Photocatalytic reduction of CO2 using surface-modified CdS photocatalysts in organic solvents

The photocatalytic reduction of carbon dioxide on CdS particles with and without surface modification by several kinds of thiol compounds was investigated in various kinds of solvents. Formate and carbon monoxide were obtained as the major reduction products, and the ratio of the former to the latter was largely influenced by the kind of solvents when naked cadmium sulfide was used as the photocatalyst, and with increase of the dielectric constant of the solvent, the ratio increased. Even if CdS particles were modified by thiol compounds, the effect of the solvent was not eventually altered, but the ratio of formate to carbon monoxide became greater with increase of the surface modification of CdS. The observed effect of the surface modification of CdS is discussed in terms of involvement of Cd2+ sites adjacent to surface vacancies of CdS photocatalysts in adsorption of anion radicals of CO2. (C) 1998 Elsevier Science S.A.