Morphology Controllable Synthesis of Nanostructured Boehmite and γ-Alumina by Facile Dry Gel Conversion

A facile dry-gel conversion process was developed for crystallization of trihydrate-alumina nanoparticles and boehmite AlOOH nanofibers with controllable morphologies from solid powder of amorphous aluminum hydroxide precipitate. By steam treatment at 200 degrees C, the amorphous dry gel of aluminum hydroxide precipitate was crystallized, and the morphology of resulting nanomaterials was found to be dependent on the ratio of water-to-gel applied. When the water-to-gel ratio was 1:1, nanoparticles of hydrated aluminum oxide with particle size of 80 +/- 10 nm were obtained. Increase of the water-to-gel ratio to 2:1 resulted in the formation of nanoribbons of AlOOH with lengths of 1-2 mu m and widths of 100 nm, and further increase of the water-to-gel ratio led to the formation of nanorods of boehmite AlOOH with diameters of 20-30 nm and lengths of 200-500 nm. After thermal treatment at 600 degrees C, the nanostructured hydrated aluminum oxide and boehmite was transformed to gamma-Al2O3, and the morphologies were well preserved. The morphology of the nanostructures was analyzed with transmission electron microscopy (TEM) and field emission scanning electronic microscopy (FESEM). The phase transformations were characterized by X-ray diffraction (XRD), differential scanning calorimetry and thermo-gravimetric analysis (DSC-TGA), Fourier transform infrared (FTIR), Raman, and magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy.