Beyond CO2 uptake: structure-property trade-offs in sponge-like porous sorbents for post-combustion CO2 capture

Sponge-like porous materials have emerged as promising candidates for carbon dioxide (CO2) capture owing to their high surface area, tuneable pore architecture, and adjustable surface chemistry. Among them, carbon-based adsorbents, amine-functionalized solids, and metal–organic frameworks have attracted considerable attention due to their potential for reversible and energy-efficient CO2 capture. Their relevance is particularly evident in post-combustion applications, where adsorption systems must operate under low CO2 partial pressures, humid gas streams, and repeated adsorption–desorption cycles. Despite the extensive literature available, adsorption performance is still frequently assessed through isolated metrics, while a critical discussion of the intrinsic trade-offs governing different sorbent families remains limited. This review examines the current state of the art of sponge-like porous sorbents for post-combustion CO2 capture, focusing on the structure–property relationships governing adsorption within confined porous environments. Particular attention is devoted to the interplay between pore accessibility, adsorption energetics, diffusion kinetics, regenerability, moisture tolerance, and structural stability. The main classes of porous sorbents are comparatively analysed in terms of adsorption mechanisms, thermodynamic behaviour, transport phenomena, and operational constraints, highlighting how improvements in one property frequently introduce penalties in another. Beyond conventional equilibrium uptake values, the discussion emphasizes integrated performance descriptors, including working capacity, cyclic stability, volumetric productivity, adsorption kinetics, and humidity tolerance. A comparative framework is proposed to rationalize the balance between competing material properties under realistic operating conditions. Finally, current limitations and future research directions are discussed, highlighting the need for more standardized and application-oriented criteria for evaluating next-generation porous adsorbents for practical CO2 capture processes.