Efficacy study of Argon and helium cold plasma jet for organic dye degradation*

The degradation of two organic dyes Rhodamine B and Methylene Blue is studied using the atmospheric pressure cold plasma jet. Under the same experimental reactor configuration only with a change in the feed gas from Argon to Helium, the treatment efficacy of both the plasmas is verified. A sinusoidal high voltage (1–6.5 kV), 25 kHz frequency is used to excite the argon and helium plasma jets. The aqueous dye sample of 1.5 ml is treated with the developed plasma jets. The effect of applied voltage, sample initial pH (3, 7 &10) and conductivity (1-20 mS/cm), treatment time (1-30 min), dye -concentration (1, 10 & 50 ppm), and sample-plasma distance on dye degradation are studied for both Rhodamine B, and Methylene Blue dye. For all sets of experiments, more efficacy is obtained using an Argon plasma jet compared to Helium. Further, the quantification of short-lived •OH radical using Coumarin-based chemical probe method and the long-lived H₂O₂ Potassium iodide (KI) based colorimetric method is performed. The individual effect of each of these two Oxygen species is also carried out, and it was found that the strong oxidant •OH radical has a major effect on dye degradation. The experimental configuration and outcomes for both the dyes treatment will be presented.