Ionic Lignin Polymers for Controlled CO₂ Capture, Release, and Conversion into High-Value Chemicals

In this study, an innovative and cost-effective ionic polymer for CO₂ capture and utilization for the first time, using abundant and nonfood-based biomass lignin is reported. The modified ionic polymer synthesizes through the reaction of glycidyltrimethylammonium chloride with lignin under alkaline conditions to yield quaternary ammonium ionic functionality. Subsequently, the hydroxide-based pure ionic lignin polymer is employed for CO₂ capture from both direct air and concentrated CO₂ sources at room temperature and atmospheric pressure. Structural characterization of the polymers is accomplished through ¹H, ¹³C, and 2D-heteronuclear single quantum coherence (HSQC) NMR, and FT-IR spectroscopy. The CO₂ capture process is established through the formation of bicarbonate ions alongside the presence of CO₂. The captured CO₂ is precisely quantified by using inverse-gated proton decoupled ¹³C NMR with an internal standard (trioxane). Remarkably, the captured-CO₂ amounts of ionic lignin polymer are 1.06 mmol g^-1 (47 mg g^-1) from concentrated-CO₂ source and 0.60 mmol g^-1 (26 mg g^-1) from direct-air. The captured-CO₂ in ionic lignin polymer is released in controlled manner and utilized in the synthesis of cyclic carbonate, showcasing the productive application of the captured carbon. Moreover, the fully controlled recovering of ionic lignin polymer achieves via repeated CO₂ release ↔ CO₂ capture.