Infrared laser diagnostics of the plasma-photocatalyst interaction in a pulsed low pressure discharge

The combination of a plasma with a porous semi-conductor surface (TiO$_{2}$ photocatalytic material) has been recently reported to oxidize volatiles organic compounds (VOC) at a low energy costs [1]. However, activation mechanisms of the photocatalytic surface by the plasma are not clearly identified to the day. In order to improve the understanding of the synergy of the plasma-photocatalysis combination for C$_{2}$H$_{2}$ removal, time resolved in-situ measurements of infrared laser absorption spectroscopy are performed in a low pressure pulsed DC discharge in air containing less than 1000 ppm of C$_{2}$H$_{2}$. The time resolution of the infrared lead-salt diode laser is about 1ms. Time resolved measurements are carried out during a series of single pulses (10 to 100 ms) in a closed plasma reactor. It is shown that the combination of TiO$_{2}$ with external UV irradiation leads a strong enhancement of the C$_{2}$H$_{2}$ oxidation rate under plasma exposure. Similarly, adsorption/desorption characteristic time of C$_{2}$H$_{2}$ on TiO$_{2}$ is modified by the presence of the plasma. \newline [1] S. Futamura, H. Einaga, H. Kabashima, L.Y. Hwan, Catal. Today 89, 89 (2004).