Responsive Porous Material for Discrimination and Selective Capture of Low-Concentration SO2

The efficient removal of low-concentration SO2 is of great significance but challenging due to the competitive adsorption of CO2. Herein, we report the efficient capture of low-concentration SO2 with high selectivity over CO2 by Mn(INA)2 (INA = isonicotinate) with a designed pore structure. Notably, the channels of Mn(INA)2 exhibit large cavities and narrow bottlenecks, leading to the exclusion of the larger molecules of N2 and CH4. An interesting phenomenon was observed through single-crystal X-ray diffraction experiments where SO2 "opened" the bottlenecks and entered the cavities via the rotation of the pyridine ring (12.2°) to enlarge the cavities to accommodate SO2 molecules. These responsive properties of Mn(INA)2 to SO2 molecules afford high SO2/CO2 separation selectivity. In addition, first-principles dispersion-corrected density functional theory (DFT-D) calculations elucidate that the high-density host–guest interactions including duple Sδ+···Oδ− electrostatic interactions, multiple Hδ+···Oδ− dipole–dipole interactions, and guest–guest interactions between SO2 molecules are responsible for the sensitive response of the material toward low-concentration SO2 (2000 ppm). The efficient SO2 capture properties of Mn(INA)2 are further demonstrated by the breakthrough experiments. Moreover, the material is stable and easy to scale up, which makes it promising for low-concentration SO2 removal.