Synthesis of nanoparticles of zeolitic imidazolate framework ZIF-94 using inorganic deprotonators

A novel synthesis process of ZIF-94 (also known as SIM-1) is developed for particle size tuning, using either NaOH or NH4OH as a deprotonator. ZIF-94 originate from MOFs and have several advantages over traditional porous materials, in terms of their chemistry, structure and applications as catalysts, adsorbents, biocides and membrane materials. The existing synthesis process for ZIF-94 at a scale-up level produces particles of approximately 250 nm in size; an even smaller size is expected to result in an even better gas separation performance and catalytic activity. In this study, it was found that NaOH results in ZIF-94 particles with well-defined crystal structures, while in the case of NH4OH, the particles agglomerate to produce random shaped bigger particles. The optimum base to metal ratio was found to be 2 : 1 (NaOH : Zn), which shows a compromise between the particle size (114 ± 3 nm) and BET specific surface area (254 ± 4 m2 g−1). Furthermore, the synthesized nanoparticles underwent thorough characterization by XRD, TGA, N2 adsorption and electron microscopy revealing the lowest SEM average particle size of 84 ± 3 nm.