Crystal formation and size control of zeolitic imidazolate frameworks with mixed imidazolate linkers

The effect of synthesis parameters, such as batch composition and synthesis temperature, on the formation and crystal size of zeolitic imidazolate frameworks (ZIFs) using mixed linkers, imidazole (Im) and benzimidazole (bIm), were studied by X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM). ZIF-7 and ZIF-62 were identified as the main phases and a phase diagram relating the batch composition and the final product was constructed based on XRPD and SEM. The range of batch composition giving rise to ZIF-7 and ZIF-62 was identified from the phase diagram. Changes of crystal size and morphology of ZIF-7 and ZIF-62 in terms of batch composition and synthesis temperature were studied by SEM and different trends were observed for the two ZIFs. Thermogravimetric analysis (TGA) and in situ XRPD showed that ZIF-62 possesses a similar high thermal stability as ZIF-7.