CO₂ absorption over ion exchange resins: The effect of amine functional groups and microporous structures

The moisture-swing sorbent of amine-based anion exchange resins is one of the most promising materials for direct carbon capture from ambient air to alleviate excessive emissions of CO2. In this study, how the physical and chemical properties of amine-based anion exchange resins affect their carbon capture performances is studied systematically, through different kinds of resins. Contrary to previous understandings, the effect of the chemical functional groups on the overall capture performance is found to far outweigh that of the physical properties. It is found that the main property that determines the absorption capacity is the chemical one, i.e., the amine functional groups, while properties dominating the absorption kinetics are the physical ones, i.e., particle size and microporous structures. The absorption capacity of resins loaded with strong amine groups is strikingly higher than that with weak amine groups. The mechanism is explored by a combination of molecular dynamics and quantum chemical calculations. The most superior sorbent is the macro-porous strong base resin due to its strong amine groups and large inner pore sizes. The present study provides new insights into selecting suitable absorbents or preparing better ones for enhanced direct air capture of CO2.