| In the past decades, Fe3O4 microspheres have been widely used in cells isolated, genetic engineering, information storage and catalyst field owing to their unique physical and chemical properties. It has been well-known that the properties of Fe3O4 microspheres are closely related to their size, crystalline and surface chemical structure. Therefore, it is crucial to prepare Fe3O4 microspheres and their composite materials with uniform size, high crystallinity, desired surface properties, and easily to be functionalized. In this thesis, Fe3O4 microspheres and their composite materials were successfully prepared, and their performance in the field of catalysis was investigated. The main contents and results are focused on the follows:1. In the presence of NaOH, Fe3O4 microsphere was prepared by using FeCl2.H2O as iron source, glycol as solvent without any surfactant under hydrothermal conditions. The control experiments were conducted to investigate the formation mechanism and morphology changes of Fe3O4 microspheres by XRD, SEM, TEM, MPMS and Physical and chemical adsorption of nitrogen analyzer. The results showed that Fe3O4 microspheres, which were assembled by the primary particles of less than 30nm, were size uniformity, highly crystalline, and superparamagnetic at room temperature. The growth mechanism of Fe3O4 microspheres may be like the follows:FeCl2 first generates the Fe(OH)2 complexes with ethylene glycol in the presence of NaOH in ethylene glycol. Then the complexes occurs disproportionation reaction generating Fe and Fe3O4. Fe converts into Fe3O4 with the increase of reaction temperature and reaction time.2. Inspired by mussel gland secretion of adhesion proteins, dopamine is chosen as the surface modification agent. A uniform polydopamine (PDA) layer, which has structure similar to that of the mussel adhesion protein, was deposited on the surface of Fe3O4 microspheres by self-polymerization of dopamine. The influence of reaction conditions on the thickness of the polydopamine coating layer, morphology and crystallinity of the products were characterized by IR, SEM, TEM. The results reveals that the thickness of coating layer increases with the increasing of mechanical agitation time and the amount of dopamine, whereas the increasing amplitude decreases as the mechanical agitation time and the amount of dopamine continue to extend. The crystallinity of the products becomes better and their morphology changes from rough surface spherical into smooth surface polygon with the increase of the calcination temperature.3. Silver loaded magnetic microspheres were obtained by adding the polydopamine coated Fe3O4 microspheres to the aqueous solution of silver nitrate at room temperature. Polydopamine acts as both adsorbent and reducing agent of Ag ions, resulting in the formation of Ag nanoparticles. The structure and morphology of products were characterized by TEM, SEM, XRD, EDS and so on. The results showed that Ag content in the product was improved with the increase of concentration of silver nitrate in the reaction solution.4. The reduction reaction between methyl orange and NaBH4 was chosen as a model reaction to investigate the catalytic activity and recycled magnetic properties of silver loaded magnetic microspheres. The results showed that silver loaded magnetic microspheres can be rapidly separated from the solution by adding an external magnetic field. The stabilizing and dispersion effect of polydopamine effectively prevents the silver nanoparticles from aggregation and running off from the supporter. The catalytic efficiency remains greater than 90% after recycling six times. The catalytic efficiency of the degradation is related to the reaction temperature, pH, catalyst dosage and concentration of NaBH4, whereas the Na2SO4 concentration had a little effect on the methyl orange degradation rate. |
PDF Full Text Request