Preparation and microstructure of titanate nanowire thin films by spray Layer-by-Layer assembly method

Abstract

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), ...

Preparation and Microstructure of Titanate Nanotube Thin Films by Spray Layer-by-Layer Assembly Method

“…It is much faster than conventional LbL method. Note that this spray LbL conditions were suitable for the thin-film processing of TiO 2 anatase nanoparticles and titanate nanowires [11]. It is also worthy of note that the conventional LbL (by alternate immersion for 20 min) was already efficiently used for covering titanate nanotubes over textiles [14].…”

“…The spray LbL method in this study was the same as that in our previous study [11], which was based on the report by Kim et al on a conventional LbL method for colloidal TiO 2 [12]. Hydrophilic, negatively charged glass substrates were obtained by 1 wt% KOH aq.…”

“…4(c) and 4(d)), onedimensional nanostructure can be clearly observed. Figure 5 shows the appearance of spray suspensions: from the left, 0.1% titanate nanotubes, 0.1% titanate nanowires [11], 0.1% TiO 2 anatase nanoparticles [11], and 1% TALH. Titanate and TiO 2 suspensions were adjusted in pH=2 by HCl.…”

“…Appearance of spray suspensions: from the left, 0.1% titanate nanotubes, 0.1% titanate nanowires [11], 0.1% TiO 2 anatase nanoparticles [11], and 1% TALH. Arrows show eye-visible large agglomerates.…”

Doped TiO 2 aerogels as alternative catalyst supports for proton exchange membrane fuel cells: A comparative study of Nb, V and Ta dopants

“…It is cheap and has been studied for long, especially for application in solar cells [9,10] or for its photocatalytic properties [11,12]. Different morphologies have thus already been developed, nanoparticles, nanotubes or even aerogels [13][14][15][16][17][18][19][20][21][22][23] for instance. Morphology is a major feature of PEMFC catalyst supports, especially at the cathode side, since it governs diffusion limitations related to gas diffusion towards (oxygen) and from (water) catalytic sites inside the cathodic catalyst layer.…”