Red-Shifted Absorptions of Cation-Defective and Surface-Functionalized Anatase with Enhanced Photoelectrochemical Propertiesстатья
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Дата последнего поиска статьи во внешних источниках: 15 августа 2019 г.
Аннотация: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 TiO2, which was assigned to changes in titanium−
anion ionocovalent bonding. Under illumination, electron paramagnetic resonance
spectroscopy revealed the formation of Ti3+ and O2− radicals which were not detected
in defect-free TiO2. 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
Ti3+ and O2−, 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.