Efficient, Selective, and Reversible SO₂ Capture with Highly Crosslinked Ionic Microgels via a Selective Swelling Mechanism

Abstract SO₂ capture through physisorption is a promising environmental benign technology to eliminate the emission of SO₂. However, designing an efficient adsorption material with high capacity and selectivity of SO₂ as well as excellent reversibility remains challenging. Here, a class of highly crosslinked nonporous poly(ionic liquid)s (PILs) xerogels is prepared with high ionic density by photopolymerization of Gemini IL monomers and a microfluidic technology is further explored to prepare the corresponding monodisperse PIL microgels with uniform and controllable sizes at the diameter range from 43 to 250 µm. This kind of novel dense nonporous ionic xerogels/microgels completely exclude the adsorption of common gases (CO₂, CH₄, etc.), but exhibit very high SO₂ adsorption capacity (498 mg g⁻¹) via selective swelling mechanism. Unprecedented SO₂/CO₂ and SO₂/CH₄ uptake selectivities with the value up to 614 and 1992, respectively, are achieved. The selective swelling mechanism is validated by optical microscope and differential scanning calorimetry measurements. More importantly, these kinds of xerogels show excellent reversibility in adsorption–desorption cycles. Column breakthrough experiments confirm the excellent performance of these PIL xerogels in SO₂ capture. This work demonstrates that designing a nonporous material that has specific swelling interactions with certain molecules can be an effective strategy for realizing extremely high selectivity.