Study On Fabrication And Photoelectrocatalytic Degradation Of 4-Chlorophenol Over TiO₂ Based Nanotubes

Titanium oxide(TiO₂)nanotubes with uniform morphology are fabricated by electrochemical anodic oxidation method.Combining with some modern physical methods used to characterize the structure,morphology and optical properties of the prepared samples, such as scanning electron microscopy(SEM),X-ray diffraction(XRD),X-ray photoelectron spectroscopy(XPS),UV-Vis diffuse reflectance spectroscopy(UV-Vis DRS),and so on.The results indicate that the as-prepared TiO₂ nanotubes of 90 nm in diameter,20 nm in wall thickness and 1μm in length are grown perpendicular to the titanium substrate.The samples are anatase phase with a fraction of rutile phase.UV-Vis DRS analysis shows that the band gap energy of TiO₂ nanotubes is 3.28 eV.The photoelectrocatalytic(PEC)properties of the as-prepared TiO₂ nanotubes are investigated through the photoelectrodegradation of 4-chlorophenol(4-CP)solution under ultraviolet light irradiation.It is revealed that the PEC degradation efficiency is higher than the sum of photocatalytic and electrochemical processes,which has a synergetic effect.The factors influencing the degradation of 4-CP by the PEC process such as initial concentration of 4-CP,bias potential,pH,UV light intensity and concentration of electrolyte are examined. The stability of TiO₂ nanotubes is also evaluated.The results of the eight repeated experiments under the same experimental conditions show that the PEC degradation efficiency of 4-CP can be kept at above 80%.It is proved that the reaction follows the first-order reaction kinetics.TiO₂/ZnO composite nanotubes are fabricated via a two-step route including electrochemical anodic oxidation method and hydrothermal process.The results of SEM and XPS indicate that the composite nanotubes are made up of TiO₂ and ZnO with diameter ranging from 60 to 80 nm and length of 300 nm.The anatase phase of titanium oxide and the hexagonal wurtzite phase of zinc oxide forms are identified by XRD.Compared with TiO₂ nanotubes,the as-prepared samples have stronger absorbance in UV area and exhibit higher PEC activities,the degradation efficiency of 4-CP is 96.1%in 180 min.Moreover,N-doped TiO₂ nanotubes are fabricated by electrochemical anodic oxidation method.The morphology of the doped samples and the concentration of the incorporated anionic dopants are strong functions of electrolyte composition,potential and anodization time.For N-doped samples UV-Vis DRS indicates a red shift in the primary absorption threshold as well as significant optical absorption in the visible wavelength.N-doped TiO₂ nanotubes exhibit strong PEC activity under visible light irradiation with 4-CP degradation efficiency of 28.7%.