Insight into interaction between biochar and soil minerals in changing biochar properties and adsorption capacities for sulfamethoxazole

Biochars produced from wheat straw at 400 °C (BC400) and 700 °C (BC700) were treated with three typical soil minerals to examine the effects of soil minerals on biochar properties and adsorption capacity for sulfamethoxazole (SMX). Mineral treatment enlarged the surface area and pore size of biochar, and the electron donating capacity (EDC) of the mineral-treated biochars also increased due to the increased phenolic group in BC400 and the enhanced conjugated π-electron system in BC700, respectively, which in turn affected the adsorption capacity of biochars for SMX. The adsorption of SMX on BC700 was increased after mineral treatment due to the facilitating effect of π-π electron donor-acceptor interaction as indicated by the positive correlation of surface adsorption amount (QA) of SMX with EDC of biochars (R2 = 0.92-0.96). In contrast, mineral treatment decreased SMX adsorption on BC400, which could be attributed to the potential association of organic matter with minerals via coprecipitation and adsorption, in addition to the weak adsorption capacities of soil minerals for SMX. These results can provide a new insight for better understanding the interaction between biochar and soil minerals and its effect on adsorption capacity of biochar for organic pollutants.