ABSTRACT

Semiconductors may also be used as powdered substances, dispersed as slurries in aqueous or nonaqueous solvents, or as photocatalysts in gas-solid reactions. The particles of such materials have been considered as minute electrolysis cells.* Under illumination at wavelengths shorter than the band gap, these particles may cause photocatalytic reactions, including the reduction of carbon dioxide to carbon monoxide and to several organic compounds, such as formic acid and methanol. The simplicity of operating such photocatalytic reactions has stimulated consid­ erable recent efforts to improve the efficiency and selectivity of such processes to desired products. In some cases, high quantum yields of formic acid were reported, and in a few cases also of methanol and ethanol.