Easy switching of selective vapor permeation by tuning the surface free energy of graphene oxide membranes

Abstract

Membrane-based separation for the dehydration and purification of organic chemicals, referred to as pervaporation and vapor permeation, has been widely studied as a feasible alternative to traditional distillation. Graphene oxide (GO) laminates or membranes have attracted great interest for the dehydration of chemicals as they allow selective water permeation owing to their hydrophilic nature. In this study, we effectively tuned the permeation selectivity of GO membranes by adjusting their surface free energy via simple dry treatments and explore its mechanism on the permeation of binary vapor, represented by the collaborative permeation and hindering effect. Oxygen (O₂) plasma treatment rendered the membrane surface superhydrophilic, thereby enhancing selective water permeation from water–alcohol binary vapors. The corresponding hydrophilic membrane exhibited greater water flux and separation factor than the unmodified membrane. On the other hand, XeF₂ gas treatment changed the surface characteristic of the GO membrane from hydrophilic to hydrophobic, altering its permeation selectivity from water to alcohol. These findings demonstrate that the surface modification of GO membranes via dry treatment methods is highly effective for switching the selectivity of the membrane to water or organic solvents/vapors. In water-alcohol binary vapor permeation through a GO membrane, water and alcohol molecules interact, promoting collaborative permeation explained by their solubility parameters. This interaction allows minimal alcohol permeation with water, The hindering effect cause alcohol to slow down water transport, altering the slip length of water. During water transport through GO membranes, ballistic water transport was observed when the slip length of water reached ∼100 nm.