Since two-dimensional (2D) materials were discovered, particularly graphene and graphene oxide (GO), intensive efforts have been made on utilising these materials as building blocks to form laminar membranes via various methods. The unique 2D channels in these laminar membranes offer a new approach to control the mass transport, which might have some promising potentials in various applications, e.g. energy harvesting, seawater desalination, organic solvent separation and dehydration. The nanochannels of these membranes, formed between 2D GO nanosheets, allow species with smaller sizes than those of the channels to permeate, while blocking all other larger species. Although lamellar GO membranes have been intensively investigated, they are not stable in aqueous solutions due to the hydration of hydrophilic GO nanosheets, which results in very poor salt rejection. Our new experimental and simulation results found that either reducing GO to rGO or chemical cross-linking could improve the stability of graphene-based laminar membranes and dramatically increase the salt rejection, particularly NaCl rejection for seawater desalination. The water flux and salt rejection can be further tuned by tailoring the internal geometries of these membranes via various methods, such as creating artificial nanopores, increasing the number of intrinsic nanowrinkles, adding cation spacers and exploring other 2D materials.
Xiwang Zhang is a Professor in Department of Chemical Engineering at Monash University, Australia and the Director of Australian Research Council (ARC) Research Hub for Energy-efficient Separation. He received his PhD in Chinese Academy of Sciences in 2006. His research interests focus on membrane and advanced oxidation technologies for water treatment. He has authored and co-authored more than 100 peer-reviewed journal papers, including Advanced Materials, J. Am. Chem. Soc, Advanced functional materials, Angew. Chem. Int. Ed., Applied Catalysis B, Water Research, Chemical Communications, Environmental Science & Technology, Journal of Membrane science, etc.