Highly porous biochar engineered from agricultural waste for efficient removal of sulfonylurea herbicides in aqueous systems.

Abstract

Pesticide contamination in aquatic environments, particularly due to sulfonylurea herbicides, has become a growing concern. Herein, a highly porous biochar was synthesized using potassium bicarbonate (KHCO₃) as a green activating agent through a one-step pyrolysis and acid washing process. Among the different samples, KBC-6 exhibited the highest specific surface area (3548.8 m² g^-1), the greatest defect density, and abundant oxygen-containing functional groups. As a result, KBC-6 demonstrated impressive adsorption capacities of 227.5 mg g^-1 for bensulfuron-methyl (BSM) and 195.9 mg g^-1 for nicosulfuron (NIC) at 298 K. The adsorption process followed pseudo-first-order kinetics and was well-described by the Freundlich model, with physical mechanisms, including pore filling, hydrogen bonding, and π-π interactions, contributing 49.4 % and 52.7 %, 15.7 % and 13.6 %, and 25.6 % and 23.9 % for BSM and NIC, respectively. KBC-6 achieved high removal efficiency of BSM and NIC across a wide range of conditions, including pH 5-9, 0.1 M anions, 10 M ionic strength, and 0-100 mg L^-1 humic acid. After six regeneration cycles, KBC-6 maintained over 72.3 % removal efficiency. Fixed-bed column tests showed treatment volumes of 244.16 BV for BSM and 222.93 BV for NIC, and the treated effluent did not affect soybean root growth or fresh weight, indicating its safety. These results suggest that KHCO₃-activated biochar provides a cost-effective and eco-friendly solution for removing sulfonylurea herbicides from polluted water.