期刊
JOURNAL OF PHYSICAL CHEMISTRY C
卷 117, 期 44, 页码 22784-22796出版社
AMER CHEMICAL SOC
DOI: 10.1021/jp406835n
关键词
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资金
- Ghent University BOF [01P02911T, 01D31608]
- GOA [01G00710]
- Long Term Structural Methusalem Grant [01M00409]
- Foundation of Scientific Research Flanders (FWO)
- European Research Council through the European Community [240483]
- Interuniversity Attraction Poles Programme [P7/05]
- Belgian Science Policy Office
Six new functionalized vanadium hydroxo terephthalates [V-III(OH)(BDC-X)]center dot n(guests) (MIL-47(V-III)-X-AS) (BDC = 1,4-benzenedicarboxylate; X = -Cl, -Br, -CH3, -CF3, -OH, -OCH3; AS = as-synthesized) along with the parent MIL-47 were synthesized under rapid microwave-assisted hydrothermal conditions (170 degrees C, 30 min, 150 W). The unreacted H2BDC-X and/or occluded solvent molecules can be removed by thermal activation under vacuum, leading to the empty-pore forms of the title compounds (MIL-47(V-IV)-X). Except pristine MIL-47 (+III oxidation state), the vanadium atoms in all the evacuated functionalized solids stayed in the +IV oxidation state. The phase purity of the compounds was ascertained by X-ray powder diffraction (XRPD), diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, Raman, thermogravimetric (TG), and elemental analysis. The structural similarity of the filled and empty-pore forms of the functionalized compounds with the respective forms of parent MIL-47 was verified by cell parameter determination from XRPD data. TGA and temperature-dependent XRPD (TDXRPD) experiments in an air atmosphere indicate high thermal stability in the 330-385 degrees C range. All the thermally activated compounds exhibit significant microporosity (S-BET in the 305-897 m(2) g(-1) range), as verified by the N-2 and CO2 sorption analysis. Among the six functionalized compounds, MIL-47(V-IV)-OCH3 shows the highest CO2 uptake, demonstrating the determining role of functional groups on the CO2 sorption behavior. For this compound and pristine MIL-47(V-IV), Widom particle insertion simulations were performed based on ab initio calculated crystal structures. The theoretical Henry coefficients show a good agreement with the experimental values, and calculated isosurfaces for the local excess chemical potential indicate the enhanced CO2 affinity is due to two effects: (i) the interaction between the methoxy group and CO2 and (ii) the collapse of the MIL-47(V-IV)-OCH3 framework.
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