▎ 摘　　要

The impact of inorganic ions present in aqueous environment on the structural stability of graphene oxide (GO) membrane has raised increasing attention. This study investigated how the competition of co-existing cations with Na+ affected GO membrane structure and separation performance. Results showed that the presence of Na+ alone (NaCl solution) led to significantly increased membrane flux (400% of the ultrapure water flux) and decreased rejection (from 17.2% to 3.5%). However, the flux and rejection of GO membrane were more stable when the solutions contained co-existing K+ or Ca2+. The separation performance variation was attributed to the structural variation of the GO membrane. Characterized by X-ray diffraction, the orderly laminar structure of GO membrane completely disappeared in NaCl solution but was well maintained in NaCl/KCl or NaCl/CaCl2 solution. The concentration required for stabilization was 1 mM for co-existing Ca2+, which was lower than that of K+ (5 mM). The ability of co-existing K+ or Ca2+ to eliminate the negative effect of Na+ was ascribed to their priority to enter nano-capillary channels via stronger attractive interactions with GO nanosheets. Owing to the small size of K+ or bridging effect of Ca2+ with GO nanosheets, interlayer interactions within GO membrane were enhanced, and thus, its structure was stabilized.