Fabrication of silica coated Al2O3 nanoparticles via a fast and facile route utilizing microwave irradiation

A facile, simple and rapid method based on microwave irradiation for preparing silica coated alumina (γ-Al2O3) nanoparticles is presented. Microwave heating resulted in a thin but homogenous coverage of silica on the γ-Al2O3 nanoparticles surface within a very short time. The structure of the non-coated and silica coated γ-Al2O3 particles were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray photoelectron spectroscopy (XPS), X-ray fluorescence spectroscopy (XRF), high-resolution transmission electron microscopy (HR-TEM), CHN elemental analysis and zeta potential measurements. Changes in the shape of the zeta potential pH dependence corresponding to formation of silica layers were accompanied by changes in the FT-IR and XPS spectra. HR-TEM images of the silica coated particles revealed that the γ-Al2O3 were coated with silica with typical diameters of about 3–4 nm. The coating of γ-Al2O3 nanoparticles with silica improves their dispersibility as indicated by the zeta potential measurements.