Abstract
Dual-filler MMMs have attracted special interests in recent years because of the possibility of producing synergetic effect. This study is aimed at exploring the underlying synergy between two-dimensional (2D) nanosheets and a non-2D filler in mixed matrix membranes for gas separation. MXene or graphene oxide (GO) as typical nanosheet filler is selected to be in pair with a non-2D filler, SiO2 or halloysite nanotubes (HNTs), with Pebax as the polymer matrix. In this way, four pairs of binary fillers are designed and the corresponding four groups of MMMs are fabricated. By tuning the mass ratio of binary fillers, synergetic effect is found for each group of MMMs. However, the two 2D fillers found different preferential non-2D partners. GO works better with HNTs than SiO2, while MXene prefers SiO2 to HNTs. To be noted, GO/HNTs renders the membranes the maximum enhancement of CO2 permeability (153%) and CO2/N2 selectivity (72%) compared to Pebax control membrane, while each of them as single filler only brought about very limited enhancement of CO2 separation performance. The possible mechanisms are thoroughly discussed in terms of filler dispersion, nanosheet flexibility, and the tortuosity and connectivity of the surface diffusion pathways along nanosheets.
Highlights
Mixed matrix membranes (MMMs), containing a continuous polymer phase and a dispersed inorganic filler phase was introduced by Kulprathipanja in 1980s (Kulprathipanja et al, 1988)
We fabricate a series of dual-filler MMMs by matching two non-2D fillers, SiO2 and halloysite nanotubes (HNTs), with two 2D fillers, graphene oxide (GO) and MXene, respectively
All dual-filler MMMs exhibit superior gas separation performance compared to the corresponding single filler MMMs, revealing the existence of synergetic effect between each pair of fillers
Summary
Mixed matrix membranes (MMMs), containing a continuous polymer phase and a dispersed inorganic filler phase was introduced by Kulprathipanja in 1980s (Kulprathipanja et al, 1988). Different from Chemical functionalization, this strategy was proposed to enhance the interfacial adhesion at the nanometer scale rather than molecular level, which is expected to reduce the possibility of interfacial rigidification This strategy has proved valid for zeolites and other silicate fillers (Shu et al, 2007a,b; Bae et al, 2009), and it needs more attention when other molecular sieves are used as fillers. The interaction between dual fillers and the matrix might improve their dispersion, providing different functional domains within a membrane They might provide a unique way to control the morphology of permeation channels (Wang et al, 2019a). A synergy is likely to occur between dual fillers, and significantly improve the membrane performance
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