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

In this paper, we present a comprehensive study on low hydration Ir/IrO 2 electrodes, made of an Ir core and an IrO 2 shell, that are designed and synthesized with an innovative, green approach, in order to have a higher surface/bulk ratio of Ir−O active centers. Three materials with different hydration degrees have been deeply investigated in terms of structure and microstructure by means of transmission electron microscopy (TEM) and synchrotron radiation techniques such as high-resolution (HR) and pair distribution function (PDF) quality Xray powder diffraction (XRPD), X-ray absorption spectroscopy (XAS), and for what concerns their electrochemical properties by means of cyclic voltammetry and steady-state I/E curves. The activity of these materials is compared and discussed in the light of our most recent results on hydrous IrO x . The main conclusion of this study is that the Ir core is noninteracting with the IrO x shell, the latter being able to easily accommodate Ir in different oxidation states, as previously suggested for the hydrated form, thus explaining the activity as electrocatalysts. In addition, in operando XAS experiments assessed that the catalytic cycle involves Ir(III) and (V), as previously established for the highly hydrated IrO x material.

Anatase−brookite composite nanocrystals were synthesized successfully by a controlled sol−gel reaction followed by a prolonged hydrothermal aging or by mild calcinations (300 and 450 °C). The physicochemical and photocatalytic properties of the synthesized TiO2 composites were studied along with several commercially available nanocrystalline TiO2 samples showing different features. Rietveld refinements of the powder X-ray diffraction pattern were used to track the brookite content systematically and to generally assess the phase composition of the different samples and their crystallite sizes. SEM, TEM, and HRTEM were used to characterize the particle morphology, size, and surface faceting. BET/BJH analyses combined with mercury porosimetry determinations were employed to characterize the surface area, porosity, and pore size distribution. The surface state of the TiO2 samples was analyzed by XPS by studying, in detail, the region of oxygen 1s to produce the OH/Otot surface ratio. The photocatalytic activity of all of the samples was tested both for degradation of NO x in the gas phase and for the oxidation of 2-chlorophenol in the liquid phase. The different samples showed the same sequence of activity for the two reactions. The highest degradation and mineralization efficiencies were achieved in the case of samples showing smaller crystallite sizes and larger surface areas. The photocatalytic activity of the anatase−brookite composite, submitted to the hydrothermal treatment, was found to be the highest for both reactions, even greater than that of a single-phase anatase sample showing a much-larger surface area. The different contributions to the photocatalytic performance of the TiO2 nanocrystals are critically discussed.