Sonochemical insertion of silver nanoparticles into two-dimensional mesoporous alumina

Nanocomposites of Ag nanoparticles/mesoporous γ-Al₂O ₃ were synthesized by sonochemical treatment of the precursors. The sonicated product consisted of Ag nanoparticles dispersed in the bayerite [Al(OH)₃]/ boehmite [AlO(OH)] matrix. Upon calcination under argon, the Ag nanoparticles were found to be incorporated in a mesoporous structure of γ-Al₂O₃. For a solid containing 3.7 wt % Ag nanoparticles, the nanoparticles remained on the surface of mesoporous alumina and hence BET surface area increased as compared to pristine γ-Al ₂O₃, whereas for 10.5 wt % Ag nanoparticles, the surface area decreased. HRTEM studies corroborated this fact and showed that, at higher Ag concentrations, Ag nanoparticles blocked the pores and also increased the diameter of the pores of mesoporous alumina. The products with the 3.7 wt % silver concentration had uniform pores with narrow pore size distribution of the pores, although the TEM pictures indicated wormhole channel motifs. The formation of the mesoporous structure was governed by the templating behavior of the organic groups (mainly formic acid) attached to the alumina nanoparticles. The shape of the pores closely resembled the two-dimensional hexagonal mesoporous structure with the P6mm space group, as observed from small-angle X-ray diffraction experiments. Diffuse reflection optical spectra at 27 °C showed an absorption band (419-424 nm) due to the surface plasmon of Ag inside the ceramic matrix.