Selective Capture of Carbon Dioxide under Humid Conditions by Hydrophobic Chabazite-Type Zeolitic Imidazolate Frameworks†

Abstract

Hydrophobic zeolitic imidazolate frameworks (ZIFs) with the chabazite (CHA) topology are synthesized by incorporating two distinct imidazolate links. Zn(2-mIm)_0.86(bbIm)_1.14 (ZIF-300), Zn(2-mIm)_0.94(cbIm)_1.06 (ZIF-301), and Zn(2-mIm)_0.67(mbIm)_1.33 (ZIF-302), where 2-mIm=2-methylimidazolate, bbIm=5(6)-bromobenzimidazolate, cbIm=5(6)-chlorobenzimidazolate, and mbIm=5(6)-methylbenzimidazolate, were prepared by reacting zinc nitrate tetrahydrate and 2-mIm with the respective bIm link in a mixture of N,N-dimethylformamide (DMF) and water. Their structures were determined by single-crystal X-ray diffraction and their permanent porosity shown. All of these structures are hydrophobic as confirmed by water adsorption isotherms. All three ZIFs are equally effective at the dynamic separation of CO₂ from N₂ under both dry and humid conditions without any loss of performance over three cycles and can be regenerated simply by using a N₂ flow at ambient temperature.