Metallic 1T-LixMoS2 co-catalyst enhanced photocatalytic hydrogen evolution over ZnIn2S4 floriated microspheres under visible light irradiation

Abstract

Lithium intercalated 1T allotropes of molybdenum disulfide/zinc indium sulfide (1T-Li_xMoS₂/ZnIn₂S₄) composites were synthesized using a two-step hydrothermal method. The as-prepared samples were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflectance absorption spectra, photoluminescence emission spectra and Raman spectra. The results indicate that the lithium intercalation reaction transforms the MoS₂ crystal from the hexagonal structure (2H phase) to the trigonal 1T phase. By introducing metallic 1T-Li_xMoS₂ as a co-catalyst, the photocatalytic hydrogen (H₂) evolution activity of the ZnIn₂S₄ microspheres is significantly enhanced under visible light irradiation. The enhanced photocatalytic activity is mainly attributed to the fact that the metallic 1T-Li_xMoS₂ promotes the efficient separation of the photoexcited electrons and the holes of ZnIn₂S₄ microspheres because of its high electrical conductivity and high densities of the active sites. The photoexcited electrons of ZnIn₂S₄ microspheres can not only transfer to the edge sites of 1T-Li_xMoS₂, but also to the basal plane active sites of 1T-Li_xMoS₂. Furthermore, the photocatalytic activity is dependent on the content of 1T-Li_xMoS₂ in the composites. The 2.0 wt% 1T-Li_xMoS₂/ZnIn₂S₄ sample shows the highest H₂ production rate of 332.4 μmol h⁻¹, which is 2.4 times higher than that of bare ZnIn₂S₄ and 1.3 times higher than that of 2.0 wt% 2H-MoS₂/ZnIn₂S₄, and it remains stable even after three photocatalytic cycling tests.