Electrochemical oxidation of pyrrole, pyrazole and tetrazole using a TiO2 nanotubes based SnO2-Sb/3D highly ordered macro-porous PbO2 electrode

A highly ordered three-dimensional macro-porous PbO2 (3D porous PbO2) electrode has been prepared for electrochemical oxidation of nitrogen-heterocyclic compounds. The 3D porous PbO2 electrode was fabricated by templated electrochemical deposition method with TiO2 nanotube arrays as substrate and SnO2-Sb as intermediate layer. The morphology and composition characterization of the 3D porous PbO2 electrode was performed by field emission scanning electron microscopy and X-ray diffraction, which revealed a uniform distribution of highly ordered macro-porous β-PbO2 structure. The Brunner−Emmet−Teller analysis suggested the electrode possessed large specific surface area of 37.39 m2·g−1. Electrochemical measurements indicated the electrode had a favourable oxygen evolution potential of 1.89 V and inner voltammetric charge of 14.48 mC·cm−2, which were higher than that of conventional PbO2 electrode. Furthermore, the electrochemical oxidation and TOC removal percentage of pyrrole, pyrazole and tetrazole obtained by 3D porous PbO2 electrode were 93.4%, 72.7%, 61.2% and 66.7%, 57.3%, 38.6% respectively, which were also superior to conventional PbO2 electrode. The intermediates were detected and analyzed by high-performance liquid chromatography, gas chromatography-mass spectrometer, and ion chromatography to propose a degradation pathway of pyrrole, pyrazole and tetrazole. Finally, quantum chemical calculation was introduced in this study by density function theory method, which is consistent with the experimental detection.