Electrodeposition of Cu doped ZnS and evaluation of its photocatalytic property

These days, development of new photocatalyst materials have been interested, which can absorb visible light and have photocatalytic activities towards various reaction. In this study, we focused on ZnS as a new photocatalyst material. We prepared ZnS by electrodeposition. At first, we tried to synthesis ZnS with different electrolytic bathes in terms of additive composition and pH. Comparing the properties of samples, the best bath condition was containing EDTA and adjusting pH to 2.00. Secondly, we tried to make the band gap energy of ZnS small by Cu doping. We prepared 3 different bathes in terms of the concentration of Cu; the ratio of Cu to Zn was 1 mol%, 5 mol% and 10 mol% (Cu1, Cu5 and Cu10). The band gap energy of the samples were 2.6 eV, 2.8 eV and 2.4 eV, respectively. The bandgap energy of ZnS without Cu was 3.6 eV, so we assumed that Cu played the role of making band gap energy narrow. According to the XPS analysis, the chemical state of Cu was Cu(metal), CuO, CuS, Cu2O and Cu2S. The chemical state of Zn was Zn(metal), ZnO, ZnS, and Cu10 contains larger amount of ZnS than Cu1 and Cu5. The results of cyclic voltammetory implied that formation of ZnS was suppressed in Cu1 and Cu5. Band gap energy of Cu doped ZnS was 2.8 eV for Cu1, 2.4 eV for Cu5 and 2.6 eV for Cu10, and all of them can absorb visible light(λ < 500 nm). The conduction band potential of Cu1, Cu5 and Cu10 was more highly negative than TiO2 one. It implies that Cu doped ZnS would have stronger phothocatalytic activity for reduction than TiO2 one.