Preparation of Phosphorus-Doped Boron Nitride Aerogel and Its Heavy Metal Ion Adsorption Properties

This study developed phosphorus-doped boron nitride aerogel (P-BNaerogel) through a sol-gel method combined with low-dimensional boron nitride (BN) assembly, aiming to address the critical challenge of removing heavy metal ions in industrial wastewater. Structural characterization using X-ray photoelectron spectroscopy (XPS) and synchrotron X-ray absorption fine structure (XAFS) demonstrated that phosphorus doping introduced P—O—C and P—O functional groups, increased the interlayer spacing of BN from 0.334 nm to 0.347 nm, and enhanced mesopore volume by 32.7%. Nitrogen adsorption-desorption isotherms further revealed a specific surface area of 465.4 m2/g and an ultralight bulk density of 0.80 mg/cm3, significantly lower than that of the undoped BNaerogel (1.24 mg/cm3). Adsorption experiments conducted at 25 ℃ showed that P-BNaerogel exhibited a Cu2+ adsorption capacity of 413.3 mg/g, outperforming BNaerogel by 14.4%, with maximum capacities for Zn2+, Cd2+, and Pb2+ reaching 338.5, 253.9, and 234.8 mg/g, respectively. Kinetic analysis indicated that the adsorption process followed pseudo-second-order kinetics (R2 > 0.985) for P-BNaerogel, driven by chemisorption via coordination bonds between metal ions and P=O groups, whereas BNaerogel adhered to pseudo-first-order kinetics (R2 > 0.996), indicative of physical adsorption. The Langmuir isotherm models (R2 > 0.990) confirmed monolayer adsorption in both materials. Competitive adsorption tests in mixed solutions highlighted the selectivity of P-BNaerogel for Cu2+, with a selectivity coefficient α(Cu/Pb) of 2.17, which was attributed to d-orbital electron interactions between Cu2+ and P—O groups. Thermodynamic studies identified 25 ℃ as the optimal temperature, beyond which the adsorption capacity decreased due to accelerated desorption kinetics. The superior adsorption performance of P-BNaerogel was attributed to three synergistic effects: (1) phosphorus-induced active sites accelerating surface reactions, (2) optimized mesoporous structure (average pore size reduced to 2.9 nm from 3.4 nm in BNaerogel) enhancing ion diffusion, and (3) stabilized coordination environments via P—O bonding. Furthermore, the scalable synthesis using low-toxicity precursors (boric acid, melamine, and red phosphorus) and the ultralight density of the material <1 mg/cm3 enable cost-effective fabrication and integration into dynamic filtration systems for large-scale wastewater treatment. Future research will focus on pilot-scale validation of long-term stability and mechanistic studies to elucidate the selective adsorption pathways in complex multi-ion environments.