Comparative Study of Ultrasound Stimulation and Conventional Heating Methods on the Preparation of Nanosized γ-Al2O3

This work addresses the advantages of the ultrasound stimulation method over the conventional heating method for the preparation of nanosized gamma-Al2O3. The gamma-Al2O3 obtained by calcination of boehmite at 600 degrees C is derived from the inexpensive aluminum chloride salt by the precipitation route. Thermal evolution, phase transformation, surface area, and particle size distribution of the boehmite and gamma-Al2O3 are characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared analysis (FT-IR), nitrogen adsorption desorption isothermal data, and dynamic light scattering analysis (DLS). The gamma-Al2O3 prepared by ultrasound stimulation has higher surface area (256 m(2) g(-1)), bigger pore diameter (6.06 nm) and larger cumulative pore volume (0.388 cm(3) g(-1)) than the conventional heating method (surface area, pore diameter, and pore volume of 219 m(2) 5.61 nm, 0.307 cm(3) g(-1), respectively), which are even higher than the value reported in the literature for gamma-Al2O3 synthesized at 100 degrees C for 24 h aging (pore diameter of 4.27 nm and pore volume of 0.26 cm(3) g(-1)). The sonication applied during the aging of boehmite sol reduces the crystallite size (or particle size) and increases the porosity. The boehmite and gamma-Al2O3 obtained by sonication have the highest porosity of 46% and 59%, respectively, without using any structure directing agent. The crystallite size calculated from XRD analysis using Scherrer's equation is found to be 2.32 and 3.13 nm for boehmite and gamma-Al2O3 obtained by ultrasound stimulation, respectively, which is due to the formation of microjets during sonication. The particle size analysis result reveals the formation of nanosized gamma-Al2O3 particles by ultrasonication with a mean particle size of 51 nm. In conclusion, the boehmite and gamma-Al2O3 prepared by ultrasound stimulation are better than the samples synthesized by the conventional method.