Materials Science

From MOFs to Mesoporous Oxides

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Science  21 Jun 2013:
Vol. 340, Issue 6139, pp. 1377
DOI: 10.1126/science.340.6139.1377-d
CREDIT: T. K. KIM ET AL., JOURNAL OF THE AMERICAN CHEMICAL SOCIETY (7 MAY 2013) © 2013 AMERICAN CHEMICAL SOCIETY

Mesoporous oxides can be made starting with organic frameworks, such as micelles, that form a template for metallorganic precursors. After the precursors react to form the oxide, the template can then be removed. Kim et al. have used crystalline metal organic frameworks (MOFs) as the precursors for magnesium and cerium oxides that develop mesoscale porosity. They made the MOF precursors with adipic acid, HOOC(CH2)4COOH, as the linker. The solvothermal reaction of a magnesium or cerium salt with this ligand and methanol and dimethylacetamide created MOFs in which each metal ion was coordinated to five or six oxygen atoms. Heating these materials under a flowing nitrogen atmosphere to 500°C and then holding these materials at that temperature for 12 hours created crystalline oxides. These oxides had a hierarchical structure of mesopores on the scale of tens of nanometers connected by larger pores on the scale of 50 to 100 nm. The magnesium oxide material also exhibited a high capacity for adsorption of carbon dioxide (∼9% by weight) from combustion gas. The authors argue that the thermal decomposition process creates organic species that act as micellar templates (“porogens”) that are removed during the thermal treatment. Thermal treatment of a MOF made with a more stable aromatic linker did not form the mesoporous oxide but instead led to nanoparticle formation.

J. Am. Chem. Soc. 10.1021/ja401869h (2013).

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