Boehmite Nanostructures Research Articles

Gallium-Doped Boehmite Nanotubes and Nanoribbons. A TEM, EDX, XRD, BET, and TG Study

Gallium-doped boehmite nanostructures with varying Ga content have been prepared at low temperatures via a soft-chemistry route in the presence of poly(ethylene oxide) (PEO) surfactant. The effect of Ga content, hydrothermal temperature, and mixing procedures on the growth of boehmite nanostructures was systematically studied. The resultant boehmite nanostructures were characterized by transmission electron microscopy (TEM), energy-dispersive X-ray (EDX) microanalysis, X-ray diffraction (XRD), N2 adsorption, and thermogravimetric analysis (TGA). Nanotubes with an average length of ∼90 nm and internal and external diameters of 2−5 nm and 3−7 nm, respectively, were formed when the added Ga molar percentage was ≤5%; when the added Ga percentage was >10%, an amorphous phase dominated the sample with a mixture of nanosheets, nanotubes, and nanoribbons being formed. Synthesis at slightly higher temperatures (120 °C) for an added Ga molar percentage of ≤5% resulted in longer nanotubes. For high-Ga-content boehmites, large crystals were formed when hydrothermally treated at 120 °C. The detailed characterization of the resultant Ga-doped boehmite nanostructures is presented.

Self-Assembly of Flowerlike AlOOH (Boehmite) 3D Nanoarchitectures

In this work, a hydrothermal route using an ethanol-water solution to progressively synthesize a sequence of flowerlike three-dimensional gamma-AlOOH boehmite nanostructures without employing templates or matrixes for self-assembly is presented. The flowerlike boehmite nanoarchitectures exhibit three hierarchies of self-organization, i.e., single-crystalline nanorods, nanostrips, and bundles, which are characterized by scanning and transmission electron microscopy. The sequence of products obtained after different processing times indicates a self-assembly mechanism. The hydrogen bonding on the surface of nanorods or nanostrips possibly plays a key role, as identified by FTIR spectra of the products after they had been heated to 1000 degrees C. The specific surface area and pore-size distribution of the obtained product as determined by gas-sorption measurements show that the boehmite nanoarchitectures exhibit high BET surface area and porosity properties.

A Facile and Controllable Synthesis of γ‐Al2O3 Nanostructures without a Surfactant

AbstractBoehmite [AlOOH] nanoneedles, nanorods, and nanotubes were successfully synthesized by a facile sol‐hydrothermal method without using any surfactant. Calcination of the corresponding boehmite nanostructures at 700 °C gave the corresponding γ‐Al2O3 nanoneedles, nanorods, and nanotubes. The resulting products were characterized by XRD, TEM, HRTEM, and FT‐IR spectroscopy. We found that the conditions used to produce the sol and the pH value of the hydrothermal process have important effects on the nucleation and growth of nanostructured materials. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

A microstructural investigation of nanostructured boehmite films prepared by the sol–gel route

The microstructure of dispersed aqueous boehmite systems during the preparation of xerogel membranes was investigated in relation to the textural properties of the final film. When the boehmite sols are dried at room temperature and atmospheric pressure, a transparent film is obtained. During the solvent evaporation process, the sols undergo a macroscopic change, namely a sol–gel transition, leading finaly to the formation of a porous glass. As shown by X-ray diffraction, the air-dried films are well-structured xerogels resulting from an uniplanar arrangement of the primary plate-like crystallises with the (020) axis normal to the film layer. Assessment of the microstructural evolution using small-angle X-ray scattering experiments demonstrated that a reorganisation of the particles occurs at the gel point. This phenomenon, which can be explained by an excluded volume effect when interacting particles approach in solution during the solvent evaporation, leads to a birefringent gel phase where primary colloidal particles adopt a cooperative face-face preferential state extending over macroscopic scales (>1 micron). This particular structure persists on substantial concentration of the gel phase and clearly shows that the crystallite organisation found in the film exists before the xerogel formation. It is suggested that the gelation mechanism is responsible for the structure and porous texture of the films.