Enhancement of CO 2 reduction activity under visible light irradiation over Zn-based metal sulfides by combination with Ru-complex catalysts

Abstract Hybrid photocatalysts composed of metal sulfide semiconductors combined with various Ru-complex catalysts were synthesized for use during visible light-driven CO 2 reduction with powder suspension systems. A variety of Zn-based sulfides, including Ni-doped ZnS, (CuGa) 0.8 Zn 0.4 S 2 and (AgIn) 0.22 Zn 1.56 S 2 , were adopted by conducting the CO 2 reduction reaction in acetonitrile containing an electron donor. The photocatalytic activities were found to be largely dependent on the basic characteristics of the Ru-complex and the metal sulfide. The results demonstrate that several of these sulfide semiconductors improve the CO 2 reduction selectivity when employed in the semiconductor/metal-complex system, and that (AgIn) 0.22 Zn 1.56 S 2 or Ni (0.2 mol%)-doped ZnS combined with a neutral Ru-complex incorporating a phosphonate ligand [Ru(4,4′-diphosphonate-2,2′-bipyridine)(CO) 2 Cl 2 ] exhibit the highest CO 2 photoconversion activity when synthesizing formic acid, with a turnover number above 100, which catalysts were stable for 16 h irradiation. These results suggest that metal sulfides are potential candidates for use in powdered semiconductor/metal-complex systems for selective CO 2 photoreduction.