Ultrahigh and Selective SO₂ Uptake in Inorganic Anion-Pillared Hybrid Porous Materials

The efficient capture of SO₂ is of great significance in gas-purification processes including flue-gas desulfurization and natural-gas purification, but the design of porous materials with high adsorption capacity and selectivity of SO₂ remains very challenging. Herein, the selective recognition and dense packing of SO₂ clusters through multiple synergistic host-guest and guest-guest interactions by controlling the pore chemistry and size in inorganic anion (SiF₆^2- , SIFSIX) pillared metal-organic frameworks is reported. The binding sites of anions and aromatic rings in SIFSIX materials grasp every atom of SO₂ firmly via S^δ+ ···F^δ- electrostatic interactions and O^δ- ···H^δ+ dipole-dipole interactions, while the guest-guest interactions between SO₂ molecules further promote gas trapping within the pore space, which is elucidated by first-principles density functional theory calculations and powder X-ray diffraction experiments. These interactions afford new benchmarks for the highly efficient removal of SO₂ from other gases, even if at a very low SO₂ concentration. Exceptionally high SO₂ capacity of 11.01 mmol g^-1 is achieved at atmosphere pressure by SIFSIX-1-Cu, and unprecedented low-pressure SO₂ capacity is obtained in SIFSIX-2-Cu-i (4.16 mmol g^-1 SO₂ at 0.01 bar and 2.31 mmol g^-1 at 0.002 bar). More importantly, record SO₂ /CO₂ selectivity (86-89) and excellent SO₂ /N₂ selectivity (1285-3145) are also achieved. Experimental breakthrough curves further demonstrate the excellent performance of these hybrid porous materials in removing low-concentration SO₂ .