posted on 2024-01-26, 15:06authored byKurtis
M. Carsch, Adrian J. Huang, Matthew N. Dods, Surya T. Parker, Rachel C. Rohde, Henry Z. H. Jiang, Yuto Yabuuchi, Sarah L. Karstens, Hyunchul Kwon, Romit Chakraborty, Karen C. Bustillo, Katie R. Meihaus, Hiroyasu Furukawa, Andrew M. Minor, Martin Head-Gordon, Jeffrey R. Long
High or enriched-purity
O2 is used in numerous industries
and is predominantly produced from the cryogenic distillation of air,
an extremely capital- and energy-intensive process. There is significant
interest in the development of new approaches for O2-selective
air separations, including the use of metal–organic frameworks
featuring coordinatively unsaturated metal sites that can selectively
bind O2 over N2via electron
transfer. However, most of these materials exhibit appreciable and/or
reversible O2 uptake only at low temperatures, and their
open metal sites are also potential strong binding sites for the water
present in air. Here, we study the framework CuI-MFU-4l (CuxZn5–xCl4–x(btdd)3; H2btdd = bis(1H-1,2,3-triazolo[4,5-b],[4′,5′-i])dibenzo[1,4]dioxin),
which binds O2 reversibly at ambient temperature. We develop
an optimized synthesis for the material to access a high density of
trigonal pyramidal CuI sites, and we show that this material
reversibly captures O2 from air at 25 °C, even in
the presence of water. When exposed to air up to 100% relative humidity,
CuI-MFU-4l retains a constant O2 capacity over the course of repeated cycling under dynamic breakthrough
conditions. While this material simultaneously adsorbs N2, differences in O2 and N2 desorption kinetics
allow for the isolation of high-purity O2 (>99%) under
relatively mild regeneration conditions. Spectroscopic, magnetic,
and computational analyses reveal that O2 binds to the
copper(I) sites to form copper(II)–superoxide moieties that
exhibit temperature-dependent side-on and end-on binding modes. Overall,
these results suggest that CuI-MFU-4l is
a promising material for the separation of O2 from ambient
air, even without dehumidification.