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In this paper, sodium percarbonate (SPC) was activated by ozone (O3) from plasma for catalytic treatment of dye wastewater. Methyl blue (MB), a typical industrial dye, was selected as the target dye contaminant. Results showed that enhancing O3 dosage and reducing MB concentration were beneficial to MB degradation. Compared to acid condition, a higher removal efficiency of MB was obtained in alkaline condition. With an increase of SPC dosage, the removal efficiency of MB first was raised, and then it declined. Under the optimal dosage of 50 mg/L, the removal efficiency of MB reached 85.7% with 30 min treatment time. The energy efficiency was improved from 5.21 g/kWh to 5.71 g/kWh. A synergetic effect can be established between O3 and SPC. Radical capture experiments verified that ·OH, ·O2−, 1O2, and ·CO3− played important parts in MB degradation. With increasing reaction time, the amount of total organic carbon (TOC) declined and the amount of ammonia nitrogen (NH3-N) increased. The addition of SPC enhanced the solution’s pH value and conductivity. The degradation pathway was proposed based on density functional theory (DFT) analysis and relevant literatures. The toxicity of MB was alleviated after O3/SPC treatment. The O3/SPC process was also suitable for the treatment of other dyes and actual wastewater.

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