Two groups of TiO 2 thin films were deposited onto Corning glass substrates by the RF magnetron sputtering in reactive argon gas containing 20% oxygen and by the sol-gel technique combined with dip coating. The films prepared by RF sputtering were annealed for 15 min at 650 • C with different rates of increase of temperature with the aim to search for the TiO 2 anatase phase formation. Besides, with the same aim, a set of the TiO 2 films prepared by sol-gel technique was doped with Co in the concentration range from 0 to 8% by weight. Influence of the rate of increase of temperature and Co doping on the anatase phase formation have been observed and estimated by x-ray diffraction and Raman scattering. Structure deformation induced by rapid heating and Co doping is considered as the main reason affecting the anatase phase formation in TiO 2 thin films.

Samples of nitrogen-doped titanium dioxide (anatase, 0.2 ≤ N ≤ 1.0 wt%) prepared by the sol-gel method were investigated using X-band EPR spectroscopy, photoconductivity and photocatalysis measurements. N• and NO• paramagnetic defects in N-TiO 2 have been observed; their concentrations and spin-Hamiltonian parameters were calculated. An increase both in the rate of the generation of free charge carriers and in the rate of photocatalysis was found in N-TiO 2 in contrast with non-doped titania under visible light. The correlation of the density of the observed radicals with the photoconductivity and photocatalysis data is discussed.

Manipulating the atomic structure of semiconductors is a fine way to tune their properties. The rationalization of their modified properties is, however, particularly challenging as defects locally disrupt the long-range structural ordering, and a deeper effort is required to fully describe their structure. In this work, we investigated the photoelectrochemical properties of an anatase-type structure featuring a high content of titanium vacancies stabilized by dual-oxide substitution by fluoride and hydroxide anions. Such atomic modification induces a slight red-shift band gap energy of 0.08 eV as compared to pure TiO 2 , which was assigned to changes in titanium–anion ionocovalent bonding. Under illumination, electron paramagnetic resonance spectroscopy revealed the formation of Ti III and O 2 – radicals which were not detected in defect-free TiO 2 . Consequently, the modified anatase shows higher ability to oxidize water with lower electron–hole recombination rate. To further increase the photoelectrochemical properties, we subsequently modified the compound by a surface functionalization with N -methyl-2-pyrrolidone (NMP). This treatment further modifies the chemical composition, which results in a red shift of the band gap energy to 3.03 eV. Moreover, the interaction of the NMP electron-donating molecules with the surface induces an absorption band in the visible region with an estimated band gap energy of 2.25–2.50 eV. Under illumination, the resulting core–shell structure produces a high concentration of reduced Ti III and O 2 – , suggesting an effective charge carrier separation which is confirmed by high photoelectrochemical properties. This work provides new opportunities to better understand the structural features that affect the photogenerated charge carriers.

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