*3.1. X-ray Diffraction (XRD)*

Figure 1 corresponds to diffractograms of TiO2í*x*N and TiO2, highlighting anatase and rutile phases. The shifting of peaks to the left is evidence of an enlargement of the unit cell, demonstrating the insertion of nitrogen atoms into the crystalline structure. Since the TiO2 usually has oxygen vacancies that introduce localized states of Ti+3 [6], it is possible to insert some impurities that are compatible and dope the catalyst to improve performance. In this case, the nitrogen (N<sup>í</sup><sup>3</sup> ) is likely to enter into the structure for having an atomic radius and electronegativity similar to O<sup>í</sup><sup>2</sup> . In this manner, the nitrogen supplies the anionic deficiency. Precisely, it is the nitrogen inserted in the interstices as a substitution of oxygen, which induces occupied electronic states on intervals known as the forbidden energy band (band gap) [13]. This process can facilitate the formation of electron-hole pairs, using stimuli such as electromagnetic radiation of wavelengths greater than 400 nm.

**Figure 1.** X-ray diffractogram (XRD) of Aeroxide P25 (TiO2) *vs.* TiO2í*x*N*y*; phases anatase (A) and rutile (R).
