Effect of atmospheric exposure on the growth of citrate-capped silver nanoparticles

Citrate-capped Ag nanoparticles are prepared at 8 oC in aqueous solution by a modified ‘Turkevich’ approach using NaBH4 as reducing agent. Spherical Ag nanoparticles are observed in fresh solution having average size 10–15 nm with a narrow size distribution. UV–vis–NIR spectroscopic result shows a ‘surface plasmon resonance’ induced absorption peak at 389 nm in fresh solution. When the nanoparticles are exposed to atmosphere for 7 days, an enhancement in average size from 10 to 22 nm is observed and corresponding absorption peak is shifted from 389 to 425 nm. When exposure time is increased for a very long duration (17 months), chain formation in Ag nanoparticles is observed. The elemental state of Ag nanoparticles is confirmed with X-ray photoelectron spectroscopic study. The formation and growth mechanism of Ag nanoparticles is explained.