CO₂ capture adsorbents functionalized by amine – bearing polymers: A review

Efforts to capture CO₂ from anthropogenic sources as well as from the air are being continuously intensified as to battle the greenhouse gas effects and climate change. Capture by liquid solvent absorption, mainly involving amines, is the common industrial practice, yet capture relying on solid adsorbents is increasingly gaining interest due to its potential for less energy-demanding and more efficient operation. Despite the large variety of porous adsorbents being explored, such as zeolites, carbons, mesoporous silicas, graphene and related structures, polymers, and metal-organic frameworks, it still remains challenging to find a proper material to cover all the critical specifications, i.e. with respect to CO₂ capacity, selectivity, chemical and thermal stability, fast kinetics, cyclability, low energy consumption, low manufacturing cost, and mechanical robustness. To this end, combining highly CO₂-phylic amines with the most robust of the developed solid porous materials through functionalization of the latter is a highly promising approach. Consequently, particular emphasis is given to increase the number of amine functional groups per unit of support area, enhance CO₂-phylicity of the amines, and provide suitable diffusion pathways to enhance CO₂ capacity. Towards achieving this goal, use of amine-bearing polymer functionalities is being highly investigated. This work critically and comparably reviews current progress on polymeric amine - functionalized solid adsorbents and their performance in CO₂ capture. It examines works based on various polymers, including polyethylenimine, polypropylenimine, polyallylamine, polyaniline, amino dendrimers, and hyperbranched polyamines. Based on the extracted comparisons, optimal systems are proposed and envisioned and future trends and directions are stated.