HeterogeneousPhotochemic al

Electron Transfer

Autho r

Michael Grätzel, Ph .D .

Chapter lTheoretical Aspects of Electron-Transfer Reaction s1 .

General Features of Electron-Transfer Reactions 1II .

Adiabatic Outer Sphere Electron-Transfer Reactions in Solutions : MarcusTheory 5

III .

Nonadiabatic Electron-Transfer Reactions 1 0A. Classical Description of Nonadiabatic Electron-Transfe r

Reactions 1 2B. Semiclassical Description of Nonadiabatic Electron-Transfe r

Reactions 1 4

C. Quantum Mechanical Treatment of Nonadiabatic Electron-Transfe rReactions 1 8

IV .

Heterogeneous Electron-Transfer Reaction 2 1

A .

Energetics of Interfacial Electron-Transfer Reactions, Fermi Level ,and Redox Potential of a Solution 2 2

B .

Distribution of Electronic Energy Levels in Solid Conductors andElectrolytes 2 61. Metals 2 62. Semiconductors 2 73. Electronic Energy Levels in Solution 3 0

C .

Interfacial Electron-Transfer Kinetics, Empirical Rate Laws fo rElectrochemical Reactions, and Comparison with Theory 3 21. Conducting Electrodes 3 22. Semiconducting Electrodes 3 6

D .

Interpretation of the Preexponential Factor in Electrochemica lReactions 3 9

E .

Heterogeneous vs . Homogeneous Reorganization Energies 4 1References 4 1

Chapter 2Light Energy Harvesting and Photoinduced Electron Transfer in Organized Molecula rAssembliesI .

Introduction 43II .

Transfer of Electronic Excitation Energy in Micellar Assemblies 43A. Intramicellar Triplet Energy Transfer 44B. Triplet-Triplet Annihilation in Confined Reaction Space 49C. Excitation Energy Conduction Along a Micellar Surface to a

Reaction Trap 5 2D. Long-Range Intramicellar Singlet Energy Transfer 54

III .

Photoinduced Electron Transfer in Micellar Assemblies 5 9A. Electrical Potential of a Solution in the Vicinity of a Charged Molecular

Assembly 5 9B. Photo ion ization 62C. Intramicellar EIectron Transfer 64D. Photoinduced Electron Transfer in Functionalized Micella r

Assemblies 67E. Light-Induced Charge Separation Through Hydrophobic Electron

Storage in Micellar Aggregates 69F. Micellar Model Systems for Photosynthesis 70

IV .

Light-Induced Electron Transfer in Inverted Micelles and Microetnulsions 71

V .

Photoinduced Electron Transfer and Transmembrane Redox Reactions i nVesicles 7 3

A. Structural Features of Vesicles and Bilayer Lipid Membranes 7 3B. Photoinduced Electron-Transfer Reactions in Vesicle

Dispersions 7 5VI .

Electron Transfer in Monolayer Assemblies 82VII . Light-Induced Charge Separation in Aqueous Dispersions of Inorganic

Colloids and Polyelectrolytes 8 3References 84

Chapter 3Charge Transfer Reactions in Semiconductor System sI .

Introduction 87II .

Properties of Semiconductor Particles 87A .

Structural Properties 871. Size and Shape : Macroparticles, Colloids, and Particles 8 72. Lattice Defects 90

B .

Optical Properties 9 11.

Optical Absorption of Bulk Semiconductors and Colloida lParticles : Mie Theory 9 1

2. Optical Absorption of Very Small Particles : QuantumSize Effects 94

3. Photoluminescence of Semiconductor Particles an dElectrodes 9 7

4. Quantum Size Effects in the Photoluminescence of Colloida lSemiconductors 9 9

C .

Electronic Properties 1001.

Band Edge Positions 10 02. Space Charge Layers and Band Bending 102

3. Space Charge Layers in Semiconductor Particles 1064. Fermi Level Pinning 1085. Light-Induced Charge Separation 1096. Trapped vs . Free Charge Carriers in Small Semiconducto r

Particles 11 1III .

Experimental Methods 11 3IV.

Dynamics of Charge Carrier Trapping and Recombination in Smal lSemiconductor Particles 114

V .

Dynamics of Interfacial Charge Transfer Processes 11 8VI .

Photosensitized Electron Injection in Colloidal Semiconductors 126VII. Applications : Photocatalysis 13 1

A. Photocleavage of Hydrogen Sulfide 132B. Photodegradation of Organic Wastes and Pollutants 13 3C. Photodecomposition of Water: Solar Energy Conversion 135D. Incorporation of Colloidal Semiconductors in Supramolecular

Assemblies 144VIII . Concluding Remarks 144References 145

Index 151