**1. Introduction**

Titanium dioxide, with the chemical formula TiO2, is one of the most valuable raw material and has been used in several applications including photocatalysis, medicine, sensors, paints, environment, solar energy, and others. TiO2 has excellent corrosion resistance, good thermal and chemical stability, and low cost [1].

With the development of nanotechnology, TiO2 nanoparticles (NPs), with attractive properties, have been widely fabricated and developed. In the past decades, the demand of titanium dioxide NPs observed remarkable growth because of its specific properties. Moreover, titania is accepted as a pharmaceutical and food additive [2]. It is also used in destruction of viruses and bacteria, inactivation of cancerous cells, as well as clean-up of oil spills [3]. TiO2 NPs are employed for elimination of emerging contaminants [4]. Moreover, TiO2 NPs are one of the excellent semi-conducting materials applied in solar cells because of their good chemical stability, low toxicity, low cost, and high photocatalytic activity for the degradation of organic impurity [5, 6]. Furthermore, TiO2 NPs are widely used as photo-anode materials because of their powerful absorption of light particularly in UV range, good chemical solubility, excellent photo-corrosion resistance and low cost [7, 8]. TiO2 is widely used as photocatalyst material due to its suitable energy band gap, which is less than 3.5 eV [9].

The recent advances in TiO2 nanostructures and their applications have been summarized by Reghunath et al. [10]. Chen and Mao [11] have reported a review on the

synthesis, properties, modifications, and applications of TiO 2 NPs. Environmental and energy applications of titanium dioxide have been discussed by Ge et al. [ 12 ]. Mao et al. [ 13 ] have completed a review on the recent progress in TiO 2 based catalysis for energy systems. In their work, Nur et al. [ 14 ] have investigated the development of TiO 2 for improved dye degradation under UV-vis irradiation. In addition, the correlation between the improved in photocatalytic activity and various surface modifications have been reported [ 15 ]. Fujishima and Honda [ 16 ] prepared TiO 2 used as photoelectrode for splitting water via photoelectrochemical water splitting.

 This chapter provides recent advances in the synthesis of titanium dioxide NPs and their performance in different applications.
