Figure 3. Greater stability of an aqueous solution of AgNPs-PVP (0.25 mM) than unprotected AgNPs (0.25 mM), demonstrated via visual inspection and UV-vis spectrophotometry . A) Photographs of an aqueous solution of unprotected AgNPs (0.25 mM) that was freshly made and after 7 days of storage under ambient conditions, along with the UV-vis spectra under each condition. B) Photographs of an aqueous solution of AgNPs-PVP that was freshly made and after 7 days of storage under ambient conditions, along with the UV-vis spectra under each condition. The maximum absorption at 404 nm remained throughout the storage.