Operando study of water vapor transport through ultra-thin graphene oxide membranes

The paper reports operando study of ultra-thin (50 nm) graphene oxide membranes by grazing incidence x-ray scattering in air dehumidification experiments. Absorption of water vapors in GO layers follows a modified Kelvin equation revealing condensation in an elastic slit, while desorption of water is limited by a few outer GO layers providing bottleneck restrictions to water transport and resulting in classical H2-type isotherms. GO interlayer distances (d) vary in range from 7.2 angstrom to 11.5 A depending on partial water pressures in a feed stream and permeate. The permeance of water vapor through GO decreases steadily with decreasing interlayer distance between GO sheets from similar to 80 000 l/(m(2) . atm . h) to similar to 30 000 l/(m(2) . atm . h) falling down to negligible values below d approximate to 9.2 angstrom. Water transport in GO is described by Poiseuille equation and hopping diffusion depending on the number of water layers between GO planes, and was modelled with semi-empirical methods. It is shown the performance of thin GO membranes is strongly governed by the interstitial water quantity as dictated by water partial pressure.