The superior performance of silica gel supported nano zero-valent iron for simultaneous removal of Cr (VI)

Abstract

Pure nano zero-valent iron (NZVI) was fabricated under optimum conditions based on material production yield and its efficiency toward acid blue dye-25 decolorization. The optimum prepared bare NZVI was immobilized with two different supports of silica and starch to fabricate their composites nanomaterials. The three different prepared zero-valent iron-based nanomaterials were evaluated for removal of hexavalent chromium (Cr(VI)). The silica-modified NZVI recorded the most outstanding removal efficiency for Cr(VI) compared to pristine NZVI and starch-modified NZVI. The removal efficiency of Cr(VI) was improved under acidic conditions and decreased with raising the initial concentration of Cr(VI). The co-existence of cations, anions, and humic acid reduced Cr(VI) removal efficiency. The removal efficiency was ameliorated from 96.8% to 100% after adding 0.75 mM of H2O2. The reusability of silica-modified NZVI for six cycles of Cr(VI) removal was investigated and the removal mechanism was suggested as the physicochemical process. Based on Langmuir isotherm, the maximal Cr(VI) removal capacity attained 149.25 mg/g. Kinetic and equilibrium data were efficiently fitted using the pseudo-second-order and Langmuir models, respectively confirming the proposed mechanism. Diffusion models affirmed that the adsorption rate was governed by intraparticle diffusion. Adsorption thermodynamic study suggested the spontaneity and exothermic nature of the adsorption process. This study sheds light on the technology that has potential for magnetic separation and long-term use for effective removal of emerging water pollutants.