Infrared and Near-Infrared Spectrometry of Anatase and Rutile Particles Bandgap Excited in Liquid
At a Glance
Section titled āAt a Glanceā| Metadata | Details |
|---|---|
| Publication Date | 2022-12-21 |
| Journal | The Journal of Physical Chemistry B |
| Authors | Zhebin Fu, Hiroshi Ånishi |
| Institutions | Kobe University, Institute for Molecular Science |
| Citations | 8 |
Abstract
Section titled āAbstractāChemical conversion of materials is completed in milliseconds or seconds by assembling atoms over semiconductor photocatalysts. Bandgap-excited electrons and holes reactive on this time scale are key to efficient atom assembly to yield the desired products. In this study, attenuated total reflection of infrared and near-infrared light was applied to characterize and quantify the electronic absorption of TiO<sub>2</sub> photocatalysts excited in liquid. Nanoparticles of rutile or anatase were placed on a diamond prism, covered with liquid, and irradiated by steady UV light through the prism. Electrons excited in rutile particles (JRC-TIO-6) formed small polarons characterized by a symmetric absorption band spread over 10000-700 cm<sup>-1</sup> with a maximum at 6000 cm<sup>-1</sup>. Electrons in anatase particles (JRC-TIO-7) created large polarons and produced an asymmetric absorption band that gradually strengthened at wavenumbers below 5000 cm<sup>-1</sup> and sharply weakened at 1000 cm<sup>-1</sup>. The absorption spectrum of large electron polarons in TIO-7 was compared with the absorption reported in a Sr-doped NaTaO<sub>3</sub> photocatalyst, and it was suggested that excited electrons were accommodated as large polarons in NaTaO<sub>3</sub> photocatalysts efficient for artificial photosynthesis. UV-light power dependence of the absorption bands was observed in N<sub>2</sub>-exposed decane liquid to deduce electron-hole recombination kinetics. With light power density <i>P</i> > 200 W m<sup>-2</sup> (TIO-6) and 2000 W m<sup>-2</sup> (TIO-7), the polaron absorptions were enhanced with absorbance being proportional to <i>P</i><sup>1/2</sup>. The observed 1/2-order power law suggested recombination of multiple electrons and holes randomly moving in each particle. Upon excitation with smaller <i>P</i>, the power-law order increased to unity. The unity-order power law was interpreted with recombination of an electron and a hole that were excited by the same photon. In addition, an average lifetime of 1 ms was estimated with electron polarons in TIO-6 when weakly excited at <i>P</i> = 20 W m<sup>-2</sup> to simulate solar-light irradiation.