In-Depth Experimental and Computational Investigations for Remarkable Gas/Vapor Sorption, Selectivity, and Affinity by a Porous Nitrogen-Rich Covalent Organic Framework

摘要

Porous nitrogen-rich covalent organic frameworks (COFs) are most challenging materials for selective CO2 capture, separation, and conversion for a substantive impact on the environment and clean energy application. On the other hand, separation of industrial cyclic congeners (benzene/cyclohexane) by the host-guest interaction through pi-electron-rich and -deficient centers in a COF is the key. On the basis of the strategic design, a triazine-based benzbis(imidazole)-bridged COF (TBICOF) has been synthesized under polycondensation conditions and structurally characterized by various analytical techniques. Because of the presence of a benz-bis(imidazole) ring, TBICOF exhibits permanent stability and porosity in the presence of acid and base monitored by the wide-angle X-ray pattern and N-2 sorption studies. The enhanced CO2 uptake of 377.14 cm(3) g(-1) (73.4 wt %) at 195 K confirms its high affinity toward the framework. CO2 sorption is highly selective over N-2 and CH4 because of very strong interactions between CO2 and triazine and benz-bis(imidazole)-functionalized pore walls of TBICOF as clearly evident from the isosteric heat of adsorption and ideal adsorbed solution theory calculation, which is higher than other reported functionalized metal-organic frameworks or COFs. Interestingly, TBICOF also behaves as a heterogeneous organocatalyst for chemical fixation of CO2 into cyclic carbonates under ambient conditions. The pi-electron-deficient triazine and benz-bis(imidazole) moieties have been utilized for selective sorption and separation of benzene (641.9 cm(3) g(-1)) over cyclohexane (186.2 cm(3) g(-1)). Computational studies based on density functional theory and grand canonical Monte Carlo molecular simulations further support the selectivity of CO2 (over N-2 and CH4) and benzene (over cyclohexane).