Rijia Lin

Mixed-Matrix Membranes with Metal-Organic Framework-Decorated CNT Fillers for Efficient CO2 Separation.

Carbon nanotube (CNT) mixed-matrix membranes (MMMs) show great potential to achieve superior gas permeance because of the unique structure of CNTs. However, the challenges of CNT dispersion in polymer matrix and elimination of interfacial defects are still hindering MMMs to be prepared for high gas selectivity. A novel CNT/metal-organic framework (MOF) composite derived from the growth of NH2-MIL-101(Al) on the surface of CNTs have been synthesized and applied to fabricate polyimide-based MMMs. Extra amino groups and active sites were introduced to external surface of CNTs after MOF decoration. The good adhesion between the synthesized CNT-MIL fillers and polymer phase was observed, even at a high filler loadings up to 15%. Consequently, MMMs containing the synthesized MOF/CNT composite exhibit not only a large CO2 permeability but also a high CO2/CH4 selectivity; the combined performance of permeability and selectivity is even above the Robeson upper bound. The strategy of growing MOFs on CNTs can be further utilized to develop a more effective approach to further improve MMM performance through the decoration of MOFs on existing fillers that have high selectivity to specific gas.

Propylene/propane selective mixed matrix membranes with grape-branched MOF/CNT filler

In this study, we fabricated mixed matrix membranes (MMMs) comprising a novel carbon nanotube/metal–organic framework (MOF) filler for efficient propylene/propane separation. Tomographic focused ion beam scanning electron microscopy was applied to quantitatively evaluate the filler dispersion and filler/polymer interfacial void ratio. The dispersion of ZIF-8 in MMMs was improved by the confined growth of ZIF-8 on the carbon nanotube (CNT) surfaces, yielding a simultaneous enhancement of C3H6 membrane permeability and C3H6/C3H8 selectivity. Excellent adhesion between the synthesized ZIF-8/CNT fillers and polymer matrix is observed, with only 0.086% void volume fraction, even at a high filler loading. The in situ growth of MOFs on CNTs shown here can provide an effective way to design mixed matrix membranes with improved filler dispersion, structural features and separation performance.

Synthesis and characterization of three amino-functionalized metal-organic frameworks based on the 2-aminoterephthalic ligand.

The incorporation of Lewis base sites and open metal cation sites into metal-organic frameworks (MOFs) is a potential route to improve selective CO2 adsorption from gas mixtures. In this study, three novel amino-functionalized metal-organic frameworks (MOFs): Mg-ABDC [Mg3(ABDC)3(DMF)4], Co-ABDC [Co3(ABDC)3(DMF)4] and Sr-ABDC [Sr(ABDC)(DMF)] (ABDC = 2-aminoterephthalate) were synthesized by solvothermal reactions of 2-aminoterephthalic acid (H2ABDC) with magnesium, cobalt and strontium metal centers, respectively. Single-crystal structure analysis showed that Mg-ABDC and Co-ABDC were isostructural compounds comprising two-dimensional layered structures. The Sr-ABDC contained a three-dimensional motif isostructural to its known Ca analogue. The amino-functionalized MOFs were characterized by powder X-ray diffraction, thermal gravimetric analysis and N2 sorption. The CO2 and N2 equilibrium adsorption capacities were measured at different temperatures (0 and 25 °C). The CO2/N2 selectivities of the MOFs were 396 on Mg-ABDC, 326 on Co-ABDC and 18 on Sr-ABDC. Both Mg-ABDC and Co-ABDC exhibit high heat of CO2 adsorption (>30 kJ mol(-1)). The Sr-ABDC displays good thermal stability but had a low adsorption capacity resulting from narrow pore apertures.

Metal organic framework based mixed matrix membranes: an overview on filler/polymer interfaces

Membrane technology for gas separation has attracted significant attention because of its low energy consumption. However, most polymeric membranes suffer from the trade-off between mass transport rates and separation efficiency. Metal–organic frameworks (MOFs) are promising candidates to fabricate mixed matrix membranes (MMMs) for gas separation due to their high surface area and porosity, adjustable pore sizes and controllable surface functionality. This review presents the recent opportunities and challenges faced in MOF-based MMM fabrication, emphasizing the MOFs/polymer interfacial morphology. The state-of-the-art solutions and strategies for improving the filler/matrix interface are reviewed and evaluated in detail. Finally, the characterisation and understanding of the MMM interface morphology and future research directions are outlined. This review will offer some insights for fabricating MMMs with optimal interface morphology and separation performance.