Photochemical reduction of oxygen catalysed by colloidal cadmium selenide

Abstract

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.