Photoelectrocatalytic degradation of sulfamethoxazole over S–Scheme Co3Se4/BiVO4 heterojunction photoanode: An experimental and density functional theory investigations

Abstract

We have carried out comprehensive experimental and density functional theory simulations of Co3Se4/BiVO4 heterojunction to understand the relationship between interface and enhanced photocatalytic activity. This study demonstrates the photoelectrochemical degradation of sulfamethoxazole (SMX) with a photoanode developed based on S–Scheme heterojunction. The difference in the energy levels of the band gaps and conduction bands of BiVO4 and Co3Se4 makes them suitable semiconductors for the fabrication of an S–Scheme heterojunction. The BiVo4/Co3Se4 composite is prepared by solvothermal method and characterized using X–ray diffraction (XRD), field emission–scanning electron microscopy (FE–SEM), transmission electron microscopy (TEM), Energy Dispersive X–Ray Analysis (EDX), Ultraviolet–Visible Diffuse Reflectance Spectroscopy (UV–DRS). The photoelectrochemical properties of the fabricated photoanode are studied using Electrochemical impedance spectroscopy (EIS), Mott–Schottky, and photocurrent response. The UV–DRS spectra show an improved band gap (1.88 eV) for the composite in comparison with pristine BiVO4 (2.39 eV). The XRD patterns reveal the presence of monoclinic phases of BiVO4 and Co3Se4 in the composite. This is further confirmed by the microscopic studies that show the surface coating of Co3Se4 on BiVO4. The composite photoanode shows improved photocurrent density and low charge transfer resistance in comparison with the pristine semiconductors. Theoretical calculations reveal charge redistributions at the interface between Co3Se4 and BiVO4. Furthermore, the density of states, Bader charge and electrostatic potential drop reveals that the synergistic effect of built-in electric field directed from the BiVO4 surface to the Co3Se4 surface facilitates the efficient separation of charge carriers in the Co3Se4/BiVO4 interface and thus prevents carrier recombination rate. This provides the composite with the capacity to effectively degrade SMX with improved efficiency. At optimum conditions, the SMX degradation efficiency reached 75% with a rate constant of 0.0115 min–1. The holes majorly facilitate the degradation of SMX, as revealed by the scavenger study. Comparative studies indicate that photoelectrocatalytic contributions supersede photocatalytic and electrocatalytic contributions.