Evaluation and Optimization of Operating Parameters in the Photocatalytic Reduction of Hexavalent Chromium (Cr (VI)) Using a Full Factorial Design

Photocatalytic process is one of the modern treatment methods which can be efficiently used for the treatment of wastewaters containing pollutants with priority such as hexavalent chromium. So in this study, the effects of various operating parameters and optimum conditions for the reduction of Cr (VI) in the presence of ZnO/HZSM-5 nanocomposite were investigated using a full factorial design method. In this study, ZnO/HZSM-5 nanocomposite was sanitized by Hydrothermal/impregnation method. The structure and morphology of Nanocomposite were studied by XRD, UV/vis, and FESEM techniques. In order to evaluate the photocatalytic reduction of hexavalent chromium using ZnO/HZSM-5 nanocomposite, full factorial technique was used. The effects of reaction time, pH, UV intensity, and initial chromium concentration were studied. The results of XRD showed that the nanocomposite was properly formed and had a crystalline phase. FESEM images showed that active phase (ZnO) was uniformly spread on the surface in nanometric size. The results of Fisher test (F-Value) indicated that the initial concentration of hexavalent chromium plays the most important role in the process. Under optimal conditions (initial concentration of chromium = 10 mg/L, UV light intensity = 125 W, pH = 5, and reaction time = 60 minutes), the removal efficiency was 98.72% with a desirability of 0.985 for hexavalent chromium. Finally, the normal probability analysis indicated that the data had a normal distribution. According to the result, it was indicated that the initial concentration of chromium was the most effective parameter in the process. Hence, the full factorial method can be used as an effective method for optimizing the conditions of the photocatalytic process in removing hexavalent chromium.