Purified Poly(ionic liquid) with TFMS⁻ anion captures CO₂ seven times more efficiently

Context Poly(ionic liquid)s (PILs) combine the CO₂‑loving nature of ionic liquids with the solid form of polymers, making them attractive for carbon‑capture membranes. Traditional anion‑exchange methods leave behind metal‑containing salts that mask true performance. A joint team from Nitto Boseki Co., Ltd. and Tohoku University tackled this impurity problem.

Key Facts The researchers started with poly(diallyldimethylammonium chloride) – a polymer densely packed with positive charges and chloride (Cl⁻) as the counter‑anion. They first stripped all chlorine‑based inorganic salts using a precise purification step. Scanning Electron Microscopy coupled with Energy‑Dispersive X‑ray Spectroscopy (SEM‑EDX) confirmed that chlorine was undetectable, proving complete removal of the by‑product salts. Next, they swapped the chloride for three larger anions: acetate (AcO⁻), thiocyanate (SCN⁻), and trifluoromethanesulfonate (TFMS⁻). The size of the anion grew from acetate to TFMS⁻. CO₂ adsorption tests showed a clear trend: larger anions allowed more CO₂ molecules to bind. The TFMS⁻‑based PIL recorded an adsorption capacity seven times higher than the untreated, chloride‑containing material. The work, led by Associate Professor Kouki Oka of the Institute of Multidisciplinary Research for Advanced Materials at Tohoku University, appears online in *Reaction Chemistry & Engineering* (doi:10.1039/D5RE00535C) as of March 9, 2026.

What It Means By eliminating residual salts and deliberately choosing a bulky counter‑anion, the team demonstrated a straightforward route to dramatically improve CO₂ capture in solid polymers. The finding supplies a concrete design rule—prioritize larger anions after thorough purification—for next‑generation gas‑separation membranes and capture devices. As the climate agenda pushes for scalable carbon‑removal technologies, such material tweaks could translate into lower energy costs and higher capture efficiencies.

Looking Ahead Future work will test the TFMS⁻‑based PIL in real‑world membrane modules and assess long‑term stability under industrial flue‑gas conditions.