Abstract:
The widespread presence of antibiotics in the environment poses a critical threat of antimicrobial resistance, making the development of efficient antibiotic removal technologies a key challenge in environmental remediation. Utilizing widely available and low-cost biochar for antibiotic adsorption represents a promising solution. Watermelon peel, rich in nitrogen- and oxygen-containing functional groups, serves as an ideal precursor for synthesizing biochar with superior adsorption capacity for pharmaceutical molecules. The watermelon peel-derived biochar (WBC) was synthesized via pyrolysis, followed by comprehensive physicochemical characterization. The effect of pH on the adsorption performance of WBC was investigated, and the adsorption behaviors of WBC toward multiple pharmaceuticals were systematically evaluated in both single- and co-adsorption systems. The single-adsorption system included four typical antibiotics, while the co-adsorption system incorporated four typical antibiotics and two antipsychotic drugs. The results demonstrated that pH significantly influenced WBC's adsorption efficiency of antibiotics. In single-adsorption systems, WBC exhibited the highest adsorption capacity for enoxacin (ENO), with a theoretical maximum of 64.73 mg/g. In co-adsorption systems, WBC exhibited significant differences in adsorption capacity for different drugs, which was mainly attributed to the different physicochemical properties of drug molecules, affecting the adsorption behavior of biochar and its occurrence. Clozapine (CLZ) displayed competitive adsorption dominance in co-adsorption systems, exhibiting a combined monolayer-multilayer adsorption pattern. The trimethoprim (TMP) adsorption mode was different from that of single-adsorption systems, due to CLZ being adsorbed by WBC through hydrophobic interactions and had a significant adsorption advantage in the co-adsorption process. The adsorption sites of TMP were occupied, and TMP adsorption mode shifted from multilayer adsorption in single systems to monolayer adsorption. Notably, reduced adsorption capacities in co-adsorption systems were linked to competitive occupation of WBC's active sites. The research results further revealed that hydrogen bonding and π—π interactions served as primary driving forces, supplemented by electrostatic and hydrophobic interactions. This study elucidated the strength relationship between various adsorption mechanisms on WBC in the co-adsorption process of multiple drugs, providing a reference for the treatment of complex antibiotic pollution and the targeted modification of biochar materials.