Graphitic carbon nitride nanosheets embedded in poly(vinyl alcohol) nanocomposite membranes for ethanol dehydration via pervaporation

Graphitic carbon nitride (g-C 3 N 4 ) is an innovative soft two-dimensional (2D) nanomaterial. Due to its lamellar structure, similar to graphite layers, g-C 3 N 4 has attracted significant interest as a new class of filler for the fabrication of novel polymeric nanocomposite membranes. In this study, highly water-selective hybrid membranes with excellent water/ethanol separation performance and superior water channels were fabricated by incorporating g-C 3 N 4 nanosheets into a poly(vinyl alcohol) (PVA) matrix. g-C 3 N 4 was synthesized via thermal oxidation “etching”, using melamine as a precursor. The ultrathin and nanoporous structures formed were characterized through transmission electron microscopy, Fourier transform infrared spectra, and X-ray diffraction. Due to the strong interfacial interactions among g-C 3 N 4 , succinic acid (Sa) and the PVA matrix, the hybrid nanocomposite membranes showed both high swelling resistance and mechanical stability. Furthermore, the addition of g-C 3 N 4 can significantly improve the membrane’s hydrophilicity and heat-resistance properties. Importantly, membrane permeability improved greatly because the ordered alignment and the regular pore structure of g-C 3 N 4 resulted in ordered water channels for rapid transportation of water molecules. The total flux and separation factor of this new membrane can reach about 6332   g/(m 2   h), and 30.7 for 90% wt.% ethanol, respectively. Compared with the cross-linked pure PVA membrane (2337   g/(m 2   h) and 11.2), the flux and separation factor can be improved simultaneously. Namely, the composite membrane can break the “trade-off effect” effectively. Furthermore, the nanocomposite membrane exhibited an excellent long-term operating stability. After operating for over 120   h with a 90   wt% ethanol/water system at 75   °C, the total flux and separation factor remained at their initial values. This is a step forward in the application in pervaporation separation processes of organic-inorganic hybrid membranes with superior properties incorporating 2D porous fillers (e.g., g-C 3 N 4 ).