Photochemical reduction of oxygen catalysed by colloidal cadmium selenide
Colloidal CdSe sensitises the photoreduction of O2 and methyl viologen (MV2+) by cysteine. In the absence of cysteine the semiconductor is rapidly photo-oxidised. Rates of O2 photoreduction and yields of MV˙+ tend towards a maximum value for MV2+ concentrations of 10–2 mol dm–3. Flash-photolysis and steady-state measurements of O2 reduction are interpreted by a mechanism which shows that the low quantum yields are due to rapid recombination of photogenerated charge carriers. Only 2% of the photogenerated electrons are available to reduce O2.