Abstract
The mechanism of methylene blue (MB) oxidation initiated by hydroxyl radicals (·OH) in a gas–liquid multiphase plasma reactor was investigated. Direct current corona plasma was applied to produce ·OH. The effects of liquid solution pH and plasma-forming gas components (air, N2, He, CO2) were evaluated. The removal of MB exceeded 90 % after 3 h of treatment under an air atmosphere at neutral pH, and it was shown to be mainly through the function of ·OH. Further experiments demonstrated that ·OH was mainly produced through electron-molecule collision processes. The energy efficiency of the process was assessed to be as high as 3.8 × 10−3 mol/kWh when the removal of MB reached 95.7 %. This high value was due to the countless liquid droplets greatly increasing the contact surface area. The results using CO2 as the forming gas indicated that the carbonate in solution has a negative effect on the generation of ·OH.
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