Effect of trap states on photocatalytic properties of boron-doped anatase TiO₂ microspheres studied by time-resolved infrared spectroscopy

Abstract

The photocatalytic hydrogen and oxygen evolution switching effect in the water splitting of two boron-doped anatase TiO2 microspheres was elucidated from the viewpoint of trap states.

Observation of the Polaron Excited State in a Single-Crystal ZnO

“…To explore exactly the specific excitation process of polaronic states, the kinetics probed at 5 μm with the scanned excitation energy from 2.75 to 3.44 eV are shown in Figure a. , Table S2 lists the corresponding fitting parameters of kinetics. Above the band gap excitation at 3.44 eV, the rising time is within the instrument response of 150 fs, which indicates the fast intraband cooling of carriers .…”

“…By finely tuning the superposition of the two beams both in time and space, a mid-IR supercontinuum was generated by four-wave mixing. The mid-IR probe light was detected by a liquid-nitrogen-cooled 64-element mercury–cadmium–telluride-coupled spectrometer (iHR 320, HORIBA Jobin Yvon). ,− The visible probe light from 400 to 800 nm and IR light from 1.8 to 3.0 μm were detected by the spectrograph based on the complementary–metal–oxide–semiconductor (CMOS) (model: AvaSpec-ULS2048CL-EVO-RS and AvaSpec-NIR256-2.5-HSC-EVO-PRW2). The time delay between the pump beam and the probe beam was controlled by a motorized delay stage.…”

“…It is postulated that the oxygen vacancy (V O ) in ZnO can form a polaron owing to the high localization of electrons and the large relaxation of the surrounding lattice after optical excitation. ,− It is also predicted that the excitation from the ground states of V O can form the excited polaronic states V O ++ within CB. , However, compared with the prototypical material of TiO 2 , direct monitoring of the photoexcited polaron related to V O at femtosecond temporal resolution for ZnO has not been achieved. ,, Here, in order to temporally monitor the dynamics of the photoexcited polaron from the band gap states with state-resolution, femtosecond TA spectroscopy with the scanned excitation energy is utilized. Since the free carrier has a typical IR absorption spectrum in the Drude model, ,, the broad probing region from visible light to mid-IR is utilized to distinguish the photoexcited polaron from the CB electrons. Consequently, oscillation on the dynamics of polaron due to the coupling of electrons with the phonon in SC ZnO has been observed, which corresponds to acoustic phonons with a frequency of around 50 GHz, in contrast to the coupled high-frequency phonon of TiO 2 .…”

Rules for Selecting Metal Cocatalyst Based on Charge Transfer and Separation Efficiency between ZnO Nanoparticles and Noble Metal Cocatalyst Ag/ Au/ Pt

“…As shown in Table , when Ag is deposited on ZnO NPs, the relaxation rate of N 1 changes from 1/8.5 ps −1 to 1/5.3 ps −1 , which leads to an electron transfer rate for N 1 to Ag being as 1/14.1 ps −1 , which is comparable to that for electron transfer from TiO 2 to Pt of 1/12.9 ps −1 . In contrast, when Au and Pt are loaded on ZnO, the relaxation rate for N 1 becomes smaller as 1/10.1 ps −1 and 1/10.9 ps −1 respectively.…”

Review of Z-Scheme Heterojunctions for Photocatalytic Energy Conversion

“…To clarify the efficient interfacial charge transfer via a direct Z-scheme pathway, the real-time carrier dynamics were tried to tracked by the time-resolved transient absorption spectra (TAS) under 400 nm excitation ( Fig. 3e-h) [210][211][212][213] . According to the variation of absorption bands and the decay kinetics parameters (lifetime) of the TAS spectra, the Z-scheme mechanism was unambiguously confirmed 118 .…”