Nanoporous Thulium(III)–Organic Framework for High Catalytic Performance on the CO2-Epoxide Cycloaddition

Abstract

Considering that the greenhouse effect is the most concerning environmental issue globally, selective capture and resource utilization of CO₂ have attracted widespread attention. Herein, we report a highly robust thulium(III)–organic framework of {[Tm₂(μ₂-OH)(CPPDDA)(H₂O)₂]·3DMF·2H₂O}_n (NUC-108), which is obtained from the exquisite combination of undocumented multifunctional clusters of [Tm₄(μ₂-OH)₂(COO)₁₀(H₂O)₄] and organic ligands of 4,4′-(4-(4-carboxyphenyl)pyridine-2,6-diyl)diisophthalic acid (H₅CPPDDA). NUC-108 possesses the following unique merits: (i) the undocumented functional tetranuclear rare-earth clusters of [Tm₄(μ₂-OH)₂(COO)₁₀(H₂O)₄] serve as the nodes, in which Tm³⁺ ions can be activated as Lewis acid sites and μ₂-OH anions are Lewis base sites; (ii) the high-porosity zeolite architecture contains three kinds of channels: 12.29 × 9.74 Ų and 8.92 × 4.97 Ų along the b axis and 12.76 × 8.95 Ų along the c axis; (iii) uncoordinated pyridine moieties as Lewis base sites further endow the host framework with functionality; and (iv) resistance to weak acidic and alkaline aqueous solutions as well as various organic solvents. Notably, NUC-108a can effectively separate CO₂ from a binary CO₂/CH₄ mixture with high adsorption selectivity, which should be due to the enough Lewis basic sites of pyridine groups and μ₂-OH moieties. Furthermore, under mild conditions and without any organic solvent, NUC-108a can also be used as an effective recoverable catalyst to facilitate the cycloaddition of CO₂ with epoxides with the aid of tetrabutylammonium bromide. Hence, these findings are beneficial for guiding the development of highly stable and active catalysts for carbon utilization.