Preparation And Catalytic Study Of The Core-Shell Nanostructure

The core-shell nanostructures represent a class of nanocomposites with a distinctive core@shell configuration and can be broadly defined as an ordered assembly system in which one nanomaterial（inner material） is covered by another nanomaterial（outer layer material） via chemical bond or other interactions. There are a variety of core-shell nanostructures, both classic core-shell nanostructures and yolk-shell nanostructures are included in it. Their tailorability and functionality in both the cores and shells can endow the core-shell nanostructures with many new functions which could not been obtained from single nanomaterial, thus rendering them attractive for applications in catalysis, biomedical, pharmaceutical, optics and other fields. So, how to design and prepare multifunctional core-shell nanostructures is the key to improve the performance of the core-shell nanostructures materials. Herein, core-shell Ag@TiO2@Pt nanostructures and yolkshell MgO@NiTiO3 nanostructures were prepared by simple chemical method, scanning electron microscopy（SEM）, transmission electron microscopy（TEM）, X-ray diffraction（XRD） and other characterization methods were systematically studied on the as-obtained nanomaterials. The results were as follow:1. The Ag@TiO₂@Pt core-shell nanostructures were successfully fabricated via a simple hydrothermal process followed by a photochemical reduction under xenon lamp irradiation. Large surface area, small size of the Pt nanoparticles endows the core-shell nanostructures excellent catalytic properties. The synthesis procedure of the Ag@TiO2@Pt core-shell nanostructures involves two processes, firstly, prepared Ag@TiO2 nanostructures via hydrothermal approach, the shell TiO2 nanosheets "growth" in the core Ag nanowire surface vertically, this structure with a large surface area provides the basis for the next step in situ loading Pt nanoparticles. Secondly, deposited of Pt nanoparticles on TiO2 ultrathin nanosheets to form Ag@TiO2@Pt core-shell nanocomposite via photochemical reduction. To investigate the morphology and composition evolution of the Ag@TiO2@Pt core-shell nanostructures, the influence of reaction parameters such as Ag:Ti molar ratio, reaction temperature and the concentration of platinum source were investigated. The catalytic efficiency of the Ag@TiO2@Pt core-shell nanocomposites was confirmed by the hydrogenation of p-nitrophenol into p-aminophenol with NaBH4 as reducing agent in aqueous phase. The conversion rate of p-nitrophenol was yielded as high as ～94% for 12 min under ambient atmosphere and room temperature. The reuse result suggested that they also possessed high stability.2. The MgO@NiTiO₃ yolk-shell nanostructures were successfully prepared via a convenient solvent reaction followed by calcination at 600 oC for 3 h in air. The synthesis procedure of the yolk-shell MgO@NiTiO3 nanocomposite involves four processes:（1） preparation of template MgCO3 nanorods;（2） preparation of MgCO3@ NiCO3 core-shell nanocomposites via metathesis reaction;（3） deposition of amorphous TiO2 on the surface of MgCO3@ NiCO3 nanocomposites via a sol-gel approach to prepare MgCO3@ NiCO3@TiO2 nanocomposites;（4） preparation of the MgO@NiTiO3 yolk-shell nanostructures through calcination process. The shell component can be regulated and controlled through changing the amount of the titanium source, and changing the reaction time can achieve a controllable core. Nickel titanate（NiTiO3） shell possess excellent photoresponse in the visible light region extends nanocomposite light response range, the core MgO particles enhance the stability of the nanostructure, the void increases the surface area of yolk-shell MgO @ NiTiO3 nanocomposites. Yolk-shell MgO @ NiTiO3 nanocomposites exhibited excellent photocatalytic activity in the degradation of methylene blue under visible light irradiation. The reuse result suggested that they also possessed high stability.