A review on the synthesis of the various types of anatase TiO2 facets and their applications for photocatalysis

Anatase titanium dioxide, as one of the most well-known functional materials, is widely utilized in various fields of the environment and energy. In recent decades, much attention has been attracted to the surface engineering of the anatase crystal at a microscopic level for a better understanding of the relationship between surface and photocatalytic activity. In this review, a brief description is presented for the synthesis of the low-index facets ({0 0 1}, {1 0 0}, {1 0 1}, {1 1 0} and {1 1 1}) and high-index facets. Besides, the comparison between the photocatalytic activity of the faceted anatase and common types of TiO2(mostly P25) is performed in this review. Meanwhile, a comprehensive study for the comparison between photocatalytic performance (organic pollutants photodegradation and water splitting) of the various types of the low-index facets and high-index facets is performed. The location of the band edge and band gap value in semiconductors during photocatalytic reaction play an important role in energy requirements for electron transfer and the light absorption respectively; so, band gap and band edge location in various types of anatase TiO2 facets are investigated. The recombination rate of the photogenerated electron-hole pairs is commonly described as one of the main limiting factors for the photocatalytic activity of the TiO2. In this review, the effect of the tailored facets of anatase crystal on the charge carrier's separation as a promising strategy is completely described. Finally, the novel ideas for future studies on the facets engineering of the anatase crystals are also suggested.