Page 16 - Read Online

Page 12 of 21 Liu et al. Microstructures 2023;3:2023001 https://dx.doi.org/10.20517/microstructures.2022.23

[80]
Figure 7. Simplified interfacial hole hopping scheme for integrated photoanode .

Transient absorption spectroscopy (TAS)
Time-resolved spectroscopy is a new field developed by pulse technology combined with weak and transient
signal detection methods, focusing on the investigation of the interaction between light and the sample.
TAS is a pump-probe time-resolved technique that has been widely used to investigate dynamic processes.
TAS can directly obtain information on the molecular ground, excited, oxidation and reduction states at
[84]
different relaxation times and is therefore an effective means to explore the kinetics of charge transfer .
Tamaki et al. studied the intrinsic dynamics of electron-hole pairs in the range from femtoseconds to
picoseconds and found that the holes could be trapped on the nanoparticle surfaces rapidly while the
[85]
electrons were slowly trapped in the bulk phase with long lifetimes . Wang et al. used TAS to
fundamentally understand the charge carrier dynamics of hole-accepting CDs as cocatalysts . The
[71]
+
transient absorption spectra of g-C N measured with and without Ag electron scavengers showed that the
4
3
signal observed at 510 nm was mainly attributed to photogenerated holes, while the wide signal at 700 nm
was attributed to photogenerated electrons. The amplitude of CDs/CN at 700 nm was higher than that of
m
pure CN, indicating that the holes were transferred to CDs efficiently and the number of long-lived
m
electrons in CN was increased.
For heterostructured systems, Lian et al. synthesized CdS/ZnS core/mesoporous-shell (CdS@mZnS)
[86]
heterostructures with superior photocatalytic activity . TAS and the time-resolved microwave conductivity
revealed efficient photoinduced hole transfer from the CdS core to the ZnS shell. The long-lived
photoinduced charge separation (> 2.4 ms) via defect-mediated hole transfer resulted in good catalytic
[86]
activity and stability for CdS@mZnS . Andrews et al. also demonstrated sub-picosecond hole-transfer
kinetics in β-Sn V O /CdSe heterostructures by TAS measurements . The three-dimensional TA color
[87]
2
5
0.23
maps of β-Sn V O nanowires and β-Sn V O /CdSe heterostructures were acquired. The bare β-Sn V O
2
5
2
0.23
0.23
2
5
5
0.23
nanowires have two broad induced absorption bands at 500-600 and 650-750 nm, assigned to excited holes
in the mid-gap state and β-Sn V O electrons in the conduction band, respectively. The results
0.23
5
2
demonstrated that the β-Sn V O /CdSe heterostructures have rapid excited-state charge transfer
0.23
5
2
kinetics .
[87]
Time-resolved photoluminescence (TRPL) spectroscopy
[88]
In addition to TAS, TRPL spectroscopy is another effective means to probe electron transfer kinetics .
With the development of science and technology, the temporal resolution of fluorescence spectroscopy has
reached the femtosecond scale (< 100 fs). Direct hole transfer rate tests can be carried out by adding a small
amount of hole sacrificial agent to the catalyst with the corresponding carrier lifetime achieved by TRPL
spectroscopy. Yu et al. tested the lifetime of photogenerated carriers of InP/ZnS-S QDs using TRPL