Hydrothermal Synthesis and Surface Characteristics of Novel Alpha Alumina Nanosheets with Controlled Chemical Composition

Novel alpha alumina (alpha-Al2O3) nanosheets with controlled chemical compositions were synthesized at 450 degrees C under 10.3 MPa pressure by the hydrothermal treatment of boehmite powder (gamma-AlOOH) in the presence of soluble salts of metal dopants, alpha-Al2O3 seeds, and 5% SiO2 morphology modifier. Detailed XRD, SEM, HRTEM, STEM, and XEDS characterization was performed and it was found that the as-synthesized nanosheets were in most cases the phase-pure alpha-Al2O3 crystals exhibiting very strong (001) faceting, thicknesses of 10-50 nm, aspect ratios up to a few hundreds, and specific surface areas up to 35 m(2)/g. Metal dopants from nearly every group of the Periodic Table were present in these alpha-Al2O3 nanosheets in concentrations up to similar to 0.5 atom % either as solid solutions or as nano-sized inclusions. A thorough surface analyses using X-ray photoelectron spectroscopy (XPS), measurements of nitrogen adsorption isotherms at -196 degrees C, temperature-programmed desorption (TPD), and zeta potential measurements, revealed a very wide range of control of the surface charge, surface purity, and acid base properties of the alpha-Al2O3 nanosheets by selection of different dopants and controlling their distribution within the nanosheets. The BET surface area values of the hydrothermally synthesized nanosheets were stable up to 1200 degrees C. Such novel doped alpha-Al2O3 nanomaterials can be useful in a variety of applications such as catalysis, chemical-mechanical planarization, composites, and ceramics.