**1. Introduction**

Titanium dioxide (TiO<sup>2</sup> ), so-called titania, has shown excellent properties for functional coating materials. As a semiconductor, it functions as photoactive materials. Designing the morphology down to the scale of nanometer, which is called nanostructured, results in some new properties to be envisaged. Synthesis routes are designed to achieve the desired properties

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for certain applications. A high-surface-area titania is beneficial as photoanode in photoelectrochemical solar cells to obtain efficient light harvesting due to the characteristics of dyemonolayer adsorption. However, high surface area is not enough for efficient photoanodes. The titania must also have high crystallinity of the photoactive phase, which is mostly anatase crystalline phase. The presence of microporosity is not favorable for the dye adsorption, hindering efficient dye adsorption. Previous studies have shown that there is a compromise between high surface areas with porosity and crystallinity of the anatase phase [1–3]. For multifunctional textiles, amorphous titania is favored due to strong adherence to the surface of the cellulose-based fabrics [4] compared to the crystalline phase of titania. Interestingly, 1D-nanostructured titania, such as nanorods or nanotubes, has shown notable photocatalytic activity under the visible light irradiation.

and acidic route (**Figure 1**) are discussed. Hydrothermal interaction between block-copolymer surfactant and the anatase seeds is illustrated. Results on the adsorption of Ru-"black dye"

Nanostructured Titanium Dioxide for Functional Coatings

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The preparation of anatase seed is aimed at obtaining nanocrystals with less than 5 nm size, as the thickest wall obtained for mesoporous titania so far does not exceed 5 nm [11]. Hydrothermal technique was proposed to be the technique of choice to prepare the anatase seeds, due to its simplicity and its good reproducibility [9]. The resultant materials were then

Two main routes of the seed preparation, as displayed in **Figure 1**, were proposed. It comprises the hydrothermal hydrolysis and condensation of titanium precursor at a neutral and an acidic condition. A mixture of ethanol in water was used as the hydrolysis media. Ethanol was introduced as a cosolvent to slightly slow down the hydrolysis and condensation rates. It was also chosen to obtain higher oxide content from the hydrolytic condensation of titanium (IV) tetraisopropoxide compared to the process using its parent alcohol [12]. Then, in the second route, acid is introduced to further retard the condensation [13, 14] and obtain clear solution seeds. **Figures 2** and **3** show the dark- and bright-field TEM images of the resulted

The seed suspensions were obtained after 4 h hydrothermal treatment at 80°C. The brightand dark-field TEM images of this seed as well as its selected area electron diffraction (SAED) pattern are presented in **Figure 2**. Diffuse ring SAED pattern indicates the formation of a very small polycrystalline material, which has been indexed as the anatase crystal phase of titania [1]. The presence of bright spots all over the sample region shows the uniform distribution of these crystal phases, while the magnified image in the dark-field TEM image presents the observed lattice strain from [101] anatase phase. Based on the TEM image, the crystal size is around 5 nm as designed. However, the seed solution was a milky solution. Anatase seeds

obtained from neutral hydrothermal route can be recovered as a very light powder.

**Figure 1.** Flow diagram of the approach used in anatase seed preparation via hydrothermal technique.

examined either by XRD or TEM for the presence of the anatase nanocrystals.

anatase seeds resulted from neutral and acidic solution, respectively.

onto selected powders are included.

Here, synthesis route to obtain high-surface-area titania with full domain of anatase phase will be presented and discussed. Some results for the application of the resulted mesostructured titania for dye-sensitized solar cells (DSSC) will be included. Secondly, applications to functional coating for textile and wood are also deliberated by considering photocatalytic and hydrophilic/hydrophobic mechanism. Combining nanostructured titania and silica resulted in excellent antibacterial coatings. Recent results of nanorod titania and silica as antifouling coating on wood are presented.
