Efficient removal of phosphate and fluoride by PEI-grafted amino/rare earth co-modified porous BN: Behavior and mechanisms

Phosphorus and fluorine are essential elements of living organisms. However, excessive phosphate and fluoride can severely harm the balance of aquatic ecosystems and public health. Therefore, it is particularly important to develop an adsorbent that combines good adsorption capacity, simple synthesis and easy separation for wastewater treatment. Based on this, we pioneered a novel porous boron nitride material-based composite (p-BN) through PEI grafting and rare earth (La/Ce) modification (2PEI/ASBN-Ln (Ln = La, Ce)). The point of zero charge (pH pzc ) of 2PEI/ASBN-La reached 10.0, significantly improving the carrier's surface negativity and overcoming the electrostatic repulsion issue in anion adsorption. Additionally, the N content of the modified adsorbents exceeded 50%, and the amino group content increased, further enhancing the density of adsorption sites. The adsorption capacities of fluoride and phosphate for the optimal sample 2PEI/ASBN-La reached 112.165 mg g −1 and 79.547 mg g −1 , respectively, while also exhibiting effective removal of other pollutants in water, significantly broadening its applicability. The adsorption mechanism study revealed that the removal process involves multiple pathways, including physisorption, ion exchange and complexation. Specifically, phosphate removal was dominated by strong complexation through ligand exchange, whereas fluoride adsorption relied more on ion exchange and strong electrostatic attraction at amino and rare earth metal sites. More importantly, we further introduced magnetic nanoparticles into the adsorbent (2PEI/ASBN-La (Fe 3 O 4 )). VSM tests showed that its saturation magnetization reached 19.116 emu g −1 , enabling rapid magnetic separation under an external magnetic field. Collectively, this study provides innovative perspectives for the water treatment and recycling sector.