Influence of water on room-temperature preparation of silver nanoparticles using poly(vinyl pyrrolidone) as reducing agent.

Silver nanoparticles (Ag NPs) were prepared via a wet-chemical method in the presence of poly(vinyl pyrrolidone) (PVP) without other reducing agents at room temperature. The influence of the addition of water on the preparation of Ag NPs was investigated. It was found that water addition has a significant influence on the reduction reaction, resulting in changes of shape, size and optical properties of the particles. When large amounts of water were added, the reduction rate was very slow. However, when small amounts of water were used, the opposite effects on the reaction process were observed, initial inhibition effect and final promotion effect. Two main possible mechanisms were proposed to explain the opposite effects of two reaction stages with small amounts of water addition: (1) the initial inhibition effect was induced by free oxygen in water, which would react preferentially with the reducing species in the system; (2) the promotion effect thereafter may be due to the differences of chain extension of PVP molecules and electron transfer rate in ethanol and water.