Bi-based Compounds Modified TiO₂ Nanotube Films And Their Photocathodic Protection Effects

Photocathodic protection is a new metal corrosion protection method.The optical energy can be converted into electrical energy through the photoelectric conversion by semiconductor materials,which can provide photocathodic protection for metals.There is no need to consume anodes or supply external power,so this method has attracted considerable attention of corrosion researchers since it is an environmentally friendly and sustainable technique.TiO2 semiconductor materials are stable and widely used as photoanodes.However,a single TiO2 semiconductor only absorb ultraviolet light,the photogenerated electron-hole pairs in it are easily recombined,so its visible light utilization rate and the photoelectric conversion efficiency are too lowIn this work,TiO2 nanotube films were modified with other narrow bandgap semiconductors.Namely,Bi-based semiconductor compounds with excellent photoelectric properties were selected to modify the prepared TiO2 nanotube films.Bi-based semiconductor nanoparticles were deposited onto the TiO2 nanotube films by suitable methods for preparing TiO2 nanotube composite films with high photoelectrochemical performances.Under the assistance of hole trapping agents,the composite films could provide excellent photocath odic protection for 403 stainless steel(403SS).The main contents and results of the research are as follows:(1)A TiO2 nanotube film was prepared on the surface of a Ti foil via an anodic oxidation method.Then,BiVO4 nanoparticles were deposited on the inner and outer surfaces of the TiO2 nanotubes by a low temperature solvothermal method to prepare BiVO4/TiO2 nanotube composite film.The composite film prepared by the solvothermal reaction at 100 'C for 5 h had optimal photoelectrochemical properties,and its forbidden band gap was about 2.43 eV.Compared with the TiO2 nanotube film,the photocurrent desity of the BiVO4/TiO2 composite film was increased to about 8.5 times,and was about 271 ?A·cm-2.Under white light irradiation,the BiVO4/TiO2 composite film reduced the electrode potential of 403SS in a 0.5 mol·L-1 NaCl solution by 520 mV,and the charge transfer resistance of 403SS was decreased to 15.8 k?·cm2.Meanwhile,the photocathodic protection mechanism of the composite film was revealed.(2)A BiFeO3/TiO2 nanotube composite film w-as prepared by combining an anodic oxidation process with solvothermal reaction.The optimum solvothermal reaction condition was 150 ? for 7 h.The band gap of the BiFeO3/TiO2 composite film was about 2.33 eV.Under white light illumination,the photocurrent density of the composit film reached to 373 ?A·cm-2,which was about 8.3 times that of the TiO2 nanotube film.In addition,the BiFeO3/TiO2 composite film reduced the potential of 403 SS in a 0.5 mol·L-1 NaCl solution by 560 mV under white light irradiation,exhibiting surperior photocathodic protection effect.(3)CdSe nanoparticles and Bi2S3 nanoparticles were deposited on the TiO2 nanotube film by constant current density electrodeposition and a successive ionic layer adsorption and reaction method,respectively.The Bi2S3/CdSe/TiO2 nanotube composite film was equipped with a cascade band structure.Under white light illumination,the photocurrent density of this ternary composite film could reached to 670 ?SA·C·cm-2,which was about 17.6 times that of the TiO2 nanotube film.The Bi2S3/CdSe/TiO2 composite fil:m could provide excellent photocathodic protection for 403SS in a 0.5 mol·L-1 NaCl solution,and reduced the potential of 403SS by 690 mV.The above prepared composite films remained stable during the testing time of 30 h for the measurements of the 403 SS potential,meaning that the films had the excellent corrosion resistance and photocathodic protection performance.