Abstract
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.
Highlights
Titanium dioxide is the most widely used photocatalyst material due to its semiconductor characteristics, which make it a remarkable option for photocatalysis applications involving solar or other sources of radiation [1,2,3]
P25 is a commercial TiO2 form that is found in the literature as active regarding the photocatalytic degradation of contaminants under sunlight or visible light radiation; it should be used for comparative purposes when selecting an alternative photocatalyst
Lee et al [44] revealed that the N–TiO2 prepared by the modified sol–gel method coupled with ultrasound irradiation presents a strong disinfection capacity over Escherichia coli and Staphylococcus aureus comparing to the undoped material
Summary
Titanium dioxide is the most widely used photocatalyst material due to its semiconductor characteristics, which make it a remarkable option for photocatalysis applications involving solar or other sources of radiation [1,2,3]. It was proved that for both the anatase and rutile phases of TiO2 , the N 2p states were located just above the top of the O 2p valence band, which means a red shift of the absorption band edge to the visible region [23] It indicates that nitrogen is the best nonmetal dopant to TiO2 , improving the photocatalytic activity at the visible light radiation, which means a low-cost energy source for the degradation of contaminants. In this context, N–TiO2 catalysts are interesting in this field, and lots of information about them can be found in the literature. Future perspectives regarding this kind of catalyst will be discussed considering the wastewater treatment applications
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