Steam-assisted solid wet-gel synthesis of high-quality nanorods of boehmite and alumina

A simple solid-phase method was developed for synthesis of high-quality boehmite nanorods by steam-assisted wet-gel conversion process. gamma-Al2O3 nanorods with clear-cut edge have been successfully obtained by thermal treatment of boehmite nanorods at 600 degrees C for 5 h. The nanorods of boehmite and gamma-Al2O3 were characterized by X-ray diffraction (XRD), Raman spectroscopy, and field emission scanning electron microscope (FESEM) with energy-dispersive spectroscopy (EDS), transmission electron microscopy (TEM), and high-resolution tranmission electron microscopy (HRTEM) with selected area electron diffraction (SAED) spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FTIR), magic-angle spinning (MAS) Al-27 nuclear magnetic resonance (NMR), and thermogravimetric and differential thermal analysis (TGA-DTA). The growth of boehmite was found to be greatly affected by the conditions used for precipitation of AI(NO3)(3) with NH4OH aqueous solution. When precipitation was conducted under pH 5.0 or pH 7.0, nanorods of boehmite with lengths in the range of 100-400 nm and uniform diameters (20-30 nm) were obtained by steaming the solid wet gel at 200 degrees C for 48 h, whereas irregular boehmite particles were obtained from the wet gel precipitated under alkaline condition (pH 10.0). The directed crystallization of boehmite nanorods was attributed to the preferential growth along the longitudinal axis under supersaturated hydrothermal condition with the assistance of steam. The 1D nanostructure of boehmite was well preserved after being converted to gamma-Al2O3 without sintering among the highly dispersed nanorods. This approach allows us to fabricate high-quality nanorods of boehmite and gamma-Al2O3 with controlled size and morphology using cost-effective solid-phase chemical methods at a large scale.