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 Ca2+ 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 Mg2+ ions which led to significant agglomeration. Behavior of these engineered nanoparticles was similar in a natural freshwater medium. •DLS and NTA are quick, helpful techniques for size characterization of ENPs.•AgNP-PVP agglomerate in 1 week only in the presence of high Mg2+ concentration.•AgNP-Cit agglomerates between 150 nm and 1000 nm in 1 week depending on Ca2+ and NOM.•TiO2 has high tendency to agglomerate between 400 nm and 1000 nm in 1 week.•Environmental relevant concentration of NOM may lead to stabilization in 1 week. Agglomeration studies of engineered nanoparticles in media simulating freshwater are useful for the prediction of their behavior in freshwater.