Two-dimensional ammonia-linked COF structures with different substituents for the adsorption and separation of sulfur hexafluoride: A theoretical study

Abstract

As one of the most potent greenhouse gases, SF₆ has a significant economic and environmental impact on the purification and recovery of exhaust gases from the semiconductor industry. The adsorption and separation performance of SF₆ on a two-dimensional covalent organic framework TAT-COFs-1-AB with different functional groups (SO₃H, Et, NH₂, OMe, OH, H) was investigated by using grand canonical Monte Carlo (GCMC) simulations and density functional theory (DFT) calculations. The results show that the adsorption at low pressure depends on the interactions between the SF₆ and COF frameworks, while at high pressure it is mainly affected by the porosity. The highest adsorption capacity of 8.44 mmol/g (298 K, 100 kPa) is exhibited by TAT-COF-1-AB-H, which has the highest porosity. Chemical functionalization was found to be effective in enhancing the SF₆/N₂ selectivity. Among all the functionalized COFs, TAT-COF-1-AB-NH₂, with the highest specific surface area and strong heat of adsorption, showed the highest selectivity. The simulation of self-diffusion also shows consistent results with the GCMC simulation. The findings highlight that the adsorption capacity is influenced by substituent and porosity, with SF₆ showing a consistent preference for adsorption at hollow sites, as evidenced by binding energy and charge transfer analyses.