Development of surface-modified galvanised steel as an immobilised photocatalyst for textile wastewater treatment

Abstract

The quest for cost-effective photocatalytic material and a simple process for wastewater degradation has inspired the development of immobilised ZnO photocatalyst by surface-modifying the commercial galvanised steel via plasma electrolytic oxidation process (PEO). In this work, galvanised steel underwent oxidation via PEO using a suitable base electrolyte system (borax and sodium aluminate). The optimum time for effectively converting zinc in the galvanised steel to ZnO is investigated. The 90 s PEO process effectively converted ZnO with the bandgap value of 3.30 eV. Additionally, vanadium was doped into the ZnO by adding sodium metavanadate (0.3 to 1.2 g/L) to the base electrolyte to reduce the bandgap. The effect of dopant concentration on the surface morphology, phase analysis, optical properties, recombination rate and separation efficiency of charge carriers were investigated. Also, the photocatalytic efficiency was measured by evaluating methylene blue dye's degradation under UV light irradiation. It was found that 0.9 g/L of sodium meta vanadate addition to the base electrolyte system was shown crystalline ZnO with near-visible light absorption (3.15 eV) along with reduced electron-hole recombination. Finally, the vanadium-doped ZnO photocatalyst showed 95 % MB dye degradation with a rate constant K = 0.014 min−1 under UV light.