Enhanced CO2 Adsorption by Insertion Reaction in the Nanospace of a Porphyrin-based MOF

Here we report enhanced CO2 molecular recognition ability by incorporating insertion reaction into a metal porphyrin complex in a metal-organic framework (MOF). PCN-222(Cu)-INA was synthesized by the reaction of PCN-222(Cu) [Zr6O8(H2O)8(Cu-TCPP)2], where Cu-TCPP = Cu(II) tetrakis(4-carboxyphenyl)porphyrin, and isonicotinic acid (INA). PCN-222(Cu)-INA exhibited a 1.5 times larger CO2 adsorption amount than PCN-222(Cu) at 298 K and 1 bar. The mechanism involving insertion reaction of CO2 into Cu–N bonds enhanced the adsorption, which was revealed by in situ IR spectroscopy and theoretical calculations. Here we report enhanced CO2 adsorption by insertion reaction in Cu porphyrin-based metal–organic frameworks. To enhance CO2 affinity, the accessible metal ion sites (AMSs) of porphyrin units were modified by post-synthetic reaction with isonicotinic acid (INA). The mechanism of the enhancement of CO2 adsorption was revealed by in situ IR spectroscopy that showed reversible insertion reaction of CO2 into Cu–N bonds, which was also supported by theoretical calculations.