(215e) Visualization of Coupled Mass Transfer and Reaction Between Plasma and Liquid Phase in a Hybrid Gas-Liquid Dielectric Barrier Discharge Reactor for Water Purification

The interaction of cold plasma with liquid water has been widely applied as an integrated approach of advanced oxidation processes (AOPs) for water purification. A novel approach, i.e., the reactive planar laser induced fluorescence (reactive-PLIF) technique, was proposed to visualize the coupled process of mass transfer of chemically active species (O₃, H₂O₂, •OH, •H, •O, etc.) and instantaneous oxidation reaction between plasma and liquid phase in a hybrid gas-liquid dielectric barrier discharge (DBD) reactor, by quantitatively recording the dynamic change of concentration field of fluorescence dye (e.g., Rhodamine B) in the liquid layer during its decoloration process. Firstly, the decoloration dynamics were revealed under different discharge voltage in oxygen atmosphere. The increase of the discharge voltage can give rise to the increase of the density of DBD plasma filaments, which impacted on the surface of the liquid layer. As a result, more reactive species (O₃, H₂O₂, •OH and other radicals detected by optical emission spectroscopy) were generated, together with the intensification of the convective transport in the liquid layer. The induced flow patterns were confirmed by particle image velocimetry (PIV) measurements, indicating that the convective transport dominated the distribution of the reactive species. The above results demonstrated that the significant enhancement of the Rhodamine B decoloration efficiency with the increase of the discharge voltage can be attributed to the simultaneous intensification of the mass transfer and reaction. Secondly, the decoloration dynamics in the discharge atmosphere of inert gas (e.g., argon) were revealed in comparison with the oxygen discharge at the same discharge voltage. The argon discharge showed denser DBD filaments so as to yield higher intensity of radicals (•OH, •H, •O, etc.) and H₂O₂ concentration. However, the Rhodamine B decoloration efficiency in the oxygen discharge was remarkably higher than the argon discharge because of O₃ formation, which indicated that O₃ plays more important role in Rhodamine B degradation due to the reactive species. This study provided straightforward analysis on the mechanism of the interaction between discharge plasma and polluted water with focus on the fundamental plasma physics and plasma chemistry, which will be beneficial to develop highly-efficient cold plasma technique for AOPs.