Pervaporation desalination with graphene oxide membranes: The influence of cation type and loading

The paper reports pervaporation desalination performance of graphene oxide (GO) membranes for salts solutions. Asymmetrical membranes consisting of GO layer (~5 μm) on polyethersulfone supports prepared via pressure-assisted filtration were utilized in the experiments. The initial performance of membranes attaining 27 kg·m−2 h−1 for pure water feed at 80 °C is substantially suppressed with pervaporation from salts solutions down to ~4.5 kg·m−2 h−1 at 0.6 M NaCl concentration. Salts rejection exceeds 99.9 %. According to in-situ and in-operando X-ray scattering study the interlayer distance of GO seriously expands upon ions absorption (up to 5 wt%), varying from 1.45 to 2.67 nm for different cations. The decrease of water permeance, despite of increasing width of the nanochannels, is revealed to originate from increasing activation energy of water molecules transport and diminution of the free volume available for diffusion by >50–80 %. Thus, dynamically changing interlayer distance and loading of graphene oxide with ions are considered the key factors governing the membrane performance. The intercalation of carbon-based spacers (nanoribbons and fullerenols) into interlayer space can be utilized to improve membrane performance. This increases the permeate flux by 70 % compared to pristine GO membranes.