On the Kinetics and Mechanism of Electrochemical Decomposition of 3- Chloropyridine in Aqueous Solution

Electrochemical oxidation of 3-chloropyridine (3-ClPYR), as a model pollutant, on a modified β-PbO2 electrode was examined by bulk electrolysis. Parameters affecting the removal and reaction rate of 3-ClPYR, such as current density, pH and initial concentration, were investigated. The results showed that 3-ClPYR could be readily decomposed under the attack of hydroxyl radicals (·OH) electrochemically generated on the modified β-PbO2 anode, the removal of 3-ClPYR was confirmed satisfactorily to fit pseudo-first order kinetics, the rate constant was mainly governed by current density and pH of 3-ClPYR solution. The evolution of intermediates was examined with 200 mg·L-1 of 3-ClPYR at pH 6.2, 3.0 g·L-1 of Na2SO4 and 160 mA·cm-2 of current density. Pyridine was firstly formed via starting with the scission of C-Cl bond. When the initial concentration of 3-ClPYR was above 600 mg·L-1, 2, 3-dichloropyridine and 3, 5- dichloropyridine were also detected in a very small quantities owing to the addition of chlorine radicals (·Cl). Then, pyridine and chlorinated pyridine were further cleaved to organic acids (oxalic acid, acetic acid, formic acid and propionic acid) and inorganic ions (Cl-, NO2 -, NO3 -, ClO-) via opening the nitrogen containing heterocyclic ring, indicating the promising use of electrochemical technique for clean and safe removal of nitrogen containing heterocyclic compounds from industrial effluents.