Fabrication of a novel PbO₂ electrode with rare earth elements doping for p-nitrophenol degradation

A novel PbO₂ electrode modified with rare earth elements (La, Ce, Gd and Er) doping (named as Re-PbO₂) was prepared by electrodeposition in the present study. The micro-morphology and crystal structure of Re-PbO₂ were characterized by scanning electronic microscopy (SEM), energy dispersive spectroscope (EDS), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Their electrochemical properties were determined by linear sweep voltammetry (LSV), cyclic voltammetry (CV), accelerated life test and hydroxyl radicals (•OH) formation analysis. Electrochemical oxidation of p-nitrophenol (p-NP) by Re-PbO₂ compared with un-doped PbO₂ has been investigated and the degradation rate followed the order of Er-PbO₂ > Gd-PbO₂ > La-PbO₂ > Ce-PbO₂ > PbO₂. Especially for Er-PbO₂, the pseudo-first order kinetic for p-NP (k_p-NP) degradation was 0.41, which was only 0.19 for un-doped PbO₂. Rare earths elements doping improved the oxidation ability of Re-PbO₂ mainly through reducing grain size, increasing oxygen evolution potential, enlarging electrochemical active surface area and enhancing •OH formation ability. In addition, existing formation of oxygen species on PbO₂ electrode surface was investigated by XPS. For Re-PbO₂, percentage of lattice oxygen species (O_ads) were higher than that on the un-doped one. These results demonstrated that rare earth elements can enhance the oxidation ability of PbO₂ electrode significantly.