[Nano-silver colloids prepared by electrolysis and research on its SERS activity]

Three kinds of nano-silver colloids have been prepared by electrolysis of silver rod using sodium citrate solution and AgNO3 mixed with polyvinyl alcohol solution as electrolyte and applying 7 V direct current for one hour. Nano-silver colloids have been investigated by means of TEM, absorption spectrum, electrophoresis experiment and SERS. The particle size ranges roughly from 20 nm to 25 nm (spheroid) for sample 1, from 20 nm to 35 nm (spheroid) for sample 2, and from 30 to 80 (many-sided) for sample 3, featuring absorption maximum at 404, 421 and 434 nm, respectively. The surface charge of these three kinds of colloidal silver particles is positive. In order to test if these nano-silver colloids can be used for SERS research, the cationic molecular fuchsine basic, methylene blue, anionic molecular benzoic acid, methyl orange, neutral molecular alcidine orange, and Sudan red were used. It was found that these nano-silver colloids have strong SERS activity. Furthermore, the nano-silver colloids that used AgNO3 mixed with polyvinyl alcohol solution as electrolyte has the strongest SERS activity among all the tested molecules. The SERS of methyl orange has been obtained on the nano-silver colloids, which has not been obtaind on the colloids prepared by electrolysis of silver rod using sodium citrate solution and on the gray and yellow silver colloids prepared by traditional means. The possible reason has been explained. One major advantage of this method (using AgNO3 mixed with polyvinyl alcohol solution as electrolyte) is the absence of the spectral interference.