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.