Probing Charge Carrier Behavior in Engineered Photocatalysts with Time-Resolved Visible to Mid-IR Absorption Spectroscopy

Abstract

Light-induced catalytic reactions on the photocatalyst surface are initiated by excited charge carriers. Therefore, the observed photocatalytic behavior is sensitive to the charge carrier behavior. In this regard, understanding charge carrier behavior is important to help us more efficiently improve the photocatalytic activity, which is often limited by unfavorable charge carrier dynamics and poor charge carrier management. In this review, we discuss how charge carrier behavior is elucidated in a diverse array of photocatalytic systems with time-resolved visible to mid-IR absorption spectroscopy (TRVIR) to reveal the reason behind their high activity. TRVIR is a promising technique that combines a visible-NIR probe and a near-mid-IR probe to characterize the behavior of both electron and hole. Interpretation of TRVIR spectra is described in sufficient detail here to shed light on how charge carriers behave upon structural modifications, thereby allowing one to foresee proper modifications for future photocatalysts. Perspectives are then presented to stimulate further discussions.

How Effective Are Sub-Bandgap States in AgInS2 Quantum Dots for Electron Transfer?

“…In ternary I–III–VI 2 semiconductor QDs, extraction of both conduction band and sub-bandgap state electrons is necessary to realize better light conversion efficiencies. − Charge trapping/electron relaxations into the intragap states compete with the interfacial electron transfer as the two events proceed in similar ultrafast time scales . In metal oxides like TiO 2 , the reducing power (photocatalytic ability) of electrons in the trap state is significantly lowered by these trapping events. − Conversely, with electrons residing in the intragap state, their mobility is hindered, hence decreasing the probability of recombination . This claim is supported by the long-lived nature of these intragap states as reported for ternary I–III–VI 2 semiconductor quantum dots. ,,, …”

Perspective, Review, and Featured Articles of 2023

“…A popular topic is using time-resolved spectroscopic techniques to elucidate the dynamics of various chemical and photophysical transformations. Sudrajat et al gave an extensive presentation of the study and management of charge carriers in photocatalysts . Ultrafast spectroscopic techniques usually suffer from low spatial resolution; however, with the development of visible light transient absorption and two-dimensional microscopy both the dynamics and heterogeneity can be studied on surfaces.…”