No abstract

Dynamics of charge carriers generated by femtosecond UV (160 fs, 390 nm) excitation in five standard TiO2 photocatalytic powders (JRC-TIO-1, -2, -3, -4, and -5 supplied by the Catalysis Society of Japan) in a vacuum and air was investigated by means of time-resolved femtosecond diffuse reflectance spectroscopy, and was discussed from the viewpoints of crystal structure (anatase and rutile), particle size, and surrounding condition around the particles. Anatase TiO2 catalysts showed very rapid (less than 1 ps) and very slow electron−hole recombination processes, while rutile ones did not show any rapid decay. For catalysts composed of small particles, slower electron−hole recombination was observed in air compared with that in a vacuum, which was well explained in terms of upward band bending near the surface due to adsorption of oxygen. The relationship between the observed charge carrier dynamics and photocatalytic reactivity is also discussed.

Plasmonic materials have drawn emerging interest, especially in nontraditional semiconductor nanostructures with earth-abundant elements and low resistive loss. However, the actualization of highly efficient catalysis in plasmonic semiconductor nanostructures is still a challenge, owing to the presence of surface-capping agents in their synthetic procedures. To fulfill this, a facile non-aqueous procedure was employed to prepare well-defined molybdenum oxide nanosheets in the absence of surfactants. The obtained MoO(3-x) nanosheets display intense absorption in a wide range attributed to the localized surface plasmon resonances, which can be tuned from the visible to the near-infrared region. Herein, we demonstrate that such plasmonic semiconductor nanostructures could be used as highly efficient catalysts that dramatically enhance the hydrogen-generation activity of ammonia borane under visible light irradiation.