**1. Introduction**

Crystalline mesoporous metal oxide materials are potential candidates for a number of applications, such as battery electrodes [1], fuel cells [2, 3], optoelectronic devices [4], photovoltaic devices [5], and photocatalysis [6], due to their variable oxidation states and unusual magnetic, electronic, and optical properties compared to silicates. In particular, titania-based mesoporous materials have been extensively investigated since titania is transparent in the visible region, nontoxically biocompatible, and photocorrosion-free and can be fabricated by relatively cheap methods. For these numerous properties, titania is employed for various applications in diverse scientific fields, ranging from self-cleaning coatings [7], lithium-ion batteries (LIBs) [8], photocatalysis [9], new-generation solar cells [10], and membrane [11]

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

to antibacterial applications [12]. However, to design efficient systems and devices for the above-cited uses, stable materials with a well-defined crystalline structure, highly controlled crystallite size and shape, as well as high available surface area and accessible pore networks able to ensure contact with catalytic substrates, polymers, or nanospecies are required [13]. Although the early mesoporous materials were produced in the form of powders, some applications, such as membranes, low-dielectric-constant interlayers, optical sensors, and optoelectronic devices, require ultralow-k dielectrics and low-refractive-index materials with a good mechanical stability and of hydrophobic nature. These requirements led to the preparation of mesoporous thin films [14–16]. After a brief description of the different TiO<sup>2</sup> polymorphs and properties, the present chapter will therefore be dedicated to mesoporous TiO2 thin films (MTTFs), reviewing the different preparation methods reported throughout the literature, the main characterization techniques employed to study the structure and the morphology of the prepared thin films, and finally the description of their most successful applications.
