Self-assembled mesoporous zeolitic imidazolate framework-8 (ZIF-8) nanocrystals bearing thiol groups for separations technologies

Abstract

Colloidal suspensions of Zn-based ZIF-8 metal-organic framework (MOF) particles were synthesized (both micrometer μ-ZIF-8- and nanometer n-ZIF-8-sized, respectively). Postsynthetic modification was carried using 2-amino-ethanethiol (cysteamine or Cys), a thiol-bearing monodentate ligand, and particles obtained were employed for the assembly of films on gold-coated electrode surfaces. The results obtained show that, aside from conferring chemical affinity toward Au, when suitable molar ratios are employed, cysteamine modification causes partial coordinative chemical etching of inherently microporous ZIF-8 units, thus giving rise to additional mesoporosity. Cysteamine concentration and exposure time were found to act as control parameters ultimately determining the transport properties of porous films obtained, which can then feature, e.g., size-exclusion effects. The colloidal modification strategies like the one hereby described can be employed for the preparation of robust nano-organized MOF thin films with hierarchical porosity, which bear great potential for its application in separation technologies.