Removal of tetracycline by electrochemical oxidation using a Ti/SnO2-Sb anode: characterization, kinetics, and degradation pathway

A Ti/SnO2-Sb anode was prepared and used for the electrochemical oxidation of tetracycline (TC). The effects of the reaction conditions, including the current density (5-25 mA cm(-2)), the distance between anode and cathode (5-25 mm), and the initial TC concentration (5-100 mg L-1), on the electrochemical degradation kinetics of TC, were investigated. The degradation of TC followed pseudo-first-order kinetics (R-2 > 0.95). The TC degradation efficiency increased with the applied current density and decreased with the increase of the distance between anode and cathode. The TC degradation efficiency was almost the same when the initial TC concentration was less than 20 mg L-1 but decreased when it was higher than 20 mg L-1. Higher total organic carbon removal efficiency was obtained with a higher applied current density. The mineralization current efficiency gradually fell with increasing applied current density. A degradation pathway was proposed for the electrochemical oxidation of TC: Radicals produced from electrochemical oxidation attack the double bonds, phenolic group, and amine group in TC, resulting in the formation of the intermediate compounds with m/z values of 461, 477, 432, 509, 480, 448, and 525, which are then oxidized to an intermediate with m/z value of 496.