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

• DOI: 10.1021/jacs.0c06570
• Publication Date: 2020-07-29T19:20:03Z
• Authors: Adam Jaffe; Michael E. Ziebel; David M. Halat; Naomi Biggins; Ryan A. Murphy; Khetpakorn Chakar...; Jeffrey A. Reimer; Jeffrey R. Long
• Keywords: Surface Properties; Iron; Temperature; General Chemistry; 02 engineering and technology; 01 natural sciences; 0104 chemical sciences; Oxygen; 13. Climate action; Chemical Sciences; Pyrazoles; Adsorption; Particle Size; 0210 nano-technology; Oxidation-Reduction; Metal-Organic Frameworks

Developing O2-selective adsorbents that can produce high-purity oxygen from air remains a significant challenge. Here, we show 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 strong and selective adsorption O2 over N2 at ambient (25 °C) or even elevated (200 temperature. A combination gas analysis, single-crystal X-ray diffraction, magnetic susceptibility measurements, range spectroscopic methods, including 23Na solid-state NMR, Mössbauer, photoelectron spectroscopies, employed as probes uptake. Significantly, results support mechanism involving outer-sphere electron transfer to form superoxide species, subsequently stabilized by intercalated alkali metal cations reside in one-dimensional triangular pores structure. We further demonstrate uptake behavior similar an expanded-pore analogue thereby gain additional insight into mechanism. The chemical reduction robust render it binding through such represents promising underexplored strategy for design next-generation adsorbents.