Silica-coating of AgI nanoparticles with a Stöber method was carried out to find out reaction conditions for control of the shell thickness. The AgI nanoparticles were prepared from AgClO4 and KI with the use of 3-mercaptopropyltrimethoxysilane (MPS) as a silane coupling agent and dimethylamine (DMA) catalyst for alkoxide hydrolysis. The silica-coating was performed at 4.5×10-6-4.5×10-5 M MPS, 11-20 M water, 0.002-0.1 M DMA and 0.005-0.04 M tetraethylorthosilicate at AgI concentrations of 0.1-1 mM. Consequently, AgI-silica core-shell particles could be prepared with the use of 4.5×10-5 M MPS, 20 M water, 0.01 M DMA and 1 mM AgI. Silica shell thickness could be varied from 15 to 28 nm with an increase in the TEOS concentration from 0.005 to 0.04 M.
In recent years, the authors studied on fabrication of silica-coated AgI (AgI-SiO 2 ) nanoparticles with a Stö ber method toward new X-ray contrast agents. In the Stö ber 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-SiO 2 nanoparticles were prepared with a modified Stö ber method using NaOH as a catalyst instead of amine in the present work. The AgI nanoparticles were prepared from AgClO 4 and KI with the use of 3-mercaptopropyltrimethoxysilane (MPS) as a silane coupling agent and NaOH catalyst for alkoxide hydrolysis. The silicacoating was performed at 4?5610 25 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-SiO 2 particles as small as ca. 30 nm could be successfully fabricated at the concentrations of 4?5610 25 M MPS, 20M water, 0?0011M NaOH, 0?001M AgI and 0?004M tetraethylorthosilicate.
Submicron-sized polystyrene spheres incorporating fluorescence dyes (fluorescent microspheres) were coated with silica by means of a seeded polymerization technique based on the Stöber method. Silica-coating of the fluorescent microspheres with a size of 100 nm was performed in the presence of 0 -10 g/l polyvinylpyrrolidone (PVP), 1 -13 mol/l water, 0 -0.8 mol/l aq. ammonia and 0.00038 -0.2 mol/l tetraethoxyorthosilicate (TEOS). The addition of PVP was found to suppress the generation of free silica particles and produced no shell-free fluorescent microspheres improving the uniformity of shell thickness of silicacoated fluorescent microspheres. Silica shell thickness increased from 11 to 63 nm with increasing TEOS concentration at 10 g/l PVP, 0.4 mol/l aq. ammonia and 11 mol/l water. Silica-coated fluorescent microspheres showed more stable fluorescence to laser-irradiation than uncoated fluorescent microspheres.
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