Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) (5 mmol) and
2-methylimidazole (mIm) (40 mmol) were dissolved in
separate 100 mL portions of methanol. The two clear solutions
were combined and stirred rapidly for 1 h, during which time
the combined solution became cloudy due to the precipitation
of nanoparticles (NPs) of ZIF-8. The ZIF-8 colloid was then
separated from the solution by three cycles of centrifugation at
14 000 rpm for 15 min and resuspension of the nanoparticles in
ethanol. The final suspension was stored for use for up to 3
weeks. No sedimentation was observed during this time. For
powder X-ray diffraction (pXRD) analysis, the solvent was
removed using rotary evaporation, and the product was further
dried at room temperature in a desiccator with reduced
pressure.