Simultaneous Removal Of Cr(?) And Acid Orange 7 From Water Solution By Dielectric Barrier Discharge Plasma

Dye wastewater containing a large number of dye molecules and heavy metal ions cause tremendous pollution to the ecological environment.In recent years,non-thermal plasma technology has been widely used in the treatment of waste gas and wastewater.Most of the researches only focus on the oxidative degradation of organics by non-thermal plasma.However,the reduction of non-thermal plasma has a little attention.Non-thermal plasma technology not only has oxidation but also reduction Therefore,it provides theoretical possibilities for simultaneously oxidizing organic pollutants and reducing pollutants in water.In this study,the dielectric barrier discharge plasma technique(DBD)was used to remove AO7 and Cr(?)in water.Firstly,the feasibility of simultaneous removal of AO7 and Cr(?)by DBD was verified.By analyzing the UV-vis spectra of AO7 and Cr(?),it can be concluded that both AO7 and Cr(?)can be simultaneously removed in DBD.Then the effects of different reaction parameters on the removal efficiency of AO7 and Cr(?)were investigated,such as concentration of AO7 and Cr(?),discharge voltage,pH,organic matter and inorganic metal cation.The experimental results show that the coexistence of AO7 and Cr(?)has synergistic effect.The pH of the solution is also an important parameter.When the pH of the solution drops from 10.5 to 3.0 in the system of existing AO7 and Cr(?)alone,the removal rates of AO7 and Cr(?)increased from 60.18%and 66.67%to 93.80%and 94.12%respectively.When the solution contains both AO7 and Cr(?),the removal efficiency of AO7 and Cr(?)also increase with the decrease of pH,but the effect of pH on the removal efficiency is weak.The effect of discharge voltage is relatively simple.When the discharge voltage was rised from 80.0V to 120.0V,the removal rates of AO7 and Cr(?)increased from 62.17%and 53.6%to 89.96%and 88.0%,respectively.When the solution contains organic or inorganic metal cations,the removal efficiency of AO7 and Cr(?)will have some changes-The organic matter in the solution hinder the degradation of AO7 and promote the reduction of Cr(?),such as methanol,ethanol,isopropanol,acetic acid,citric acid,oxalic acid.When the solution contains inorganic metal cations(Cu(?),Co(?),Ni(?),Mn(?),and Fe(?))inhibit the reduction of Cr(?),the effect on AO7 degradation is small.And the analysis of emission spectra for the DBD and free radical experiments were carried out.The result confirms the existence of N2 radicals and OH radicals during the DBD.Therefore,it provides a theoretical basis for the simultaneous removal of AO7 and Cr(?)in water by DBD.The free radical experiments have demonstrated the important role of·OH and ·H in the removal of AO7 and Cr(?)in DBD.Finally,the degradation products of AO7 in the DBD reaction system were analyzed by HPLC and LC-MS/MS.The main degradation pathway of AO7 in the DBD reaction system was deduced.The degradation pathway at AO7 can be summarized as follows:AO7 is attacked by·OH,the azo bond(-N=N-)in AO7 is broken,the solution is decolorized,and sulfanilamide and naphthalenes with amino groups are generated.And then the amino group is oxidized to nitro or replaced by hydroxy.While hydroxy is oxidized to aldehyde,aldehyde is oxidized to acid.Then the benzene ring is opened,AO7 is degraded to CO2 and H2O through a series of reactions.