Micron-Thick Graphene Oxide Films for the Selective Permeation of CO₂

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In this study, we characterize the gas transport properties of micrometer-thick graphene oxide (GO) films to elucidate how to control the barrier and membrane properties using GO sheets as a model 2D material. GO films were prepared by the vacuum filtration method using different flake sizes ranging from 1 μm to 300 nm. The prepared GO films show distinct film properties in terms of d-spacing and crystallite size which affect the tortuosity and channel width. Although there were only slight differences in the aforementioned features, the gas transport characteristics dramatically changed, particularly the enhanced CO₂ permeability of approximately 60 times. Furthermore, we found critical channel width changes in d-spacing in the range of 0.91–0.85 nm and crystallite size in the range of 23.5–20.5 nm. Consequently, this resulted in a shorter diffusion pathway ratio between vertical and horizontal transportation of gas molecules which is a transition region for switching from a barrier character without notable gas selectivity to a permeation property with reasonable gas selectivity.