Evaluation of influence of cold atmospheric pressure argon plasma operating parameters on degradation of aqueous solution of Reactive Blue 198 (RB-198)

The intention of this work is to remove Reactive Blue 198 (RB-198) dye components from simulated water solution using cold atmospheric pressure argon plasma jet. Aqueous solutions of RB-198 dye were treated as a function of various operating parameters such as applied potential, reaction time and distance between the plasma jet and surface of the liquid. The efficiency of the degradation of RB-198 molecules was explored by means of UV-Vis spectroscopy. The reactive species involved during the treatment process were examined by optical emission spectra (OES). The present hydroxyl radicals (OH• radical) and hydrogen peroxide (H₂O₂) in the plasma-treated aqueous dye solutions were investigated using various spectroscopic techniques. The other parameters such as total organic carbon (TOC), conductivity and pH were also reviewed. The toxicity of plasma-treated RB-198 solution was finally studied by diffusion bacterial analysis and by tracking seed germination processes. The results show that a higher degradation percentage of 99.27% was acquired for the RB-198 treated at higher reaction time and applied potential, and shorter distance between the plasma jet and water surface. This may be due to the formation of various reactive oxygen (OH• radical, atomic oxygen (O) and H₂O₂) and nitrogen species (nitric oxide (NO) radicals and N₂ second positive system (N₂ SPS)) during the processes as confirmed by OES analysis and other spectroscopy analysis. TOC (17.7%–81.8%) and pH (7.5–3.4) values of the plasma-treated RB-198 decreased significantly with respect to various operation parameters, which indicates the decomposition of RB-198 molecules in the aqueous solution. Moreover, the conductivity of plasma-treated RB-198 aqueous solutions was found to have increased linearly during the plasma treatment due to the formation of various ionic species in aqueous solution. The toxicity analysis clearly exhibits the non-toxic behavior of plasma-treated RB-198 aqueous solution towards the bacterial growth and germination of seeds.