Enhancement of photocatalytic activity of titanium dioxide using non-metal doping methods under visible light: a review

Titanium dioxide (TiO2) is an efficient photocatalyst for removing organics in photocatalytic wastewater treatment, but its low photoactivity limits its practical applications in a visible-light-driven chemical reaction. Many efforts have been made in the activation of the visible light absorption property on TiO2 photocatalyst. In this paper, a thorough review of current non-metal doping methods of TiO2 to improve photocatalyst activation under visible light is presented. The focus of this study is on doping non-metals onto TiO2 by several methods to enhance its visible light photoactivity. Besides, the resultant characteristics of the chemical structure, physical structure, and optical properties of the doped photocatalysts are discussed. This review enables a better understanding of current advantages and disadvantages that can arise during the production of non-metal-doped TiO2 and its applications. The annealing and hydrothermal methods are found to be more efficient in preparing doped photocatalysts with respect to time and costs. When choosing between these two approaches, the hydrothermal method can be applied using a variety of precursors, whereas the annealing methods are restricted only to solid form precursors. Thus, the hydrothermal method is a more favorable method of non-metal doping of TiO2. However, studies should focus on the effects of different factors involved in each synthesis/preparation method to determine optimal preparation conditions.