Microwave-assisted hydrothermal synthesis of transition-metal doped ZnIn 2S 4 and its photocatalytic activity for hydrogen evolution under visible light

Abstract

Aiming at the enhancement of photocatalytic activity for hydrogen evolution over ZnIn 2S 4, different transition metals (Cr, Mn, Fe, Co) are doped into the lattices of ZnIn 2S 4 to narrow the band gap. The doped ZnIn 2S 4 is characterized by XRD, Raman, UV–vis spectra, photoluminescence spectra, SEM and XPS techniques. The photocatalytic evaluation shows that Mn-doped ZnIn 2S 4 performs photocatalytic activity 20% higher than undoped ZnIn 2S 4, while Cr-, Fe-, and Co-doped ZnIn 2S 4 perform poorer activities in an order of Cr > Fe > Co. Based on the combined characterization results, the band structures of doped ZnIn 2S 4 are schematically depicted, which illustrates the different effects of transition-metal doping on the photocatalytic activity for hydrogen evolution. For Mn-doped ZnIn 2S 4, the enhancement of photocatalytic activity could be due to narrowed band gap induced by Mn doping. However, for Cr-, Fe-, and Co-doped ZnIn 2S 4, the suppressed photocatalytic activities should be attributed to the dopant-related impurity energy levels localizing the charge carriers or acting as non-radiative recombination centers for photoexcited electrons and holes. Hence, this study indicates that it is of great importance to make the in-depth investigation on the effects of band structures on the photocatalytic activity, especially for the doped semiconducting photocatalysts.