Theoretical insight into the degradation of diclofenac by hydroxyl and sulfate radicals in aqueous-phase: Mechanisms, kinetics and eco-toxicity

Abstract

Diclofenac (DCF) is a widely used non-steroidal anti-inflammatory drug, which has attracted more and more attention due to its biotoxicity and refractory degradation. The objective of this study was to systematically analysis the transformation mechanisms, kinetics and toxicity of DCF initiated by •OH and SO4•– in persulfate oxidation process. In this study, the degradation mechanism of DCF has been performed by density functional theory (DFT) methods, and the toxicity of the by-products was studied by computational toxicology. The results show that the reactivity of benzylic position of DCF is higher than that of chlorinated aromatic ring, indicating •OH and SO4•– are more likely to react in benzylic position. By comparing the initiation reactions of •OH and SO4•–, it was found that •OH-initiations were the predominant pathway in the degradation process. The kinetic calculations show that the degradation rate constants were positively correlated with temperature. Furthermore, the calculated toxicological results indicate that the toxicity level of most products is reduced, but the hydrolysates remain toxic and deserve more attention for the degradation by-products of DCF. The comprehensive theoretical study is helpful to reveal the microscopic mechanism of DCF transformation and AOP-wastewater remediation.