The impact of the functionalization of silica mesopores on the structural and biological features of SBA-15

Hydrophobic and hydrophilic silver-functionalized SBA-15 silica nanocomposites were prepared via direct synthesis using the so-called BOTTOM-UP approach to nanotechnology. This process enables silica-based nanocomposites with a controlled metal content to be fabricated. XRD, XPS, Raman, SEM-EDX and TEM methods were used to describe the physicochemical properties of these systems. The surface atomic content of silver (XPS) was estimated at approximately 0.03 at.% and 0.04 at.% compared to the bulk signal (SEM-EDX), which was determined to be about 0.33 at.% and 0.48 at.%, respectively for the non-silylated and silylated systems. The XPS studies that were carried out for these two structures revealed the presence of elemental and/or oxidized silver on the surfaces. However, in the more volumetric XRD studies, there was no clear signal that corresponded to this metal, which suggests the presence of an ionic form of silver. Calcination was used to obtain the silver-decorated porous silica ceramic composites, for which the calcination temperature was determined from TGA/DTG studies. The calcination resulted in the compensation of the surface and bulk atomic content of silver at approximately 0.1 at.% (on both the surface and the bulk). The wettability measurements classified silylated specimens as well as silylated and calcined systems as being hydrophilic and hydrophobic, respectively. Low-angle diffraction confirmed the mesoporous character of the silica with hexagonal pore channels regardless of the degree of functionalization or calcination. The Raman data illustrated the impact of the silver on the propyl-carbonate chains and silica structure. Finally, the most vigorous bactericidal activity was found against Staphylococcus aureus and Escherichia coli for a hydrophilic system with a low silver content and a calcined sample with a slightly higher silver concentration.