Synthesis of Metal Colloids
Colloidal metals-originally called sols-first generated interest because of their intense colors, which enabled them to be used as pigments in glass or ceramics. The most extensively studied metal as a colloid is gold because of its well-known optical properties. The research on colloidal gold dates back to the 18th century. Hans Heinrich Helcher, who was a philosopher as well as a doctor, published a formal report on colloidal gold in 1718. During the 19th and 20th century,
colloidal gold was used extensively in medicine, dying silk fabrics, and colored glasses and ceramics. In 1857, Faraday reported the formation of deep red solutions of colloidal gold by reduction of an aqueous solution of chloroaurate (AuCl4-) using phosphorus in CS2 (a two-phase system) in a well-known work. He studied the effect on optical properties of thin films of colloidal gold under mechanical force. In the 19th century, a great deal of theoretical and experimental research was conducted on many colloidal metals, especially from d-block elements.