The stability of graphene oxide (GO) nanofiltration (NF) membrane in aqueous environment: Progress and challenges

Recently, advanced membranes based on a 2D material of graphene oxide (GO) for NF have drawn great attention due to their striking, dramatic separation performances which are much higher than traditional membranes. However, stability, which is a precondition for practical applications, has become the bottleneck of the GO membranes for water treatment. Fortunately, the stability of GO membranes in water has received significant attention, and many fruitful efforts have been recently devoted to solving this problem. It is therefore critical to update the broader scientific community on the important advances in this interdisciplinary field. Herein, we review the recent progress made in improving the stability of GO membranes in water. Fundamental issues, including the origin of the instability of GO membranes in water, and influences of the chemical properties of GO itself on the stability of the resultant membranes have been discussed. We also explore the diverse structural design and surface/interface engineering strategies for improving the stability of GO membranes in water, including the introduction of hydrogen bonding or intermolecular interactions via insertion of polyelectrolytes, cross-linking by molecules or ions, or blending of graphene-based materials, as well as improving the interactions between GO selective layers and substrates. The existing challenges and a forward-looking perspective are also outlined, suggesting directions to take in the design of GO and other 2D material-based membranes with outstanding stability and high separation performance for practical applications.