KHCO3-activated Camellia oleifera shell biochar for IMI removal: synergistic role of microporous network and edge C=O dipoles

Engineered biochar from agricultural waste offers a sustainable route for water remediation, yet how different activation strategies reshape the dense lignocellulosic matrix of hard-shell biomass for targeted pollutant removal remains unclear. This study systematically compared the removal efficiency of imidacloprid (IMI) by Camellia oleifera shell biochar modified with different activators (strong bases, weak bases, oxidants, Lewis acids, and Brønsted acids). Among these, KHCO 3 achieved optimal performance through in-situ CO 2 and H 2 O gasification, enabling controlled micropore assembly while safeguarding the sp 2 -conjugated carbon backbone. The KHCO 3 -activated sample (CH) displays a well-developed microporous network (specific surface area = 791.00 m 2 g −1 , I D /I G = 0.95), abundant edge-located C=O dipoles, and a preserved sp 2 -conjugated carbon skeleton, affording 93.42% IMI removal efficiency (3.1 fold over pristine biochar of 30.02%) as well as a Langmuir adsorption capacity of 451.37 mg g −1 at 318 K. The adsorption process is spontaneous (Δ G° = -20.87 to −27.66 kJ mol −1 ) and endothermic (Δ H° = +80.38 ± 2.04 kJ mol −1 ), and the adsorption behavior is governed jointly by physical and chemical mechanisms. DFT calculations reveal that the superior performance originates from synergistic π-π electron donor–acceptor interactions and interfacial hydrogen bonding between edge C=O dipoles and the nitroimino group of IMI, with the CH system exhibiting a more negative adsorption energy (−0.73 vs −0.63 eV). Practical evaluation confirms robust reusability (16.05% decay over five cycles), broad environmental tolerance, and reliable fixed-bed performance. This work offers mechanistic insights into the correlations among activation chemistry, pore architecture and electronic structure for rational biochar design.