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Red-Shifted Absorptions of Cation-Defective and Surface-Functionalized Anatase with Enhanced Photoelectrochemical Properties

Abstract : 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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https://hal.archives-ouvertes.fr/hal-02325543
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Submitted on : Tuesday, October 22, 2019 - 11:47:56 AM
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Jiwei Ma, Wei Li, Nikolay T. Le, Jesús Díaz-Real, Monique Body, et al.. Red-Shifted Absorptions of Cation-Defective and Surface-Functionalized Anatase with Enhanced Photoelectrochemical Properties. ACS Omega, ACS Publications, 2019, 4 (6), pp.10929-10938. ⟨10.1021/acsomega.9b01219⟩. ⟨hal-02325543⟩

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