H3PO4-modified biochar derived from pear branches for efficient neonicotinoid removal

The widespread presence of neonicotinoids (NEOs) in environmental matrices has raised significant concerns regarding their potential ecotoxicological effects and risks to human health. This study aims to address this issue by converting underutilized pear branch waste into a high-performance NEO adsorbent and elucidating the adsorption process. Pristine biochar (BC) and four modified biochars (H 3 PO 4 -, KOH-, humic acid-, and 2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO)-modified BC) were produced from pear branch waste through nonmetallic doping and pyrolysis at 700°C. The adsorption performance for four NEOs (clothianidin, thiamethoxam, imidacloprid, and acetamiprid) was systematically evaluated. Batch experiments showed that H 3 PO 4 -BC had superior removal efficacy (67.8%–81.0%) for the four NEOs at an initial concentration of 10 mg L −1 , using a dosage of only 5 mg. This was attributed to its high specific surface area and abundance of oxygen-rich functional groups, which facilitated multi-mechanism adsorption. The adsorption process was heterogeneous and involved multisite binding. Furthermore, it was spontaneous (Δ G < 0) and endothermic (Δ H > 0), with an increase in entropy (Δ S > 0). Optimal adsorption occurred under acidic conditions owing to protonation of the NEOs. In addition, background ions caused minimal interference. The following adsorption pathways contributed to the overall process: hydrogen bonding (35.2%–41.4%), pore filling (14.4%–38.3%), hydrophobic partitioning (3.1%–27.2%), π–π electron donor–acceptor interactions (15.3%–17.0%), and ion exchange (1.5%–8.7%). This study directly addresses gaps in the literature by transforming pear branch waste into a high-value adsorbent and by providing a quantified, multi-mechanistic framework for designing adsorbents to remove NEOs from aquatic environments.