ELECTROCHEMICAL PURIFICATION OF WASTEWATERS CONTAINING AZOBENZENE

DOI: 10.6060/tcct.20165912.5422
Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2016. V. 59. N 12. P. 118-126

The possibility of electrochemical purification of wastewaters containing azobenzene was studied. The electrolysis was carried out in the electrochemical cell with separated cath-ode and anode compartments and platinum electrodes. Firstly, the electrochemical behaviour of azobenzene at platinum electrode was investigated. The insertion of azobenzene in the 0.1 M solution of sulfuric acid led to the appearance of cathodic currents in the “hydrogen” re-gion of cyclic voltammograms (CVs). These currents corresponded to the electrochemical re-duction of azobenzene. It is important that these reactions occurred at the “hydrogen” region of potentials where the hydrogen adatoms existed at the surface of platinum. More likely, that the reduction of azobenzene proceeds through the interaction of hydrogen adatoms with azo-benzene molecules at the electrode surface. The “double-layer” region of CVs did not change significantly; the currents measured in it were less in comparison with pure solution of 0.5 M H2SO4. There were no sharp differences between the pure solution of sulphuric acid and so-lution containing azobenzene. Nevertheless, the visible disappearance of the color of azoben-zene was observed during the electrochemical treatment. Probably, the oxidation of azoben-zene was caused by the interaction of its molecules with the active forms of oxygen generat-ing at the platinum anode in the course of electrolysis. The particular attention was paid to the indentification of the products of electrochemical transformation. It was shown that the cathode reduction is not unsuitable for this purpose due to the formation of toxic benzidines in the solutions under treatment. This may be result of benzidine rearrangement which occurs in acid solutions. However, the use of neutral and alkaline solutions is impossible because the electroreduction of azobenzene does not take place under these conditions. The electrooxida-tion leads to formation of less toxic products. Among them the polyphenols have been sup-posed. Based on this fact the electrochemical oxidation may be considered as a possible technique for destruction of azobenzene.

Key words: wastewater treatment, azobenzene, electroreduction, electrooxidation, produts of re-duction and oxidation

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2016, Т. 59, № 12, Стр. 118-126

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