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Heteroaggregation-driven regulation of levofloxacin adsorption by nano-biochar-goethite complexes in aquatic environments

Ma F, Cai Y, Li Q, Li R, Wang W

Environmental science. Processes & impacts, 2026

Abstract

The heteroaggregation of naturally occurring substances is crucial for the transportation, transformation, and fate of biochar nanoparticles (BNPs). This study systematically investigates the heteroaggregation behavior between BNPs and goethite (GT), with particular emphasis on their colloidal stability, interaction energetics, and the resulting effects on levofloxacin (LEV) adsorption. BNPs exhibited the highest colloidal stability at pH 7.5. In mixed systems, the coexistence of BNPs and GT enhanced the dispersion of GT particles while simultaneously diminishing the stability of BNPs. The maximum energy barriers (Φmax) for homo- and hetero-aggregation followed the order GT-GT (-10.4 × 10-18 J) -18 J) -17 J), indicating that GT tends to undergo homopolymerization prior to subsequent heteroaggregation with BNPs. Both Na+ and Ca2+ promoted BNP-GT heteroaggregation, with Ca2+ exhibiting a markedly stronger effect as evidenced by the lower critical coagulation concentration (CCC). When BNP concentration remained below the critical threshold (40 mg TOC per L), BNP effectively enhanced GT dispersion. However, above this threshold, extensive heteroaggregation occurred, forming large and compact heteroaggregates. Heteropolymer formation partially shielded the surface functional groups of BNPs, thereby restricting LEV access to available adsorption sites. Nonetheless, at elevated LEV concentrations, LEV molecules were able to penetrate the heteropolymer matrix or induce structural…

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