Synergistic radical/nonradical pathways in Fe3O4@CoFe-LDH nanocomposite for peroxymonosulfate-activated tetracycline degradation: mechanism and interface engineering

Fe 3 O 4 @CoFe-LDH, a magnetic composite, and its counterpart, CoFe-LDH, were successfully synthesized via a co-precipitation method and systematically investigated for their performance and mechanism in activating peroxymonosulfate (PMS) for tetracycline (TC) degradation. Fe 3 O 4 @CoFe-LDH possessed a typical LDH structure with Fe 3 O 4 nanoparticles uniformly dispersed in the CoFe-LDH matrix, forming a heterojunction interface that effectively combined the magnetism of Fe 3 O 4 and the high catalytic activity of CoFe-LDH. Magnetic analysis (VSM) indicated a saturation magnetization of 23.93 emu/g for the composite, enabling magnetic separation and recovery within 30 s, significantly enhancing the practical applicability. Under optimal conditions (0.07 g/L catalyst, 0.75 mM PMS, pH 6–8, 25 °C), Fe 3 O 4 @CoFe-LDH/PMS achieved 97.6 % TC (25 mg/L) degradation, outperforming CoFe-LDH (93.9 %). Radical quenching and ESR revealed sulfate radicals (SO 4 •- ) and nonradical ( 1 O 2 ) as dominant species, with Fe 2+ /Fe 3+ –Co 2+ synergism promoting 1 O 2 pathways. Density functional theory (DFT) calculations showed enhanced charge transfer and reduced activation energy at the heterojunction. After four cycles, Fe 3 O 4 @CoFe-LDH retained 82.3 % activity (vs. 73.2 % for CoFe-LDH) and exhibited strong anti-interference (86.8–92.4 % TC removal in natural water), highlighting its engineering potential.