Abstract:

Nanostructured TiO₂ and many titanates are of tremendous fundamental and technological interests for a wide range of applications not only in areas such as catalysis, but also for energy or hydrogen storage because of their unique structure and large surface area [1–3]. TiO₂ and titanates in form of nanotubes, nanowires or nanobelts can be fabricated by reaction of raw TiO₂ and NaOH [4,5]. Nanostructured TiO₂ can also be directly fabricated by dealloying Al-Ti ribbon using a simple and highly efficient corrosion process [6], where the reaction solution is one of the key factors for the morphology and structure of the final product.

In the present work, several TEM techniques are employed to study the morphology, crystal structure and composition of products from Al_85at.%-Ti_15at.% ribbons dealloyed in NaOH, KOH and HCl solutions. Figure 1, 2 and Table 1 show the analytic results for the dealloyed product in NaOH solution. A polycrystalline layered structure with ~0.75 nm lattice distance is observed (Fig.1). Around 8 at.% Na were identified by EDX analysis of different areas (Table 1). In order to further study the structure of this phase, a radial distribution function (RDF) was calculated based on electron diffraction to provide the distribution of atomic distances and compared to a simulated RDF for crystalline Na₂Ti₆O₁₃ structure, which shows good agreement (Fig.2a). The determined structure is supported by XRD result in Fig.2b, which shows that this product consists of two compositions, Na₂Ti₆O₁₃ phase and some anatase TiO₂. Multivariate statistical analysis of 2500 EDX spectra of an area of 100 nm × 100 nm is used to image the Na₂Ti₆O₁₃/TiO₂ distribution and electron tomography is used to provide three dimensional (3D) information of the morphology. Comparing the structures fabricated by different dealloying solutions will lead to understand the formation mechanism and to better control nanostructures TiO₂-based compounds.

Keywords: TiO₂-based nanocomposites, Dealloying, Layer structure.

Acknowledgement: Wu Wang is grateful for the financial support of the China Scholarship Council (CSC) for PhD study.

References

[1]         Allen MR, Thibert A, Sabio EM, Browning ND, Larsen DS, Osterloh FE. Chem Mater 2010;22:1220.

[2]         Wagemaker M, Kentgens a PM, Mulder FM. Nature 2002;418:397.

[3]         Bavykin D V., Lapkin A a., Plucinski PK, Friedrich JM, Walsh FC. J Phys Chem B 2005;109:19422.

[4]         Kasuga T, Hiramatsu M, Hoson A, Sekino T, Niihara K. Langmuir 1998;14:3160.

[5]         Kasuga T, Hiramatsu M, Hoson a, Sekino T, Niihara K. Adv Mater 1999;11:1307.

[6]         Xu C, Wang R, Zhang Y, Ding Y. Nanoscale 2010;2:906.

Figures:

Figure 1: TEM image (a) and SAED pattern (b) of dealloyed product in NaOH.

Figure 2: Simulated RDF results (a) and XRD pattern (b) of dealloyed product in NaOH.

Table 1: Quantify EDX results of dealloyed product in NaOH.

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