Etching and acidifying graphene oxide membranes to increase gas permeance while retaining molecular sieving ability

Graphene oxide (GO) nanosheets stacked in parallel with subnanometer channels can exhibit an excellent size-sieving ability for membrane-based gas separation. However, gas molecules have to diffuse through the tortuous nanochannels, leading to low permeability. Herein we demonstrate two versatile approaches to modify the GO (before membrane fabrication by vacuum-filtration) to collectively increase gas permeability, etching using hydrogen peroxide to generate in-plane nanopores and acidifying using hydrochloric acid. For example, a membrane prepared at a pH of 5.0 using the 4-h-etched GO (HGO-4h) shows He permeability of 5.3 Barrer and He/CH₄ selectivity of 800, which are 5 times and 1.5 times those of the GO membranes, respectively. Decreasing the pH from 5.0 to 2.0 for HGO-4h enhances He permeability to 57 Barrer and He/CH₄ selectivity to 1,800. The HGO-4h prepared at the pH of 2.0 exhibits separation properties of H₂/CO₂, H₂/N₂, He/N₂, and He/CH₄ surpassing their corresponding upper bounds.