Electron-transfer reactions on CdSe colloids as studied by pulse radiolysis

Abstract

Optical effects due to size quantization have been observed for CdSe colloids with particle diameters < 50 Å. Electron-transfer reactions from different electron donors such as (CH₃)₂ĊOH and ĊO^–₂ radicals to CdSe colloidal particles were studied by pulse radiolysis. The optical properties of excess electrons show an absorption maximum at 300 nm which corresponds to trapped electrons and formation of Cd⁺ sites in the bulk and at the surface of semiconductor particles. Cd⁺ sites are not long-lived: they undergo further reduction to Cd⁰. The equilibrium of electron transfer between nitrobenzene anion radicals and CdSe colloidal particles in acetonitrile solution was also studied with pulse radiolysis. The equilibrium concentration of nitrobenzene anion radicals in the presence of CdSe colloids can be exploited to derive the redox potential of semiconductor colloids; a value of –1.20 ± 0.05 V vs. SCE was determined.