Microwave-Solvothermal Synthesis of Various Polymorphs of Nanostructured TiO2 in Different Alcohol Media and Their Lithium Ion Storage Properties

The various polymorphs (anatase, rutile, and brookite) of TiO2 with different nanomorphologies have been synthesized by a facile microwave-assisted solvothermal process without surfactants, employing TiCl4 or TiCl3 as precursors in various alcohol (ethanol, propanol, butanol, and octanol) media. The samples have been characterized by X-ray diffraction (XRD), electron microscopy, and Brunauer-Emmett-Teller (BET) surface area analysis. The Ti/Cl ion concentration, reaction pH, and size of the alcohol molecule are found to control the morphology, crystal structure, and crystallite size of the TiO2 particles. Among the various TiO2 polymorphs synthesized, the rutile TiO2 spheres built up of nanorods that were synthesized with TiCl4 in octanol have an average pore size and surface area of, respectively, 5 nm and 404 m(2)/g and exhibit the best electrochemical performance with a capacity of >200 mAh/g after 100 cycles and high rate capability. The excellent electrochemical properties originate from the nanorod-building morphology and mesoporosity of TiO2 spheres that provide good electrical contact, accommodates the strain smoothly, and facilitates facile lithium-ion diffusion.