Visible Light Hydrogen Production By CdZnS Photocatalysts Prepared in Ethylenediamine Aqueous Solution

Abstract

Recently, semiconductor photocatalysts are expected to be a strategy to solve the energy demand and environmental pollution. Many researchers have attention, and have been developed photocatalysts for hydrogen production. Among them, metal sulfides (i.e. CdS, ZnS, MoS2, etc.), metal oxides (i.e. TiO2, Fe2O3, NiOx, RuO2) are regarded as good candidates for the photocatalytic H2 production. CdS is highly important as a photocatalyst because of the low band gap energy (~2.4 eV) and high activity under visible light irradiation for the photocatalytic hydrogen evolution reaction (HER) [1]. However, pure CdS tends to form particle aggregation and inherent photocorrosion, resulting in a higher recombination rate of charge carrier limited its application. One of the effective ways is by combing CdS with ZnS to form CdZnS (cadmium zinc sulfide) [2]. CdZnS has been regarded as a promising photocatalyst, but it has fast recombination of photogenerated electron-hole pairs. Therefore, the photocatalytic hydrogen evolution activity of sulfide semiconductor can be significantly improved by loading noble metals as cocatalysts to provide active sites for proton reduction.In this work, we report excellent H2 production performance when PdS, Pt are used as cocatalyst for CdxZn1-xS, which was synthesized via a simple solvothermal synthesis method. The resulting photocatalysts exhibit enhanced hydrogen production from water in 0.25 M Na2SO3 + 0.35 M Na2S as a sacrificial agent.The crystalline structures of as-prepared CdxZn1-xS were analyzed by XRD. The XRD peaks of Cd0.5Zn0.5S are weaker and broader than those of one prepared in the absence of ethylenediamine during the solvothermal synthesis. These results indicate that the addition of ethylenediamine has a certain inhibitory effect on the growth of the grain of Cd0.5Zn0.5S.Cd0.5Zn0.5S photocatalyst was selected as optimal one in this photocatalytic activity test. The photocatalytic H2 production over PdS deposited Cd0.5Zn0.5S was enhanced comparing that of pristine Cd0.5Zn0.5S, showing greater about two times. Further, in the presence of dual cocatalysts, namely PdS and Pt, the photocatalytic H2 production was about 2.4 times higher than that of pristine Cd0.5Zn0.5S. In summary, this work showed that CdxZn1-xS photocatalysts were synthesized successfully by a simple solvothermal method. With ethylenediamine in the solvothermal process, the crystallinity of CdxZn1-xS photocatalysts was lower than that of one prepared by the hydrothermal method. The use of dual co-catalysts, namely PdS and Pt, were effective for the photocatalytic H2 production under visible light.