Biochar–bentonite composite enabling antibiotic removal and greenhouse gas mitigation in waters

Antibiotic contamination and greenhouse gas (GHG) emissions frequently co-occur in eutrophic waters, posing threats to ecosystem health and climate stability. Here, a biochar–bentonite (BC–BT) composite was developed to degrade antibiotics and mitigate GHG emissions. The composite exhibited a large specific surface area (46.6 m²·g⁻¹) and defect-rich carbon structure, facilitating efficient peroxymonosulfate (PMS) activation via both radical (•OH as the dominant species, with minor contributions from O₂^·-) and non-radical (¹O₂ as a secondary pathway) routes, while SO₄^·- exhibits a negligible role in norfloxacin (NOR) degradation. Under optimal conditions (0.1 g·L⁻¹ catalyst, 0.5 mM PMS, pH 7), the BC–BT/PMS system achieved >90% NOR removal, while requiring only 0.02 g·L⁻¹ equivalent BC input from the composite, outperforming most reported PMS-based catalytic systems. The composite at 0.1 g·L⁻¹ demonstrated broad pH tolerance (3–9), excellent reusability, and resistance to coexisting anions and humic acid, maintaining 71–98% performance across diverse natural waters. Mechanistic analysis revealed that NOR transformation occurred via defluorination, hydroxylation, decarboxylation, and piperazine-ring cleavage, ultimately yielding low-molecular-weight products. Moreover, BC–BT suppressed carbon dioxide (CO₂) and methane (CH₄) emissions from eutrophic microcosms, e.g., reducing total GHG equivalents by 23%–47% under moderate or severe eutrophic condition, highlighting synergistic pollution control and carbon mitigation. This work provides mechanistic and environmental insights for designing low-cost, sustainable carbon–clay composite that couple advanced oxidation catalysis with ecological regulation, offering a scalable pathway toward carbon-neutral water remediation.