We demonstrate new molecular-level concepts for constructing nanoscopic metal oxide objects. First, the diameters of metal oxide nanotubes are shaped with angstrom-level precision by controlling the shape of nanometer-scale precursors. Second, we measure (at the molecular level) the subtle relationships between precursor shape and structure and final nanotube curvature. Anionic ligands are used to exert fine control over precursor shapes, allowing assembly into nanotubes whose diameters relate directly to the curvatures of the 'shaped' precursors.

We report the identification and elucidation of the mechanistic role of molecular precursors and nanoscale (1-3 nm) intermediates with intrinsic curvature in the formation of single-walled aluminosilicate nanotubes. We characterize the structural and compositional evolution of molecular and nanoscale species over a length scale of 0.1-100 nm by electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy ((27)Al liquid-state, (27)Al and (29)Si solid-state MAS), and dynamic light scattering. Together with structural optimization of key experimentally identified species by solvated density functional theory calculations, this study reveals the existence of intermediates with bonding environments, as well as intrinsic curvature, similar to the structure of the final nanotube product. We show that "proto-nanotube-like" intermediates with inherent curvature form in aqueous synthesis solutions immediately after initial hydrolysis of reactants, disappear from the solution upon heating to 95 °C due to condensation accompanied by an abrupt pH decrease, and finally form ordered single-walled aluminosilicate nanotubes. Detailed quantitative analysis of NMR and ESI-MS spectra from the relevant aluminosilicate, aluminate, and silicate solutions reveals the presence of a variety of monomeric and polymeric aluminate and aluminosilicate species (Al(1)Si(x)-Al(13)Si(x)), such as Keggin ions [AlO(4)Al(12)(OH)(24)(H(2)O)(12)](7+) and polynuclear species with a six-membered Al oxide ring unit. Our study also directly reveals the complexation of aluminate and aluminosilicate species with perchlorate species that most likely inhibit the formation of larger condensates or nontubular structures. Integration of all of our results leads to the construction of the first molecular-level mechanism of single-walled metal oxide nanotube formation, incorporating the role of monomeric and polymeric aluminosilicate species as well as larger nanoparticles.

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We report a detailed investigation of the defect structures in aluminosilicate single-walled nanotubes via multiple advanced solid-state NMR techniques. A combination of 1 H− 29 Si and 1 H− 27 Al FSLG-HETCOR, 1 H CRAMPS, and 1 H− 29 Si CP/MAS experiments were employed to evaluate the proton environments around Al and Si atoms in the final nanotube structure. The 1 H CRAMPS spectra of dehydrated aluminosilicate nanotubes revealed the proton environments in great detail. Integration of these results with the findings from the 1 H− 29 Si and 1 H− 27 Al FSLG-HETCOR and 1 H− 29 Si CP/ MAS data allows the structural assignment of all the chemical shifts and the identification of various types of defect structures in the aluminosilicate nanotube wall. In particular, we identify five main types of defect structures arising from specific atomic vacancies in the nanotube structure. It is estimated that ∼16% of Si atoms in the nanotube inner wall are involved in a defect structure. The characterization of the detailed structure of the nanotube wall is expected to have significant implications for its chemical properties and applications.

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The fabrication of ultrathin (300 nm) aluminosilicate nanotube-poly(vinyl alcohol) composite membranes with partial vertical alignment of the nanotubes (up to 33 %), by solution-casting methods on porous polymeric substrates, is reported. Ah igh loading (up to 60 vol %) of nanotubes is achieved. Ac omprehensive microstructural characterization of the membranes is performed by ac ombination of SEM, TEM, grazing-incidence wide-angle X-ray scattering measurements, and simulations. This investigation shows that the nanotubes are individually dispersed and partially aligned in the polymeric matrix by the use of appropriate matrix and substrate materials. Permeation measurements of gas probe molecules (CO 2 and CH 4 )o nt wo different types of membranes, one containing bare nanotubes and the other containing amine-functionalized nanotubes, also support the proposed microstructure of the thin nanocomposite membranes.[a] Prof.

Diffusion of tetrafluoromethane (CF 4 ) in single-walled aluminosilicate nanotubes was studied by means of pulsed field gradient (PFG) NMR and molecular dynamics (MD) simulations. The application of a high magnetic field and high magnetic field gradients allowed 13 C PFG NMR measurements of diffusion to be performed under conditions of sufficiently large signal-to-noise ratios for a broad range of CF 4 loadings. The PFG NMR data were analyzed to obtain the diffusivities for diffusion of CF 4 inside the nanotube aggregates, in which the sorbate displacements exceeded the average length of individual nanotubes. In addition, the corresponding diffusivities under conditions of fast exchange of CF 4 molecules between nanotubes or nanotube aggregates and the surrounding gas phase in a nanotube bed were also estimated. The experimental CF 4 diffusivities inside the nanotube aggregates were found to be several times smaller than the corresponding diffusivities obtained by MD for diffusion inside the defect-free nanotubes. This difference points to the existence of additional transport resistances inside the nanotube aggregates under the conditions of the reported PFG NMR measurements, i.e., when the gas molecules diffuse through several nanotubes interconnected along the nanotube lengths inside the aggregates. Such additional transport resistances are likely to originate from diffusion through thin layers of microporous material, which is expected to connect the individual nanotubes in the aggregates.

A novel colloidal method is presented to synthesize silver nanoparticles on aluminosilicate nanotubes. The technique involves decomposition of AgNO 3 solution to Ag nanoparticles in the presence of aluminosilicate nanotubes at room temperature without utilizing of reducing agents or any organic additives. Aluminosilicate nanotubes are shown to be capable of providing a unique chemical environment, not only for in situ conversion of Ag ? into Ag 0 , but also for stabilization and immobilization of Ag nanoparticles. The synthesis strategy described here could be implemented to obtain self-assembled nanoparticles on other single-walled metal oxide nanotubes for unique applications. Finally, we demonstrated that nanotube/nanoparticle hybrid show strong antibacterial activity toward Gram-positive Staphylococcus epidermidis and Gram-negative Escherichia coli.