VOLUME 19 NUMBER 2 (July to December 2026)

Atmospheric pressure plasma jet-assisted decolorization of malachite green and natural orange dye

This study investigates the decolorization of aqueous solutions of malachite green (MG) and natural orange dye using direct and indirect treatments with a non-thermal atmospheric-pressure plasma jet (APPJ). In the direct treatment, the dye solutions were exposed directly to the plasma plume, whereas the indirect treatment was carried out using plasma-activated water (PAW) generated by exposing water to the plasma jet prior to its application to the dye solutions. Dye decolorization efficiencies were quantified using UV–Vis spectroscopy by monitoring changes in the characteristic absorbance of the dyes, from which concentrations were derived, during treatment. The direct plasma treatment achieved maximum decolorization efficiencies of 95.32 ± 0.29% for MG and 92.47 ± 1.29% for natural orange dye within 45 minutes. In contrast, the indirect treatment using 60-minute PAW exposure resulted in decolorization efficiencies of 19.20 ± 2.60% for MG and 24.90 ± 1.35% for natural orange dye. Physicochemical parameters such as pH, conductivity, total dissolved solids (TDS), and dissolved oxygen (DO) were significantly altered due to the generation of reactive oxygen and nitrogen species (RONS) during direct plasma treatment, as identified by optical emission spectroscopy. Kinetic analyses revealed that the decolorization of MG and natural orange dye followed second-order kinetics under direct plasma treatment. These findings highlight the potential of APPJ-based treatments as a promising strategy for effective dye wastewater remediation.