1 Membranes prepared from layers of graphene oxide (GO) offer substantial 2 advantages over conventional materials for water treatment (e.g. greater flux), but the 3 stability of GO membranes in water has not been achieved until now. In this study the 4 behavior of GO membranes prepared with different quantities and species of cations has 5 been investigated to establish the feasibility of their application in water treatment. A 6 range of cation-modified GO membranes were prepared and exposed

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... o aqueous 7 solutions containing specific chemical constituents. In pure water, unmodified and 8 Na-modified GO membranes were highly unstable, while GO membranes modified with 9 multivalent cations were stable provided there were sufficient quantities of cations 10 present; their relative capability to achieve GO stability was as follows: Al 3+ > Ca 2+ > 11 Mg 2+ > Na + . It is believed that the mechanism of cross-linking, and membrane stability, is 12 via metal-carboxylate chelates and cation-graphite surface interactions (cation-π 13 interaction), and that the latter appears to increase with increasing cation valency. The 14 instability of cation (Ca or Al)-modified GO membranes by NaCl solutions during 15 permeation occurred as Na + exchanged with the incorporated multivalent cations, but a 16 high content of Al 3+ in the GO membrane impeded Al 3+ /Na + exchange and thus retained 17 membrane stability. In solutions containing biopolymers representative of surface waters 18 or seawater (protein and polysaccharide solutions), Ca-GO membranes (even with high 19 Ca 2+ content) were not stable, while Al-GO membranes were stable if the Al 3+ content 20 was sufficiently high; Al-formed membranes also had a greater flux than Ca-GO 21 membranes. 22 23 7 biopolymer treatment 24 25 42 although ceramic membranes enjoy a distinct advantage in strength, thermal stability, 43 solvent resistance, and longer lifetime, they are more complex and expensive to fabricate, 44 and more brittle (Karan et al., 2012; Han et al., 2013). Therefore, ideal filtration 45 membranes should be made by a simple process, and possess the advantages of both 46 8 kinds of membranes (Han et al., 2013).