ChemRxiv
These are preliminary reports that have not been peer-reviewed. They should not be regarded as conclusive, guide clinical practice/health-related behavior, or be reported in news media as established information. For more information, please see our FAQs.
1/1
0/0

Selective, High-Temperature O2 Adsorption in Chemically Reduced, Redox-Active Iron-Pyrazolate Metal–Organic Frameworks

preprint
revised on 23.06.2020 and posted on 25.06.2020 by Adam Jaffe, Michael Ziebel, David M. Halat, Naomi Biggins, Ryan Murphy, Khetpakorn Chakarawet, Jeffrey A. Reimer, Jeffrey R. Long
Developing O2-selective adsorbents that can produce high-purity oxygen from air remains a significant challenge. Here, we show that chemically reduced metal–organic framework materials of the type AxFe2(bdp)3 (A = Na+, K+; bdp2 = 1,4-benzenedipyrazolate; 0 < x ≤ 2), which feature coordinatively saturated iron centers, are capable of strong and selective adsorption of O2 over N2 at ambient (25 °C) or even elevated (200 °C) temperature. A combination of gas adsorption analysis, single-crystal X-ray diffraction, magnetic susceptibility measurements, and a range of spectroscopic methods, including 23Na solid-state NMR, Mössbauer, and X-ray photoelectron spectroscopies, are employed as probes of O2 uptake. Significantly, the results support a selective adsorption mechanism involving outer-sphere electron transfer from the framework to form superoxide species, which are subsequently stabilized by intercalated alkali metal cations that reside in the one-dimensional triangular pores of the structure. We further demonstrate similar O2 uptake behavior to that of AxFe2(bdp)3 in an expanded-pore framework analogue and thereby gain additional insight into the O2 adsorption mechanism. The chemical reduction of a robust metal–organic framework to render it capable of binding O2 through such an outer-sphere electron transfer mechanism represents a promising and underexplored strategy for the design of next-generation O2 adsorbents.

Funding

Interrogating Selective Metal-Adsorbate Interactions in Metal-Organic Frameworks

Basic Energy Sciences

Find out more...

History

Email Address of Submitting Author

adamjaffe@berkeley.edu

Institution

University of California, Berkeley

Country

United States

ORCID For Submitting Author

0000-0002-9886-0249

Declaration of Conflict of Interest

These authors declare no competing financial interest

Version Notes

Jaffe_Long_ChemRxivmanuscript4 Version 4 changes: minor polishing of crystal structure figures

Exports

Logo branding

Exports