Synthesis And Properties Of Fe₃O₄-based Multifunctional Core-shell Nanoparticles

Magnetite (Fe3O4) nanomaterials have been widely applied in the fields of biomedical engineering and magnetic recording, due to their superparamagnetic properties resulted from the small size. Because of their facilities in practical applications, magnetite nanocrystals are usually integrated with other functional materials (e.g., luminescent materials and photocatalysts) to form multifunctional nanocomposites. Owing to the structural stability and integrity, core-shell configuration of nanomaterials has been the research focus in the development of multifunctional nanomaterials. In this dissertation, we discuss the synthesis and properties of two kinds of core-shell nanocomposites, i.e., porous Fe3O4@Y2O3:Ln (Ln=Eu, Yb/Er) magnetic-luminescent nanoparticles and Fe3O4@TiO2magnetic nanophotocatalysts.First, we present a facile route to prepare magnetic-luminescent bifunctional nanoparticles. Through using carbon-coated Fe3O4nanoparticles derived from carbonized ferrocene as templates, we have obtained porous magnetic-luminescent Fe3O4@Y2O3:Ln (Ln=Eu, Yb/Er) nanoparticles. It is found that carbon-coated Fe3O4(Fe3O4@C) not only offer a magnetic core but also provide a good depositing surface to establish a uniform layer of Y2O3precursor. After removal of the templates, the core-shell nanoparticles exhibit a porous nanostructure. N2adsorption-desorption isotherms reveals that these porous bifunctional nanoparticles possess a large surface area of32m2/g. After being doped with different lanthanide ions, these core-shell nanoparticles can exhibit various down-and up-conversion emissions. Magnetic measurements also indicate that these bifunctional nanoparticles display superparamagnetic behavior and high magnetization at room temperature. Such core-shell nanoparticles with superparamagnetic characteristic, good luminescent properties and porous nanostructure, may find concrete applications in future biomedical engineering such as simultaneous detection and separation of biomolecules, and drug delivery.Second, we demonstrate a facile method to synthesize Fe3O4@TiO2nanoparticles with a small size and well-defined yolk-shell nanostructure. Through using tiny Fe3O4@SiO2nanoparticles as templates accompanying a slow hydrolytic titanium precursor, we succeed in coating a thin TiO2layer on the Fe3O4@SiO2nanoparticles, keeping the whole particle size below50nm. More interestingly, most of the SiO2layer can be simultaneously etched off during the TiO2coating, producing an obvious interstitial void in each Fe3O4@TiO2nanoparticles. The left thin SiO2layer can still efficiently prevent photodissolution between the interior Fe3O4core and the outer TiO2layer. The prepared product has been characterized by transmission electron microscopy (TEM), X-Ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and vibrating sample magnetometer (VSM), and its formation mechanism is proposed. Thickness of the TiO2shell can be tailored, and its effect on the photocatalytic activity has also been investigated. These small yolk-shell Fe3O4@TiO2nanocatalysts are expected to be applied in a variety of fields due to its low density, high surface area, superparamagnetic behavior and good photocatalytic activity.