The combined effect of light irradiation and chloride on the physicochemical properties of silver nanoparticles

Understanding the effect of various environmental factors on the transformation of silver nanoparticles (Ag NPs) is crucial to determine their toxicity and fate in the environment. Ag NPs are inevitably exposed to sunlight and will be in contact with chloride (Cl(−)), a ubiquitous ligand in natural water, once released into the environment. In this study, the combined effect of Cl(−) and light on various physicochemical properties (optical property, dissolution, morphology, surface charge) of different sizes Ag NPs was studied. The results showed that light irradiation, in the presence of Cl(−), led to a great decrease in the concentration of dissolved Ag and a remarkable increase in the zeta potential of Ag NPs, as well as the generation of some tiny Ag NPs and fusion aggregates. AgCl was suggested to rapidly coat onto Ag NPs after exposure to Cl(−). And the AgCl layer was obviously destroyed by photoreduction under light irradiation. Meanwhile, the Ag NP size exhibited a great impact on the destruction of the AgCl layer. It was further observed that the AgCl layer gradually re-formed when the light was removed, which suggested that Ag NPs might present different states during the daytime and at night in aquatic environments.