Invited Paper PS1-MoA4
Plasma Reactive Species Formation in Liquids

Monday, October 21, 2019, 2:40 pm, Room B131

Plasma reactive species which are directly originated in an atmospheric pressure plasma jet (APPJ) and/or indirectly produced in liquids can drive a plethora of chemical reactions. Despite the rapid growth in interest in this type of plasma, our fundamental and comprehensive knowledge of the chemistry which plasma induces in multiphase systems is still needed to be achieved. One of the approaches to obtain this goal is a development of sophisticated interrogation techniques to provide such characterization. In our laboratory, we developed in situ optical absorption technique, and used ferrous sulfate (Fricke) solution in which species were detected under plasma interaction to quantify the total yield of these species under different experimental conditions. A yield of ferric (Fe3+) ions measured using this technique was attributed to the formation of plasma reactive species provided and/or originated in the solution. The results indicated that the number of reactive species formed was proportional to plasma frequency and voltage. However, the Fe3+ yield per pulse decreased with increased frequency. To obtain a better understanding of the processes and species involved in the chemical reactions due to plasma exposure, Fe3+ yields were calculated and compared to the experimental data. At higher frequencies, there was insufficient time to complete all reactions before the next pulse reached the solution; at lower frequencies, the Fe3+ yield was higher because of the relatively longer time available for reactions to occur. It is also known that gas composition of APPJ as well as ambient conditions influence plasma chemistry and thus also reactions in liquids which are in contact with plasma. We performed systematic studies to probed changes in plasma electrical properties, by adjusting the fraction of oxygen and water vapor in the plasma jet environment and feed gas. While DNA was used to identify chemical changes that occurred in the plasma jet under these various experimental conditions. We determined optimal conditions at which increase in the damage to the molecular probe was significant. This increase can be attributed primarily to the formation of reactive species caused by water and oxygen decomposition in the APPJ. At the same time, we observed no change in the plasma electrical power when oxygen or water vapor were added to the jet environment but decreased when these gases were introduced to the feed gas. This indicates that the effects of plasma chemistry supersede those due to the power applied for APPJ ignition.