Preparation Of Zn-doped TiO₂ Nanotubes Electrode And Its Application In Pentachlorophenol Photoelectrocatalytic Degradation

Photocatalytic oxidation is a kind of photosensitive oxidation method using n-style semiconductor as a photocatalyst, which is based on. the energy band theory of this photocatalyst. Of most photocatalysts used in wastewater treatment, TiO₂ has been used most commonly because it is cheap, and, is more effective and stable. However, the high recombination rate of the photoinduced electron/hole pairs and the low light utilization efficiency to solar irradiation in photocatalysis process make it hard to be put into practical application. Selective doping of some metals had been proved to be an efficient route to improve the photoactivity of TiO₂. Those doped metals can not only act as the active center for separating photoinduced electron/hole pairs, but also induce red shift in UV-vis absorption spectrum, and consequently improve the utilization efficiency of visible fight.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 photoelectron spectroscopy (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: 20mg/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 (400μw/cm²) and visible light radiation (4500μw/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. Zn-doped TiO₂ nanotubes electrode are rather stable.The effect factors of the photoelectrocatalytic degradation of PCP in solutions by Zn-doped TiO₂ nanombes electrode were investigated, such as light intensity, bias potential and the concentration of Zn doping. It's found that the degradation efficiency of PCP is enhanced when increasing light intensity, or bias potential. The optimum concentration of Zn doping was found to be 0.909%.