Demonstration of the Surface-Effect on Chemical Properties of Finely Divided Particles

Colloidal metal particles have appeared as important starting points for the generation of nanostructures and devices. However, the use of colloidal metal particles like Ag and Au colloids dates back to hundreds of years. Ag and Au colloids were used as colouring agents in ceramics and stained glass windows. Depending on their size and aggregation, these colloidal metal particles produce yellow, red, purple, blue or green colours. Similarly, these particles show many other interesting physical and chemical properties, which are often drastically different from their bulk counterparts. Many of the properties such as solubility, chemical reactivity, etc. are affected by their small sizes and high surface to volume ratio. We are familiar with the surface area effects on the catalytic properties of finely divided particles of transition metals like platinum or palladium. By making catalyst particles very small, large surface areas are achieved with a small volume of material. Due to large surface area of contact and also microscopic roughness of the surface, colloidal particles are more reactive than their bulk counterparts. We shall demonstrate the surface area effects on the chemical properties of Ag colloids.