Abstract
Graphene oxide (GO) membranes have demonstrated great potential in gas separation and liquid filtration. For upscale applications, GO membranes in a hollow fibre geometry are of particular interest due to the high-efficiency and easy-assembly features at module level. However, GO membranes were found unstable in dry state on ceramic hollow fibre substrates, mainly due to the drying-related shrinkage, which has limited the applications and post-treatments of GO membranes. We demonstrate here that GO hollow fibre membranes can be stabilised by using a porous poly(methyl methacrylate) (PMMA) sacrificial layer, which creates a space between the hollow fibre substrate and the GO membrane thus allowing stress-free shrinkage. Defect-free GO hollow fibre membrane was successfully determined and the membrane was stable in a long term (1200 hours) gas-tight stability test. Post-treatment of the GO membranes with UV light was also successfully accomplished in air, which induced the creation of controlled microstructural defects in the membrane and increased the roughness factor of the membrane surface. The permeability of the UV-treated GO membranes was greatly enhanced from 0.07 to 2.8 L m−2 h−1 bar−1 for water, and 0.14 to 7.5 L m−2 h−1 bar−1 for acetone, with an unchanged low molecular weight cut off (~250 Da).
Highlights
Graphene oxide (GO), a functional derivative of graphene, has been considered as a promising membrane material and GO membranes have shown to be effective separation barriers in environmental and chemical engineering application[1,2,3,4,5,6,7,8]
The idea of sacrificial layer aided GO membrane fabrication was implemented with porous yttrium stabilised zirconia (YSZ) hollow fibre substrates (Fig. 2(a))
The YSZ hollow fibre support has an outer diameter of 1 mm, and a high pure water flux of 1200 L m−2 h−1 bar−1, which ensures a negligible permeation resistance in the substrate compared to the GO membrane layer
Summary
Graphene oxide (GO), a functional derivative of graphene, has been considered as a promising membrane material and GO membranes have shown to be effective separation barriers in environmental and chemical engineering application[1,2,3,4,5,6,7,8]. Our recent research revealed that supported GO membranes are unstable in dry state, at least on ceramic hollow fibre substrates[20]. This is due to the shrinkage generated during the drying course, which produces enormous tensile stress in the GO membrane and leads to defects. To tackle the instability problem, GO hollow fibre membranes can be reserved in water after initial drying to avoid further shrinkage, so that fatal defects can be prevented[20] Such a strategy was shown to work well, but the resultant membranes could only be used for limited wet separation processes such as nanofiltration and pervaporation. The UV post-treatment has greatly enhanced the permeability of the GO membranes, enabling their successful usage for nanofiltration purposes
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