**1. Introduction**

TiO2 is an extraordinarily versatile material. In 1964, Kato et al. used a TiO<sup>2</sup> suspension for the photocatalytic oxidation of tetralin (1,2,3,4-tetrahydronaphthalene) [1]. In 1972, the "Honda-Fujishima Effect" first described by Fujishima and Honda intensively promoted the photocatalytic field [2]. This discovery led to a new application of TiO<sup>2</sup> in water splitting using solar energy as the driving force of the process as well as solar energy conversion.

> © 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 date, TiO2 nanomaterials have attracted the interest of many scientists. The focus is to modify TiO<sup>2</sup> structural properties or to combine supportive materials to demonstrate that TiO<sup>2</sup> nanomaterials are excellent photocatalysts, which can be used as dopants in novel metal-TiO<sup>2</sup> systems such as Pt-doped TiO2 [3], Au-doped TiO2 , or graphene/TiO2 /carbon dot composites developed as visible light photocatalysts [3, 4].

In this chapter, we focus on blue TiO<sup>2</sup> as a visible-light-driven photocatalyst and its preparation methods. The blue TiO<sup>2</sup> nanomaterial contains Ti3+ with an abundant oxygen vacancy, which can absorb visible and infrared light as well as UV light, producing more electrons and holes and also facilitating better electrical conductivity than pristine TiO<sup>2</sup> [5]. In the future, we would like to further address the beneficial applications in clean energy storage media and protecting the environment, including the hydrogen evolution reaction, carbon dioxide reduction, and degradation of pollutants by using noble blue TiO<sup>2</sup> under visible light.
