Activation of peroxydisulfate by iron dichloride with hydroxylamine promoted sulfapyridine degradation

Sulfapyridine (SPY) is a ubiquitous environmental contaminant belonging to the sulfonamide antibiotics. Previous studies showed that hydroxylamine (HA) can improve the performance of advanced oxidation processes (AOPs) by promoting Fe(II) regeneration, yet the reaction mechanisms were not elucidated. Therefore, the role of HA and the degradation mechanisms of SPY were systematically studied therein. The SPY degradation efficiency increased from 77.5% to 91.6% after HA was added. With radical scavenger experiment, a function of HA to promote •OH production for SPY degradation was clarified. The major radical from SO4•- and •OH to •OH with addition of HA in Fe(II)/potassium peroxydisulfate (PDS). Results showed that alkali, acid condition and high PDS concentration all contributed to SPY degradation. According to experimental results, density functional theory (DFT) was used to calculate the degradation pathway of SPY. Rate-limiting path was obtained by comparing the rate constants calculated from the transition-state theory. The cleavage of C-C bond in benzene ring with the slowest rate was essential to degrade SPY, which not only promotes the mineralization of SPY, but also prevent the production of toxic TPs effectively. This study provides valuable insight into the SPY degradation in HA/Fe(II)/PDS.