Optimized Synthesis Of Zeolitic Imidazolate Frameworks And Their Adsorption Properties

Zeolitic imidazolate frameworks are a subclass of metal-organic frameworks, which possess the same topologies as those that can be found in zeolites. ZIFs have the advantages of MOFs such as huge surface area, uniform aperture, adjustable pore size, diverse structure topologies, and tunable functionalities etc. Compared to other types of metal-organic framework materials, ZIFs exhibit exceptionally high hydrothermal, chemical, and thermal stability. Hence, ZIFs have attracted increasing attention in many applications such as gas storage, separation, catalysis, and chemical sensors. The research of this thesis was focused on the optimized synthesis of ZIFs and investigating their adsorption properties. The main results are summarized as follows:1. Optimal synthesis of ZIF-7. By adding the excessive benzimidazole ligand or the different modulating ligands, ZIF-7with uniform morphology and particle size was synthesized. The results show that the crystal size of ZIF-7decreases with increasing the added amount of the ligand. When CH3COONa is used as a modulating ligand, the morphology and size of the resulting ZIF-7crystals is not uniform. On the other hand, when diethylamine (DEA) is used as a modulating ligand, ZIF-7crystals with hexagonal prism in morphology and uniform size can be synthesized. The results from the adsorption isotherms of CO2indicate that the ZIF-7sample synthesized by DEA as the modulating ligand has a high adsorption capacity while the sample synthesized using the excessive ligand has a relatively low adsorption capacity due to some pores blocked by the excessive ligand.2. Adsorption and separation by ZIF-7. The adsorption isotherms of CO2, N2O, C2H4, and C2H6on ZIF-7were measured. Due to the gate-opening effects of ZIF-7, the adsorption isotherms show that the corresponding threshold pressures of the adsorptives control their uptakes and the desorption of the adsorbed molecules. Based on the difference in the threshold pressure between CO2and N2O, their mixture separation was studied in detail by means of a breakthrough-column technique, and the results show that CO2and N2O mixtures can be separated by ZIF-7. 3. Optimal synthesis of ZIF-8. By using different solvents, ZIF-8crystals with uniform morphology and size were synthesized. Using methanol as the solvent, ZIF-8nanocrystals were formed and the crystal size decreased with increasing the dosage of diethylamine added in the synthesis solution. When water was used as the solvent, ZIF-8with pore-opening structure was synthesized as well. The developed synthesis method overcomes the problem that ZIF-8synthesized in an aqueous solution cannot have a pore-opening structure. Moreover the method has an environmentally friendly advantage.4. Synthesis of CuCl/ZIF-8and its application in the separation of C3H6/C3H8. The monolayer dispersion of CuCl on ZIF-8to make CuCl/ZIF-8adsorbent for the selective adsorption of C3H6and C3H8mixtures was preliminarily investigated. The results show that Cu+can be reduced to metallic Cu and the framework of ZIF-8is damaged during the monolayer dispersion under the applied preparation conditions.