EFFECT OF SOLVENTS ON PHOTOCATALYTIC REDUCTION OF CARBON-DIOXIDE USING TIO2 NANOCRYSTAL PHOTOCATALYST EMBEDDED IN SIO2 MATRICES

Photocatalytic reduction of CO2 in various kinds of solvents was studi ed using TiO2 nanocrystals embedded in SiO2 matrices (Q-TiO2/SiO2) as the photocatalyst. It was found that the major reduction products were formate and carbon monoxide, and their total amount increased on incr easing the concentration of CO2 dissolved. The ratio of formate to car bon monoxide was greatly influenced by the kind of solvent, and increa sed on increasing the dielectric constant of the solvent. If bulk TiO2 was used as the photocatalyst, the rate of CO2 reduction was low comp ared to that obtained with Q-TiO2/SiO2, but the ratio of formate to ca rbon monoxide obtained was not greatly different from that obtained wi th the Q-TiO2/SiO2. The effect of solvent on the reduction behavior of CO2 is discussed in terms of stabilization of reaction intermediates. (C) 1997 Elsevier Science S.A.