2012

Towards efficient polyoxometalate encapsulation in MIL-100(Cr): influence of synthesis conditions

​J. Juan-Alcañiz, M. Goesten, E.V. Ramos Fernandez,  J. Gascon, F. Kapteijn, New Journal of Chemistry  36 (2012), 977-987, Towards efficient polyoxometalate encapsulation in MIL-100(Cr): influence of synthesis conditions
J. Juan-Alcañiz, M. Goesten, E.V. Ramos Fernandez, J. Gascon, F. Kapteijn
N/A
2012
​The one-pot encapsulation of phosphotungstic acid in the metal–organic framework MIL-100(Cr) has been studied under different synthesis conditions. Both conventional and microwave heating methods have been explored for three different solvent systems: pure aqueous or organic (DMF) phase and biphasic mixtures (water/2-pentanol). Biphasic systems yielded crystals with similar textural properties as those formed in water. The use of DMF as solvent promotes the formation of gel-like solids with dual porosity and enhanced accessibility. The addition of phosphotungstic acid (PTA, H3PW12O40.xH2O) to the MIL-100(Cr) synthesis mixture results in its direct encapsulation. 31P MAS NMR, elemental analysis, N2 adsorption and FT-IR spectroscopy confirm the incorporation of PTA in the sample. The highest PTA encapsulation loading (30 wt%) was obtained by synthesis with microwave heating in biphasic solvent systems (W/Cr molar ratio range between 0.5 and 0.25). Microwave irradiation decreases the time of synthesis (from 4 days to 3 hours) while the use of biphasic media preserves the PTA integrity without affecting the formation of the MOF. The interaction of PTA with the MIL-100(Cr) structure results in some loss of the Lewis acidity, while the Brønsted acidity is hardly affected.
DOI: 10.1039/C2NJ20587D