Electrostatically Driven Selective Adsorption of Carbon Dioxide over Acetylene in an Ultramicroporous Material

Separating acetylene from carbon dioxide is important but highly challenging owing to their similar physical properties and molecular dimensions. Herein, we report highly efficient electrostatically driven CO2/C2H2 separation in an ultramicroporous cadmium nitroprusside (Cd-NP) with compact pore space and complementary electrostatic potential well fitting for CO2, thus enabling molecular quadrupole moment recognition of CO2 over C2H2. This material shows a high CO2/C2H2 uptake ratio of 6.0 as well as remarkable CO2/C2H2 selectivity of 85 under ambient conditions with modest CO2 heat of adsorption. Neutron powder diffraction experiments and molecular simulations revealed that the electrostatic potential compatibility between pore structure and CO2 allows it to be trapped in a head-on orientation towards the Cd center, whereas the diffusion of C2H2 is electrostatically forbidden. Dynamic breakthrough experiments have validated the separation performance of this compound for CO2/C2H2 separation.