Comparison of helium and argon for the production of carbon monoxide (CO) by a plasma jet for biomedical applications

Abstract

Carbon monoxide (CO) has anti-inflammatory properties and its production by plasma could be a significant advantage in the field of plasma medicine. We characterized a pulsed kHz-driven plasma jet to produce CO for biomedical applications. With no target interaction, the CO2 conversion into CO, the breakdown voltage and energy delivered to the plasma were investigated for two noble carrier gases: helium and argon. The breakdown voltage and the energy delivered to the plasma in argon gas were twice as high as in helium. The breakdown voltage was barely affected by the gas flow rate and the applied voltage, while it decreased slightly with the excitation frequency because the amount of residual charges increases with the frequency. However, the energy delivered to the plasma was not particularly affected by a change in frequency or gas flow rate, while it increased linearly with the applied voltage. CO production rose from a couple of ppm to about 2000 ppm for a specific energy input from 2 to 2000 J/L (5 x 10-4 to 5200 x 10-4 eV/(atom or molecule)), making this plasma source safe in terms of CO production for biomedical applications. Unlike literature results, the nature of the noble carrier gas did not have an impact on CO production. The CO concentration produced with 0.3% CO2 admixture increased linearly with the specific energy input (SEI) until reaching a plateau at about 70%. This implies that loss processes were negligible and that CO2 dissociation was mainly due to energetic particles such as electrons and excited noble atoms. The conversion decreased with the ratio of CO2. Helium and argon as carrier gases are equivalent in terms of CO production and the CO concentration can be controlled by the SEI and the ratio of CO2.