The large consumption and discharge of diclofenac(DCF) lead to its frequent detection in surface water and groundwater, posing great threats to humans and ecosystems. This study explored the oxidation kinetics of DCF ...The large consumption and discharge of diclofenac(DCF) lead to its frequent detection in surface water and groundwater, posing great threats to humans and ecosystems. This study explored the oxidation kinetics of DCF by permanganate(Mn(Ⅶ)), and expounded the underlying reason for the unusual p Hdependency that was unclear in previous studies. The kinetics of DCF analogues(i.e., aromatic secondary amines) by Mn(Ⅶ) oxidation were comparatively investigated. Then, a tentative kinetic model involving the formation of an intermediate between Mn(Ⅶ) and DCF or its analogues was proposed to fit the p H-rate profile. Since DCF contained two chloro groups, and a carboxyl group which could be ionized by negative electrospray ionization, a precursor ionization scanning approach was used for the first time for detection of N-containing chlorinated oxidation products. New degradation pathways of DCF containing ring opening, carboxylation, carbonylation, electrophilic addition, hydroxylation and dehydrogenation were proposed based on the identified oxidation products. Moreover, it was demonstrated that the introduction of various reducing agents such as Mn(Ⅱ), Fe(Ⅱ) and bisulfite significantly improved the oxidation kinetics of DCF by Mn(Ⅶ). The positive effects of Mn(Ⅱ) and Fe(Ⅱ) were mainly attributed to the accelerated formation of MnO_(2)that acted as a catalyst or co-oxidizer contributing to DCF degradation. The presence of bisulfite caused two-stage kinetics, where a sharp drop of DCF concentration followed by a slowdown of DCF removal. In the first stage, potent reactive manganese species(e.g., Mn(Ⅲ), Mn(V), and Mn(VI)) and sulfate radical were generated during reaction of bisulfite with Mn(Ⅶ), whereas bisulfite was depleted fast due to excess Mn(Ⅶ) concentrations and the system became the Mn(Ⅶ)/MnO_(2)system in the second stage. These results provide new insight into reaction mechanism of DCF with Mn(Ⅶ)as well as propose a feasible strategy for enhancing the treatment of DCF contaminated water by Mn(Ⅶ).展开更多
基金financially supported by the program for the National Natural Science Foundation of China (Nos. 51979044,42177045 and 42107053)the Guangdong Natural Science Funds for Distinguished Young Scholar (No. 2019B151502023)+2 种基金Guangdong International Training Program for Outstanding Young Talentsthe China Postdoctoral Science Foundation (No. 2021M700878)Guangdong-Hong Kong-Macao Joint Laboratory for Contaminants Exposure and Health (No. 2020B1212030008)。
文摘The large consumption and discharge of diclofenac(DCF) lead to its frequent detection in surface water and groundwater, posing great threats to humans and ecosystems. This study explored the oxidation kinetics of DCF by permanganate(Mn(Ⅶ)), and expounded the underlying reason for the unusual p Hdependency that was unclear in previous studies. The kinetics of DCF analogues(i.e., aromatic secondary amines) by Mn(Ⅶ) oxidation were comparatively investigated. Then, a tentative kinetic model involving the formation of an intermediate between Mn(Ⅶ) and DCF or its analogues was proposed to fit the p H-rate profile. Since DCF contained two chloro groups, and a carboxyl group which could be ionized by negative electrospray ionization, a precursor ionization scanning approach was used for the first time for detection of N-containing chlorinated oxidation products. New degradation pathways of DCF containing ring opening, carboxylation, carbonylation, electrophilic addition, hydroxylation and dehydrogenation were proposed based on the identified oxidation products. Moreover, it was demonstrated that the introduction of various reducing agents such as Mn(Ⅱ), Fe(Ⅱ) and bisulfite significantly improved the oxidation kinetics of DCF by Mn(Ⅶ). The positive effects of Mn(Ⅱ) and Fe(Ⅱ) were mainly attributed to the accelerated formation of MnO_(2)that acted as a catalyst or co-oxidizer contributing to DCF degradation. The presence of bisulfite caused two-stage kinetics, where a sharp drop of DCF concentration followed by a slowdown of DCF removal. In the first stage, potent reactive manganese species(e.g., Mn(Ⅲ), Mn(V), and Mn(VI)) and sulfate radical were generated during reaction of bisulfite with Mn(Ⅶ), whereas bisulfite was depleted fast due to excess Mn(Ⅶ) concentrations and the system became the Mn(Ⅶ)/MnO_(2)system in the second stage. These results provide new insight into reaction mechanism of DCF with Mn(Ⅶ)as well as propose a feasible strategy for enhancing the treatment of DCF contaminated water by Mn(Ⅶ).
