Photoelectrocatalytic degradation of emerging organic pollutants in water on an FTO/BiVO₄/NiS photoanode

This study demonstrates the facile synthesis of bismuth vanadate-nickel sulfide (BiVO₄/NiS) heterojunction via a solvothermal process coated on a fluorine-doped tin oxide (FTO) substrate for photoelectrochemical (PEC) degradation of sulfamethoxazole (SMX) and Rhodamine B (RhB). The two semiconductors were rationally designed for the p-n heterojunction as it enhances the charge-separation and light-absorbing properties for efficient degradation of organic pollutants. The successful preparation of the BiVO₄/NiS composite was confirmed using structural, morphological, and optical analysis such as X-ray diffraction (XRD), transmitted electron microscopy (TEM), energy dispersive X-ray analysis (EDX), scanning electron microscopy (SEM), ultraviolet–visible diffuse reflectance spectroscopy (UV-DRS). The electrochemical and photoelectrochemical properties were investigated using electrochemical impedance spectroscopy (EIS), Mott-Schottky (M−S), and photocurrent response. Compared with the individual components, the FTO/BiVO₄/NiS photoanode showed an enhanced photocurrent response of 0.4 mA/cm² at 1.5 V potential, 16 and folds higher than the pristine BiVO₄. The composite showed a band gap of 1.9 eV, 2.28 eV, and 2.18 eV for the FTO/NiS, FTO/BiVO₄, and FTO/BiVO₄/NiS, respectively. Moreover, the PEC degradation of the two analytes indicated that the FTO/BiVO₄/NiS photoanode successfully degraded SMX (58%) and RhB (73%) in 120 min time intervals with a rate constant of 0.00755 min⁻¹ and 0.108 min⁻¹. Scavenger studies revealed that holes and superoxides were significant contributors to the mineralization of the analytes.