Selective generation of reactive oxygen species in plasma-activated water using CO2 plasma

In this study, we discuss a process for selectively generating reactive oxygen species (ROS), such as H2O2 and dissolved O3, in plasma-activated water (PAW) using pure CO2 as a plasma-forming gas. A detailed comparison of the gas species/radicals present in plasma and the properties of PAW when using CO2 and air as plasma-forming gases is presented. Our results show that PAW generated with CO2 has a significantly higher pH and lower oxidizing potential and electrical conductivity compared to PAW generated with air. Species formed in PAW (CO2) due to CO2 plasma-water interaction include dissolved O3, H2O2, dissolved CO2, CO32− ions, etc. Moreover, the concentration of NO2− and NO3− ions in PAW (CO2) is beyond the detection limit. PAW (CO2) has a substantially higher concentration of H2O2 than PAW (air). Furthermore, increasing the plasma treatment time with water significantly increases the concentration of H2O2 and dissolved O3 in PAW (CO2). In conclusion, our study demonstrates that selective generation of ROS in PAW is possible using CO2 as a plasma-forming gas, leading to a higher H2O2 concentration compared to air.