Silica-coating of AgI semiconductor nanoparticles

A method for silica-coating of AgI nanoparticles is proposed, which applies Stöber method in the presence of a silane coupling agent, 3-mercaptopropyltrimethoxysilane (MPS), with the use of dimethylamine (DMA) catalyst for alkoxide hydrolysis. The AgI nanoparticles were prepared from AgClO4 and KI. The silica-coating was performed with 0–2.3 × 10−5 M MPS, 11–20 M water, 0–0.1 M DMA and 0.0004–0.15 M tetraethyl orthosilicate (TEOS). The addition of MPS suppressed generation of free silica particles and improved uniformity of shell thickness. Silica shells were formed at water concentrations of 11–15 M, but excess water (20 M) caused aggregation of free silica particles, and resulted in formation of gel network. The silica shell thickness could be varied from 3 to 33.0 nm as the TEOS concentration was increased from 0.0004 to 0.04 M at 4.5 × 10−6 M MPS under the condition of 11 M water and 0.01 M DMA.