Table Of ContentPhotocatalysts and Electrocatalysts
in Water Remediation
Photocatalysts and Electrocatalysts
in Water Remediation
From Fundamentals to Full Scale Applications
Edited by
Dr Prasenjit Bhunia
Silda Chandra Sekhar College, India
Dr Kingshuk Dutta
Central Institute of Petrochemicals Engineering and Technology (CIPET), India
Dr S. Vadivel
Saveetha Institute of Medical and Technical Sciences, India
This edition first published 2023
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v
Contents
Preface ix
About the Editors xi
List of Contributors xiii
Acknowledgements xv
1 F undamentals and Functional Mechanisms of Photocatalysis in
Water Treatment 1
1.1 Introduction 1
1.2 Different Photocatalytic Materials for Water Treatment 2
1.3 In-depth Mechanisms of Photocatalysis 9
1.4 Visible Light Driven Photocatalysts for Water Decontamination 20
1.5 Summary 25
2 Different Synthetic Routes and Band Gap Engineering of Photocatalysts 39
2.1 Introduction 39
2.2 Synthesis of Photocatalysts 40
2.3 Properties of Ideal Photocatalytic Material 57
2.4 Engineering Photocatalytic Properties 58
2.5 Energy Bandgap 59
2.6 Engineering the Desired Band Gap 64
2.7 Photocatalytic Mechanisms, Schemes and Systems 69
2.8 Summary and Perspectives 71
3 Photocatalytic Decontamination of Organic Pollutants from Water 81
3.1 Introduction 81
3.2 Photocatalytic Degradation Mechanisms of Organic Contaminants 82
3.3 A dvanced Photocatalytic Materials for Decontamination of
Organic Pollutants 83
3.4 S olar/Visible-light Driven Photocatalytic Decontamination of Organic
Pollutants 85
3.5 E merging Scientific Opportunities of Photocatalysts in Removal of Organic
Pollutants 87
3.6 L imitations of Photocatalytic Decontamination and Key
Mitigation Strategies 95
3.7 Summary and Future Directions 96
vi Contents
4 Photocatalytic Removal of Heavy Metal Ions from Water 105
4.1 Introduction 105
4.2 Mechanistic Insights on Photocatalytic Removal of Heavy Metal Ions 110
4.3 S olar/Visible-light Driven Photocatalysts for the Removal of
Heavy Metal Ions 113
4.4 Selective Heavy Metal Ion Removal by Semiconductor Photocatalysts 123
4.5 Major Drawbacks and Key Mitigation Strategies 125
4.6 Summary and Future Directions 126
5 Smart Photocatalysts in Water Remediation 135
5.1 Introduction 135
5.2 Advances in the Development of Visible-light Driven Photocatalysts 138
5.3 Advances in Photocatalyst Immobilization and Supports 142
5.4 Advances in Nonimmobilized Smart Photocatalysts 144
5.5 Advances in Improving the Efficiency of Light Delivery 149
5.6 Advances in Biomaterials for Designing Smart Photocatalysts 157
5.7 Advances Toward Improving Photocatalytic Activity via External Stimuli 159
5.8 A dvances in Inhibiting the Photocorrosion of Semiconductor-based
Photocatalysts 164
5.9 A dvances in Recycling Photocatalysts: Assessing the
Photocatalyst Life Cycle 166
5.10 Summary, Future Challenges, and Prospects for Further Research 167
6 F undamentals and Functional Mechanisms of Electrocatalysis in Water
Treatment 189
6.1 Introduction 189
6.2 Electrocatalysis Treatment 190
6.3 Properties and Characteristics of Different Electrocatalysis Techniques 192
6.4 Case Studies and Successful Approaches 202
6.5 Conclusion 217
7 D ifferent Synthetic Routes of Electrocatalysts and
Fabrication of Electrodes 229
7.1 Introduction 229
7.2 Fundamental Principles of Alkaline Water Oxidation 230
7.3 E lectrochemical Evaluating Parameters of Electrocatalysts for OER
Performance 231
7.4 Electrocoagulation 233
7.5 Electroflotation 233
7.6 Electrocoagulation/flotation 233
7.7 Electro-oxidation in Wastewater Treatment 233
7.8 Doped Diamond Electrodes 234
7.9 Conclusion 235
Contents vii
8 Electrocatalytic Degradation of Organic Pollutants from Water 241
8.1 Introduction 241
8.2 Principles and Fundamental Aspects of Electrooxidation 242
8.3 Electrode Materials and Cell Configuration 244
8.4 Performance Assessment Indicators and Operating Variables 250
8.5 Electrochemical Filtering Process: A Hybrid Process Based on
Electrooxidation and Filteri ng 253
8.6 Integration of Electrooxidation-based Processes in Water/Wastewater
Treatment Technological Flow 259
9 Electrocatalytic Removal of Heavy Metal Ions from Water 275
9.1 Introduction 275
9.2 Fundamentals 277
9.3 Advantages and Disadvantages of the Electrocatalytic Approach 283
9.4 Summary 284
10 Combined Photoelectrocatalytic Techniques in Water Remediation 289
10.1 Introduction 289
10.2 Photoelectrocatalysts for Treatment of Water Contaminants 292
10.3 Simultaneous Removal of Organic and Inorganic Pollutants 302
10.4 Conclusions and Perspective 304
Index 311
ix
Preface
A wide array of wastewater treatment alternatives are being investigated nowadays, and
this is owing to the increase in polluted wastewater generation because of the growth in
population and industrial activities. Advanced oxidation processes (AOPs) have become, in
the last few years, a selected alternative due to several advantages, such as their nonselec-
tive degradation of pollutants and their easy setup. Photo-based processes have always
been one of the most preferred AOP options, due to the possibility of using solar radiation
that may reduce the AOPs’ high elevated costs. Photocatalysis processes fall under the AOP
category, and it is studied worldwide for various applications. A photocatalyst is defined as
a “catalyst able to produce, upon absorption of light, chemical transformations of the reac-
tion partners” [1]. The excited state of a photocatalyst interacts repeatedly with the reac-
tion partners, resulting in the formation of reaction intermediates, and regenerates itself
after each cycle of such interactions. In effect, the photocatalyst is activated with radiation,
which brings about the separation of electrons and holes from, respectively, the valence
and conduction bands of semiconductor photocatalysts. This, in turn, starts a series of
chain reactions that lead to the generation of oxidants and, ultimately, to pollutant degra-
dation. However, even photocatalysis has limitations for future applications; for instance,
the electrons and holes are usually recombined, long treatment times are required, etc. As
a solution, the combination of photocatalysis with the application of an electrochemical
field (photoelectrocatalysis) has been contemplated.
On the other hand, electrochemistry, an interdisciplinary field of interfacial charge
transfer, has been introduced for the decontamination of both organic and inorganic pol-
lutants, and therefore has developed significant worldwide interest toward water remedia-
tion. In this connection, electrocatalytic oxidation and reduction usually work together to
decompose organic contaminants, and convert heavy metal ions from their toxic to non-
toxic form in electrocatalytic advance oxidation processes (EAOPs). Although this tech-
nique was elucidated long back in the 1970s, it is only in recent years that the electrocatalysts
have become highly encouraging materials toward water remediation. Electrocatalysts
degrade or convert the contaminants (organic or inorganic) through profound collision of
a very clean reagent – “the electron”; therefore, the technique is recognized as environmen-
tally benign. In addition, this technique has been found to be highly versatile toward deg-
radation of various contaminants, including dyes, pesticides and herbicides, phenolic
compounds, pharmaceuticals, etc., and is also able to convert heavy metal ions from their
