Magnetically separable CoFe2O4/ZrO2 nanocomposite for the photocatalytic reduction of hexavalent chromium under visible light irradiation

[Display omitted] •CoFe2O4/ZrO2 nanocomposite was synthesized for photoreduction of Cr(VI).•A visible light photocatalytic process for reduction of Cr(VI) was proposed.•The enhancing photocatalysis mechanism was discussed.•A maximum photoreduction efficiency up to 83 % was obtained. In this study, CoFe2O4/ZrO2 nanocomposite was synthesized by hydrothermal method for photoreduction of hexavalent chromium. ZrO2 nanoparticles were modified by CoFe2O4 nanoparticles to increase the photocatalytic activity of the nanocomposite. The prepared nanocomposite was then characterized by Scanning electron microscopy (FESEM), Fourier transform infrared (FTIR) spectroscopy, X- ray diffraction (XRD), Dynamic light scattering (DLS),Vibrating sample magnetometer (VSM) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS). In the second part of the research, the effect of pH (2–8), irradiation time, photocatalyst dosage (0.005–0.03 g) and chromium solution concentration (10–50 mg/L) on the photocatalytic reduction of hexavalent chromium under visible light were investigated. Increase in irridation time and photocatalyst dosage had a positive impact on photocatalytic reduction. Additionally, photocatalytic reduction of hexavalent chromium in alkalic environment was less than that of the acidic environment. A maximum photoreduction efficiency up to 83 % was obtained at optimum condition, i.e. pH = 2, 0.02 g photocatalyst, 10 ppm chromium solution. Finally, kinetic studies using pseudo-first order model (simplified Langmuir-Hinshelwood equation) suggested that the implemented model was suitable for describing the experimental data.