Syntheses And Fluorescence Properties Of Nanocrystals Of Metal-Organic Frameworks

As a new class of multifunctional porous materials, metal-organic frameworks (MOFs) have attracted considerable interest, owing to not only their intriguing structural motifs but also their potential applications in gas storage, photonics, catalysis, medicine, selective guest adsorption and magnetic materials. More recently, synthesis of nanoscale MOFs (NMOFs) built up by metal ions and various polyfunctional organic ligands components at the molecular level has recently afforded a new class of highly tailorable hybrid nanomaterials. Scaling down these materials to the nano-regime has enabled their use in a broad range of applications including biomedical imaging, MRI contrast agents and catalysis. These results underscore the exciting opportunities of developing next-generation functional nanomaterials based on molecular components.Some traditional techniques, such as formation and precipitation of particles triggered by the introduction of a solvent into a solution of ligands, microemulsion techniques and solvothermal synthesis, are applied to prepare MOFs and NMOFs. In this dessertation, we present a morphology-controlled synthesis of NMOFs by using a template-assisted method for potential fluorescent sensing of nitroaromatic explosives. Actually, surfactants and polymers have been widely utilized as surface stabilizers and templates in the synthesis of nanoparticles. The presence of surfactant molecules during the formation of particles can decrease the surface energy, control the growth and shape of the particles, which is due to their binding to the nanoparticle surface.The main contents of this dessertation are as follows:1. Nanocrystals of two-dimensional (2-D) MOFs, Zn(BDC)·xH2O (x= 1-2) 1, [Dy2(BDC)3(H2O)4]n 2 and [Eu2(BDC)3(H2O)2]n 3, were synthesized at an ambient temperature and atmospheric pressure under different conditions. The structures were confirmed by powder X-ray diffraction (XRD) patterns. In addition, scan electron microscopy (SEM) and transmission electron microscopy (TEM) images of 1-3 reveal that size and shape of nanocrystals can betuned by varying the reaction time. 2. Fluoresent sensing of nitrobenzene,2-nitrotoluene,4-nitrotoluene, 2,4-dinitrotoluene and 2,6-dinitrotoluene to nanocrystals have been studied respectively. The results indicate that nanocrystals of MOFs 1,2 and 3 are highly sensitive to nitroaromatic compounds. The results may be helpful for designing novel fluorescence sensor for the sensing of explosives.3. We also present a morphology-controlled synthesis of NMOFs by using a polymer-assisted method. The results indicated that size and shape of nanocrystals can be tuned by varying the reaction time in the presence of polymer. The samples in this work exhibited strong blue solid state photoluminescence properties. The sensing of nitroaromatic compounds in an acetonitrile solution was quantitatively analyzed by a fluorescence spectrometric titration experiment. The experimental data suggest that the nanocrystals are highly sensitive to nitroaromatic compounds. This may be helpful for designing novel fluorescence sensor for the sensing of organic guests.