Enhanced removal of florfenicol by distributing nanoscale zerovalent iron onto activated carbon: Mechanism and toxicity evaluation

Abstract

Antibiotics, especially halogenated antibiotics, inevitably discharged into environment are of great concern worldwide. Nanoscale zerovalent iron (nZVI)-based materials have been promising for the removal of halogenated antibiotics, but their susceptibility to oxidation and aggregation badly limits their application. Herein, activated carbon (AC)-supported nZVI (nZVI-AC) was synthesized to remove florfenicol (FF), a widely used broad-spectrum halogenated antibiotic, under ambient conditions. nZVI-AC had the strongest adsorption affinity to FF and most conductive to FF, and the reaction rate constant (k1) of FF removal by nZVI-AC (0.320 min−1) was increased by 106.7 times with the support of AC (0.003 min−1). Freundlich and DA models showed good fits for FF adsorption by nZVI-AC, and hydrogen bonding, van der Waals forces and chemisorption were the dominant mechanisms for FF adsorption. The van der Waals forces and chemisorption contributed to the enhanced adsorption capacity of the composite system, and the strong synergistic effect of AC and nZVI in nZVI-AC accelerated electron transfer towards adsorbed FF, thus facilitating the further dehalogenation. The removal of FF by nZVI-AC was dependent on solution pH and CrO42− concentrations, and suppressed by humic acid, while barely affected by Cd2+. Escherichia coli survival assessment and theoretical simulation evaluation demonstrated the superior efficacy of nZVI-AC in detoxifying FF with the detection of non-toxic FF intermediates. By comprehensively analyzing the environmental factors, removal mechanisms and potential degradation pathways of FF treated by nZVI-AC, this study provides further insights into the risk assessment of intermediates and their toxicity, assigning new perspectives for practical application of nZVI-based technologies to efficiently remove the amount and also reduce the toxicity of FF and other emerging contaminants in water.