Electrocatalytic degradation of ibuprofen in aqueous solution by a cobalt-doped modified lead dioxide electrode: influencing factors and energy demand

Abstract

A Co-doped modified PbO₂ electrode was prepared to electrocatalytically oxidize IBU in aqueous solution. The effects of initial IBU concentration (40–320 mg L⁻¹), initial pH (4–10), current density (3–30 mA cm⁻²), natural organic matter and small molecular organic acid were investigated. The structure, morphology and electrochemical properties of the electrode were studied by X-ray diffraction, scanning electron microscopy, linear sweep voltammetry and cyclic voltammograms. The doping of Co may decrease the particle size and increase the lifetime of PbO₂, which favors the electrocatalytic activity. The results indicated that the Co-PbO₂ electrode exhibited a highly effective oxidation capacity for IBU. After 60 min of electrolysis, the removal of IBU and COD at a current density of 3 mA cm⁻² for 80 mg L⁻¹ of IBU reached 98.7% and 32.1%, respectively, and the degradation of COD was 53.6% after 180 min of reaction. The reaction apparently followed a first-order kinetics model. When the IBU initial concentration was 80 mg L⁻¹, the highest reaction rate and energy efficiency were observed. Considering the energy demand and space efficiency, the applied current density of 3 mA cm⁻² was the most suitable. Lower pH favored degradation because the oxygen evolution reaction was restrained. The addition of low concentrations (10 mg L⁻¹) of humic acid and fulvic acid could promote the degradation of IBU, whereas high concentrations (20–40 mg L⁻¹) inhibited the degradation of IBU. Moreover, the addition of oxalic acid and citric acid (0.1–0.5 mmol L⁻¹) could inhibit IBU degradation. Finally, the possible reaction pathways were proposed.