No abstract

Although polymers of intrinsic microporosity (PIMs) have been recognized as highly permeable membrane materials in gas separation, the physical aging phenomenon seriously affected their performance due to the collapse of micropores. In this work, we report an alternative approach to alleviate the physical aging of PIM-based membranes, as demonstrated by pillaring the PIM-1 membrane with defect-engineered metal–organic framework (MOF) nanoparticles. With excellent interfacial compatibility between the defective UiO-66-FA and PIM-1 by the formation of hydrogen-bond networks, the incorporated MOF nanoparticles acted as pillars of the resulting mixed matrix membranes (UiO-66-FA/PIM-1 MMM) to prevent the collapse of the micropores of the PIM-1 membrane and hence reduce its aging. Concurrently, defective MOFs in the polymer matrix endow the resulting MMMs with fast diffusion pathways and facilitate CO2 transport. Compared with the pristine PIM-1 membrane, UiO-66-FA/PIM-1 MMM displayed maintained CO2/N2 selectivity of about 23.1 but a sharp increased CO2 permeability from 3980 to 16,591 barrer. Only a 25% reduction in CO2 permeability was observed for the UiO-66-FA/PIM-1 MMM after 160 days of operation under the mixed-gas CO2/N2 separation conditions, which is less than the equivalent losses of 40 and 76% for the counterpart MOF-based hybrid membrane and PIM-1, respectively. Given that the performances of the resulting membranes far surpass the 2008 Robeson upper bound, this study may provide a feasible way for sustainable development of PIM-based MMMs in gas separation application.

Mixed matrix metal-organic framework (MOF) membranes show excellent application prospects in gas separation. However, their stability in various practical application scenarios is poor, especially under humid conditions. Herein, we encapsulated a hydrophobic ionic liquid (IL) into the cavity of MOFs, which effectively mitigated the competition between H 2 O and CO 2 in humid gas mixtures, leading to stable and high-performance gas separation. For this reason, the resulting membranes using polymer of intrinsic miroporosity-1 (PIM-1) as a polymer matrix show good CO 2 /N 2 separation performance and long-term test stability under humid environment. In particular, the 20 wt% IL-UiO/ PIM-1 shows a high permeability of 13,778 Barrer and competitive CO 2 /N 2 separation factor of $35.2, transcending the latest upper bound. Besides, the according membrane module exhibits slightly decreased CO 2 permeability and selectivity, promoting the application of self-supporting membranes. This work provides a reliable strategy for the rational design of MOF-based hybrid membranes under extreme conditions.

The separation of light olefins from paraffins using membrane technology is highly desired; however, synthetic polymer membranes generally suffer a pernicious trade-off between permeability and selectivity. Herein, we show that this limitation can be overcome by constructing selective gas transfer pathways in a polymer matrix, as demonstrated by incorporating composites of ionic liquids and zeolitic imidazolate frameworks (ZIFs) to form mixed-matrix membranes. Using propylene/propane separation as a model system, dramatic improvements in the propylene permeability of 218.4 Barrer and propylene/propane separation factor of 45.7 were achieved compared to the values obtained using individual components as a filler. The synergy between the high solubility of the gas molecules in ionic liquids and the size screening ability of ZIF exacerbates the difference in the transmission of propylene and propane, thus leading to superior separation performance. This work presents a promising strategy for the design of membranes for efficient gas separation.

Mesoporous materials | Metal-organic frameworks | Cycloaddition | Steam etching | Dye removalThe introduction of mesoporosity into the microporous metal-organic frameworks (MOFs) is expected to expand their applications. Herein, we report a green and facile method to obtain hierarchically porous MOF structures by using an air-steam etching process. By virtue of the protonation reaction between the imidazole moiety and water vapor, the protonated imidazole related linkers leave the framework, resulting in the formation of mesopores in the zeolitic imidazolate frameworks (ZIFs), as exemplified by ZIF-8. Given the mild etching process, the materials' structural integrity and crystallinity are well maintained. Accordingly, the hierarchical porous ZIF-8 exhibited enhanced performance in the dye removal as well as CO 2 cycloaddition reaction with epichlorohydrin in comparison with microporous ZIF-8, owing to the accelerated mass transfer arising from mesoporous structures. Remarkably, the proposed steam etching approach is generally applicable, which can be readily extended to other ZIFs, such as ZIF-14, ZIF-69, and ZIF-71, thus representing a powerful strategy to construct hierarchically porous MOF materials.