Nitrogen-Doped Titanium Dioxide Active in Photocatalytic Reactions with Visible Light: A Multi-Technique Characterization of Differently Prepared Materials

Abstract

Nitrogen-doped TiO 2 materials were successfully prepared following three different preparation routes (sol-gel, mechanochemistry, and oxidation of TiN) and characterized by X-ray diffraction, electron microscopy, and various spectroscopic techniques. All samples absorb visible light, and the one obtained via sol-gel, showing the anatase structure, is the most active in the decomposition of organic compounds under visible light. Various nitrogen-containing species have been observed in the materials, whose presence and abundances depends on the preparative route. Ammonium NH 4 + ions are residual of the synthesis using ammonium salts (sol-gel, mechanochemistry) and are quite easily eliminated, as shown by the parallel behavior of both NMR and XPS spectra. Cyanide CNions form at high temperature in parallel with the phase transition of the solid to rutile. Molecular nitric oxide forms in the case of materials exhibiting close porosity. The already reported bulk radical species, N b • , is the only paramagnetic center observed in all types of samples, and is responsible for the visible light sensitization of TiO 2 . A mechanism for the formation of such a species in chemically prepared N-doped TiO 2 materials is for the first time proposed based on the reduction of Nitric Oxide (NO) at oxygen vacancies

TiS2 transformation into S-doped and N-doped TiO2 with visible-light catalytic activity

“…However, nitrogen is incorporated in the TiO 2 (N-TiO 2 ), with the N 1s peak at 400.0 eV. This peak which has been observed in the previous reports of N-doped anatase and rutile is attributed to interstitial N, probably in the connection of Ti-O-N or Ti-N-O [34][35][36][37][38]. According to the nitrogen and titanium peak areas and the reported sensitivity factors, the N/Ti atomic ratio is estimated to be ~7.0% [39].…”

Influence of the chemical synthesis on the physicochemical properties of N-TiO2 nanoparticles

“…It is reported in the literature, in fact, that a high level of doping does not necessarily correspond to a high photocatalytic performance [10,11]. The dopant element, in fact, usually lead to active species for photocatalysis under visible light but, at the same time, it can form species having a detrimental effect on the material photoactivity [12]. Therefore, this variation of the chemical synthesis of N-TiO 2 can be directly related to the photocatalytic efficiency under visible light irradiation.…”

Modification of titania nanoparticles for photocatalytic antibacterial activity via a colloidal route with glycine and subsequent annealing

“…[5][6][7] Numerous attempts were made, for instance, to incorporate nitrogen, sulfur, and/or fluorine into titania nanoparticles, for making them responsive to visible light. [8][9][10][11][12][13][14] Out of a number of such functionalization techniques, dry processing such as comilling oxide particles with appropriate anion sources in a solid state is recognized to be beneficial, [15][16][17] while a number of colloid-chemical processing of titania fine particles for the similar purposes are documented as well. [18][19][20] Comilling of titania nanoparticles with polytetrafluoroethylene (PTFE) in air, for instance, brings about fluorinedoped TiO 2 nanoparticles, as we reported recently.…”