Graphene, a two dimensional single atomic carbon layer, is an attractive material for thin film and membrane applications. Graphene oxide (GO) synthesized from chemical exfoliation is a commonly used precursor for graphene based materials. GO membranes made by assembling small GO flakes have demonstrated great potential in gas separation and liquid filtration. For upscale applications, GO membranes in hollow fibre geometry are of particular interest due to the high surface area per volume and easy assembly features at module level.
In our research group, inorganic hollow fibres have been developed for various membrane processes. Among all types of hollow fibre substrates, ceramic hollow fibre is an excellent candidate for GO membranes due to its low mass transfer resistance, robust mechanical property and inert chemical nature, which enable it to work under extreme conditions. However, our recent study revealed that GO membranes on ceramic hollow fibre are unstable in dry state, mainly due to drying-related shrinkage . A simple way to tackle the stability problem is to reserve GO hollow fibre membranes in water after initial drying to avoid further shrinkage and the formation of fatal defects. Though such a strategy worked well to preserve the microstructure of GO membranes, it limits the applications of GO membranes to wet processes. Modifications of the membranes at dry state will also be difficult. In another approach, GO hollow fibre membranes were stabilized by using a porous poly(methyl methacrylate) (PMMA) sacrificial layer, which created a space between the hollow fibre substrate and the GO membrane that allows stress-free shrinkage. Defect free GO hollow fibre membrane was successfully determined and the membrane was stable in a long term (1200 hours) gastight stability test.
Post treatment of the stabilized GO membranes was also successfully carried out using UV radiation. The UV treatment changed the surface of GO membranes to superhydrophilic, and induced mild reduction that could have led to some controlled defect formations. All these modifications have enhanced the performance of GO hollow fibre membranes in both aqueous and solvent nanofiltration, while still maintaining the molecular sieve property of GO membranes. The pure water and acetone flux increased from 0.05 to 2.8 LMH, and from 0.14 to 7.5 LMH, respectively, with a molecular weight cut-off lower than 250 Da.
 Aba, N.F.D., et al., Graphene oxide membranes on ceramic hollow fibers – Microstructural stability and nanofiltration performance. Journal of Membrane Science, 2015. 484(0): p. 87-94