Quantification of adsorption mechanisms distribution of sulfamethoxazole onto biochar by competition relationship in a wide pH range

Abstract

This study aimed to investigate the degree of contribution of adsorption mechanisms of sulfamethoxazole (SMX) on corncob-derived biochar CC800 through competition experiments. The SMX adsorption was governed by diverse mechanisms under different pH, resulting in high pH dependent adsorption of SMX on biochar. The adsorption of SMX on CC800 in the presence of ions was evaluated, demonstrating that the ion exchange mechanism had a weak effect on the adsorption. The intense competitiveness of SMX structural analogs verified π+–π electron donor-acceptor (EDA) effect was the dominant adsorption mechanism of SMX on CC800 at low pH, and the negative charge-assisted hydrogen bond (CAHB) was critical to the adsorption at high pH. The adsorption mechanisms contribution of SMX on CC800 were further quantified. The SMX adsorption on CC800 was mainly controlled by 51% pore filling and 43% π+–π EDA effect in the acid region, 62% pore filling mechanism and 25% (−)CAHB mechanism in the alkalic region, and less than 5% of hydrophobic interaction and ion exchange. Consequently, the above mechanisms provided a theoretical basis for biochar application to remove sulfonamide antibiotics and other similar organic contaminants and targeted design of biochar products. Also, this quantification method can be extended to quantify the adsorption mechanisms between other antibiotics or organics and biochar adsorbent materials by selecting suitable adsorption competitors.