Improvement of ZnO by textural modification and metal doping for atrazine photocatalysis

Abstract

Atrazine is the herbicide used for controlling broadleaf and grassy weeds. Contamination of atrazine has been found in environment particularly in cultivated area. Atrazine can cause hazard to bacteria, plankton, plants, animals, and human. The objective of this study is to develop ZnO, Ce-ZnO, and Cu-ZnO catalysts fabricated on Al2O3 by mechanical coating technique (MCT) applied for the degradation of atrazine contaminated water under visible light irradiation. ZnO, Ce-ZnO, and Cu-ZnO were successfully synthesized by the simple chemical method using sticky rice starch (S) and polyvinylpyrrolidone (P) as templates. Under visible light irradiation, the 0.02Ce-ZnO (S) showed efficient removal of atrazine at the pH of the isoelectric point. The S template could represent an environmental friendly alternative for the catalyst synthesis compared to the P template. Ce-ZnO (S) at both 0.02 and 0.1 molar ratios of doping showed the higher atrazine removal than Cu-ZnO (S). The 0.02Ce-ZnO (S) 5:1 and the commercial ZnO were used further in the study of photocatalytic degradation of atrazine. The optimal catalyst loadings were 0.1 g for catalyst powder, 2.5 g for ZnO_550, and 5.0 g for 0.02Ce-ZnO (S) 5:1 bead per 100 mL atrazine solution (5 mg/L). Discharge of Zn into atrazine solution was quite insignificant. The SO42– and Cl– anions enhanced the atrazine removal while CO32–, HCO3–, and HPO42– anions inhibited the atrazine removal. 0.005Ag-0.005Ce-ZnO was successfully prepared and presented superiority on atrazine degradation (87% at 180 min). The kinetics of the atrazine removal relied on Langmuir-Hinshelwood-Hougen and Watson (LHHW) model. However, the total organic carbon (TOC) decreased only 64–65% at 180 min, and cyanuric acid was not observed as the final product in atrazine photocatalytic degradation