Studies On ZIF-8Synthesis By Nonpolar Solvent And The Effects Of Adding Organic Amines On ZIFs Synthesis

Zeolitic imidazolate frameworks (ZIFs) are a new subclass of metal-organic frameworks (MOFs) with zeolitic topology. So ZIFs have features of structural and functional diversity and high surface areas like MOFs. Meanwhile, in the structure of ZIFs, the metal ions are coordinated with nitrogen atoms in the ring of imidazole. The angle of M-IM-M is about145°, which is very close to the angle of Si-O-Si in the zeolites. Thus, ZIFs own high thermal stability similar to zeolites. Due to the excellent properties of ZIFs, they have extensive application prospects in many fields such as adsorption and seperation, catalysis, magnetism and so on. At present, scientists are devoting to the study of the synthesis and application of ZIFs.We have focused on the synthesis and rule study of ZIFs. ZIF-8was synthesized with nonpolar n-heptane and polar methanol and DMF by vapor-assisted conversion method. The crystallization processes of ZIF-8under different liquid phases (n-heptane, methanol, DMF) were studied. Then the effects of the molar ratios of zinc acetate/2-methylimidazole [Zn(OAc)2·2H2O/MIM], the reaction temperature, the reaction time and the dosage of liquid phases on the synthesis of ZIF-8were investigated. What’s more, we studied the effect of the addition of organic amines into the liquid phases on the synthesis of ZIFs. The main contents and results of this paper includes:1. We successfully synthesized pure ZIF-8by vapor-assisted conversion method with nonpolar n-heptane replacing polar methanol and DMF. In addition, the crystallization processes of ZIF-8under the three liquid phases were studied. It was found that the transformation rate from anhydrous zinc acetate and MIM to ZIF-8phase by n-heptane was obviously faster than that by methanol or DMF. The phenomenon may be attributed to two reasons:(1) the nonpolar property and hydrophobicity of n-heptane may contribute to the solid phase transformation from anhydrous zinc acetate and MIM to ZIF-8phase (zinc acetate and MIM are not easily dissolved in n-heptane);(2) the relative high volatility of n-heptane can relative easily generate enough vapor that triggers the solid phase transformation. Meanwhile, we found that the formation process of ZIF-8followed the Avrami equation:y=1-exp(—ktn), where k is scaling constant, n is the Avrami constant.2. The effects of different organic amines (triethylamine, ethylenediamine, n-butylamine) on the reaction between Zn(OAc)2·2H2O and MIM were studied by adding different amount of different organic amines into the liquid phases. The all obtained products were ZIF-8phase. But we found that the addition of the three organic amine can decrease the size of ZIF-8particles. By scanning electron microscope (SEM) characterization, we discovered that the morphology of ZIF-8was like ball by adding a certain amount of ethylenediamine. We conducted that ethylenediamine can be used to control the morphology of ZIF-8crystal.3. The effects of adding different amount of organic amines (triethylamine, ethylenediamine, n-butylamine) on the reaction between Zn(OAc)2·2H2O and imidazole (IM) were studied. We found that:(1) The phases of the reaction products may be different by adding different amount of organic amine into the same liquid phase;(2) The phases of the reaction products may be different by adding different kinds of organic amines into the same liquid phase. It suggested that the addition of different organic amines into the liquid phases has effects on the reaction between Zn(OAc)2-2H2O and IM.