Tunable interlayer spacing of composite graphene oxide-framework membrane for acetic acid dehydration

Minute amount of poly(vinyl alcohol) (PVA) was used to cross-link graphene oxide (GO) nanosheets to prepare composite graphene oxide-framework (GOF) membranes with a nacre-like structure. The PVA provided additional increase in viscosity of GO suspension which made the solution casting of a large-area composite GOF membrane possible. The membranes were applied to separate an acetic acid-water mixture through pervaporation. The ATR-FTIR and XPS analyses confirmed the covalent bonding between GO and PVA as ether bonds were formed. This influenced the changes in water contact angle where it increased from 40.8° (pristine GO) to 62.7° (GO-PVA8wt%). X-ray diffraction showed that d-spacing of GOF was higher than GO due to the intercalation of PVA. The d-spacing of GO layer from dry to wet state has a difference of 2.59 Å but addition of PVA lowered the difference to 0.38 Å. The newly formed covalent bonds between GO and PVA might suppressed the stretching of d-spacing. It shows that the swelling was prevented and the interlayer spacing can be tuned. The composite GO-PVA8wt% membrane has a short d-spacing and provided an outstanding pervaporation performance at 80 °C with a permeation flux of 463.9 g m−2 h−1 and water concentration in permeate of 97.7%.

The PVA acts as a cross-linker between the GO nanosheets and form a nacre-like structure which is highly-ordered. The GOF layer selectively chooses the smaller water molecules to pass through the nanosheets while preventing the larger acetic acid molecules.157