Persulfate activation by oxidation biochar supported magnetite particles for tetracycline removal: Performance and degradation pathway

In this study, the oxidation biochar supported magnetite particles (OBC-Fe3O4) was prepared to activate persulfate (PS) for antibiotic tetracycline (TC) degradation. The as-prepared OBC-Fe3O4 exhibited the better catalytic performance for PS activation due to its abundant oxygen-containing groups on the surface and Fe3O4 particles. In the OBC-Fe3O4/PS system, TC was degraded and removed through the synergistic effects of catalyst's adsorption and sulfate radical (SO4•−) oxidation. The optimum conditions were determined as pH 3.0, PS concentration 10 mM and OBC-Fe3O4 dosage 0.4 g/L, which resulted in 92.3% of TC removal within 2 h. The electron spin resonance (ESR) and radicals quenching studies revealed the mechanism of TC degradation in OBC-Fe3O4/PS system included the radical and nonradical pathway involving the generation of SO4•−, •OH and 1O2, while SO4•− and •OH radicals played more dominant role in the reaction. Moreover, the intrinsic atom arrangements of carbon hybridization, defective sites and persistent free radicals (PFRs) on the catalysts also related to its catalytic efficiency. Eight transformation products were identified which mainly derived from oxidation of double bonds, loss of dimethyl amino, dehydration, oxidation of aromatic ring and cleavage of carboatomic ring of TC. Consequently, a possible degradation pathway of TC was suggested. Overall, OBC-Fe3O4 could be an economic and high-efficiency heterogeneous catalyst for PS activation to remove organic pollutants in waste water.