Fig. 1. Concentric tubular dielectric barrier discharge low-temperature plasma reactor

Fig. 2. Standard curve of methyl red solution at 521 nm

Fig. 3. UV visible absorption spectra of methyl red solutions at different pHs (color online)

Fig. 4. Changes of methyl red solution at 521 nm under different discharge powers: (a) absorbance curves over time; illustration: curves of removal rate over time; (b) graph of color changes over time

Fig. 5. Changes in methyl red solution at 521 nm under different initial concentrations: (a) absorbance curves over time; illustration: curves of removal rate over time; (b) graph of color changes over time

Fig. 6. Changes in methyl red solution at 521 nm under different initial pHs: (a) absorbance curves over time; illustration: curves of different pHs over time; (b) graph of color changes over time

Fig. 7. (a) Changes in absorbance of solution at 521 nm under different atmosphere conditions; illustration: variation of pH during solution degradation under different atmosphere conditions; (b) color change of solution under different atmosphere conditions