Role of GO content in ZnO/@ x wt% GO NCs for the reduction of Cr(VI) pollutant from wastewater stream

Due to severe environmental and health risks associated with Cr(VI), there is an urgent need to prioritize the development of new and efficient photocatalysts for its reduction. To solve this issue, three different nanocomposites (NCs) of Zinc oxide (ZnO) with Graphene oxide (GO), i.e. ZnO/@GO were prepared via hydrothermal process, by varying GO concentrations (10, 20, and 30 wt%). The goal is to investigate the impact of GO concentration on the photoreduction of Cr(VI) to Cr (III) in an aqueous system. Various physical properties such as crystallinity, morphology, elemental composition, and optical characteristics of the samples were analyzed using Powder X-ray diffraction (P-XRD), Scanning electron microscopy with Energy dispersive X-ray (SEM–EDX), Ultraviolet–Visible spectroscopy (UV–VIS), Diffuse reflectance spectroscopy, and Photoluminescence spectra, respectively. Photocatalytic reduction of Cr(VI) to Cr (III) was investigated using prepared different ZnO/@GO NCs samples under solar light illumination at room temperature within a pH range of 5.0–6.0. Notably, the highest reduction of 95% was achieved with 10 wt% GO-doped ZnO NCs (ZnO/@10 wt% GO NCs). Kinetic analysis reported the pseudo second-order model and rate constants were found to be 0.349, 0.0123, and 0.001 mol⁻¹L⁻¹1 min⁻¹ for the used three different composites, respectively. This data indicates a confirmed decline in the reduction of Cr(VI) to Cr (III) with the increasing concentration of GO in prepared NCs. In last, reduction mechanism was examined which confined the role of ̇OH species in the conversion of Cr(VI) to Cr (III).