Electrochemical Behavior And Simultaneous Determination Of Multi-pollutants At Bdd Electrode

BDD is one of the most popular electrode materials. It exhibits several excellent electrochemical properties, including a wide electrochemical potential window in either aqueous or non-aqueous media, very low background current, corrosion resistance and etc., which make it a promising electrode material for both the determination and the degradation of environmental pollutants. However, it is well-known that environmental pollutants have several special properties, such as the similarity for both their component structure and quality, difficulty of separation, the complex multi-components and etc. So based on BDD electrode's unique electrochemical advantages, it is of utmost significance to study the electrochemical behavior of multi-component pollutants and to realize the simultaneous determination of them.In this paper, we firstly studied the electrochemical behavior and interaction of multi-component organic pollutants and of several kinds of heavy metal ions at BDD electrode. Then cyclic voltammetry, differential pulse voltammetry, differential pulse stripping voltammetry and other electrochemical techniques were adopted to investigate the feasibility of voltammetric separation and simultaneous determination of mutil-pollutant system at BDD electrodes. Finally, an analytic method for the direct and swift determination of multi-component environmental pollutants with low-cost was established satisfyingly.Consequently, our research job which is concerning the feasibility of electrochemical oxidation of representative non-biodegradable and refractory aromatic compounds at boron-doped diamond electrode is a challenging and primary one for the further research of direct electrochemical oxidation and degradation of aromatic compounds.(1) Simultaneous electrochemical determination of multi-component system of organic pollutants was realized at BDD electrode. Here, cyclic voltammetry and differential pulse voltametry were adopted to study the electrochemical redox behavior of phenol, hydroquinone, 4-nitrophenol at BDD electrode. We also discussed the absorption competition among organic pollutants primarily in this work; And then the separation of multi-component systems, such as phenol and hydroquinone, phenol and 4-nitrophenol, hydroquinone and 4-nitrophenol, phenol, hydroquinone and 4-nitrophenol, has been implemented. As a result, a simple and sensitive method for simultaneous determination of multi-component of hydroxybenzene pollutants has been established.(2) With the electrochemical behavior of multi-metal-ion system investigated, a method of simultaneous determination of multi-metal-ion system has also been set up. Choosing Ag⁺, Cu²⁺, Pb²⁺, Sn²⁺ as our research objects, cyclic voltammetry, differential pulse voltammetry, differential pulse stripping voltammetry and other electrochemical techniques were used here to investigate the electrochemical redox behavior of both single-metal-ion system and multi-ion system at BDD electrode in nitric acid solution or in acetate buffer solution respectively. Whereafter, the interaction among metal ions was studied during their co-deposition process at BDD electrode. And the feasibility of electrochemical separation of multi-metal-ion system was discussed. Finally, the simultaneous determination of multi-metal-ion system at BDD electrode was realized.(3) The electrochemical oxidation of aromatic compounds at BDD electrode was studied. For this purpose, linear sweep voltammetry and differential pulse voltammetry were adopted for the investigation of electrochemical oxidation of benzene, toluene, m-xylene, p-xylene and ethylbenzene at BDD electrode in 0.5 M H2SO4 solution as a supporting electrolyte. The absorption of aromatic compounds at BDD was studied by chronocoulometry, the electrochemical oxidation mechanism of aromatic compounds was further dicussed by chronoamperometry and the redox behavior of aromatic compounds at BDD electrode was investigated by cyclic voltammetry. As a result of these explorations, it was found that there was no reduction peak emerged during the whole negative scanning process of cyclic voltammetry, which means that the redox reaction of aromatic molecules should be irreversible. To prove this assumption, our following research was mainly focused on analysing the redox behavior of aromatic molecules at BDD electrode during the positive linear sweeping process. And our experimental results indicated that the oxidation peak quantity of benzene, toluene, m-xylene, p-xylene and ethylbenzene at BDD electrode is 2, 3, 3, 3 and 4 respectively. And the difference between these data and the varieties of H atoms with different charge density on the aromatic molecules calculated theoretically is found to be only 1. The highest oxidation potential was located at a potential higher than the oxygen evolution potential at BDD electrode, which may be caused by the opening of benzene ring. Simultaneously, the oxidation peak emerged at the lowest oxidation potential may be induced by the oxidation of H atoms on benzene ring with the same charge density. So according to the above results, we believe that there should be a very close relationship between the multiple oxidation peaks which are amidst the two oxidation peaks located at both the lowest potential and the highest potential and the oxidation of H atoms located on the benzene substituent groups, such as-CH₂-and-CH₃ respectively. According to our supposition, if substituent existed, then the greater the varieties of H atoms on the substituent are, the more oxidation peaks of aromatic molecules at BDD electode would be, and the lower the initial oxidation potential of aromatic molecules would be. For example, the initial oxidation potentials of benzene, toluene and ethylbenzene are 1.91V, 1.75V and 1.67V respectively. If the substituents on benzene ring were the same ones, then the larger the quantity of substituents is, the more easily the aromatic would be oxidized. For example, the initial oxidation potentials of p-xylene and toluene are 1.63V and 1.75V respectively. Besides, it was observed that the substituent location would have no effect on the property of oxidation. For example, the initial oxidation potentials of p-xylene and m-xylene are 1.63V and 1.64V respectively. The results are interesting and promising. It indicates that the direct electrochemical oxidation of aromatic molecules at BDD electrode can be realized, Under different oxidation potentials, both the oxidation extent and the oxidized products' structure of aromatic molecules can be under control effectively.