Photoinduced Simultaneous Thermal and Photocatalytic Activities of MnO2 Revealed by Femtosecond Transient Absorption Spectroscopy

Solar light-induced catalysis has recently received great interest in efficiently and economically degrading volatile organic compounds, which deteriorate indoor and outdoor air quality. However, a few studies explored its essential photophysical and photochemical processes. Herein, the femtosecond transient absorption spectroscopy was used to investigate the decay of photogenerated holes in MnO2 with different Mn vacancies. About 67-93% of photogenerated holes recombined within a very short time (<130 ps), resulting in enhanced thermal catalytic activity of MnO2. Besides, really a small portion of photogenerated holes remained unchanged in the detection time period (1400 ps). ESR tests further confirm that photocatalytic pathway plays a significant role in degrading VOCs besides the thermal catalytic pathway when MnO2 is under illumination of UV-visible light. The introduction of an appropriate content of Mn vacancy did prolong the lifetime of photogenerated carriers. This work clarifies the mechanism of photoirradiation in improving the catalytic activity of MnO2 and the effect of manganese defects on the catalytic reaction.

Automated summary

The study utilized femtosecond transient absorption spectroscopy to investigate the decay of photogenerated holes in MnO2 with different Mn vacancies. It was found that a majority of photogenerated holes recombined within a very short time, enhancing the catalytic activity of MnO2. Additionally, introducing an appropriate amount of Mn vacancies extended the lifetime of photogenerated carriers and confirmed the importance of the photocatalytic pathway in degrading volatile organic compounds.