Detection And Research Of The Hydroxyl Radicals That Generated By Electrochemical System

With the rapid development of industry in our country, particular focus was given to the water problem. The poor biodegradability organic wastewater makes us to facing the unprecedented challenge. It is difficult to achieve satisfactory results by using the traditional method. Very recently, electrochemical oxidation technologie had been investigated for its advantages, such as it has good environmental compatibility, high efficiency, non-secondary pollution, ease of control, and amenability to automation. The electrochemical oxidation technologie has attracted much attention of researchers both domestic and overseas. Hydroxyl radical(·OH) is generated by the electrochemical oxidation reaction as a strong oxidizer. Therefore, detecting the generation and influence of ·OH for optimizing reaction conditions and reactor design, researching the mechanism of electrochemical oxidation of organic compounds are very important.Adding [emim]BF4 to the Ti/ PbO2 electrode was prepared by selecting electrodepositing. Scanning electron microscopy(SEM), X-ray diffraction(XRD), electrocatalytic performance experiment of activity and stability were employed for this study. The Ti/ PbO2 electrode was optimal with 50mg/L [emim]BF4 at 50℃. This new type electrode was treated as an excellent one owing to its great crystalline morphology, uniform and dense in out-layer microstructure, high activiy and stable in property. The high performance Ti/ PbO2 electrode was proved to be ·OH producing electrode.High performance liquid chromatography with ultraviolet detection(HPLC-UV) was employed to determine the amount of ·OH by using salicylic acid(SA) or 4-hydroxybenzoic acid(4-HBA) as a probe in electrochemical reaction system. Chromatographic separation was performed under isocratic conditions, using a mobile phase of a 40:60(v/v) mixture of methanol and water(pH 3.5) at 30℃ with a flow rate of 1.0m L/min for 20 min. The system has an injection value with a 20μL loop. The effects of some important factors, such as the trapping efficiency of different selected probes and the initial concentration of probes, were investigated. The resolution and the coefficient correlation of the new method can achieve preferable results. The results showed that the electrochemical reaction of SA or 4-HBA with ·OH fitted the first-order kinetics and the relative rate constant was 2.1833×10-4s-1 or 1.3500×10-4s-1 respectively. The capacity of SA was three times than 4-HBA, SA has a higher sensitivity than 4-HBA. Therefore, SA was considered as the optimum probe in this paper.SA was chosen as the probe in electrochemical oxidation system. The influence of ·OH generation rules in electrochemical oxidation system was investigated from the property of electrolyte, the condition of electrolysis reactor, and the input energy. The results showed that the generation rate of ·OH would increase with the increasing reaction pH value, so the alkaline electrolyte was favorable for generating ·OH. The increasing current density increased the generation rate of ·OH, while the current density was over 10mA/cm2, the increasing trend of the ·OHs’ generation rate was gradually flat. The generation rate of ·OH increased first and then decreased with support electrolytes selected in lower concentrations. The optimum reaction condition was chosen at 0.03mol/L Na2SO4 as supporting electrolyte. Inorganic inhibitor was stronger than organic inhibitor during the ·OH generating process, and the inhibition effect of Na2CO3 on producing ·OH was the strongest. When the plate spacing was increased, the generation rate of ·OH would increased frist and then decreased. The electrolysis efficiency was the highest, when the plate spacing set as 3cm. Stainless steel could save energy consumption in electrochemical system.