Researchers in Japan have developed a new carbon capture material that absorbs significantly more carbon dioxide simply by changing the size of its counter anions.

The joint research team from Nitto Boseki Co., Ltd. and Tohoku University found that carefully engineered polyionic liquids, or PILs, can dramatically improve CO2 adsorption performance after purification and anion exchange.

The researchers reported that the material achieved up to seven times higher CO2 adsorption capacity compared to the original raw material. The findings could help improve future carbon capture systems and gas separation membranes.

The work focuses on diallyldimethylammonium-based PILs, materials known for combining the CO2 affinity of ionic liquids with the stability and processability of polymers.

Bigger anions trap CO2

Capturing carbon dioxide from industrial emissions remains one of the major technological challenges in reducing greenhouse gas emissions. PILs have emerged as promising candidates because they can selectively interact with CO2 while remaining stable in solid form.

However, researchers said conventional synthesis methods leave behind inorganic salt impurities that interfere with performance evaluation and material efficiency.

To address this problem, the team developed a purification process that completely removed residual inorganic salts from the PILs. Using SEM-EDX analysis, the researchers confirmed the removal of chlorine and other reaction byproducts from the final materials.

The researchers then examined how different counter anions affect CO2 adsorption behavior. They replaced chloride ions with three different anions of increasing size: acetate, thiocyanate, and trifluoromethanesulfonate.

The experiments showed that larger anions consistently improved the material’s ability to adsorb carbon dioxide.

According to the study, the PIL using the largest anion delivered the highest CO2 uptake, reaching adsorption levels seven times greater than the untreated starting material.

Purity boosts performance

The team focused specifically on poly(diallyldimethylammonium chloride), also known as P[DADMA][Cl], because of its high density of positive charges.

Researchers said residual metal ions from inorganic salts formed during synthesis had not been fully examined in earlier studies. Those impurities may have masked the true adsorption capabilities of the materials.

By eliminating those contaminants, the researchers were able to observe a much clearer relationship between anion size and CO2 adsorption performance.

The study also establishes a possible design strategy for future carbon capture materials. Instead of relying only on new polymer chemistries, engineers may be able to improve performance by precisely tuning anion size and purity levels.

Beyond carbon capture devices, the findings could also support the development of advanced gas separation membranes for industrial use.

The researchers believe the approach may help improve technologies aimed at capturing atmospheric carbon dioxide as well as emissions from factories and power plants.

The study was published in Reaction Chemistry & Engineering.