Interrogating solar photoelectrocatalysis on an exfoliated graphite–BiVO4/ZnO composite electrode towards water treatment

Abstract

A novel photoanode consisting of an exfoliated graphite–BiVO₄/ZnO heterostructured nanocomposite was fabricated. The material was characterised with scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD). Photoelectrochemical studies were carried out with cyclic/linear sweep voltammetry and chronoamperometry. The solar photoelectrochemical properties of the heterojunction photoanode were investigated through the degradation of rhodamine B in water. The results revealed that the nanoparticles of BiVO₄ and ZnO were well entrapped within the interlayers of the exfoliated graphite (EG) sheets. Improved charge separation was achieved in the EG–BiVO₄/ZnO composite electrode which resulted in superior photoelectrochemical performance than individual BiVO₄ and ZnO electrodes. A higher degradation efficiency of 91% of rhodamine B was recorded using the composite electrode with the application of 10 mA cm⁻² current density and a solution pH of 7. The highest total organic carbon removal of 74% was also recorded with the EG–BiVO₄/ZnO. Data from scavenger studies were used to support the proposed mechanism of degradation. The electrode has high stability and reusability and hence lends itself to applications in photoelectrocatalysis, especially in water treatment.