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.