Enhanced Visible Light Sensitization of N-Doped TiO₂ Nanotubes Containing Ti-Oxynitride Species Fabricated via Electrochemical Anodization of Titanium Nitride

Abstract

The concentration and chemical state of nitrogen represent critical factors to control the band-gap narrowing and the enhancement of visible light harvesting in nitrogen-doped titanium dioxide. In this study, photocatalytic TiO2–N nanoporous structures were fabricated by the electrochemical anodization of titanium nitride sputtered films. Doping was straightforwardly obtained by oxidizing as-sputtered titanium nitride films containing N-metal bonds varying from 7.3 to 18.5% in the Ti matrix. Severe morphological variations into the as-anodized substrates were registered at different nitrogen concentrations and studied by small-angle X-ray scattering. Titanium nitride films with minimum N content of 6.2 atom % N led to a quasi-nanotubular geometry, whereas an increase in N concentration up to 23.8 atom % determined an inhomogeneous, polydispersed distribution of nanotube apertures. The chemical state of nitrogen in the TiO2 matrix was investigated by X-ray photoelectron spectroscopy depth profile analysis and correlated to the photocatalytic performance. The presence of Ti–N and β-Ti substitutional bonds, as well as Ti-oxynitride species was revealed by the analysis of N 1s X-ray photoelectron spectroscopy high-resolution spectra. The minimum N content of 4.1 atom % in the TiO2–N corresponded to the lowest Ti-oxynitride ratio of 13.5%. The relative variation of N-metal bonds was correlated to the visible light sensitization, and the highest Ti–N/Ti oxynitride ratio of 3.3 was attributed to the lowest band gap of 2.7 eV and associated with a 3-fold increase in the degradation of organic dye. Further increase of N doping led to a dramatic drop of Ti–N/Ti oxynitride ratio, from 3.3 to 0.4, which resulted in a loss of photocatalytic activity. The impact of the chemical state of nitrogen toward efficient doping of TiO2 nanotubes is demonstrated with a direct correlation to N loading and a strategy to optimize these factors based on a simple, rapid synthesis from titanium nitride.

Multifunctional and Durable Coatings for Stone Protection Based on Gd-Doped Nanocomposites

“…This limitation is particularly restrictive, as UV radiation corresponds to only 3% of the solar irradiance at the surface of Earth [17]. Many scientists have focused their research on enhancing the photocatalytic and antimicrobial activity of pure TiO 2 NPs by doping with different materials; transition-metal ions, and other metals and ions of non-metals [18][19][20]. However, the application of visible light-active TiO 2 NPs is limited to some fields such as water treatment, photovoltaic cells, etc.…”

Engineering Schottky-like and heterojunction materials for enhanced photocatalysis performance – a review

“…The optical band-gap associated with pristine TiO 2 was 2.9, while the ZnO-TiO 2 exhibited a band-gap of 2.6, showing a significant red-shift due to type II band alignments in the core-shell ZnO-TiO 2 heterojunction structures and quantum confinement effect exhibited by ultrathin layer of ZnO 91 . The narrowing of the band-gap extended the light harvesting abilities of the heterojunctions towards visible light 3 . The improved electronic and optical properties of the hetero-structures led to an enhancement of the photocatalytic efficiency 92 .…”

“…91 The narrowing of the band-gap extended the light harvesting abilities of the heterojunctions towards visible light. 3 The improved electronic and optical properties of the hetero-structures led to an enhancement of the photocatalytic efficiency. 92 The photo-catalysis of MB solution using ZnO–TiO 2 showed a kinetic constant of 9.5 × 10 −3 min −1 , while pristine TiO 2 nanowires degraded MB at a kinetic constant of 5.35 × 10 −3 min −1 .…”

“…The options for the enhancement of catalytic performance and visible light activation of the materials involve metal or non-metal doping of semiconductors 3 and defect engineering in catalytic nanostructures such as graphene 4 . Most promising engineering strategy involves the design of electronic barriers, which are introduced at the junction of a conductive and a semiconducting layer 5 .…”

NANORURKI TiO2: SYNTEZA I ZASTOSOWANIE

“…Nanorurki TiO 2 były również poddane różnym modyfikacjom mającym na celu polepszenie właściwości tego materiału w zakresie promieniowania UV, ale także rozszerzenie jego aktywności do zakresu widzialnego. Pośród tych modyfikacji można wyróżnić: a. domieszkowanie niemetalami i metalami [28][29][30][31]; b. osadzanie nanocząstek metali szlachetnych i kropek kwantowych [32][33][34]; c. tworzenie heterozłączy półprzewodnikowych [35][36][37]; d. tworzenie układów hybrydowych organiczno-nieorganicznych [38,39]; Innym zastosowaniem TiO 2 są barwnikowe ogniwa fotowoltaiczne (ang. dye sensitized solar cells, DSSC), których budowa opiera się na grubej warstwie TiO 2 z zaadsorbowanym na powierzchni tej warstwy barwnikiem tworząc anodę.…”