Preparation Of TiO₂ Nonastructure And Photogenerated Cathodic Protection Of Composites On Metals

TiO₂ has been one of the most important semiconductors for its good environmental friendliness and chemical stability.Its function receives lots of attraction because there is no energy consumed and its film can exist some defects which do not influence its application.However,TiO₂ cannot take full use of the sunlight since its wide band gap?3.2eV?can only respond to ultraviolet ray.Its difficults for the cathodic protection in the darkness because the fast recombination of photo-generated electron-hole?e--h+?pairs.To solve these drawbacks,modifying TiO₂ and its composite films had been studied in this paper.By using semiconductor coupling and noble-metal deposition,Ag/Ag₃PO₄/TiO₂,Ag/CoFe2O₄/TiO₂ composites were prepared to improve the ability of photogenerated cathodic protection.The purpose of this study is to fabricate TiO₂ nanocomposites and to develop simple-operation immersion-deposition,photo reduction deposition and hydrothermal method in order to deposit narrow-bandgap semiconductors and noble metal on the surface of nano-TiO₂ films,and to investigate its potential protection for metals.The correlation between the surface structure of TiO₂-based composite and photoelectrochemical properties was also investigated.The most important things about this study is to increase the amounts of transfer electrons and to release the recombination of photo-generated electron-hole?e--h+?pairs and to obtain the photocathodic protection performances under darkness after fabricating the TiO₂ nanocomposites.The mechanism of the photocathodic protection of the modified TiO₂ composite is also discussed in this thesis.TiO₂ nanowire arrays with special nano network were fabricated by one step electrochemical anodization method.And then the TiO₂ nanowire were modified on the surface.The surface morphology,optical properties and composition were characterized by scanning electron microscope?SEM?,UV-vis diffuse reflectance?UV-vis?and X-ray photoelectron spectroscopy?XPS?,respectively.The photogenerated cathodic protection of pure TiO2 and its composites on 304 stainless steel?304 SS?were measured by using 3.5%NaCl to simply simulate ocean water.The main results are as follows:?1?The influence of reaction time and electrolyte concentration during the preparation of pure TiO₂ nanowire was investigated.It was shown that the pure TiO₂ nanowire prepared with 2 M NaOH after reacting for 180 min exhibited the best photocathodic protection for 304 SS and the longer lifetime of the photoinduced carriers.?2?Ag₃PO₄ and Ag were deposited on the TiO₂ nanowire with immersion-deposition and photoreduction deposition.The effects of Ag₃PO₄ cycle times and Ag content on the photocathodic protection of the composite were investigated and the composite which exhibited the best protection performance were selected.Results show that the composites with best photocathodic protection for 304 SS were prepared by using 6 cycles Ag₃PO₄ and 0.1 M AgNO3 solution on the surface of the TiO₂.In the Ag/Ag₃PO₄/TiO₂,co-sensitization withAg₃PO₄ and Ag nanoparticles leads to high transient photocurrent of 70 ?A·cm^-2.The photopotential of the 304 SS coupled the composite photoanode was about-550 mV under illumination.It also can protect the 304 SS even in the darkness.?3?CoFe₂O₄ and Ag were deposited on the TiO₂ nanowire with hydrothermal method and photoreduction deposition methods.Results show that the Ag/CoFe2O₄/TiO₂ composite film is composed of uniform anatase TiO₂ nanowire,CoFeO₄ and Ag nanoparticles.To enhance the separation efficiency of photoinduced carriers,the best protection composites were selected in the condition of 9 h reaction time and 0.1 M AgNO3 solution.The photocurrent generated by the Ag/CoFe2O₄/TiO₂ composite under visible light can reach approximately 450pA cm^-2.The photo potential of the 304 SS coupled the composite photoanode was about-970 mV under illumination.It also can protect the 304 SS even in the darkness.