Controlled Construction of Cu(I) Sites within Confined Spaces via Host-Guest Redox: Highly Efficient Adsorbents for Selective CO Adsorption.

Abstract

Here, we designed a double-solvent/host-guest redox combined strategy to construct Cu+ sites in metal-organic frameworks (MOFs) for the first time. As a proof of concept, a representative MOF MIL-100(Fe) with tunable valence states of cations was employed as the host. The combined strategy realizes selective introduction of Cu2+ precursors to the interior pores of MIL-100(Fe), remarkably minimizing the aggregation of Cu2+ and subsequently formed Cu+ species. Owing to the proper reducibility of in situ formed Fe2+ in the frameworks, controlled conversation of Cu2+ to Cu+ with ∼100% yield is achieved in the absence of any additional reducing agents. These characteristics make the obtained materials Cu+-modified MIL-100(Fe) highly active in selective CO adsorption. The CO adsorption capacity is up to 3.75 mmol·g-1 at 298 K and 1 bar, which is superior to all other Cu+-containing adsorbents reported so far such as CuCl/activated carbon (2.5 mmol·g-1), CuCl/γ-Al2O3 (1.0 mmol·g-1), and CuCl/SBA-15 (0.50 mmol·g-1). The same adsorbent also exhibits quite high selectivity of CO over N2, and the ideal adsorption solution theory selectivity reaches 424. The outstanding CO adsorption performance make the present adsorbents great potential in separation of CO from various mixtures.