Soft confinement of water in graphene-oxide membranes

The spatial confinement of water in graphene-oxide membranes has been studied at room temperature using deep inelastic neutron scattering. This technique enabled the non-invasive measurement of water levels in hydrated and dried specimens, as well as of proton mean kinetic energies. For the first time, the latter observables are provided for the special case of graphene-oxide membranes. Absolute values of the mean kinetic energy provide direct insight into the local chemical environment of the proton under spatial confinement. In conjunction with parallel X-ray diffraction, atomic force microscopy, and thermal-gravimetric analysis measurements, our experimental results show that the characteristic, quasi-twodimensional confinement of water between graphene-oxide sheets results in a binding environment remarkably similar to that in the bulk. We surmise that this behaviour arises from a small fraction of hydroxyl groups relative to water molecules in graphene-oxide membranes, as well as the predominance of non-specific and weak interactions between water and the underlying nanostructured substrate.