Efficient SO₂ Capture Mediated via a Gradient Electric Field in Electron-Rich Conjugated Porous Aromatic Frameworks

The deep removal of sulfur dioxide (SO₂) from flue gas is of significant importance for environmental protection, yet developing adsorbents with high uptake capacity and selectivity, as well as excellent cycling stability, remains a formidable challenge. Herein, two porous aromatic frameworks (PAFs) with electron-rich conjugated structures (termed PAF-TrP and PAF-SBF) were prepared for the selective capture of SO₂ from flue gas. A systematic investigation involving static gas adsorption, dynamic breakthrough experiments, stability tests, and molecular-level simulations demonstrated that both PAFs exhibit an exceptional SO₂ capture performance. Under conditions of 298 K and 1 bar, the uptake capacities of SO₂ in PAF-TrP and PAF-SBF reach 259.1 and 344.7 cm^-3·g^-1, respectively. The IAST (ideal adsorbed solution theory) selectivities of PAF-TrP and PAF-SBF toward SO₂ in the SO₂/N₂ binary gas mixture are 4159.3 ∼ 902.8 and 3769.1 ∼ 844.3, respectively, at 298 K and 1 bar. Molecular-level simulation calculations based on density functional theory (DFT) revealed the intrinsic mechanism underlying the highly selective SO₂ capture by the two PAFs. Specifically, the localized charge separation on the electron-rich aromatic conjugated frameworks of both PAFs generates a gradient electric field, which induces strong dipole-dipole and dipole-π interactions with polar SO₂ molecules. Additionally, the construction mode of the two PAFs via strong covalent linkages endows them with remarkable stability and favorable regenerability. This study represents a meaningful endeavor toward developing high-performance adsorbents for flue gas desulfurization.