Imparting Brønsted acidity into a zeolitic imidazole framework

In this work, we demonstrate the impartment of Brønsted acidity into a zeolitic imidazole framework, ZIF-90, via post-synthetically oxidizing the aldehyde group into carboxylate group to afford ZIF-90-COOH. The preservation crystallinity and porosity after post-synthetic oxidation was confirmed by powder X-ray diffraction studies and N₂ gas adsorption analysis respectively. The successful conversion of the aldehyde group into carboxylate group was verified by FT-IR studies, which resulted in remarkable enhancement of methylene blue uptake in the resultant ZIF-90-COOH due to the strong electrostatic interactions between cationic methylene blue and the anionic carboxylate group.