Amine-modified kaolinite-derived activated alumina as an adsorbent for CO₂ capture: A review

The growing demand for low-energy, stable, and regenerable solid sorbents for post-combustion CO₂ capture has renewed scientific interest in alumina-based materials derived from kaolinite, especially when modified with amine functional groups. This review synthesizes emerging advances in preparing activated alumina supports from kaolinite and critically examines how amine grafting, impregnation, and hybrid surface engineering enhance CO₂ chemisorption under industrially relevant conditions. Kaolinite-to-alumina conversion provides a thermally robust, abundant, and low-cost substrate with high surface hydroxyl density, offering ideal anchoring sites for primary and polyamine modifiers. Recent studies show that amine incorporation fundamentally alters the adsorption mechanism from physisorption to cooperative chemisorption through carbamate and bicarbonate formation, resulting in markedly higher capture capacities at low CO₂ partial pressures. The review highlights how variations in calcination temperature, acid activation, pore tailoring, and the molecular architecture of the amine phase influence sorbent performance, diffusion pathways, and cyclic stability. Particular emphasis is placed on overcoming persistent challenges, including amine leaching, pore blockage, oxidative degradation, and moisture-induced deactivation, through strategies such as hierarchical pore creation, nanoscale amine dispersion, and hybridization with carbonaceous or metal-oxide additives. The article further evaluates the regeneration energetics and long-term durability of these sorbents and their compatibility with flue gas impurities such as SO₂ and NOₓ. Overall, the review positions amine-modified activated alumina from kaolinite as a technically promising and economically viable pathway for next-generation carbon capture systems, while identifying key research gaps in stability enhancement, scale-up, and structure-function optimization required to accelerate industrial deployment.