Capture of aromatic organic pollutants by hexagonal boron nitride nanosheets: density functional theoretical and molecular dynamic investigation

The adsorption mechanisms and dynamic behaviors of pollutants on the surface of hexagonal boron nitride (h-BN) nanosheets are interesting and fundamentally important for their practical application. In this work, the adsorption of typical aromatic organic pollutants, including benzene, polycyclic aromatic hydrocarbons (PAHs) and their derivatives (hydroxyl-PAHs and nitro-PAHs), and polybrominated diphenyl ethers (PBDEs), on the surface of an h-BN monolayer was investigated by density functional theory (DFT) and molecular dynamics (MD) methods. Benzene, PAHs and their derivatives favored adsorption on the top(N) sites by co-planar configuration with the aromatic rings nearly parallel to the h-BN surface. The adsorption energies increased with the number of aromatic rings of the adsorbate. For PBDEs, the adsorption configurations were determined by the bromine substitution pattern. For BDE congeners with 6 or 6'-substituents, T-shaped configurations with one phenyl ring perpendicular to the surface were formed due to the steric-hindrance effect. Other BDE congeners would adopt a co-planar configuration to maximize the pi-pi stacking interaction through torsion angle rearrangement. The adsorption energy was found to be linearly correlated with the hydrophobicity of the pollutants. Thermodynamic and electronic analysis indicated that the adsorption processes of pollutants on the h-BN surface are spontaneous, exothermic and physical in nature. The rapid adsorption observed from MD simulation demonstrated that h-BN could capture aromatic pollutant molecules and confirmed that h-BN-based nano-materials should have potential in environmental applications.