Nanoscale zero-valent iron loaded on boron-doped coffee grounds highly efficiently activates peroxymonosulfate to degrade tetracycline

The practical application of unmodified biochar in advanced oxidation processes (AOPs) is constrained by its limited surface functional groups and the inherent drawbacks of nanoscale zero-valent iron (nZVI), including particle aggregation and oxidative instability. To address these challenges, nZVI catalysts with controlled boron doping ratios were synthesized via coffee grounds modification, followed by systematic evaluation of their catalytic performance, mechanistic pathways, and operational parameters. Under optimized conditions (0.12 g L⁻¹ nZVI@B₁-BC and 1 mM peroxymonosulfate (PMS)), near-complete tetracycline (TC) removal (99.1 %) was achieved within 30 min. Remarkably, boron doping enhanced TC degradation kinetics by 1.51-fold compared to undoped counterparts, highlighting the pivotal role of heteroatom engineering in tailoring catalyst reactivity. The nZVI@B₁-BC composite demonstrated exceptional robustness across diverse aqueous matrices, exhibiting strong tolerance to coexisting anions, humic acid (up to 25 mg L⁻¹), and pH fluctuations (3−11). Radical quenching experiments and electron paramagnetic resonance (EPR) analysis identified hydroxyl radicals (•OH) and sulfate radicals (SO₄^•−) as dominant reactive oxygen species (ROS), while HPLC-MS elucidated three potential TC degradation pathways involving dehydroxylation, demethylation, and ring-opening reactions. This work advances the rational design of biochar-supported nZVI catalysts and provides actionable insights for optimizing persulfate activation systems in antibiotic-contaminated water remediation.