The Formation Mechanism of Ag/SBA-15 Nanocomposites Prepared via <I>In-Situ</I> pH-Adjusting Method

In this paper, the mesostructures and formation mechanism of Ag/SBA-15 nanocomposites by in-situ "pH-adjusting" method were studied. Characterization results, such as X-ray powder diffraction, N2 adsorption-desorption isotherms and Transmission electron microscope, showed that the resultant materials exhibited highly ordered hexagonal mesoporous structures, which were strongly correlated to the pH values in the synthesis solution. The pH value also strongly affected the incorporation of silver nanoparticles into the channels. When the pH value of the solution was < or = 7.5, the highly ordered Ag/SBA-15 nanocomposites were synthesized successfully; moreover, more and more Ag(NH3)+ reacts with Si-OH groups in the channels, which resulted in the increase of silver nanoparticles in the channels with the increase of the pH value. Further increasing the pH value, overmuch OH- reacts with Ag+, leading to the decrease of the coated Ag species and the structural order of Ag/SBA-15 nanocomposites. It was found that silver ions could be automatically reduced to silver atoms during the crystallization procedure.