Preface ........................................................ XI
Acknowledgments .............................................. XIII
1 Introduction ............................................... 1
1.1 A Brief History of Photochemistry .......................... 1
1.2 Catalysis, Photochemistry, and Photocatalysis .............. 5
2 Molecular Photochemistry ................................... 9
2.1 Absorption and Emission .................................... 9
2.2 Intensity of Electronic Transitions ....................... 14
2.2.1 Contribution of Nuclei ............................. 74
2.2.2 Contribution of Spin ............................... 17
2.2.3 Contribution of Orbitals ........................... 17
2.3 Excited States Radiative Lifetimes ........................ 17
2.4 Energy and Electron Transfer .............................. 19
2.4.1 Energy Transfer .................................... 19
2.4.2 Electron Transfer .................................. 21
2.5 Proton Transfer and Hydrogen Abstraction .................. 23
2.6 Photosensitization ........................................ 23
2.7 Rates and Quantum Yields .................................. 25
2.8 Quenching of Excited States ............................... 26
2.8.1 Identification of the Reactive Excited State ....... 28
2.9 Absorption, Emission, and Excitation Spectra .............. 28
2.10 Classification and Reactivity of Excited States ........... 30
2.10.1 Organic Molecules .................................. 30
2.10.1.1 ππ* States .................................... 30
2.10.1.2 n,π* States ................................... 30
2.10.1.3 Charge-Transfer (CT) States .................... 32
2.10.1.4 Triplet and Singlet Oxygen Reactions ........... 36
2.10.2 Inorganic and Organometallic Complexes ............. 38
2.10.2.1 Metal-Centered (MC) states ..................... 39
2.10.2.2 Ligand-Centered (LC) States .................... 42
2.10.2.3 Charge Transfer Metal to Ligand (CTML) States .. 42
2.10.2.4 Charge Transfer Ligand to Metal (CTLM) States .. 42
2.10.2.5 Charge Transfer to Solvent (CTTS) States ....... 43
2.10.2.6 Intervalence Transfer (IT) States .............. 43
3 Molecular Photocatalysis .................................. 47
3.1 Hydrogйnation of 1,3-Dienes ............................... 47
3.2 Co-Cyclization of Alkynes with Nitriles ................... 47
3.3 Enantioselective Trifluoromethylation of Aldehydes ........ 48
3.4 Photoinduced Electron Transfer Catalysis .................. 50
3.5 Reduction and Oxidation of Water .......................... 51
4 Photoelectrochemistry ..................................... 55
4.1 Electronic Structure and Nature of Excited States ......... 55
4.1.1 The (Optical) Bandgap .............................. 55
4.1.1.1 Measurement of the Bandgap Energy .............. 58
4.1.1.2 Influence of Crystal Size ...................... 63
4.1.2 The Photonic Bandgap ............................... 64
4.1.3 Emission Spectra ................................... 65
4.2 Photocorrosion ............................................ 68
4.3 Interfacial Electron Transfer ............................. 70
4.3.1 Introduction ....................................... 70
4.3.2 Thermal Interfacial Electron Transfer (IFET) ....... 73
4.3.2.1 IFET at the Metal/Liquid Interface ............. 73
4.3.2.2 IFET at the Semiconductor/Liquid Interface ..... 76
4.3.3 Photochemical Interfacial Electron Transfer ........ 78
4.3.3.1 IFET in Large Semiconductor Crystals ........... 78
4.3.3.2 IFET in Small Semiconductor Crystals ........... 82
5 Semiconductor Photocatalysis .............................. 85
5.1 Mechanisms, Kinetics, and Adsorption ...................... 85
5.1.1 General Classification of Reactions ................ 85
5.1.2 Rates, Quantum Yields, and Their Comparability ..... 91
5.1.2.1 Direct Semiconductor Photocatalysis ............ 91
5.1.3 Influence of Semiconductor Nature and Particle
Size on Chemical Selectivity ...................... 108
5.1.3.1 Control of Chemoselectivity by Surface States
and Redox Amplification ........................... 110
5.2 Characterization of Photocatalysts ....................... 111
5.2.1 General Methods ................................... 111
5.2.2 Flatband and Quasi-Fermi Potentials ............... 112
5.2.2.1 Measurements in Absence of Light .............. 112
5.3 Preparation and Properties of Photocatalysts ............. 124
5.3.1 Pristine Compounds and Solid Solutions ............ 128
5.3.1.1 ТiO2 .......................................... 128
5.3.1.2 WO3 ........................................... 129
5.3.1.3 α-Fe2O3 ....................................... 130
5.3.1.4 BiVO4 ......................................... 130
5.3.1.5 Ta2O3, TaON, Ta3N5, and MTaO2N ................. 130
5.3.1.6 CuO, Cu2O ..................................... 131
5.3.1.7 GaN-ZnO ....................................... 131
5.3.1.8 CdS and ZnS ................................... 133
5.3.2 Grafting of CdS and ТiO2 onto Inorganic Supports .. 133
5.3.2.1 Grafting onto a Nonconducting Support ......... 133
5.3.2.2 Grafting onto a Semiconducting Support ........ 135
5.3.3 Grafting of Metal Halides and Metal Oxides onto
Titania ........................................... 136
5.3.3.1 Metal Chloride-Grafted Titania ................ 136
5.3.4 Metal-Loaded Powders .............................. 141
5.3.5 Nonmetal-Modified Titania ......................... 141
5.3.5.1 Nitrogen-Modified Titania ..................... 142
5.3.5.2 "Carbon'-Modified Titania ..................... 146
5.3.5.3 Miscellaneous ................................. 147
5.4 Type A Reactions ......................................... 148
5.4.1 Water Splitting ................................... 149
5.4.1.1 One-Particle Photocatalysis ................... 153
5.4.1.2 Two-Particle Photocatalysis ................... 155
5.4.1.3 Reduction and Oxidation of Water .............. 157
5.4.2 Aerobic Oxidations ................................ 159
5.4.2.1 Direct Photocatalysis ......................... 159
5.4.2.2 Indirect Photocatalysis ....................... 165
5.4.3 Nitrogen Fixation ................................. 165
5.4.3.1 Fixation by UV Irradiation .................... 165
5.4.3.2 Fixation by Visible Irradiation ............... 167
5.4.3.3 Formation of Ammonia, Hydrazine, and Nitrate .. 169
5.4.3.4 Role of Chloride Ions ......................... 171
5.4.3.5 Mechanism ..................................... 172
5.4.4 Carbon Dioxide Fixation ........................... 173
5.4.5 Organic Reactions ................................. 176
5.4.5.1 Oxidative C-N Cleavage ........................ 177
5.4.5.2 Intramolecular C-N and C-C Coupling ........... 178
5.4.5.3 Intermolecular C-C and C-N Coupling ........... 178
5.4.5.4 Intermolecular С-О Coupling ................... 181
5.4.5.5 Anaerobic Dehydrodimerization and
Intermediary Water Reduction ...................... 182
5.5 Type В Reactions ......................................... 188
5.5.1 C-N Coupling ...................................... 188
5.5.2 C-C Coupling ...................................... 192
5.5.2.1 Addition of Olefins to Imines ................. 192
5.5.2.2 Addition of Olefins to Amines ................. 198
5.5.3 C-H Activation of Alkanes ......................... 198
5.6 Environmental Aspects .................................... 202
5.6.1 Abiotic Nitrogen Fixation ......................... 202
5.6.2 Photocatalysis and Chemical Evolution ............. 203
5.6.3 Detoxification of Air and Water ................... 204
5.6.4 Antibacterial and Antiviral Effects ............... 204
5.6.5 Amphiphilic Properties of Titania ................. 205
5.7 Titania in Food and Personal Care Products ............... 206
5.8 Photoreactors ............................................ 206
5.8.1 Laboratory Photoreactors .......................... 206
5.8.2 Solar Photoreactors and Kinetic Modeling .......... 208
References .................................................... 211
Index ......................................................... 245
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