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 ZIFs 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 Å2) and ZIF-301-S1 (6.5 × 6.6 Å2) exhibited exceptional molecular length separation of acetone (6.4 × 5.8 Å2) and butanol (8.4 × 5.5 Å2). Liquid-phase adsorption and breakthrough experiments confirmed their separation performance, and GCMC simulations provided further insights into the separation mechanism.
1,3-propanediol (1,3-PDO) is a high-value chemical that can be produced via glycerol hydrogenolysis or biological fermentation. The main products of glycerol hydrogenolysis include 1,3-PDO and 1,2-propanediol (1,2-PDO). The properties of propanediol isomers are extremely similar, which are difficult to effectively separate them. Based on the differences in the shape of ellipsoidal 1,3-PDO and spherical 1,2-PDO, ZIF-300 with a 6-member ring (6-MR) trap between cha and d6r cages that can match spherical 1,2-PDO have been selected for the separation of propanediol isomers. ZIF-300 series materials (named ZIF-300-S1, ZIF-300-S2 and ZIF-300-S3) with different 6-MR trap orientations have been constructed by variable the ratio between the small-sized 2-methylimidazole (mIm) and large-sized 5-bromobenzimidazole (bbIm) links. Theoretical and experimental results show that ZIF-300-S3 (Zn(mIm) 1.04 (bbIm) 0.96 ) preferentially adsorbed 1,2-PDO over 1,3-PDO because the 6-MR trap with uniform large bbIm/small mIm links distribution faces essentially the small d6r cage, which can better match spherical 1,2-PDO. In contrast, ZIF-300-S1 (Zn(mIm) 0.82 (bbIm) 1.18 ) show low uptake of 1,2-PDO and 1,3-PDO because the 6-MR trap with main large bbIm links distribution faces essentially the larger cha cage, which show weak confinement of 1,2-PDO and 1,3-PDO. The dynamic column adsorption (1,2-PDO/1,3-PDO: 50/50 g L −1 ) results exhibited that the adsorption capacity of ZIF-300-S3 for 1,2-PDO can be as high as 64.7 mg g −1 and selectivity for 1,2-PDO/1,3-PDO was 2.0. This work provides valuable insights into the construction of ZIFs materials with tunable 6-MR trap for effective separation of isomers.
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