Photocatalytic reduction of hexavalent chromium using Zn2SnO4–ZnO modified g-C3N4 composite

Abstract

In this study, a novel hierarchical g-C3N4/Zn2SnO4–ZnO heterojunction system was reported as an efficient photocatalyst for the reduction of Cr(VI). The fabrication of the composite involved the synthesis of the complex metal oxide (Zn2SnO4–ZnO), followed by the in-situ integration into graphitic carbon nitride. The structure, morphology, and optical properties of the as-prepared tertiary composite were determined using various analytical techniques. The results indicated the improvement in surface area and the electronic structure of the semiconductor heterostructures. Photocatalytic measurement showed the efficiency of the ternary composite to cause a reduction of the band gap energy, delayed charge recombination process and enhancement of the visible light absorption. Reaction parameters including the solution pH, photocatalyst (g-C3N4/ZTO-ZnO) dosage, and the initial concentration of Cr(VI) on the degradation efficiency of the photocatalyst were evaluated. The solution pH was varied from 2 to 8, and pH 2 displayed the highest removal of Cr(VI) with 99.2 % removal efficiency for the g-C3N4/ZTO-ZnO, while the ZTO-ZnO exhibited 72 % efficiency. Finally, the kinetic study of the photocatalytic reaction showed an increase in the overall rate constant k with the increase in initial concentration of Cr(VI). The outstanding performance of the ternary composite compared to the bare complex metal oxide makes the innovative g-C3N4/Zn2SnO4–ZnO composite a promising material for the removal of Cr(VI) from aquatic environment.