Photocatalytic reduction of hexavalent chromium over ZnO nanorods immobilized on kaolin

The photocatalytic reduction of hexavalent chromium (Cr(VI)) using ZnO nanorods immobilized on kaolin clay was studied. Scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) analysis demonstrated favorable immobilization of ZnO nanorods onto the kaolin. The efficiency of the UV/ZnO/kaolin process for reduction of Cr(VI) was about 88.0%, which was more effective than the UV/ZnO process (43.7%). The photocatalytic reduction of Cr(VI) was increased from 35.7 to 97.1%, with increasing photocatalyst dosage from 0.25 to 3 g/L, respectively. The reaction rate constant (k_obs) was decreased from 0.0769 to 0.0072 1/min, and the value of electrical energy per order (EEo) was increased from 62.4 to 666.7 (kW·h/m³) with increasing initial Cr(VI) concentration from 10 to 50 mg/L, respectively. The photocatalytic reduction of Cr(VI) was increased from 88.3 to 98.5% in the presence of citric acid, while the presence of phenol, ethylenediaminetetraacetic acid and oxalic acid resulted in decreasing the photocatalytic reduction of Cr(VI) to 70.2, 53.2, and 36.4%, respectively.