Enhanced norfloxacin degradation by iron and nitrogen co-doped biochar: Revealing the radical and nonradical co-dominant mechanism of persulfate activation

The long-term abuse of antibiotics such as norfloxacin (NOR) poses a significant threat to aquatic environments. The development of efficient and economical treatments is still a pain point in the industry. Herein, we reported a directly robust carbonization-pyrolysis method to synthesize iron and nitrogen co-doped biochar material (Fe@N co-doped biochar) that was first applied to NOR removal through persulfate (PS) activation. The catalytic performance and operating factors were systematically investigated. It was found that 10 mg/L NOR achieved 95% degradation within 20 min under optimal reaction conditions. The removal rate of NOR could still achieve 80% and almost 50% of NOR was completely mineralized after five cycles. Through combined electron-paramagnetic-resonance analysis, quenching experiments, and X-ray-photoelectron-spectroscopy tests, center dot OH, center dot SO4-, and O-1(2) were confirmed as reactive oxygen species in catalytic reaction. Iron activated PS to produce center dot OH and center dot SO4- through electron transfer and nitrogen-containing functional groups (graphitic N, C-OH/C = N) accepted electrons from PS to generate O-1(2). The radical pathway involving hydroxyl radicals and the nonradical pathways involving singlet oxygen together accounted for the rapid degradation of NOR. The degradation pathways were comprehensively established, including defluorination, decarboxylation, piperazine ring breakage and nalidixic ring transformation. This study shed light on a new mechanism of radical and nonradical co-dominated PS activation and proposed a simple and inexpensive antibiotic wastewater treatment system.