Chemistry of nanosized silica-coated metal particles EM-study

Colloidal gold and silver are difficult to manipulate. The surfaces are normally coated with organic acids or polymers, and conventional methods for thin metal oxide coatings normally result in clumping and heterocoagulation. We have recently developed a method to silica-coated gold and silver particles which avoids any particle coalescence. The method can be applied to a wide range of nanoparticles [1, 2]. In this report we present some results from studies into chemical reactions of nanosized coated metal particles using high resolution transmission electron microscopy. The chemical reactions were carried out on silica-coated silver and gold nanoparticles in aqueous solution. The reaction of a single Ag@SiO2 nanoparticle with I-2 to form AgI was monitored directly by transmission electron microscopy. As well the dissolution of Au cores by cyanide ion led to the creation of monodisperse, hollow, nanosized silica particles.