Preparation And Performance Of Shape-Controlled Silica-Based Core-Shell Materials

Micro-and nano-materials with core-shell structures show better characteristics than single-component and conventional composite materials, and have extensive potential applications in heterogeneous catalysis. Thus, much attention in material science and chemical engineering has been focused on structure design, preparation and optimization of core-shell materials. At present, structure and size of core-shell materials can be well controlled while control of shape of shape and their continuous preparation remain a challenge. In the view of above, different shape-controlled core-shell materials were prepared and continuous preparation method was developed in this thesis based on silica, and their catalytic and electrochemical performance was detailed studied. This work could be regarded as basic researches for controllable preparation and application expansion of core-shell materials.Aerosol-based spray drying method was employed to prepare Au@TiO2/SiO2 core-shell materials to continuously prepare core-shell materials. And they were applied in 4-nitrophenol (4-NP) catalytic reduction. The materials have spherical shape, TiO2 fibers on the surface and Au nanoparticles coated in TiO2/SiO2 hollow skeleton. Conversion of 4-NP reduction was up to 95% when molar ratio of 4-NP and NaBH4 was 500:1, content of catalyst was 0.15 mg/mL at 20?. Catalytic performance of the materials did not decrease after cycling and 4-NP reduction was up to 90% after 8 cycles.To achieve well controlling of shape and structure of core-shell materials with better reusability, magentic iron oxide@SiO2-Au@C core-shell materials with pseudocube, ellipsoid and peanut shapes were preparaed with hard-template method and applied in 4-NP catalytic reduction. Their calcination temperature and Au loading content was also optimized. The materials have clear shapes, uniform sizes and core-shell structure. Highly monodispersed Au particles with size of ?6 nm were scattered between silica and carbon layers. Superparamagnetic property of the materials was from magnetic iron oxide which in-situ converted from ?-Fe203 in calcination. Conversion of 4-NP reduction was up to 90% when molar ratio of 4-NP and NaBH4 was 500:1, content of catalyst was 0.15 mg/mL at 20?. The materials could be recycled by external magnetic field. Catalytic performance did not decrease after 7 cycles. Magnetic properties and catalytic performance of the materials were maintained after calcination at 700?.To expand the application of shape-controlled template method, dual-layer hollow NiS electrode material with pseudocube, ellipsoid and peanut shapes were preparaed by hydrothermal method with silica as templates and their instrinsic electrochemical performance was evaluated. The materials have uniform sizes and clear dual-layer hollow structure. Nickel silicate and nickel sulfide phases existed at the same time. The materials have pseudocapacitance properties with good reversibility. Peak potentials of oxidization and reduction was 0.27 and 0.15 V at low scanning rate (10 mV/s). Ellipsoid-like materials have the best specific capacitance up to 206 F/g at current density of 1 A/g.