Tunable ellipsoidal cage in ZIF-300 and ZIF-301 for size-selective acetone/butanol separation†

Abstract

In this work, ZIF-300 and ZIF-301 derivatives with tunable ellipsoidal cage sizes were synthesized by adjusting the ratio between the small-sized mIm and large-sized bbIm/cbIm ligands. During ZIF synthesis, when the amount of the fixed ligand is equimolar to Zn²⁺, adjusting the content of the other ligand does not yield a continuously tunable structure. In contrast, maintaining an excess of one ligand relative to Zn²⁺ and varying the content of the other ligand enables the formation of ZIF derivatives with continuously tunable chemical compositions and ellipsoidal cage sizes. This tunability is likely due to the increased concentration of the fixed ligand, which enhances its competitive coordination ability within the ZIF framework. Consequently, ZIF-300 and ZIF-301 derivatives with adjustable long-axis cage sizes ranging from 6.5 Å to 9.6 Å were successfully prepared. Notably, the small cage-sized ZIF-300-S1 (6.5 × 6.1 Ų) and ZIF-301-S1 (6.5 × 6.6 Ų) exhibited exceptional molecular length separation of acetone (6.4 × 5.8 Ų) and butanol (8.4 × 5.5 Ų). Liquid-phase adsorption and breakthrough experiments confirmed their separation performance, and GCMC simulations provided further insights into the separation mechanism.