Controlled Synthesis Of TiO₂Nanocrystals And Their Photoelectric Properties

Titanium dioxide （TiO₂） nanocrystals have been subjected to extensive research inthe fields of photocatalysis, gas sensor, solar cells, and lithium ion batteries, due to theirlow cost, photostability, and nontoxicity. Recently, it has been demonstrated thatcontrolled synthesis of TiO₂nanocrystals enables to enhance their photocatalytic andelectrochemical properties. In this thesis, controlled synthesis of octahedral anataseTiO₂has been performed by a simple hydrazine-mediated solvothermal approach.Various reaction conditions were investigated in detail, such as reaction time,temperature, titanium sources, and reaction media. Using different nitrogen sources andtitanium sources, spindle-like TiO₂nanostructures and TiO₂nanorods can be obtained.The TiO₂samples were characterized with XRD, Raman, SEM, TEM, FT-IR, XPS, andUV/Vis techniques, and further tested as a candidate in photocatalysis and in lithium ionbattery. The results show that:（1） Using titanium（IV） sulfate and hydrazine hydrate with concentration more than45%as the starting materials, anatase TiO₂octahedra can be obtained with high yield,and good crystallinity, under the reaction conditions at200°C for36h.（2） Using ammonia instead of hydrazine hydrate and/or titanium tetrachlorideinstead of titanium sulfate, spindle-like TiO₂nanocrystals and TiO₂nanorods can beacquired at200°C for36h, respectively.（3） TiO₂octahedra of pure antase phase have good crystallinity; spindle-like TiO₂nanocrystals have a A/R binary structure; and TiO₂nanorods have a A/B/R ternarystructure.（4） Both the octahedra and the spindles of anatase phase have strong absorbance inthe UV/Vis spectrum ranging from200to380nm, yet the bandgap of the two samplesdiffers from each other. This result is evidence that the size and morphology ofnanostructures have an important effect on their physicochemical properties.（5） In photocatalysis experiments, methyl orange （MO） was used as a probe dye toevaluate the photoactivity of the catalysts. With respect to the decomposition of MO inaqueous solution without any external oxidation and reduction radical-generatingsources, the octahedral, spindles, and nanorods show higher photoactivity compared toP25.（6） Lithium ion batteries （LIBS） were constructed to evaluate the electrochemical properties of the TiO₂samples. Cyclic voltammograms test results indicate thatoctahedral TiO₂nanocrystals have a stable structure to provide a good environment forintercalation/detercalation of lithium ions. Constant current charge-discharge test resultsindicate that the above three kinds of TiO₂/LIBS have a good ability for storing lithiumions, respectively. Therefore, the as-prepared TiO₂nanostructures with specialmorphology have great potentials in the fields of photocatalysis and lithium ionbatteries.