@ Reham, polyvinylpyrrolidone is added as a stabilizing agent during the synthesis process of silver nanoparticles that reduces the size of nanoparticles and produces a more stable colloidal nanosilver in comparison to uncoated nanoparticles. PVP capping layer negatively affects the antibacterial properties of silver nanoparticles. Normally, In producing metal nanoparticles via polyol synthesis, the PVP is broadly applied as a stabilizer and shape controlling agent in which the PVP and metal interact via the carbonyl group and nitrogen atom of the pyrrolidine ring.
If you are reducing silver ions with hydrazine hydrate or borohydride, then PVP is needed as a stabilizer for nanoparticles so that they do not grow in size and do not settle. If you are reducing silver ions with a plant leaf extract, then the extract already contains stabilizers.
Additionally, the stability of the silver nanoparticles increases and they can be exchanged to an organic medium. In this article Article Plasmonic gold-embedded TiO2 thin films as photocatalytic se...
, we used PVP stabilised Au NPs to synthesise a Au NP-embedded titania thin film, but atm I'm working with Ag NPs stabilised with PVP and it works as well.