Preparation of magnetic Kudzu root residue biochar and its application in sulfamethoxazole wastewater

To tackle the issues associated with conventional biochar treatment of sulfamethoxazole (SMX) wastewater—such as limited adsorption capacity, inadequate solid-liquid separation efficiency, and significant pollution risks coupled with low resource conversion efficiency during the disposal of herbal residues—a new magnetic biochar material was developed specifically for the treatment of SMX wastewater. Utilizing Kudzu root residue , which is a byproduct from traditional Chinese medicine production, magnetic Kudzu root residue biochar (MKRRBC) was synthesized through a combined carbonization and KOH activation process, incorporating Fe²⁺/Fe³⁺ co-precipitation. The material was comprehensively characterized using BET surface area analysis, XPS, VSM and other techniques. A systematic investigation was conducted on the effects of adsorption conditions, along with analyses of adsorption kinetics, thermodynamics, and regeneration performance. The findings reveals that MKRRBC possesses oxygen-containing functional groups and active sites of Fe₃O₄, demonstrating superparamagnetism (with a saturation magnetization of 15.21 emu·g⁻¹) and a hierarchical pore structure (specific surface area of 891.07 m²·g⁻¹). The maximum adsorption capacity is found to be 384.6 mg·g⁻¹, with a retention of 84.7% capacity after five regeneration cycles. The adsorption process is predominantly governed by π-π interactions, hydrogen bonding, and Fe₃O₄ coordination synergy. This process exhibits pseudo-second-order kinetics (R²=0.9999) and follows the Langmuir isotherm model (R²=0.9927-0.9931), demonstrating characteristics of a spontaneous, exothermic process with decreased system disorder. This innovative material integrates high-efficiency adsorption with magnetic separation capabilities, offering a new approach for the treatment of pharmaceutical and aquaculture wastewater containing SMX while facilitating the resource utilization of kudzu root residue.