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Two-dimensional, graphene-based materials have attracted great attention as a new membrane building block, primarily owing to their potential to make the thinnest possible membranes and thus provide the highest permeance for effective sieving, assuming comparable porosity to conventional membranes and uniform molecular-sized pores. However, a great challenge exists to fabricate large-area, single-layered graphene or graphene oxide (GO) membranes that have negligible undesired transport pathways, such as grain boundaries, tears, and cracks. Therefore, model systems, such as a single flake or nanochannels between graphene or GO flakes, have been studied via both simulations and experiments to explore the transport mechanisms and separation potential of graphene-based membranes. This article critically reviews literature related to single- to few-layered graphene and GO membranes, from material synthesis and characteristics, fundamental membrane structures, and transport mechanisms to potential separation applications. Knowledge gaps between science and engineering in this new field and future opportunities for practical separation applications are also discussed. 

Single layer graphene oxide (SLGO) was studied as a novel coating material to drastically improve the antifouling performance of polyether sulfone (PES) hollow fiber (HF) membranes in membrane bioreactor (MBR) application. By selectively modifying the membrane surface, only a small amount of SLGO coating (6.2 mg m −2 ) was needed to achieve acceptable membrane performance. The UV treatment of the SLGO coating further assisted in improving the antifouling properties of the as-prepared PES HF membranes. By comparing the transmembrane pressure of pristine PES HF and PES_GO 6.20_ UV X (X = 0–1.5 h) membranes in a MBR for wastewater treatment at a fixed water flux, the PES_GO 6.20_ UV 1.0 membrane coated with 1 h UV-treated SLGO was demonstrated to substantially relieve the bio-fouling problem. To understand the influence of SLGO modification on membrane performance, FESEM, ATR-FTIR, and AFM analyses were conducted to characterize the as-prepared membranes, and the SLGO deposition mechanism was also proposed in this study. 

We demonstrated for the first time that inkjet printing can be a low-cost, easy, fast, and scalable method for depositing ultrathin (7.5–60 nm) uniform graphene oxide (GO) nanofiltration membranes on polymeric supports for highly effective water purification. A large area (15 × 15 cm 2 ) GO nanofiltration membrane was printed successfully on a modified polyacrylonitrile (M-PAN) support. Water permeance and rejection of small organic molecules (<1 nm, charged and uncharged) of printed GO membranes can be adjusted by controlling the GO “ink” concentration and/or printing time. Compared with commercial polymeric nanofiltration membranes, printed GO membranes, after optimization, showed approximately one order of magnitude higher water permeance and much higher rejection (>95%) of small organic molecules. Printed GO membranes also showed excellent performance in removing pharmaceutical contaminants, with ∼95% rejection and <10% water permeance decline over extended-period permeation testing. We believe that inkjet printing could be an effective method for preparing ultrathin GO membranes for effective water nanofiltration purification.