Trace SO₂ Gas Capture in Stable 3D Viologen Ionic Porous Organic Framework Microsphere

Eliminating trace sulfur dioxide (SO₂) using nanoporous adsorbents is industrially preferred yet of great challenge due to the competitive adsorption of CO₂. Herein, we reported a highly stable 3D viologen porous organic framework (Viologen-POF) microsphere via one pot polymerization reaction of 4,4′-bipyridine and tetrakis(4-(bromomethyl)phenyl)methane. Compared to the previously reported irregular POF particles, viologen-POF microsphere shows better mass transfer uniformity. Owing to the intrinsic separated positive and negative electric charges center in viologen-POF microspheres, it exhibits excellent SO₂ selective capture performance, which can be collaboratively confirmed by static single-component gas adsorption, time-dependent adsorption rate, and multicomponent dynamic breakthrough experiments. Viologen-POF exhibits high SO₂ absorption capacity (1.45 mmol g^-1) at ultralow pressure of 0.002 bar and high SO₂/CO₂ selectivity of 467 at 298 K and 100 kPa (SO_2/CO₂, 10/90, v/v). The theoretical calculations based on density functional theory (DFT) and DMol³ modules in Material Studio (MS) were also performed to elucidate the adsorption mechanism of viologen-POF toward SO₂ at the molecular level. This study represents a new type of viologen porous framework microsphere for trace SO₂ capture, which will pave the way on the applications of ionic POF for toxic gas adsorption and separation.