Quantification Of The Hydroxyl Radicals In The Plasma Electrochemical System

There are many active components in the plasma.When the plasma comes into contact with the liquid,it will cause a variety of physical and chemical reactions at the plasma-liquid interface,resulting in the formation of a plasma electrochemical system.The hydroxyl radical(OH),owing a strong oxidizing property,is one of the many highly active substances in the plasma electrochemical system.Because OH is extremely reactive,it can quickly react with other substances,and it plays an important role in the application of a series of plasma electrochemical systems.Therefore,it is very important to quantitatively detect the OH radicals in the plasma electrochemical system.However,due to the extremely short existence of OH radicals,it is difficult to directly detect them,so many detections are based on indirect methods.In order to better extend the application of plasma electrochemical system,we used an indirect detection technology,the molecular probe method,to quantify the OH radicals in the plasma electrochemical system.Four chemical probes are used to detect OH radicals,Indigo Carmine(IC),Ferrous Sulfate(FeSO4),Disodium Terephthalate(NaTA)and Methyl Orange(Methyl Orange,MO).The above four substances have high reaction rates with respect to OH radicals,and basically they do not participate in the reaction with other active substances in the liquid phase.In addition,these chemical probes or their reacted derivatives have relatively sensitive color or fluorescence characteristics,and therefore it is easy to perform quantitative measurements by spectroscopic method.In the IC experiment,we investigated the relationship between the yield of OH radicals and the initial concentration of molecule probe through the decomposition rate of IC.It is consistent with the theoretical analysis,we found that the OH yield increases with the increase of the initial concentration of the molecule probe due to the existence of a competitive reaction.In the experiments of ferrous sulfate and disodium terephthalate,we quantitatively measured the production of OH radicals in the liquid phase in the plasma electrochemical system according to the related principle of the competitive reaction of OH radicals.For the current of 30 mA using liquid as cathode,the yield of the liquid phase OH radicals is 237 μmol/min given by the ferrous sulfate experiment,and 310μmol/min given by the the NaTA experiment.In the experimental part of MO,we focused on the effects of different experimental conditions on the decomposition of MO.The results showed that the yield of the liquid OH radicals is affected by the pH value,discharge current,and liquid polarity.High yield of the OH radicals is obtained at the conditions of low pH value,high current and liquid cathode.