Pressure-assisted self-assembly technique for fabricating composite membranes consisting of highly ordered selective laminate layers of amphiphilic graphene oxide

We prepare highly ordered flexible layers of graphene oxide (GO) on modified polyacrylonitrile substrates by the pressure-assisted self-assembly technique. This composite membrane shows excellent performance during the pervaporation separation of a 70 wt.% isopropyl alcohol (IPA)/water mixture: 99.5 wt% water in permeate and 2047 g m−2 h−1 permeation flux. Despite the specific GO deposition increase from 4.3 to 43.3 × 10−5 g cm−2 (ninefold layer thickness growth), its effect on the permeation flux is not significant, as manifested by only a little decrease in the flux. At 70 °C feed temperature, the permeate water concentration remains 99.5 wt% and the permeation flux reaches 4137 g m−2 h−1. The high selectivity may be due to the dense GO film consisting of highly ordered and packed laminates, allowing water but inhibiting IPA molecules to pass through. GO is demonstrated to be amphiphilic: water molecules adsorb first at the hydrophilic edge (hydroxides) and then rapidly diffuse through the hydrophobic core (mainly carbon), forming a water passage channel that promotes high permeation flux. When water molecules permeate through the GO layers, they accumulate and form a monolayer structure that pushes the successive layers away from each other, leading to widening of the d-spacing.