Optimized performance and mechanistic analysis of tetracycline hydrochloride removal using biochar-based alginate composite magnetic beads for peroxymonosulfate activation

Tetracycline, an antibiotic notorious for its ecotoxicity and propensity to induce bacterial resistance, poses significant threats to ecosystems and human health. In this study, we synthesized a magnetic biochar-iron-lanthanum cross-linked alginate beads (Fe/La@BCB) composite material through a gel-calcination method to activate peroxymonosulfate (PMS) for the degradation of tetracycline hydrochloride (TCH). Results revealed that under pH 7 conditions, employing 0.2 g/L Fe/La@BCB and 0.3 g/L PMS, TCH's removal efficiency and mineralization rate (30 mg/L) within 60 min were 90.52 % and 30.49 %, respectively. The degradation of TCH was attributed to the synergistic action of multiple reactive oxygen species (SO₄^-•, •OH, ¹O₂ and O₂^•-) as evidenced by free radical quenching experiments. Specifically, the electron transfer among Fe/La oxides, oxygen-containing functional groups, and defective structures played a pivotal role in generating free radicals upon activation of PMS. Furthermore, the catalyst demonstrated remarkable long-term stability, maintaining a removal efficiency of 79.87 % even after six consecutive cycles. Analysis of intermediate degradation products elucidated degradation pathways of TCH involving hydroxylation and ring-opening reactions. In conclusion, this novel magnetic catalyst exhibits high efficiency, facile recovery, and robust structural stability, making it highly promising for effectively activating PMS to degrade antibiotics in wastewater. Moreover, it offers insights into addressing catalyst recovery challenges in practical applications.