Preparation And Performance Of Cd_1-xZn_xS Photocatalyst For H₂ Evolution From Water Splitting

As the increasing global energy and environmental problems, hydrogen energy as the future energy carrier has attracted great attention. Compared with traditional hydrogen production methods, photocatalytic hydrogen production from water splitting using semiconductors is more clean and economic. Therefore, the studies on photocatalytic hydrogen production from water splitting using solar energy have great scientific research value. Recently, the photocatalytic properties of Cd S mixed with Zn S, a kind of wide band gap semiconductor, to form Cd_1-xZn_xS solid solution have been paid a great deal of attention. The aim of this paper was to prepared Cd_1-xZn_xS-based photocatalysts with highly efficient H2 production activity by a simple systhesis method.In this paper, the crystals obtained through a coprecipiation and hydrothermal method were not a simple mixture of Zn S and Cd S, but Cd_1-xZn_xS solid solution. The Cd0.3Zn0.7S with the value of x being 0.7 exhibited the optimal H2 production activity（885.4 umol·h-1） when prepared with Na2 S as sulfur source, three times of the one of pure Cd S.Ni S/Cd_1-xZn_xS can be prepared by a simple hydrothermal method. Notably, the H2 evolution rate of 0.5 mol% Ni S/Cd0.3Zn0.7S（1840 μmol·h-1） was found to be 2.1- and 1.3-fold greater than those of Cd0.3Zn0.7S（884 μmol·h-1） and 0.5 wt% Pt/Cd0.3Zn0.7S（1390 μmol·h-1）, respectively, when Na2S-Na2SO3 were used as sacrificial agents. The apparent quantum efficiency of 0.5 mol% Ni S/Cd0.3Zn0.7S at 420 nm was 36.8% and its solar energy conversion efficiency was 4.7% at 320 nm-2500 nm. The characterization of this material by X-ray diffraction（XRD）, ultraviolet-visible diffuse reflection spectroscopy（DRS）, transmission electron microscopy（TEM） and X-ray photoelectron spectroscopy（XPS） showed that the Ni S particles provided the active sites required for H2 evolution, thus transferring the photo generated electrons. And the p-type Ni S intimately loaded on the surface of n-type Cd0.3Zn0.7S could form p-n junctions, which could effectively reduce the recombination rate of photogenerated electrons and holes. Therefore, the photocatalytic activity of the catalyst towards H2 production was enhanced.In this paper, some major factors which influenced the photocatalytic activity of the Ni S/Cd0.3Zn0.7S photocatalysts were discussed here. The results showed that: The best loading temperature and time of the hydrothermal method was 180℃and 5 hours, respectively; When sodium sulphide and nickel acetate were used as raw materials to load Ni S cocatalysts, the H2 production activity of Ni S/Cd0.3Zn0.7S could be significantly enhanced; Ni S/Cd0.3Zn0.7S photocatalyts exhibited the highest H2 evolution rate in lactic acid sacrificial agent, while its H2 evolution rate in methanol sacrificial agent was nearly zero; The H2 evolution rate of Ni S/Cd0.3Zn0.7S photocatalysts prepared by hydrothermal method was higher than that prepared by photodeposition and coprecipitation method.In this paper, the influence of Pt and Co on the photocatalytic activity of the Cd0.3Zn0.7S photocatalysts was also disscussed. The H2 evolution rate of 0.5 wt% Pt/Cd0.3Zn0.7S（1390 μmol·h-1） was found to be 1.6 greater than those of Cd0.3Zn0.7S（884 μmol·h-1）, and 1 wt% Co/Cd0.3Zn0.7S（974 μmol·h-1） exhibited the highest H2 evolution rate, when Na2S-Na2SO3 were used as sacrificial agents. Besides, the best photodeposition time of the 0.5 wt% Pt/Cd0.3Zn0.7S photocatalysts prepared by the photodeposition method in 30 Vol% methanol agents was three hours.