Tio <sub> 2 </ Sub> Preparation And Properties Of The Matrix Composite Oxide

In this dissertation, monodisperse spherical SiO₂ and TiO₂ particles, TiO₂/SiO₂ core/shell particles and Li-Ti-O composites have been synthesized, respectively, of which photocatalytic activities and electrochemical performances have been characterized, accordingly. The details are presented as follows.Firstly, monodisperse spherical SiO₂ particles were prepared by a sol-gel method in the ultrasonic bath. The results show that monodisperse SiO₂ particles with diameters 120～150 nm could be obtained at 45℃with initial molar concentrations of tetraethylortho silicate, ammonia and deionized water of 0.3 mol/L, 2.5 mol/L and 15 mol/L, respectively.Secondly, monodisperse spherical TiO₂ particles were synthesized via a modified sol-gel approach assisted by ultrasonic treatment. The FTIR pattern indicates that the resulting precursors are mainly composed of titania glycolates.Thirdly, TiO₂/SiO₂ core/shell particles were prepared through an in-situ hydrolysis of tetraethylortho silicate under ultrasonic irradiation by employing nano-sized TiO₂ colloids as precursors. The results indicate that the well dispersed TiO₂/SiO₂ core/shell particles could be obtained when the molar ratios of titanium dioxide, tetraethylortho silicate, ammonia and deionized water are 1:40:2:200, the synthetic temperature is 45℃, and the calcination temperature is 600℃. XRD and TEM tests demonstrate that the TiO₂/SiO₂ composites are constructed of anatase TiO₂ nanoparticles coated with a layer of amorphous SiO₂ and have a size around 200 nm.Further, Li-Ti-O composites were prepared via a citric acid complexing sol-gel route. The effects of reaction conditions on the crystal structures and morphologies of the products were also investigated.For the photocatalytic activities, the as-prepared monodisperse TiO₂ particles and TiO₂/SiO₂ core/shell particles were employed as photocatalysts in the decomposition of methyl orange solution under UV irradiation, respectively. The results show that none of the two decomposition reactions complies with the first-order reaction, whereas more complicated kinetic processes are observed. The TiO₂/SiO₂ core/shell particles exhibit better photocatalytic activities than the monodisperse TiO₂ particles.To investigate the electrochemical performances, the as-prepared three kinds of samples were employed as anode active materials for lithium-ion batteries, respectively, in which lithium foils were used as the counter electrode and reference electrode, respectively. The results indicate that the Li-Ti-O based electrode exhibits the best stability while the TiO₂ based electrode exhibits the worst. The potential plateaus for discharging and charging of the TiO₂ based electrode were at ca. 1.3 V and 2.25 V, and the potential plateaus for discharging and charging of the TiO₂/SiO₂ based electrode were at around 0.2 V and 0.75 V, respectively. However, the potential plateaus for discharging and charging of the Li-Ti-O based electrode were at about 1.45 V and 1.62 V, respectively. Therefore, it is reasonable to state that the coating of SiO₂ on TiO₂ not only influences on its surface structures but debases the potential plateaus. Meanwhile, the Li-Ti-O composites improve the capacity of the TiO₂ based electrode.