| dc.description.abstract | Metal-organic Frameworks (MOFs) are one of the most exciting classes of chemical structures to be discovered in the past decade. Because of their high surface area and thermal stability, MOFs has great behavior in catalysis, drug delivery, gas storage, and molecular separation. MOFs consist of metal nodes and organic linkers, which are connected by coordinate bond. Electrons provided from organic linkers will occupy the empty orbitals from metal atoms to form a strong covalent bond. Especially the MOFs contain zirconium-oxygen bonds, exhibit outstanding thermal and chemical stability. For example, UiO-66, UiO-67, MOF-801, are composed by zirconium cluster and dicarboxylic acid, such as terephthalic acid, biphenyl-4,4′-dicarboxylic acid, and fumaric acid, exhibit excellent thermal and chemical stabilities. However, conventional methods for obtaining MOF materials require a lot of time, organic solvent under high temperatures. Due to our lab utilizes mechanochemistry to synthesize UiO-66-F4 in short time and reduce the solvent cost dramatically. With this concept, we try to synthesize more and more MOFs by this method, meanwhile, the derives of UiO-66 are our first target.
To synthesize MOFs with mechanochemistry, the metal reactant must be changed. Traditionally, we synthesize MOFs with metal salts such as ZrCl4, and ZrOCl2. These metal salts easily dissolve into the organic solvent such as dimethylformamide (DMF) and Dimethylsulfoxide (DMSO). However, when the reactants in the reaction grinding can, there is only little solvent inside, so we have to use zirconium cluster to synthesize the zirconium organic frameworks. Zirconium clusters are synthesized with zirconium propoxide and monoprotic acids such as methacrylic acid and acetic acid. These two clusters are used in my experiments and I successfully synthesize UiO-66 and UiO-67 with these clusters. However, the mechanism of mechanochemistry is the key point we wonder. So I synthesize zirconium-MOFs with different conditions, I changed pH values, solvent volumes, and clusters, to figure out what make MOFs crystallized successfully in the reaction. At last, I found that suitable reaction speed is the key point to synthesize the MOFs. In the basic condition, the dissociation of organic linkers will be too fast to form crystal structures, most reactants will form the amorphous products. In contrast, when the organic linkers in acidic environments the proton will not dissociate easily, and the reaction will not progress, neither. In the end, we exploit this concept to synthesize MOF-801 with mechanochemistry successfully and hope the experiences can be utilized in the future.
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