Enhanced photocatalytic degradation of methylene blue using zinc vanadate nanomaterials with structural and electrochemical properties

The development of Zn₃(VO₄)₂ nanomaterials was successfully achieved via a green chemistry method utilizing Moringa Oleifera extract. The photocatalytic performance of the synthesized nanomaterials was tested for the degradation of methylene blue (MB) under visible light irradiation. The optical properties, crystalline structure, and composition of the nanomaterials were analysed using photoluminescence (PL), X-ray diffraction (XRD), diffuse reflectance spectroscopy (DRS), Fourier-transform infrared spectroscopy (FTIR), and high-resolution transmission electron microscopy (HRTEM). XRD and HRTEM data revealed that the nanomaterials prepared at 500 °C and 700 °C exhibited high crystallinity and were quasi-spherical with a range of particle sizes and irregular shapes. The electrochemical properties were evaluated using cyclic voltammetry (CV), linear sweep voltammetry (LSV), and electrochemical impedance spectroscopy (EIS). The CV response showed broad redox peaks and peak separations indicative of pseudo-capacitive behaviour arising from faradaic reactions, which are pseudo-reversible. EIS results indicated that the electrochemical behaviour of the electrode material was influenced by both reaction kinetics and diffusion processes. Furthermore, the photocatalytic degradation of MB using Zn₃(VO₄)₂ nanomaterials was evaluated under visible light irradiation. The experiments considered various parameters, including MB concentration, catalyst loading, and pH. The results demonstrated an impressive degradation efficiency, reaching 87% removal of MB at pH 5.0 after 120 min of exposure to visible light. Kinetic analysis showed that the degradation followed a pseudo-first-order model (R² > 0.98), with high R² values and observed rate constants, highlighting the potential for optimizing catalyst use in environmental applications, particularly in the removal of organic pollutants like MB from wastewater.