CO 2 sorption kinetics of poly(ethylenimine) (PEI)-impregnated MIL-101, γ-alumina, and UVM-7 silica were investigated by the zero-length column technique for the purpose of understanding the effect of amine content, adsorbent porosity, and adsorption temperature on CO 2 sorption rates. Each of the adsorbents was impregnated with three different amine contents (20, 35, and 50 wt%) and the effective diffusion time constants were determined at 25 C. For each respective adsorbent, it was found that increasing the amine content results in diminished diffusion rates. Additionally, it was found that the pore size of the support has a profound effect on diffusional kinetics, where microporous MIL-101 yielded substantially slow desorption rates upon amine-functionalization compared to mesoporous γ-alumina. PEIimpregnated UVM-7 silica was further investigated at 50 and 75 C in order to provide insight into the effect of temperature on sorption kinetics. The results indicated that PEI-impregnated UVM-7 exhibited faster sorption kinetics at higher temperatures. Upon desorption, PEI-UVM-7 silica exhibited two distinct regions of masstransfer control that occur at different sorption times. This is best explained by first the occurrence of surface diffusion followed by diffusion out of the bulky PEI polymer chains. The findings of this study provide novel kinetic characterizations on promising amino-adsorbents for carbon capture applications. K E Y W O R D S γ-alumina, CO 2 capture, diffusion time constant, MIL-101, UVM-7 silica, ZLC technique 1 | INTRODUCTION The rapid rise of anthropogenic CO 2 emissions resulting from fossil fuel combustion has been widely identified as the primary cause to the increase in global temperatures, due to the deleterious effects of this greenhouse gas. 1 Hence, development of cost-effective carbon capture processes is essential for mitigation of CO 2 emissions. 1-4 Aqueous monoethanol amine absorption is regarded as the benchmark technology for post-combustion CO 2 capture, but suffers from high-energy penalties upon solvent regeneration. 3 Alternatively, the direct removal of CO 2 from ambient air has arisen as an attractive option in recent years that could be implemented in residential areas to mitigate emissions resulting from transportation sources. 4,5 Therefore, solid-state adsorbents have been intensively studied as a viable, cost-effective alternative to absorption-based amine scrubbing for practical carbon capture applications. Solid adsorbents, traditionally including zeolites, carbon molecular sieves, activated carbons, activated alumina, and metal-organic frameworks (MOFs), are physical adsorbents and have been extensively studied due to their high efficiency, low regeneration requirements, and long-term stability. 6 However, these adsorbents suffer from inferior capture capacities compared to aqueous amine-scrubbing, as well as reduced working capacities in humidified conditions. 7 Therefore, recent research has focused on the incorporation of amine moieties
