Photocatalysis and Water Purification E-Book

• Herausgeber: Wiley-VCH
• Kategorie: Fachliteratur
• Serie: Materials for Sustainable Energy and Development
• Sprache: Englisch

Seitenzahl: 828

Veröffentlichungsjahr: 2013

Beschreibung

Water is one of the essential resources on our planet. Therefore, fresh water and the recycling of waste-water are very important topics in various areas. Energy-saving green technologies are a demand in this area of research. Photocatalysis comprises a class of reactions which use a catalyst activated by light. These reactions include the decomposition of organic compounds into environmental friendly water and carbon dioxide, leading to interesting properties of surfaces covered with a photocatalyst: they protect e.g. against incrustation of fouling matter, they are self-cleaning, antibacterial and viricidal. Therefore, they are attractive candidates for environmental applications such as water purification and waste-water treatment. This book introduces scientists and engineers to the fundamentals of photocatalysis and enlightens the potentials of photocatalysis to increase water quality. Also, strategies to improve the photocatalytic efficacy are pointed out: synthesis of better photocatalysts, combination of photocatalysis with other technologies, and the proper design of photocatalytic reactors. Implementation of applications and a chapter on design approaches for photocatalytic reactors round off the book. 'Photocatalysis and Water Purification' is part of the series on Materials for Sustainable Energy and Development edited by Prof. G.Q. Max Lu. The series covers advances in materials science and innovation for renewable energy, clean use of fossil energy, and greenhouse gas mitigation and associated environmental technologies.

Leseprobe

Table of Contents

Related Titles

Title Page

Copyright

Editorial Board

Series Editor Preface

Preface

About the Series Editor

About the Volume Editor

List of Contributors

Part I: Fundamentals: Active Species, Mechanisms, Reaction Pathways

1: Identification and Roles of the Active Species Generated on Various Photocatalysts

1.1 Key Species in Photocatalytic Reactions

1.2 Trapped Electron and Hole

1.3 Superoxide Radical and Hydrogen Peroxide (O2⋅− and H2O2)

1.4 Hydroxyl Radical (OH⋅)

1.5 Singlet Molecular Oxygen (1O2)

1.6 Reaction Mechanisms for Bare TiO2

1.7 Reaction Mechanisms of Visible-Light-Responsive Photocatalysts

1.8 Conclusion

References

2: Photocatalytic Reaction Pathways – Effects of Molecular Structure, Catalyst, and Wavelength

2.1 Introduction

2.2 Methods for Pathway Determination

2.3 Prototypical Oxidative Reactivity in Photocatalytic Degradations

2.4 Prototypical Reductive Reactivity in Photocatalytic Degradations

2.5 The Use of Organic Molecules as Test Probes for Next-Generation Photocatalysts

2.6 Modified Catalysts: Wavelength-Dependent Chemistry of Organic Probes

2.7 Conclusions

References

3: Photocatalytic Mechanisms and Reaction Pathways Drawn from Kinetic and Probe Molecules

3.1 The Photocatalyic Rate

3.2 Surface Speciation

3.3 Multisite Kinetic Model

3.4 Conclusion

References

Part II: Improving the Photocatalytic Eff icacy

4: Design and Development of Active Titania and Related Photocatalysts

4.1 Introduction – a Thermodynamic Aspect of Photocatalysis

4.2 Photocatalytic Activity: Reexamination

4.3 Design of Active Photocatalysts

4.4 A Conventional Kinetics in Photocatalysis: First-Order Kinetics

4.5 A Conventional Kinetics in Photocatalysis: Langmuir–Hinshelwood Mechanism

4.6 Topics and Problems Related to Particle Size of Photocatalysts

4.7 Recombination of a Photoexcited Electron and a Positive Hole

4.8 Evaluation of Crystallinity as a Property Affecting Photocatalytic Activity

4.9 Electron Traps as a Possible Candidate of a Recombination Center

4.10 Donor Levels – a Meaning of n-Type Semiconductor

4.11 Dependence of Photocatalytic Activities on Physical and Structural Properties

4.12 Synergetic Effect

4.13 Doping

4.14 Conclusive Remarks

Acknowledgments

References

5: Modified Photocatalysts

5.1 Why Modifying?

5.2 Forms of Modification

5.3 Modified Physicochemical Properties

Summary

References

6: Immobilization of a Semiconductor Photocatalyst on Solid Supports: Methods, Materials, and Applications

6.1 Introduction

6.2 Immobilization Techniques

6.3 Supports

6.4 Laboratory and Industrial Applications of Supported Photocatalysts

6.5 Conclusion

References

7: Wastewater Treatment Using Highly Functional Immobilized TiO2 Thin-Film Photocatalysts

7.1 Introduction

7.2 Application of a Cascade Falling-Film Photoreactor (CFFP) for the Remediation of Polluted Water and Air under Solar Light Irradiation

7.3 Application of TiO2 Thin-Film-Coated Fibers for the Remediation of Polluted Water

7.4 Application of TiO2 Thin Film for Photofuel Cells (PFC)

7.5 Preparation of Visible-Light-Responsive TiO2 Thin Films and Their Application to the Remediation of Polluted Water

7.6 Conclusions

References

8: Sensitization of Titania Semiconductor: A Promising Strategy to Utilize Visible Light

8.1 Introduction

8.2 Principle of Photosensitization

8.3 Dye Sensitization

8.4 Polymer Sensitization

8.5 Surface-Complex-Mediated Sensitization

8.6 Solid Semiconductor/Metal Sensitization

8.7 Other Strategies to Make Titania Visible Light Active

8.8 Conclusions

Acknowledgment

References

9: Photoelectrocatalysis for Water Purification

9.1 Introduction

9.2 Photoeffects at Semiconductor Interfaces

9.3 Water Depollution at Photoelectrodes

9.4 Photoelectrode Materials

9.5 Electrodes Preparation and Reactors

9.6 Conclusions

References

Part III: Effects of Photocatalysis on Natural Organic Matter and Bacteria

10: Photocatalysis of Natural Organic Matter in Water: Characterization and Treatment Integration

10.1 Introduction

10.2 Monitoring Techniques

10.3 By-Products from the Photocatalytic Oxidation of NOM and its Resultant Disinfection By-Products (DBPs)

10.4 Hybrid Photocatalysis Technologies for the Treatment of NOM

10.5 Conclusions

References

11: Waterborne Escherichia coli Inactivation by TiO2 Photoassisted Processes: a Brief Overview

11.1 Introduction

11.2 Physicochemical Aspects Affecting the Photocatalytic E. coli Inactivation

11.3 Using of N-Doped TiO2 in Photocatalytic Inactivation of Waterborne Microorganisms

11.4 Biological Aspects

11.5 Proposed Mechanisms Suggested for Bacteria Abatement by Heterogeneous TiO2 Photocatalysis

11.6 Conclusion

References

Part IV: Modeling. Reactors. Pilot plants

12: Photocatalytic Treatment of Water: Irradiance Influences

12.1 Introduction

12.2 Reaction Order in Irradiance: Influence of Electron–Hole Recombination and the High Irradiance Penalty

12.3 Langmuir–Hinshelwood (LH) Kinetic Form: Equilibrated Adsorption

12.4 Pseudo-Steady-State Analysis: Nonequilibrated Adsorption

12.5 Mass Transfer and Diffusion Influences at Steady Conditions

12.6 Controlled Periodic Illumination: Attempt to Beat Recombination

12.7 Solar-Driven Photocatalysis: Nearly Constant nUV Irradiance

12.8 Mechanism of Hydroxyl Radical Attack: Same Irradiance Dependence

12.9 Simultaneous Homogeneous and Heterogeneous Photochemistry

12.10 Dye-Photosensitized Auto-Oxidation

12.11 Interplay between Fluid Residence Times and Irradiance Profiles

12.12 Quantum Yield, Photonic Efficiency, and Electrical Energy per Order

12.13 Conclusions

References

13: A Methodology for Modeling Slurry Photocatalytic Reactors for Degradation of an Organic Pollutant in Water

13.1 Introduction and Scope

13.2 Evaluation of the Optical Properties of Aqueous TiO2 Suspensions

13.3 Radiation Model

13.4 Quantum Efficiencies of 4-Chlorophenol Photocatalytic Degradation

13.5 Kinetic Modeling of the Pollutant Photocatalytic Degradation

13.6 Bench-Scale Slurry Photocatalytic Reactor for Degradation of 4-Chlorophenol

13.7 Conclusions

Acknowledgments

References

14: Design and Optimization of Photocatalytic Water Purification Reactors

14.1 Introduction

14.2 Catalyst Immobilization Strategy

14.3 Synergistic Effects of Photocatalysis and Other Methods

14.4 Effective Design of Photocatalytic Reactor System

14.5 Future Directions and Concluding Remarks

Acknowledgments

References

15: Solar Photocatalytic Pilot Plants: Commercially Available Reactors

15.1 Introduction

15.2 Compound Parabolic Concentrators

15.3 Technical Issues: Reflective Surface and Photoreactor

15.4 Suspended or Supported Photocatalyst

15.5 Solar Photocatalytic Treatment Plants

15.6 Specific Issues Related with Solar Photocatalytic Disinfection

15.7 Conclusions

Acknowledgments

References

Index

Related Titles

Duke, M., Zhao, D., Semiat, R. (eds.)

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2013

ISBN: 978-3-527-32987-8

Cecen, F., Aktas, Ö.

Activated Carbon for Water and Wastewater Treatment

Integration of Adsorption and Biological Treatment

2012

ISBN: 978-3-527-32471-2

Gottschalk, C., Libra, J. A., Saupe, A.

Ozonation of Water and Waste Water

A Practical Guide to Understanding Ozone and its Applications

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Ganoulis, J.

Risk Analysis of Water Pollution

2009

ISBN: 978-3-527-32173-5

Parmon, V. N., Vorontsov, A. V., Kozlov, D., Smirniotis, P.

Photocatalysis

Catalysts, Kinetics and Reactors

2008

ISBN: 978-3-527-31784-4

Wiesmann, U., Choi, I. S., Dombrowski, E.-M.

Biological Wastewater Treatment

Fundamentals, Microbiology, Industrial Process Integration

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Turovskiy, I. S., Mathai, P. K.

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The Editors

Prof. Dr. Pierre Pichat

CNRS, Ecole Centrale de Lyon

(STMS), Photocatalyse et

Environnement

69134 Ecully CEDEX

France

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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Boschstr. 12, 69469 Weinheim, Germany

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Print ISBN: 978-3-527-33187-1

ePDF ISBN: 978-3-527-64542-8

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Materials for sustainable energy and development (Print) ISSN: 2194-7813

Materials for sustainable energy and development (Internet) ISSN: 2194-7821

Editorial Board

Members of the Advisory Board of the “Materials for Sustainable Energy and Development” Series

Professor Huiming Cheng

Professor Calum Drummond

Professor Morinobu Endo

Professor Michael Grätzel

Professor Kevin Kendall

Professor Katsumi Kaneko

Professor Can Li

Professor Arthur Nozik

Professor Detlev Stöver

Professor Ferdi Schüth

Professor Ralph Yang

Series Editor Preface

The Wiley Series on New Materials for Sustainable Energy and Development

Sustainable energy and development is attracting increasing attention from the scientific research communities and industries alike, with an international race to develop technologies for clean fossil energy, hydrogen and renewable energy as well as water reuse and recycling. According to the REN21 (Renewables Global Status Report 2012 p. 17) total investment in renewable energy reached $257 billion in 2011, up from $211 billion in 2010. The top countries for investment in 2011 were China, Germany, the United States, Italy, and Brazil. In addressing the challenging issues of energy security, oil price rise, and climate change, innovative materials are essential enablers.

In this context, there is a need for an authoritative source of information, presented in a systematic manner, on the latest scientific breakthroughs and knowledge advancement in materials science and engineering as they pertain to energy and the environment. The aim of the Wiley Series on New Materials for Sustainable Energy and Development is to serve the community in this respect. This has been an ambitious publication project on materials science for energy applications. Each volume of the series will include high-quality contributions from top international researchers, and is expected to become the standard reference for many years to come.

This book series covers advances in materials science and innovation for renewable energy, clean use of fossil energy, and greenhouse gas mitigation and associated environmental technologies. Current volumes in the series are:

Supercapacitors. Materials, Systems, and Applications

Functional Nanostructured Materials and Membranes for Water Treatment

Materials for High-Temperature Fuel Cells

Materials for Low-Temperature Fuel Cells

Advanced Thermoelectric Materials. Fundamentals and Applications

Advanced Lithium-Ion Batteries. Recent Trends and Perspectives

Photocatalysis and Water Purification. From Fundamentals to Recent Applications

In presenting this volume on Supercapacitors, I would like to thank the authors and editors of this important book, for their tremendous effort and hard work in completing the manuscript in a timely manner. The quality of the chapters reflects well the caliber of the contributing authors to this book, and will no doubt be recognized and valued by readers.

Finally, I would like to thank the editorial board members. I am grateful to their excellent advice and help in terms of examining coverage of topics and suggesting authors, and evaluating book proposals.

I would also like to thank the editors from the publisher Wiley-VCH with whom I have worked since 2008, Dr Esther Levy, Dr Gudrun Walter, and Dr Bente Flier for their professional assistance and strong support during this project.

I hope you will find this book interesting, informative and valuable as a reference in your work. We will endeavour to bring to you further volumes in this series or update you on the future book plans in this growing field.

Brisbane, Australia

G.Q. Max Lu

31 July 2012

Preface

Thousands of articles, patents, and reviews have appeared about heterogeneous photocatalysis using semiconductors, mainly TiO2. Among them, many deal with the purification of water, which is obviously a very important problem for our environment and poses a challenge. Because of this abundance of publications, it is very difficult even for the experts to get a clear view of “photocatalysis and water purification”. In my opinion, this book – which gathers reviews from eminent scientists with a long experience in the field – will allow the readers to gain the general view they expect. The knowledge on the fundamentals is integrated with the potential implementation of photocatalytic water purification using UV lamps or solar light. To that end, this book is structured in four sections with a total of 14 chapters.

The three opening papers explore the fundamentals. Chapter 1 focuses on the active species, especially the oxygen species, which follow the excitation of the photocatalyst by band gap irradiation, and provides information on the roles of these species. Chapter 2 identifies the degradation pathways of organic pollutants and indicates how these pathways are influenced by the pollutant molecular structure, the photocatalyst, and irradiation characteristics. Dealing also with pathways, Chapter 3 presents a synthetic and critical view of the kinetic models and shows how the effects of various parameters can be rationalized.

Improving the photocatalytic efficacy is obviously an extremely important question that is addressed in Chapters 4–9. Understanding how the diverse characteristics of the photocatalyst intervene and whether these characteristics can be tailored to increase the efficacy is considered in Chapters 4 and 5. On the basis of a critical appraisal of the present knowledge it is concluded in Chapter 4 that it is, unfortunately, premature to indicate uncontestable guidance for photocatalyst design. Chapter 5 discusses in detail the various ways by which the photocatalyst can be modified. The use of composite materials is also taken into account. The conclusion is similar to that of Chapter 4. As the photocatalyst is in practice rarely dispersed in the water to be treated, Chapter 6 covers the main methods used to immobilize the photocatalyst and details the nature, shapes, and advantages and disadvantages of the supporting materials. Chapter 7 focuses on the interest of TiO2 thin films and gives examples of the types of reactors in which they can be employed; some of the means allowing one to make these films sensitive in the visible region of the solar spectrum are also discussed. Chapter 8 provides a detailed and critical review of all the methodologies utilized for visible-light sensitization of photocatalysts and indicates how to properly evaluate the results. Finally, as the recombination of the photoproduced charge carriers is the main flaw of heterogeneous photocatalysis, there is also the possibility to effect the separation of these charge carriers by use of an applied potential. Chapter 9 reports on this technique, called photoelectrocatalysis, and concludes that the design of reactors needs further progress to achieve effective water purification.

Most studies regarding water photocatalytic purification refer to both organic pollutants representative of the different categories of organic compounds and to great classes of exogenous pollutants such as pesticides, dyes, and pharmaceuticals. It was therefore deemed necessary to also include in this book a section on the effects of photocatalysis on natural organic matter (NOM) and bacteria which are found in many waters. In some cases eliminating NOM in the course of the purification is desirable; NOM can also hinder the removal of pollutants. Consequently, Chapter 10 is devoted to photocatalysis and NOM; it is concluded that, in general, photocatalysis cannot be applied as a stand-alone process, but its coupling with another technique can be beneficial. Chapter 11 covers the photocatalytic inactivation of bacteria and explains in depth how the active species issued from excitation of the photocatalyst can damage the membrane and degrade the organic constituents of bacteria.

The last section deals with modeling and reactors. Chapter 12 focuses on the influence of irradiation, which is the initiation step of photocatalysis and stresses that irradiance measurement is essential; however, the observed kinetics is also influenced by other factors whose relative importance must be determined for reactor design. Chapter 13 demonstrates that rigorous mathematical modeling based on data collected at the laboratory and bench scales enables one to simulate the performance of photocatalytic slurry reactors of different shapes, sizes, irradiation systems, and configurations. Chapter 14 includes examples of reactors using photocatalysis as a stand-alone process or combined with another AOP; it also emphasizes that immobilization of the photocatalyst must be carefully studied and that further progress in photocatalyst sensitization to visible light is highly desirable. Chapter 15 reviews the characteristics of diverse types of solar reactors including full-size demonstration plants with a detailed presentation regarding the utilization of sun light; it is concluded that appraisal of the possibilities for both pollutants removal and disinfection requires further comparison with other technologies.

I think this book covers all the main topics of “photocatalysis and water purification”. It will be helpful for students beginning research in the field and for technicians and scientists involved in the treatment of water by other technologies, who would like to learn about photocatalysis and its potentialities. Even senior scientists in the field will certainly be interested in the opinion of colleagues about some of the issues.

I sincerely thank the contributors for their response to my solicitation, their time, and efforts. I am also very grateful to the reviewers and the Wiley staff.

Pierre Pichat

About the Series Editor

Professor Max Lu

Editor, New Materials for Sustainable Energy and Development Series

Professor Lu's research expertise is in the areas of materials chemistry and nanotechnology. He is known for his work on nanoparticles and nanoporous materials for clean energy and environmental technologies. With over 500 journal publications in high-impact journals, including Nature, Journal of the American Chemical Society, Angewandte Chemie, and Advanced Materials, he is also coinventor of 20 international patents. Professor Lu is an Institute for Scientific Information (ISI) Highly Cited Author in Materials Science with over 17 500 citations (h-index of 63). He has received numerous prestigious awards nationally and internationally, including the Chinese Academy of Sciences International Cooperation Award (2011), the Orica Award, the RK Murphy Medal, the Le Fevre Prize, the ExxonMobil Award, the Chemeca Medal, the Top 100 Most Influential Engineers in Australia (2004, 2010, and 2012), and the Top 50 Most Influential Chinese in the World (2006). He won the Australian Research Council Federation Fellowship twice (2003 and 2008). He is an elected Fellow of the Australian Academy of Technological Sciences and Engineering (ATSE) and Fellow of Institution of Chemical Engineers (IChemE). He is editor and editorial board member of 12 major international journals including Journal of Colloid and Interface Science and Carbon.

Max Lu has been Deputy Vice-Chancellor and Vice-President (Research) since 2009. He previously held positions of acting Senior Deputy Vice-Chancellor (2012), acting Deputy Vice–Chancellor (Research), and Pro-Vice-Chancellor (Research Linkages) from October 2008 to June 2009. He was also the Foundation Director of the ARC Centre of Excellence for Functional Nanomaterials from 2003 to 2009.

Professor Lu had formerly served on many government committees and advisory groups including the Prime Minister's Science, Engineering and Innovation Council (2004, 2005, and 2009) and the ARC College of Experts (2002–2004). He is the past Chairman of the IChemE Australia Board and former Director of the Board of ATSE. His other previous board memberships include Uniseed Pty Ltd., ARC Nanotechnology Network, and Queensland China Council. He is currently Board member of the Australian Synchrotron, National eResearch Collaboration Tools and Resources, and Research Data Storage Infrastructure. He also holds a ministerial appointment as member of the National Emerging Technologies Forum.

About the Volume Editor

Professor Pierre Pichat

Pierre Pichat, as “Directeur de Recherche”, with the CNRS (National Center for Scientific Research, France), has been active in heterogeneous photocatalysis for many years and has founded a laboratory principally based on this field in Lyon, France. His research activity has concerned both basic investigations and applications regarding not only the photocatalytic treatment of water but also self-cleaning materials and the purification of indoor air. He has been invited to publish reviews or these domains. He has received an Appreciation Award acknowledging his pioneering contributions.

List of Contributors

Orlando M. Alfano

Universidad Nacional del Litoral and CONICET

Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)

Paraje El Pozo. Colectora Ruta Nacional N° 168

3000, Santa Fe

Argentina

Rossano Amadelli

University of Ferrara

CNR-ISOF, U.O.S. of Ferrara

Department of Chemistry

Via L. Borsari 46

I-44121 Ferrara

Italy

Rose Amal

The University of New South Wales

School of Chemical Engineering

ARC Centre of Excellence for Functional Nanomaterials

Tyree Energy Technologies Building

Sydney NSW 2052

Australia

Masakazu Anpo

Osaka Prefecture University

(Vice President & Executive Director)

Research Organization for the 21st Century

1-1 Gakuencho, Naka-ku, Sakai

599-8531 Osaka

Japan

Rodolfo J. Brandi

Universidad Nacional del Litoral and CONICET

Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)

Paraje El Pozo. Colectora Ruta Nacional N° 168

3000, Santa Fe

Argentina

Alberto E. Cassano

Universidad Nacional del Litoral and CONICET

Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)

Paraje El Pozo. Colectora Ruta Nacional N° 168

3000, Santa Fe

Argentina

Chuncheng Chen

Institute of Chemistry

Chinese Academy of Sciences (CAS)

Beijing National Laboratory for Molecular Sciences

Key Laboratory of Photochemistry

No. 2, 1st North Street, Zhongguancun

Beijing 100190

China

Pilar Fernández-Ibáñez

Plataforma Solar de Almería (CIEMAT)

Carretera Senés, km 4

04200, Tabernas (Almería)

Spain

Akira Fujishima

Kanagawa Academy of Science and Technology

Photocatalyst Group

KSP East 421, 3-2-1 Sakado, Kawasaki

Kanagawa 213-0012

Japan

and

Tokyo University of Science

Division of Photocatalyst for Energy and Environment

Research Institute for Science and Technology

1 – 3 Kagurazaka, Shinjuku-ku

Tokyo 162-8601

Japan

Yu Horiuchi

Osaka Prefecture University

Department of Applied Chemistry

1-1 Gakuencho, Naka-ku, Sakai

599-8531 Osaka

Japan

William S. Jenks

Iowa State University

Department of Chemistry

3760 Gillman Hall

Ames, IA, 50011-3111

USA

Nicolas Keller

Laboratoire des Matériaux

Surfaces et Procédés pour la Catalyse

Ecole Européenne de Chimie

Polymères et Matériaux

CNRS and Strasbourg University

25 rue Becquerel

67087, Strasbourg Cedex

France

Valérie Keller

Laboratoire des Matériaux

Surfaces et Procédés pour la Catalyse

Ecole Européenne de Chimie

Polymères et Matériaux

CNRS and Strasbourg University

25 rue Becquerel

67087, Strasbourg Cedex

France

May Lim

The University of New South Wales

School of Chemical Engineering

ARC Centre of Excellence for Functional Nanomaterials

Tyree Energy Technologies Building

Sydney NSW 2052

Australia

Sanly Liu

The University of New South Wales

School of Chemical Engineering

ARC Centre of Excellence for Functional Nanomaterials

Tyree Energy Technologies Building

Sydney NSW 2052

Australia

Wanhong Ma

Institute of Chemistry

Chinese Academy of Sciences (CAS)

Beijing National Laboratory for Molecular Sciences

Key Laboratory of Photochemistry

No. 2, 1st North Street, Zhongguancun

Beijing 100190

China

Sixto Malato

Plataforma Solar de Almería (CIEMAT)

Carretera Senés, km 4, 04200

Tabernas (Almería)

Spain

Maneil Ignacio Maldonado

Plataforma Solar de Almería (CIEMAT)

Carretera Senés, km 4, 04200

Tabernas (Almería)

Spain

Masaya Matsuoka

Osaka Prefecture University

Department of Applied Chemistry

1-1 Gakuencho

Naka-ku, Sakai

599-8531 Osaka

Japan

Valter Maurino

Univ. degli Studi di Torino

Dipt. di Chimica, Analitica

Via Pietro Giuria 5

10125 Torino

Italy

Claudio Minero

Univ. degli Studi di Torino

Dipt. di Chimica, Analitica

Via Pietro Giuria 5

10125 Torino

Italy

Atsuko Y. Nosaka

Nagaoka University of Technology

Department of Materials Science and Technology

Kamitomioka-cho 1603-1

Nagaoka, 940-2188

Japan

Yoshio Nosaka

Nagaoka University of Technology

Department of Materials Science and Technology

Kamitomioka-cho 1603-1

Nagaoka, 940-2188

Japan

Tsuyoshi Ochiai

Kanagawa Academy of Science and Technology

Photocatalyst Group

KSP East 421, 3-2-1 Sakado

Kawasaki

Kanagawa 213-0012

Japan

and

Tokyo University of Science

Division of Photocatalyst for Energy and Environment

Research Institute for Science and Technology

1 – 3 Kagurazaka

Shinjuku-ku

Tokyo 162-8601

Japan

Bunsho Ohtani

Catalysis Research Center

Hokkaido University

North 21, West 10

Sapporo 001-0021

Japan

Isabel Oller

Plataforma Solar de Almería (CIEMAT)

Carretera Senés, km 4, 04200

Tabernas (Almería)

Spain

David Ollis

North Carolina State University

Department of Chemical and Biomolecular Engineering

911 Partners Way

Raleigh, NC 27695-7905

USA

Yaron Paz

Technion-Israel Institute of Technology

Department of Chemical Engineering

3200, Haifa

Israel

Maria Inmaculada Polo-López

Plataforma Solar de Almería (CIEMAT)

Carretera Senés, km 4, 04200

Tabernas (Almeréa)

Spain

Cesar Pulgarin

Ecole Polytechnique Fédérale de Lausanne (EPFL)

Institute of Chemical Science and Engineering, GGEC 1015 Lausanne

Switzerland

Julián Andrés Rengifo-Herrera

Universidad Nacional de La Plata-UNLP CCT La Plata-CONICET

Centro de Investigación y Desarrollo en Ciencias Aplicadas “Dr. J.J. Ronco”- CINDECA

Departamento de Química

Facultad de Ciencias Exactas

Calle 47 No. 257, 1900 La Plata

Buenos Aires

Argentina

Angela Giovana Rincón

University of Cambridge

Department of Chemistry

Lensfield Road

Cambridge, CB2, 1EW

UK

Didier Robert

Laboratoire des Matériaux

Surfaces et Procédés pour la Catalyse

CNRS and Strasbourg University

Antenne de Saint-Avold

Université de Lorraine

12 Rue Victor Demange

57500, Saint-Avold

France

Luca Samiolo

University of Ferrara

CNR-ISOF

U.O.S. of Ferrara

Department of Chemistry

Via L. Borsari 46

I-44121 Ferrara

Italy

Maríia L. Satuf

Universidad Nacional del Litoral and CONICET

Instituto de Desarrollo Tecnológico para la Industria Química (INTEC)

Paraje El Pozo. Colectora Ruta Nacional N° 168

3000, Santa Fe

Argentina

Nurit Shaham-Waldmann

Technion-Israel Institute of Technology

Department of Chemical Engineering

3200, Haifa

Israel

Masato Takeuchi

Osaka Prefecture University

Department of Applied Chemistry

1-1 Gakuencho

Naka-ku, Sakai

599-8531 Osaka

Japan

Takashi Toyao

Osaka Prefecture University

Department of Applied Chemistry

1-1 Gakuencho

Naka-ku, Sakai

599-8531 Osaka

Japan

Davide Vione

Univ. degli Studi di Torino

Dipt. di Chimica Analitica

Via Pietro Giuria 5

10125 Torino

Italy

Zhaohui Wang

Institute of Chemistry

Chinese Academy of Sciences (CAS)

Beijing National Laboratory for Molecular Sciences

Key Laboratory of Photochemistry

No.2, 1st North Street, Zhongguancun

Beijing 100190

China

and

Donghua University

College of Environmental Science and Engineering

No.2999, North Renmin Road

Shanghai 201620

China

Jincai Zhao

Institute of Chemistry

Chinese Academy of Sciences (CAS)

Beijing National Laboratory for Molecular Sciences

Key Laboratory of Photochemistry

No. 2, 1st North Street, Zhongguancun

Beijing 100190

China

Part I

Fundamentals: Active Species, Mechanisms, Reaction Pathways

1

Identification and Roles of the Active Species Generated on Various Photocatalysts

Yoshio Nosaka and Atsuko Y. Nosaka

TiO2 photocatalysts have been utilized for the oxidation of organic pollutants [1–5]. For further practical applications, the improvement in the photocatalytic efficiency and the extension of the effective wavelength of the irradiation light are desired. From this point of view, better understanding of the primary steps in photocatalytic reactions is prerequisite to develop prominent photocatalysts. The properties of TiO2 and the reaction mechanisms in molecular level have been reviewed recently [6]. Therefore, this chapter describes briefly active species involved in the photocatalytic reactions for bare TiO2 and TiO2 modified for visible-light response, that is, trapped electrons, superoxide radical (O2⋅−), hydroxyl radical (OH⋅), hydrogen peroxide (H2O2), and singlet oxygen (1O2).

1.1 Key Species in Photocatalytic Reactions

Since the photocatalytic reactions proceed usually with oxygen molecules (O2) in air, the reduction of oxygen would be the important process in photocatalytic reduction. On the other hand, taking into account that the surface of TiO2 photocatalysts is covered with adsorbed water molecules in usual environments and that photocatalysts are often used to decompose pollutants in water, oxidation of water would be the important process in photocatalytic oxidation. As shown in Figure 1.1, when O2 is reduced by one electron (Eq. (1.1)), it becomes a superoxide radical (O2⋅−) that is further reduced by one electron (Eq. (1.2)) or reacts with a hydroperoxyl radical (HO2⋅, i.e., protonated O2⋅−) to form hydrogen peroxide (H2O2). The latter reaction is largely pH dependent because the amount of HO2⋅, whose pKa is 4.8, changes largely at pH around neutral [7]. One-electron reduction of H2O2 (Eq. (1.3)) produces hydroxyl radical (OH⋅). In the field of radiation chemistry, it is well documented that OH⋅ is produced by one-electron oxidation of H2O with ionization radiation. However, the formation of OH⋅ in the photocatalytic oxidation process has not been confirmed, as described later.

1.1

1.2

1.3

Figure 1.1 One-electron reduction steps of oxygen to OH radical and two-electron oxidation step of water to H2O2 observed in the TiO2 photocatalyst.

Figure 1.2 shows the standard potentials [8] for the one-electron redox of active oxygen species as a function of pH of the solution. The conduction band (CB) bottom for anatase and rutile TiO2 along with valence band (VB) top of TiO2 is also depicted. The pKa values for H2O2 and OH⋅ are 11.7 and 11.9, respectively [7]. Therefore, the linear lines showing pH dependence in change the inclination at the individual pH. It is notable that in the pH range between 10.6 and 12.3, one-electron reduction resulting in OH formation (Eq. ()) occurs at a higher potential than that resulting in HO formation (Eq. ()). As commonly known, the potential of the VB of TiO is low enough to oxidize HO, suggesting the possibility of the formation of OH. However, the potentials in the figure are depicted based on the free energy change in a homogeneous aqueous solution. Therefore, it does not always mean that the one-electron oxidation of HO by VB holes at the surface of TiO solid takes place in the heterogeneous system. Since the oxidation of HO to HO and O is also possible, only the potential difference between VB and OH should not be used easily for explaining the possibility of the formation of OH. The competition between OH-radical-mediated reaction versus direct electron transfer has been studied as the effect of fluoride ions on the photocatalytic degradation of phenol in an aqueous TiO suspension [9]. Under a helium atmosphere and in the presence of fluoride ions, phenol is significantly degraded, suggesting the occurrence of a photocatalytically induced hydrolysis [9].