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Chem Commun (Camb). 2019 Sep 30. doi: 10.1039/c9cc04555d. [Epub ahead of print]

The thermally induced decarboxylation mechanism of a mixed-oxidation state carboxylate-based iron metal-organic framework.

Author information

1
Department of Chemistry, Texas A&M University, College Station, TX 77843, USA. zhou@chem.tamu.edu.
2
Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843, USA.
3
Framergy Inc. College Station, TX 77843, USA.
4
Department of Chemistry, Texas A&M University, College Station, TX 77843, USA. zhou@chem.tamu.edu and Department of Biochemistry and Biophysics, Texas A&M University, College Station, TX 77843, USA.
5
Department of Chemistry, Texas A&M University, College Station, TX 77843, USA. zhou@chem.tamu.edu and Department of Materials Science and Engineering, Texas A&M University, College Station, TX 77843, USA.

Abstract

Investigations into a thermally generated decarboxylation mechanism for metal site activation and the generation of mesopores in a carboxylate iron-based MOF, PCN-250, have been conducted. PCN-250 exhibits an interesting oxidation state change during thermal treatment under inert atmospheres or vacuum conditions, transitioning from an Fe(iii)3 cluster to a Fe(ii)Fe(iii)2 cluster. To probe this redox event and discern a mechanism of activation, a combination of thermogravimetric analysis, gas sorption, scanning electron microscopy, 57Fe Mössbauer spectroscopy, gas chromatography-mass spectrometry, and X-ray diffraction studies were conducted. The results suggest that the iron-site activation occurs due to ligand decarboxylation above 200 °C. This is also consistent with the generation of a missing cluster mesoporous defect in the framework. The resulting mesoporous PCN-250 maintains high thermal stability, preserving crystallinity after multiple consecutive high-temperature regeneration cycles. Additionally, the thermally reduced PCN-250 shows improvements in the total uptake capacity of methane and CO2.

PMID:
31565709
DOI:
10.1039/c9cc04555d

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