Preparation of Chestnut Shell Biochar Loaded with Zinc/Manganese for Effective Removal of Oxytetracycline from Aqueous Solution

Abandoned biomass derived from agricultural production has been widely applied to deal with environmental challenges. This work prepared biochar modified by zinc and manganese (Zn/Mn–BC) through straightforward impregnation pyrolysis for the removal of oxytetracycline from wastewater. Characterizations, adsorption performance, reusability, and mechanisms were studied. Results showed that the Zn/Mn–BC had the highest OTC adsorption capacity (60.81 mg/g) and exhibited finer separation performance at low OTC concentrations. Notably, Zn/Mn–BC can keep a high removal rate (75.86%) of OTC after 5 cycles. The kinetic and isotherm models reveal that the adsorption process is multi-layer chemisorption. Thermodynamic data indicates that OTC adsorption by Zn/Mn–BC is an exothermic, spontaneous process with decreasing entropy. In addition, the possible mechanisms of adsorption are mainly electrostatic, hydrogen bonds, π–π stacking interactions, and especially metal oxide bonds (M–O) for OTC removal. This study not only realizes the strategy of turning waste into a treasure of chestnut shell but also provides an alternative and sustainable adsorbent for antibiotics from wastewater.