Colloidal semiconductor photoelectrochemistry

This review concentrates on John Albery s work in the field of colloidal semiconductor photoelectrochemistry. John s major contributions to this area, as in so many others, have been through his astounding facility for generating useful asymptotic solutions for highly complex kinetic models of electrochemical systems. So as to put John s work in colloidal photoelectrochemistry into context. Sections 9.1-9.3 of this chapter provide a review of the more salient kinetic models of semiconductor photocatalysis developed over the last 20 years or so. Section 9.4 then concentrates on the Alberian view and presents, for the first time, John s model of the chronoamperometric behaviour of colloidal CdS. 

Moser, J. Graetzel, M. Photoelectrochemistry with colloidal semiconductors Laser studies of halide oxidation in colloidal dispersions of Ti02 and a-Fe203, Helv. Chim. Acta 1982, 65, 1436. 

This review is a discussion of the kinetic modelling of the photoelectrochemistry of colloidal semiconductor systems. This area is currently attracting significant attention from the scientific community due to the applications of colloidal semiconductors within two rapidly advancing research fronts heterogeneous photocatalysis and nanocrystalline particle technology. 

Thus, it can be seen that a study of the steady state photoelectrochemistry of colloidal semiconductors with the ORDE can provide information relating to the energy distribution of the particle surface states, the photogenerated carrier density and the quantum efficiency of carrier generation. The next section describes how to obtain information pertaining to intraparticle charge carrier dynamics from a study of the behaviour of transient photocurrents at the ORDE. 

Passive films (corrosion) Photoredox processes with colloidal semiconductor particles as photocatalyst (e.g., degradation of refractory organic substances) Photoelectrochemistry (e.g., photoredox processes at semiconductor electrodes)... 

Hotchandani S, Kamat P (1992) Charge-transfer processes in coupled semiconductor systems. Photochemistry and photoelectrochemistry of the colloidal cadmium sulfide-zinc oxide system. J Phys Chem 96 6834—6839... 

The photoanodic dissolution also occurs in the electrochemistry and photoelectrochemistry of compact electrodes of these materials. In fact, it is the most serious obstacle to the practical use of semiconductors such as CdS in photoelectrochemical cells The product of corrosion in the absence of oxygen is sulfur. In the presence of oxygen, sulfate ions are formed as in the case of the colloidal particles... 

Kamat, P. V. Ebbesen, T. W. Dimitrijevic, N. M. Nozik, A. J. Photoelectrochemistry in semiconductor particulate systems. Part 12. Primary photochemical events in CdS semiconductor colloids as probed by picosecond laser flash photolysis, transient bleaching, Chem. Phys. Lett. 1989, 157, 384. 

Patrick, B. Kamat, P. V. Photoelectrochemistry in semiconductor particulate systems. Part 17. Photosensitization of large-bandgap semiconductors. Charge injection from triplet excited thionine into ZnO colloids, J. Phys. Chem. 1992, 96, 1423. 

Photocathodes. It is a fact that O2 generation is much more difficult than hydrogen generation in solar photoelectrochemistry. This is true in the colloidal artificial membrane systems just as much in their bulk semiconductor counterparts. The difficulty of catalytlcally managing four oxidizing equivalents (4e ) per O2 molecule from water, compared to only two reducing equivalents for H2 production (beginning with 2H ), may account for this. 

Research on size quantization in colloidal systems was responsible for the development by Bard and coworkers of a new field in photoelectrochemistry, that of nanodot electrodes [19, 20]. An ordered or disordered monolayer or sub-monolayer of nanometer-sized semiconductor particles is attached to a conducting substrate either directly or via a self-assembled organic monolayer. The monolayer acts as a spacer, allowing the distance between the dot and the substrate to be varied. Absorption of light by the semiconductor dots gives rise to processes similar in many ways to those observed in bulk electrodes. However, because of the size quantization and the distinctive electrode geometry, striking new effects are found. 

Kalyanasundaram K., Gratzel M. Applications of functionalized transition metal con5)lexes in photonic and optoelectronic devices. Coord. Chem. Rev. 1998 77 347-414 Kamat P.V. Photoelectrochemistry in particulate systems. 3. Phototransformations in the colloidal TiOa-thiocyanate system. Langmuir 1985 1 608-611 Kamat P.V., Bedja I., Hotchandani S., Patterson L.K. Photosensitization of nanocrystalline semiconductor films. Modulation of electron transfer between excited ruthenium complex and SnOa nanocrystalUne with an externally applied bias. J. Phys. Chem. 1996 100 4900-4908 Kamat P.V., Vinodgopal K. Environmental photochemistry with semiconductor nanoparticles. Mol. Supramol. Photochem. 1998 2 307-350... 

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