Preparation Of Amine Free Silica-Coated Agi Nanoparticles With Modified Stober Method

In recent years, the authors studied on fabrication of silica-coated AgI (AgI-SiO2) nanoparticles with a Stober method toward new X-ray contrast agents. In the Stober method, amines are often used as catalysts for silica formation, so that it is probable that amine is left in the silica-coated particles. Since amines are harmful to the human body, amine free particles are desired for medical use. From this viewpoint, amine free AgI-SiO2 nanoparticles were prepared with a modified Stober method using NaOH as a catalyst instead of amine in the present work. The AgI nanoparticles were prepared from AgClO4 and KI with the use of 3-mercaptopropyltrimethoxy-silane ( MPS) as a silane coupling agent and NaOH catalyst for alkoxide hydrolysis. The silicacoating was performed at 4.5 x 10(-5) M MPS, 15-22.5M water, 0.0008-0.0024M NaOH and 0.0004-0.009M tetraethylorthosilicate at an AgI concentration of 0.001M. AgI-SiO2 particles as small as ca. 30 nm could be successfully fabricated at the concentrations of 4.5 x 10(-5)M MPS, 20M water, 0.0011M NaOH, 0.001M AgI and 0.004M tetraethylorthosilicate.