Sodium titanate nanowires as a stable and easily handled precursor for the shape controlled synthesis of TiO2and their photocatalytic performance

Sodium titanate nanowires (STNWs), a stable and easily handled precursor, were used for the shape controlled synthesis of TiO2. By varying the composition of the reaction solutions, the morphology of TiO2 could be readily controlled by the hydrothermal treatment of the STNWs. Three different shapes of TiO2: nanospindles, hollow microspheres, and one dimensional chain-like aggregates, were prepared without using any templates by adding a small volume of HF (1 mL) or (and) H2O2 (5 mL) to the hydrothermal solutions. The structures, textures, morphologies, optical properties, adsorption capacities, and photocatalytic activities of the samples were carefully investigated. Chain-like TiO2 aggregates showed the highest photocatalytic performance for the degradation of methyl orange. A "dissolution–nucleation" process was proposed for the transformation of STNWs to nanospindles and hollow microspheres, while a topochemical reaction process was described for the formation of the chain-like TiO2 aggregates. The dissolution of STNWs, and the nucleation and growth of TiO2 were affected by the additions of H2O2 and HF. H2O2 benefits the crystallization of TiO2, while HF favors the formation of plate-like particles and surface fluorination. The impact of these roles on the morphologies, surface structures, and photocatalytic behaviors of the prepared TiO2 samples was prospectively interpreted based on the characterization results and reported references.