Morphological evolution and reconstruction of silver nanoparticles in aquatic environments: the roles of natural organic matter and light irradiation.

With the proliferation of silver nanoparticles (AgNPs), their potential entry into the environment has attracted increasing concern. Although photochemical transformation is an important fate of AgNPs in aquatic environments due to their strong light absorption, little is known about the evolution and transformation mechanisms of AgNPs. This study investigated the morphological evolution and reconstruction of AgNPs during photoconversion in the presence of natural organic matter (NOM). In the dark, the AgNPs formed chain-like structures through bridging effects with NOM at concentrations of 0.1 and 1 mg/L, and the proportion of Ag(+) in solution in the presence of 10 mg/L NOM was reduced by roughly half compared with that in the absence of NOM. Under irradiation, NOM participated in the photoreaction of AgNPs and can decelerate the photoreaction of AgNPs via several mechanisms, including light attenuation, the formation of a NOM coating, and competing with Ag for photons. Additionally, NOM can substitute for citrate as a stabilizing agent to compensate for the loss of AgNP stability due to citrate mineralization under extended irradiation, producing stable triangular nanosilver in aquatic environments. This study sheds light on the behavioral differences of AgNPs in different aquatic systems, which create uncertainties and difficulties in assessing the environmental risks of AgNPs.