Tubular and fibrous nanostructures of titanates have recently been synthesized and characterized. Three general approaches (template assisted, anodic oxidation, and alkaline hydrothermal) for the preparation of nanostructured titanate and TiO2 are reviewed. The crystal structures, morphologies, and mechanism of formation of nanostructured titanates produced by the alkaline hydrothermal method are critically discussed. The physicochemical properties of nanostructured titanates are highlighted and the links between properties and applications are emphasized. Examples of early applications of nanostructured titanates in catalysis, photocatalysis, electrocatalysis, lithium batteries, hydrogen storage, and solar‐cell technologies are reviewed. The stability of titanate nanotubes at elevated temperatures and in acid media is considered.

A systematic analysis of the influence of preparation conditions in the alkali hydrothermal synthesis on the morphology of TiO 2 nanotubes is performed using HRTEM and low temperature nitrogen adsorption. The possible mechanisms of nanotube formation are reviewed and a mechanism based on the key stage of wrapping of intermediate multilayered titanate nanosheets is suggested. The driving force for wrapping is considered to be the mechanical stress arising during crystallisation/dissolution. The average diameter of the nanotubes was found to depend on the temperature and on the ratio of weight of TiO 2 to the volume of sodium hydroxide solution. An increase in the temperature from 120 to 150 uC results in an increase in the average nanotube diameter. Subsequent increases in the temperature result in the formation of non-hollow TiO 2 nanofibers with an average diameter of 75 nm, a wide distribution in diameter and a length in excess of 10 mm. The increase of the TiO 2 : NaOH molar ratio results in an increase in the average diameter of nanotubes and a decrease of surface area. The average inner diameter of TiO 2 nanotubes varied between 2 and 10 nm. The pore-size distribution was evaluated from TEM, and low-temperature nitrogen adsorption data using the BJH method. It was shown that nitrogen adsorption is a suitable method for characterisation of the pore morphology of nanotubes. Experimental detailsReagents Titanium dioxide, anatase (TiO 2 ), sodium hydroxide (NaOH), sulfuric acid (H 2 SO 4 ), and hydrogen peroxide 27.5% (H 2 O 2

Recent advances in the synthesis, characterisation and applications of elongated titanate and TiO2 nanostructures (including nanotubes, nanofibres and nanorods) are reviewed. The physicochemical properties of nanostructures, such as high surface area, efficient ion‐exchange properties, electron and proton conductivity and high aspect ratio, are described in connection with a particular application. Practical aspects of the preparation, stability and transformation of elongated titanates are considered. A critical survey of the literature is provided together with the development of prospectiveenergy applications of elongated titanates in catalysis, photocatalysis, electrocatalysis, solar cells, fuel cells, lithium batteries and hydrogen storage. Other applications utilising the high aspect ratio of elongated nanostructures include biomedical implants, sensors, drug delivery systems and smart, tribological composite coatings. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)

The sorption of hydrogen between the layers of the multilayered wall of nanotubular TiO2 was studied in the temperature range of -195 to 200 degrees C and at pressures of 0 to 6 bar. Hydrogen can intercalate between layers in the walls of TiO2 nanotubes forming host-guest compounds TiO2 x xH2, where x < or = 1.5 and decreases at higher temperatures. The rate of hydrogen incorporation increases with temperature and the characteristic time for hydrogen sorption in TiO2 nanotubes is several hours at 100 degrees C. The rate of intercalate formation is limited by the diffusion of molecular hydrogen inside the multilayered walls of the TiO2 nanotube. 1H NMR-MAS and XRD data confirm the incorporation of hydrogen between the layers in the walls of TiO2 nanotubes. The nature and possible applications of the observed intercalates are considered.