A systematic evaluation of agglomeration of Ag and TiO2 nanoparticles under freshwater relevant conditions.

This study aims to investigate effects of freshwater components in order to predict agglomeration behavior of silver nanoparticles coated with citrate (AgNP-Cit), polyvinylpyrrolidone (AgNP-PVP), and of TiO2 nanoparticles. Agglomeration studies were conducted in various media based on combinations of ions, natural organic matter (humic, fulvic acid) and surfactants (sodium dodecyl sulfate, alkyl ethoxylate), at a constant ionic strength of 10 mM over time for up to 1 week. Agglomeration level of AgNP-Cit and TiO2 was mostly dependent on the concentration of Ca(2+) in media, and their size strongly increased to micrometer scale over 1 week. However, AgNP-Cit and TiO2 were stabilized to particle size around 500 nm in the presence of NOM, surfactants and carbonate over 1 week. AgNP-PVP maintained their original size in all media except in the presence of Mg(2+) ions which led to significant agglomeration. Behavior of these engineered nanoparticles was similar in a natural freshwater medium.