Effect of current-limiting resistors on dissolution of reactive species through a sub-RF plasma jet interacting with liquid media: Impact on dye degradation and physico-chemical properties of treated liquid.

This study investigates the influence of current-limiting resistors connected between the beaker plate and electrical ground on the dissolution of reactive species in liquid media. A series of five resistors, ranging from 100 Ω to 1 MΩ, were employed to simulate conditions from a short-circuit path to an electrically insulated pathway at the ground terminal. The plasma jet was operated under optimized conditions for gas-phase species generation, specifically at 30 kHz, 9 kV_pp, and an argon flow rate of 1.5 LPM. Measurements revealed an inverse proportionality between the peak-to-peak current and resistor values.

Key physicochemical properties - including pH, solution conductivity (σ_sol), total dissolved solids (TDS), oxidation reduction potential (ORP) and concentration of hydroxyl,peroxide and nitrate —were monitored alongside liquid temperature at varying treatment times. It was found that the (σ_sol, TDS) sharply increases for lower values resistors as a function of treatment times. However, higher values of resistors led to a gradual increase in these parameters, followed by saturation at extended treatment times. A consistent decrease in pH was observed, attributed to the accumulation of nitrate ions, as confirmed by ion-selective probe measurements. Hydroxyl, peroxide and nitrate concentration also follows a analogous trend. A comprehensive discussion of the findings will be presented.