Controllable Synthesis And Properties Of TiO₂ Nanostructures

As an important wide-band-gap semiconductor, TiO2 exhibits excellent performance in environmental protection, gas sensors, and lithium-ion batteries due to its unique physical and chemical properties. In this dissertation, TiO2 nanorods, core-shell nanospheres and microspheres have been prepared through controlling hydrolysis rate and concentration of Ti4+ ions by hydrothermal approaches and their photocatalytic and electrochemical performances have been investigated. The main points have been summarized as follows:1. Different TiO2 nanostructures have been hydrothermally prepared through controlling hydrolysis and nucleation rate of Ti4+ ions by urea and H2O2 in (NH4)2 TiFe aqueous solution. Anatase TiO2 nanorods with diameters of 10-30 nm and lengths up to 300-500 nm were evolved from the intermediate monoclinic H2Ti5O11·3H2O in the presence of H2O2 and urea whereas TiO2 core-shell nanospheres with diameters of 300-500 nm were obtained with the sole assistance of urea via Ostwald ripening effect and TiO2 microspheres with diameters of about 1-2 μm were formed in the presence of only H2O2. Photocatalytic degradation of Rhodamine B (RhB) has been used to evaluate their activities. The results indicate that the anatase TiO2 nanorods have superior photocatalytic efficiency to the core-shell nanospheres and microspheres counterparts owing to their larger specific surface area and higher yield of ·OH radicals. This work not only offers a simple and promising route to controllable synthesis of various TiO2 architectures, but also provides a new insight for improving photocatalytic performance of TiO2 through morphological engineering, which will expect potential applications in environmental remediation.2. TiO2 core-shell nanostructures with diameters of 500-600 nm have been prepared hydrothermally through controlling the concentration of Ti4+ ions in the presence of H2O2 and urea. The formation mechanism of the TiO2 core-shell nanostructures were investigated by changing the reaction time and concentration of Ti4+. The results indicate TiO2 core-shell nanostructures are formed under the control of hydrolysis rate of Ti4+ ions and "Ostwald ripening". Lithium storage performance of TiO2 core-shell nanosturctures as electrodes in lithium-ion batteries have been investigated. The results indicate that compared with commercial TiO2 nanoparticles, anatase TiO2 core-shell nanosturctures have larger specific surface area, good dispersion, unique porous structures and excellent structural stability, which shorten Li+ diffusion distance and increase the contact area with the electrolyte. Thus, they exhibit a superior rate capability and cycling performance. TiO2 core-shell nanostructures can deliver a discharge capacity of 344 and 72 mAh g-1 at 0.1 C and 10 C rates. Moreover, TiO2 core-shell nanostructures deliver a discharge capacity of 140 mAh g-1 at 1 C after 100 cycles.