The Study On Modification Of TiO₂Nanotubes And Their Associated Photoelectrochemical Activity

TiO₂nanotube （NT） array has become one of the promising photocatalystsmaterials in environmental and energy engineering applications. The excellentproperties of TiO₂NT are attributed to their unique structure and electron transferefficacy. In recent years, many modifications on TiO₂NT have been investigated tofurther improve the photoelectric conversion efficiency. In this work, the TiO₂NT onTi-5Zr alloy sheet was fabricated by anodic oxidation. To further improve thephotochemical catalysis, TiO₂NT arrays were modifed with narrow band gapsemiconducting nanoparticles and noble metal catalysts. Three different nano-scaleTiO₂, including SnSe/Ag-TiO₂NT, SrTiO₃/TiO₂NT and SrTiO₃/TiO₂nanoflower （NF）were successfully fabricated. The phase composition, microstructure andphotoelectrochemical activities of the abovementioned TiO₂nanomaterials wereevaluated. In specific, the results of this work demonstrated that:（1） SnSe and silver （Ag） nanoparticles were sequentially deposited on TiO₂NT bypulsed electrochemical deposition and polyol chemistry process, respectively. SnSeand Ag nanoparticles were evenly deposited on the TiO₂NT mouth and sidewall. Theaverage diameter of SnSe nanoparticles is about30nm, which is larger than that ofAg nanoparticles （about5nm）. The UV-Vis absorption spectra of the SnSe/Ag-TiO₂NT exhibited obvious redshift, which can be attributed to the synergistic effect ofSnSe, Ag and TiO₂NT. The results implied that the SnSe/Ag-TiO₂NT material is apromising catalyst for photocatalysis.（2） Hetero-structured SrTiO₃/TiO₂nanostructure was synthesized in situ byhydrothermal method. The effects of Sr2+concentration and reaction time on themorphology of SrTiO₃/TiO₂nanostructure were investigated. The low concentrationof Sr （less than0.1M） didn’t change the morphologies of TiO₂NT obviously.However, the wall thickness of the nanotubes is slightly increased from approximately20to54nm and the inner diameter of the NT is reduced to125nm. When theconcentration of Sr2+reached to0.2M, a crossbedded nanoflower structure wasformed.（3） The photoelectrochemistry of the above three different nanostructure was alsostudied. The highly ordered SrTiO₃/TiO₂NT arrays with one-dimensional structure showed better photoelectrochemistry, since they are easier for the transfer of chargecarriers than particulate catalyst. The annealed SrTiO₃/TiO₂NT reduced the loss ofcharge carriers, which was confirmed by the electrochemical impedance spectroscopy（EIS） analysis. Mott-Schottky analysis provides the charge carrier densities andlocation of the apparent fat band potentials （UFB） of the photocatalysts. The UFBofSrTiO₃/TiO₂NT exhibited more negative shift than other samples, which indicatedthat SrTiO₃/TiO₂NT nanostructure is more favorable for an improvement ofphotoconversion effciency.