No abstract

Titanate nanowires were synthesized through the hydrothermal synthesis route (10 M NaOH, 130 °C) from anatase in a rotating autoclave. A combined TEM, SEM, XRD, FT−Raman, and N2 adsorption investigation of the reaction products as a function of time revealed that the 60−150 nm wide and ∼5 μm long nanowires are in fact formed by the merging of self-assembled nanotube bundles. The nanowires are able to further self-assemble into ∼5 μm wide and longer than 30 μm long, dense “superbundles” if the reaction is allowed to run long enough. We propose that the spontaneous nanotube arrangement could be caused by the rotation-assisted oriented attachment of the tubes.

We discuss the formation mechanism of titania nanotubes synthesized by the hydrothermal method. On the basis of a comprehensive analysis of TEM, HRTEM, FT-Raman, and N(2) adsorption data, we point out some major shortcomings of the currently accepted trititanate sheet rollup mechanism. We suggest that a novel formation mechanism, oriented nanotube crystal growth from nanoloop seeds, can explain the experimental findings better than the ones proposed so far.

Mesoporous silica was synthesized in the presence of metal (Au, Pt, and Ag) nanoparticles in the 2-20 nm range. Sample characterization was performed by X-ray diffraction and electron microscopy. The metal nanoparticles in the 2-10 nm range were successfully incorporated into the ordered mesoporous SBA-15 structures; 20 nm particles, whose diameter is larger than the SBA-15 pore size, could not be inserted. In the case of 5 and 10 nm diameter nanoparticles, regardless of which metal, the mesopore channels expanded in order to accommodate the metal particles. By using mixtures of metal nanoparticles of two different sizes, it was found that the inclusion and the resultant pore size were controlled by the larger size metal particles.