Surface oxygen functionality controls selective transport of metal ions through graphene oxide membranes

Scientists from the U.S. Department of Energy’s Pacific Northwest National Laboratory have discovered that reducing graphene oxide membranes with ultraviolet light alters the oxygen functional groups on the graphene oxide surface. This modification results in a novel separation mechanism that is selective for charge rather than size. Exposure to ultraviolet light selectively removed hydroxyl groups from the graphene oxide planes, leading to enhanced interactions of metal cations with functional groups located at the edges of the graphene oxide. This, in turn, resulted in a lower ratio of free mobile lithium cations in solution compared to calcium cations.