| In recent years, it was found that TiO2thin film has the photoelectrochemical anti corrosion characteristics, it can play the role of metal photocathode protection in corrosive media and has excellent photoelectrochemical response, being the basis for TiO2films to play photocathode protective effect, thus the research about TiO2thin film with higher photoelectrochemical response possesses a great significance in improving its photocathode protective effect. This paper carries out modification about TiO2thin film by adding La3+and Zn2+in TiO2thin film to improve its photoelectrochemical response. XRD, IR, SEM and UV-vis are adopt for characterizing sample’s phase structure, performance and surface morphology; the TiO2semiconductor characteristics Mott-Schottky theory is used for testing the flat band of TiO2, the carrier amount of space-charge layer as well as the width of the space-charge layer; at last, in0.2M NaSO4solution, the open-circuit potential test, impedance spectroscopy and polarization curve test are used for comprehensively evaluate its photocathode protection performance. The photoelectrochemical response of the TiO2thin films of pure magnesium surface is investigated for the first time. The first-principles is adopt for the calculation of pure anatase TiO2and TiO2doped band structure and state density, to explore the impact of doping on light absorption of TiO2from the perspective of theoretical chemistry.Meanwhile, TiO2thin film has a strong ability of acid and alkali-resistant, anti-light corrosion, and adhesion, with good covering ability, which make it a promising anti-corrosion protection material. This paper takes pure magnesium as the object of study, through adding La3+and Zn2+in TiO2, prepares TiO2doped thin film on the surface of pure magnesium, and adopts XRD, DSC/TG, SEM, and the composition and structure of the characterization specimen; the corrosion behavior of TiO2coated pure magnesium in3.5%NaCl solution is studied through potentiodynamic polarization, electrochemical impedance spectroscopy and other characterization methods.Main study deliverables obtained in this paper are as follows:①he study about photoelectrochemical response of TiO2thin film. Take the changing value of open circuit before and after lighting as the evaluation criteria, through orthogonal experiments, investigate the effects of heat treatment temperature, thin film layers, the volume percentage of H2O2and TiO2to photoelectrochemical response of TiO2thin film. Carry out the modification about TiO2thin film by doping La3+and Zn2+, investigate the effects of the doping concentration, heat treatment temperature,thin film layers, the volume percentage of H2O2and TiO2on photoelectrochemical response TiO2doped film. The study found that the temperature is the most important factor to affect the photoelectrochemical response of TiO2thin film, and the temperature for three kinds of films to have the best optimum photoelectrochemical response is300℃, which is because after the heat treatment at300℃,TiO2grains is perfect, the flat-band potential is negative, and the amount of carrier is high.Open-circuit potential changing values of three TiO2thin film after heat treatment at300℃before and after lighting are respectively:543.6mv,837.8mv,896.9mv, which shows TiO2thin film has good photoelectrochemical response Doped La3+and Zn2+could improve the photoelectrochemical response of TiO2thin film, which is because of the increasing amount of carrier. Doped La3+could inhibit the growth of grain and the transition of polymorph, endow TiO2thin film a larger specific surface area, and doped La3+will cause uneven surface charge of TiO2thin film and more activity centers on surface, which is conducive to the occurrence of the surface reaction, so that the photo-generated electron-hole pairs could be effectively separated; while doped Zn2will form a shallow potential well in TiO2thin film, generate ZnO clusters on surface of TiO2thin film and form a composite semiconductor with TiO2, thereby increasing photoelectrochemical response of TiO2thin film. This paper coats the modified TiO2thin film on pure magnesium, for the first time finds that the TiO2thin film shows photoelectrochemical response on pure magnesium, and provides an experimental basis for achieving photogenerated cathodic protection of TiO2thin film on the surface of pure magnesium.②The first-principles calculations about electronic structure shows that:The pure TiO2has a wide forbidden bandwidth near the Fermi level, Eg=2.21eV. Forbidden bandwidth of La3+doped TiO2Eg=2.11eV, optical absorption curve calculations show that La3+doped TiO2absorption edge red shift compared with pure TiO2, expand the spectral response range. Forbidden bandwidth of Zn2+doped TiO2Eg=1.58eV, optical absorption curve calculations show that Zn2+doped TiO2absorption edge red shift compared with pure TiO2and La3+doped TiO2, expand the spectral response range.③he study about the corrosion resistance of TiO2thin film on pure magnesium. The impact of TiO2sol concentration, thin film layers, the heat treatment temperature on the corrosion resistance of TiO2thin film on the surface of pure magnesium is examined by orthogonal experiment, maximum impedance of1083Ω is reached, which is significantly improved compared with its pure magnesium impedance value of41-Ω, indicating that the TiO2thin film could effectively improve the corrosion resistance of pure magnesium.At the same time, it can be found through study that the TiO2thin film cracking as the temperature rises is an important reason for the decline of the corrosion resistance of the TiO2thin film. The modification by doping La3+and Zn2+to TiO2thin film, and finding the heat treatment temperature are still the key factors affecting the corrosion resistance of doped TiO2thin film;its optimum heat treatment temperature is300℃, impedance values were:822.5Ω and1437Ω, the corrosion resistance of the pure magnesium is significantly improved, and showing the doping TiO2thin film more complete at a high temperature. |
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