Synergetic degradation of Acid Orange 7 (AO7) dye by DBD plasma and persulfate

Abstract

The synergetic degradation performance of Acid Orange 7 (AO7) by dielectric barrier discharge plasma (DBDP) and persulfate (PS) was examined. Addition of PS in AO7 solution hardly degraded any AO7 in 50min, but when DBDP was initiated over the solution surface, PS greatly enhanced the decolorization efficiency of AO7, and the improvement efficacy depended on the addition dosage of PS, the applied voltage, the air discharge gap and the gas discharge atmosphere. An increase in AO7 decolorization efficiency of 60% was obtained for AO7 solution of 5mg/L at a PS addition dosage of 100:1 (molar ratio of PS to AO7) and a discharge power of 3.6W, correspondingly, the decolorization rate of AO7 was accelerated by 6.7 times. The improvement on AO7 degradation mainly attributes to the enhanced production of sulfate radical (SO4−) and hydroxyl radicals (OH) which are produced from the activated PS by DBD plasma. The activators of PS were tentatively speculated as the UV irradiation and heat released in discharge channels, and hydrated electrons may also play a role in the activation process of PS. The intermediates identified by GC–MS and the TOC measurement show that addition of PS into AO7 solution had little effect on the degradation pathways of AO7, but greatly improved the mineralization of AO7, which was mainly due to the increased production of SO4− and OH.