Titanium dioxide (TiO2) nanotubes have attracted much attention because of their unique chemical properties,including high photocatalytic activity,strong oxidizing power,non-toxicity,large surface area,high surface-to-volume ratio and unique optical property.TiO2 nanotubes were widely investigated for their potential applications[1,2] such as photocatalysis,dyedsensitive solar cells (DSSC),gas sensors,air and water purifiers,and so on.Various methods for the syntheses of the TiO2 nanotubes were proposed,causing a large variety of morphology and probably the properties of the TiO2 nanotubes.For example,the diameters and structure of the walls of nanotubes may be very different,mainly depending on the varying preparation methods.[5,6] Hitherto,in general,there are three geometry configurations of the tube walls,which are widely adopted,including trititanate,[5] lepidocrocite-like[4] and an anatase structure.[3] The anatase structure was firstly found in nanotubes prepared by the hydrothermal method from anatase powder based on XAED and HRTEM investigations several years ago.[7] The lepidocrocitelike structure is supported by the electron diffraction study by Akita,[8] who proposed a crystalline structure of nanotubes different from that of anatase.The trititanate structure H2Ti3O7,also found by XRD and SAED investigations,[5] provided another proper model for TiO2 nanotubes.In spite of numerous experimental results,the atomic-level information on the structure of TiO2 nanotubes is still ambiguous.