Charge carrier dynamics in photocatalysts

　Photocatalytic activity comprises a series of elementary steps, such as photoinduced electron–hole pair generation, charge carrier trapping, and redox reactions at the catalyst surface. We aim to study photocarrier recombination dynamics using time-resolved spectroscopy. Carrier recombination usually reduces photocatalytic reaction yields by consuming electron–hole pairs. Localized trapping sites may prevent recombination, but the concomitant reduction in redox activity due to trapping would degrade activity. Therefore, controlling carrier trapping sites toward efficient reactions is of considerable interest. We have tackled this problem by combining the following strategies with conventional transient absorption spectroscopy: (1) controlling water vapor pressure to precisely tune water coverage at the catalyst surface thereby allowing us to reveal adsorbate induced charge trapping at the TiO2 surface; (2) single particle imaging using an optical microscope, which allows us to investigate particle size dependence of the carrier dynamics; and (3) ultrafast pump-probe spectroscopy that shows coherent phonon signals, which indicates the carrier trapping site’s local phonon structure.

References

1. “Water-Assisted Hole Trapping at the Highly Curved Surface of Nano-TiO2 Photocatalyst”, Kenji Shirai, Gianluca Fazio, Toshiki Sugimoto, Daniele Selli, Lorenzo Ferraro, Kazuya Watanabe, Mitsutaka Haruta, Bunsho Ohtani, Hiroki Kurata, Cristiana Di Valentin, and Yoshiyasu Matsumoto J. Am. Chem. Soc., 140, 1415–1422 (2018).

2. "Effect of Water Adsorption on Carrier Trapping Dynamics at the Surface of Anatase TiO2 Nanoparticles", Kenji Shirai, Toshiki Sugimoto, Kazuya Watanabe, Mitsutaka Haruta, Hiroki Kurata, and Yoshiyasu Matsumoto Nano Lett., 16, 1323–1327 (2016).

3. "Particle Size Dependence of Carrier Dynamics and Reactivity of Photocatalyst BiVO4 Probed with Single-Particle Transient Absorption Microscopy", Mitsunori Yabuta, Atsuhiro Takeda, Toshiki Sugimoto, Kazuya Watanabe, Akihiko Kudo, and Yoshiyasu Matsumoto J. Phys. Chem. C, 121, 22060–22066 (2017).

4. "Electron−Phonon Coupling Dynamics at Oxygen Evolution Sites of Visible-Light-Driven Photocatalyst: Bismuth Vanadate", Norihiro Aiga, Qingxin Jia, Kazuya Watanabe, Akihiko Kudo, Toshiki Sugimoto, and Yoshiyasu Matsumoto J. Phys. Chem. C, 117, 9881−9886 (2013).

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