Photoelectrocatalytic degradation of sulfamethoxazole over S-Scheme Co3Se4/BiVO4 heterojunction photoanode

This work 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. This can be attributed to the effective charge carrier separation occasioned by the heterojunction created in the composite. This provides the composite with the capacity to effectively degrade SMX with improve 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.