Preparation and Property of a Negatively Charged Colloidal Nano-silver

Negatively charged colloidal nano-silver particles were successfully prepared by the colloidal chemical method. A 1.7% solution of silver nitrate (2 mL) was diluted with deionized water to 100 mL. A 1% solution of tannic acid (1 mL) was added dropwise to the solution stirring, then a 1% solution of potassium carbonate anhydrous (3~4 drops) was added to the mixed solution. Finally ,a red-brown silver sol was obtainned,which was stable at room temperature for seven months. It has been testified that the silver sol is a negatively charged colloid by experiment of electrophoresis. The sizes of particles were determined by Hitachi H-800 transmisson electron microscope. Absorption spectroscopy and SERS were used to determine of the main properties. Absorption spectroscopy was obtained with UV-1201. Raman spectra were recorded with RENISHAW MIK 1000 Raman micro-spectroscopy. The 514.5 nm line of an argon ion laser with about 3 mW was used. It has been found that the mean diameter of the particles was 11 nm; it had absorption maximum at 422 nm; Strong SERS spectra were observed when cationic molecules of fuchsin basic and methylene blue and neutral molecule of 1,10-phenanthroline were adsorbed on it respectively, but no SERS for the anionic molecule of Indolebutyric acid.