CO2 adsorption on fluorinated covalent triazine frameworks (CTFs): Structure remodeling and performance enhancement

Abstract

In consideration of the fact that covalent triazine frameworks (CTFs) have shown great potential and application prospects as CO2 adsorbent to alleviate the greenhouse effect and climate change by adsorption process for carbon emissions, a kind of promising activated fluorinated covalent triazine frameworks (referred to O-CTFs) was prepared as the adsorbent to enhance CO2 adsorption. The O-CTFs was prepared by structure remodeling of the fluorinated CTFs based on a series of ring-opening, substitution and polymerization reactions. The remodeling mechanism was revealed by theoretical calculations and those characterization methods of SEM, BET, EDS, FTIR, XPS, 13C-NMR and HRMS. Subsequently, the adsorption thermodynamics and kinetics of CO2 on the CTFs and O-CTFs were systematically investigated to reveal the influence of structure remodeling on CO2 adsorption behaviors. The results showed that the structure remodeling developed porous structure by forming more mesopores and micropores, then modified surface group distribution by forming new nitrogen- and oxygen-containing groups such as pyridine and pyrrole rings. The increase of pore volume, especially micropore volume, resulted in the dynamic capacity promotion by 217.5 % at 273 K. And the dual screening effects of surface group distribution and porous structure led to the CO2/N2 selectivity improvement by 202.4 %. Then the amount increase of the mesopores promoted the rate increase of CO2 adsorption by 59.9 % by means of accelerating the internal diffusion of CO2 in porous structure. In addition, the isosteric heat of adsorption decreased by 10.0 %, meaning that CO2 molecules were easily desorbed from the O-CTFs. These are beneficial for the preparation of promising CO2 adsorbent and extended application of CO2 adsorption processes.