Synthesis and characterization of an antibacterial powder based on the covalent bonding of aminosilane-stabilized silver nanoparticles to a colloidal silica

Stable dispersions of silver nanoparticles (Ag NPs) were synthesized employing glycerol as both a solvent and reducing agent, and 3-aminopropyl trimethoxysilane (APTMS) as a stabilizer. Average sizes varied between 13 and 55 nm, depending on the molar ratio of APTMS/Ag. Terminal alkoxysilanes reacted with OH groups of glycerol leading to the covalent bonding of glycerol moieties to the chain ends of the stabilizer. This produced extremely stable colloidal dispersions from which NPs could not be extracted with solvents immiscible with glycerol (as THF). Ag NPs were covalently bonded to the surface of a colloidal silica by hydrolysis/condensation of terminal Si–O–C bonds of the stabilizer with superficial SiOH bonds of silica. TEM images revealed the presence of individual NPs and small clusters of NPs attached to the silica surface. These clusters were presumably generated by intermolecular reactions among chain ends of the stabilizer producing Si–O–Si bonds. The antibacterial properties of the resulting powder were confirmed by conventional tests employing a culture of Escherichia Coli.