Abstract
The effect of metal-cluster redox identity on the thermal decarboxylation of a series of isostructural metal-organic frameworks (MOFs) with tetracarboxylate-based ligands and trinuclear μ3-oxo clusters was investigated. The PCN-250 series of MOFs can consist of various metal combinations (Fe3, Fe/Ni, Fe/Mn, Fe/Co, Fe/Zn, Al3, In3, and Sc3). The Fe-based system can undergo a thermally induced reductive decarboxylation, producing a mixed valence cluster with decarboxylated ligand fragments subsequently eliminated to form uniform mesopores. We have extended the analysis to alternative monometallic and bimetallic PCN-250 systems to observe the cluster's effect on the decarboxylation process. Our results suggest that the propensity to undergo decarboxylation is directly related to the cluster redox accessibility, with poorly reducible metals, such as Al, In, and Sc, unable to thermally reduce at the readily accessible temperatures of the Fe-containing system. In contrast, the mixed-metal variants are all reducible. We report improvements in gas adsorption behavior, significantly the uniform increase in the heat of adsorption going from the microporous to hierarchically induced decarboxylated samples. This, along with Fe oxidation state changes from 57Fe Mössbauer spectroscopy, suggests that reduction occurs at the clusters and is essential for mesopore formation. These results provide insight into the thermal behavior of redox-active MOFs and suggest a potential future avenue for generating mesoporosity using controlled cluster redox chemistry.
| Original language | English |
|---|---|
| Pages (from-to) | 5487-5493 |
| Number of pages | 7 |
| Journal | Materials Advances |
| Volume | 2 |
| Issue number | 16 |
| DOIs | |
| State | Published - Aug 21 2021 |
Funding
This research was supported by the Center for Gas Separations Relevant to Clean Energy Technologies, an Energy Frontier Research Center funded by the U.S. Department of Energy (DOE) Office of Science (Basic Energy Sciences) under Contract Number DE-SC0001015. H. F. D., G. S. D., and M. R. R. acknowledge the U.S. Department of Energy (DOE) Office of Science Graduate Student Research (SCGSR) program and the Office of Science (Basic Energy Sciences) Scientific User Facilities (SUF) Division for funding. The SCGSR program is administered by the Oak Ridge Institute for Science and Education (ORISE) for the DOE under contract number DE-SC0014664. M. R. R. also acknowledges the U.S. Department of Energy (DOE) Office of Science (Basic Energy Sciences) for additional research funding. H.-C. Z. acknowledges the Robert A. Welch Foundation for a Welch Endowed Chair (A-0030) and the financial support of the Qatar National Research Fund NPRP award NPRP9-377-1-080. P. A. L. acknowledges the National Institute of Health (R35 GM127021) for funding the Mössbauer spectroscopy studies. The authors would also like to thank Dr Di-Jia Liu for the XAS data and interpretation. This research used the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility, operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357. The Materials Characterization Facility, Mass Spectrometry Laboratory, X-ray Diffraction Laboratory, and NMR User Facility at Texas A&M University are also acknowledged.
| Funders | Funder number |
|---|---|
| Office of Science Graduate Student Research | |
| SCGSR | |
| National Institutes of Health | R35 GM127021 |
| U.S. Department of Energy | |
| Welch Foundation | A-0030 |
| Office of Science | |
| Basic Energy Sciences | DE-SC0001015 |
| Argonne National Laboratory | DE-AC02-06CH11357 |
| Oak Ridge Institute for Science and Education | DE-SC0014664 |
| Qatar National Research Fund | NPRP9-377-1-080 |