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Sensitizing effects of BiVO4 and visible light induced production of highly reductive electrons in the TiO2/BiVO4 heterojunction
摘要： BiVO4 is an e?cient and stable visible active photoanode material. However, due to its unfavorable conduction band position which falls below the H2 reduction potential, it fails to carry out the complete water splitting reaction. On the other hand, larger band gap TiO2 is able to photocatalytically split water, thanks to its negative conduction band energy. Aiming at verifying the possibility of sensitizing TiO2 with BiVO4 and employing the so obtained composite material in photocatalytic water splitting under visible light, we prepared and photoelectrochemically characterized TiO2/BiVO4 heterojunction electrodes. The photocatalytic reduction of methyl viologen, an electron acceptor probe with a reduction potential close to that of protons, was used to evaluate the reducing ability of the photoactive materials under visible light. An apparently counterintuitive electron transfer from photoexcited BiVO4 to the TiO2 conduction band occurs in the TiO2/BiVO4 heterojunction, resulting in TiO2 sensitization and production of highly reductive electrons, which appears to be favored by the band alignment occurring at the heterojunction.
关键词： Methyl viologen reduction,Photo(electro)catalysis,TiO2,BiVO4,Heterojunction,Visible light sensitization
更新于2025-09-10 09:29:36
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Enhanced Visible Light Sensitization of N-doped TiO2 Nanotubes Containing Ti-Oxynitride Species Fabricated via Electrochemical Anodization of Titanium Nitride
摘要： 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 concentration and studied by Small-Angle X-ray Scattering. Titanium nitride films with minimum N content of 6.2 at% N led to a quasi-nanotubular geometry, whilst an increase in N concentration up to 23.8 at% 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 at% 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 to a threefold 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 photocatalytic activity. The impact of the chemical state of nitrogen towards efficient doping of TiO2 nanotubes is demonstrated with a direct correlation to the N loading and a strategy to optimise these factors based on a simple, rapid synthesis from titanium nitride.
关键词： visible light sensitization,photocatalytic performance,titanium nitride,nitrogen-doped titanium dioxide,electrochemical anodization
更新于2025-09-04 15:30:14