Resembling Graphene/Polymer Aerogel Morphology for Advancing the CO₂/N₂ Selectivity of the Postcombustion CO₂ Capture Process

The separation of CO₂ from N₂ remains a highly challenging task in postcombustion CO₂ capture processes, primarily due to the relatively low CO₂ content (3-15%) compared to that of N₂ (70%). This challenge is particularly prominent for carbon-based adsorbents that exhibit relatively low selectivity. In this study, we present a successfully implemented strategy to enhance the selectivity of composite aerogels made of reduced graphene oxide (rGO) and functionalized polymer particles. Considering that the CO₂/N₂ selectivity of the aerogels is affected on the one hand by the surface chemistry (offering more sites for CO₂ capture) and fine-tuned microporosity (offering molecular sieve effect), both of these parameters were affected in situ during the synthesis process. The resulting aerogels exhibit improved CO₂ adsorption capacity and a significant reduction in N₂ adsorption at a temperature of 25 °C and 1 atm, leading to a more than 10-fold increase in selectivity compared to the reference material. This achievement represents the highest selectivity reported thus far for carbon-based adsorbents. Detailed characterization of the aerogel surfaces has revealed an increase in the quantity of surface oxygen functional groups, as well as an augmentation in the fractions of micropores (<2 nm) and small mesopores (<5 nm) as a result of the modified synthesis methodology. Additionally, it was found that the surface morphology of the aerogels has undergone important changes. The reference materials feature a surface rich in curved wrinkles with an approximate diameter of 100 nm, resulting in a selectivity range of 50-100. In contrast, the novel aerogels exhibit a higher degree of oxidation, rendering them stiffer and less elastic, resembling crumpled paper morphology. This transformation, along with the improved functionalization and augmented microporosity in the altered aerogels, has rendered the aerogels almost completely N₂-phobic, with selectivity values ranging from 470 to 621. This finding provides experimental evidence for the theoretically predicted relationship between the elasticity of graphene-based adsorbents and their CO₂/N₂ selectivity performance. It introduces a new perspective on the issue of N₂-phobicity. The outstanding performance achieved, including a CO₂ adsorption capacity of nearly 2 mmol/g and the highest selectivity of 620, positions these composites as highly promising materials in the field of carbon capture and sequestration (CCS) postcombustion technology.