Abstract
ABSTRACT In this study, the influence of HCO3 − on NO3 −-induced photosensitive degradation of sulfamethoxazole (SMX) under UV irradiation was investigated. It was found that the removal of SMX by UV in the presence of NO3 − improved significantly compared to its photolysis, which was confirmed to be due to the role of hydroxyl radical (HO•) formed through UV-activated NO3 −. However, the addition of HCO3 − in UV/NO3 − system could further enhance SMX degradation, which was verified to be ascribed to the formed carbonate radical (CO3 •−) through the reaction of HCO3 − with HO•. The second-order rate constant of CO3 •− with SMX was determined to be 2.58 × 108 M−1 s−1. In UV/NO3 −/HCO3 − system, the reactive species for SMX removal were HO• and CO3 •−, and the contribution of CO3 •− to SMX degradation might be much higher than that of HO•. The concentration of NO3 − was almost unchanged after reaction in UV/NO3 − and UV/NO3 −/HCO3 − systems because of its regeneration. Based on the detected four transformation products, the possible degradation pathways of SMX in UV/NO3 −/HCO3 − system were proposed including hydroxylation, amino-oxidation and bond cleavage.
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