Graphene oxide nanosheet: an emerging star material for novel separation membranes

Advanced membranes that enable ultrafast permeance are very important for processes such as water purification and desalination. Ideally, an efficient ultrafast membrane should be as thin as possible to maximize the permeance, be robust enough to withstand the applied pressure and have a narrow distribution of pore size for excellent selectivity. Graphene oxide nanosheets offer an encouraging opportunity to assemble a brand new class of ultrathin, high-flux and energy-efficient sieving membranes because of their unique two-dimensional and mono-atom thick structure, outstanding mechanical strength and good flexibility as well as their facile and large-scale production in solution. The current state-of-the-art in graphene oxide membranes will be reviewed based on their exceptional separation performance (gas, ions and small molecules). We will focus on the structure of nanochannels within the graphene oxide membranes, the permeance and rejection rate, and the interactions between graphene oxide sheets. The separation performance of graphene oxide membranes can be easily influenced by the state of oxygen-containing groups on the graphene oxide sheets, which provides much more straightforward strategies to tune the pore size of graphene oxide nanochannels when compared to other filtration membranes. We will illustrate in the review theoretical calculations to elucidate the potential of precisely controlling the ionic and small molecular sieving and water transport behaviour through graphene oxide nanochannels. This review will serve as a valuable platform to fully understand how the ions, small molecules and water are transported through the laminar graphene oxide membrane as well as the latest progress in graphene oxide separation membranes.