Influence of Fe, Ni, and Cu Doping on the Photocatalytic Efficiency of ZnS: Implications for Prebiotic Chemistry

The mineral sphalerite (ZnS) is a typical constituent at the periphery of submarine hydrothermal deposits on Earth. It has been frequently suggested to have played an important role in the prebiotic chemistry due to its prominent photocatalytic activity. Nevertheless, the need for {\lambda} < 344 nm UV radiation, which accounts for a very minor part of the energy range of the incoming solar spectrum, limits the application of this semiconductor. In this paper we employed a simple co-precipitation method for the fabrication of Fe, Ni, and Cu-doped ZnS colloids and investigated their activities in the photocatalyzed reduction of fumaric acid. The results show that the photocatalytic activity of pristine ZnS is almost identical with that of 0.1 atom% Fe-doped ZnS, but decreases by doping 0.1 atom% Ni. However, it can be significantly enhanced by doping Cu because this dopant makes the optical absorption edges of ZnS shift from UV band to longer wavelengths. The optimal doping concentration was found to be 0.3 atom%. Even under {\lambda} > 450 nm light irradiation, the photocatalyst Zn1-xCuxS can drive the reduction of fumaric acid to produce succinic acid. Given the existence of this doped semiconductor in the hydrothermal vents on early Earth and its capability to utilize both UV and visible light, ZnS might have participated more efficiently than ever estimated in the prebiotic chemical evolution.