Functionalized modulators in imine-linked covalent organic frameworks (COFs)

Covalent Organic Frameworks (COFs) are porous materials with high surface areas, making them interesting for a large variety of applications including energy storage, chemical sensing, and gas separation. In gas separation and sensing, functionalization beyond the COF linkage can result in selective COF-gas interactions, tailoring the properties for the desired application. However, not all functional groups are compatible with the synthetic conditions needed for COF formation. Modulators, which are typically mono-functionalized building blocks that would terminate the reaction, have been shown to maintain or even improve the COF porosity by slowing down the reaction kinetics. Herein, we report on a series of several para -functionalized (OMe, Me, F, Cl, CF 3 , NO 2 ) amine modulators to introduce additional functionality into the framework to study the selective CO 2 /N 2 gas separation under flue gas conditions. Thorough characterization of the modulated COFs showed that the modulators are located on the outside of the polymeric sheet and get replaced by benzidine molecules, favoring a regular network formation over a homogeneous modulator distribution. The fractions of eventually incorporated modulator vary per functional group between 2.1% (NO 2 -modulated COF) and 8.9% (Me-modulated COF) while maintaining high BET surface areas (>1800 m 2 /g). It was found that all modulated COFs adsorb moderate quantities of CO 2 and show comparable CO 2 /N 2 IAST selectivity values under flue gas conditions. A higher number of functional groups in the framework was shown to enhance the IAST selectivity. • Functionalized modulated COFs with high porosity. • Modulator located at periphery of COF. • Regular network formation favored over homogeneous modulator distribution. • Higher number of functional groups in COFs enhance CO 2 /N 2 IAST selectivity.