Preparation of amine free silica-coated Agl nanoparticles with modified stöber method

In recent years, the authors studied on fabrication of silica-coated Agl (Agl-SiO₂) nanoparticles with a Stober method toward new X-ray contrast agents. In the Stöber 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 Agl-SiO₂ nanoparticles were prepared with a modified Stöber method using NaOH as a catalyst instead of amine in the present work. The Agl nanoparticles were prepared from AgCIO₄ and Kl 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 × 10_-5M MPS, 15-22·5M water, 0·0008- 0·0024M NaOH and 0·0004-0·009M tetraethylorthosilicate at an Agl concentration of 0·001M. Agl-SiO₂ particles as small as ca. 30 nm could be successfully fabricated at the concentrations of 4·5 × 10_-5M MPS, 20M water, 0·0011M NaOH, 0·001M Agl and 0·004M tetraethylorthosilicate.