the previous three decades, the capacity of magnetic data storage has increased in a linear fashion in terms of data storage. Magnetic hard disc drive technology is based on the physics of magnetic nanostructures, which lies at the heart of the technology. It is quite likely that, in the future, new technologies such as heat-assisted magnetic recording or BPM (bit patterned media) will enable areal densities to go far above 1 Terabit/inch2 (Terris and Thomson, 2005).

Figure 4.6. In biology, the use of multifunctional magnetic nanoparticles has a wide range of possible applications. Source: https://onlinelibrary.wiley.com/doi/book/10.1002/3527600140.

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Two-dimensional (2D) dot-arrays and other pattern-decorative magnetic nanostructures, like 2-D dot-arrays, have piqued the attention of scientists because of the potential applications they hold, for example, magnetic information storage and nonvolatile MRAM (Guo et al., 2005). In order to meet the need as a component of ultrahigh-density magnetic data storage systems, the bit size is being reduced to the nanoscale scale. As the volume of the grains, V = D2t/4, is lowered throughout the scaling method, the magnetization of the grains may develop variables owing to thermal variations, resulting in data loss. Because data loss due to thermal instability becomes increasingly important as the physical size of the nanostructures in the decorative array reduces, it is becoming increasingly important (Weller and Moser, 1999). As a result, future data storage technologies must be able to resist the SPM phenomenon. It should be noted that the L10FePt alloy is one of the most capable materials for future ultrahigh-density magnetic storage devices due to the fact that it possesses a large uniaxial magnetocrystalline anisotropy, which results in a high degree of thermal stability of magnetization during operation (Andriotis et al., 2005). Because of the poor intergranular exchange coupling between the particles in the current longitudinal data storage media, it is possible to regard them as a set of independent particles. The system may, however, be driven to produce long-range ordered superferromagnetic (SFM) spheres, which are plainly unsuited for use in data storage, as we detailed in the super-ferromagnetic section. Furthermore, because the SFM alignment is designed to combat high TMR (tunneling magnetoresistance) values, random magnetic access memory applications are not a good fit for SFM technology. Although Superferromagnetic materials are sometimes known as soft magnetic materials, their high permeability and low loss make them almost perfect materials for low-loss materials in microelectronics, high-permeability, sensing devices, and power management built for high-frequency operation (Ningthoujam et al., 2008).

4.4.1. Magnetic Materials in Hyperthermia It has recently been discovered that MN can be used as a possible mechanism of hyperthermia in cancer treatment. To destroy cancer cells, hyperthermia is a sort of a medical procedure in which bodily tissue is subjected to elevated temperatures (42–44°C) that is greater than the body’s normal temperature (37°C) for a period of time. When used in conjunction with radiation and some chemotherapy medications, this method of cancer treatment is one of the cancer treatments options available. The application of external sources

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to cancer cells is referred to as “ extracellular or external hyperthermia,” and the delivery of MN within cancer cells is referred to as “intracellular hyperthermia.” Tumor cells heated by peripheral sources do not reach hyperthermic temperatures because the cell membrane, which is made of lipids, is thermally insulating (Laget et al., 1998, 1999; Bousseksou et al., 2004). As a result, more heat from an external source must be delivered in order to reach the therapeutic temperature. In clinical situations, however, this results in blisters, burns, swelling, blood clots, and bleeding. As a result, the implementation of hyperthermia using this technique has encountered certain practical difficulties. In contrast, intracellular heating employing internalized MN at the tumor site offers an effective and safe method of applying hyperthermia to the tumor. Further research is needed to determine the clinical benefits and therapeutic efficacy of intracellular hyperthermia on extracellular hyperthermia in the treatment of cancer. Furthermore, the creation of surface-functionalized nanoparticles through the use of modern technologies may result in a more effective treatment modality for use in clinical applications in the future. Is it possible to employ all MNs is hyperthermia? MNs such as Fe3O4, Mn-, -Fe2O3 and, Ni-, and Co-doped ferrites are commonly used in hyperthermia therapy since they have a high magnetic moment below an external magnetic field, which can cause hysteresis loss and outcome in a substantial increase in temperature enough for the treatment. Certain materials, on the other hand, become ferromagnetic when their particle sizes are reduced to the nanometer range or smaller (Panigrahy et al., 2010). It is possible that such sorts of materials will be ineffective for hyperthermia therapy due to their extremely low magnetic moments (Vishwakarma et al., 2011). We should point out that iron and cobalt nanoparticles are susceptible to oxidation under alkaline and acidic environments, which are expected to differ in various tissue sections inside the body, respectively. Oxide nanoparticles (for example, Fe3O4), on the other hand, are very stable in both mildly alkaline and acidic environments and are biocompatible. Because of their low magnetic moment, very small Fe3O4 nanoparticles are not suitable for hyperthermic applications. For hyperthermic applications, small Fe3O4 nanoparticles (5 nm) are not valuable. However, yet with a particle size of 35 nm, FePt, FePd, CoPd, and CoPt nanoparticles would consequence in substantial heat production, but their stability in alkaline and acidic media is less than that of their oxide complements (Buffer and Line, 1997).

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4.4.2. Magnetic Materials in Data Storage Magnetic-semiconductor memory systems and high-capacity disc drives, among other things, make use of magnetic materials. In terms of data capacity growth over time, disc drive devices have achieved the greatest increase, making disc drives the premier storage solution for digital information. In recent years, the increase in areal density has exceeded 100% per year growth. Depending on the disc size, the complete data capacity of a disc is approximately equal to the areal density multiplied by the recording area. Several bits of knowledge have contributed to this rapid surge in areal density, including improvements in the technology of “flying” heads with reduced space on the data coding, disc surface, rectification, and error discovery, developed servo-control structures for accurate management of magnetic recording heads on data tracks, and advancements in the mechanical constructions that make up a disc drive, as well as advancements in the motors that drive the discs. The magnetic random-access memory, often known as MRAM, is a crucial new technology for high-speed memory systems that have appeared in latest years (Daniel et al., 1998).

4.5. TECHNOLOGY OF MAGNETIC RECORDING The magnetic recording has been around for almost a century. In its most basic form, magnetic recording involves the use of a magnetic structure driven by an existing that contains all of the data to be recorded in order to generate a magnetic field designed to alter the state of magnetization in a tightly packed magnetic medium, which was previously known as a magnetic wire but is now known as a magnetic layered or an optical tape hard drive. The read and write heads of disc drives are separate thin-film structures placed on the back of a mechanical slider that “flies” over the disc surface using a hydrodynamic air bearing (Comstock, 2002). This is due to the magnetic storage surface, which is a thin sheet of cobalt metal alloy, is observed with the reading and writing sections combined. The numerical data is written in the magnetic film as transitions between the two magnetization states, with a width that is nearly equal to the width of the write head. The length of the transition zone among the oppositely focused directions of magnetization is identical to that of the transition region between magnetic domains. The write head is made up of tiny ferromagnetic alloy sheets patterned into a magnetic chain. A pancake coil with 10 or fewer spins couples the current to the chain to form a magnetic field at the gap. Layers of polymer photoresist protect the coil from metallic magnetic bonding. In the past, the most often utilized

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alloy for magnetic films in write heads was Ni80Fe20 permalloy, which can be electroplated in thin films. The capability to record on a recording medium with enhanced coercivity isn’t the only problem with write heads made of magnetic materials. It is also critical that the write head is efficient (Comstock and Workman, 1989). Efficiency (η) in this instance is defined as the ratio: (2) where; I is the amplitude of the write current pulse; and Hg is the magnitude of the magnetic field in the gap of the write head. High efficiency is needed to permit write-current amplitude and frequency that are easily provided by incorporated circuits.

4.6. PERSPECTIVES AND SUMMARY Because they may concurrently show fascinating features like adjustable magnetic, mechanical, dielectric/electric, optical, and thermal properties, functional magnetic materials are a vast cause of technological applications. Refrigeration and processing, information storage, heat, and recording technologies might all benefit from these materials. Though pure magnetocaloric qualities and material prices get the most attention, additional features like heat conductivity, mechanical properties, environmental effect, and electrical resistivity have lately received attention. The refrigeration sector is a multibillion-dollar industry, so this new technology has a lot of potentials (Figgis et al., 1962; Schleyer et al., 1997). At least 80% of the magnetic refrigerant should be transition metals with significant magnetic moments, such as Fe or Mn. It should also include certain low-cost p-metals, like Si or Al, that may be utilized to fine-tune the material’s working point. For the advancement of magnetic recording and rapid random-access memory, or MRAM, technologies, a diverse spectrum of magnetic materials is required. The storage capacity of magnetic data storage has increased linearly. The physics of magnetic nanostructures lies at the center of magnetic hard disc drive skill, and new technologies are anticipated to push areal densities well beyond 1 Terabit/inch2 in the future. In hyperthermia, a larger amount of magnetic heat production by a stable fluid in a shorter exposure duration is the goal. Because of their high specific absorption rate, chemical stability, and low magnetic moment, nano ferrites are a promising

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candidate for hyperthermia applications (SAR). An appropriate selection of surfactant layer, magnetic core, and liquid type can impact cancer therapy depending on which heat-generating mechanism is desired (Bloomberg et al., 1996; Wang and Taratorin, 1999).

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CHAPTER

5

METAL OXIDE NANOPARTICLES FOR ANTI-BACTERIAL AND WASTEWATER APPLICATIONS

CONTENTS 5.1. Introduction..................................................................................... 116 5.2. Wastewater...................................................................................... 118 5.3. Importance of Nanoparticles............................................................ 122 5.4. Metal Oxide Nanoparticles (MONPS).............................................. 125 References.............................................................................................. 150

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5.1. INTRODUCTION Clean water is essential for the survival of all living beings. As a result of fast industrialization and a tremendous population boom, the pollution of current water supplies has grown over the world. In agriculture, there has been significant growth in both the need for and use of clean water. The consumption of clean and fresh water contaminated with a wide range of contaminants in industrial, home sectors, and further types of consumption accounts for approximately 70%, 22%, and 8% of total water consumption, respectively (Helmer and Hespanhol, 1997; Ali and Aboul-Enein, 2004). Heavy metal ions and dyes are the two most important types of contaminants. Water containing these contaminants should not be utilized for drinking reasons unless it has been thoroughly purified first When these heavy metal ions have entered the water, it is exceedingly hard to remove them completely. They are harmful to all living species and have a significant negative impact on ecosystems and water quality. Because of this, these pollutants must be removed from polluted water in order to avoid their detrimental impacts on individuals and the environment from occurring. Water supply openings are currently confronted with a wide range of issues. Approximately 780 million people do not have access to potable water in their homes or communities across the world (Rai et al., 2005 Herschy, 2012). In the impacted areas, which are primarily in underdeveloped nations where management of wastewater is typically non-existent, immediate action is needed to prevent further contamination. Although already in place, wastewater treatment and management technologies are increasing their capacity to deliver sufficient clean water to fulfill environmental and human requirements (Bavasso et al., 2016). Increased water supplies and arrangements may be possible as a result of recent advancements in nanotechnology and nanoscience. It is projected that the incredibly integrated, effective, and multifunctional advances made possible by nanoscience and nanotechnology would result in high rates of operation, as well as sufficient and economical wastewater treatment solutions when associated with huge infrastructure (Qu et al., 2013; Vilardi et al., 2017). Environmentally friendly and cost-effective strategies for removing these contaminants from the environment are essential (de Mendonca et al., 2014; Stoller et al., 2016). In the literature, a variety of procedures for wastewater treatment have been described, including solvent extraction, reverse osmosis, evaporation, and ultrafiltration, among others. These

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approaches, on the other hand, remove pollutants from water without converting them into potentially harmful end products (Anjaneyulu et al., 2018). By oxidation, it is quite simple to produce a complete breakdown, either chemically or photochemically. A potent oxidant, the hydroxyl free radical, is generated and used by each oxidative activity in order to decrease the impact of contaminants on the environment. Activated hydrogen peroxide can be employed as an oxidant, such as ultraviolet (UV) light, as a Fenton reagent, or as a metal ion once it has been activated (Slokar and Le Marechal, 1998; Forgacs et al., 2004). Nanomaterials are mostly employed in the treatment of large-scale wastewater and water issues. The word “nanomaterial” refers to a particle with a diameter of one nanometer or one trillionth of a meter (Auffan et al., 2009; Vilardi et al., 2018). Chemical nanomaterials are widely employed in a variety of industries, including environmental monitoring, biomedical, and pharmaceutical research, optoelectronics, and electronics, the cosmetics and apparel industry. The presence of these small nanomaterials causes a variety of changes in the physical characteristics of the material, including an increase in the volume to surface area ratio and the influence of quantum qualities on particle size. Unlike the qualities of regular materials, the properties of nanoparticles are drastically different from those of conventional materials, including their magnetic, optical, and electrical properties, among other things. Nanomaterials include characteristics like high adsorption, reactivity, and catalytic activity, which are all connected with them (Khan et al., 2019). Nanoparticles have gained significant attention over the last few decades and have been successfully employed in a variety of domains, such as medicine, sensing, biology, catalytic chemistry, and active development and research (Biju, 2014; Kamaly et al., 2016). Several studies have shown that nanoparticles are effective in the remediation of wastewater. As a result of their enormous surface area and compact diameters, nanoparticles have a high level of adsorption capacity and reactivity. Numerous types of pollution sources, such as bacteria, organic pollutants, emerging pollutants, and inorganic anions, have been documented to have decomposed into diverse types of nanomaterials across the world. Nanoparticles, such as zerovalent nanoparticles, carbon nanotubes, nanocomposites, and metal oxide nanoparticles (MONPs), are capable tools for use in various wastewater ecosystems (Amil Usmani et al., 2017). MONPs, zerovalent nanoparticles, carbon nanotubes, and nanocomposites are examples of such promising tools (Chiavola et al., 2016, 2017).

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Nanomaterials enable the development of innovative water-supply systems that make use of both traditional and unusual water sources. Several wastewater treatment approaches have been developed in recent years to address a variety of problems (Yang et al., 2019a, b). In a recent review by Dimapilis et al. (2018), zinc oxide nanoparticles have been an effective disinfecting agent for contaminated wastewaters. For example, solvent extraction, reverse osmosis, microfiltration, gravity separation, sedimentation, distillation u, precipitation, ultrafiltration, adsorption, electrodialysis/electrolyte separation, ion exchange, flotation, and are some of the most prominent processes used in water treatment (Saleh and Gupta, 2012; Stoller et al., 2018). A review by Viladi et al. (2018) reviewed the existing usage of MONPs with their influence on biological wastewater treatment methods, as well as the development of future applications. They also summarized the many approaches that have been utilized to test the inhibition of nitrification through MONPs, as well as the related results that have been produced using these methodologies. In their review, Yang et al. (2013) evaluated the destiny and possible impacts of four types of nanoparticles on anaerobic digestion and wastewater treatment: nano zerovalent iron, silver nanoparticles (AgNPs), nano Zinc oxide (ZnO), and nano titanium dioxide (TiO2). They spoke on the effects of non-metallic and MONPs on both wastewater treatment and anaerobic sludge digesting processes. Sing and colleagues (2019) concentrated their attention on the utilization of nanoparticles in wastewater treatment. The authors of this chapter went into great depth about three types of MONPs: iron oxide, ZnO, and TiO2 (Fei et al., 2011).

Mineral oxides such as MnO2, Fe3O4/Fe2O3, MnO2, Al2O3, and CeO2, as well as their uses in water treatment, in addition, several metal oxides have been mentioned in various studies (on nanoparticles), but there has not been a comprehensive study of metal oxides for wastewater treatment (Yang et al., 2019b). Abdelbasir and colleagues (2019) went into great length on nanoparticles for industrial wastewater treatment. In this chapter, they discuss the industrial uses of three metal oxides (TiO2, Fe3O4/Fe2O3, and ZnO) that have been discovered thus far (Lu et al., 2016).

5.2. WASTEWATER Wastewater is an urban waste liquid compound containing pollutants like organic materials, bacteria, soluble inorganic complexes, and the usage of hazardous heavy metals. Wastewater is a liquid product that is produced by

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the treatment of municipal waste. Physical, biological, and chemical features of clean water are altered as a result of the presence of these pollutants (Abou El-Nour et al., 2010). Wastewater can be split into industrial and municipal wastewater from waste sources, which commonly contains feces and urine, agricultural, and industrial wastewater sources, along with domestic components and inorganic and organic chemicals (Adams et al., 2006; Baek and An, 2011). Industrial and municipal wastewater from waste sources, which frequently contains urine and feces, agricultural, and industrial wastewater sources, as well as domestic compositions and organic and inorganic chemicals. Figure 5.1 illustrates the many sources of wastewater (Varjani et al., 2017; Mauter et al., 2018). Wastewater includes enormous numbers of microorganisms, such as viruses, bacteria, and protozoa, as well as harmful compounds, like heavy metals, radionuclides, and trace elements, and should be treated with caution. The discharge of wastewater is also a significant source of waterborne infections, including potentially fatal disorders including typhoid and cholera. As per the World Health Organization, more than 1.5 million children under the age of five died in 2004 because of contaminated water (Al-Thabaiti et al., 2008). Figure 5.1 depicts the many contaminants that can be found in water (Du et al., 2020). Nowadays, wastewater treatment is required due to the harmful effects of pathogens on humans and animals, as well as the dangers posed by wastewater pollution to agricultural operations and livestock. The treatment of wastewater at the individual and governmental levels must be taken into consideration in order to safeguard the environment from contamination. Water purification from diverse pollutants can be accomplished by the use of physical, chemical, and biological techniques in the treatment of wastewater (Bartram and Ballance, 1996; Bitton, 2005). Total solids, dye, and other physical features of wastewater are all present (Borgohain and Mahamuni, 2002), as are other types of wastewaters (fixed, volatile, dissolved, and suspended).

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Figure 5.1. Different sources of wastewater. Source: https://www.researchgate.net/figure/Sources-of-wastewater-streams_ fig1_275953389.

Total dissolved solids are measured in parts per million (ppm) of total dissolved solids. For dissolved solids, the particle sizes vary from 0.01 to 1.00 microns (Cheremisinoff, 2002; Chang and Zeng, 2004). Organic chemicals, inorganic chemicals, and gaseous chemicals are the three types of chemical contaminants found in wastewater. Fats and oils, carbohydrates, and proteins are the most common organic contaminants in wastewater, accounting for about 50%, 40%, and 10% of total organic impurities (Shon et al., 2006), respectively. Organic pollutants found in wastewater include primary impurities, surfactants, and impurities, as well as other organic contaminants. Water quality may be determined by measuring biological oxygen requirement and chemical oxygen required, which are the most realistic markers of organic contaminants in water. Several inorganic contaminants, like, phosphorus trace elements, heavy metals, nitrogen compounds, and other harmful inorganic components, can be found in wastewater (Daus et al., 2004). The use of nanotechnology in water treatment can provide novel solutions for catalysis and adsorption, as well as electrostatics, reactivity, and adjustable pore volume. Nanotechnology can also provide sensors and optical electronics with high aspect ratios, as well as hydrophilic and hydrophobic interactions. Efficacious, flexible, and adaptable techniques based on nanotechnology are available for the production of low-cost water, high-performance, and wastewater solutions. Furthermore, nanotechnology

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has the potential to be inexpensively developed to clean up and rebuild uncommon water sources. Table 5.1 presents a description of the technologies that have been developed for the removal of toxins from wastewater. Table 5.2 presents a summary of the key limitations of traditional water purification methods that have been developed. Table 5.1. Wastewater Treatment Procedures That have been Employed in the Past Method

Main Characteristic(s)

Chemical precipitation

Separation of produced products/pollutant absorption

Flotation

Separation process

Flocculation/coagulation

Separation of the generated products/pollutant uptake

Filtration

Use of a nondestructive process and solid material

Chemical oxidation

Use of an oxidant

Biological treatment

Use of biological cultures

Thermal oxidation/Incineration

Destruction through combustion

Ion exchange

Nondestructive process

Membrane filtration

Nondestructive separation

Electrochemistry

Electrolysis (E)

AOP (advanced oxidation process) photolysis

Destructive techniques, emerging processes

Evaporation

Concentration technique, thermal process, and Separation process

Liquid-liquid extraction

Separation technology

Table 5.2. Traditional Water Purifying Systems have Limitations Method

Limitations

Flotation

High initial investment costs, pH-dependent selectivity, and high operational and maintenance costs.

Flocculation and coagulation

This process is complicated and inefficient since it requires alkaline additions to attain an optimal pH.

Chemical precipitation

It is important to use an excessive amount of the reagent. Its product might be a low-quality combination, limiting its use. It is not a very discerning approach.

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Initial capital costs are considerable, as are ongoing maintenance and operational costs.

Biological treatment

Microorganisms are sensitive to their surroundings. Microbial cells can be destroyed by intermediates. This procedure is both costly and time-consuming.

Membrane filtration

Small and medium-sized businesses face high investment costs. High energy requirements. Membrane filtering systems come in a variety of shapes and sizes.

Incineration/ thermal oxidation

High running cost, High initial capital cost.

Electrochemistry

Equipment with an original high cost and a high maintenance cost.

Evaporation

Expensive when dealing with large amounts of wastewater. Small and medium-sized businesses face high investment costs.

AOP (advanced oxidation processes) photolysis

Technical restrictions and limited throughput make it economically unviable for medium and small businesses.

Liquid-liquid (solvent) extraction

High investment

Ultrafiltration

This technique needs high energy and fails to remove dissolved inorganics.

Nanofiltration

This process needs pre-treatment and a large amount of water cleaning energy. The retention of univalent ions and salt was low.

Carbon filter

Fluoride, nitrates, salt, metals, and other contaminants are not removed with this procedure. Mold can grow here, and undissolved particles can cause blockage.

Microfiltration

Metals, fluoride, salt, nitrates, volatile organics, pigments, and other contaminants are not removed with this procedure. Cleaning is required on a regular basis, and membrane fouling might arise.

5.3. IMPORTANCE OF NANOPARTICLES The shape and size of nanoparticles, as well as the morphologic structure of the substance, are the most important characteristics of nanoparticles. In the influence of chemical agents, the surface and interfacial characteristics of surfaces and interfaces may be altered (surfactants). Through the preservation of particle charge and the modification of the particle’s outermost layer, these agents can act as indirect stabilizers against aggregation. Contingent to the method of development and the life cycle of a nanoparticle, it should be possible to anticipate a fairly complicated structure. For example, several

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distinct agents condense on the particle during cooling in the conventional production method of nanoparticles, which is subjected to a variety of various ambient atmospheres during the chilling process. As a result, complicated surface chemical procedures are needed, and just a small amount of particulate model systems have been conveyed to this point. To manipulate the surface characteristics of nanoparticles as well as their interactions with their environment, polyelectrolytes have been used at the nanoparticlesliquid boundary for several years. Various industrial applications include lubrication, stability, adhesion, and the operated flocculation of colloidal scatterings (Mazilu et al., 2012). They are also utilized in the pharmaceutical industry (Figure 5.2).

Figure 5.2. Various pollutants found in water. Source: https://stylesatlife.com/articles/types-of-pollutions/.

In accordance with their shape, size, and physical l and chemical characteristics, nanoparticles may be divided into several categories. Among these categories are: Some of these nanoparticles are classified as ceramic

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nanoparticles, semiconductor nanoparticles, carbon-based nanoparticles, polymeric nanoparticles, metal nanoparticles, and lipid-based nanoparticles, among other things. Figure 5.3 depicts a number of nanoparticles that are routinely employed. Aspects of nanoparticles’ chemical and physical characteristics are complicated, and their atomic and molecular origins play a role in this. Individual components on a broad or extended surface have qualities that are completely different from the properties of tiny clusters in terms of electrical and optical characteristics, as well as their reactivity. The interactions among particles at the nanoscale scale can be influenced by weak van der Waals forces, stronger polar and electrostatic contacts, and covalent interactions. The interaction among nanoparticles can influence particle aggregation in a fluid based on the polarization and viscosity of the fluid, among other factors. When the surface of a coagulating colloid is modified, it can either increase or decrease its coagulation propensity.

Figure 5.3. Commonly used types of nanoparticles. Source: https://www.researchgate.net/figure/Commonly-used-types-ofnanoparticles_fig3_348793693.

When it comes to discussing chemical and physical processes, the interactions among nanoparticles and between nanoparticles and the interactions

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among nanoparticles and fluid are extremely significant. Because of the tiny number of molecules present in the active surface layer, it is hard to describe their characteristics. The surface energy, charge, and solvation are the key characteristics to take into consideration. Figure 5.4 depicts some of the most regularly used methods of wastewater treatment (Gehrke et al., 2015).

Figure 5.4. Wastewater treatment by nanoparticles. Source: https://www.sciencedirect.com/science/article/pii/ S2590182621000023.

5.4. METAL OXIDE NANOPARTICLES (MONPS) Metal oxide nanoparticles (MONPs) are produced entirely of metal precursors and are used in a variety of applications. These nanoparticles serve an important role in a wide range of fields, including the material sciences, chemistry, and physics. Temperature-controlled elements have the ability to create a wide variety of oxide compounds. With an electronic structure, they can display metallic properties, semiconductors, or insulators. They can be made up of any number of fundamental geometries along with an electronic structure. In addition to their famous localized surface plasmon resonance attributes, these nanoparticles exhibit a variety of unusual optoelectrical properties. In the visible electromagnetic spectrum, there is a significant absorption band shown by noble metals and alkali nanoparticles, for example, Cu, Au, and Ag, among others (Dreaden et al., 2012). Wastewater treatment procedures that have been employed in the past, the shape, size, and facet of metal nanoparticles synthesized during the synthesis process are all very important.

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Metal nanoparticles offer a wide range of uses in science and research because of their superior optical characteristics. It is standard practice to apply gold nanoparticle coating in SEM analysis to improve the electronic stream, which enables the acquisition of high-quality SEM pictures. Metal oxides of nanoscale size exhibit a variety of remarkable characteristics, such as a high elimination capacity and selectivity for heavy metals. It is believed that they offer considerable promise as promising heavy metal adsorbents. Among the metal oxide-based nanomaterials are manganese oxides, nanosized iron oxides, titanium oxides, cerium oxides, zinc oxides, magnesium oxides, aluminum oxides, and zirconium oxides, to name a few examples. Some of the most often utilized forms and uses of MONPs are depicted in Figure 5.5. As seen in Figure 5.5, this work only examines five different forms of MONPs and their uses in wastewater treatment. In terms of anti-bacterial activity as well as dye removal from wastewater, the shape, size, and aggregation of MONP are all important considerations. As a result, synthesis techniques are primarily concerned with the size, morphological arrangement, stability, and dispersion of the final product. This review study primarily focuses on antimicrobial activity (particularly anti-bacterial), adsorption, and photocatalytic degradation, with some consideration of other topics. When it comes to anti-bacterial activity, the cell membrane and wall are the most major defense barriers to bacterial resistance in the external environment.

Figure 5.5. Metal oxide nanoparticles are used in a variety of applications. Source: https://www.researchgate.net/figure/Common-applications-of-metaloxide-nanoparticles_fig5_348793693.

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Adsorption kinetics is critical in explaining the pace at which a solvent is absorbed and the amount of time required for adsorption. The use of linear and nonlinear pseudo-first and second-order kinetics is commonly used in adsorption kinetic investigations at different time intervals, as well as in other applications. Adsorption studies are conducted primarily to determine the influence of pH on initial contact time and removal efficiency. In addition, isotherms of adsorption are required to characterize the interactions of pollutants with adsorbent surfaces, and they are also required to describe how adsorbents are employed to maximize the usage of pollutant elimination through aqueous solutions.

5.4.1. Zinc Oxide Nanoparticles as a Disinfectant As a result of its great chemical stability and outstanding photocatalytic activity when it comes to eliminating contaminants from water, zinc oxide is considered to be a good photocatalyst. While at normal temperature, ZnO exhibits a broad bandgap (3.37 eV) and a high exciton binding energy (60 meV), both of which are important properties. There are many different ZnO nanostructures that may be generated, such as nanowires, nanosheets, nanorods, nanobelts, and complicated hybrid structures, among others. In particular, hollow spheres are a source of worry among these nanostructures because of their high light-harvesting competencies and significantly improved photocatalytic activity, along with their low density, large surface area, and excellent surface permeability. As a result of its physical and chemical features, including its super oxidative capability, high electrochemical stability, low toxicity, and low cost, ZnO has the potential to be a viable photocatalytic material for performing the photocatalytic activity. Therefore, among other metal oxides, zinc oxide is the earliest and most often utilized material for heterogeneous photocatalysis, and it is also the most abundant. However, despite the fact that the photocatalytic approach has various advantages, the presence of a fast recombinant photo-excited carrier in ZnO reduces the photocatalytic effectiveness and the production of photocurrent. A number of in-depth research are now being undertaken to alter non-metal additions and ZnO with metal in order to boost its optical and electrical characteristics in order to improve its photocatalytic activity. Because of its unique qualities, ZnO is regarded to be one of the most potent catalysts for the remediation of polluted drinking water. These properties are:

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• Low cost; • Abundance; • Nontoxicity. ZnO has a lot of potential in electro-mechanical nanoscale manufacturing, for example. Wurtzite has a hexagonal structure, which aids in the suitability and control of growth. Negative O surfaces and positive Zn surfaces combine to form electronic dipoles, which allow for the polarization of temperature and voltage in specific planes and directions of the surface. Although nanoparticles are not now considered pollutants, their water stability is critical in determining possible dangers since, in the future, water treatment facilities may have problems eliminating nanoparticles from the environment. The structure of nanoparticles can have an effect on their physical characteristics. In this way, the penetration, translocation, and reactivity of nanoparticles inside the plant might cause varied responses in different plants to similar nanoparticles (Rastogi et al., 2017). Barrios et al. (2016) demonstrated that capping nanoparticles have a greater influence on plant responses as compared to those exposed to bare nanoparticles in a plant experiment. Plants interact with water, air, and soil on a constant basis, and all of these elements may include designed nanoparticles (Figure 5.6) (Baruah et al., 2012).

Figure 5.6. Metal oxide nanoparticles come in five different varieties. Source: https://www.researchgate.net/publication/348793693_The_role_of_ some_important_metal_oxide_nanoparticles_for_wastewater_and_antibacterial_applications_A_review.

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Due to the fact that plants are also devoured by animals, it is possible that nanoparticles will be transported to them. Additionally, there is a potential that nanoparticles will enter the food chain and become harmful to humans (Gondal et al., 2011). A number of different processes are employed in the synthesis of ZnO. As seen in Figure 5.7, these approaches may be broadly classified into three categories: physical technologies, biological technologies, and chemical technologies. Chemical synthesis may also be classified into two categories: liquid-phase synthesis and gas-phase synthesis. In addition, high-energy ball milling, laser ablation, and physical, chemical, and solid vapor deposition can all be classified as physical synthesis techniques. It is also possible to separate physical synthesis into three categories: microbe-mediated, plantmediated, and waste materials (Jones et al., 2008; Sharma et al., 2019).

Figure 5.7. ZnO nanoparticles were synthesized using a variety of approaches. Source: https://www.hindawi.com/journals/jnm/2017/8510342/.

Baruah et al. (2012) conducted a thorough investigation of the potential of photocatalysis as a viable disinfection approach. As a photo catalyzer, a metal oxide that is capable of oxidizing contaminants in water and carbon dioxide is incorporated after being exposed to light energy, like, visible, and UV light. The electrons are created by a hole in the valence belt and a conduction band in the conduction band. It was discovered that photogenerated electrons and holes were produced during the breakdown of microbiological pollutants (Zafar et al., 2019).

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ZnO concentrations were found to be lower in an experiment reported in Bartram and Ballance (1996) than in previous investigations, including antibacterial action. This was allegedly attributed to the smaller particle sizes or the comparatively low protein/salt concentration of the growth medium (minimal Davis media), which prevented the thickening of nanoparticles from occurring. By including nanoparticles in the experiment, it was discovered that gram-positive Bacillus Subtilis was found to be greater than gram-negative bacteria. E. coli is a kind of bacteria (Yuvaraja et al., 2018). Jones et al. (2008) investigated the potential that a tiny quantity of UV or fluorescent light, which emits 4% of UV light, may activate zinc oxide in the lab. The findings demonstrate that environmental laboratory settings for ZnO nanoparticulate are enough for biocidal action and that the amount of biocidal activity is most likely dependent on the size of the nanoparticles. The findings suggest that ZnO may be employed as an anti-bacterial agent when exposed to visible light (Azizi et al., 2017). A thorough investigation of the elimination methods of industrial nanoparticles for water treatment has not yet been completed. Zhang et al. (2008) investigated the features of commercial MONPs Fe2O3, SiO2, NiO, and ZnO and deleted them based on their discursiveness, water stability, and other characteristics. Nanoparticles mix easily in tap water and silica, and they are not eliminated by ultrasonic or chemical dispersants, as is the case with larger particles. The amount of alcoholic material eliminated accounts for less than 80% of the total mass of nanoparticles removed from the sample. It has been observed that the behavior of MONPs in water is influenced by their physical characteristics as well as their interactions with other water components (Bottero et al., 2011). When three MONPs: ZnO, TiO2, and SiO2 were tested for stability in an aqueous solution, Tso et al. (2010) discovered that nanoparticles fast precipitate and aggregate into pure water. The use of ultrasonic effects to partition nanoparticles in water has proven to be the most effective way too far. The findings indicate that nanoparticles varied their stability when exposed to different water conditions. Because organic colloids (surfactants and humic chemicals) are present in water and wastewater samples, they agglomerate more quickly than pure water. This is consistent with the findings of Li et al. (2011), who discovered that in water, the toxicity of ZnO nanoparticles is influenced by water chemistry. Esmailzadeh et al. (2016) investigated nanocomposites made by combining low-density polyethylene and zinc oxide with Bacillus subtilis,

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a general Enterobacter aerogenes, and food spoiler bacterium, a pathogenproduced bacteria that may contaminate food and water. Anti-bacterial effects tend to be more significant in the case of gram-positive bacteria. The findings of the investigation also revealed a clear correlation between the anti-bacterial action and the concentration of ZnO nanoparticles in the composition (Cruz et al., 2018; Ahmad, 2019). Gram-positive (Bacillus subtilis) coatings and ZPN (ZnO polyurethane nanocomposite) Escherichia coli (gram-negative) with various concentrations of ZnO nanoparticles ranging from 0.1% to 2.0% ZPN coating anti-bacterial activity of bacteria were investigated in this study. In the study of El Saeed et al. (2015), it was discovered that gram-positive bacteria were more susceptible to gram-negative bacteria when exposed to 2% ZnO nanoparticles (Monsef Khoshhesab and Souhani, 2018). Motshekga and colleagues (2015) produced a nanocomposite in which silver and zinc oxide nanoparticles are manufactured and dispersed to chitosan on a bentonite-supported basis. The bacteria Enterococcus faecalis was employed to assess the anti-bacterial activity of the solution. Zinc oxide (ZnO) and Bentonite-chitosan nanocomposites comprising silver showed excellent anti-bacterial activity. In contrast, ZnO exhibited the most antibacterial activity, with a clearance efficiency of a minimum of 78% shown. It has also been hypothesized that the anti-bacterial action of nanoparticles is influenced by the abundance of bacteria in the environment (Baruah et al., 2010a, b; Premanathan et al., 2011). Adams et al. (2006) discovered that Escherichia coli and Bacillus subtilis are both bactericidal to ZnO nanoparticles. According to the findings of the investigations by Bartram and Ballance (1996), particle size does not alter anti-bacterial activity, and their activity on Bacillus subtilis is equivalent in light and dark conditions, although there is stronger light activity on Escherichia coli. At a concentration of 10 parts per million (ppm), Bacillus subtilis showed a 90% growth decrease. At 1,000 parts per million (ppm), only a 48% growth decrease in Escherichia coli was found (Li et al., 2013).

5.4.2. Copper Oxide Nanoparticles Even though the specific time period of copper’s discovery is unknown, it is believed to have occurred in the Middle East about 9000 BCE (Heinlaan et al., 2008; Ivask et al., 2010). Copper is the earliest metal known to humanity, having been utilized for sterilization of wounds and water by the Egyptians around 2000 BCE. Copper is the most abundant metal in nature. Copper

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offers a number of advantageous characteristics, including strong corrosionresistance, cheap cost, and anti-bacterial activity (Raghupathi et al., 2011). Copper (II) oxide is a semiconductor with a monoclinically organized crystal structure. It possesses a variety of beneficial chemical and physical properties, including superconductivity at solar energy efficiency, high temperatures, anti-bacterial action, cheap cost, and relative stability (Ren et al., 2009), among others. As a result of their excellent electrochemical properties, CuO nanoparticles are utilized in a variety of technological applications, including catalysis and the production of batteries. It is possible to create nanoparticles of various sizes and shapes utilizing a variety of processes, including high-temperature combustion, electrochemical techniques, sonochemical techniques, and novel rapid precipitation procedures (Eliseev et al., 2000; Dagher et al., 2014). The surface-to-volume ratio falls as the particle size increases, increasing the number of reactive sites. CuO’s electrical and optical characteristics are, as a result, significantly enhanced compared to their equivalents (Wang et al., 2002; Son et al., 2009). The consequence has been the development of several techniques for the production of CuO nanoparticles of various sizes. Reetz and Helbig (1994) generated highly distributed CuO nanoparticles by utilizing a sodium hydroxide and precursor as a reduction agent in a solution of sodium hydroxide. The CuO nanoparticles that were produced had an average size of 6 nm. It is possible to produce CuO nanoparticles with an excellent performance by using the solution’s plasma approach. The advantages of this technology are that it does not necessitate the employment of sophisticated apparatus and that the shape and size of the CuO nanoparticle may be regulated with relative ease. CuO nanoparticles are generated as an electrolyte, a copper cable cathode, and is a citrate buffer K2CO3 (pH: 4.8), with a voltage range of 105–130 V. The copper cable cathode is made of copper, and the electrolyte is made of citrate buffer K2CO3 (pH: 4.8). The diameter of the CuO nanoparticle blossom is less than 100 nm. With a decrease in the concentration of K2CO3 electrolyte, the size of CuO nanoparticle decreases. When voltages of 130 and 105V are employed, spherical, and porous spherical CuO nanoparticles are produced, and when the voltages of 105 and 130 V are employed, a porous spherical CuO nanoparticle is produced (Zhu et al., 2004). The presence of a copper oxide/hydroxide layer on Cu nanocube surfaces has been discovered to have a significant role in improving the

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electrocatalytic stability and activity of the hydrocatalyst. Other researchers have successfully used Cu2O nanotubes covered in graphene nanoscales (Cu2O/GNs), which are potential glucose and hydrogen peroxide sensors because they are very sensitive, enzyme-free, and have a long lifetime (Faúndez et al., 2004; Fathima et al., 2008). In recent years, copper oxide nanomaterial study has exploded due to the material’s fundamental compatibility, low-cost production methods, and outstanding electrochemical capabilities, all of which have led to a considerable increase in the material’s popularity. Copper oxide polymorphs include copper oxide (Cu2O) and copper oxide (CuO). Copper oxide polymorphs include two varieties of copper oxide (Cu2O) and copper oxide (CuO) polymorphs. These two oxides are the two most important stoichiometric chemicals in the CuO system. Copper oxide is a dark solid with a density of 6.4 g/cm3. It also has a melting point of 1,330°C and is insoluble in water. CuO is an intrinsic p-type semiconductor with a relatively small bandgap (1.2–1.85 eV) and a number of attractive properties that allow it to be used in a wide range of applications. CuO is a semiconductor with a relatively small bandgap (1.2–1.85 eV) and a number of attractive properties that allow it to be used in a wide range of applications. A variety of anions, cations, and neutral surfactants were utilized by Fathima and colleagues, including SDS, Triton X-100, dodecyl trimethyl ammonium bromide, and various quick deposition techniques, among others. CuO nanorods have been the subject of substantial research. The ion SDS has the greatest connection with cationic CuO nanoparticles, and this association is dependent on the negative charge of the surfactant. Other findings, on the other hand, indicate that surfactants play a crucial role in the formation and application of nanomaterials (Fathima et al., 2008). CuO nanoparticles have shown anti-bacterial action; however, just a few investigations have been undertaken on this topic. According to Wang et al. (2002), produced CuO nanoparticles have strong anti-bacterial action in contrast to meticillin-resistant Escherichia coli and Staphylococci aureus at low bactericidal doses. In spite of the fact that CuO, NiO, ZnO, and Sb2O3 nanoparticles all have an anti-bacterial impact on bacteria, CuO nanoparticles have been proven to be the most harmful on gram-negative bacteria such as Bacillus subtilis when compared to the other MONPs. CuO nanoparticles, on the other hand, have been shown to be more effective against Escherichia coli than gram-positive bacteria. With the use of bulk

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and nano-CuO, researchers evaluated the impacts of CuO on Vibrio fischeri, Daphnia Magna, and Thamnocephalus platyurus. The findings indicate that CuO nanoparticles are stronger anti-bacterial than CuO in bulk, which is consistent with previous research (Borgohain et al., 2000). CuO’s specific process of bacterial disinfection is still a mystery to scientists. Only a few possible mechanisms have been published, with one of these mechanisms being that the Cu ions produced by the nanoparticles come into touch with the bacterial cell membrane, causing damage to the bacterial cell membrane. Ruparelia et al. hypothesized that the Cu ions generated during the reaction might cause illness in the DNA spiral structure as a result of the ions’ interaction with the DNA molecules (Hong et al., 2002). The most recent method to be postulated is oxidative stress. ROS can be created by CuO nanoparticles, varying on the pace at which the CuO nanoparticles decompose, according to the findings of Ivask et al. (2010). ROS can cause damage to the bacterial cell structure (Tables 5.3 and 5.4). Table 5.3. Existing ZnO Nanoparticles Technologies and Their Use in Wastewater Treatment (Hong et al., 2002; Ivask et al., 2010) SL. No.

Year

Application

Characteristics

1.

2010

Photocatalytic degradation: methylene blue Antimicrobial activity: Escherichia coli

Particle sizes are 260 and 80 nm. Particle type: nanorods. The greatest inhibitory zone for Escherichia coli was 4.4 cm2. Methylene blue photodegradation was 93% under 963 Wm2 white-light irradiation, while methyl orange photodegradation was 35%.

2.

2012

Antimicrobial activity: Escherichia coli and Staphylococcus aureus

Surface area: Sample1 = 34.27 cm2, Sample2 = 47.54 cm2 and Sample3 = 39.12 cm2. Particle type: nanorods. Average particle size 5–7 nm. Escherichia coli and Staphylococcus aureus may be rendered immobile by sunlight in 99% of cases. Under room illumination settings, 80% of Escherichia coli and 59% of Staphylococcus aureus cells might be inactivated.

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3.

2010

Photocatalytic degradation: methylene blue

Average particle size 5–7 nm. Particle type: nanorods. Surface area: Sample 1 = 34.27 cm2, Sample 2 = 47.54 cm2 and Sample 3 = 39.12 cm2. Methylene blue’s photocatalytic activity was found to have increased by 8%.

4.

2011

Antimicrobial activity: Escherichia coli

Average particle size 19 ± 7 nm. The toxicity of nano-ZnO to Escherichia coli in the five mediums was as follows: phosphate-buffered saline > ultrapure water > NaCl > minimum Davis > Luria-Bertani.

5.

2006

Antimicrobial activity: Escherichia coli and Bacillus subtilis

Particle sizes 67 and 820 nm. Bacillus subtilis growth was reduced by 90% at a concentration of 10 ppm. At 1,000 ppm, Escherichia coli showed just a 48% decrease in growth.

6.

2011

Antimicrobial activity: Escherichia coli

Average particle size 20–40 nm. For anti-bacterial action, a high bacterial degradation rate (0.24 min1) was detected.

7.

2008

Antimicrobial activity: Staphylococcus aureus

Average particle size 84 nm. Nanoparticles with smaller particle sizes exhibited 95% growth inhibition at one mM concentration (0.008%), but nanoparticles with bigger particle sizes had only 40–50% growth inhibition at five mM of ZnO.

8.

2015

Antimicrobial activity: Escherichia coli and Bacillus subtilis

The ZnO nanoparticles demonstrated a clear inhibitory impact on the development of both Escherichia coli and Bacillus subtilis at a loading level of 2.0 wt.%.

9.

2015

Antimicrobial activity: Bacillus subtilis and Enterobacter aerogenes

Diameter and length of particle 400 and 50 nm. Both Enterobacter aerogenes and Bacillus subtilis may be inhibited by nanocomposites containing 2 and 4 wt.% ZnO. The nanocomposite containing four wt.% ZnO has a stronger inability impact.

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10.

2013

Antimicrobial activity: Escherichia Coli

A pH range of 5.7 to 8.7 had no discernible effect. Bacterial mortality dropped dramatically from 80 to 90% at pH 8.3 to roughly 10–20% at pH 8.7.

11.

2015

Antimicrobial activity: Enterococcus faecalis and Escherichia coli

Average particle size 86 nm. The maximum removal effectiveness was discovered to be 78%.

12.

2019

Adsorption: Cr(VI)

Average particle size 31 nm. Cr(VI) has the highest adsorption capability at pH 2. The adsorption capacity decreases as the pH value rises. At 50°, the maximal monolayer adsorption capacity was 139.47 mg/g.

13.

2011

Antimicrobial activity: Escherichia coli, Staphylococcus aureus, and Pseudomonas aeruginosa

Average particle size 25 nm. Gram-positive bacteria like Staphylococcus aureus had a stronger influence than gram-negative bacteria like Escherichia coli and Pseudomonas aeruginosa.

14.

2018

Antimicrobial activity: Salmonella typhimurium and Escherichia coli Photocatalytic degradation: methylene blue

Particle size between 2 and 50 nm. The Dubinin-Radushkevich model best suited the MB equilibrium data. Among 1.76 and 2.00 kJ/mol was the adsorption energy (E).

15.

2017

Adsorption: Pb(II)

Particle sizes 10.01 ± 2.6 nm The adsorption process was then followed by the pseudo-second-order model. At pH 5, the highest removal was found to be 93%. The process of adsorption was spontaneous and endothermic.

16.

2018

Adsorption: Acid black 210 (AB210) dyes and reactive blue 19 (RB19)

Average particle size 12 nm. Adsorption rate is fast, with equilibrium adsorption achieved after 15 minutes of shaking. The most effective pH for removing RB19 was 3. The pseudo-second-order model was followed by both dyes. Langmuir’s isothermal model was the best fit for the experimental data. RB19 and AB210 had the highest adsorption capacities of 38.02 and 34.13 mg/g, respectively.

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17.

2019

Adsorption: Azo dyes

Particle sizes 75–150 nm. At pH 6, ZnO-NPs in the quantity of 0.3 g demonstrated the highest dye removal effectiveness (40 ppm). Langmuir’s isothermal model was the best fit for the experimental data. The pseudo-second-order model was used to describe the adsorption process.

18.

2018

Adsorption: As(III)

The adsorption process was then followed by the pseudo-second-order model. At pH 7, the highest removal was found to be 52.63 mg/g. The process of adsorption was spontaneous and endothermic. Langmuir’s isothermal model was the best fit for the experimental data.

19.

2008

Antimicrobial activity: Thamnocephalus platyurus, Vibrio fischeri, and Crustaceans Daphnia Magna

Particle sizes 25–70 nm. L(E)C50 (mg l1) for nanoZnO, bulk ZnO, and ZnSO4 7H2O: 8.8, 3.2, 6.1 (Daphnia magna); 1.8, 1.9, 1.1 (Vibrio fischeri); and 0.24, 0.18, 0.98 (Vibrio fischeri), respectively.

20.

2019

Adsorption: Arsenic (As(V))

The typical particle width is roughly 7 nm, while the average length is around 80 nm. At neutral pH, the maximal capacity is 4,421 mg/g (7). Langmuir’s isothermal model was the best fit for the experimental data.

21.

2010

Antimicrobial activity: Escherichia coli

Average particle size 30 nm. Surface area (m2g–1) 12.9 Toxicity (30-min and 2-h EC50, mg compound l-1) of cCuO for E. coli AB1157 = 50.5 ± 15, E. coli JI130 = 39.7 ± 16, E. coli JI131 33.0 ± 1.9, E. coli AS393 = 47.6 ± 5.5, E. coli JI132 = 14.8 ± 0.1, E. coli AS391 = 11.4 ± 5.4

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Table 5.4. Methods for Making ZnO Nanoparticles in a Variety of Sizes Size (nm)

Preparation Method

References

1–10

Sol-gel

Eliseev et al. (2000)

3–5

Microwave irradiation

Wang et al. (2002)

3 and 5

Colloid-thermal synthesis

Son et al. (2009)

3–9

Alcohothermal decomposition of copper acetate

Hong et al. (2002)

4

Electro-mechanical synthesis

Borgohain et al. (2000)

4

Precipitation synthesis

Sahooli et al. (2012)

5–35

Microemulsion system

Han et al. (2008)

6

Alcohothermal decomposition of copper acetate

El-Trass et al. (2012)

7–9

Sol-gel techniques

Carnes et al. (2002)

10 to several microns

Sonochemical synthesis

Vijaya et al. (2001)

11–35

Precipitation pyrolysis

Rehman et al. (2011)

15–20

Solid-state reaction

Jia et al. (1998)

15–30

Thermal decomposition

Das et al. (2012)

20–30

Spinning disk reactor

Chang et al. (2011)

Nevertheless, the mechanism is only employed on Escherichia coli bacteria. Researchers have used a straightforward green synthesis technique to generate Cu2O nanoparticles in a red-colored cubic. Cu2O nanoparticles thermally oxidize to natural monoclinic CuO nanoparticles at 600°C. Copper oxide nanoparticles have demonstrated their usefulness in wastewater photodegradation and antimicrobial activities. The degradation of wastewater by BM and TE was found to be 91% and 90%, respectively. Although CuO inhibits the development of E. coli and Staphylococcus aureus, it is more efficient against Bacillus licheniformis and Pseudomonas aeruginosa (Han et al., 2008; Sahooli et al., 2012). Mousa et al. (2013) employed the fast precipitation approach to make CuO nanoparticles in the presence and absence of TOAB (tetraethylammonium bromide), a stabilizer for adjusting nanoparticle size. CuO-TOAB nanoparticles with stabilized nanoparticles have higher antibacterial activity than those without TOAB. When wastewater samples were evaluated at 25°C and 35°C, the surfactant activity of nanoparticles was astonishingly high (El-Trass et al., 2012).

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5.4.3. Silver Oxide Nanoparticles Silver oxide (Ag2O) nanoparticles are magnetic nanostructured oxide particles with a large surface area. Those are spherical or faceted. Silver oxide nanoparticles typically have a particle size of 20 to 80 nm and a surface area of 10 to 50 m2/g. Ultra-high purity, transparent, and high purity silver oxide nanoparticles are also accessible in dispersed and coated forms. They can also be disseminated in the AE nanofluid manufacturing group. In the solution, surface charge or surfactants technology is used to define nanofluids as suspended nanoparticles (Reetz and Helbig, 1994; Zhu et al., 2004). Nanocomposites, nanohorns, nanowhiskers, nanopyramids, and nanorods are examples of other nanostructures. Various nanomaterials have been described as anti-bacterial agents, including silver oxide nanoparticles, which have high anti-bacterial action and are now being investigated and employed for many commercial applications (Martinez and Silley, 2010). As illustrated in Figure 5.8, Ag2O nanoparticles have been manufactured utilizing a variety of processes that may be characterized as gas, solid, or liquid-phase approaches. Chemical and physical production techniques for Ag2O nanoparticles are well known (Nakamura et al., 2019).

A silver oxide nanoparticle aggregation was created by Jiang et al. (2015). Under both artificial and natural light, the synthesis demonstrated excellent photocatalytic activity. The results show that methyl orange (MO) decomposes fully in 40 minutes when exposed to near-infrared (NIR) light and in 120 seconds when exposed to sunshine, artificial UV light, or artificial visible light. Using Lippia citriodora plant powder, Li et al. (2019) presented a green combustion production of Ag2O nanoparticles. The Ag2O nanoparticles exhibit outstanding antifungal and anti-bacterial action against A. aureus and S. aureus. To make Ag2O nanoparticles, Shah et al. (2019) employed As a reducing agent, Paeonia emodi fresh extracts of leaves were used. In 180 minutes, the nanoparticles decreased methylene blue (MB) by 97.78%. Two grampositive and two gram-negative bacteria were used to investigate the antibacterial activity of the Ag2O nanoparticle. Gram-negative bacteria are inhibited by the Ag2O nanoparticles that were manufactured (Hu et al., 2006; Trinh et al., 2020; Parhi, 2021). To make Ag2O nanoparticles, Dharmaraj et al. (2021) employed Bacillus thuringiensis SSV1. The nanoparticles that were created were spherical and monodispersed. Staphylococcus aureus and Escherichia coli, Enterococcus faecalis, Proteus mirabilis, and Pseudomonas aeruginosa were all inhibited

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by silver oxide nanoparticles (Gram-negative). Using diverse plant extracts, Manikandan et al. (2017) demonstrated a green production of Ag2O nanoparticles. The nanoparticles were shown to have significant antibacterial action in contrast to Staphylococcus aureus (Carnes et al., 2002; Faúndez et al., 2004).

5.4.4. Titanium Oxide Nanoparticles Titanium oxide (TiO2) nanoparticles have been the most extensively investigated metal oxides in recent decades. TiO2 is the most outstanding photocatalyst to date due to its photostability, low cost, high photocatalytic activity, and chemical and biological stability (Guo et al., 2015; Guesh et al., 2016). Due to the UV stimulation and substantial bandgap energy (3.2 eV), charge separation inside particles is usually caused in TiO2. Since TiO2 nanoparticles have low selectivity, they can degrade a wide range of pollutants, including chlorinated organic compounds, polycyclic aromatic hydrocarbons (PAHs), dyes, phenols, pesticides, heavy metals, arsenic, and cyanide. TiO2 nanoparticles have photocatalytic capabilities that can destroy an extensive range of microorganisms, including gram-negative bacteria and gram-positive viruses, fungus, algae, and protozoa. Titanium oxide is utilized in a range of applications, including disinfectants and white pigments, food color taste enhancer additions, and organic compound breakdown. Anatase, rutile, and brookite are the three distinct crystalline forms of TiO2. Rutile and anatase in their pure form can be produced at low temperatures, making them ideal for the photocatalytic process. As illustrated in Figure 5.8, multiple techniques have been used to make TiO2 nanoparticles (Vijaya et al., 2001).

TiO2 nanometal is less costly than other nanomaterials and has strong chemical and thermal stability as well as minimal toxicity in humans. They are frequently utilized in anti-biofouling and wastewater purification, in addition to their photocatalytic capabilities. The fundamental benefit of TiO2 nanoparticles is that they have an infinite lifespan and do not degrade when exposed to bacteria or organic substances. Other advantages of TiO2, such as photo-induced hydrophilicity and strong oxidant power, make this membrane method appealing. The development of self-cleaning membranes can help to prevent fouling and sustain membrane water penetration. Several ways for producing TiO have been published in the literature.

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Researchers described two different TiO membrane preparation processes. First, eco-friendly chemistry is employed, in which a grafting polymerization process in the aqueous phase is employed in order to prepare integration to the surface of PAA-PVDF that has been previously made. Finally, PAA-PVDF membranes are resistant to UV light (Ohsaka et al., 2008). TiO nanoparticles (20 nm) were self-built on the surface of the hydrophone TiO2 colloidal suspension by dipping membranes in 0.05% WT per- of the membranes (160 W) has adhered on the surface of the TiO nanoparticles (20 nm), hydrophone TiO2 colloidal suspension was selfassembled on the surface of the hydrophobic PVDF membrane to fix TiO2 nanoparticles (Tables 5.5 and 5.6) (Jia et al., 1998; Rehman et al., 2011). Table 5.5. Methods for Dealing with CuO Nanoparticles That are Now Available, as well as Their Application in Wastewater Treatment (Fathima et al., 2008) SL. No.

Year

Characteristics

Application

References

1.

2008

Average particle size 9 nm. CuO was found to be beneficial in experiments with Escherichia coli and Staphylococcus aureus bacteria on a disc diffusion basis. Bacillus subtilis had the greatest sensitivity to CuO nanoparticles of all the bacteria tested.

Antimicrobial activity: Bacillus subtilis, Escherichia coli, and Staphylococcus aureus

Ruparelia et al. (2008)

2.

2019

Unannealed Cu2O, 300°C annealed CuO, and 30–90 nm nanoparticle sizes were measured for the unannealed Cu2O, 36–73 nm for the annealed CuO, and 30–90 nm for the annealed CuO. 600°C annealed CuO had the greatest degrading ability when tested in the presence of MB (methylene blue) (91%) and TE (textile effluent) (90%). CuO that had been annealed at 300°C had the most anti-bacterial activity against Staphylococcus aureus, Escherichia coli, Bacillus licheniformis, and Pseudomonas aeruginosa.

Photocatalytic degradation: TE (textile effluent) and MB (methylene blue) Antimicrobial activity: Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Bacillus licheniformis

Nwanya et al. (2019)

3.

2010

Average particle size 30 nm. Antimicrobial activity: Surface area (m2g–1) 12.9 Escherichia coli cCuO has a toxic effect on E. coli strains AB1157 and JI130, as well as E. coli, strains JI131 and AS391. The toxicity of cCuO was determined for E. coli AB1157, E. coli JI130, E. coli JI131, E. coli AS391, E. coli AS393, E. coli AS393.

Mousa (2013)

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4.

2018

Average particle size 61.7 nm. Bacillus cereus was shown to be more vulnerable to biosynthesized CuO NPs than any of the other pathogens that were studied. The best inhibition zone for Bacillus cereus was reported to be 25.3 x 1.80 when 100 (g/ml) CuO nanoparticle was used.

Antimicrobial activity: Bacillus cereus, Proteus mirabilis, Vibrio anguillarum, Staphylococcus aureus, Edwardsiella tarda, Aeromonas caviae, and Aeromonas hydrophila

Nabila and Kannabiran (2018)

5.

2015

Particle sizes in the range 7–12 nm. pH = 6 had the highest action against Enterococcus faecalis (92%), Fecal coliform (89%), and Total coliform (88%). pH = 7 had the lowest activity. It was discovered that increasing the pH after 6 lowered the rate of bacterial inhibition growth.

Antimicrobial activity: Total coliform, Fecal coliform, and Enterococcus faecalis

Mousa (2013)

6.

2014

Particle sizes in the range 5–8 nm. The antimicrobial activity of the CuO nanoparticle was determined by measuring its minimum inhibitory concentration (MIC), which was 0.15 mg/ml against Salmonella typhimurium, Klebsiella pneumonia, and Enterobacter aerogenes correspondingly.

Antimicrobial activity: Enterobacter aerogenes, Salmonella typhimurium, and Klebsiella pneumonia

Rani et al. (2014)

7.

2019

Particle sizes in the range 7–14 nm. The CuO nanoparticles MIC (minimum inhibitory concentration) versus Escherichia coli and Staphylococcus aureus was 3.75 mg/ml and 2.50 mg/ml, respectively, according to the results of the study.

Antimicrobial activity: Staphylococcus aureus and Escherichia coli

Javadhesari et al. (2019)

8.

2019

Particle size 190.93 ± 2.84 nm. CuO nanoparticles were shown to be an excellent anti-bacterial nanomaterial, suppressing the development of both Salmonella typhimurium bacteria and Escherichia coli by a large margin.

Antimicrobial activity: Escherichia coli and Salmonella typhimurium

Ahamed et al. (2014)

9.

2014

Average particle size 23 nm. The bacteria Enterococcus faecalis and Escherichia coli were shown to be the most sensitive to CuO nanoparticles. The bacteria Klebsiella pneumonia was shown to be the least sensitive.

Antimicrobial activity: Pseudomonas aeruginosa, Enterococcus faecalis, Escherichia coli, Proteus vulgaris, Klebsiella pneumonia, Shigella flexneri, Staphylococcus aureus, and Salmonella typhimurium.

Ahamed et al. (2014)

Metal Oxide Nanoparticles for Anti-Bacterial and Wastewater Applications

143

10.

2016

Average particle size 9 nm. The ideal conditions were determined to be an adsorbent dose of 0.5 g/l, a pH of 7, and a contact period of 30 minutes using this method. The isothermal Langmuir model proved to be the most accurate fit for the experimental data. The maximum adsorption capacity of BR 14 is 27.4 mg/g, while the maximum adsorption capacity of BV 16 is 16.8 mg/g. The adsorption procedure was performed once the pseudo-second-order model was completed.

Adsorption: basic violet 16 (BV 16) and basic red 14 (BR 14)

Naghizade Asl et al. (2016)

11.

2014

Average particle size 60 nm. CuO at a concentration of 0.5 mg/l killed 99.92% of 7,105 CFU/ml Bacillus anthracis cells in 30 minutes, which was the best effectiveness.

Antimicrobial activity: Bacillus anthracis

Pandey et al. (2014)

12.

2012

Average particle size 40 nm. The isothermal Langmuir model proved to be the most accurate fit for the experimental data. A spontaneous and endothermic adsorption event occurred throughout the adsorption phase. When the pH of the water was more than 8, 100% arsenic was eliminated.

Adsorption: Arsenic (As(V))

Goswami et al. (2012)

13.

2017

The adsorption procedure was performed once the pseudo-second-order model was completed. A spontaneous and endothermic adsorption event occurred throughout the adsorption phase. Freundlich’s isothermal model was found to be the most accurate for the experimental results. CuO nanoparticles demonstrated the greatest dye removal at pH 8 for MGO (83.4%) and pH 2 for MO (93.2%).

Adsorption: MGO (malachite green oxalate) and MO (methyl orange)

Kumar et al. (2017)

14.

2019

Average particle size 20 nm. At basic pH, it was discovered that removal effectiveness was 95%. (6).

Adsorption: Lead (Ii)

Naseem and Durrani (2021)

15.

2014

The average particle width is around 5 nm, while the average particle length is approximately 50 nm. A spontaneous and endothermic adsorption event occurred throughout the adsorption phase. At basic pH, it was discovered that removal effectiveness was 90% (9.0).

Adsorption: Pb (II)

Raul et al. (2014)

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Figure 5.8. Main synthetic methods employed with Ag2O nanoparticles. Table 5.6. Existing Ag2O Nanoparticle Production Technologies and Their Application in Wastewater Treatment are Discussed (Naseem and Durrani, 2021) SL. No.

Application

Characteristics

Year

1.

Anti-bacterial activity: Lactobacilli sp. and Streptococcus mutans.

Average particle size 42.7 nm. 2017 The highest doses of 250 g were observed to provide the greatest inhibitory zones against Lactobacilli sp. and Streptococcus mutans.

2.

Photocatalytic activity: MO (methyl orange)

Average particle size 8.33 nm. 2015 The surface area of 0.4726 m2/g The degradation of methyl orange by Ag2O under visible or UV light irradiation was complete in 120 seconds.

3.

Antimicrobial activity: Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa, Aspergillus niger and Candida albicans.

Average particle size 772 nm. 2014 The maximum inhibitory zone values were reported for Ag nanoparticle concentrations of 300 (g/ml).

Metal Oxide Nanoparticles for Anti-Bacterial and Wastewater Applications 4.

Activity: Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Bacillus subtilis Photocatalytic activity: Methylene blue antimicrobial

Average particle size 38.29 2019 nm. 97.78% of the Methyl blue was destroyed by Ag2O after 180 minutes of exposure to ultraviolet or visible light. More so than against grampositive bacteria, Ag2O nanoparticles have demonstrated a significant growth inhibition effect against gramnegative bacteria.

5.

Adsorption of MG (malachite green)

Particles with an average size of 55 nm. Adsorption capacity at its maximum is 90.909 mg/g. The Langmuir isotherm model was found to be the most accurate match to the experimental data. The adsorption procedure was performed once the pseudosecond-order model was completed.

2016

6.

Anti-bacterial activity: Escherichia coli and Staphylococcus aureus

Particle sizes in the range 10–20 nm. The anti-bacterial efficacy of the Ag2O nanoparticles produced versus Escherichia coli and Staphylococcus aureus at PH 5 and 7 was exceptional in comparison to previous studies.

2011

7.

Anti-bacterial activity: Staphylococcus aureus Photocatalytic activity: AO8 dye

Average particle size 20 nm. By the end of 180 minutes, about 95% of the AO8 dye had been destroyed by Ag2O. When tested against Staphylococcus aureus, the Ag2O nanoparticle demonstrated outstanding anti-bacterial activity.

2019

145

After adding 0.05 weight percent TiO to the acrylic acid monomer, an initiator and a cross-linking agent were added. The identical process was employed for the first procedure, and this reactive solution was immersed in PVDF membranes to create a barrier. Nanoparticles also serve as an efficient catalyst in a variety of oxidation processes. They have a high catalytic

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An Overview of Inorganic Compounds

sensitivity to pollution molecules and are capable of converting them into ecologically benign compounds. These nanomaterials have several distinctive qualities, such as a large nano size, strong reactivity, and surface area. TiO2 photocatalysis, in specific, is important in the elimination of different pollutants from surface water. Several scientists have used visible or UV light, undoped or doped nanoparticles, and non-metal/metal doping to photodegrade many kinds of pollutants like pharmaceuticals, organic pesticides, and organic dyes. Guesh et al. (2016) produced TiO2 nanoparticles as a contamination elimination substrate. Multiple metals (Zn, Cu, Ni, Cd, and Pb) were removed concurrently from San Antonio tap water and a pH eight solution using nanoparticles. Researchers used hydrothermal techniques to make TiO2 nanowire. Heavy metal residues (Fe3+, Cu2+, Pb2+, Zn2+, and Cd2+) were removed from polluted water using the produced nanoparticle (Figure 5.9) (Heinlaan et al., 2008).

Figure 5.9. Major synthetic techniques used for Ti2O nanoparticles. Source: https://link.springer.com/referenceworkentry/10.1007% 2F978-3-030-11155-7_9-1.

5.4.5. Iron Oxides Nanoparticles Iron oxide nanoparticles have been frequently employed to remove heavy metals in recent years due to their ease of usage and availability. Improved membrane characteristics, large surface area, high tensile strength, and tiny particle size are all advantages of iron oxide-based nanomaterials. Nano

Metal Oxide Nanoparticles for Anti-Bacterial and Wastewater Applications

147

adsorbents include magnetic magnetite (Fe3O4), nonmagnetic hematite (Fe2O3), and magnetic maghemite (Fe2O4). Because of the tiny size of nano sorbent materials, separation, and retrieval from polluted water are significant hurdles for water treatment. Fe3O4 and -Fe2O4 are, on the other hand, simple to extract and recover from the system. Both have been effectively employed as sorbent materials to extract various heavy metals from wastewater. As demonstrated in Figure 5.10, numerous approaches have been used to make iron oxide nanoparticles (Table 5.7). Table 5.7. Existing TiO2 Nanoparticle Production Technologies and Their Usage in Wastewater Treatment are Discussed (Naseem and Durrani, 2021) SL. No.

Year Characteristics

Application

1.

2011 The average particle size of nano TiO2 is 8.3 nm, Adsorption: Pb, Zn, Cu, while the average particle size of bulk TiO2 is Ni, and Cd 329.8 nm. The surface area of nano TiO2 is 9.5 m2/g, whereas the surface area of bulk TiO2 is 185.5 m2/g. Neither the nanoparticles nor the nanoparticles particles were depleted at pH 6, but at pH 8, no exhaustion occurred.

2.

2012 The TiO2 nanoparticles that were produced demon- Anti-bacterial activity: strated preliminary disinfection of Escherichia coli human pathogens and and human diseases. Escherichia coli

3.

2008 Particle sizes 25–70 nm. For TiO2 nanoparticles that were generated, Thamnocephalus platyurus exhibited greater sensitivity than Daphnia Magna.

4.

2013 Average particle size 10 nm. Photocatalytic activity: Surface area (m2g–1) 132. RhB (Rhodamine B) and 96.9% of 1 mol L–1 RhB was ionized at theoretical MB (methylene blue). pH 5.69, according to the results of an experiment. Both MB and RhB behaved in accordance with pseudo-first-order kinetics.

5.

2010 Particle size, on average, is 30 nm. Antimicrobial activity: 12.9 surface area (m2g1) of bTiO2 for E. coli Escherichia coli AB115720,000, E. coli J13020,000, E. coli JI13120,000, E. coli AS39320,000, E. coli JI132 = 94 12 and E. coli AS391 = 118 43. Toxicity (30min and 2-h EC50, mg compound l1) for E. coli AB115720,000, E. coli JI130

Antimicrobial Activity: Thamnocephalus platyurus, crustaceans Daphnia Magna, and Vibrio fischeri

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6.

2006 Average particle size 330 nm. The toxicity of the produced TiO2 on Bacillus subtilis was found to be greater than that of Escherichia coli.

Antibacterial activity: Bacillus subtilis and Escherichia coli

7.

2014 Average particle size 30 nm. The absorption efficiency of TiO2 was: Cu2+ = 75.24, Pb2+ = 97.6, Zn2+ = 35.18%, Cd2+ = 64.89 and Fe3+ = 79.77

Removal of heavy metal (Fe3+, Cu2+, Pb2+, Zn2+, and Cd2+).

8.

2018 The average particle size is 25 nanometers. The surface area (m2g1) is more than 14. The pH value of 8 resulted in the highest sorption effectiveness.

Elimination of Zn (II) and Sr (II) ions

9.

2005 Surface area 50 m2/g. Anti-bacterial activity: The photocatalytic peroxidation of Escherichia coli Escherichia coli cells was shown to be effective.

10.

2006 120 nm film thickness. Anti-bacterial activity: In visible light, the eradication of Escherichia coli Escherichia coli bacteria was 99.99% effective.

11.

2016 Average particle size 50 nm. 4-Chlorophenol (4-CP), Surface area (m2g–1) 53.3. phenol, and o-cresol are For 0.5 mM 4-CP (2.5 hours), a maximum degrada- all photodegraded under tion of 99% was reached, followed by 94% for ultraviolet light. 0.5 mM o-cresol (3 hours) and 97% for 0.25 mM chlorophenol (3 hours).

12.

2016 Average particle size 7.30 ± 1.70 nm. Photocatalytic activity: In under 60 minutes, UV irradiation destroyed 98% Methylene orange (MO) of the 10 ppm MO in the sample.

13.

2016 Particle sizes 6–14 nm. Removal of Cr(III) and Subsequent to exposure to sunshine, the material Cr(VI) had maximum removal effectiveness of 99.02% for Cr (total) in 60 minutes.

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Figure 5.10. Major synthetic techniques used for iron oxide nanoparticles. Source: https://www.sciencedirect.com/science/article/pii/ S2590182621000023.

Using alternative ligands (e.g., mercaptobutyric acid and meso-2,3dimercaptosuccinic acid) or polymers, nanoparticles containing iron oxides have been created to modify their adsorption capabilities. There have been claims of a flexible ligand shell that enables the inclusion of a wide range of functional groups while maintaining the characteristics of Fe3O4 nanoparticles. A polymer shell has also been discovered to reduce particle aggregation and increase nanostructural dispersion stability. Polymer molecules may act as metal ion binders, making them a “carrier” of metal ions from treated water. Due to its strong magnetic response, specific surface area, and elevated porosity, iron-based nanomaterials have lately demonstrated a remarkable sorption potential, resulting in an amazing sorption capacity. Because of their large BET surface area, super magnetic characteristics, and high pore volume, iron-based nanoparticles have gotten a lot of interest in recent years (Nguyen et al., 2016). The elimination of harmful heavy metals like Pb(II), Cu(II), and Cd(II)has been found to be efficient using various carob forms and paramagnetic particles (Fe2O3).

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CONTENTS 6.1. Introduction..................................................................................... 164 6.2. Energy Generation Applications....................................................... 169 6.3. Energy-Conversion Applications...................................................... 177 6.4. Energy Storage Applications............................................................. 184 References.............................................................................................. 190

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6.1. INTRODUCTION To achieve highly effective energy consumption, our civilization has been confronted with an increasing number of critical obstacles. Multifunctional nanomaterials have been gaining popularity in the realm of energy applications, and this trend is expected to continue. Electrical and thermal properties of materials play a critical role in a wide range of energy applications, including energy conversion, generation, transmission, and storage. Materials also have optical and catalytic properties that are important in energy applications. Triboelectric, piezoelectric, thermoelectric, catalytic, photovoltaic (PV), and electrochromic materials have all had significant influences on a wide range of energy applications at the nanoscale scale and beyond (Lee, 2011; Wang et al., 2021). Unique qualities of inorganic nanoparticles, such as their high thermal and electrical conductivity, chemical durability, and wide surface area, make them extremely viable in energy-related applications. In energy applications, a review of the most recent development and research of multifunctional inorganic nanomaterials has been provided in this chapter, which was written from the standpoint of various energy applications. Also included are demonstrations of the specific functions of inorganic nanomaterials to increase their performances and of the incorporation of nanomaterial functionalities into a device to improve the overall performance of the device. The restrictions imposed by scaling the relationships among energy devices and multifunctional inorganic nanomaterials, on the other hand, maybe traced back to the beginning of the process (Kennedy, 2014; D’Odorico et al., 2018). Energy, food, and water are always in need by humans. The history of human civilization is also the history of storing and harnessing energy in a variety of forms and applications. The world’s population is around 7 billion people now, and it is expected to expand to 9 billion by 2050, and then to approximately 10 billion by 2100. As the world’s population and economy continue to increase at their current rates, the global energy supply will be put under extra strain (Chu and Majumdar, 2012). According to the International Energy Agency, the world’s energy need will improve from approximately 12 billion t.o.e. in 2009 to either 18-billion-ton oil equivalents (t.o.e.) or 17 billion t.o.e. (ton oil equivalents) by 2035 under the new policy or existing policy circumstances, respectively. As a result of the present and future policies, carbon dioxide discharges are predicted to grow from 29 gigatons per year to 43 gigatons per year or 36 gigatons per

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year, respectively. Moreover, the evidence shown above demonstrates how human beings have become increasingly concerned about energy scarcity and environmental degradation, both of which are exacerbated by dwindling fossil fuel supply and rising demand. It follows thus that the new technology to take full advantage of copious “green” energy sources is being developed like thermoelectric energy, mechanical energy, and solar energy is a viable strategy for meeting our long-term energy needs while also achieving bearable environmental progress. Furthermore, the usage of energy in the 21st century must be environmentally friendly. It has been a foundation of the world’s expanding wealth and financial progress to have access to clean, affordable, and dependable energy (Figure 6.1) (Larcher and Tarascon, 2015; Wang et al., 2020).

Figure 6.1. Different energy uses, such as storage, conversion, energy generation, saving, and transmission, are highly reliant on the various functionalities of different types of materials. Nanomaterials such as piezoelectric, thermoelectric, photovoltaic, triboelectric, catalytic, and electrochromic materials have made significant contributions to a wide range of energy-related fields. Source: https://pubs.rsc.org/en/content/articlelanding/2020/nr/c9nr07008g.

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It is commonly understood that human existence is intimately linked to a wide range of energy uses, all of which are required to face the global problem of supplying abundant and future viable energy. The numerous energy applications involve applications for energy generation, conversion, saving, storage, and transport, among others. A broad range of functions in both the conventional and renewable energy industries are covered in this overview of the literature (Nozik, 1978; Zhang et al., 2017). The search for alternative sources of electricity generation to conventional fossil fuel combustion continues to be a hot issue for focusing on the growing need for energy supply. In this case, the harvester creates electrical energy from mechanical vibrations, light, and heat, among other things. In the following step, the electrical energy is corrected, acclimatized, and stored in batteries or capacitors for use in different applications, like, self-powered, and wireless sensors or low-voltage electronic circuits. Additionally, human society depends on energy conversion, which is defined as the transition of energy from forms given by nature to forms that may be employed by humans. Significant attention has been paid in recent years to various direct energy conversion technologies, most particularly solar cells and hydrogen fuel cells. Even though there are many different forms of renewable energy, including tidal, solar, wind, geothermal, and biomass, they are all fundamentally intermittent and cause significant variations in the power system when they are integrated into the grid (Lilliestam and Hanger, 2016). As a result, improved energy storage technologies are required to take full advantage of the diverse energy sources available. Clearly, we must dramatically enhance our ability to store energy before we can transition away from a fossil-fuel-based economy and toward one based on renewable technology. Batteries and supercapacitors have recently been the focus of a great deal of study. The fact that wind, solar, and hydroelectric energy sources are frequently located far away from densely occupied areas that are the customers for renewable energy utilization presents another significant challenge; as a result, electricity generated from these detached renewable energy bases is essential to be shared with cost-effective energy transmission structures (Figure 6.2) (Bonaccorso et al., 2015; Hochella et al., 2019).

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Figure 6.2. (a) The free-energy landscape for the production and interactions that determine the usual condition of nanomaterials in the environment is depicted in this conceptual representation. (b) Representation of the band model for chemical bonding among metal atoms in a schematic diagram. (c) According to the extent of delocalization of valence electrons in the metal cluster, there are corresponding energies levels of the valence electrons. Source: https://www.researchgate.net/publication/337361200_multifunctional_inorganic_materials_for_energy_applications.

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Material-based systems that are intended to fulfill numerous jobs through the sensible integration of distinct functionalities are known as multifunctional materials or multifunctional materials-based systems. They are supposed to provide system-level efficiency in addition to the efficiency of their individual elements. In general, its function can be performed in a concurrent or sequential manner, and it can be done on the same length scale or arranged in a hierarchical manner (Azmi et al., 2017; Chen, 2017). As seen in Figure 6.2, multifunctional properties of materials are frequently required by applications. These exceptional characteristics may include, among other things, unusual electrical, magnetic, and optical properties, which have the potential to have significant implications for medical, spintronics, electronics applications, and a variety of other devices. The integration of several functionalities into a single material system is a significant task. A system of this nature would have to be properly developed to accomplish numerous responsibilities using distinct functions in combination. Most of the time, every function provides a unique chemical or physical process that can result in system-level changes that go beyond the individual pieces. When it comes to battery electrode materials, good electrochemical reaction reversibility, strong electrochemical reactivity, low toxicity, and superior chemical stability are essential. Materials with unique characteristics are required for the battery’s enhanced functionality. As an instance, inflexible batteries, the electrode should have an adaptable function that permits the battery to keep its excellent performance even when it is bent to an extreme degree. High ionic conductivity is required in the electrolyte material of solidstate batteries to maintain the ion transport rate within the battery, which is not accessible in common solid materials. Piezoelectric, thermoelectric, PV, triboelectric, and catalytic materials have all made significant contributions to a wide range of energy applications at the nanoscale scale and beyond. With their distinct characteristics, including good thermal and electrical conductivity, a large surface area, and chemical stability, multifunctional inorganic nanoparticles are playing an increasingly important role in the development of innovative energy applications with improved performance (Chen, 2017). In energy generating applications, nanoscale materials have been shown to help almost quadruple the performance of thermoelectric materials by nearly doubling the size of the particles (Blackburn et al., 2018). Nano structuring is a cutting-edge approach for increasing the number of active sites in catalytic materials, particularly in energy conversion applications. Energy applications of inorganic materials are illustrated in further sections.

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6.2. ENERGY GENERATION APPLICATIONS Energy production, also called energy gathering, is the process of converting unusable types of energy, including mechanical motion and heat, into usable forms of energy that would otherwise be lost. This has the potential to make a significant contribution to resolving the difficulties associated with the anticipated fossil fuel shortfall soon, along with reducing emissions and hazardous waste released into the environment. The ways of energy creation discussed in this section include thermoelectric, piezoelectric, and triboelectric phenomena, among others. The execution of these ideas is dependent on the multifunctionality of the materials used in their construction. Across the past several decades, scientists have concentrated their efforts on the investigation of multifunctional materials, which has aided the advancement of the field of energy generation. Nevertheless, the device’s capabilities, such as its stability, conversion proficiency, and output voltage, are still insufficient to fulfill realistic expectations in these areas (Seh et al., 2017). It is only via the advancement of nanotechnology that we can begin to address these issues in a meaningful way. A wide range of properties of materials changes when their size is reduced to the nanometer range. These include thermal conductivity, electrical conductivity, mechanical quality factor, and dielectric constant, among others. These changes are caused by distinctive superficial and macroscopic quantum tunneling effects, bulk effects, and quantum dimension effects. Thus, multifunctional nanomaterials are extremely important in the field of energy generation and storage (Wang et al., 2020). It is important to notice that certain property characteristics are interdependent with one another. The diffusion of the majority carriers and electromotive extraction, whether electrons or holes, is the basis for most TE devices, and the carrier concentration has an impact on the parameters that may be optimized. As seen in Figure 6.3(b), the electrical conductivity of ZT materials rises as the carrier density enhances, which is advantageous for ZT materials in general. The coefficient of Seebeck, on the other hand, falls while the thermal conductivity rises, both of which are unfavorable to ZT. By adjusting the interdependence of S, and t, it is possible to get the highest possible ZT value for the material at a given temperature (Hochella et al., 2019). Traditional theory and tests have demonstrated that nanomaterials can provide significant enhancements to the ZT in a variety of applications. Hicks and Dresselhaus conducted the first theoretical investigation on

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thermoelectric nanoparticles in 1993, which was published in Physical Review Letters. Both quantum-confined nanomaterials and nanoscale interfaces, according to the researchers, would significantly improve the ZT (Shi et al., 2019; Zhang et al., 2021). As a consequence of these experiments, it was shown that nanoparticles had a substantially doubled ZT value compared to bulk materials. In addition to the various thermoelectric nanomaterials, chalcogenides, for example, bismuth telluride, lead telluride, and tin selenide, as well as carbon-based compounds, for example, fullerene, and carbon nanotubes, have demonstrated benefits and piqued the curiosity of many researchers (Figure 6.3(c)). Tin selenide (SnSe) has received a great deal of consideration since the innovation of its record ZT of 2.6 ± 0.3 at 923 K alongside the b-axis of a single crystal, which attracted the interest of the scientific community. Although single crystals of SnSe are well-suited for thermoelectric devices, they are not well-suited for thermoelectric devices owing to the unique requirements of crystal growth procedures, the potentially high cost of manufacture, and poor mechanical qualities. As a result, doped SnSe and polycrystalline have emerged as possible alternative contenders for single crystal applications. In this study, a thin layer of SnSe nanosheets was created by utilizing a straightforward thermal evaporation approach, and the resulting ZT was 0.05 at 501 K. In spite of the fact that the value was lower than that of the SnSe single crystal, it was the maximum ZT aimed at a SnSe film over 70 K that had been documented to date. A significant contribution to the exceptional thermoelectric performance was the hitherto unheard-of low κt, which was achieved largely through the lowering of the lattice component (Zhu et al., 2017; Tan et al., 2019). It has been demonstrated that the ZT of a p-type polycrystalline Cd-doped SnSe may be as high as 1.7 at 823 K when cation vacancies and localizedlattice engineering are used in conjunction, and this is approximately true (Heremans et al., 2013; Zhou et al., 2014). It is estimated that there is around 29% of the total available cation space in the sample, which contributes to a very high hole carrier concentration of approximately 2.6 × 1019 1/cm3, which in turn results in a very high S2 of approximately 6.9 μW/cm. K2. As a result of the doping of Cd, there were numerous nanoscale crystal flaws, including dislocations and intense local lattice distortions, as well as points of failure, which led to the material’s poor thermal conductivity (t) of roughly 0.33 W/ m. K (Luo et al., 2019).

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Figure 6.3. (a) Schematic representation of a TE module constructed from a thermocouple with n-type thermoelectric legs. (b) Schematic depicting the interaction of the different TE characteristics with the carrier density, illustrative of the difficulty in attempting to optimize the material ZT density. Singlewalled carbon nanotube systems have been studied in detail, and the forms of the individual curves have been derived from this research. (c) The optimum ZT values for various standard TE materials have increased over time. Source: https://www.semanticscholar.org/paper/Multifunctional-inorganicnanomaterials-for-energy-Wang-Liang/692cdfb05abae2d8af848f56a18d0280d 9a7cbca.

At medium temperature, PbTe is a state-of-the-art thermoelectric material that exhibits excellent conductivity. High band degeneracy and hence a respectable effective mass are guaranteed by the extremely symmetric crystal structure of the compound. It is due to the bond inharmonicity generated by the minor movement of thermal conductivity of the lattice Pb atoms may be preserved at a relatively low level in this system. To improve the thermoelectric performance of PbTe-based materials, a great deal of work has been put forward. Through the introduction of InSb multi-nanophases into the n-type PbTe matrix, it was possible to synthesize an InSb composite with a 4% lead content (Zhang et al., 2017; Kong et al., 2019). At 773 K, the sample PbTe-4% InSb yielded the greatest ZT of 1.83, which was recorded. The sample PbTe-5% InSb had the greatest average ZT, which was about 1.0, setting a record for n-type PbTe-based materials and setting a new world record. The simultaneous increase in S2 and decrease in t over the full temperature range resulted in the exceptional performance observed. In particular, the higher S2 was primarily owing to a considerably improved

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absolute Seebeck coefficient because of multiphase energy filtering results, and the lowered t may be explained in terms of phonon scattering due to the included multinanophases (Hou et al., 2020). A new n-type thermoelectric nanomaterial with Sb doping and GeTe alloying has been discovered. GeTe alloying resulted in an increase in the electron effective mass and bandgap, resulting in a significant increase in the Seebeck coefficient, which reached 280 volts per kelvin at 673°C. In the meantime, the high density of point defects caused by the supersaturated state resulted in a significant decrease in t, which was reduced to 0.56 W/m. K at 573 K. Furthermore, the production of nanostructures has the potential to improve the S2 and lower the t all at the same time. Thus, a ZT value of 1.38 was achieved at 623 K for the Pb 0.988Sb0.012Te-13% GeTe-nano, and a high average ZTavg value of around 1.04 was obtained in the temperature range between 300 and 773 K for the same material (Tan et al., 2017). Additionally, the increased TE act of anionic-doped PbTe nanoparticles has been observed, in addition to the enhancement of cationic doping. As an illustration, a high ZT of roughly 1.4 at 900 K was achieved in PbTe containing 1.25% Sb and containing 12% S injected via S. PbTe has a bandgap that has been expanded by the introduction of S, which suppresses bipolar conduction while increasing electrical conductivity and electron concentration. Moreover, point defects triggered second phase nanostructuring, which resulted in a significant reduction of the t to around 0.5 W m1 K1 at 900 K, resulting in a significant reduction of the t. In addition, by substituting S for Te, it was discovered that the Seebeck coefficient of PbTe increased, which was attributed to the greater effective mass of electrons in PbS compared to that of PbTe. All these modifications led to the overall enhancement of the ZT system (Xie et al., 2018).

6.2.1. Piezoelectric Materials When mechanically strained, some inorganic crystals, in which the charge centers of the anions and cations correspond with one another in their intact condition, are electrically polarized and deformed. Polarization charges emerge on the surfaces of the crystal in pairs that are diametrically opposed to one another, resulting in a voltage differential among the identical surfaces (MacLeod et al., 2017; Qu et al., 2021). Whenever this distorted crystal is coupled to an exterior load, the free electrons are compelled to travel via the exterior circuit to moderately screen the piezo potential and create a novel equilibrium condition, which is the energy generation method, as shown in

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the diagram. When treated to an electrical field, the same crystal shows the opposite action, causing mechanical strain or distortion in the crystal. The piezoelectric effect was discovered for the first time in 1880 by Pierre Curie and French physicists Jacques, who named it after their father, Pierre Curie. 21 of the 32 crystal classes lack an inversion center of symmetry, and 20 of these crystal classes can show piezoelectricity (Fan et al., 2016; Invernizzi et al., 2016). Barium titanate (BaTiO3), lead zirconate titanate (PZT), and Zinc oxide is examples of common piezoelectric materials (BaTiO3, BTO). An important factor in the functioning of a ZnO nanogenerator (NG) is the connection of the piezoelectric and semiconducting characteristics of the material (Figure 6.4).

Figure 6.4. (a) Atomic model of the wurtzite-structured ZnO. (b) The piezoelectric characteristics of the material, as well as the various piezo potentials in the tension and compression modes of the material, were investigated. (c) The piezoelectric potential distribution in a ZnO nanowire subjected to axial strain was calculated using numerical methods. Source: https://www.semanticscholar.org/paper/Multifunctional-inorganicnanomaterials-for-energy-Wang-Liang/692cdfb05abae2d8af848f56a18d0280d 9a7cbca.

Surface coating and plasma etching procedures were used in conjunction to improve Kevlar microfiber–ZnO nanowires composite construction tested for mechanical stability and reliability for use in a piezoelectric NG, resulting in a unique methodology (PENG) (Han et al., 2018). The hybrid structure made of improved microfibers and nanowires demonstrated

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excellent flexibility, toughness, and durability characteristics. Furthermore, the improved ZnO nanowires-covered fiber was beneficial in terms of increasing the permanence of the PENG structure. The PENG’s short-circuit current and open-circuit voltage was 4.8 pA and 1.8 mV, respectively, when the circuit was closed. Furthermore, after 3,600 seconds of operation, no degradation in the output performance of the improved PENG was observed (Zhang et al., 2017). According to earlier research, the majority of 2D transition-metal dichalcogenides (TMD) materials display piezoelectric capabilities, as opposed to their bulk parent crystals in the bulk state. Surprisingly, for monolayer MoS2 the computation of the piezoelectric coefficient indicated that the monolayer structure displayed a greater piezoelectric coupling than the bulk wurtzite-structured materials, which was in accordance with density functional theory. It has been proposed to use a sulfur-vacancy-passivated monolayer MoS2 PENG. By applying the S-treatment technique to the clean MoS2 surface, it was possible to efficiently passivate the S vacancies. The S vacancy site displayed a proclivity to form covalent bonds with S functional groups when exposed to oxygen. Because of the considerable study and development of high-performance piezoelectric materials since the 1950s, piezoelectric ceramics have played a critical role in the advancement of technology in a wide range of fields. PZT ceramics, which are outstanding piezoelectric materials and have been extensively employed in piezoelectric electronic devices, exhibit a wide range of electrical characteristics depending on how their compositions are customized using additives (Zheng et al., 2017; Wen et al., 2018). Nevertheless, in PZT ceramic materials growing environmental and health concerns about the toxicity of lead have prompted the quest for highperformance lead-free piezoelectric materials to replace lead-containing alternatives. In recent years, KNN ceramics have emerged as one of the most favorable lead-free options due to their relatively high overall performance and low toxicity. The alkali-oxide volatility and deliquescence, on the other hand, caused the piezoelectric characteristics of KNN-based ceramics to decrease. An improved piezoelectric coefficient (d33 = 570 ±10 pCN-1) was observed in a new (1-x-y) K1-wNawNb1-zSbzO3-yBaZrO3-xBi0.5K0.5HfO3 ternary system, which is the highest value yet recorded in KNN-based ceramics. Due to the coexistence of nanoscale strain domains (1–2 nm in size) and a high density of ferroelectric domain borders, the d33 value was found to be extremely high (>100) (Wen et al., 2018).

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6.2.2. Triboelectric Materials It has been known since antiquity that triboelectricity is an electrical phenomenon that occurs when two charged particles collide. When a charge separation happens because of contact, charge separation occurs. This includes the physical interaction of two materials having contrasted electrostatic characteristics, which results in the formation of a positively charged substance and a negatively charged material. If the components are separated later, a net potential difference exists between the two groups of materials. When the two triboelectric surfaces are separated, the electrostatic charges between them act as a capacitive energy device in terms of energy storage and transmission. Early electrostatic generators, like the van de Graaff generator “and the “friction machine, were developed because of this development (Ning et al., 2018). Triboelectric nanogenerators (TENG), which combine the triboelectric effect with electrostatic induction, were initially developed in 2012 and have since become widely used (Wu et al., 2019). Any material having a different charge affinity can theoretically be utilized to make a TENG, resulting in a large variety of materials at opposing sides of the triboelectric series that are able to excellent performance. On the surface of PVDF, the AgNWs were composited to serve as triboelectric layers, which resulted in the production of high-performance TENGs with low power consumption (Figure 6.5).

Figure 6.5. TENG theoretical models are presented here. (a) Schematic depiction of the first TENG and the cycle of operation that it goes through. (b) The displaced current model of a TENG operating in the contact separation mode. (c) The electrical circuit model of a TENG that is equivalent to the real thing.

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Source:https://www.researchgate.net/publication/337361200_multifunctional_ inorganic_materials_for_energy_applications.

Because of electrostatic interactions seen among dipoles of the PVDF chains and surface charges of the nanowires, the accumulation of AgNWs to PVDF encouraged the creation of the polar crystalline a-phase, which was previously seen. While this was happening, it was discovered that adding nanowires to the PVDF matrix improved the ability to trap the generated turbocharges. Due to the increased surface-charge potential and chargetrapping capacities of the PVDF-AgNW composite nanofibers, the TENG output performance was greatly improved. Aside from that, the PVDFAgNW composite nanofibers demonstrated remarkable mechanical stability in addition (Seung et al., 2017; Cheon et al., 2018). Triboelectric active materials with high surface charge densities have been developed as nanocomposite material systems, according to the findings. The ferroelectric copolymer matrix, poly, was combined with a BaTiO3, high dielectric ceramic material, to form a nanocomposite material with excellent electrically manipulated polarization, charge-trapping capability, and robust triboelectric charge-transfer attributes. This ferroelectric composite-based TENG generated 1,130 V of output voltage and 1.5 mA of output current under a pushing force of 6 kg-f at a frequency of 5 Hz, resulting in improved power-generating capability (Zhang et al., 2020). When it comes to practical applications, it is necessary to prevail over the interference of external conditions on the functioning of a TENG. Nanocomposite materials were created to improve the high-temperature resistance and wear resistance of TENGs. When it comes to tough settings, a TENG was developed that exhibited a different wear-resistant triboelectric material that was created by hybridizing a nanocomposite with an organic triboelectric layer. The coating was immediately applied to critical wearresistant components. In this experiment, the nano-sized aluminum balls impacted directly with the two PTFE sheets, increasing the amount of triboelectricity generated up and down. Using a low-friction of 8.1 N and room temperature, the researchers discovered that the nanocomposite exhibited excellent wear resistance, with a mean dynamic friction coefficient of around 0.69 m at the low-friction setting. This material exhibited good high-temperature tolerance, wear-resisting ability, and hardness, making it suitable for usage as a major supporting element in automotive brake pads, for example. Furthermore, it was discovered that the TENG production was 221 V, 27.9 A/cm2, and 33.4 C/cm2, with the voltage being 221 V, 27.9 A/cm2,

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and the current being 33.4 C/cm2. Another practical necessity is the ability to produce direct current. An older type of TENG transformed frictional energy into electricity by creating alternating current triboelectricity. However, this type of TENG was hampered by its low current density and the necessity for rectification, which made it inefficient. Using a sliding Schottky nanocontact, a continuous, direct current along with a maximum density of 106 A/m2 could be created directly without the need for an external voltage source, and this current could last indefinitely. A conductive atomic force microscope tip was used to slide across a thin sheet of molybdenum disulfide, which was also used to demonstrate the theory (MoS2). The anomalously high current density, according to the results of the finite element simulation, can be attributed to the nonequilibrium carrier-transport phenomena, which is facilitated by the substantial local electrical field (105–106 V/m2) at the conductive nanoscale tip (Peng et al., 2016).

6.3. ENERGY-CONVERSION APPLICATIONS 6.3.1. Solar Cells The internal photocurrent efficiency in solar cells, which is the portion of absorbed photons that are transferred into electrical current. The exterior quantum efficiency, which is the portion of incident photons that are converted into the energy conversion efficiency, and electrical current are the three most important figures of merit. While significant progress has been made in the field of PV devices, and more work must be done to significantly enhance the conversion efficiency of solar cells (Wang et al., 2017). Silicon has been the most frequently utilized absorber up to this point, and it presently dominates the solar-electricity gadget industry. P–n junction-based silicon PV devices, often known as first-generation solar cells, have the productivity of up to 25% and are among the most efficient PV devices available today. The advancement of second-generation PVs, which are based on thin-film technology, has been spurred by the need to boost the efficiency of solar panels. The productivity of second-generation PVs, on the other hand, is lower than that of silicon. 3rd generation PVs depends on the commercialization of developing technologies such as organic PV cells, dye-sensitized solar cells, and quantum dot solar cells. Perovskites are one of the materials that are being used in solar cells nowadays, and they have grown increasingly popular in solar cells throughout the world.

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Perovskites have risen to prominence in recent years as potential materials for highly efficient solar cells, flexible, and low-cost due to their high efficiency and flexibility (Wang et al., 2020). Despite their processing benefits, the poor strength of the perovskite materials in terms of humidity, oxygen, light, and heat must be solved before the technology can be commercialized on a large scale. cubic nanocrystals of CsYbI3 displayed significant excitation-independent emission as well as high photoluminescence quantum yields of 58%, indicating that they were excitation-independent emitters (Shi et al., 2020). Perovskite solar cells (PSCs) have advanced significantly in recent years, with power conversion efficiencies of over 20% currently being achieved by PSCs. A large part of this outstanding performance may be due to the distinctive features of perovskite materials, which include their strong absorption over a wide range of visible wavelengths and their long diffusion length (Li et al., 2018). Electron-transporting materials (ETM) employed in photonic crystals (PSCs) have a significant impact on their performance because of the differences in diffusion lengths between electrons and holes (hole diffusion lengths vs. electron diffusion lengths). With identical energy band positions and physical qualities to titanium dioxide, ZnO materials have substantially greater electron mobility than titanium dioxide, which might possibly increase the efficiency of electron transport and minimize recombination loss when used as an ETM (Dong et al., 2018). Firstly, ZnO has extremely high transmittance within the visible spectrum and, more significantly, is a very cheap cost material. Second, ZnO is a crystallization and doping agent that is simple to use. A layer structure in ZnO crystals results in distinct growth rates along with different directions at the same time. A variety of ZnO nanostructures may be easily created because of this process. It has been reported that triple cation perovskite based ZnO solar cells based on MA (methylammonium) and Cs (cadmium) co-alloyed FA (formamidinium) exhibit high efficiency. ZnO solar cells, along with a high crystallization of several cation perovskite absorbers, demonstrated high efficiency of more than 20% compared to conventional cells (McMeekin et al., 2016; Saliba et al., 2016). The open-circuit voltage of the produced perovskite cells was 1.2 V, and the power conversion efficiency (PCE) was 14.7% on 0.715 cm2 cells, according to the researchers. Four-terminal tandem cells with a 25% efficiency might be created by merging these perovskite cells with a silicon cell with a 19% efficiency, according to the researchers. The insertion of rubidium cations into the PSC increased the performance of the PV system

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(Aristidou et al., 2017). A stable efficiency of up to 21.6% was reached on tiny areas, as well as electroluminescence of 3.8%. When perovskite films based on CH3NH3PbI3 were exposed to oxygen and light, the films quickly degraded (Peiris et al., 2017). The rapid oxygen diffusion into CH3NH3PbI3 films was followed by the photo-induced production of highly reactive superoxide species, indicating that the films were highly reactive. Perovskite films comprised of tiny crystallites produce higher yields of superoxide but have lesser stability than larger crystallite films. Iodide vacancies were shown to be the preferred locations for the photo-induced production of superoxide species from oxygen in ab initio simulations, indicating that this is the case. The hole-conducting property of NiO in printable PSC was increased by using an N2 blow-drying approach. In terms of PV performance, the best-performing device displayed an open circuit voltage of 0.97 V, a phenomenal short-circuit current density of 22.38 mA/cm2, and a fill factor of 0.50, leading to a photoconversion efficiency of 10.83% (Wang et al., 2017). The PCE of a solar cell based on this Sb2S3 film was 4.3%, which is the highest figure recorded in solution-processed planar heterojunction solar cells depending on Sb2S3 films to date (Xi et al., 2017). Under low temperatures, partial exchange of FA+ by MA+ can result in the formation of the phase, which is favorable to the stability of perovskites. Furthermore, by partially substituting FA+ with a Cs+ (cesium cation), the stability in contrast to light illumination and moisture may be significantly increased; the stability can be further improved by using a combination of three cations: FA+/MA+/Cs+. Inverted solar cells depending on perovskite were grown atop CuSCN-mediated nanostructures, resulting in extremely high efficiency (Zhang et al., 2017, 2021). First, using a mild electrodeposition approach at room temperature and three distinct CuSCN nanostructures, we attached them to PSCs with a reversed heterojunction as p-type inorganic hole-transport layers. A bication lead iodide 2D perovskite component might be used to stabilize the inorganic -CsPbI3 perovskite phase in high-efficiency solar cells by reducing the amount of bication lead iodide present. However, under normal environmental circumstances, the phase instability of -CsPbI3, which has the largest bandgap for tandem solar cell applications, is a source of concern. A tiny quantity of 2D EDAPbI4 perovskite, including the EDA (ethylenediamine) cation, might be used to stabilize -CsPbI3 to prevent the creation of the nonperovskite phase, which would otherwise be undesired. Cesium doping might be used to create a stable, high efficiency 2D PSC structure. The PCE of Cs+Doped 2D

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(BA)2(MA)3Pb4I13 PSC was as high as 13.7%, which was the maximum among the described 2D devices, and it had outstanding humidity resistance (Zhao et al., 2017; Guo et al., 2019). For solar cells, the use of cationtransmutation to create stable inorganic Pb free halide perovskites may be a viable solution to the primary problem of low device stabilities coupled with inherent material instability in these materials. The objective here is to transfer two divalent Pb2+ into one trivalent M3+ and one monovalent M+, in a double-perovskite structure, resulting in the formation of a diverse class of quaternary halides, which may then be used to make other materials (Zheng et al., 2017). The presence of ionic defects on the surfaces and grain boundaries of organic-inorganic halide perovskite films are harmful to the efficiency and stability of PSCs, as well as the stability of PSCs. As a result, in hybrid PSCs, the use of quaternary ammonium halide anions and cations led to the development of defect passivation technology (Bashir et al., 2018). It is possible that an inorganic interlayer of spinel cobaltite oxides (Co3O4), which suppresses charge recombination and extracts holes effectively, might significantly improve the performance of carbon-based PSC. The chargecarrier recombination and transport mechanisms at the carbon–perovskite interface limit the amount of PCE that may be produced. When compared to conventional carbon devices, the devices with the screen-printed Co3O4 interlayer had a PCE of 13.27%, which was 18% higher than devices with the typical carbon interlayer (Han et al., 2018). A monolithic perovskite/ Cu(In, Ga)Se2 tandem solar cell with a 22.43% efficiency was developed using Cu(In, Ga)Se2. The efficiency of non-encapsulated devices operating in ambient circumstances after 500 hours of aging under constant 1-sun illumination was found to be 88% of their initial efficiency (Hu et al., 2018). The current density of nanostructured CuInS2 PV devices is a significant factor in restricting the performance of these devices, which highlights the poor charge-carrier transport in CuInS2 nanoparticle films (Kang and Cho, 2020). It is common to use ZnS as the shell material for CuInS2 core passivation since it has the advantage of increasing the photoluminescence quantum yield from the CuInS2 nanoparticles by a factor of two or three. The substitution of a monovalent Ag cation for the normal divalent Zn cation surface termination results in minor increases in charge-carrier transport across nanostructured films. As a result of the surface termination, CuInS2 nanoparticles are exposed to lower-energy electronic states directly on their surfaces, lowering charge-carrier restraint and boosting the charge-carrier mobility among them.

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In recent years, it has been established that halide perovskites with a typical structural formula of ABX3 are potentially useful. Inorganic halide perovskites are gaining in popularity because of their increased stability in the presence of moisture, sunlight, and high temperatures. Organic halide perovskites are composed of inorganic A-site cations, like Cs+ and organic halide ions. These inorganic halide perovskite nanoparticles have a controlled shape and optoelectronic characteristics that may be tuned, as well as increased quantum efficiency (Li et al., 2019).

6.3.2. Fuel Cells Fuel cells use oxygen or other oxidizing agents to transform chemical energy from a fuel into electricity. Their advancement is linked to the creation and storage of hydrogen. The incorporation of fuel cells in electronics several obstacles face: I find electrodes suited for flexible electronics; (ii) replacing costly noble metals, for example, gold, ruthenium, platinum, and their alloys as electrocatalysts; and (iii) avoiding metal electrode poisoning. Ahead of fuel cells can be regarded as a significant technology for energy conversion in electronic devices; a new class of materials with high efficiency, low cost, and durability must be developed to address these challenges. Because of its great efficiency and lack of pollution, fuel cells are currently gaining a lot of interest as an alternative energy source (Figure 6.6) (Qiao et al., 2018; Chen et al., 2019).

Figure 6.6. Schematic depicting the construction of certain common inorganic halide perovskite crystal structures (ABX3), their transformation into diverse nanostructures, and finally their integration into numerous applications. Source: https://pubs.rsc.org/en/content/articlelanding/2020/nr/c9nr07008g.

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DMFCs and PEMFCs are widely regarded as the most promising fuel cell technologies for usage in portable devices, for example, cellular phones, laptop computers, and personal digital aides, because of their low operating temperature and high-power density. 46 Because of their high catalytic activity, nanoparticles made of platinum with their alloys have traditionally been utilized as catalysts in fuel cells (Shujin et al., 2021). However, one of the major roadblocks to the commercialization of DMFCs is the expensive cost of the catalyst. As a result, one of the key goals of scientists is to improve platinum’s catalytic performance while simultaneously reducing the amount of catalyst required. To boost the performance of the catalyst, one option is to utilize a supporting material. Catalytic supporting materials in fuel cells must be stable and consistently disseminated (Mahmood et al., 2015; Speirs et al., 2015). Due to their strong electric conductivity and inexpensive cost, researchers have discovered that innovative nanostructured carbon materials may be employed as improved catalyst supports in fuel cells in recent years. Various nano-architectures have demonstrated good potential to accelerate the slow cathodic and anodic processes, with a variety of sizes, shapes, compositions, and structures (Zang et al., 2020). A surfactant-assisted metalorganic framework technique was used to create an anatomically dissolved Co-doped carbon catalyst along with a core-shell configuration. With a halfwave potential of 0.84 V vs. the RHE, the catalyst demonstrated remarkable oxygen reduction reaction (ORR) activity as well as improved stability in corrosive acidic conditions (Choi et al., 2015; Sun et al., 2020).

6.3.3. Fuel Cells: Solid Oxide Electrolysis Cells (SOECs) A solid oxide electrolysis cell (SOEC) is a device that utilizes and transforms electrical energy form passing electrons to chemical energy of the fuel. In a typical SOEC, gas is fed to the porous cathode and when required electrical potential for water splitting is supplied to the SOEC electrodes, water molecules will dissociate to form hydrogen gas in the cathode and oxygen gas in the anode ( see Figure 1).

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Figure 6.7. Hydrogen production by High Temperature Steam Electrolysis by Solid Oxide Electrolysis Cell (SOEC) (Mendoza,

The electrochemical half-cell reactions in the SOEC are the steam electrochemical reduction, 𝐻2𝑂 +2𝑒− → 𝐻2 + 𝑂2−





(1)



(2)

and the oxygen synthesis: ½ 𝑂2− → 2𝑒− + ½ 𝑂2





This is achieved by the flow of electrons from the anode to the cathode by means of an external power source. The electrolyte conducts the charge carriers from the cathode to the anode. Oxygen ions are drawn through the electrolyte by an applied electrochemical potential. The ions liberate their electrons and recombine to form molecular 𝑂2 on the anode side.

High temperature steam electrolysis (HTE) on the other hand is an environmentally acceptable process for hydrogen production in the growing hydrogen markets [8]. In high temperature steam solid oxide electrolysis, gas in the form of steam is fed in the SOEC at ideal temperatures of 800 - 1000˚C. The high temperature of steam as the feed stream is expected to consume less electrical energy as compared to those performed at lower temperatures. In this process, energy is supplied in the mixed form of electricity and heat which makes it cheaper than consumption of pure electrical energy. The high temperature accelerates the reaction kinetics reducing energy losses.

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Theoretically, electrolysis is the decomposition of water into hydrogen gas and oxygen gas and takes place when current is passed through at a standard potential difference of -1.23 V. Water electrolysis has no side reactions that can yield undesired by products, therefore, the net balance is: H2O → ½ O2 + H2





(3)

However, real electrolysis of water in SOECs requires higher voltages for the reaction to take place - which is definitely higher than -1.23 V. This part is known as overpotentials or overvoltage. Numerous literature have mentioned that overpotentials can be attributed to resistance to the transport of reactant species approaching the reaction site and the transport of product species leaving the reaction site; also, it can be in terms of the behavior and activity of the electrodes as the transport of materials takes place, on top of the effects being exerted by the electrolyte material during the electrochemical process. The success of hydrogen production and energy relies on the efficient development of hydrogen technology. Most research works done on SOEC today is in the experimental level with emphasis on new materials to cope with the system requirements such as operating temperature, material make-up and stable operation.

6.4. ENERGY STORAGE APPLICATIONS One of the most promising approaches to alleviate the present energy problem, as well as worldwide environmental issues, is to create renewable energy storage systems. Exploration of appropriate active materials is a critical component in the development of low-cost, highly stable, highly efficient, and environmentally acceptable energy storage systems (Duan et al., 2019). Future research should focus on nanomaterials with a large specific surface area to close the gap among the realized and predicted capacitance without restricting the loading mass. 103 Supercapacitors and batteries, as well as other electrochemical energy storage technologies, are essential for allowing renewable but intermittent energy sources like wind and solar (Shui et al., 2015; Sial et al., 2018). In supercapacitors, charge is held just at the surface and is not restricted by diffusion processes, allowing for high power. Supercapacitors are also more adjustable and have a longer cycle life since discharging and charging do not need a bulk-phase change. 105 In comparison to supercapacitors, batteries store charge due to redox processes in the

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mass phase of electrode materials, which results in a higher energy density but inferior power performance. In recent years, the need for efficient rechargeable batteries has become so visible and pervasive that its myriad requirements and functions have almost become ordinary knowledge (Mori et al., 2018).

6.4.1. Supercapacitors Supercapacitors have a high charge-discharge rate, a high energy density, and a long cycle life, making them a good bridge between secondary batteries and regular capacitors. Supercapacitors store energy by redox processes or ion adsorption, with most of the charge transmitted at or near the electrode material’s surface. Supercapacitors are suited for applications that require a high-power density of a minimum of 10 kW kg-1, which is a factor of 10 higher than lithium-ion batteries. Because of the enormous specific surface area of carbon dots (CDs), the electrochemical performance of regular supercapacitors depending on carbon materials can be significantly increased when hybridized with CDs (Yang et al., 2020). Xue’s group produced novel colloidal electrode materials that may offer better specific capacitance than electrical double-layer capacitors and standard pseudocapacitors (Gentil et al., 2017; Zhao et al., 2021). In colloidal supercapacitors, the electrode materials were produced in situ, using chemical and electrochemical aided coprecipitation to change transition metal salts and rare commercial earth in alkaline electrolyte. Multiple-electron faradaic redox processes may be used in these colloidal supercapacitors, resulting in ultrahigh specific capacitance, frequently more than one-electron capacitance. Ce3+, Yb3+, Er3+, Fe3+, Mn2+, Fe2+, Co2+, Ni2+, Cu2+, Sn2+, and Sn4+ are among the multiple-valence metal cations employed in these developed colloidal supercapacitors. Colloidal supercapacitors appear to be attractive possibilities for next-generation high-performance devices (Lin et al., 2018; Qin et al., 2018). In situ electrochemical activation of a NiCl2 electrode has also been used to create highly electroactive Ni-based colloidal electrode materials. At a current density of 3 A g-1, the activated Ni-based electrodes had the maximum specific capacitance of 10,286 F g1, suggesting that a threeelectron faradaic redox reaction (Ni3+ Ni) happened. The charge-transfer resistance was observed to decrease with potential cycling and continuous potential activation. Multiple electron reactions have been found to be an

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effective way to boost the energy density of supercapacitors by activating and using them. Cu2+ →Cu + e- redox reaction was quick and reversible in water-soluble CuCl2 electrodes, and they had a very high specific pseudo capacitance of around 5,442 F/g. The Cu2+ was shown to be responsible for the higher value. The CuCl2 electrode’s chemical and crystallization transformations were discussed. For tin chloride salt pseudo capacitors, an in-situ crystallization process was established. Highly active SnO/Sn colloids were in situ crystallized inside the black carbon matrix after experiencing combined electrochemical/chemical crystallization and faradaic redox processes. This electrode design allowed for quick ion/electron transport and efficient use of the salt electrode’s active tin cations (Li and Van Nguyen, 2018). In supercapacitors, rare earth elements have also been used. The direct usage of commercial Ce(NO3)3 as electrode material in KOH electrolytes resulted in an ultrahigh-specific capacitance of 2,060 F/g without any extra processing. Ce3+/Ce4+ has the potential to provide a highly practical specific capacitance that is near to its theoretical value. A commercial ErCl3 salt electrode in an alkaline aqueous electrolyte was used to show a novel ErCl3 alkaline aqueous pseudo capacitor device. The material’s synthesis took place on the same geographical and chronological scale. An electricfield-assisted chemical coprecipitation of ErCl3 in KOH aqueous electrolyte resulted in highly electroactive ErOOH colloids being crystallized in situ. These ErOOH colloids immersed in carbon black and a PVDF matrix was extremely redox-active, with an 86% cation utilization ratio and a certain capacitance of 1,811 F/g, surpassing the one-electron redox theoretical capacitance (Er3+/Er2+). Figure 6.7 shows the electrochemical performance and manufacturing technique. In alkaline electrolytes, YbCl3 pseudo capacitor electrodes were produced, revealing a high cation utilization ratio. Faradaic redox and chemical coprecipitation reactions crystallized the electrochemically reactive YbOOH colloids (Wei et al., 2019).

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Figure 6.7. The ErCl3 pseudo capacitor’s electrochemical performance and construction technique. Source: https://europepmc.org/article/MED/31808494. Note: (a) Charge/discharge curves for varied current densities and 0.55 V potential range. (b) Depending on the weight of ErCl3.6H2O Er3+ ion. (c) The manufacture of the ErCl3 pseudo capacitor in situ is depicted in this schematic illustration. The electrode was first made using commercial ErCl36H2O salts in a slurry-coating manufacturing process.

The electrochemical behavior of the YbCl3 pseudo capacitor was investigated in relation to crystallization kinetics. The specific capacitance of the YbCl3 pseudo capacitor was 2,210 F/g, which was extremely high (Guo et al., 2019).

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6.4.2. Batteries For energy storage, the battery is an important component because, in the form of chemical energy, it can store electrical energy and subsequently release it via reverse electrochemical processes. Batteries have seen extraordinary progress in both research and commercialization over the last few decades (Wang et al., 2018). Increasing pressures on batteries are being placed on batteries because of frequent difficulties and social advancement. As a result, improved batteries must have a higher energy density, higher power density, longer cycle life, and greater safety. In the meantime, comfort, and convenience are other areas of battery development since they must be lightweight, wearable, and flexible. Negative and positive electrodes, a separator, and an electrolyte are all important parts of a battery. Inorganic nanoparticles are becoming increasingly important as electrode materials to meet the aforesaid requirements (Wu et al., 2020). The ion insertion/extraction process is used to store energy in the battery. Consider a lithium-ion battery: through the discharging process, the cathode material is oxidized, causing lithium ions to be extracted from the electrode bulk phase. Simultaneously, in the anode material, a reduction process occurs, causing the lithium ions in the electrolyte to produce an alloy or a metal. On both electrodes, reversible processes take place during the charging phase. As a result, the electrode reactions are determined by the electrode material’s functions, particularly its ionic and electronic conductivity. Electrode materials with efficient ion migration pathways, high electronic conductivity, and many reactive sites have a high-capacity potential. Furthermore, ion insertion/extraction deforms the structure of electrode materials, causing volume changes or even collapsing the channels, resulting in capacity loss (Ghausi et al., 2018). Previous research has found that shrinking materials to the nanoscale exposes more active sites, allowing the electrode capacity to approach the theoretical value. On the capacity of lithium-ion batteries, the influence of the size of the manganese dioxide electrode was examined by Xue et al. MnO2 includes two forms of Mn centers: one is the effective Mn center, which may participate in faradaic reactions, while the other is incapable of contacting the electrolyte. The fraction of effective Mn centers in the faradaic reaction determines the specific capacitance of MnO2. The link between effective Mn and particle size was determined. Effective Mn rose

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dramatically when particle size was reduced to a few nanometers, according to their findings. When the MnO2 size was < 1 nm, effective Mn was equal to 1, suggesting that the specific capacitance of MnO2 should reach its theoretical value. Calculations can also differentiate the charge storage mechanism in insertion/extraction or adsorption/desorption processes (Wu et al., 2015). Mendoza (2022) in her short discussion on batteries explained that Electricity or electrical energy of the battery is produced because of the transfer or movement of electrons from one point to another. In a battery, these electrons are transferred by the reversible electrochemical reactions simultaneously taking place, repeatedly in the anode and the cathode coined as reduction and oxidation reaction. During the charging process, an external power source is attached to the battery to initiate the transport of electrons by attracting these electrons towards the positive terminal and travels towards the negative terminal to reach the conductive layer. The electrons flow through the external circuit since they cannot flow through the electrolyte. Simultaneously, the positive lithium ion is then attracted to the anode surface through the electrolyte. The battery achieves the full state of charge when all the electrons are transferred to the other side and all the lithium metals are inserted into the anode. During discharge energy is taken from the battery. This happened when the external power source is removed and replaced by a load, say a flashlight. The lithium ion attracted onto the conductive layer of the anode eventually moves back to the cathode passing through the electrolyte. At the same time electrons are transferred from the anode to the cathode creating current passing through the flashlight (electricity is generated). This process takes place until all lithium ion moved back to the cathode – the battery now reaches its full state of discharge. It is noteworthy to remember, that there is no charging process in primary batteries. When a primary battery reaches its full state of discharge, they are then discarded (or sent to recycle plants). Also, these processes must be maintained within the desirable temperature window to avoid degeneration of the electrolyte which will allow contact between anode and cathode materials and leads to safety issues. To ensure safety, a separator is used which ensures that anode and cathode materials are isolated from each other.

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CHAPTER

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APPLICATIONS OF INORGANIC SEMICONDUCTING MATERIALS IN ELECTRONICS

CONTENTS 7.1. Introduction..................................................................................... 200 7.2. Bottom-Up Techniques.................................................................... 201 7.3. Top-Down Approaches.................................................................... 204 7.4. Mechanics....................................................................................... 208 7.5. Epidermal Electronics...................................................................... 209 References.............................................................................................. 218

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7.1. INTRODUCTION Development in the deterministic assembly and synthesis of developed groups of single crystalline inorganic semiconductor nanomaterial has laid the groundwork for the development of high-running electronics on malleable and even elastomeric substrate during the last several years. The findings enable the development of classes of systems that possess features that are not possible to replicate using standard wafer-based technologies. Electronic devices that depend on the extraordinary constructs/forms/ shapes of these semiconductors can provide mechanical properties, for example, stretchability, and flexibility, that were previously thought to be only accessible through comparatively low-performance organic materials, while also exhibiting superior operational characteristics because of their exceptional charge transport features, according to the authors. The incorporation of high-functioning electronic functionality on a variety of curvilinear geometries, along with linear elastic mechanical reactions to significant strain deformations, is particularly relevant in bio-inspired designs and bio-integrated devices, as well as other applications. This chapter provides an overview of current developments in flexible electronics relying on inorganic semiconductor nanomaterials, the major design techniques that have been employed, and instances of device components and segments that have potential applications in biomedicine (Someya et al., 2004; Zardetto et al., 2011). There is a great deal of interest in materials and manufacturing processes that allow electronic devices to be produced directly on flexible metal foils or plastic sheets in a scalable manner and with the high-performance operation, and this interest is growing. Recent further related initiatives are attempting to build abilities in making electronics efficient to not only bending with also stretching, with elastomers serving as the substrates in these endeavors (Kim et al., 2008; Viventi et al., 2011). Such systems can establish close, conformal interactions with complicated curvilinear surfaces, like those seen in biology, while also being resistant to high degrees of strain and stress. Traditional, rigid technologies, such as those created on glass panels or on surfaces of semiconductor wafers, are unable to achieve any of these features. Wearable electronics paper-like displays and health-monitoring systems are only a few of the areas where flexible electronic devices have significant promise for application (Rogers et al., 2010; Yokota et al., 2016).

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As the foundation for all common and commercialized types of electronic devices, inorganic semiconductors are superior to organic semiconductors in several ways, such as long-term stability and high field-effect mobilities under environmental stress, electrical, and mechanical. Inorganic semiconductors are also more cost-effective than organic semiconductors in several ways. The constraints in the materials choices and production procedures of inorganic semiconductors, as well as the traditional processing methods connected with them, provide a significant obstacle in their use (Lee et al., 2011; Fang et al., 2016). Examples include the fact that most polymer substrates are discordant with the high temperatures necessary in typical processes for depositing materials, crystallizing materials, and doping materials. Furthermore, production through roll-to-roll printing across vast fields at a low cost per unit area can, in certain situations, be accomplished more simply with active organic ingredients than with their inorganic equivalents since active organic materials are more readily available. The results of recent research reveal those appropriate material selections, integration techniques in mechanically compliant systems, design layouts, and enable the usage of the highest functioning monocrystalline inorganic semiconductors in ways that affect these restrictions (Kim et al., 2010; Kang et al., 2016). Semiconductor material architectures that are ultrathin and often nanoscale in size enable heterogeneous incorporation into rubber or plastic substrates, together with all other constituents required to provide advanced electronic operation. Important factors that contribute to mechanical flexibility in these situations contain (1) economizing of flexural rigidity through the cube of the thickness of the structure and (ii) decrease of bending-induced strain through the usage of impartial mechanical plane plans, both of which can be achieved by using neutral mechanical plane designs (Park et al., 2008; Rogers et al., 2011).

7.2. BOTTOM-UP TECHNIQUES “Bottom-up” techniques, in which controlled growth produces 2D (twodimensional) nanomembranes or nanoribbons, 1D NWs (nanowires), 0D (zero-dimensional) nanoparticles, or intricate geometries that integrate multiple such structures, can be used to fabricate the necessary nanoscale inorganic semiconductor building blocks. The most investigated techniques use nanostructured materials (NWs), where there are several instances of flexible/ stretchable electronics that take advantage of the exceptional

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electrical, mechanical, and optical properties of these materials to great effect (Dasgupta et al., 2014; Kagan et al., 2016). According to one illustrative example, hydrothermal development of vertically oriented ZnO NWs results in inactive materials for adaptive haptic imaging systems, as seen in Figure 6.7. ZnO is used to adjust the current flow by combining its semiconducting and piezoelectric capabilities. The NWS are electrically connected to the bottom and top electrodes, where they transform external mechanical inputs interested in an electronic regulating signal that modulates current flow. It is demonstrated that this technique may be scaled up using a sensor matrix of 9,292 pixels that was developed in accordance with this concept. A crucial component of this system is the use of flexible and transparent electrodes, transparent substrates, as well as packing materials (SU8 and parylene). Instead of using optimized conditions to grow NWs directly on the target device substrate, NWs created on inherent substrates and assembled to desired substrates using physical transfer or other methods offer greater versatility in terms of material selection when compared to the direct growth method described above. An example of such an approach is the integration of NWs of Ge and Si formed by the nanocluster-catalyzed solid–liquidvapor process across huge regions in well-associated configurations using a nanoscale combing method on the nanoscale. An anchoring zone (with strong interfacial contacts) and an aligning region (with weak interfacial interactions) are provided on the target substrate by lithographically designed surfaces, which function as guides for the process (Yao et al., 2013). More than 98.5% of the NWs can be constructed and associated in the required direction with less than 1° variation on this basis, with crucial factors including contact pressures with the growing substrate, speed of translation, and directionality (as seen in Figure 7.1(b)). It is feasible to create large arrays of NW FETs (field-effect transistors) in this manner, with good uniformity and repeatability, as described, for instance, by statistical features of the performing of Si/Ge NW transistors in one application (Yao et al., 2013). Other articles provide in-depth analyses of flexible electrical technologies based on the natural environment (NW) (Figure 7.1).

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Figure 7.1. Stretchable and flexible electronic devices that use monocrystalline semiconductor nanomaterials formed expending synthetic, bottom-up methods. Source: https://www.nature.com/articles/nnano.2010.132. Note: (a) A transparent and flexible array of transistors that employ vertically associated ZnO NWs and are configured into a system that permits for largearea tactile imaging are used in this system. (b) Ge/Si NW transistors are assembled from NWs utilizing a nanoscale combing process to generate a complete transistor. (c) Monolayer MoS2 and WS2 growth on a wafer-scale for the fabrication of transistors with high mobilities. (d) Roll-to-roll transfer of graphene sheets as a potential route to industrialization for large-scale transparent and flexible electrodes on a flexible substrate.

A growing body of current work highlights the usefulness of 2D materials, for example, transition metal dichalcogenides (TMD) and graphene which are examples of NMs created utilizing the bottom-up approach (Cheng et al., 2014; Wu et al., 2014). These and further 2D materials developed by chemical vapor deposition (CVD) have outstanding electrical characteristics and can now be produced in large-scale forms, making them appropriate for application in high-performance flexible electronic devices with tremendous flexibility. Synthesis of wafer-scale monolayers of WS2 and MoS2 via metal-

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organic chemical vapor deposition has shown very encouraging findings, particularly in WS2 (Cheng et al., 2014). Figure 7.1(c) shows that gas-phase precursors of (C2H5S), W(CO)6, Mo(CO)6, and H2 provide very uniform exposure of monolayers and that a layer-by-layer growth method may be used at enormous scales to achieve this coverage. Photographs were taken with an annular darkfield scanning transmission electron microscope, and a darkfield transmission electron microscope can be used to confirm that the MoS2 film is continuous as it is being formed. Clusters of WS2 and MoS2 FETs have field-effect movements of 29 and 18 cm2 V1 s1, respectively, making them ideal for a wide range of applications (Fiori et al., 2014).

7.3. TOP-DOWN APPROACHES The use of lithographic etching and processing to describe semiconductor nano/micro materials from thin-film sources or bulk material with the predetermined regulator over key spatial arrangements and dimensional characteristics is an alternative to bottom-up methods such as those defined in the preceding section. The former method, such as trenching the surfaces of single-crystalline silicon wafers with 111 passivating and orientation the sidewalls and top surfaces, prepares the substrate to be anisotropically etched preferentially in the direction of the 111 orientations. 3, pp. Despite the fact that NRs have been the most thoroughly investigated, a series of cycles of this method, each of which creates a high-density or a single wafer-scale NM cluster of them, as seen in Figure 7.2. Figure 7.2(a) (on the left) depicts a schematic representation of the fabrication process. Initially, an etch resist photolithographically patterning to define the lateral dimensions of an array of microbar structures. These microbar structures are interconnected so that they form a continuous membrane, but with tiny holes to permit access of the etchant to the core regions (Yamada et al., 2012; Akinwande et al., 2014). The thicknesses of the bars are determined by reactive ion etching of the visible Si in a direction vertical to the surface of the wafer during the fabrication process. Passivating the top surface and sidewalls of these structures, then immersing them in a bath of KOH bath distributes a waferscale nanometer-scale NM by preferring undercut-etching Si in the 111> direction. In this case, the NM is still attached to the fundamental wafer, even though it is otherwise freestanding. Thin membranes ranging in thickness

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from 2 to 30 microns, with area coverages of up to 90% depending on the distance between microbars, and total sizes up to 2 x 2 cm, potentially on the scale of the wafer itself, have been accomplished. Related procedures for NRs illustrate the technique’s scalability obsessed by sub-micron thickness regimes by demonstrating the scalability of this technology (Mack et al., 2006; Baca et al., 2007). NMs produced in this manner are very well suited for transfer printing onto flexible surfaces using well-established transfer printing processes. It is possible to reprocess the remaining source wafer following chemical polishing of the surface by rinsing in KOH to produce successive generations of NMs, with the potential to convert most of the material contained inside the wafer itself into NM form. The micrograph pictures in Figure 7.2(a) (right) depict an instance of a membrane that is of the 3rd generation. An additional strategy, which is particularly suitable for NRs, is to regulate the reactive ion etch to produce highly defined rippling sidewall geomorphologies, as seen in the diagram representation of Figure 7.2(b) (left). Angled physical vapor deposition of metal from a paralleled cause produces coatings that are selectively applied on the top surfaces of these ripples in this application. These coatings may be used as disguises for anisotropic wet etching, much as they have in the past, but in a way that allows multilayer packs of ribbons or membranes to be released in a single process rather than many steps. The imagery of bulk amounts of Si NRs created in this manner is shown in Figure 7.2(b) (right), which includes both optical and scanning electron microscopy (SEM) images (Ko et al., 2006). The third type of top-down strategy makes use of embedded layers that are meant to be selectively deleted to effect release in a different way. The most popular way, as seen in Figure 7.2, is to employ silicon on insulator wafers (SOI) (top). Specifically, in this example, holes cut into the top silicon provide entrance to hydrofluoric acid, which is used to etch away the underlying SiO2 layer, resulting in the release of a layer of silicon in freestanding form (Huang et al., 2011). As seen in Figure 7.2, the resultant Si NMs can be exceedingly flexible (bottom). 37 The use of available commercially SOI wafers allows for the fabrication of NMs with thicknesses as thin as roughly 20 nm.

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Further processing, depending on consecutive cycles of etching and oxidation, can result in ultrathin Si NMs along with thicknesses varying from 1.4 to 10 nm, depending on the material. When self-made monolayers, 2D materials, and additional ultrathin constructions are used in conjunction with other ultrathin structures, it is feasible to create very thin and flexible devices. The thicknesses used in this regime can have an impact on the transport qualities (Yamada et al., 2012). The Heteroepitaxial development of a trilayer of Si/SiGe/Si NMs resting on an SOI wafer results in a strain in the crystal lattice in advanced cases. When the compressive strain from the SiGe layer is released, it redistributes toward this unstrained Si, resulting in regulated amounts of strain in the NMs. It is possible to adjust both mobility and band offsets using elastic strain relaxation from released NMs from SOI wafers, which is an additional control mechanism. Using this method of strain engineering, it is possible to improve the properties of flexible devices made of these materials. These and other Si NMs may be used to fabricate high-speed flexible electronic devices, some of which have operating frequencies more than 1 GHz, such as PIN diodes, MOSFETs, and single-pole single-throw controls, among other things. It is possible that Ge NMs can be used for photodetection by using other SOI-like substrates because of their strong absorption over a wide variety of wavelengths (Baca et al., 2007). The use of alternate stacks of AlGaAs (aluminum gallium arsenide) and GaAs (gallium arsenide), in combination with hydrofluoric acid, as a starting point to produce vast amounts of GaAs NMs by selective removal of the AlGaAs, is another example. 2d71 illustrates the formation of AlGaAs and GaAs layers on a bulk GaAs wafer as well as the selective HF etching of GaAs nanometer-sized particles (NMs). This method may be used to make multilayers that are similar in appearance in large quantities. The use of AlGaSb sacrificial layers allows for the construction of ultrathin InA NMs, while transfer printing permits for the incorporation of additional substrates, resulting in the production of one-of-a-kind, heterogeneously integrated electrical devices (Lasky, 1986).

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Figure 7.2. Single crystalline inorganic nanoribbons and nanomembranes, created utilizing lithographically controlled, top-down techniques, are being investigated further. Source: https://pubmed.ncbi.nlm.nih.gov/20485431/. Note: (a) Anisotropic etch of a bulk wafer substrate result in the formation of flexible Si NM (left). The use of this method repeatedly allows to produce large amounts of Si NMs from a single wafer. (b) On an SOI wafer, an example of the migration of a-Si NM from the device silicon layer is shown (top). As seen in the optical picture, a wrinkled Si NM was formed in this method. (c) Figure 7.1 shows an illustration of a procedure for producing large numbers of Si NRs from a bulk wafer by stacking several layers of the material (left). This method produces enormous amounts of NRs, which may be photographed and analyzed using scanning electron microscopy (right). (d) Multilayers of GaAs and AlAs produced on a bulk GaAs wafer are seen in this illustration. The optical picture depicts a group of GaAs NMs that have formed because of the selective extraction of AlAs layers in the substrate. Yoon et al. (2011)

Using pure inorganic boundaries along with low interface trap densities and excellent stability, in addition to the increased electrostatic connection to the gate electrode, it was possible to achieve superior switching qualities. Further one-of-a-kind possibilities arise from the application of strained layers, which result in the spontaneous creation of tubular forms in the released material. NMs When compared to bottom-up approaches, these sorts of top-down technologies have several benefits since they try to utilize

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instead of displacing the most sophisticated processes in thin-film and wafer development (Kaltenbrunner et al., 2013). Moreover, better consistency and yield in device manufacturing are achieved by engineering control over essential structural parameters, as well as lithographically defined 3D orientation and order. Multilayer approaches, like those presented here, can be extremely significant in cost-sensitive applications because of their flexibility.

7.4. MECHANICS Neutral mechanical plane and thin geometries layouts are used primarily in the design of flexible electronic systems that employ the kinds of inorganic semiconductor nano/microstructures mentioned in the previous sections. As the cube of the thickness increases, the flexural stiffness drops proportionally, resulting in a difference of greater than 15 orders of magnitude among Si NMs with thicknesses of 10 nm and raw silicon wafers with thicknesses of one millimeter. An instance of bendability in Si NMs is depicted in Figure 7.3(a) (Someya et al., 2016). The bending strain coupled with a particular radius of curvature reduces linearly with the thickness, offering a further benefit coupled with thin geometries, in addition to the previously mentioned benefit. In addition, the energy release rate related to delamination between a substrate and a film reduces linearly with film thickness, allowing for the robust combination of NMs with substrates made of incompatible materials to produce heterogeneous electronic systems to be achieved. Figure 7.3(b) shows an example of how these principles may be coupled to make flexible thin-film transistors by printing Si NRs onto plastic sheets and forming them into thin-film transistors (Kim et al., 2008). While mechanical flexibility can open a wide range of applications that are not possible with conventional providing a strong foundation of electronics, stretchy features add an additional level of division by allowing for conformal integration onto complicated, non-developable surfaces as well as the ability to function under deformations involving large strains. Stretchable characteristics are particularly useful in medical applications.

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Stretchable inorganic semiconductors have been reported for the first time, and the buckling of Si NRs on an elastomer substrate was exploited to produce what was known as a “wavy” configuration. Because the geometry of this hard/soft composite may alter in reaction to applied strain; there is no need to worry about significant stresses occurring in the silicon. When forming the required structure, one easy method is to attach the Si NRs to a stretched elastomer and then remove the stretch. Because of a non-linear buckling instability, compressive loads are applied to the originally flat Si NRs, causing them to spontaneously convert into highly periodic wavy forms, as seen in Figure 7.3(c). Amplitude and wavelength of the signal are determined by the thickness of silicon and other important material parameters (Yokota et al., 2016).

7.5. EPIDERMAL ELECTRONICS Elastomeric films or thin plastic sheets containing assemblies of inorganic semiconductors can be used as active components in high-performance electronic sensing or actuation platforms that have a high degree of mechanical deformability or bendability. Aspects of life-support systems that interact with live creatures are among the most appealing applications for such kinds of electronics. The active inorganic materials used in these applications have designs like the ones mentioned above and are embedded in soft elastomeric matrices, which provide the foundation for combined groupings of devices. Multifunctional sensors, active/passive circuit elements (e.g., transistors, diodes, and resistors), wireless power coils, and RF communication components are examples of such devices (e.g., inductors, capacitors, oscillators, and antennas). Construction of platforms that are appropriately compliant to cover soft, complicated curvilinear tissues may be achieved by careful design-driven through analytical and computational models of the mechanics and materials. Physical parameters, including such area mass density, thickness, thermal properties, elastic modulus, and stretchability that are effective, can be matched to those of biological materials, for example, the epidermis, to achieve the desired results. In certain circles, these later sorts of devices are described as epidermal electronics. On the left, you can see a multifunctional instance designed to permit the measurement of EP signals produced by the human body. Figure 7.4(a) (right) illustrates another multipurpose example (Sekitani et al., 2010).

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The active electronic materials, electro-physiological sensors, and components are inserted in a thin, low modulus silicone elastomer in an open, serpentine filamentary mesh design. An illustration of such a gadget, peeling away from the user’s forehead after usage, is depicted in Figure 7.4(a) (center). Electroencephalogram data acquired during the shutting and opening of the eyes is depicted in Figure 7.4(a) (right). Alpha rhythms are shown to emerge when the subject’s eyelids are closed while he or she is awake in the data shown below. The signal quality is comparable to that of data gathered with traditional, bulk electrodes that are connected to the scalp via conductive gels, which is a significant improvement (Chortos et al., 2016). Figure 7.4(b) depicts a multifunctional dermal electronic system that includes electrical stimulation electrodes as well as strain sensors, temperature, and EMG that are installed on the skin surface. The gadget retains its effectiveness without imposing any significant restrictions on the skin’s natural movements. Figure 7.4(b) shows how the devices interact with the long head of the biceps brachii and the lateral head of the triceps brachii muscles to demonstrate their stimulation capacity (center). A robot arm may be controlled by extending or flexing the elbow joint, which provides EMG signals that can be used to control the arm (Tee et al., 2015). Feedback is provided by stimulation, which is defined by the coordinated functioning of the two electrodes shown in Figure 7.4(b). This outcome is important because it may be used as a control interface for a prosthesis. Another potential is that comparable devices can be used as sensory skins on robotic limbs, which is something that should be studied as well. Figure 7.4(c) (left) depicts an illustration of a prosthetic hand with artificial skin covering the surface of the device. The mechanical stretchability is depicted in the inset. There are temperature, pressure, and strain sensor arrays in this platform that can detect Spatio-temporal distributions of strain correlated with complicated movements, as well as thermal characteristics and ambient humidity, among other things. Using the examples of using a keyboard and catching a ball in Figure 7.4(c) (right), we can see how well Si NMs pressure sensors operate in a variety of situations (Chen and Liu, 2013).

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Figure 7.3. Design methods for stretchable and flexible electronics. Source: https://pubmed.ncbi.nlm.nih.gov/24509865/. Note: (a) Images of a-Si NM taken with a scanning electron microscope (SEM) to illustrate the tremendous degree of mechanical flexibility it possesses because of its thin geometry. (b) Flexible Si NRs for transistors. (c) Strainable Si NRs with a periodic wavy structure, produced on an elastomer substrate, and adhered to the substrate. (d) Controlled buckling of Si NRs caused by adhesion spots on a fundamental elastomer that have been lithographically defined. The design patterns for stretchy electronics, as well as the accompanying MicroXCT pictures of the patterns after stretching, are shown in the top illustration. From left to right, the uniaxial restraints are 55%, 75%, 40%, and 35% of the total restraints, respectively. Fan et al. (2016).

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Figure 7.4. Skin-like or epidermal electronic system. Source: https://www.researchgate.net/publication/269414595_Stretchable_silicon_nanoribbon_electronics_for_skin_prosthesis. Note: (a) System with interconnected electrodes, wireless devices, and semiconductor components in a multipurpose configuration is seen in this illustration (left). These technologies have the capability of conformally laminating onto the skin’s surface (center). The spectrograms depict recorded EEG data that corresponds to an aroused subject when the subject’s eyes are closed and when the subject’s eyes are opened. (b) Under stretching, this image shows a multifunctional epidermal device installed on the forearm that is capable of both detecting and stimulating (left). Image shows the devices attached to the biceps and triceps of a robotic arm for the purpose of regulating the angles of

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the elbow of the arm (center). During the robotic arm’s alternation among flexion/extension of the elbow angle, the correlated EMG signals from two devices were recorded. (c) Illustration of a stretchy synthetic skin integrated with Si NM-based pressure, strain, and temperature sensor arrays (left). Illustrations of how to use a prosthetic limb include photos of a prosthetic hand typing on a keyboard and holding a ball with a prosthetic hand (center). Figure 7.4c shows the plots of the matching response of the SiNM pressure sensor (right). (Kim et al., 2008).

Several instances of these types of active electronic systems that have been described need connections to power supply or external data acquisition devices to function properly. The use of hard cables is a possibility. However, wireless alternatives are more commonly favored these days. Figure 7.5 illustrates expanded versions of the design concepts for wireless communications in transdermal electronics, which may be used to give a solution (Imani et al., 2016).

Figure 7.5. Wirelessly operated epidermal electronic systems. Source: https://yonsei.pure.elsevier.com/en/publications/soft-thin-skin-mounted-power-management-systems-and-their-use-in-.

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Note: (a) A stretchy epidermal electronic system that combines linked commercial chips in a blocked microfluidic environment for a completely wireless EP sensor, as well as an instance of the device on the forearm in twisted and compressed states, are shown in the images below (center). The waveforms obtained with the device installed on the sternum are shown in this example of ECG data collected with the device. (b) An illustration of a wireless stretchable optoelectronic system put on the forearm, as well as the theory of operation of the system (left). Spectroscopic data collected by a commercially available near-IR (NIR) oximetry device (center) and a wireless dermal oximetry device (right) bonded onto the same forearm were compared to each other in the time domain. (c) Diagram illustrating the working principle and configuration of a wireless stretchy optoelectronic system installed on the forearm (left). Spectroscopy data collected by a commercially accessible NIR (near-infrared) device (center) and a wireless dermal oximetry device (right) bonded onto the forearms at two different places are shown in the figure (Lee et al., 2011).

These systems are built on the foundation of commercial inorganic, chipscale electronics that are linked via thin-film metal traces. Additional device functionality can be achieved by incorporating various active components depending on inorganic materials on soft polymer substrates as flexible backplanes, as previously described. An open mesh structure and fractal geometry are used for the assembly of customized chip-scale inorganic devices that are sealed within stretchable microfluidic chambers. The EP signals are recorded with a high signal-to-noise ratio, and the readout and wireless communication are performed using a multiplexed readout. Figure 7.5(a) (left) depicts a picture of a device that is driven by radiofrequency energy transfer and is configured in a twisted configuration. Figure 7.5(a) depicts a finished device that has been bonded to the surface of the forearm and is in a distorted condition (center). It is possible to record electrocardiograms (ECGs) without the need for a tether because of the device’s capacity to monitor EP signals, as shown in Figure 7.5(a) (right). There are obvious Q, R, and S waveforms in the data, as well as a high signal-to-noise ratio. Using NFC (near-field communication), to transmit multicolor light from LEDs and detect it using photodetectors, another instance of battery-free, wireless epidermal electronics is demonstrated. The technique is used to analyze the optical characteristics of the skin. Tissue oxygenation, heart rate, UV exposure, pressure pulse dynamics, and skin color may all be monitored using such designs (Rogers et al., 2011). Image of an epidermal system equipped with red and infrared LEDs put on the preparation for the quantitative dimension of tissue oxygenation and its temporal variations, as well as a schematic representation of the operating principle, is shown

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in Figure 7.5(b) (left) (inset). As shown in Figure 7.5(b) (center and right), there was an increase in total hemoglobin in the event of a venous blockage, as measured by a commercial oxygen meter and compared to data received by a wireless epidermal device (Figure 7.5(a)). The outcomes indicate the degree of precision that may be attained (Dasgupta et al., 2014). On the left, you can see an optical picture of a device that has a temperature sensor as well as a wireless data transmission module. On the right, you can see data storage, battery array power control, and a wireless power supply system. Using this platform, you will be able to store information about temperature changes on your skin in memory and wirelessly transfer that information to others. An example of a practical application is shown in Figure 7.5(c) (center), which shows a battery-incorporated NFC device on the prepare of a person riding a stationary bike in comparison to a wirelessly powered NFC device devoid of a battery module on the opposite side of the arm. Both the battery-powered and wirelessly powered NFC devices exhibit identical temperature responses, as seen in Figure 7.5(c). The findings are reliable with the infrared camera records shown in Figure 7(c). The findings suggest that wireless epidermal electronics is a feasible technology (Zhang et al., 2016). The use of alternative manifestations of the fundamental materials and design concepts allows for dramatically diverse sorts of applications and form factors. Using the same principles, for example, it is possible to build completely integrated optoelectronic systems that fit onto thin polymer filaments, which can then be injected into soft tissues, as well as the brain, using the same principles. Thin geometries not only allow for more flexibility; however, they also help to reduce tissue injury through attachment, including scarring and inflammation after the device has been used. In Figure 7.6(a) (left), a schematic sketch of such a system is shown in exploded view. It is comprised of microscale InGaN LEDs (-ILEDs), an optical detector, as well as EP sensors and thermal and actuators, all of which are mounted on a releasable insertion microneedle that is intended to give adequate rigidity to allow insertion into the targeted tissue. A flexible device efficient of transmitting optoelectronic and electrophysiological function to the depths of the brain with wireless and untethered operation is created when the functional components stack and align together into a single unit. These investigations, in which light emission may either accelerate or block the action of genetically targeted neurons, are extremely useful because of the functionality provided by this technique. When related to outmoded approaches based on external light sources and fiber optic cables, the tether-

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free operation offers numerous advantages, including the ability in intricate 3D environments to conduct studies of social interactions, activity, and other situations that would otherwise result in entanglement of the fiber optics. The use of advanced designs in filamentary, flexible antennas results in downsized designs and soft mechanics that are suited for complete implantation, as seen in Figure 7.6(b) (left) (Fiori et al., 2014). This antenna not only decreases the total dimensions and weight of the entire system by approximately two orders of magnitude when compared to previously published designs, but it also allows broad bandwidth operation, which increases the dependability of the system’s operation. It is feasible to implant the soft interface in sites where fixation to hard, bony structures is not viable, such as below the leg muscles for optogenetic activation of a peripheral nerve, as shown in Figure 7.6(b). It is also conceivable to insert a device into the epidural space as an interface between the brain and the spinal cord. Look at Figure 7.6(c) (right). Biological research and clinical treatment will benefit from these and other new instruments that are based on the fundamental ideas of flexible and inorganic electronics (Kang et al., 2015).

Figure 7.6. Implantable wireless optogenetic system. Source: https://koreauniv.pure.elsevier.com/en/publications/soft-stretchablefully-implantable-miniaturized-optoelectronic-sy.

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Note: (a) Images of an exploded assessment of a multifunctional, intravenous optoelectronic device that integrates microelectrodes, inorganic microscale light-emitting diodes (I-LEDs), Si NM photodetectors, temperature, and electrophysiological sensors, all of which are combined on a releasable injection microneedle. Sequence of photos showing the injection and extraction of the microneedle after a coating of silk was dissolved to act as a temporary adhesive (top centers). A wireless optogenetic system with a free-moving mouse that is both lightweight and flexible. In a Y-maze, heat maps of activity during mobility were created (bottom frames). (b) An illustration of a completely implanted stretchy wireless optogenetic device in an exploded view schematic diagram (left).

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CHAPTER

8

INORGANIC NANOPARTICLES FOR BIOMEDICAL APPLICATIONS

CONTENTS 8.1. Introduction..................................................................................... 226 8.2. Unguided Drug Delivery Systems.................................................... 228 8.3. Magnetically-Guided Drug Delivery Systems................................... 230 8.4. Optically-Triggered Drug Delivery Systems...................................... 234 References.............................................................................................. 238

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8.1. INTRODUCTION Many biological applications, like molecular sensing devices, diagnostic imaging, and drug delivery systems, have been spurred on by the development of nanoparticles in recent years. The scope of this review is limited to inorganic nanoparticles for drug delivery applications. Targeted drug delivery systems and sustained release drug delivery systems are intended to improve the therapeutic effectiveness of medications while also limiting the drug’s area of impact to certain regions of the body. Ideally, the ideal drug delivery system should not be withdrawn too quickly from either the region of interest or the systemic circulatory system, and it should allow for the least amount of drug outflow away from the target location. Drugs released through the carriers should retain their functional activity, and dropped drug carriers should be removed from the systemic circulation when they have been cleared (Ahn et al., 2001; Zhu et al., 2004; Petrak, 2006). With nanoparticles’ typical size ranging from 100 nanometers to several micrometers, there has been a resurgence in interest for their potential uses in intravenous administration, pulmonary administration, and intracellular administration. The use of nanoparticles resulted in a significant increase in efficiency for pulmonary administration. Polymeric and liposomes drug carriers with a diameter of less than 100 nm have been shown to have improved permeability and localization to tumor locations, making them promising candidates for cancer therapeutic applications. This was ascribed to a lower diffusive barrier for nanoparticles, which was expected given the estimated size of gap junctions in the tumor vasculature, which ranged from 100 to 600 nm. In addition to particle size, the surface features of nanoparticles would have an impact on the uptake and dispersion of nanoparticles within cells (Allen, 2002; Alexiou et al., 2006). Surface modification of nanoparticles is frequently necessary to increase the compatibility, stability, and functioning of the particles themselves. Surfactants, which acted as molecular linkers and increased particle stability, were used to modify the surface properties of nanoparticles, resulting in better particle stability. Surfactants would lower the surface energy of nanoparticles and increase their stability by serving as an obstacle to accumulation, either by repulsive electrostatic forces or steric hindrance or by reducing the surface energy of nanoparticles. The presence of functional groups on surfactants has made it possible to couple nanoparticles along with biomolecules such as medicines or antibody molecules (see Figure 8.1). If

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the surface-functionalized nanoparticles were also changed with antibodies, they would be capable of operating as drug carriers, with the possibility for selective localization if the particles were also altered with antibodies (Averitt et al., 1997; Avnir et al., 2006).

Figure 8.1. Surface functionalization of inorganic nanoparticles as seen in a schematic. Source: https://link.springer.com/chapter/10.1007/978-3-540-49661-8_11.

It is well recognized that ceramics like calcium phosphates, Titania, and silica are biocompatible materials. It has been discovered that the usage of inorganic ceramic nanoparticles provides greater chemical and thermal stability than the use of polymeric nanoparticles (Foster et al., 2001; Singh et al., 2006). As a result, encapsulating pharmaceuticals within ceramic particles would provide superior protection against the denaturation of labile agents. As the percentage of surface atoms increases and the separation among energy states increases with reducing size, inorganic nanoparticles display exceptional optical, electrical, and magnetic properties that differ from their mass counterparts, inorganic nanoparticles are becoming increasingly important (Babes et al., 1999; Barnard, 2006). The shape, crystal structure, size, surface contacts, and sphere interactions of nanoparticles might all be controlled, allowing for the tailoring of their properties. When compared to bulk Au, the Au nanoparticles with diameters of 5,100 nm exhibited a clear size-dependent absorption band at 520,570 nm, but Au nanoparticles with diameters of 5,100 nm did not display any absorption within the visual range (Figure 8.1). Furthermore, various surfactants may be used to control the optical characteristics of metallic nanoparticles. As a result, the physical features of inorganic nanoparticles might be used to permit local release at specific locations of interest with customizable responsiveness and sensitivity by manipulating their size and shape. Magnetic nanoparticles containing drugs might be steered to a precise location under the influence of an applied magnetic field, where they could be released. In a similar vein, localized drug release from optically active drug nanocarriers might be

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produced by employing light to stimulate drug release from the nanocarriers (Ben-Nissan, 2004; Behrens et al., 2006).

8.2. UNGUIDED DRUG DELIVERY SYSTEMS For the most part, ceramic nanoparticles have been created for use in continuous drug release systems to increase delivery efficiency, eliminate unwanted systemic effects, and provide more patient comfort. In clinical applications, the most often utilized ceramic materials are calcium phosphate and silica, which are both minerals (e.g., hydroxyapatite). They were shown to provide the most significant contribution in the areas of bone repair, bone regeneration, and tissue engineering, in addition to nonviral gene delivery systems (Vallet-Regi, 2006a, b). When it comes to bone restoration, calcium-based ceramic materials have the edge over other polymeric materials because of their superior bonding to living bone and their capability to catalyze bone growth because of enhanced nucleation of apatite. Calcium-based ceramic materials are also less expensive than other polymeric materials. For example, hydroxyapatite is a ceramic that is comparable in composition to the mineral component of bone (Berry and Curtis, 2003; Brannon-Peppas and Blanchette, 2004). It has become possible to integrate biomolecules and medicinal substances with ceramic particles to generate materials that operate as controlled release systems. The chemical functionality and activity of the biomolecules that were attached to the ceramics influenced the performance of the material. Matrix structure, pore size, and surface functional groups are all important factors in determining the adsorption characteristics of ceramic materials. Surface functional groups might be further adjusted by utilizing different chemical species to increase the capacity of the surface to bind different biomolecules to diverse surfaces. Interfacial interactions among ceramic matrix and biomolecules would have an impact on the chemical activity of biomolecules (Brinker and Sherrer, 1990; Bruce and Sen, 2005). An ideal bio-doped ceramic would have excellent long-term stability in potentially unfavorable circumstances, for biomolecules a high loading density that is still bioactive and be resilient to biomolecule leaching. Biodoped ceramic materials have been employed in the creation of non-invasive surgical applications, either as a porous solid component or as an injectable substance (e.g., implants).

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8.2.1. Chemical Synthesis of Ceramic Nanomaterials Sol-gel precipitation and processing are two of the most important chemical synthesis processes for ceramics. Sol-gel techniques were traditionally used to create metal hydroxyls by hydrolysis of metal alkoxide, M(OR)x precursors in the existence of alcohol as a co-solvent in the existence of other solvents. This was observed by the condensation of metal hydroxyl groups, which resulted in the formation of either water or alcohol as a byproduct of the process. The chain length of metal alkoxide precursors, temperature, solvent, surfactants, mechanical agitation, and pH were all extensively employed to influence the growth kinetics and nucleation of metal alkoxide precursors during the processing process. As condensation progressed, more aggregates were generated, and the viscosity of the sol increased, resulting in the creation of a gel in the following hours. Gel shrinkage would occur because of capillary forces acting on the pores when the solvent is removed. The Stöber process, which was created based on sol-gel principles, was used to manufacture silica particles of a variety of various sizes (Zhou et al., 1994; Green et al., 2003). The precipitation of metallic salts and bases is another typical approach, which is particularly useful for the formation of hydroxyapatite. The pH of the starting solution was the most important factor in determining the growth kinetics and nucleation. When different temperatures were applied to the crystallization process, the amount of crystallization and the avoidance of the formation of undesirable secondary phases were regulated (Caruso, 2002; Chan, 2006).

8.2.2. Functionalization of Ceramic Nanomaterials Silica nanoparticles with no surface modification did not appear to reduce and transfer DNA, contrary to previous findings. To distribute DNA utilizing nanoparticles, the elongated long-chain DNA molecules were reduced to minimize the amount of space they occupied in the occupied spatial volume. After being modified with amino silanes on silica nanoparticles, the existence of surface amino groups would allow them to form a strong bond with plasmid DNA and function as a gene delivery carrier. It might be possible to avoid DNA from being destroyed by environmental enzymes by employing silica nanoparticles as a gene delivery vehicle. Furthermore, when compared to other commercially available DNA transfection vectors, it was shown that DNA-loaded silica nanoparticles had a greater ability to penetrate cells (Chatterjee et al., 2003; Chavanpatil et al., 2006). Transfection effectiveness of available commercially transfection vectors has been reported to be

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increased by a factor of 17 when silica nanoparticles are employed. Nonviral gene delivery carriers based on calcium phosphate are another type of non-viral gene delivery carrier that is widely employed. It is known that DNA may be adsorbed on exposed calcium phosphate, which makes calcium phosphate materials attractive candidates for use as gene delivery carriers because of their biodegradability, biocompatibility, and known adsorptive potential of DNA on bare calcium phosphate. It was discovered that calcium phosphate gene carriers might be created by co-precipitating calcium phosphate particles with DNA in the laboratory. In contrast to viral techniques, lower levels of gene expression were seen when using non-viral ways. There were issues connected with endosomal escape, poor protection of DNA from nuclease destruction, and ineffective nuclear absorption, all of which were contributing factors (Chow et al., 2006; Coradin and Livage, 2007).

8.3. MAGNETICALLY-GUIDED DRUG DELIVERY SYSTEMS 8.3.1. Magnetic Guiding Using an applied magnetic field, magnetically responsive delivery devices that have been injected into the systemic circulation are guided to the desired regions of attention. It is possible to create an external magnetic field of 0.81 to 1.7 T by placing an array of magnets or a magnet near a lesion or tumor, which can be either externally inserted or implanted. The therapeutic compounds were then released using another trigger, like an oscillating magnetic field or ultrasonic waves, to provide the desired effect (Yong et al., 2004; Yu and Chow, 2004). The use of large magnetic particles insulation materials matrix to construct magnetically modulated drug delivery systems has been proven to increase the rate of drug release when an oscillating magnetic field is applied. According to the findings, drug release rates depend on the features of the magnetic field and the polymer qualities. When the holding magnets were eliminated, the particles would either reallocate into the blood supply, where they would eventually be vacant by the reticuloendothelial system, or they would remain inside the region of attention, where they would eventually be cleared by extravasation, depending on their location (Dolmans et al., 2003; Frangioni, 2003).

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8.3.2. Properties and Chemical Synthesis of Magnetic Nanostructures Since iron-based magnetic nanoparticles, notably magnetite (Fe3O4) and maghemite (γ-Fe2O3), have superior chemical stability and lower toxicity when associated with alternative cobalt- and nickel-based magnetic nanomaterials, they are the most often utilized. Magnetic nanoparticles have been created utilizing a variety of chemical processes that allow researchers to regulate the nucleation and growth rates of the particles. It was discovered that the growth rates and nucleation were responsible for the size, shape, and content of the particles produced, whilst the size dispersion was determined by the decoupling of growth rates and nucleation (Figure 8.2) (Gupta and Gupta, 2005; Gould, 2006).

Figure 8.2. (a) 7 nm; (b) 11 nm; and (c) 13 nm J-Fe2O3 nanoparticles produced employing thermal decomposition of organometallic precursors. Source: https://pubs.rsc.org/en/content/articlelanding/2003/cc/b207789b.

The magnetic particles must have a strong superparamagnetic and magnetization behavior at room temperature in order to guide and immobilize the magnetic particles to the desired location. If particles had a high saturation magnetization, they would be more simply constrained in a magnetic field to an area with lower external magnetic fields if the external magnetic fields were lower (West and Halas, 2000). Thermal energy may be enough to cause variations in magnetization directions as the size of the particle diminishes. As a result, particles less than a threshold size would be magnetized through an applied magnetic field but would lose their permanent magnetism when the applied field was removed (Hilger et al., 2000; Hayden and Häfeli, 2006). Agglomeration would be less likely to occur in particles with this superparamagnetic behavior because attractive magnetic forces

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would be less effective in driving agglomeration. In exchange for the ideal superparamagnetic behavior, lowering particle size would result in a reduction in saturation magnetization, which would constitute a trade-off. Greater cellular uptake and embolism risk may be associated with smaller particles with lower saturation magnetization, while lower cellular uptake and embolism risk may be associated with bigger particles (Hirsch et al., 2003; Hong et al., 2005).

8.3.3. Functionalization of Magnetic Nanoparticles An oxide surface, metallic, or polymeric is applied to magnetic nanoparticles to increase either their stability against agglomeration, bioavailability, or capacity to interact with biological molecules. Particles were frequently surface functionalized with a polymeric, inorganic, or organic layer, which was accomplished employing encapsulation or ligand exchange techniques. During the chemical synthesis process, a coating of organic surfactants was applied to the particles to prevent them from clumping together. However, it is possible that such surfactants will not offer the requisite chemical functionality required for their future uses (Hood, 2004; Hughes, 2005). As a result, multiple ligand exchange procedures were used to replace the surfactants that were coating the particles with other surfactants (U.S. Food and Drug Administration, 2000; Waynant et al., 2001). An aqueous polymer solution might be used to coat particles with an inorganic salt precipitate, which could then be used to coat the particles. It was usual practice to encapsulate Fe3O4 or γFe2O3 particles in starch or dextran to promote solubility and biocompatibility. A second demonstration occurred when it was proven that following surface modification, an anticancer medication was attached to γ-Fe2O3 particles coated with polymethyl methacrylic acid (Figure 8.3). Silica-coated particles have improved stability, as well as surface silanol groups that can be used for covalent coupling. A silica coating was generated on the particle surface because of the condensation and hydrolysis of organ silanes that had been accumulated on the surface of the particle. The properties of the final surface layer were determined by reaction factors, for example, solvent temperature, type, and time, along with the amounts of catalyst and organosilanes utilized in the reaction (Hyeon et al., 2001; Hyeon, 2003).

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Figure 8.3. The transmission electron micrograph and associated electron diffraction pattern of J-Fe2O3 particles coated with polymethyl acrylic acid are shown (Yu and Chow, 2004). Source: https://pubs.rsc.org/en/content/articlelanding/2004/jm/b404964k.

8.3.4. Biocompatibility of Magnetic Nanoparticles for Drug Delivery It has been observed that, in addition to inherent side effects, the surface coating of nickel ferrite nanoparticles coated with oleic acid played an essential influence in the cytotoxicity of these nanoparticles (Yin et al., 2005). Using uncoated nickel ferrite particles, it was discovered that particle size was not a major determinant in cytotoxicity when there were no ‘toxic’ functional groups on the surface of the particles. In contrast, nickel ferrite particles with diameters of 150 nm and 10 nm coated with oleic acid were shown to be cytotoxic (Turkevich et al., 1951; Jin and Ye, 2007). Oleic acid molecules were not harmful when they were present as monomers, as was the case in this study. Cytotoxicity, on the other hand, was seen when they formed micelles or coated on ferrite particles, i.e., when their functional groups were spatially aligned, as was the case in this study. When one or two layers of oleic acid were put on the surface of the particles, the cytotoxic impact of the bigger particles was greater than that of the smaller particles. This might be connected to interfacial interaction areas and surfactant reactivity, which were both reliant on particle size in the first place (Figure 8.4) (Kittel, 2005; Jurgons et al., 2006).

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Figure 8.4. Representation of the different interaction regions of a single particle with a single layer of oleic acid coating. Source: https://pubmed.ncbi.nlm.nih.gov/15949547/. Note: A single big particle had a wider interaction area and had a greater number of functional groups. Even though a large number of small particles improved the number of contact points, there were fewer functional groups at every interaction point because of the large number of small particles. (Yin et al., 2005).

8.4. OPTICALLY-TRIGGERED DRUG DELIVERY SYSTEMS It has been used for photodynamic, photoablation, and biomedical imaging treatment because of its deep penetration into live tissues and high signalto-background ratio. Near-infrared (NIR) light (O 650 1,000 nm) has been used for photodynamic therapy, photoablation, and biomedical imaging. The absorption and scattering qualities of tissues would determine the amount to which NIR light might go through them. Hemoglobin, melanin, and water are the primary tissue absorbers of NIR light, whereas the composition, size, and shape of tissue parts determine how much light scatters (Kreibig and Vollmer, 1995; Kumta et al., 2005). The scattering and absorption characteristics of the material would impact the volumetric energy distribution generated through laser irradiation and would serve to define the limits of localized NIR-activated medication delivery systems. The use of microwatt sources has been shown to pass through with 10 cm of breast tissue and 4 cm of skull tissue when NIR light is used (Weissleder, 2001). To activate medication release, a targeted drug delivery system including tissue penetrative NIR light and NIR-sensitive nanoparticles was designed. This has the potential

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to enhance chemotherapy treatment by reducing harmful side effects while also allowing for less invasive treatment of malignancies that are surgically inoperable at the same time (Lübbe et al., 1999; Love et al., 2005).

8.4.1. Properties of NIR-Sensitive Nanoparticles and Chemical Synthesis Metallic nanoshells and metallic nanoparticles with size-dependent optical characteristics, notably chemically balanced Au nanoparticles, have been used as molecular sensors in a variety of applications. In particular. As sensors, the binding of molecules would result in plasmon resonance alterations either or fluorescence amplification depending on the type of molecule bound. Oldenburg et al. (1998) developed NIR-sensitive metallic nanoshells with shell and size thickness-dependent properties for use in imaging, hyperthermia, temperature-responsive delivery systems, and immunochemical assay. The NIR-sensitive nanoparticles used in the NIRactivated drug delivery system were manufactured by reducing HAuCl4 with Na2S to create the system (Templeton et al., 2000; Tirelli, 2006). Nanoparticles produced in this manner were chemically stable and displayed two distinct absorption bands, one at 530 nm and another in the NIR range between 650 and 1,100 nm. The nanoparticles that were created were composites of amorphous Au2S and crystalline Au, according to the researchers. Neither Au nor Au2S nanoparticles exhibited the NIR absorption observed in the as-synthesized nanoparticles, which indicated that they were not present. There was no indication that NIR absorption qualities were connected to a core-shell structure, as has been hypothesized in previous research in the scientific literature. The NIR absorption, as a result, was most likely caused by interfacial effects on particle polarization caused by the insertion of amorphous Au2S into a mainly crystalline Au matrix, as previously stated (Luo, 2005; Luo and Saltzman, 2006).

8.4.2. Functionalization of NIR-Sensitive Nanoparticles As seen in Figure 8.5, the functionalization of NIR-sensitive Au-Au2S nanoparticles with surfactants has made it easier to load anticancer medicines into the nanoparticles. When distinct hydrocarbon chain lengths were utilized to change the nanoparticles, the interfacial interactions among the nanoparticles and the surfactants were altered as a result. The loading of anticancer medicines regulated by surfactant interfacial interactions was shown to be inversely proportional to the length of the surfactant

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chain. The inorganic-organic interfacial interactions among surfactants and nanoparticles, as well as the optical characteristics of NIR-sensitive drug delivery systems, may also be exploited to modify optical properties (Moghimi et al., 2001; Pinchuk et al., 2004). The release of the drug was initiated by NIR laser irradiation employing an Nd: YAG pulse laser operating at 1,064 nm. The effects of NIR laser irradiation on the microstructural and structural alterations of Au-Au2S nanoparticles were investigated. We were able to deduce information on the NIR-triggered drug release mechanism from the expected degree of thermal impacts, as well as the microstructural and structural changes generated through NIR irradiation (Pitkethly, 2004; Prasad, 2004).

Figure 8.5. Au-Au2S nanoparticles with a cisplatin-loaded surface modification (Ren and Chow, 2003). Source: https://www.researchgate.net/publication/222590180_Synthesis_of_ nir-sensitive_Au-Au2S_nanocolloids_for_drug_delivery.

8.4.3. Biocompatibility of NIR-Sensitive Nanoparticles for Drug Delivery Breast cancer cells were used to test the in vitro cytotoxicity of the NIRsensitive Au-Au2S drug delivery system for its potential therapeutic use (Sheludko, 1996; Tan, 2006). Surfactant-modified nanoparticles and drug-loaded surfactant-modified nanoparticles were tested in vitro for cytotoxicity. Tan et al. (2007). The toxicity of drug-loaded surfactant-modified nanoparticles in vitro was shown to be dependent on the surfactant utilized for drug adsorption. The outcomes of released medications in the supernatant fraction collected following NIR

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irradiation of drug-loaded-surfactant-modified nanoparticles were studied in vitro. The released substance was discovered to have been chemically altered, resulting in greater toxicity (Figure 8.6) (Salgueiriño-Maceira et al., 2003; Qiang et al., 2006).

Figure 8.6. The biodistribution of Au-Au2S nanoparticles in KM mice treated with intra-tumor injection at various time periods was investigated. Source: https://link.springer.com/content/pdf/10.1007/s10856-007-3210-7.pdf.

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INDEX

A Adsorption 117, 118, 120, 126, 127, 136, 137, 143, 145, 149, 150, 152, 153, 154, 156, 160 agriculture 116 AlGaAs (aluminum gallium arsenide) 206 anaerobic digestion 118, 161 antennas 209, 216 B Barium titanate 173 Biodoped ceramic materials 228 biomolecules 226, 228 BPM (bit patterned media) 102 C Calcium-based ceramic materials 228 calcium chloride 27 calcium phosphates 227, 240 capacitors 209 carbides 2 carbohydrates 22 Carbon 2

carbonates 2, 4 carbon dioxide 2 carbon dots (CDs) 185 carbon monoxide 2, 10 carbon nanotubes 117 catalysis 93 cation 24, 26, 27, 28, 34, 36, 39 chemical durability 164 chemical elements 2 chemical nomenclature 22, 43 chemical sciences 22 chemical vapor deposition (CVD) 203 chlorofluorocarbons (CFCs) 96 commerce 23 communication 22 contaminants 116, 119, 120, 122, 127, 129, 152 crystalline microporosity 48 curvilinear geometries 200 cyanides 2, 4 D data processing 93 data storage 92, 101, 102, 103, 106, 109, 113

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diagnostic imaging 226 dielectric constant 169 digital data storage 92 diodes 206, 209, 217 drug delivery 93 drug delivery systems 226, 230, 236, 241 dyes 116, 136, 137, 140, 146, 154, 156, 157, 158, 161 E Elastomeric films 209 electrical conductivity 164, 168, 169, 172 electrochromic materials 164, 165 electronic charge transport 92 Electronic devices 200 Electron-transporting materials (ETM) 178 energy conversion 164, 166, 168, 177, 181, 190, 194 energy gathering 169 F ferromagnetic materials 100, 103 ferromagnetism 48 flotation 118 framework chirality 48 Fuel cells 181 Functional magnetic materials 92 G GaAs (gallium arsenide) 206 graphite 2 H halides 2 halogen atoms 2 halogens 25

heat 166, 169, 178, 183, 196 Heavy metal ions 116 high-capacity disc drives 105 high-speed memory systems 105 High temperature steam electrolysis (HTE) 183 human civilization 164 hydrides 2, 5 hydrochloric acid 3, 6 hydrofluoric acid 205, 206 hydrofluorocarbons (HFCs) 96 Hydrogen bonding 54 hyperthermia 101, 103, 106, 109, 112 I inductors 209 Inorganic Chemistry 4, 14, 16, 18, 19 inorganic compound 2, 4 inorganic semiconductors 201, 209 International Union of Pure and Applied Chemistry (IUPAC) 22 ion conductivity 48, 50, 89 ion exchange 118 ionic compounds 22, 23, 24, 25, 27, 28, 29, 30, 31, 33, 36, 38, 39, 40 L lead zirconate titanate 173 ligand-assisted templating’ (LAT) 55 M Macroporous materials 47, 77 magnetic field 92, 95, 97, 98, 100, 101, 104, 105, 106, 108 magnetic interfaces 92

Index

Magnetic materials 92 magnetic nanoparticles 93, 99, 101, 102, 108, 110, 113 magnetic random-access memory 105 magnetic reaction 92 Magnetic-semiconductor memory systems 105 magnetocaloric material 98 magnetocrystalline anisotropy 95, 103 Material-based systems 168 mechanical energy 165 mechanical motion 169 medical devices 92 mesopores 46, 77, 86 mesoporous silicas 46, 52, 58, 60, 65, 69, 70, 72, 73, 84, 88 metal alkoxide 229 metal oxide nanoparticles (MONPs) 117 microporous arsenates 49 microporous materials 46, 47, 48, 49, 50, 77 microporous phosphates 49 Mineral oxides 118 molecular compounds 22 molecular sensing devices 226 monatomic anions 25 MRI (magnetic resonance imaging) 93 multifunctional inorganic nanomaterials 164 multifunctional materials 48 Multifunctional nanomaterials 164 N nanocomposites 117, 130, 131, 135, 153, 157, 158

245

nanogenerator (NG) 173 nanomaterial functionalities 164 nanomembranes 201, 207, 219, 221 Nanoparticles 99, 101 nanoribbons 201, 207, 220 nanoscience 116 nanostructured materials (NWs) 201 Nanotechnology 99, 109, 111, 112 nano titanium dioxide 118 nano zerovalent iron 118 Near-infrared (NIR) 234 neutral solvent molecules 47 nitric acid 3, 5, 6 O Organic complexes 2 organic compound 22 organic molecules 2, 3 organic semiconductors 201 organometallic complexes 2 oscillators 209 oxides 2, 5, 6 oxygen reduction reaction (ORR) 182 P paramagnetism 99 Permanent magnets 93, 95 photoablation 234 photonic crystals (PSCs) 47, 178 photovoltaic (PV) 164 piezoelectric materials 173, 174 pollution 116, 117, 119, 146 Polyatomic anions 25, 29 polyatomic cations 25, 29 polyethylene oxide 54, 63, 80 Porous materials 46

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Q quaternary ammonium cations 47 R rare-earth permanent magnets 95, 113 refrigeration-magnetic cycle 98 remediation 117, 127, 152 renewable energy 166, 184 resistors 209 S scanning electron microscopy (SEM) 205 semi conductivity 48 semiconductor wafers 200 silica 227, 228, 229, 232, 239, 240 silver nanoparticles 118, 150, 153, 157, 160, 161 solar energy 165, 192, 194 spintronics 93 substances 23, 26, 37 sulfuric acid 3, 6, 12 Supercapacitors 184, 185 superferromagnetic (SFM) 103 superparamagnetic particles 100 systematic nomenclature 23 systemic circulatory system 226 T tetramethyl orthosilicate (TMOS) 56 thermal conductivity 169, 170, 171, 192

thermoelectric energy 165 Titania 227 TMR (tunneling magnetoresistance) 103 transition-metal dichalcogenides (TMD) 174 transition metals 24, 27 transmission devices 92 Triblock copolymers 54 Triboelectric nanogenerators (TENG) 175 trimethylbenzene (TMB) 54 U ultrafiltration 116, 118, 160 ultraviolet (UV) light 117 V verbal communication 22 W wastewater 116, 117, 118, 119, 120, 122, 125, 126, 128, 130, 138, 140, 147, 150, 152, 156, 157, 159, 160, 161 wastewater ecosystems 117 wastewater treatment 116, 118, 119, 125, 126, 150, 156, 160, 161 wide surface area 164 Z zerovalent nanoparticles 117 Zinc oxide 118, 131, 153, 173