Green synthesis of polymeric membranes: Recent advances and future prospects
S. Jiang, B. P. Ladewig
Current Opinion in Green and Sustainable Chemistry 21 (2020) 1-8.
Abstract: Polymeric membranes are widely used in gas separations, liquid separations, and other processes such as fuel cells. However, methods and processes for manufacturing these membranes are usually harmful to the environment and/or human health. Although many new materials and synthesis methods are reported every year, green synthesis only makes up a small proportion. Therefore, more efforts are necessary to raise researchers’ awareness to green synthesis of membranes. One popular strategy to greenly synthesize membranes is to avoid toxic organic solvents or use water to replace organic solvents completely. However, many reported green methods could only realize green synthesis partly. The ultimate goal is to synthesize membranes in a completely eco-friendly way, where raw materials, membrane preparation, post-treatment, and other involved procedures are all ‘green’.
Systematic screening of DMOF-1 with NH2, NO2, Br and azobenzene functionalities for elucidation of carbon dioxide and nitrogen separation properties
M. Xie, N. Prasetya, B. P. Ladewig
Abstract: In this study, dabco MOF-1 (DMOF-1) with four different functional groups (NH2, NO2, Br and azobenzene) has been successfully synthesized through systematic control of the synthesis conditions. The functionalised DMOF-1 is characterized using various analytical techniques including PXRD, TGA and N2 sorption. The effect of the various functional groups on the performance of the MOFs for post-combustion CO2 capture is evaluated. DMOF-1s with polar functional groups are found to have better affinity with CO2 compared with the parent framework as indicated by higher CO2 heat of adsorption. However, imparting steric hindrance to the framework as in Azo-DMOF-1 enhances CO2/N2 selectivity, potentially as a result of lower N2 affinity for the framework.
A Multifunctional, Charge-Neutral, Chiral Octahedral M12L12 Cage
S.A. Boer, K. F. White, B. Slater, A. J. Emerson, G. P. Knowles, W. A. Donald, A. W. Thornton, B. P. Ladewig, T. D. M. Bell, M. R. Hill A. L. Chaffee, B. F. Abrahams, D. R. Turner
Abstract: A chiral, octahedral M12L12 cage, which is charge neutral and contains an internal void of about 2000 Å3, is reported. The cage was synthesised as an enantiopure complex by virtue of amino‐acid‐based dicarboxylate ligands, which assemble around copper paddlewheels at the vertices of the octahedron. The cage persists in solution with retention of the fluorescence properties of the parent acid. The solid‐state structure contains large pores both within and between the cages, and displays permanent porosity for the sorption of gases with retention of crystallinity. Initial tests show some enantioselectivity of the cage towards guests in solution.
High performance cation exchange membranes synthesized via in-situ emulsion polymerization without organic solvents and corrosive acids
S. Jiang and B.P. Ladewig
Abstract: The synthesis of cation exchange membranes (CEMs) usually involves using organic solvents and/or sulfonation process. In this study, green and scalable synthesis of high performance CEMs is achieved without organic solvents and sulfonation. The synthesis is carried out via in-situ polymerization of lithium styrene sulfonate in porous support. Different preparation procedures are developed and optimized. Functional sulfonate groups were successfully loaded onto and into the membrane support, as verified by FTIR. Besides, water plays an important role during membrane synthesis. By reducing the amount of water used, the ratio of functional polymers to membrane support in the synthesized CEMs is increased. Therefore, the synthesized CEMs show increased ion exchange capacity (IEC). This is significant because it means that high IEC can be achieved without introducing cation exchange resins to the membranes. Finally, the synthesized membranes demonstrate high desalination performance. This new methodology may shed new light on preparing CEMs in an efficient and eco-friendly way.
An insight into the effect of azobenzene functionalities studied in UiO-66 frameworks for low energy CO2 capture and CO2/N2 membrane separation
N. Prasetya and B.P. Ladewig
Abstract: In this paper, a simple approach to study the fundamental aspect of the light-responsive metal–organic framework (MOF) in UiO-66 topology through a mixed-ligand approach is reported. Apart from change in the structural properties, the loading of an azobenzene linker inside the framework also affects the CO2 light-responsive properties and CO2/N2 selectivity which could help to design future low-energy CO2 adsorbents. Further study to incorporate MOFs into mixed matrix membranes using PIM-1 as the polymer matrix also indicates the benefits of having a higher azobenzene loading in the MOF to enhance the CO2/N2 separation performance since it can improve the separation performance that could not be obtained in non-functionalized fillers.
Gas permeation through single-crystal ZIF-8 membranes
C. Chen, A. Ozcan, A.O. Yazaydin, B.P. Ladewig
Abstract: Grain boundaries are an unavoidable microstructural feature in intergrown polycrystalline metal-organic framework (MOF) membranes. They have been suspected to be less size-selective than a MOF’s micropores, resulting in suboptimal separation performances – a speculation recently confirmed by transmission electron microscopy of MOF ZIF-8. Single-crystal membranes, without grain boundaries, should confine mass transport to micropores and reflect the intrinsic selectivity of the porous material. Here, we demonstrate the feasibility of fabricating single-crystal MOF membranes and directly measuring gas permeability through such a membrane using ZIF-8 as an exemplary MOF. Our single-crystal ZIF-8 membranes achieved ideal selectivities up to 28.9, 10.0, 40.1 and 3.6 for gas pairs CO2/N2, CO2/CH4, He/CH4 and CH4/N2 respectively, much higher than or reversely selective to over 20 polycrystalline ZIF-8 membranes, unequivocally proving the non-selectivity of grain boundaries. The permeability trend obtained in single-crystal membranes aligned with a force field that had been validated against multiple empirical adsorption isotherms.
Matrimid-JUC-62 and Matrimid-PCN-250 mixed matrix membranes displaying light-responsive gas separation and beneficial ageing characteristics for CO2/N2 separation
N. Prasetya, A. A. Teck, B.P. Ladewig
Abstract: The performance of two generation-3 light-responsive metal-organic framework (MOF), namely JUC-62 and PCN-250, was investigated in a mixed matrix membrane (MMM) form. Both of them were incorporated inside the matrimid as the polymer matrix. Using our custom-designed membrane testing cell, it was observed that the MMMs showed up to 9% difference in CO2 permeability between its pristine and UV-irradiated condition. This shows that the light-responsive ability of the light-responsive MOFs could still be maintained. Thus, this finding is applicable in designing a smart material. Apart from that, the MMMs also has the potential to be applied for post-combustion carbon capture. At loadings up to 15 wt%, both CO2 permeability and CO2/N2 ideal selectivity could be significantly improved and surpassed the value exhibited by most of the MOF-matrimid MMM. Lastly the long term performance of the MMM was also evaluated and it was observed that both MMM could maintain their performance up to 1 month with only a slight decrease in CO2 permeability observed for 10 wt% PCN-250-matrimid. This study then opens up the possibility to fabricate a novel anti-aging multifunctional membrane material that is applicable as a smart material and also in post combustion carbon capture applications.
A new and highly robust light-responsive Azo-UiO-66 for highly selective and low energy post-combustion CO2 capture and its application in a mixed matrix membrane for CO2/N2 separation
N. Prasetya, B.C. Donose, B.P. Ladewig
Abstract: A new and robust generation-2 light-responsive MOF with UiO-66 topology applicable for post combustion CO2 capture has been successfully synthesized and is described in this article. Azo-UiO-66 shows a satisfactory performance for CO2/N2 separation as observed through high CO2/N2 selectivity. Furthermore, due to the presence of azobenzene groups, Azo-UiO-66 also exhibits a very efficient CO2 photoswitching uptake, a characteristic that has never been observed in any generation-2 light-responsive MOF. Combined together with its robust character, this makes Azo-UiO-66 a promising candidate for highly selective and low energy CO2 capture applications. To further apply this material, Azo-UiO-66 was incorporated in Matrimid to form mixed matrix membranes (MMM). Composites with up to 20 wt% of Azo-UiO-66 were fabricated and tested. The resulting MMM showed increased performance in terms of CO2 permeability and CO2/N2 selectivity compared with the similar MOF-based MMM composites. This then shows another promising application of Azo-UiO-66 as a filler to enhance polymeric membrane performance for CO2 separation.
New Azo-DMOF-1 MOF as a Photoresponsive Low-Energy CO2 Adsorbent and Its Exceptional CO2/N2 Separation Performance in Mixed Matrix Membranes
N. Prasetya, B.P. Ladewig
Abstract: A new generation-2 light-responsive metal-organic framework (MOF) has been successfully synthesized using Zn as the metal source and both 2-phenyldiazenyl terephthalic acid and 1,4-diazabicyclo[2.2.2]octane (DABCO) as the ligands. It was found that Zn-azo-dabco MOF (Azo-DMOF-1) exhibited a photoresponsive CO2 adsorption both in static and dynamic condition because of the presence of azobenzene functionalities from the ligand. Further application of this MOF was evaluated by incorporating it as a filler in a mixed matrix membrane for CO2/N2 gas separation. Matrimid and polymer of intrinsic microporosity-1 (PIM-1) were used as the polymer matrix. It was found that Azo-DMOF-1 could enhance both the CO2 permeability and selectivity of the pristine polymer. In particular, the Azo-DMOF-1-PIM-1 composite membranes have shown a promising performance that surpassed the 2008 Robeson Upper Bound.
A scientometric study of the research on ion exchange membranes
S. Jiang, K.F.L. Hagesteijn, J. Ni, B.P. Ladewig
Abstract: A comprehensive scientometric approach was adopted to study the research on ion exchange membranes. The statistical analysis was conducted based on 21123 publications which were related to the topic of ion exchange membranes. Specifically, from 2001 to 2016, over 18000 articles were published on ion exchange membranes, indicating researchers’ great interest in this topic. Especially, compared to 2001, the number of articles published in 2016 increased approximately six-fold. This trend continued in 2017 since over 2000 articles were published in the year of 2017. Also, these articles were spread across over 1000 different journals, near 100 countries/regions and over 5000 research institutes, revealing the importance of ion exchange membrane as well as the broad research interest in this field. Besides, the properties and applications of ion exchange membranes were also discussed statistically. Furthermore, keywords analysis indicated that fuel cell and proton exchange membrane had the highest cooccurrence frequency. Finally, research areas analysis revealed that ion exchange membranes had a close relation with chemistry, energy and materials.
A review of the synthesis and characterization of anion exchange membranes
K.F.L. Hagesteijn, S. Jiang, B.P. Ladewig
Abstract: This review highlights advancements made in anion exchange membrane (AEM) head groups, polymer structures and membrane synthesis methods. Limitations of current analytical techniques for characterizing AEMs are also discussed. AEM research is primarily driven by the need to develop suitable AEMs for the high-pH and high-temperature environments in anion exchange membrane fuel cells and anion exchange membrane water electrolysis applications. AEM head groups can be broadly classified as nitrogen based (e.g. quaternary ammonium), nitrogen free (e.g. phosphonium) and metal cations (e.g. ruthenium). Metal cation head groups show great promise for AEM due to their high stability and high valency. Through “rational polymer architecture”, it is possible to synthesize AEMs with ion channels and improved chemical stability. Heterogeneous membranes using porous supports or inorganic nanoparticles show great promise due to the ability to tune membrane characteristics based on the ratio of polymer to porous support or nanoparticles. Future research should investigate consolidating advancements in AEM head groups with an optimized polymer structure in heterogeneous membranes to bring together the valuable characteristics gained from using head groups with improved chemical stability, with the benefits of a polymer structure with ion channels and improved membrane properties from using a porous support or nanoparticles.
Broadband dielectric spectroscopy of Nafion-117, sulfonated polysulfone (sPSF) and sulfonated polyether ketone (sPEK) membranes
K.F.L. Hagesteijn, S. Jiang, B.P. Ladewig
Abstract: Nafion®-117, sulfonated polysulfone (sPSF) and sulfonated polyetherketone (sPEK) are characterized using broadband dielectric spectroscopy in the frequency range of 10 MHz–100 mHz. Overall, there are 4–5 relaxation processes in these sulfonated membranes and a comparison of their spectral features allows assigning the relaxation processes. At an optimum amplitude of ∼100 mV rms , all the relaxations are clearly defined as the electrode polarization is minimized. At low temperatures (−130 °C), these membranes show a broad relaxation peak in the mid-frequency region, which quickly shifts towards the high-frequency region as the temperature is increased to −90 °C. This peak is observed in proton exchange membranes for the first time due to the use of low ac amplitude, and it is assigned to the relaxation of the confined water in the micro-pores. With all the membranes, the peak associated with -SO 3 H group relaxation is observed in the same frequency range at a temperature of ∼−80 °C.