Synergy of Adsorption and Solar Photoreduction for Removal Cr(VI) with Spinel CuFe₂O₄

The synergy effect between adsorption and solar photocatalysis to remove Cr(VI) is a new approach which is environmentally friendly and sustainable development technology. The choice of photocatalyst is crucial for achieving better performance in adsorption and photocatalytic reactions. The CuFe₂O₄ catalysts with a spinel structure were synthesized by co-precipitation and sol-gel methods, and characterized by X-ray diffraction, BET surface area, Scanning electron microscopy, Raman and Fourier-transform infrared spectroscopy (FTIR). The results of this study show that the CuFe₂O₄-co is an excellent adsorbent and photocatalyst simultaneously for Cr(VI) removal, this activity is correlated to its structural, and textural properties and a relatively narrow band gap. The catalyst is mainly crystallized in cubic inverse spinel structure and exhibits a large pore size that facilitates the accessibility of active sites by chromium ions on the surface, which can also improve absorbed light penetration. Moreover, the UV-Vis diffuse reflectance spectrum shows that the catalyst has a low band gap energy (1.2 eV), allowing a broader absorption spectrum, which enhances its capability to generate electron−hole pairs under visible light of solar irradiation. The effects of oxalic acid as a reducing agent, preparation technique, catalyst concentration, and initial dose of Cr(VI) were studied in this research. 100% reduction of Cr(VI) to Cr(III) is achieved within 1 h in the presence of small quantities of oxalic acid to maintain the рН 3 at an optimal concentration of catalyst (0.25 g/L).