Engineering CO₂-philic pathway via grafting poly(ethylene glycol) on graphene oxide for mixed matrix membranes with high CO₂ permeance

The introduction of two-dimensional (2D) nanofillers into thin-film (<1 μm thickness) mixed-matrix membranes (MMMs) remains challenging because of the interfacial issues that lead to Knudsen diffusion, thereby causing a loss of selectivity. Herein, we describe a surface modification technique that involves the application of an epoxy group ring opening process and free-radical polymerization to the graphene oxide (GO) surface to enable the grafting of CO₂-philic poly(ethylene glycol) (PEG) chains. The use of functional groups to achieve the PEG modification of GO increases the interlayer spacing between the 2D GO layers. Specifically, the abundant PEG domain between the layers provides an effective CO₂-philic pathway and minimizes the occurrence of polymer matrix/GO filler interfacial defects, resulting in excellent CO₂ permeance and selectivity. The MMM consisting of GO-glycidyl methacrylate grafted with poly(oxyethylene methacrylate) achieved the highest performance, with a CO₂ permeance of 3169 GPU, CO₂/N₂ selectivity of 37.4, and CO₂/CH₄ selectivity of 15.8. These results indicate the suitability of the as-prepared materials for commercial applications.