Non-radicals dominated degradation of sulfamethoxazole by a chemical-less microwave enhanced photolysis process

Abstract

A chemical-less microwave enhanced photolysis process (named MW/UV) was established for sulfamethoxazole (SMX) degradation and the mechanisms were specifically studied. 96.7% of SMX could be removed in an extremely short reaction time of 140 s under 400 W of microwave and 23.0 mW/cm2 of UV light at 254 nm. The half-live of SMX was greatly shortened to 5 s in MW/UV process, compared with 67 s in UV process and 1386 s in MW process. MW/UV process was also effective when applied to complex real water matrices, such as river water, seawater, and synthetic waste water. Non-thermal effects of microwave were found to play an essential role in elevating photolysis degradation efficiency. The ROS formation detected by quenching experiments and EPR test showed that SMX degradation by MW/UV followed non-radicals dominated method, although 1O2 and OH co-existed in this system. 16 intermediates in total were detected by HPLC-Q-TOF and three degradation pathways based on 1O2 and OH oxidation were proposed according to the structural characteristics of the intermediates. Besides, toxicity evaluation of SMX and its intermediates revealed that MW/UV process could effectively reduce the toxicity of SMX. This study provides an efficient and promising scheme for practical SMX degradation.