Abstract
Nanocrystalline UiO-66 and its derivatives (containing -NH2, -Br, -(OH)2) were developed via pre-synthetic functionalization and incorporated into a polyimide membrane to develop a mixed-matrix membrane (MMM) for CO2/N2 separation. Incorporation of the non-functionalized UiO-66 nanocrystals into the polyimide membrane successfully improved CO2 permeability, with a slight decrease in CO2/N2 selectivity, owing to its large accessible surface area. The addition of other functional groups further improved the CO2/N2 selectivity of the polymeric membrane, with UiO-66-NH2, UiO-66-Br, and UiO-66-(OH)2 demonstrating improvements of 12%, 4%, and 17%, respectively. Further evaluation by solubility–diffusivity analysis revealed that the functionalized UiO-66 in MMMs can effectively increase CO2 diffusivity while suppressing N2 sorption, thus, resulting in improved CO2/N2 selectivity. Such results imply that the structural tuning of UiO-66 by the incorporation of various functional groups is an effective strategy to improve the CO2 separation performance of MMMs.
Highlights
Carbon capture, storage, and sequestration (CCS) processes have been heavily researched in recent years as a potentially feasible means to minimize the increase in global CO2 concentration.CO2 capture accounts for 70% of the total cost of a typical CCS process [1,2,3]
Nanocrystalline UiO66 and its derivatives were developed via pre-synthetic functionalization with ZrCl4, and these porous fillers were used to develop matrix membrane (MMM) for the analysis of CO2 /N2 separation
It was observed that the addition of UiO-66 nanocrystals successfully improved CO2 permeability but with a slight dip in CO2 /N2 selectivity
Summary
Storage, and sequestration (CCS) processes have been heavily researched in recent years as a potentially feasible means to minimize the increase in global CO2 concentration. Zeolites or metal–organic framework (MOF)-based membranes, which demonstrate high gas selectivity, generally show poorer scalability than polymeric membranes due to their inherent brittleness [14,15,16]. In terms of the choice of polymeric membrane, an in-house polyimide, ODPA-TMPDA (the abbreviations will be elaborated in Section 2.1), was used. The synthesis of 6FDA-based polymers (6FDA = 4,40 -(hexafluoroisopropylidene)diphthalic anhydride) (e.g., 6FDA-DAM (DAM = 2,4,6-trimethyl-m-phenylenediamine), PCO2 = 681 barrer) and PIM-1 (polymer of intrinsic microporosity-1) (PCO2 = 5120 barrer) typically requires the monomers to be purified before polymer synthesis to allow the production of those polymers with a high average molecular weight in order to develop membrane with high intrinsic CO2 permeability [41,42,43,44]. The effect of different functional groups in UiO-66 on CO2 /N2 separation performance was systematically studied
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