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Aggregation and dissolution of silver nanoparticles in natural surface water.

This study investigated aggregation and silver release of silver nanoparticles suspended in natural water in the absence and presence of artificial sun light. The influence of the capping layer was investigated using uncoated particles and particles coated with citrate or Tween 80. The experiments were conducted over 15 days in batch mode using a river water matrix. Silver release was monitored over this time while the aggregation state and morphological changes of the silver nanoparticles were tracked using dynamic light scattering and transmission electron microscopy. Results indicate sterically dispersed particles coated with Tween released silver quicker than did bare- and citrate-coated particles, which rapidly aggregated. A dissolved silver concentration of 40 μg/L was reached after just 6 h in the Tween-coated particle systems, accounting for ca. 3% of the total silver. Similar levels of dissolved silver were reached in the uncoated and citrate-coated systems at the end of the 15 days. Silver release was not significantly impacted by the artificial sun light; however, the light (and citrate) imparted significant morphological changes to the particles. Their impact was masked by aggregation, which seemed to be the controlling process in this study.