Electrochemistry Degradation Of Organic Pollutants With Boron-doped Diamond (bdd) Electrode

As a new kind of the most popular electrode materials, boron-doped diamond (BDD) film electrode exhibits several excellent electrochemical properties that electrochemical catalytic anodes should possess, including high electrochemical stability, excellent and hardly deactivated catalytic property, a wide electrochemical potential window in either aqueous or non-aqueous media, and especially high oxygen evolution potential which makes BDD a prevalent electrode extensively concerned in the domestic and foreign environment and electrochemistry discipline. In this paper, BDD electrode, as a work electrode, was firstly adopted to study the electrochemical oxidation behavior of several typical organic pollutants, such as benzene, methylene blue, aroma acid. Then the degradation efficiency and the mechanism of electrochemical oxidation of these non-biodegradable and refractory organic pollutants at BDD electrode was investigated by galvanostatic oxidization degradation combined with other electrochemical techniques, UV-VIS spectrum and HPLC.The electrochemical oxidation degradation of a non-biodegradable and refractory aromatic molecule, benzene, at BDD electrode was realized. Under the current density of 10mA/cm~2, electrode area of 5cm~2, solution volume of 50ml, after 11 hours of electrochemical oxidation, the removal efficiency of TOC was achieved to be 94.3%, which means benzene at BDD electrode could be completely degraded. Moreover, in situ differential pulse voltamrnetry, UV-VIS spectrum and HPLC were used to investigate the degradation process. It was observed that during the whole process, the intermediate products of benzene primarily oxidized at BDD electrode were phenol, hydroquinone, resorcin, catechol and etc. With this process proceeding, a great amount of hydroxyl radicals emerged nearby BDD electrode, the initial and remnant benzene plus the above phenol-like intermediates was further losing electrons or subjected to these hydroxyl radicals attacking. As a result of this, these rings of benzene and phenol-like intermediates were opened. And these substances were converted into little molecules of fatty acids, such as oxalic acid and maleic acid which would be further degraded. As well-known, the oxidation potential of benzene is achieved as high as 2.8V, which makes the moderate oxidation and degradation of aromatic compounds by electrochemical technique of great significance in the field of both theoretical research and practical application. With and without chlorine presented in supporting electrolyte, the oxidation degradation of methylene blue at BDD electrode was studied respectively. The following results at BDD electrode were compared with the ones at Pt, Graphite, and DSA electrode. And it was found that the direct electrochemical oxidation of organic compounds at BDD electrode proceeded more facilely because of the higher oxygen evolution potential ofBDD electrode. It indicates that BDD electrode is fit for the direct electrochemical degradation of organic pollutants under the condition of no chlorine presented in supporting electrolyte. On the contrary, due to the same higher chlorine evolution potential at BDD electrode, it is much harder for BDD electrode to generate a great amount of chlorine which can degrade organic pollutants indirectly. Hereby, it is not of avail for increasing the current efficiency of indirect oxidation. So the unique electrochemical property of BDD electrode will not be exerted effectively. The degradation results of concentrated methylene blue solution shows that BDD electrode, compared with the other electrodes, is suitable for direct electrochemical degradation with no chlorine presented in supporting electrolyte. And the current efficiency of degradation was almost achieved to be 100%. The kinetics formula of degradation calculated from the COD values agreed with the model of first-order reaction quite well. And the degradation rate constant was calculated to be 0.00891rain-1. During the degradation process of methylene blue, the dynamic analytical data obtained from UV-VIS spectrum and electrochemical techniques indicated that the removal rate of COD and decoloration rate were isochronous, which means the whole molecule conjugate system of methylene blue was completely destructed during the oxidation process at BDD electrode. The dye molecules were therefore decolored and mineralized.The electrochemical oxidation technique at BDD electrode with ultrasound electric microfield degradation was explored. And the results gained from three methods, electrochemical oxidation, ultrasound electric microfield degradation, and electrochemical oxidation-ultrasound electric microfield degradation, were compared for the degradation of phthalic acid. It was obtained that the degradation of phthalic acid could not be achieved by only ultrasound electric microfield degradation, while the degradation efficiency of phthalic acid through only electrochemical oxidation at BDD electrode was perfect. Under the condition of current density of 20mA/cm~2, electrode area of 3.85cm~2, solution volume of 20ml, after 4 hours of electrochemical degradation, the removal efficiency of TOC was achieved to be 100%. The degradation rate of phthalic acid could be enhanced highly by electrochemical oxidation with ultrasound electric microfield degradation It was calculated that after 1.5 hours of degradation, the removal efficiency of TOC was 99.37%, which indicates that ultrasound electric microfield has an effective and strengthening effect on the oxidation process at BDD electrode. As a conclusion, we believe that the cooperative treatment through ultrasound electric microfield with electrochemical oxidation should be one of the most effective degradation techniques for the degradation of pollutants.