Transient IR spectroscopy as a tool for studying photocatalytic materials

Area of Science:

• Photocatalysis
• Spectroscopy
• Materials Science

Background:

• Thermodynamics of photocatalysts, including band edge positions, are well-studied.
• Kinetics of photoinduced charge carriers, especially at early stages, are crucial but less understood.
• Transient electronic spectra have been investigated, but transient vibrational spectra remain underexplored.

Purpose of the Study:

• To raise scientific awareness of transient IR spectroscopy (TRIR) as a complementary tool for photocatalysis research.
• To elucidate the initial steps of photocatalytic processes in solid photocatalysts.
• To showcase the application of TRIR across diverse photocatalyst types.

Main Methods:

• Review of current techniques for measuring transient IR signals of photo-excited systems, including their advantages and disadvantages.
• Application of various pump & probe techniques: dispersive, transient 2D-IR, and step-scan IR spectroscopy.
• Analysis of diverse photocatalyst examples: oxides (TiO2, NaTaO3, BiOCl, BiVO4), dye-sensitized TiO2, graphitic carbon nitride, and rhenium bipyridyl complexes.

Main Results:

• Demonstration of TRIR's applicability to materials with no inherent IR signals (e.g., TiO2) and those with distinct vibrational bands (e.g., carbon nitride).
• Successful application of different TRIR techniques to various photocatalyst systems.
• Insights into the transient vibrational behavior of photoexcited charge carriers.

Conclusions:

• TRIR is a valuable technique for understanding the fundamental, ultrafast processes in photocatalysis.
• The review provides a foundation for researchers to adopt and expand the use of TRIR.
• Further application of TRIR is expected to deepen the understanding of photocatalytic mechanisms.