| TiO2 is regarded as one of the best photocatalysts because of its non-toxicity, stability,low cost and desirable photocatalytic properties.Since the pioneer work of Fujishima and Honda for the discovery of photoelectrochemical splitting of water on TiO2 electrodes,solar water splitting for hydrogen production based on TiO2 has attracted extensive attention.However,the inactivity in the visible light region limits the practical applications of TiO2.Numerous attempts have been made to improve the inherently low efficiency of TiO2 in harvesting sunlight by shifting its spectral response into visible light range.In this thesis,a series of nanostructured TiO2 thin films were prepared by sol-gel,anodic oxidation and thermal oxidation methods.In order to improve the photoelectrochemical response of TiO2 thin films,carbon nanotubes were induced into TiO2 thin films.Besides,a novel process to fabricate N-doped TiO2 nanoporous films was proposed.The main results and conclusions can be summarized as following:1.A series of MWCNTs/TiO2 nanocomposite thin films were prepared by sol-gel method.The influence of MWCNTs' content on the photoelectrochemical properties of these nanocomposite thin films was investigated.The photoelectrochemical results show that the most appropriate amount of MWCNTs in the nanocomposite thin film is 0.04 mg/cm2.Compared to the pristine TiO2 thin film,better performance is observed for the nanocomposite thin film with its photovoltage increase by 0.23 V,its UV-Vis light photocurrent density increase twice,and the visible light photocurrent density increase nearly nine times.The results indicate that the charge transfer rate and the total absorption of simulated solar light of the nanocomposite thin film are remarkably increased because of the presence of MWCNTs thin films,which has a superior electron-conducting property,good absorption property and the tanglesome network,which provides an ideal matrix for uniform distribution of TiO2 nanoparticles.2.MWCNTs/TiO2 nanocomposite thin films in different modes were also prepared by sol-gel method and the photoelectrochemical properties of nanocomposite thin films in different modes were investigated.The results show that the photoelectrochemical properties of TiO2 thin films could be evidently enhanced by bottom distribution mode,on the contrary,decreased by surface distribution mode and uniform distribution mode.The photovoltage of the MWCNTs/TiO2 nanocomposite thin film with bottom distribution mode increase by 0.1 V,its UV-Vis light photocurrent density is nearly three times larger than that of the pristine TiO2 thin film.Its IPCE(incident monochromatic photon-to-current conversion efficiency) is also greater in all spectrum range,with the peaks of 12.4%in 340 nm and 1.9%in 660 nm.The effects of composite modes on the photoelectrochemical activities were discussed in terms of separateness of charge carriers.MWCNTs were used for improving electron-collecting efficiency and reducing carries recombination in bottom distribution mode.Therefore,the photoelectrochemical properties of TiO2 thin films could be evidently increased by distribution MWCNTs in the bottom.The design of preparing the MWCNTs/TiO2 nanocomposite thin films with bottom distribution mode is proposed for the first time,which is promising in the potential applications in solar water splitting and visible light sensitive photocatalysis.3.A hybrid dry/wet new process encompassing nitrogen plasma immersion ion implantation(N-PⅢ) and wet anodization is demonstrated to fabricate the N-doped TiO2 nanoporous films with better visible light activity.The photoelectrochemical properties of the N-doped TiO2 nanoporous films were studied.Under the UV-Vis light illumination,the photocurrent of the N-doped TiO2 nanoporous film is 510μA/cm2,which is three times greater than that of the N-doped TiO2 compact film(145μA/cm2).Under the visible light illumination, the photocurrent generated from the N-doped TiO2 nanoporous film(3.3μA/cm2) is nearly twice greater than that of the N-doped TiO2 compact film(1.9μA/cm2). The photocurrent from the N-doped TiO2 nanoporous film is also increased in compared with that of the pristine TiO2 nanoporous film under both the UV-Vis light and visible light illumination.These results indicate that the nitrogen species implanted in the nanoporous films may attribute to the interstitial ones such as Ti-O-N structure which is confirmed by XPS measurements.The porous structure is beneficial to transform TiO2 into an anatase structure by annealing treatment. The large surface area of the nanoporous structure is of advantage to efficient light collection,consequently enhancing the photoelectrochemical response of the N-doped TiO2 nanoporous films.4.A series of undoped TiO2 thin films were prepared by sol-gel,anodization and thermal oxidation methods.And their photoelectrochemical responses under visible light illumination were compared.Photoelectrochemical responses under visible light illumination are observed for all the undoped TiO2 thin films prepared by high temperature annealing treatment.This may be due to the formation of many surfaced states,for instance,oxygen vacancy and Ti4+ lattice defects,which was caused by lattice distortion during the annealing treatment and resulted in the visible light absorption.The changes of the visible light photoelectrochemical response of the undoped TiO2 thin films at different reaction conditions are the same as the changes of the UV-Vis light photoelectrochemical response.These results provide an essential reference for the further investigation of visible light sensitive TiO2 thin films.
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