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Optical and electrochemical characterizations are carried out in conjunction with first-principles calculations on pure and N-doped titania nanocrystals. These are prepared in laboratory with initial doping concentrations of triethylamine in the range of 0.1-0.5 N/Ti molar ratio. Diffuse reflectance UV-vis spectra of N-doped samples present a significant absorption in the visible region. The flatband potential (E fb ) of pure and nitrogen-doped TiO 2 (-0.6 ( 0.2 V vs NHE) is determined by impedance spectroscopy (Mott-Schottky plots) and the quasi-Fermi level, n E F * (-0.67V vs NHE) by photovoltage measurements as a function of the suspension pH in the presence of an electrochemical probe (methylviologen, MV 2þ ). Theoretical density of electronic states calculations, where several N doping versus vacancy combinations are taken into consideration, together with the optical and electrochemical experiments allow us to draw a detailed picture of the electronic features of the doped samples.

N-doped titanium dioxide is one of the most promising materials for photocatalysis in the visible region. The exact location of nitrogen in the host lattice is still under debate. Here, we synthesized a series of N-doped titania nanoparticles. Average Ti nearest neighbors distances were obtained from EXAFS experiments and compared with DFT calculations at different levels of theory. The comparison shows that N substitutes oxygen at low levels of doping, whereas oxygen vacancy creation is observed at higher dopant concentrations. Overall, this article illustrates a general method for bulk characterization based on DFT and EXAFS approaches, which can be extended to several systems.

The photocatalytic activity of N-doped nanostructured TiO 2 (TiO 2 :N) in the visible region strongly depends on the close, yet not fully understood, interplay among crystal structure distortions, nature, and concentration of lattice defects and bulk electronic states. In this work, we study correlations among the chemical identity of the nitrogen source and the microscopic features of biphasic (anatase: brookite) TiO 2 :N nanoparticles through a broad starting doping range. Triethylamine, urea, and ammonia were considered as independent nitrogen supplies. Synchrotron X-ray photoelectron spectroscopy measurements confirmed the presence of nitrogen within the nanoparticles, while X-ray powder diffraction experiments performed at both synchrotron light sources and conventional laboratory-based instruments found that the dopant monotonically lengthens the cell edge module |c| along the unique C 4 -axis, until a plateau is reached for starting N/Ti ratios greater than 0.2. The chemical nature of the precursor determines (i) the morphology of the powder at the mesoscale, (ii) the actual magnitude of the maximum lengthening of the c-vector module, and (iii) the anatase phase enrichment. Overall, we found useful hints on possible routes to control and tailor one or more of the specific features of the material (polymorph enrichment, dopant levels, surface area).

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