N–TiO2 Photocatalysts: A Review of Their Characteristics and Capacity for Emerging Contaminants Removal

Titanium dioxide is the most used photocatalyst in wastewater treatment; its semiconductor capacity allows the indirect production of reactive oxidative species. The main drawback of the application of TiO2 is related to its high band-gap energy. The nonmetal that is most often used as the doping element is nitrogen, which is due to its capacity to reduce the band-gap energy at low preparation costs. There are multiple and assorted methods of preparation. The main advantages and disadvantages of a wide range of preparation methods were discussed in this paper. Different sources of N were also analyzed, and their individual impact on the characteristics of N–TiO2 was assessed. The core of this paper was focused on the large spectrum of analytical techniques to detect modifications in the TiO2 structure from the incorporation of N. The effect of N–TiO2 co-doping was also analyzed, as well as the main characteristics that are relevant to the performance of the catalyst, such as its particle size, surface area, quantum size effect, crystalline phases, and the hydrophilicity of the catalyst surface. Powder is the most used form of N–TiO2, but the economic benefits and applications involving continuous reactors were also analyzed with supported N–TiO2. Moreover, the degradation of contaminants emerging from water and wastewater using N–TiO2 and co-doped TiO2 was also discussed.