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

Abstract

Developing O<sub>2</sub>-selective adsorbents that can produce high-purity oxygen from air remains a significant challenge. Here, we show that the chemically reduced metal–organic framework A<i><sub>x</sub></i>Fe<sub>2</sub>(BDP)<sub>3</sub> (A = Na<sup>+</sup>, K<sup>+</sup>; BDP<sup>2</sup><sup>−</sup> = 1,4-benzenedipyrazolate; 0 < <i>x</i> ≤ 2), which features coordinatively-saturated iron centers, is capable of strong and selective adsorption of O<sub>2</sub> over N<sub>2</sub> at ambient (25 °C) or even elevated (200 °C) temperature. Through a combination of gas adsorption measurements, single-crystal X-ray diffraction, and numerous spectroscopic probes, including <sup>23</sup>Na solid-state NMR and X-ray photoelectron spectroscopy, we demonstrate that selective O<sub>2</sub> uptake likely occurs as a result of 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 framework. The chemical reduction of a robust metal–organic framework to render it capable of binding O<sub>2</sub> through an outer-sphere electron transfer mechanism thus represents a promising and underexplored strategy for the design of next-generation O<sub>2</sub> adsorbents.

Toward Sustainable Li-Ion Battery Recycling: Green Metal–Organic Framework as a Molecular Sieve for the Selective Separation of Cobalt and Nickel

“…Over the past two decades, these materials gained much scientific interest due to their broad range of application, including catalysis, hydrogen storage, carbon capture, semiconductors, drug delivery systems, and biological imaging and sensing. 28−35 As sorbents, they have been investigated for the adsorption of dyes, 36 H 2 , 37 O 2 , 38 and CO 2 39 gases, as well as heavy metals 40 from aqueous solutions. Recently, we have reported on the green synthesis of a bismuth ellagate MOF by using nonhazardous chemicals in a simple synthesis process under ambient conditions.…”

Enhanced O2/N2 Separation of Mixed-Matrix Membrane Filled with Pluronic-Compatibilized Cobalt Phthalocyanine Particles

“…Nevertheless, certain metal-organic frameworks (MOFs), such as chromium(II) carboxylate MOF (Cr 3 BTC 2 ) and MOF-5, possess high O 2 /N 2 selectivity. However, their structural instability with the increase in the number of operating cycles limits the prospects of practical use [23][24][25]. On the other hand, polymers of intrinsic microporosity (PIMs) have shown high-performance for O 2 /N 2 separation [26][27][28].…”