Graphene oxide (GO) membranes are formed from the lamination of individual GO sheets into a “brick-and-mortar” structure. This lamination creates an abundance of nanochannels within the GO membrane structure that are permeable to certain chemical species. GO membranes are thus promising materials for water purification technologies. To be useful water filters, it is imperative that the GO membrane is both stable in water and that the permeation can be selected for specific chemical species. One common strategy to both enhance the water stability and permeation selectivity of GO membranes is to incorporate metal cations into the membrane structure. These cation-modified GO membranes are often formed using vacuum-assisted filtration, which can limit the cation-directed stacking of the sheets in the membrane. Here, we describe the formation of metal cation-modification of GO membranes by simply dissolving a cation-containing species in a commercially available acidic GO sheet solution followed by a slow self-assembly drying process. Properties of both the cation-GO sheet solutions (pH values and surface tensions) and the as-formed membranes (morphologies, contact angles, d-spacing values, and vibrational spectra) were characterized to determine the extent of inter-layer vs intra-layer crosslinking between the cations and the GO sheets. Our results demonstrate that trivalent cations participate in more extensive intra-layer crosslinking interactions than divalent cations, which results in membranes with greater stabilities in water. These results have implications in tuning both the stability and permeation of the GO membrane using a straight-forward and cost-effective method.

Metal cation modification of graphene oxide membranes: Effects on membrane assembly, structure, and stability

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