Preparation Of TiO₂/ZnO Composite Film And Its Photo-cathodic Protection Properties

Since TiO2film is not sacrificial, long-lasting and low cost during the process ofcorrosion protection, the photogenerated cathodic protection of TiO2film has receivedmuch attention of corrosion researchers recently. However, TiO2can only be excitedby ultraviolet light, causing the low utilization of solar energy. Besides, the quantumefficiency is low due to the rapid recombination of photogenerated electrons and holes.To overcome these problems, TiO2/ZnO composite film has been prepared and thecoupling effect of the band gap of the two semiconductors and the higher electronmobility of ZnO have been investigated on improving the photocathodic protectioneffect.TiO2/ZnO composite films with the different composite modes were prepared onthe surface of the304stainless steel (304SS) by the sol-gel technology and heattreatment. The phase composition, microstructure and light absorption properties ofas-prepared TiO2/ZnO composite film were characterized by X-ray diffraction (XRD),the scanning electron microscope (SEM) and ultraviolet-visible (UV-Vis)spectroscopy, respectively. The influences of composite modes and the annealingtemperature on the photoelectric property have been investigated by using theelectrochemical method. The results indicate that the composite film prepared by thelayered coating and double-step heating method exhibit the betterphoto-electrochemical effect due to the avoiding the interaction between TiO2andZnO in the crystallizing process. Moreover, the photo-electrochemical effect ofTiO2/ZnO composite film can be achieved the best value when the annealingtemperature of ZnO film and TiO2film is450℃and500℃, respectively.Potentiodynamic polarization curve and ac impedance were used to study thephotocathodic protection property of TiO2/ZnO composite film for304SS. It found that TiO2/ZnO films can impeded the interactions between the substrate andsurrounding, serve as a barrier layer to protect the304SS substrate from corrosion inthe dark. Under light illumination, the photocathodic protection performance ofTiO2/ZnO composite film was significantly improved in comparing with that of pureTiO2film.TiO2(P25)/ZnO composite films were prepared on the304SS and the effect ofTi/Zn molar ratio and the annealing temperature on the photoelectric property of thefilms has been investigated. The results indicate that the TiO2(P25)/ZnO compositefilm with Ti/Zn molar ratio of5:1and annealed at500℃exhibited the betterphotoelectric property. The SEM analysis show that such composite film has thethree-dimensional porous network of TiO2and ZnO nanoparticles, which enhancesthe light absorption. The UV-Vis results also showed that the TiO2/ZnO compositefilm displays a strong photo-absorption in UV light, and the absorption edge show ared shift to the visible spectrum range. On the other hand, the mixture effect of TiO2and ZnO leads to the better separation and transfer of photogenerated electrons andmuch higher quantum effciency. As a result, all above endows the TiO2/ZnOcomposite films a better photo-cathodic protection under light illumination for304stainless steel.