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.