Preration And Applications Of Cage-like Oxide Nanoparticles

Because of the advantages of large specific surface area, abundant surface active sites and low density, the cage-like nanoparticles with hollow structure have been applied as electrode materials for Lithium-ion battery, nanocatalyst, adsorbent and drug delivery. Researchers have paid close attention to preparing hollow nanocages with excellent properties using simple and efficient ways. The objective of this dissertation is to synthesize cage-like nanoparticles with different compositions and structures using the Prussian blue analogues Co3[Co(CN)6]2nanoparticles as templates. The obtained nanoparticles have been evaluated their lithium storage and catalysis performance. The reason behind their excellent properties were also investigated. Furthermore, the application of iron oxide/carbon composite with hollow structures in Lithium-ion battery and adsorption has been studied. The details are as follows:1. Co3O4nanoparticles have been prepared by a facile strategy, which involves the thermal decomposition of nanoparticles of cobalt-based Prussian blue analogues at different temperatures. The nanoparticles prepared at450,550,650,750,850℃exhibited a high discharge capacity of800,970,828,854,651mAhg-1, respectively after30cycles at a current density of50mAg-1. The nanocages produced at550℃shows the highest lithium storage capacity. It is found that the nanocages display nano-size grains, hollow structure, porous shell and large specific surface area. At the temperature higher than650℃, the samples with larger grains, better crystalline and lower specific surface area can be obtained. It is found that the size, crystallinity, morphology of nanoparticles have different effects on electrochemical performance. Better crystallinity is able to enhance the initial discharge capacity, while porous structure can reduce the irreversible loss. Therefore, the optimal size, crystallinity and cage morphology are suggested to be responsible for the improved lithium storage capacity of the sample prepared at550℃. The as-prepared Co3O4nanoparticles also have a potential application as anode material for Li-ion batteries due to their simple synthesis method and large capacity.2. Herein, hollow porous SiO2nanocubes have been prepared via a two-step hard-template process and evaluated as electrode materials for lithium-ion batteries. The hollow porous SiO2nanocubes exhibited a reversible capacity of919mAh g-1over30cycles. The reasonable property could be attributed to the unique hollow nanostructure with large volume interior and numerous crevices in the shell, which could accommodate the volume change and alleviate the structural strain during Li ions’insertion and extraction, as well as allow rapid access of Li ions during charge/discharge cycling. It is found that the formation of irreversible or reversible lithium silicates in the anodes determines the capacity of a deep-cycle battery. Fast transportation of Li ions in hollow porous SiO2nanocubes is beneficial to the formation of Li2O and Si, contributing to the high reversible capacity.3. Rattle-type Co3O4@SiO2and Co@SiO2nanoparticles were prepared via thermal decomposition of Co3[Co(CN)6]2@SiO2core-shell nanoparticles under air and N2. The uniform Co3[Co(CN)6]2nanocubes were coated with porous silica and then calcined at high temperature to generate large amount of Co3O4and Co nanocrystals in a cube-shape silica nanocapsule via thermal decomposition of a Co3[Co(CN)6]2nanocubic. The Co3O4@SiO2nanorattles exhibit excellent catalytic activity for CO oxidation, the CO conversion rate reaches100%at150℃. It is suggested that the Co3O4nanocrystals with clean surfaces were produced via this approach; moreover, porous silica shell could protect Co3O4nanocrystals from external contamination, which make these novel nanostructures exhibit a remarkable catalytic performance. Co@SiO2nanorattles with the presence of a mixture of hcp-Co and fcc-Co phases were prepared as a substitute of noble metal nanocatalyst. The nanorattles exhibit both superior catalytic activity and high stability for the reduction of p-nitrophenol. The reduction rate nearly follows pseudo-first-order kinetics and the reaction rate constant is as high as0.815min-1, and then maintained at0.565min-1even after storing for one month, which is higher than that reported for noble metal nanocatalysts.4. Ferrocene was decomposed in vacuum and supercritical CO2to prepare discontinuous Fe2O3nanoparticles wrapped multi-walled carbon nanotubes and urchin-like carbon coated Fe3O4microparticles. When used as the anode in a Li-ion battery, the hybrid material of Fe2O3nanoparticles and carbon nanotube (70.32wt%carbon nanotubes,29.68wt%Fe2O3) showed a reversible discharge capacity of515mAh g-1after50cycles at a density of100mA g-1and the capacity based on Fe2O3nanoparticles was calculated as1147mAh g-1. Three factors are responsibile for the superior performance:(1) The hollow interiors of MWCNTs provide enough spaces for the accommodation of large volume expansion of inner Fe2O3nanoparticles, which can improving the stability of electrode;(2) The MWCNTs increase the overall conductivity of the anode;(3) A stable solid electrolyte interface film formed on the surface of MWCNTs may reduce capacity fading. The urchin-like carbon coated microparticles also exhibit both superhydrophobicity and superparamagnetism due to the surface polar groups and small grain of Fe3O4, showing a contact angle of152°and a saturation magnetization of19.4emu g-1, respectively. When such particles were deposited on a sponge, the sponge was changed into an absorbing material with superhydrophobicity and superparamagnetism. The modified sponge not only displays excellent adsorption property, but also can be recycled using an external magnetic field.