Characterization of charge carrier behavior in photocatalysis using transient absorption spectroscopy

Abstract

Photocatalysis is a promising sustainable method to generate solar fuels for the future, as well as having other applications such as water/air purification. However, the performance of photocatalysts is often limited by poor charge carrier dynamics. To improve charge carrier dynamics, it is necessary to characterize and understand charge carrier behavior in photocatalytic systems. This critical review will present Transient Absorption Spectroscopy (TAS) as a useful technique for understanding the behavior of photoexcited charges in semiconductor photocatalysts. The role of TAS amongst other techniques for characterizing charge carrier behavior will be outlined. Basic principles behind TAS will be introduced, and interpretation of TAS spectra and kinetics will be discussed in the context of exemplar literature. It will be demonstrated that TAS is a powerful technique to obtain fundamental understanding of the behavior of photoexcited charges.

Characterizing photocatalysts for water splitting: from atoms to bulk and from slow to ultrafast processes

“…Time-resolved luminescence spectroscopy, and pumpprobe spectroscopic techniques, i.e., transient absorption (TA) in the visible, ultraviolet and IR range, sometimes complemented by time-resolved Raman experiments and more exotic techniques such as THz and X-ray absorption, are the most common techniques employed to gain insight into changes of the systems subsequent to excitation, i.e., into relaxation, charge transfer and recombination processes and have been extensively reviewed. [129][130][131][132][133][134][135][136] Already observing the quenching of PL intensity and changes in the PL lifetime of a photosensitizer or semiconductor in the presence of a co-catalyst can give first indication on the presence and time scale of additional energy or charge transfer processes influencing the lifetime of the emitting state. While PL spectroscopy is only sensitive to bright states, TA spectroscopy can also probe non-emitting states because it is based on the observation of changes in the electronic transitions (UV/vis/NIR) and vibrational frequencies (IR) after excitation.…”

Understanding spontaneous dissolution of crystalline layered carbon nitride for tuneable photoluminescent solutions and glasses

“…As the kinetics are independent of pulse energy (Fig. 3b), the additional pathways cannot be attributed to supplementary bi-molecular recombination 33 , and instead must indicate that the sample is intrinsically heterogeneous. Sample heterogeneity is affirmed by modification of the TA spectral shape using 350 nm excitation (ESI, Fig.…”

In Situ Investigation of Charge Performance in Anatase TiO2 Powder for Methane Conversion by Vis–NIR Spectroscopy

“…Our recent review provides further background on optical pump–probe techniques and signal interpretation in the context of heterogeneous photocatalysts. 28 …”