Comparison of deionized and tap water activated with an atmospheric pressure glow discharge.

Liquid-cathode discharge at atmospheric pressure has been excited by a direct current voltage above the surfaces of deionized and tap water. Gap voltage decreases with increasing discharge current, which suggests that the discharges above both the liquids belong to a normal glow regime. For a given discharge current, gap and power voltages of the discharge above deionized water are higher than those above tap water. The optical spectrum obtained from the water surface reveals that there are abundant active species related to oxygen, nitrogen, and water vapor, which leads to changes in the pH value, conductivity, and concentrations of NO 3 − , NO 2 − , and H2O2 in liquid. Therefore, these parameters are investigated in the two liquids as functions of discharge current and plasma activation time. For both of them, the results show that the pH value decreases, while conductivity increment and concentrations of NO 3 − , NO 2 − , and H2O2 increase with increasing discharge current or activation time. Compared to activated tap water, deionized water has a lower pH value, while higher conductivity increment and concentrations of NO 3 − , NO 2 − , and H2O2 are observed after the same activation time and discharge current. Finally, these parameters are compared for different salt types and salt concentrations after plasma activation. [ABSTRACT FROM AUTHOR]