Abstract
Colloidal silver nanoparticles were prepared by a conventional reduction of Ag + ions with NaBH 4 and with a novel approach using tannic acid (tannin) as reducing agent of Ag + ions. The formation of colloidal silver was followed by electronic absorption spectroscopy monitoring the growth of the surface-plasmon resonance band of the nanoparticles. Colloidal silver in tannin is more stable than that prepared with NaBH 4 because tannin exerts also a protective colloid function permitting to reach much higher colloidal silver concentration than in the case of NaBH 4 . Colloidal silver nanoparticles are readily reactive with ozone producing oxidized silver nanoparticles composed by argentic oxide (AgO). If the ozonation is conducted in gentle conditions the oxidized silver nanoparticles remain as colloidal suspension while if mechanical shaking is applied the particles coagulate and separate from the liquid medium as a precipitate.
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