Introduction of hydrogen bond recognition sites in ZIF-71 for effective separation of bio-diols in aqueous solutions

The bio-based diols 1,3-propanediol (1,3-PDO) and 2,3-butanediol (2,3-BDO) can form strong hydrogen bonds with water, which increases the separation difficulty of diols in aqueous solutions. Herein, a series of mixed-linker ZIF-71-clnIm_x samples with hydrogen bond–van der Waals (vdW) dual recognition sites have been constructed using 4-chloro-5-nitroimidazole (clnIm) linkers to substitute partially for the original 4,5-dichloroimidazole (dclIm) linkers of the ZIF-71 framework. The experimental and calculated results show that ZIF-71-clnIm_x with appropriate clnIm substitution proportion (x = 7.6 and 12.8 mol%) can strengthen the interaction between ZIF-71-clnIm_x and 2,3-BDO and enhance the adsorption and mass transfer of 2,3-BDO, thus achieving the efficient separation of 2,3-BDO/1,3-PDO. Molecular simulation results further verify that 2,3-BDO can simultaneously form strong H bonds with the –NO₂ of the clnIm linker and weak vdW interactions with the –Cl of the dclIm linker, which are the mixed recognition sites for 2,3-BDO adsorption intensification in aqueous solution for ZIF-71-clnIm_x.