Controllable Preparation, Characterization And Catalytic Application Of Nanoparticles With Core-shell Structure

Functional nanomaterials, like magnetic, plasmonic and semiconductor nanomaterials, have been paid extensive attention due to their unique physical and chemical properties. Magnetic nanomaterials nanoparticles (NPs) usually exhibit strong magnetic resonance under an external magnetic field and can be used in the fields of medical diagnosis and treatment, magnetic separation. Plasmonic nanomaterials are widely used in the fields of bio-medicine, catalysis and optics due to their unique surface plasmon resonance properties. The noble metal NPs are the classic representatives of the plasmonic nanomaterials. For semiconductor nanomaterials, due to their excellent photoelectric properties, they are often applicated in photocatalysis, solar cells and so on. For composite nanomaterials based on above material, enhanced properties can be acheived.More recently, controllable synthesis of bifunctional hybrid structures based on the three kinds of functional nanomaterials has attracted considerable interests for their greatly potential applications, such as bimetallic nanostructures, magnetic-based noble metals or semiconductors, metal/semiconductor hybrid nanostructures. This dissertation focuses on the controllable synthesis, characterization and application of core-shell nanoparticles basing on the three kinds of functional nanomaterials.(1) A novel and versatile approach for the preparation of PS-Ag composites is presented for the first time. In this method, the modified aldehyde group-terminal solid supports are employed to reduce Ag[(NH3)2]+ions. The in-situ reduced silver nucleus are directly coated on the surfaces of the PS spheres and then used as both seeds and catalysts for self-catalytic growth of Ag NPs. In this reaction, no additional reduction and protective agents are needed. Moreover, the size of the Ag NPs can be tuned by varying the concentration of the Ag[(NH3)2]+ions and the reaction time. Such a synthesis method would benefit the preparations and further applications of functional materials in the near future.The PS supported Ag@AuAg nanocomposites were fabricated by a seed growth route. The coating status of PS-Ag@AgAu nanocomposites is highly dependent on the amount of Au precursors, which also affects the optical properties of the resultant samples. The prepared nanocomposites show tunable catalytic activities. Under the same size and coverage of metal NPs, the catalytic activity of the bimetallic nanocomposites is superior to that of the monometallic Ag or Au nanocomposites, which is mainly attributed to the ligand and strain effects between Ag and Au atoms caused by the special core-alloy shell structure of the bimetallic NPs. Such type of nanocomposites exhibited excellent catalytic activities with good reproducibility and stability, which enable them to possess huge potential in the future practical application in catalytic technology.(2) Spindle-like ?-Fe2O3NPs were fabricated by forced hydrolysis of FeCl3in the presence of PO43-anions. The morphologies and the structures of the NPs annealed at different tempratures in H2were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), field emission scanning electron microscopy (FSEM). The results showed that the as-prepared ?-Fe2O3NPs were transformed into spindle-like Fe3O4NPs with mesoporous structure at350?. In addition, the obtained Fe3O4NPs possessed a high saturation magnetization of85.18emu·g-1. Owning to its excellent magnetic separation property and special mesoporous structure, the as-obtained Fe3O4NPs may have a great potential applications in the future.?-Fe2O3/Ag nanocomposites were fabricated via seed growth method; using the above prepared ?-Fe2O3NPs as seed and depositing Ag NPs on the surfaces of the ?-Fe203NPs. The size of the Ag NPs can be controlled by prolonging the reaction time. The photocatalytic properties of composites were studied by using the ultraviolet and visible light as excitation light source, respectively. The results showed that the photocatalytic activity of the composites were significantly enhanced comparing with the ?-Fe2O3NPs. This is mainly due to the plasmon-induced transfer of the electrons from noble metal to the conduction band of the semiconductors. Based on this, further investigation was attempted to study the size-depandent plasmon resonance effect of Ag NPs on the photocatalytic activities of the composites. The results showed that the composites possessed higher photocatalytic than that of the ?-Fe2O3NPs. Moreover, the photocatalytic activity increased with the increase of the size of the Ag NPs.(3) Core-shell y-Fe2O3@SnO2hollow nanoparticles (NPs) were synthesized by a seed-mediated hydrothermal method. Firstly, the y-Fe2O3hollow NPs were synthesized by the template-free method and then used as the cores for the growth of SnO2shells. The thickness of the shell can be simply tailored by controlling the reaction time. Various techniques, including SEM, XRD, TEM and HRTEM, were employed to investigate the morphology, structure and formation process of the special core-shell hollow structures. The combination of magnetic semiconductor (y-Fe2O3) and wide band-gap semiconductor (SnO2) endowed them great potential to be used as recyclable photocatalysts. Experiments on photo-degradation of Rhodamin B (RhB) dyes in the presence of the samples showed that the hybrid structures possessed higher photocatalytic activities than the monomer structures of SnO2and y-Fe2O3materials indicating strong coupling enhancement effect between the wide and narrow band-gap semiconductors. Moreover, the gas sensing tests of the y-Fe2O3@SnO2hollow NPs revealed that the samples exhibited fast response and recovery rates, which enable them to be promising materials for gas sensors.(4) Au/SnO2core-shell nanoparticles were prepared via a seed-mediated method. In this process, Au nanorods were used as seeds and SnO2nanoparticles were deposited on the surfaces of them. It had been found that the thickness of the SnO2shells could be tuned by changing the concentritions of the CTAB in the reaction systems. The higher of the concentration of the CTAB, the thinner of the thickness of the SnO2shell. Moreover, the SnO2shell was porous, which endowed the core-shell nanoparticles possess a high specific surface area. The photocatalytic activities of the nanoparticles with different thickness of shell were measured and made a comparison with the commercial SnO2nanoparticles. The results showed that the core-shell nanoparticles possessed much higher activities for the photo-degradation of RhB dye, which might well be attributed to the SPR-induced the enhancement of the electric field nearby the SnO2shell and the charge transfer from Au nanorod to SnO2shell.