Unveiling the role of nitrogen-related functional groups in Imidacloprid adsorption by chitosan-modified graphitic biochar: A mechanistic insight into N-containing pollutant removal

While significant progress has been made in the synthesis of nitrogen (N)-containing biochar, the fundamental mechanisms governing its interactions with N-containing pollutants, especially the role of N-related functional groups in adsorption processes, remain insufficiently explored. This study systematically investigates the adsorption behavior of imidacloprid (IMI), a representative N-containing pollutant, using a hierarchically structured N-doped graphitic biochar (NBC900) synthesized through a secondary pyrolysis approach. The optimized NBC900 exhibited an exceptional adsorption capacity of 140.1 mg·g −1 for IMI, achieving a removal efficiency of 97.2 %. The incorporation of chitosan as a nitrogen source and elevated pyrolysis temperature facilitated the formation of N-related functional groups and enhanced graphitization, which were critical for adsorption. NBC900 demonstrated excellent adaptability across a wide pH range (2−11), strong resistance to ionic strength variations, and remarkable reusability, highlighting its potential for practical applications. Comprehensive material characterizations revealed that the adsorption mechanism primarily involved chemisorption and π-π interactions, driven by the high degree of graphitization. Notably, the Lewis acid-base interactions between pyridine-N and carbonyl (C=O) groups on NBC900, as well as the nitro (-NO 2 ) and pyridine groups in IMI, provided novel insights into the adsorption mechanisms of N-containing pollutants. These findings establish a mechanistic framework for understanding of biochar's interaction with N-containing pollutants and offer a foundation for designing high-performance adsorbents for environmental remediation applications. • The adsorption capacity for IMI was 140.05 mg/g, achieving a removal efficiency of 97.2 %. • Both pyridine-N and a high degree of graphitization play crucial roles in promoting adsorption. • Lewis acid-base reactions and π-π interactions are the primary mechanisms of adsorption. • Lewis acid-base reactions complement the adsorption mechanism for N-containing pollutants.