To address the pollution problem of organic dyes, monodispersed anionic silver nanoparticles (AgNPs) with an average size of 6 nm were prepared in water media via chemical reduction method from oleic acid and n-butyl amine. The aqueous solution of the resultant AgNPs was utilized as a photocatalyst to investigate the adsorption and photodegradation behaviors of organic dyes under different light irradiation. The morphology and surface characteristics of the synthesized AgNPs were probed using TEM, XRD, FTIR and zeta potential analysis. The adsorption and degradation process of organic dyes on the AgNPs were characterized in details by UV-Vis spectrophotometer. The results showed that the AgNPs exhibited a characteristic charge- and size-selective adsorption of dyes owing to the profoundly negative charged surface, which enables the AgNPs to possess high selective degradation of Methylene Blue. More still, due to the surface plasmon resonance (SPR) effect of AgNPs, the obtained AgNPs presented a higher photocatalytic activity to Methylene Blue under UV light, visible light, and solar light compared with commercial photocatalysts. The 5 cyclic reactions revealed its high stability and reusability. In a nutshell, the proposed mechanism systematically combined the selective adsorption and the SPR effect to explain the detailed photocatalytic process of the obtained AgNPs. (C) 2018 Elsevier Inc. All rights reserved.