The influence of bicarbonate (HCO3-) and nitrate (NO3-) on the photolysis of diclofenac (DCF) under UV-254nm irradiation was investigated in this study. The effects of HCO3- dose and NO3- dose on the degradation of DCF in UV/NO3-/HCO3- system were also explored. Finally, the degradation products and reaction mechanism of DCF by UV/NO3-/HCO3- were studied. The results show that the presence of HCO3- almost had no effect on DCF photolysis in the studied conditions. The presence of NO3- could significantly enhance the degradation of DCF due to the role of generated hydroxyl radical (HO•) through the excited NO3- under UV irradiation. Compared to DCF degradation by UV photolysis in the presence of only HCO3- or NO3-, the coexist of HCO3- and NO3- could further increase the removal of DCF, which could probably ascribe to the formation of carbonate radical (CO3•-) through the reaction between generated HO• and HCO3-. The presence of CO3•- and its role on DCF degradation were confirmed by adding methanol, a scavenger of HO•, in UV/NO3-/HCO3- system. The removal of DCF in UV/NO3-/HCO3- system might include three different reaction pathways, i.e., direct UV photolysis, HO• oxidation and CO3•- oxidation, and the contribution of direct UV photolysis and free radical oxidation to DCF removal in this system was 25% and 75%, respectively. The degradation efficiency of DCF increased gradually with the increase in NO3- dose in UV/NO3-/HCO3- system, because the increase of NO3- dose could enhance the steady-state concentration of generated HO• in this system. The increase of HCO3- dose had little influence on DCF removal in UV/NO3-/HCO3- system. Eleven transformation products were detected in the degradation of DCF by UV/NO3-/HCO3- using a liquid spectrometer coupled with a quadrupole time-of-flight tandem mass spectrometer (LC-QTOF/MS). According to these identified reaction products, the probable reaction mechanism of DCF in UV/NO3-/HCO3- system was proposed showing five different degradation pathways, including dechlorination-hydrogenation, dechlorination-cyclization, decarboxylation, formylation and quinonization.
刘义青, 史鸿乐, 付永胜. HCO3-和NO3-对水中双氯芬酸紫外光解的影响[J]. 中国环境科学, 0, (): 1329-1335.
LIU Yi-qing, SHI Hong-le, FU Yong-sheng. The influence of bicarbonate and nitrate on the photolysis of diclofenac under UV irradiation. CHINA ENVIRONMENTAL SCIENCECE, 0, (): 1329-1335.
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