Highly Selective Carbon Dioxide Sorption in an Organic Molecular Porous Material

The organic molecular porous material 1 obtained by recrystallization of cucurbit[6]uril (CB[6]) from HCl shows a high CO2 sorption capacity at 298 K, 1 bar. Most interestingly, 1 showed the highest selectivity of CO2 over CO among the known porous materials so far. The remarkable selectivity of CO2 may be attributed to the exceptionally high enthalpy of adsorption (33.0 kJ/mol). X-ray crystal structure analysis of CO2 adsorbed 1 revealed three independent CO2 sorption sites: two in the 1D channels (A and B) and one in the molecular cavities (C). The CO2 molecules adsorbed at sorption site A near the wall of the 1D channels interact with 1 through hydrogen bonding and at the same time interact with those at site B mainly through quadrupole-quadrupole interaction in a T-shaped arrangement. Interestingly, two CO2 molecules are included in the CB[6] cavity (site C), interacting not only with the carbonyl groups of CB[6] but also with each other in a slipped-parallel geometry. The exceptionally selective CO2 sorption properties of 1 may find useful applications in the pressure swing adsorption (PSA) process for CO2 separation not only in the steel industry but also in other industries such as natural gas mining.