Climate change and the consumption of non-renewable resources are considered as the greatest problems facing humankind. Because of this, photocatalysis research has been rapidly expanding. TiO₂ nanoparticles have been extensively investigated for photocatalytic applications including the decomposition of organic compounds and production of H₂ as a fuel using solar energy. This article reviews the structure and electronic properties of TiO₂, compares TiO₂ with other common semiconductors used for photocatalytic applications and clarifies the advantages of using TiO₂ nanoparticles. TiO₂ is considered close to an ideal semiconductor for photocatalysis but possesses certain limitations such as poor absorption of visible radiation and rapid recombination of photogenerated electron/hole pairs. In this review article, various methods used to enhance the photocatalytic characteristics of TiO₂ including dye sensitization, doping, coupling and capping are discussed. Environmental and energy applications of TiO₂, including photocatalytic treatment of wastewater, pesticide degradation and water splitting to produce hydrogen have been summarized.

TiO2 can be prepared in the form of powder, crystals, or thin films. Liquid-phase processing is one of the most convenient and utilized methods of synthesis. It has the advantage of allowing control over the stoichiometry, production of homogeneous materials, formation of complex shapes, and preparation of composite materials. However, there may be some disadvantages such as expensive precursors, long processing times, and the presence of carbon as an impurity. In comparison, the physical production techniques, although environment friendly, are limited by the size of the produced samples which is not sufficient for a large-scale production. The most commonly used solution routes in the synthesis of TiO2 are reviewed.