Photocatalytic reduction of hexavalent chromium with illuminated ZnO/TiO2 composite

•ZnO/TiO2 composite was used as a photocatalyst for the removal of Cr(VI).•XRD and FT-IR analysis demonstrated hybridization of ZnO and TiO2 nanoparticles.•UV/ZnO/TiO2 process was more efficient than UV/ZnO or UV/TiO2 process.•Photocatalytic reduction process can be described by Langmuir–Hinshelwood model. The purpose of this work was to investigate the photocatalytic reduction of Cr(VI) with illuminated ZnO/TiO2 composite at various catalyst dosage, pH, Cr(VI) concentration, purging gas, type of organic compounds. FT-IR and XRD analysis demonstrated hybridization of ZnO nanoparticles and TiO2 particles. The photocatalytic reduction of Cr(VI) was increased with increasing photocatalyst dosage and decreasing pH. The reaction rate constant (kobs) was decreased from 0.0879 to 0.0048min−1 with increasing Cr(VI) concentration from 20 to 100mg/L. Removal efficiency of Cr(VI) by UV/ZnO/TiO2 process was about 99.99%, which was more effective than that by UV/ZnO (82.33%) and UV/TiO2 process (86.07%).