Abstract
In this study, three zeolitic imidazolate frameworks (ZIFs) with different shapesparticles (0D), microneedles (1D), and leaves (2D)were synthesized by tuning the polymeric additives. These ZIFs have been dispersed into a Pebax 2533 matrix with a loading varying from 0 to 20 wt %. The resultant mixed matrix membranes (MMMs) have been systemically characterized by various techniques. A mixed gas permeation experiment was also employed to evaluate the CO2 separation performance. The results show that there exists an optimal ZIF loading for these three series of membranes, but the values are highly dependent on the morphologies of the added ZIFs. The membranes containing ZIF particles and microneedles display the highest CO2 permeability and CO2/N2 selectivity simultaneously at 10 wt % loading, while a much lower loading, that is, ∼5 wt %, is the optimized value for ZIF leaves. Moreover, the increment in CO2 permeability is related to the ZIFs’ morphology and the order is 0D < 1D < 2D. On the other hand, the effects of the morphology on selectivity seems to be the opposite, with the ZIF of the 0D structure showing the highest selectivity. Moreover, the influences of adding ZIF fillers on the performances of the resultant MMMs under varied operating temperatures and the feed pressures were also investigated. The membrane with a 10 wt % 1D ZIF shows the highest increment in CO2 permeability (727.4 Barrer) with a CO2/N2 selectivity of ∼14 at 60 °C.
Highlights
The market size of gas separation membranes in various applications, such as air separations and natural gas sweetening/dehydration, has been expanding greatly[1−5] and is estimated to reach $1.1 billion by 2024 according to a very recent research report.[6]
Three zeolitic imidazolate frameworks (ZIFs) with different shapes were fabricated with the same Hmim/Zn2+ ratio in aqueous solution at room temperatures
The XRD pattern of the 1D ZIF matches that of the leaf ZIF-L, which is the 2D ZIF in this work. This suggests that the existence of PVA during ZIF synthesis seems to have a negligible effect on the crystal structure.[21]
Summary
The market size of gas separation membranes in various applications, such as air separations and natural gas sweetening/dehydration, has been expanding greatly[1−5] and is estimated to reach $1.1 billion by 2024 according to a very recent research report.[6]. Results show the ZIFs with different thicknesses could result in considerably distinct impacts on the CO2 separation performance: the thickest one brings about the highest CO2 permeability.[21] In the current work, following the same idea, the influences of the filler shapes on the properties of the ZIF + Pebax matrix were investigated by employing ZIF nanoparticles (0D), needles (1D), and leaves (2D). These ZIFs were prepared using different methods at room temperature, and analyzed by various characterization techniques: scanning electron microscopy (SEM), Fouriertransform infrared (FTIR) spectroscopy, and X-ray crystallography (XRD). The CO2/N2 separation performance was studied by mixed gas permeation tests and the correspondence between the morphological properties of the nanofillers and the permeation properties of the MMMs was discussed
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