Modification Of TiO₂ Nanotube Array Films And Their Photocathodic Protection Effects

TiO2 is a semiconductor material with excellent photoelectrochemical properties.It can provide photocathodic protection for metallic materials.However,TiO2 can only absorb ultraviolet light(wavelengths less than 380 nm)because of the wide band gap.In addition,the photo-induced electron-hole pairs in the TiO2 semiconductor are easy to recombine,which may decrease the photoelectric conversion efficiency.Another shortcoming is that a pure TiO2 semiconductor cannot sustain photocathodic protection in the darkness after illumination is stopped,which can limit its practical application to photocathodic protection.To address these shortcomings,some modification methods have been established for improving the photoelectrochemical properties of TiO2 semiconductor materials.In this work,different TiO2 nanotube composite films with charge storage ability were prepared for enhancing the photocathodic protection performances of the films.The main research results are listed as follows:(1)A Ag/SnO2/TiO2 nanotube composite film with energy storage ability has been prepared by anodic oxidation combined with hydrothermal reaction and pulsed electrodeposition.The optical absorption edge of the composite film showed a significant red shift compared with the pure TiO2 nanotube film.Under white light illumination,the Ag/SnO2/TiO2 composite film photoanode made the potential of the coupoled 403 stainless steel(403SS)in a 0.5 mol L-1 NaCl solution decrease by 475 mV,showing a more effective phtocathodic protection effect than the TiO2 nanotube film.After the illumination was stopped,the composite film could still maintain a certain cathodic protection for 403SS for more than 22.5 h resulting from its charge storage ability.(2)A TiO2 nanotube array film was formed on a Ti foil via anodic oxidation,MoO3 and ZnSe nanoparticles were deposited on the film successively by cyclic voltammetry and pulse electrodeposition to obtain a ZnSe/MoO3/TiO2 nanotube composite film with a cascade band structure.The results showed that the light absorption intensity of the ZnSe/MoO3/TiO2 composite film was obviously increased in the visible region compared with the pure TiO2 film.In addition,the composite film could make the potential and charge transfer resistance of the coupled 403SS in a 0.5 mol L-1 NaCl solution decrease significantly,showing a good photocathodic protection effect.(3)A combined method of cyclic voltammetry electrodeposition and hydrothermal reaction was used to synthesize a g-C3N4/MoO3/TiO2 composite film.After replacing ZnSe nanoparticles with g-C3N4 quantum dots,the composite film became a more environmentally friendly material.The results showed that the g-C3N4/MoO3/TiO2 composite film could effectively inhibit the recombination of photogenerated carriers,resulting in the improvement of the photoelectric conversion efficiency.The composite film provided a better photocathodic protection effect for the 403 SS in a 0.5 mol L-1 NaCl solution than the TiO2 film.Especially,after the illumination was turned off,the composite film could maintain the cathodic protection for 403SS,which was related to the charge storage ability of MoO3 in the film.