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

Graphitic carbon nitride (g-C3N4) is an innovative soft two-dimensional (2D) nanomaterial. Due to its lamellar structure, similar to graphite layers, g-C3N4 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-C3N4 nanosheets into a poly(vinyl alcohol) (PVA) matrix. g-C3N4 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-C3N4, succinic acid (Sa) and the PVA matrix, the hybrid nanocomposite membranes showed both high swelling resistance and mechanical stability. Furthermore, the addition of g-C3N4 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-C3N4 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 degrees 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-C3N4). (C) 2017 Elsevier B.V. All rights reserved.