Kinetics of the electrochemical oxidation of 2-nitrophenol and 4-nitrophenol studied by in situ UV spectroscopy and chemometrics

Here we report on the elimination of 4-nitrophenol (4-NPh) and 2-nitrophenol (2-NPh) from aqueous solutions by electrochemical oxidation at the dimensionally stable anodes (DSA) Ti/IrO2–SnO2–Sb2O5. The ternary oxide electrodes show high catalytic activity for the electrochemical oxidation of nitrophenolic compounds. UV–vis spectroscopy was employed to in situ monitor time-dependent concentration changes during the electrochemical oxidation of the 2-NPh and 4-NPh. A kinetic analysis of the electrochemical oxidation of 2-NPh, 4-NPh and a mixture of the two has been carried out. The electrochemical oxidation of 4-NPh and 2-NPh is governed by the hydroxyl radical reaction and obeys the first-order kinetics with the overall apparent activation energy of 8.3 and 9.2 kJ mol−1, respectively. Partial least squares (PLS) regression was performed to resolve the highly overlapping spectrophotometric signals measured from the mixture of 4-NPh and 2-NPh. In situ UV–vis spectroscopic measurements in combination with PLS multivariate calibration enabled us to determine the competitive effects during the electrochemical treatment of variety of mixtures of 2-NPh and 4-NPh, showing that the presence of 2-NPh inhibits the electrochemical oxidation of 4-NPh.