Flick of a switch alters permeability of graphene oxide

A 1μm-thin graphene oxide membrane that can be switched from being water-permeable to waterproof has been developed by a team of researchers from the UK, Belgium and Iran.

Researchers had previously made membranes whose permeability changes with pH or temperature. However, a material with an electric switching mechanism is easier to control and could simplify water purification or molecular sieving, argues research leader Rahul Nair from the University of Manchester, UK.

Made by partially breaking down graphene oxide so that it contains conducting carbon filaments, the sheets are ultra permeable, but block water when 1.8 volts are applied. The switching is reversible over the ten on-off cycles Nair’s team tested. Even being switched off for more than a week didn’t seem to decrease the material’s performance.

Infrared spectroscopy and x-ray diffraction showed that ionised water is what blocks the electrified membrane. The hydronium and hydroxyl ions form large hydrated clusters that impede transport through the material.

Eventually, smart membranes could be used beyond filtration, for example in artificial biological systems or for tissue engineering.