Construction of ZIF-300 materials with variable dual-ligand composition and tunable 6-MR trap for effective separation of propanediol isomers

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.