International audienceIncreasing the activity of a photocatalyst goes through the improvement of both its absorption (light) and adsorption (reactant) properties. For a given semiconducting material, the charge carrier separation is also a very important step. Properly combining chosen phases is one option to improve this separation (example of the commercial P25) and depositing platinum on the surface of the catalyst, another one. In some cases, coupling both may nevertheless lead to a decrease of photoactivity or at least limit the potentiality of the catalyst. A third option, consisting in modifying the morphology of the photoactive phase, has shown very promising results. In this study, we have elaborated, characterized and evaluated the hydrogen evolution potentiality (through methanol assisted water splitting) of different TiO2 morphologies: nanoparticles, nanotubes and aerogels. These materials have shown different behaviours depending on both their composition and morphology. Different types of separation processes have been claimed to account for the observed different photoactivities, with more or less pronounced synergetic effects, due to: the use of Pt as a co-catalyst, the mixture of different TiO2 phases (anatase and TiO2(B) or rutile) and the specific morphology of the samples (nanotubes or aerogels). Among all the tested samples, the TiO2 aerogel supported Pt one exhibited very promising performances, three times as active as P25 supported Pt, which is already much more active than pure P25 in our testing conditions

Hydrogen titanate nanowires were prepared by hydrothermal method in 10 M NaOH followed by ion-exchanging process. Titanate nanowire thin films were successfully obtained by spray Layer-by-Layer (spray LbL) method within a short time. Due to the good dispersion state of the nanowires in an aqueous suspension and their linear morphology, titanate nanowires effectively adsorbed on the glass substrate. As a reference, TiO2-anatase nanoparticle thin films were also prepared by spray LbL method.©2009 The Ceramic Society of Japan. All rights reserved.Key-words : Layer-by-Layer (LbL) method, Titanate nanowire, Thin film, Spray technique, TALH, Hydrothermal synthesis, Hightemperature X-ray diffraction (HT-XRD), Self assembly [Received November 17, 2008; Accepted January 15, 2009] Titanate and titania one-dimensional (1D) nanomaterials obtained by the hydrothermal method have attracted much attention since the innovative works by Kasuga et al. in 1998Kasuga et al. in -1999 1),2) Titanate nanowires, with typically 10-50 nm in diameter and 300-10000 nm (or more) in length, can be also prepared by hydrothermal method similarly to titanate nanotubes, but at slightly higher temperatures (~150-170°C, whereas typically ~110-130°C for nanotubes) and/or within stronger basic conditions (in 10 M KOH or 15 M NaOH, whereas typically 10 M NaOH for nanotubes).3),4) At higher hydrothermal temperatures and/or stronger basic (corrosive) conditions, nanosheet-like intermediate (which form scrolled nanotubes) 1),2) cannot exist stably, and hence, intrinsic one-dimensional oriented crystal growth of layered titanates becomes preferential. Titanate nanowires can be further converted into TiO2 (B) (a tunnelstructured TiO2 polymorph related to a bronze structure, NaxTiO2) nanowires or TiO2 anatase nanowires by ion-exchanging and post-heat treatment.3),5) The formation of titanate nanowires can be recognized as the "downsizing" of titanate microfibers, which were reported by Watanabe et al. in late 1970's. 6)-8)These titanate and TiO2 nanowires generally have smaller specific surface area than titanate nanotubes: e.g., ~150 m 2 /g for hydrogen titanate nanowires, 30-80 m 2 /g for TiO2 nanowires and ~300 m 2 /g for hydrogen titanate nanotubes. However, the nanowires have higher crystallinity (i.e., less defects) and higher thermal stability of 1D nanostructure. Hence, the titanate and TiO2 nanowires are suitable for photo-electro conversion applications, such as dye-sensitized solar cells (DSC) 9)-11) and photo-catalysts. 12) Our recent study revealed that TiO2 nanowires (obtained from the post-heat treatment of hydrogen titanate nanowires) showed much better hydrogen production ability due to their higher crystalinity. 12) In order to extend the application fields of these nanowires and other 1D nanomaterials, e.g. for electrodes, sensors, heterogeneous catalysts and so on, thin-film processing technologies must be established. In general, thin-film processing technologies tend to be required as rapid, precise (in nanometer order thickness), ...

TiO 2 aerogel-10 mol% TiO 2 nanowire composite was prepared by a sol-gel technique with the addition of TiO 2 nanowires to TiO 2 sol, followed by supercritical drying in CO 2 . TiO 2 nanowires (anatase with minor rutile phases) as dispersoid were prepared by a hydrothermal process followed by calcination in air at 600 • C. The TiO 2 nanowires were dispersed in a 2-propanol/H 2 O/HNO 3 solution, and the mixture was added drop by drop to a tetrabutyl orthotitanate [i.e. Ti (IV) n-butoxide] solution in 2-propanol. After gelation, the TiO 2 alcogelTiO 2 nanowire composite was dried in supercritical CO 2 to obtain the final, TiO 2 aerogel-TiO 2 nanowire composite. TEM analysis revealed that a unique "nanowire network" structure was formed within the mesoporous aerogel matrix. The aerogel-TiO 2 nanowire composite had a relatively large surface area 427 m 2 /g, with mesopores ∼ 16 nm in diameter and a pore of volume of 1.63 cm 3 /g.