Effect of Oxidized-Group-Supported Lamellar Distance on Stability of Graphene-Based Membranes in Aqueous Solutions

Graphene oxide (GO) membranes with diverse lamellar distances can achieve sieving of molecules of different sizes in aqueous solutions. Without the extra assistance of cross-linking, the increase of lamellar distance supported by self-contained oxidized groups could diminish the internal pi-pi attraction force of GO membranes, resulting in the instability of GO membranes. However, the critical value of oxidized-group-supported lamellar distance of unstable GO membranes in aqueous solutions, which is crucial in applications for precise sieving of molecules, still remains unknown. In this study, the effect of oxidized-group-supported lamellar distance on the stability of graphene-based membranes in aqueous solutions is systematically investigated. By controlling the content of oxidized groups via changing reducing condition, different lamellar distances of graphene-based membranes are obtained. With changing the lamellar distance in aqueous solutions under different pH conditions, the graphene-based membranes show distinct stability. There exists a critical lamellar distance in the aqueous solution to ensure the stability of graphene-based membranes. If the lamellar distance is less than the critical value, the membranes remain physically stable for a long time, and still provide a favorable water permeation performance. The critical lamellar distances vary in aqueous solutions depending on pH values. The results provide a valuable guidance for the applications of graphene-based membranes in aqueous solutions.