RESUMO
Design and preparation of mixed-matrix membranes (MMMs) with minimum defects and high performance for desired gas separations is still challenging as it depends on a variety of MMM synthesis parameters. In this study, 6FDA-DAM:DABA based MMMs using MOF-808 as filler were prepared to examine the impact of multiple variables on the preparation process of MMMs, including variation in polymer concentration, filler loading, volume of solution cast per membrane area, solvent type used and solvent evaporation rate, and to identify their impact on the CO2/CH4 separation performance of these membranes. Solvent evaporation rate proved to be the most critical synthesis parameter, directly influencing the performance and visual appearance of the membranes. Although less dominantly influencing the MMM performance, polymer concentration and solution volume also had an important role via control over the casting solution viscosity, particle agglomeration, and particle settling rate. Among all solvents studied, MMMs prepared with chloroform led to the best performance for this polymer-filler system. Chloroform-based MMMs containing 10 and 30 wt.% MOF-808 showed 73% and 62% increase in CO2 permeability, respectively, without a decrease in separation factor compared to unfilled membranes. The results indicate that enhanced gas separation performance of MMMs strongly depends on the cumulative effect of various synthesis parameters rather than individual impact, thus requiring a system-specific design and optimization.
RESUMO
In this work, we incorporated an ionic liquid (IL), 1-n-butyl-3-methylimidazolium methyl sulfate ([BMIM][MeSO4]) into two different metal organic frameworks (MOFs), UiO-66, and its amino-functionalized counterpart, NH2-UiO-66, to investigate the effects of ligand-functionalization on the thermal stability limits of IL/MOF composites. The as-synthesized IL/MOF composites were characterized in detail by combining X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller analysis (BET), X-ray fluorescence (XRF), infrared spectroscopies (FTIR), and their thermal stability limits were determined by thermogravimetric analysis (TGA). Characterization data confirmed the successful incorporation of the IL into each MOF and indicated the presence of direct interactions between them. A comparison of the interactions in [BMIM][MeSO4]-incorporated UiO-66 and NH2-UiO-66 with those in their 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF6])-incorporated counterparts showed that the hydrophilic IL, [BMIM][MeSO4], interacts with the 1,4-benzenedicarboxylate (BDC) ligand of the UiO-66, while the hydrophobic IL, [BMIM][PF6], is interacting with the joints where zirconium metal cluster coordinates with BDC ligand. The TGA data demonstrated that the composite with the ligand-functionalized MOF, NH2-UiO-66, exhibited a lower percentage decrease in the maximum tolerable temperature compared to those of IL/UiO-66 composites. Moreover, it is discovered that when the IL is hydrophilic, its hydrogen bonding ability can be utilized to designate an interaction site on MOF's ligand structure which will lead to a lower reduction in thermal stability limits. These results provide insights for the rational design of IL/MOF composites and contribute towards the complete elucidation of structural factors controlling the thermal stability.
RESUMO
We incorporated a water-stable ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate, [BMIM][PF6], into a water-stable metal-organic framework (MOF), MIL-53(Al), to generate the [BMIM][PF6]/MIL-53(Al) composite. This composite was examined for water purification by studying its capacity for methylene blue (MB) and methyl orange (MO) removal from aqueous solutions having either single dye or a mixture of both. Data illustrated that the removal efficiency and the maximum adsorption capacity of MIL-53(Al) were increased several times upon [BMIM][PF6] incorporation. For instance, within 1 min, 10 mg of pristine MIL-53(Al) adsorbed 23.3% MB from 10 mg/L of MB solution, while [BMIM][PF6]/MIL-53(Al) composite was adsorbed 82.3% MB in an identical solution. In the case of MO, 10 mg of pristine MIL-53(Al) achieved 27.8 and 53.6% MO removal from 10 mg/L of MO solution, while [BMIM][PF6]/MIL-53(Al) composite removed 61.4 and 99.2% within 5 min and 3 h, respectively. Moreover, upon [BMIM][PF6] incorporation, the maximum MB and MO adsorption capacities of the pristine MOF were increased from 84.5 to 44 mg/g to 204.9 to 60 mg/g, respectively. The adsorption of dyes in pristine MIL-53(Al) and [BMIM][PF6]/MIL-53(Al) followed a pseudo-second-order kinetic model and a Langmuir isotherm model. In a mixture of both dyes, the IL/MOF composite showed a doubled MB selectivity after the IL incorporation. The composite was successfully regenerated at least two times after its use in water purification to remove MB, MO, and their mixtures. Infrared (IR) spectra indicated that the MB/MO adsorption occurs on [BMIM][PF6]/MIL-53(Al) by electrostatic interactions, hydrogen bonding, and π-π interactions. These results showed that [BMIM][PF6]/MIL-53(Al) composite is a highly promising material for efficient water purification.
RESUMO
Five different imidazolium-based ionic liquids (ILs) were incorporated into a metal-organic framework (MOF), MIL-53(Al), to investigate the effect of IL incorporation on the CO2 separation performance of MIL-53(Al). CO2 , CH4 , and N2 adsorption isotherms of the IL/MIL-53(Al) composites and pristine MIL-53(Al) were measured to evaluate the effect of the ILs on the CO2 /CH4 and CO2 /N2 selectivities of the MOF. Of the composite materials that were tested, [BMIM][PF6 ]/MIL-53(Al) exhibited the largest increase in CO2 /CH4 selectivity, 2.8-times higher than that of pristine MIL-53(Al), whilst [BMIM][MeSO4 ]/MIL-53(Al) exhibited the largest increase in CO2 /N2 selectivity, 3.3-times higher than that of pristine MIL-53(Al). A comparison of the CO2 separation potentials of the IL/MOF composites showed that the [BMIM][BF4 ]- and [BMIM][PF6 ]-incorporated MIL-53(Al) composites both showed enhanced CO2 /N2 and CO2 /CH4 selectivities at pressures of 1-5â bar compared to composites of CuBTC and ZIF-8 with the same ILs. These results demonstrate that MIL-53(Al) is a versatile platform for IL/MOF composites and could help to guide the rational design of new composites for target gas-separation applications.
RESUMO
1-n-Butyl-3-methylimidazolium methyl sulfate is incorporated into MIL-53(Al). Detailed characterization is done by X-ray fluorescence, Brunauer-Emmett-Teller surface area, scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. Results show that ionic liquid (IL) interacts directly with the framework, significantly modifying the electronic environment of MIL-53(Al). Based on the volumetric gas adsorption measurements, CO2, CH4, and N2 adsorption capacities decreased from 112.0, 46.4, and 19.6 cc (STP) gMIL-53(Al) -1 to 42.2, 13.0, and 4.3 cc (STP) gMIL-53(Al) -1 at 5 bar, respectively, upon IL incorporation. Data show that this postsynthesis modification leads to more than two and threefold increase in the ideal selectivity for CO2 over CH4 and N2 separations, respectively, as compared with pristine MIL-53(Al). The isosteric heat of adsorption (Qst) values show that IL incorporation increases CO2 affinity and decreases CH4 and N2 affinities. Cycling adsorption-desorption measurements show that the composite could be regenerated with almost no decrease in the CO2 adsorption capacity for six cycles and confirm the lack of any significant IL leaching. The results offer MIL-53(Al) as an excellent platform for the development of a new class of IL/MOF composites with exceptional performance for CO2 separation.
