Synthesis And Characterization Of Nanoscale ZIFs With Well-controllable Structure

Zeolitic imidazolate frameworks (ZIFs) are a new type of porous material and have properties similar to inorganic materials zeolite, which are physically and chemically stable and their molecular structures are designable. Nanoscale ZIFs have potential applications in catalysis, nonlinear optics and drug delivery.The conventional solvent method was firstly used to synthesize ZIF-8 and ZIF-67 at room temperature, and they were characterized by PXRD, SEM, TG and BET adsorption. The size of crystal particles synthesized in water are large and have uneven distribution (particle size of ZIF-8 is 120±61nm), and those synthesized in methanol are smaller and have more uniform distribution (particle size of ZIF-8 is 55.4±7.3 nm). Besides, the ZIFs synthesized in methanol have lager BET surface area and micropore volume. In the next, the nanoscale ZIF-8 and ZIF-67 crystals were synthesized using the reverse microemulsion method (MEM). The size of crystal particles can be decreased significantly and the particle size distribution is narrow (particle size of ZIF-8 is 2.3±0.4 nm, the particle size of ZIF-67 is 2.7±0.5 nm). The surface area and micropore volume of ZIFs synthesized in MEM are comparable to those synthesized in methanol. The results of DLS characterization revealed that the sizes of crystals by MEM were less than the corresponding reverse microemulsion droplets, which showed that the droplets limited the ZIF crystals growth and aggregation. It was also shown that improving the value of W (the molar ratio of water to CTAB) could increase the diameter of water droplets. When the value of W increased from 10 to 20, ZIF crystal particle size increased from 1.7 nm to 3.1 nm. In addition, when the value of W increased to 30, the crystals changed from spherical to linear shape. Although the similar results can be achieved by increasing the reactants concentration, but the effect was not as significant as W values.The effect of reaction time on ZIF size was found to be minimum among all influencing factors.