Preparation And Characterization Of The Quintuple Sulfide For Production Of H₂ By Photocatalytic Splitting Water

Due to the gradually serious problems of energy source and environment, development of a new, clean, and renewable form of energy has drawn much attention and becomes an important priority stratagem. Hydrogen, as a clean and renewable energy, has attracted more and more attention from people. Overall water splitting for hydrogen production with the help of semiconductor, is one of the measures getting new energy. Owing to its low cost, photoelectric effect of photocatalyst and quantum effect of nano-materials, ZnS nanoparticles can be used as a highly efficient photocatalyst. However, pure ZnS is only active in the UV light region that possesses 5% in the solar spectra because its band gap is 3.5 eV. Therefore, the purpose of this work is to improve the photocatalytic activity of the photocatalyst by narrowing the band gap of ZnS as well as the response into the visible region of the spectrum.In this paper, a new kind of efficient quintuple sulfide solid solution photocatalyst Na_2x(CuIn)_xZn_3(1-x)S₃ was prepared by solvothermal method. The prepared samples were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS) and UV-vis absorption spectroscopy (UV-vis), to investigate the effects of preparation conditions on structure and performance of photocatalysts. The effects of the values of x (stoichiometric ratio), solvothermal reaction time, the concentration of sacrificial agent, the amount of photocatalyst and the content of Pt as cocatalyst on the photocatalytic activity of photocatalyst prepared were researched by the experiment of producing H2 by photocatalytic splitting water. Meanwhile, the stability of photocatalyst was investigated according to the photocatalytic reaction time. The results showed that the crystal structures of the solid solutions were alterant and, depending on the composition, while Na, Cu, In doped generally inhibited the growth of crystallite Besides, the band gap of the solid solutions was controllable by the change in the composition. In addition, the photocatalyst extended the absorption edge to the visible light range. Most importantly, the experiment result of producing H2 by photocatalytic splitting water showed that the highest rate of hydrogen production with the prepared photocatalyst Na_0.04(CuIn)_0.02Zn_2.94S₃ was 714.3μmol·h-1 under the conditions of the values of x for 0.2, solvothermal reaction time for 30h, 0.35mol/L Na₂SO₃ and 0.25 mol/L Na₂S as sacrificial agents, the amount of photocatalyst for 0.3g, which was 65 times higher than that of ZnS. When the photocatalyst was loaded with the 0.4wt% Pt, the rate of hydrogen production was up to 785.7μmol·h-1 under the same conditions, which was 10% higher than that of the photocatalyst without loading with Pt. Furthermore, the stability of photocatalyst was demonstrated by keeping the high photocatalytic activity after the photocatalytic reaction for 20h.