Origin of CO₂-philic Sorption by Graphene Oxide Layered Nanosheets and Their Derivatives

Graphene oxide (GO) is a promising 2D material for adsorbents and membranes, in particular, for the CO₂ separation process. However, CO₂ diffusion and sorption in GO and its layered structures are still not well understood because of its heterogeneous structure. Here we report CO₂ sorption in GO and its derivatives (e.g., reduced GO (rGO)) in powders and films. These CO₂ sorption behaviors reveal that GO is highly CO₂-philic via complex CO₂-functional-group-surface interactions, as compared with graphite and rGOs. Even in highly interlocked, lamellar GO films, CO₂ molecules above a certain threshold pressure can diffuse into GO interlayers, causing GO films to swell and leading to dramatic increases in CO₂ sorption. Intercalated water in GO interlayers can be removed by preferential CO₂ sorption without any changes in the GO chemical structure. This finding helps to explain the origin of CO₂ affinity with GO and has implications for preparing anhydrous GO assemblies for various applications.