Stabilizing the S-scheme ZnO/ZnCr2O4/Bi6Cr2O15 heterojunction through the application of carbon xerogel as both a solid-state mediator and reducing agent

Abstract

This study aims to evaluate the application of the carbonaceous material known as carbon xerogel as a solid-state mediator in the ZnO/ZnCr2O4/Bi6Cr2O15 heterojunction, aiming to stabilize the charge transfer pathway to an S-scheme configuration. Furthermore, the carbon xerogel was also chosen as a reducing agent for the formation of the proposed heterojunction under high temperatures, due to the reduction of the Bi6Cr2O15 into Bi0 and Cr2O3, with posterior formation of the ZnCr2O4 phase through solid-state reaction with the ZnO. The photocatalytic performance of the materials was evaluated through sulfamerazine degradation under both simulated sunlight and visible light. The X-ray diffractometry and Raman spectrometry show the formation of the ZnO, ZnCr2O4, Bi6Cr2O15, and Bi0 phases on the composite material, as expected. Furthermore, morphological modifications were observed for the zinc oxide (ZnO) after the addition of both the carbon xerogel and bismuth-based phases, resulting in a significant enhancement of specific surface area and pore volume of the materials. Photocatalysis-wise, the composite material developed obtained the highest efficiency among the materials evaluated, as the stabilization of the S-scheme heterojunction between ZnO, ZnCr2O4, and Bi6Cr2O15 by the carbon xerogel as a solid-state electron mediator and the plasmonic resonance effect provided by the metallic bismuth particles functioned towards an increase in the photocurrent generation capacity and charge carrier lifetime during photonic excitation. The hydroxyl radical was defined as the major species involved in the degradation of the sulfamerazine, indicating the successful stabilization of the S-scheme charge transport pathway between the proposed components of the photocatalyst.