Insights of ibuprofen electro-oxidation on metal-oxide-coated Ti anodes: Kinetics, energy consumption and reaction mechanisms

Electrochemical degradation of ibuprofen (IBP) was performed on three types of Ti-based metal oxide electrodes. The degradation of IBP followed pseudo-first-order kinetics and the electrochemical degradation rate constant (k) over Ti/SnO2-Sb/Ce-PbO2 (9.4 x 10(-2) min(-1)) was 2.0 and 1.7 times of the values over Ti/Ce-PbO2 (4.7 x 10(-2) min(-1)) and Ti/SnO2-Sb (5.6 x 10(-2) min(-1)), respectively. The removal of total organic carbon and the energy consumption per order for IBP degradation were 93.2% and 13.1 Wh L-1, respectively, under the optimal conditions using Ti/SnO2-SbiCe-PbO2 anode. Six aromatic intermediate products of IBP were identified by ultra-high-performance liquid chromatography coupled with a quadrupole time-of-flight mass spectrometer. The electrochemical mineralization mechanism of IBP was proposed. It was supposed that center dot OH radicals produced on the surface of anode attacked IBP to form hydroxylated IBP derivatives that were then followed by a series of hydroxylation, loss of isopropanol and isopropyl, decarboxylation and benzene ring cleavage processes to form simple linear carboxylic acids. By successive hydroxylation, these carboxylic acids were then oxidized to CO2 and H2O, achieving the complete mineralization of IBP. (C) 2016 Elsevier Ltd. All rights reserved.