Novel visible-light driven g-C3N4/Zn0.25Cd0.75S composite photocatalyst for efficient degradation of dyes and reduction of Cr(vi) in water

Abstract

A facile and template free in situ precipitation method was developed for the synthesis of a g-C₃N₄/Zn_0.25Cd_0.75S photocatalyst. The obtained products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and ultraviolet-visible diffuse reflection spectroscopy (DRS). The DRS results showed that with the increase of the g-C₃N₄ content, the light absorption edge for g-C₃N₄/Zn_0.25Cd_0.75S was blue shifted in the visible light region. The TEM images showed that the Zn_0.25Cd_0.75S particles had been finely distributed on the surfaces of the g-C₃N₄ sheets. The HRTEM images showing clear lattice fringes proved the formation of a heterojunction structure at the interfaces of g-C₃N₄ and Zn_0.25Cd_0.75S. In the photocatalytic degradation of dyes, the g-C₃N₄/Zn_0.25Cd_0.75S composite exhibited significantly enhanced activities, and the optimal g-C₃N₄ content was 20 wt%. A controlled experiment showed that the high charge separation efficiency of the photo-generated electron–hole pairs and the suitable energy band structures result in the high performance of g-C₃N₄/Zn_0.25Cd_0.75S under visible light irradiation. The g-C₃N₄/Zn_0.25Cd_0.75S sample also possessed a superior activity in the photocatalytic reduction of Cr(VI) in neutral solution. The photoelectrochemical measurements confirmed that the interface charge separation efficiency was greatly improved by coupling g-C₃N₄ with Zn_0.25Cd_0.75S. A terephthalic acid photoluminescence probing technique has been performed to detect the generation of ˙OH in the reaction system.