Enhanced Adsorption of Neonicotinoids by MnCl₂ and H₃PO₄ Co-Modified Corn Stover Biochar: Performance and Mechanism Analysis

In this study, corn stover biochar was prepared and modified with manganese (II) chloride (MnCl 2 ) and phosphoric acid (H 3 PO 4 ) to investigate the adsorption performance and mechanism of neonicotinoids represented by clothianidin (CLO). MnCl 2 promotes pore formation in biomass and enhances activation efficiency, while H 3 PO 4 boosts the specific surface area and adsorption capacity of the product. These properties make them widely used in biomass activation. The modified biochar (Mn-P-BC) exhibited an adsorption capacity of 11.5   mg·L -1 for CLO, representing a 2.8-fold enhancement compared to unmodified biochar (BC). In materials characterization, SEM and BET analysis results show that Mn-P-BC has a developed porous structure, and the surface area increases by 13.7 times compared with BC, which can provide more adsorption sites. According to the electrochemical properties, kinetics, and isotherm analyses, the adsorption mechanism for CLO was identified as involving physicochemical processes. Furthermore, density functional theory (DFT) calculations indicated that Mn-P-BC was more efficient in removing CLO compared to thiamethoxam (THM) and imidacloprid (IMI). It is shown that the mechanism of interaction between Mn-P-BC and CLO mainly involves pore filling, π-π interactions, and hydrogen bonding. In summary, the co-modification of biochar with MnCl 2 and H₃PO₄ significantly improved the adsorption performance of biochar, which provided new insights into the development of adsorbents for neonicotinoid insecticide removal.