Capturing the Long-Lived Photogenerated Electrons in Au/TiO₂ upon UV or Visible Irradiation by Time-Resolved Infrared Spectroscopy

Abstract

Gold nanoparticle modifications for TiO2 (Au/TiO2) can extend the absorption wavelength from UV to visible (Vis) and enhance the photocatalytic performance, thus fueling increasing attention as an emerging photocatalysis strategy. To explore the plasmon-enhanced photocatalytic mechanism and directly unveil the intrinsic properties of Au/TiO2, the decay kinetics of photoelectrons upon UV (355 nm) or Vis (532 nm) excitation are monitored by means of nanosecond time-resolved infrared spectroscopy, which is a unique tool offering observations without interference of the holes. Under UV irradiation, the longer lifetime of photoelectrons observed in Au/TiO2 compared to that in bare TiO2 provides unambiguous evidence for the enhanced charge separation by AuNPs. Under Vis irradiation, the long-lived (hundreds of microseconds) electrons produced by injection from AuNPs into TiO2 upon plasmon excitation are here detected for the first time. Moreover, the effects of TiO2 phase composition and the amount of AuNPs loading on the decay kinetics of long-lived photoelectrons are examined.

Dynamical evolution of the Schottky barrier as a determinant contribution to electron–hole pair stabilization and photocatalysis of plasmon-induced hot carriers

“…This result is in agreement with the observation of ps and ns hot-carrier lifetimes in TiO 2 after being transferred from Au. 19–21 (III) The presence of CO increases both the speed of the process and the amount of charge transferred (Fig. S1†).…”

“…16–18 Furthermore, the lifetime of the injected carriers in semiconductors is under vigorous research because it sets the time bounds for their exploitation. Remarkably, this has been estimated in the order of hundreds of picoseconds 19,20 to nanoseconds, 21 challenging our interpretation of the problem and raising questions regarding the chemical catalysis mechanisms. 22 On the side of theoretical research, much effort has been invested to disentangle the hot-carrier generation process and their energy distribution in several plasmonic materials by means of many-body, 23–26 DFT, 6,27 TD-DFT, 28 DFTB 29–31 and phenomenological master equation techniques.…”

Recent Advances in Plasmonic Photocatalysis Based on TiO2 and Noble Metal Nanoparticles for Energy Conversion, Environmental Remediation, and Organic Synthesis

“…These include chemical and thermal reduction, [76][77][78] sputtering, [79] ion-exchange, [80] deposition-precipitation (DP), [81] and photodeposition. [82] These strategies have been employed to generated TiO 2 NPs decorated with Au, [83][84][85][86] Ag, [87][88][89] Pd, [90,91] Ni, [92] Cu, [93][94][95] Ru, [96] and Al [97,98] NPs, for example.…”

Unraveling the Catalytic and Plasmonic Roles of g-C3N4 Supported Ag and Au Nanoparticles Under Selective Photoexcitation

“…The electrons remain captured in the metal nanoparticles while holes remain on the valence band of CN. A recent time-resolved infrared study also reveals the production of long-lived electrons in Au–TiO 2 under UV excitation . The comparatively short carrier lifetime in AuCN than in AgCN is because of the interfacial Au + trap states at the metallic Au–CN junction.…”