Adsorption of HF Pollutant on Single Vacant 2D Nanosheets: Ab Initio Molecular Dynamics Study

In the search of an efficient adsorbent for hydrogen fluoride (HF) gas without its chemical decomposition, experimentally synthesized point-defect-containing nitrogen-rich single vacant (SV) 2D sheets are studied using ab initio molecular dynamic simulations at room temperature and 1 atm pressure. Our calculations show that irrespective of initial conformations, HF gets adsorbed on the defect site by pointing H toward the sheet with reasonably high adsorption energies (-0.16 for h-BN and -0.73 eV for h-CNp). The larger adsorption energy at the h-CNp defect site appears due to the strong electrostatic interaction between the symmetric, electron-rich SV defect and the highly polar HF molecule. The unwillingness of the SV site to chemisorb HF has been further demonstrated by calculating the passage barrier of HF through this hole, as well as by showing the negligible change in bond length of H-F with time. The electrostatic driving forces to move HF toward the electron rich defect site are apparent from electrostatic potential mapping. Moreover, the long-range driving force of adsorbate toward the defect site has been demonstrated by starting the simulation with HF far away from the defect site. The adsorption nature of HF remains the same in the presence of 3-4 layers of water molecules around the defect site. Also, the adsorbed HF in the defect site have been probed through the prominent shifts in computed absorption spectra of HF trapped sheets compared to bare SV sheets.