Properties and applications of $\rm{Ar-H_2}$ atmospheric pressure plasma jets

Whether for materials processing or medical applications, the use of atmospheric pressure plasma jets (APPJs) has emerged as a relevant alternative to conventional methods. Within the APPJs research field, the search for innovation aims not only to solve existing problems, but also to explore novel options for generating plasma jets and find new possible applications. In this work, the properties of $\rm{Ar-H_2}$ APPJs generated using two plasma sources, which differ basically in the generated voltage frequency, amplitude and waveform, were studied through electrical, thermal and optical characterization. Discharge and plasma parameters were analyzed as a function of the $\rm{H_2}$ content in the gas mixture, with this parameter varying from $0\%$ to $3.5\%$. In all cases, the discharge power, electron density as well as the rotational, vibrational and gas temperatures presented a trend of growing when the proportion of $\rm{H_2}$ in the gas composition was increased. Optical emission spectroscopy revealed that the same reactive species were produced for both plasma sources, except for nitric oxide (NO), which was observed only for the one operated at higher frequency (PS #1). Applications on polymer (polypropylene, PP) and water treatment were performed using PS #1 without $\rm{H_2}$ and with $3.5\%$ of $\rm{H_2}$ in the gas mixture. NH functional groups were detected on the PP surface in the presence of $\rm{H_2}$ in the gas composition. This indicates a possible way to increase the nitrogen content on polymer surfaces. The results of water treatment revealed that ammonia ($\rm{NH_3}$) is also produced when there is $\rm{H_2}$ in the working gas. This opens an alternative for the use of plasma treated water in agriculture.