Anion Exchange Boosts Carbon Dioxide Capture Sevenfold in Polyionic Liquids

A joint research team from Nitto Boseki Co., Ltd. and Tohoku University has discovered that exchanging counter anions can significantly increase carbon dioxide (CO₂) adsorption in polyionic liquids (PILs). This finding offers a new guideline for designing high-performance CO₂ recovery devices and gas separation membranes. The research was led by Associate Professor Kouki Oka of Tohoku University's Institute of Multidisciplinary Research for Advanced Materials.

Polyionic liquids are known for their ability to attract CO₂ and their stability as solid materials. Previous anion exchange methods faced challenges in removing inorganic salt by-products. These impurities hindered accurate evaluation of the materials' true performance. The research team, including Kazuhiko Igarashi from Nittobo, successfully purified the PILs by completely removing these inorganic salts.

Researchers focused on poly(diallyldimethylammonium chloride) (P[DADMA][Cl]), a material with a high density of positive charges. They replaced the chloride ion (Cl⁻) with three different-sized anions: acetate (AcO⁻), thiocyanate (SCN⁻), and trifluoromethanesulfonate (TFMS⁻). They then examined how the size of the anion affected CO₂ adsorption.

Results showed that increasing the size of the counter anion significantly improved the CO₂ adsorption capacity. The material with the largest anion achieved a CO₂ adsorption capacity seven times greater than the original raw material. This indicates that precisely designing the anion size can enhance PIL performance.

The team confirmed the complete removal of inorganic salt impurities using Scanning Electron Microscopy-Energy Dispersive X-ray Spectroscopy (SEM-EDX). This ensured that their measurements accurately reflected the materials' intrinsic properties. This work provides a new approach to enhance CO₂ capture systems.

Developing efficient methods to capture and separate CO₂ from the atmosphere and industrial emissions is crucial for addressing global warming. This research contributes to the advancement of materials for this purpose. The findings were published in *Reaction Chemistry & Engineering*.