The increasing need for new materials capable of solar fuel generation is central in the development of a green energy economy. In this contribution, we demonstrate that black TiO(2) nanoparticles obtained through a one-step reduction/crystallization process exhibit a bandgap of only 1.85 eV, which matches well with visible light absorption. The electronic structure of black TiO(2) nanoparticles is determined by the unique crystalline and defective core/disordered shell morphology. We introduce new insights that will be useful for the design of nanostructured photocatalysts for energy applications.

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Selecting the proper doping strategy is essential to controlling the photocatalytic activity of TiO 2 -based nanomaterials. In this work, we compare impregnation and bulk synthesis methods for feeding titania nanocrystals with either Nb or Ta as transition metal dopant and N as nonmetal codopant.The resulting photocatalytic efficiency was tested toward ethanol degradation under either UV or simulated solar irradiation. Microstructure, morphology, and electronic properties at various length scales were deeply investigated and compared with DFT simulations. Instead, under UV irradiation, impregnated samples performed better than bulk synthesis ones, with Ta-doped powders being more efficient than Nb-doped and undoped TiO 2 . Under simulated solar irradiation, bulk synthesis Nbdoped materials were the most active ones, while all the impregnated samples were even less performing than the undoped TiO 2 reference. On the basis of XPS, EPR, DRS, and XRPD results, such differences were attributed to the bulk synthesis approach producing a more homogeneous distribution of guest dopants within the grains, in conjunction with a higher amount of intrinsic defects (such as O vacancies). Implications of these findings on the engineering of efficient titania photocatalysts are discussed.

Pair distribution function analysis up to tens of nanometres allows probing of the structural changes in Ce1−xGdxO2−x/2 solid solutions at varying gadolinium concentrations. Dopant ions and oxygen vacancies form extended Gd2O3-like clusters (droplets) and nanodomains which, on increasing the Gd concentration, percolate and cause a long-range phase transformation. A general crystallographic rationale is presented which could be adopted to describe phase transformations in highly doped materials.