Formation and properties of cuprous oxide semiconductor colloids

Cuprous oxide colloids were obtained by radiolytic reduction of Cu²⁺ ions in alkaline solutions in the presence of 0.05%, poly(vinyl alcohol). Methylviologen cation radicals, Eu²⁺ ions, and the organic radicals (CH₃)₂COH and C0²₋ inject electrons into colloidal Cu₂O. These electrons are first captured relatively rapidly by a mid-gap state in Cu₂O, and then they reduce Cu⁺ to Cu⁰ in a slower second step. The energy level of the mid-gap state was measured as a function of pH by equilibrating it with the MV²⁺/MV⁺ redox couple. The mid-gap state is insensitive to pH, indicating it does not involve protonic equilibrium. Photoexcitation of aqueous Cu₂O sols in the presence of MV²⁺ results in reduction of Cu₂O to Cu⁰, rather than electron transfer to MV2+ in the solution. This photoreductive corrosion can be suppressed in acetonitrile sols.