Cross-Linking with Diamine Monomers To Prepare Composite Graphene Oxide-Framework Membranes with Varying d-Spacing

Abstract

Three diamine monomers (ethylenediamine, butylenediamine, and p -phenylenediamine) were selected for cross-linking graphene oxide (GO) to prepare composite graphene oxide-framework (GOF) membranes through filtration using a pressure-assisted self-assembly technique. The membranes were applied to separate an ethanol–water mixture by pervaporation. Unmodified GO comprised only hydrogen bonds and π–π interactions, but after cross-linking it with a diamine, attenuated total reflectance–Fourier transform infrared and X-ray photoelectron spectroscopy demonstrated that the diamine was chemically bonded both to GO and the membrane support. Moreover, GO hydrophilicity was substantially altered; water contact angle increased from 24.4° to 80.6° (from cross-linking with an aliphatic structure of diamine to cross-linking with an aromatic structure). Results of X-ray diffraction showed that d -spacing in GOF layers varied from 10.4 to 8.7 Å. For GOFs presoaked in 90 wt % ethanol–water, covalent bonds between the layer and diamine could effectively suppress stretching of d -spacing. Cross-linking with ethylenediamine produced a composite membrane that exhibited a short interlayer d -spacing and delivered an excellent pervaporation performance at 80 °C: permeation flux = 2297 g/(m 2 h); water concentration in permeate = 99.8 wt %. The membrane showed stability during a long-term operation at 30 °C for 120 h.