Semiconductor Photocatalysis E-Book

Horst Kisch

• Herausgeber: Wiley-VCH
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 461

Veröffentlichungsjahr: 2014

Beschreibung

Focusing on the basic principles of semiconductor photocatalysis, this book also gives a brief introduction to photochemistry, photoelectrochemistry, and homogeneous photocatalysis. In addition, the author - one of the leading authorities in the field - presents important environmental and practical aspects.

A valuable, one-stop source for all chemists, material scientists, and physicists working in this area, as well as novice researchers entering semiconductor photocatalysis.

Leseprobe

Table of Contents

Cover

Related Titles

Title Page

Copyright

Dedication

Preface

Acknowledgments

Chapter 1: Introduction

1.1 A Brief History of Photochemistry

1.2 Catalysis, Photochemistry, and Photocatalysis

Chapter 2: Molecular Photochemistry

2.1 Absorption and Emission

2.2 Intensity of Electronic Transitions

2.3 Excited States Radiative Lifetimes

2.4 Energy and Electron Transfer

2.5 Proton Transfer and Hydrogen Abstraction

2.6 Photosensitization

2.7 Rates and Quantum Yields

2.8 Quenching of Excited States

2.9 Absorption, Emission, and Excitation Spectra

2.10 Classification and Reactivity of Excited States

Chapter 3: Molecular Photocatalysis

3.1 Hydrogenation of 1,3-Dienes

3.2 Co-Cyclization of Alkynes with Nitriles

3.3 Enantioselective Trifluoromethylation of Aldehydes

3.4 Photoinduced Electron Transfer Catalysis

3.5 Reduction and Oxidation of Water

Chapter 4: Photoelectrochemistry

4.1 Electronic Structure and Nature of Excited States

4.2 Photocorrosion

4.3 Interfacial Electron Transfer

Chapter 5: Semiconductor Photocatalysis

5.1 Mechanisms, Kinetics, and Adsorption

5.2 Characterization of Photocatalysts

5.3 Preparation and Properties of Photocatalysts

5.4 Type A Reactions

5.5 Type B Reactions

5.6 Environmental Aspects

5.7 Titania in Food and Personal Care Products

5.8 Photoreactors

References

Index

EULA

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Guide

Cover

Table of Contents

Preface

Chapter 1: Introduction

List of Illustrations

Scheme 1.1

Figure 1.1

Scheme 1.2

Scheme 1.3

Scheme 1.4

Scheme 1.5

Figure 2.1

Figure 2.2

Scheme 2.1

Figure 2.3

Scheme 2.2

Scheme 2.3

Figure 2.4

Figure 2.5

Figure 2.6

Scheme 2.4

Scheme 2.5

Scheme 2.6

Figure 2.7

Scheme 2.7

Scheme 2.8

Scheme 2.25

Scheme 2.9

Figure 2.8

Figure 2.9

Figure 2.10

Scheme 2.10

Scheme 2.11

Scheme 2.12

Scheme 2.13

Scheme 2.14

Figure 2.11

Scheme 2.15

Scheme 2.16

Scheme 2.17

Scheme 2.18

Scheme 2.19

Scheme 2.20

Scheme 2.21

Figure 2.12

Scheme 2.22

Scheme 2.23

Scheme 2.24

Scheme 2.26

Figure 2.13

Figure 2.14

Scheme 3.1

Scheme 3.2

Scheme 3.3

Scheme 3.4

Scheme 3.5

Scheme 3.6

Scheme 3.7

Scheme 3.8

Scheme 3.9

Scheme 3.10

Scheme 3.11

Scheme 4.1

Figure 4.1

Figure 4.2

Figure 4.3

Scheme 4.3

Figure 4.4

Figure 4.5

Figure 4.6

Figure 4.7

Figure 4.8

Figure 4.9

Scheme 4.2

Figure 4.10

Figure 4.11

Scheme 4.4

Figure 4.12

Figure 4.13

Figure 4.14

Figure 4.15

Figure 4.16

Figure 4.17

Figure 4.18

Figure 4.19

Figure 4.20

Scheme 4.5

Figure 4.21

Figure 4.22

Figure 4.23

Figure 4.24

Figure 4.25

Scheme 5.1

Scheme 5.2

Scheme 5.3

Scheme 5.4

Figure 5.1

Figure 5.2

Scheme 5.5

Figure 5.3

Scheme 5.6

Scheme 5.7

Scheme 5.8

Scheme 5.9

Scheme 5.10

Figure 5.4

Figure 5.5

Scheme 5.11

Scheme 5.12

Scheme 5.13

Scheme 5.14

Figure 5.6

Scheme 5.15

Figure 5.7

Figure 5.8

Figure 5.9

Scheme 5.16

Scheme 5.17

Figure 5.10

Figure 5.11

Figure 5.12

Scheme 5.18

Figure 5.13

Figure 5.14

Figure 5.15

Figure 5.16

Figure 5.17

Figure 5.18

Figure 5.19

Figure 5.20

Figure 5.21

Figure 5.22

Figure 5.23

Scheme 5.19

Figure 5.24

Figure 5.25

Figure 5.26

Scheme 5.20

Figure 5.27

Scheme 5.21

Scheme 5.22

Figure 5.28

Scheme 5.23

Figure 5.29

Scheme 5.24

Figure 5.30

Scheme 5.25

Figure 5.31

Scheme 5.26

Scheme 5.27

Scheme 5.28

Scheme 5.29

Scheme 5.30

Scheme 5.31

Scheme 5.32

Scheme 5.33

Scheme 5.34

Scheme 5.35

Figure 5.32

Scheme 5.39

Figure 5.33

Figure 5.34

Figure 5.35

Figure 5.36

Figure 5.37

Figure 5.38

Scheme 5.36

Scheme 5.37

Figure 5.39

Scheme 5.38

Figure 5.40

Figure 5.41

Figure 5.42

Figure 5.43

Figure 5.44

Figure 5.45

Scheme 5.40

Scheme 5.41

Scheme 5.42

Figure 5.46

Figure 5.47

Scheme 5.43

Scheme 5.44

Figure 5.48

Figure 5.49

Scheme 5.45

Scheme 5.46

Scheme 5.47

Scheme 5.48

Scheme 5.49

Figure 5.50

Scheme 5.50

Scheme 5.51

Figure 5.51

Scheme 5.52

Figure 5.52

Figure 5.53

Scheme 5.53

Scheme 5.54

Figure 5.54

Figure 5.55

Figure 5.56

Figure 5.57

Figure 5.58

Figure 5.59

Figure 5.60

List of Tables

Table 2.1

Table 5.1

Table 5.2

Table 5.3

Table 5.4

Table 5.5

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Horst Kisch

Semiconductor Photocatalysis

Principles and Applications

Author

Prof. Horst Kisch

Genglerstr. 18

91054 Erlangen

Germany

cover

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To Hille

Preface

Photocatalysis on semiconductor surfaces has grown tremendously in the three last decades. The reason for that is its analogy with photosynthesis, the most important natural chemical process. Photosynthesis forms the basis of human life by using visible solar light for the conversion of water and carbon dioxide to oxygen and carbohydrates. The key steps in that admirable heterogeneous photocatalytic process are photochemical charge generation, charge trapping, interfacial electron exchange, and C–C coupling. The first two steps can be mimicked to some extent by molecular systems, but not the two last steps which represent the chemical synthesis part. However, simple C–C, H–H, and C–N couplings become feasible upon irradiating a suspension of a semiconductor powder in the presence of electron donor and acceptor substrates. The light-generated charges are trapped at the surface, from where they undergo concerted interfacial reduction and oxidation reactions with the substrates. In most cases, the primary products are short-lived radicals, which are converted to final products by selective chemical bond formation. Thus, the semiconductor's action is at least twofold. It enables a proper assembly of the substrates through adsorption at the surface–solvent layer, and it catalyzes photoinduced interfacial electron transfer to and from the substrates, often coupled to proton transfer. The splitting of water, fixation of molecular nitrogen, and functionalization of alkanes exemplify the high reactivity of such heterogeneous systems. While great attention has been paid to water splitting and exhaustive aerobic degradation of pollutants, only a small part of research has explored also the synthetic aspects. The author believes that the latter may open novel aspects for organic synthesis, including, eventually, production of solar fuels and food from water, carbon dioxide, and dinitrogen.

The above brief description reveals that the multidisciplinary field of semiconductor photocatalysis combines molecular photochemistry with solid-state chemistry, materials science, heterogeneous catalysis, and electrochemistry. Accordingly, this book was written for masters students of complementary fields. It is based on lectures given at the University of Erlangen-Nürnberg. The reader should be aware of the fact that some of the experimental observations may be explained also by mechanisms different from the proposed ones. But this is typical for research in basic sciences: mechanisms may change with time but the experimental facts stay constant.1,2

After a general introduction, Chapters 1–3 deal with the basics of molecular photochemistry and with a few examples of molecular photocatalysis. Chapter 4 briefly treats the principles and methods of photoelectrochemistry that are relevant for the characterization of semiconductor photocatalysts. The main Chapter 5 finally discusses first the mechanistic and kinetic aspects followed by characterization and preparation of photocatalysts and by organic cleavage and addition reactions. Since the mechanism of the latter resembles the four key steps of photosynthesis, it is treated in some detail focusing on C–C and C–N couplings. Environmental aspects and a brief description of photoreactors are presented at the end of Chapter 5.

Erlangen

June 23, 2014

Horst Kisch

1

The one who limits sets by thinking, which in reality do not exist/and then thinks them away, has understood photocatalysis

.

2

 The author's simple modification of the first part of a poem by F. Rückert in “Die Weisheit des Brahmanen, ein Lehrgedicht in Bruchstücken.” Erstes Bändchen, p.19. Weidmann'sche Buchhandlung, Leipzig, 1836:

Wer Schranken denkend setzt, die wirklich nicht vorhanden/und dann hinweg sie denkt, der hat die Welt verstanden

.

Acknowledgments

The author is very grateful to Jan Augustynski and Detlef Bahnemann for valuable comments, and to Jörg Sutter for carefully manuscript reading.

1Introduction

1.1 A Brief History of Photochemistry

Photochemistry, which means chemical changes induced by absorption of light, constitutes the basis of human life. This is linked to the property of a green leaf to absorb the blue and red components of sunlight and generate carbohydrates and oxygen. Only water and carbon dioxide are necessary for that unique process of unprecedented selectivity, considering that only carbon dioxide is reduced even though the competitive and much more reactive oxygen molecule is present in about 600-fold excess. Thus, photosynthesis1 supports mankind with food to eat and oxygen to breathe (Equation 1.1). Therefore, it is not surprising that in the very earliest human cultures

1.1

the sun was worshiped as a god. A prominent example is Egypt, where in the fourteenth century BC pharaoh Ikhnaton rejected the many old gods and introduced a monotheistic religion based on the sun-god Aton. Also, in the Christian genesis God said, “let there be light,” after he had created the earth and heaven (Genesis, verses 3–4). Besides photosynthesis, sunlight controls also the growth of plants through the protein phytochrome [1]. The complicated action mechanism can be broken down to an olefinic cis–trans isomerization. In the protein rhodopsin, the same molecular process forms the basis of human vision.

Light absorption by other eye proteins controls the concentration of hormones such as melatonin relevant for circadian rhythms, the immune system, and seasonal defective disorders such as the “winter blues.” In the eyes of some migratory birds, another protein, cryptochrome, upon light absorption generates a short-lived triplet ion pair having a magnetic moment. Interaction with the terrestrial magnetic field seems to be the underlying mechanism of these birds' admirable navigation capability. A similar type of light-induced magnetic sensing is invoked also for the spawn-migration of some salmons (Oncorhynchus nerka) [2].2

The well-known synthesis of vitamin D in human skin is based on a sunlight-driven electrocyclic ring opening of a 1,3-cyclohexadienyl fragment. Sufficient supply of this vitamin seems to have also a positive influence on various types of cancer. Contrary to this direct chemical action of sunlight, which is localized in the skin, there is also an indirect one on the skin surface. Already, Egyptian physicians were curing skin cancer by smearing bergamot oil onto the tumor and exposing the patient to sunlight. This indirect effect is based on the oil-photosensitized formation of the very reactive singlet oxygen and is utilized nowadays under the name of photodynamic therapy (PDT) in cancer treatment. The use of artificial light sources such as optical fibers allows conducting PDT also on internal tumors. summarizes the biological actions of sunlight.