Solar Driven Photocatalytic Reduction of Cr(VI) Via Interfacial Charge Transfer in FeWO4/CuO Nanocomposite

Abstract

Hexavalent chromium (Cr(VI)) is a hazardous trace contaminant commonly present in industrial wastewater due to various anthropogenic activities, posing significant environmental and health risks. In this study, a FeWO4/CuO nanocomposite was synthesized via coprecipitation followed by thermal decomposition, and systematically characterized to determine its crystal structure, morphology, elemental composition, and optical properties. The synthesized materials were evaluated for the photocatalytic reduction of toxic Cr(VI) under natural solar irradiation. Powder X-ray diffraction (P-XRD) analysis revealed that the average crystallite size decreased from 39.90 nm for FeWO4 and 30.51 nm for CuO to 25.48 nm in the FeWO4/CuO nanocomposite, indicating improved dispersion and interaction between the components. The FeWO4/CuO nanocomposite exhibited superior photocatalytic activity, achieving 98.89% reduction of Cr(VI) to Cr(III) within 90 min, compared to 39.24% for FeWO4 and 56.54% for CuO. The reduction process followed pseudo-first-order kinetics, with a rate constant (k) of 0.0409 min–1, which is approximately five times higher than that of pure FeWO4 (0.0097 min–1) and about twice that of CuO (0.021 min–1). The effects of operational parameters, including catalyst dosage (1.2 g L−1, 98.85%), solution pH (pH 2, 98.89%), and the presence of inorganic ions, were systematically investigated, with the observed trend: Cl– < Br– < SO42– < NO3– < IO3– < CO32– < I–. Reactive species trapping experiments indicated that electrons (e–) played a dominant role in the reduction process. Furthermore, the nanocomposite demonstrated excellent stability and reusability, with only a 2.5% decrease in efficiency after five consecutive cycles.