Removal of H2PO4– in water by forestry waste biochar: Preparation, characteristics, adsorption performance, and mechanism

This study explored the application of biochar produced from the forestry residues Camellia oleifera (C. oleifera) shell (COS), chestnut shell (CNS), bamboo shoot shell (BBS), and walnut shell (WNS) to elucidate the dominant mechanism by which the combined effects of different lignocellulose structures and pyrolysis temperatures regulate the adsorption of H 2 PO 4 – by biochar. The forestry waste was carbonized at different pyrolysis temperatures to obtain biochars, after which the biochar properties, H 2 PO 4 – adsorption behavior, and underlying mechanisms were investigated. The results revealed that pyrolysis temperature was a key factor in enhancing the adsorption capacity of biochar for H 2 PO 4 – , as it promotes microporosity and expands the formation of specific surface area (S BET ), micropore surface Area (S t-plot ), and pore volume (V BJH ), which in turn provides more active sites for adsorption. The adsorption experiments revealed that CNS has the best adsorption capacity for H 2 PO 4 – (Q m  = 117 mg∙g –1 ) because of its unique radioactive needle-like fiber bundle structure, which forms a rich pore structure at 800°C. Quantitative contributions analysis revealed that functional group complexation (Q com ) constituted the dominant adsorption mechanism, with contributing 48 – 64%, as evidenced by a computed free energy of – 135.48 kcal·mol⁻¹. In addtion, the adsorption of H₂PO₄⁻ by FWB CNS exhibits good reusability and anti-interference capabilities. These findings demonstrate that CNS biochar has a great potential for removing phosphate from water.