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

ZHANG Junzhong; LIU Zheng; LIU Bo; LI Yanlong

doi:10.20078/j.eep.20240713

Abstract：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.