Non-thermal argon plasma jets of various lengths for selective reactive oxygen and nitrogen species production

Plasma jets simultaneously create a wide range of reactive oxygen species (ROS) and reactive nitrogen species (RNS), making selective production challenging. In this study, an attempt was made to address this problem by adjusting the downstream length of the plasma jet to regulate reactive species production in an AC-driven argon plasma jet. Jets with short downstream lengths are dominated by RNS, whereas longer ones are dominated by ROS. The energy impact collision between energetic electrons and diffused ambient air is primarily responsible for the generation of RNS in argon plasma. Short plasma jets have a higher electron temperature in the plasma effluent, allowing for better excitation and ionization of N2 molecules. In contrast, in longer jets, electrons transfer most of their energy to neutrals and moisture, even before the diffusion of ambient air. Thus, the production of OH radicals and H2O2 is dominant in longer plasma jets. Further, the ratio of NO2- to H2O2 in plasma-activated water decreased from 1.8 to 0.07, as the downstream length was increased from 1 cm to 10 cm. RNS-enriched short plasma jets are appropriate for immune cell activation, jets of intermediate length are suitable for gold nanoparticle formation because of the synergistic action of ROS and electron energy, and ROS-dominated longer plasma jets are excellent for methylene blue degradation. These findings are applicable to the design of plasma devices in which the generation of ROS and RNS in practical quantities is required to realize plasma technology for a wide range of applications.