In this work, we prepared 90 nm thick TiCT-graphene oxide (GO) membranes laminated on a porous support by mixing GO with TiCT. This process was chosen to prevent the penetration of target molecules through inter-edge defects or voids with poor packing. The lattice period of the prepared membrane was 14.28 Å, as being swelled with water, resulting in an effective interlayer spacing of around 5 Å, which corresponds to two layers of water molecules. The composite membranes effectively rejected dye molecules with hydrated radii above 5 Å, as well as positively charged dye molecules, during pressure-driven filtration at 5 bar. Rejection rates were 68% for methyl red, 99.5% for methylene blue, 93.5% for rose Bengal, and 100% for brilliant blue (hydrated radii of 4.87, 5.04, 5.88, and 7.98 Å, respectively). Additionally, the rejections of composite membrane were compared with GO membrane and TiCT membrane.

Laminated graphene oxide (GO) has promising use as a membrane because of its high permeance, chemical and mechanical stability, as well as the molecular sieving effect of its interlayers. However, the hydrophilic surface of GO, which is highly decorated with oxygen groups, easily induces delamination of stacked GO films in aqueous media, thereby limiting the practical application. To stabilize GO films in aqueous media, we functionalized a polymer support with branched polyethylene-imine (BPEI). BPEI adsorbed intercalated into the stacked GO sheets via diffusion during filtration. The GO/BPEI membrane obtained exhibits high stability during sonication (>1 h duration, 40 kHz frequency) in water within a broad pH range (2-12). In contrast, the GO film spontaneously delaminated upon sonication. Furthermore, BPEI treatment did not affect the filtration performance of the GO film, as evidenced by the high rejection rates (>90%) for the dye molecules methylene blue, rose bengal, and brilliant blue and by their permeation rates of ca. 124, 34.8, 12.2, and 5.1%, respectively, relative to those of a typical GO membrane.

Herein, a new carbon-based graphitic membrane composed of laminated graphitic nanoribbons with a nanometer-scale width and micrometer-scale length, the graphitic nanoribbon membrane, is reported. Compared to the existing graphitic membranes, such as those composed of graphene oxide and carbon nanotubes, the developed membrane exhibits several unique characteristics in pressure-driven systems. First, the short diffusion length through its interlayer and the free volume of its stacked nanoribbons result in high solvent flux regardless of solvent polarity (water: 25-250 L m h bar; toluene: ∼975 L m h bar; hexane: ∼240 L m h bar). The flux value for water is one order of magnitude higher, while that for nonpolar organic solvents is two to three orders of magnitude greater than the corresponding flux values obtained through commercially available nanofiltration membranes. Second, the membrane exhibits good separation performance, particularly with organic dye molecules (∼100%) and trivalent ions (∼60%), maintaining high solvent flux during extended filtration. Finally, the membrane exhibits high stability in various fluids, e.g., 1 M HCl solution, 1 M NaOH solution, toluene, ethanol, and water, as well as under hydraulic pressures of up to 50 bar. Electron microscopy observation and simulation results suggest that such distinctive features of the membrane are related to the entangled thin multilayers of the graphitic nanoribbons, which possibly originate from the high aspect ratio and narrow width of the nanoribbons.