| In marine engineering equipment,a large number of steel structural components are failure of corrosion.The anticorrosion methods can be used to improve the corrosion resistance of metals and prolong the service life of equipment,such as electrochemical protection,anticorrosion films and so on.The TiO2 and other photoelectric conversion films can convert the solar energy into electricity to protect the metals by photocathodic protection.Thus,the photocathodic protection technology of metals with photoelectric conversion coating or by coupling the photoelectric conversion film represents an energy saving,material saving and high efficiency chanracteristics,which has become one of the hot topics on corrosion and pretection in recent years.In this paper,we have prepared the TiO2 nanowire films with different structures and the nanoscale ordered array composite films by modified TiO2 nanowire films with 2D ZnIn2S4,RGO and Bi2WO6.The formation of heterojunction and electrons rapid transfer channel is beneficial for photocathodic protection properties.The main results of this dissertation are as follows:(1)Ti02 nanowire films were synthesized in situ on Ti substrate by an alkaline hydrothermal method.As a result of the growth characteristic of TiO2 films,there are two different structures for TiO2 nanowire film prepared by controlling the hydrothermal holding time:The 6 h TiO2 nanowire film prepared by hydrothermal process for 6 h reaction time.The entire surface of the Ti substrate is covered uniformly with the TiO2 nanowires and the film thickness is about 3 ?m.The TiO2 nanowires are nearly vertical to the Ti substrate,which can be used as the transmission channel of photoinduced electrons.Thus,the photoinduced electrons can transfer from the semiconductor films to Ti sunbsrate becauce of good electronic transmission performance of 6 h TiO2 nanowire film;The 24 h TiO2 nanowire film prepared by hydrothermal process for 24 h reaction time.The film thickness is greater than 12 ?m.Nano wires that exceed the thickness of the thin films bend on the surface of the thin films and form a densely oriented network.The 24 h TiO2 nanowire film possesses antireflection properties,which caused by the strong light trapping and scattering of nanowire gap.And the 1D nanowires morphology of 24 h TiO2 nanowire film makes for photogenerated electrons transfer.In addition,we can prepare composite films that modified TiO2 nanowire films with other nano-semiconductors due to ordered array structure and larger specific surface area of TiO2 nano wire films.(2)We have prepared the stem-and-leaf-like ZnIn2S4 nanosheet/TiO2 nanowire arrays composite film by modifying 24 h TiO2 nanowire film with ZnIn2S4 nanosheets.Moreover,the 6 h ZnIn2S4 nanosheet/TiO2 nanowire composite film exhibit superior photoelectrochemical properties and excellent photocathodic protection for stainless steel against corrosion.A maximum photocurrent density of 2 mA/cm2 is achieved for the 6 h ZnIn2S4 nanosheet/TiO2 nanowire composite film under white illumination,and the OCP of the 304SS coupled with the composite film immediately shifts negatively to-1.17 V vs.SCE.The main influence factors of composite film including the following aspects:Firstly,the sensitization of ZnIn2S4 for TiO2 film can expand absorption range to visible light,which improves the light adsorption property of composite film;Secondly,the well-designed morphology and structure of composite film enhance the utilization efficiency of solar energy and promote photogenerated electrons separation and transmission,so the composite film exhibit excellent photoelectrochemical properties;Thirdly,the heterostructure engineered ZnIn2S4 nanosheet/TiO2 nanowire composite film contribute to improve photocathodic protection performance for 304SS.Due to the band matching relation,the photogenerated electrons can migrate to the lower conduction band of TiO2,and are finally transported to the coupled 304SS to achieve anticorrosion protection.(3)We have prepared the ZnIn2S4 nanosheet/RGO/TiO2 nanowire composite film by modifying 6 h TiO2 nanowire film with ZnIn2S4 nanosheets and RGO.The influence factors of RGO on the composite film were explored by comparing with the ZnIn2S4 nanosheet/TiO2 nanowire composite film,including the following aspects:On the one hand,the morphology of the composite film was changed to layer-by-layer structure because of larger area RGO.On the other hand,RGO in the composite film provides the fast passages for the transport of photogenenrated electrons,which results in the high separation rate of photogenerated electrons,The composite film presents excellent photoelectrochemical properties and the photocurrent density reaches 0.25?A/cm2 under visible light.Under the simulated solar light irradiation,the ZnIn2S4 nanosheet/RGO/TiO2 nanowire composite film exhibit effective photocathodic protection for metals and the photopotential of the 304SS coupled the composite film was about-1.12 V vs.SCE.(4)The Bi2WO6/TiO2 composite films were prepared by modifying TiO2 nanowire films with 2D Bi2WO6 nano-materials,which were layer by layer assembly structure.And the effects and mechanism of photocathodic protection for composite film were investigated.The loading of Bi2WO6 can broadens the absorption range of the TiO2 nanowire film.The recombination of photogenenrated electrons and holes can be effectively suppressed by sandwich construction of the Bi2WO6 crystal in composite films.In addition,the Bi2WO6 nanoflower not only displays high specific surface area,abundant mesoporous distribution,and the narrow band gap(2.65 eV)but also facilitates transfer and separation of charge carriers.6 h TiO2 nanowire film shortens the transport distance of photogenerated electrons,which is beneficial for the photogenerated electrons transfer in semiconductor film.As a result,the photoelectrochemical properties and the photocathodic protection for Bi2WO6 nanoflower/6 h TiO2 nanowires composite film are improvd significantly. |
PDF Full Text Request