Influence of operational parameters on photocatalytic amitrole degradation using nickel organic xerogel under UV irradiation

Abstract

The objectives of this study were to analyze the influence of different operational variables and to determine the time course of total organic carbon (TOC) and medium toxicity during amitrole (AMT) photodegradation in the presence of Ni xerogel (X-Ni) as photocatalyst. A further study objective was to analyze the influence of the type of water on the photodegradation process. Results show that the degradation rate is directly proportional to the initial X-Ni concentration up to a maximum of 250 mg/L with a slight decrease thereafter, indicating progressive photon absorption saturation of the catalyst for a given incident radiation flow. At concentrations close to 250 mg/L X-Ni, the AMT photodegradation rate is not affected by further increases in X-Ni concentration. In addition, AMT photolysis is highly pH-dependent and is generally favored at pH values at which AMT is in its ionic form. The increase observed in AMT degradation rate under alkaline conditions can be attributed to the higher generation of HO· radicals. The presence of chloride reduces the AMT degradation rate, because Cl− anions behave as h+ and HO· radical scavengers. The degradation rate is also decreased by addition to the medium of organic matter, which acts as a filter. The behavior of TOC removal kinetics during AMT degradation in the presence of X-Ni is similar to that observed for AMT degradation kinetics. Finally, we highlight that photocatalysis is more effective in ultrapure water than in wastewater or tap water. In all systems, the optimal catalyst concentration is 250 mg/L. The medium toxicity increases with longer treatment time, indicating the formation of by-products that are smaller than AMT and can more readily penetrate the cell. Keywords: Ni xerogel, Amitrole, Photodegradation, Catalysis