UV-Enhanced Sacrificial Layer Stabilised Graphene Oxide Hollow Fibre Membranes for Nanofiltration

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).

Dynamic microstructure of graphene oxide membranes and the permeation flux

“…However, it is still unclear to what extent the microstructure will affect the permeation flux, and this has prevented us from understanding the transport in GO laminar structures. Chong et al showed that a pristine, well-laminated GO membrane could be turned into a more disordered structure by UV irradiation, and the water permeation was improved from 0.074 to 2.75 LMH bar −1 [23]. The finding demonstrates a critical role of the microstructure when understanding the transport mechanism in GO membranes.…”

“…GO suspension was synthesized using a modified Hummer‫׳‬s method, as described in our previous study [17,23]. The GO suspension was centrifuged to control the size of GO flakes, which was determined to be 5 -10 µm from SEM.…”

“…However, these filtration results were inconsistent among different researchers. For example, GO hollow fibre membranes were prepared by using a sacrificial layer, and they were impermeable to gases and exhibited extremely low permeability to water and acetone under pressure-driven nanofiltration conditions, with only 0.074 LMH bar −1 of pure water flux for a 150 nm thick membrane [23]. When looking into the transport passage in GO membranes, it is difficult to justify a high water permeation flux under the pressuredriven conditions.…”

Fabrication of Graphene-based Membranes for Solvent-resistant Nanofiltration

“…In practice, GO membrane were easily shrunk during the drying process and then huge tensile stresses were produced in the membrane which causing obvious defects. More recently, an effective way to solve the stability problem by using the sacrificial layer in the process of membrane preparation was tried by Li et al When the sacrificial layer was washed out, the gap between the GO layers and substrate allowed the GO membrane to shrink freely without pressure [18]. …”

“…The unique two-dimensional (2D) structure and the good stability in organic solvents endow graphene nanomaterials to be an ideal candidate for creating novel membranes [15,[21][22][23]. As a result of the uniform interlayer spacing, graphene membranes usually show superior solvents flux and precise molecular sieving for small organic reagents [8,17,18]. Herein, the methods of preparation of different kinds of SRNF membranes with graphene-based nanomaterials are introduced and the comparation of corresponding parameters of different graphene-based SRNF membranes during the filtration process are provided.…”