Preparation of Zn-doped TiO₂ nanotubes electrode and its application in pentachlorophenol photoelectrocatalytic degradation

Abstract

Zn-doped titanium oxide (TiO₂) nanotubes electrode was prepared on a titanium plate by direct anodic oxidation and immersing method in sequence. Field emission scanning electron microscopy (FESEM) showed that the Zn-doped TiO₂ nanotubes were well aligned and organized into high density uniform arrays with diameter ranging from 50 to 90 nm. The length and the thickness were about 200 and 15 nm respectively. TiO₂ anatase phase was identified by X-ray diffraction (XRD). X-ray photoelectronspectroscopy (XPS) indicated that Zn ions were mainly located on the surface of TiO₂ nanotubes in form of ZnO clusters. Compared with TiO₂ nanotubes electrode, about 20 nm red shift in the spectrum of UV-vis absorption was observed. The degradation of pentachlorophenol (PCP) in aqueous solution under the same condition (initial concentration of PCP: 20 mg/L; concentration of Na₂SO₄: 0.01 mol/L and pH: 7.03) was carried out using Zn-doped TiO₂ nanotubes electrode and TiO₂ nanotubes electrode. The degradation rates of PCP using Zn-doped TiO₂ nanotubes electrode were found to be twice and 5.8 times as high as that using TiO₂ nanotubes electrode by UV radiation (400 μw/cm²) and visible light radiation (4500 μw/cm²), respectively. 73.5% of PCP was removed using Zn-doped TiO₂ nanotubes electrode against 48.5% removed using TiO₂ nanotubes electrode in 120 min under UV radiation. While under visible light radiation, the degradation efficiency of PCP was 18.4% using Zn-doped TiO₂ nanotubes electrode against 3.2% using TiO₂ nanotubes electrode in 120 min. The optimum concentration of Zn doping was found to be 0.909%. The PCP degradation efficiencies of the 10 repeated experiments by Zn-doped TiO₂ nanotubes electrode were rather stable with the deviation within 3.0%.