Recent advances in modified biochars for the adsorptive removal of typical antibiotics from water: a comparative review of performance, influencing factors, and underlying mechanisms

Abstract

Antibiotic contamination in aquatic environments has raised increasing concern because conventional treatment processes often show incomplete removal of ionizable antibiotics. Modified biochar has emerged as a promising adsorbent, but its performance varies substantially with antibiotic class, modification route, and solution chemistry. This review provides a focused, class-resolved and quantitative comparison of modified biochars for the adsorption of tetracyclines (TCs), sulfonamides (SAs), and fluoroquinolones (FQs) across five major modification strategies: alkali activation, acid and salt activation, metal and magnetic composites, heteroatom doping, and hybrid advanced composites. Based on 50 retained primary publications, reported maximum adsorption capacities (Qmax) are interpreted as performance distributions rather than absolute rankings across heterogeneous experimental conditions. Qmax ranged from 77.60–2242.00 mg g−1 for TCs, 4.18–1083.00 mg g−1 for SAs, and 11.62–1295.40 mg g−1 for FQs. TCs showed the highest upper-range capacities because their polycyclic structures and multiple functional groups favor multipoint interactions, whereas SAs exhibited greater variability because of pH-sensitive ionization and weaker complexation ability; FQ adsorption was strongly dependent on surface electronic structure, polarity, and pH-regulated speciation. Across systems, adsorption performance reflects the coupling of hierarchical pore accessibility, surface charge, aromatic carbon domains, heteroatom-derived active sites, and metal coordination centers. These interactions are organized into a progressive interfacial framework in which pore accessibility enables retention, electrostatic interactions regulate molecular approach and orientation, π–π electron donor–acceptor interactions and hydrogen bonding provide molecular recognition and stabilization, and surface coordination contributes site-specific anchoring. Importantly, high Qmax alone does not indicate application readiness. Real-water matrix resistance, regeneration stability, leaching risk, adsorbent recovery, continuous-flow operation, preparation complexity, techno-economic feasibility, and life-cycle impacts should therefore be jointly considered when evaluating modified biochars for antibiotic-contaminated water treatment.