Effect of polymer coating composition on the aggregation rates of Ag nanoparticles in NaCl solutions and seawaters

Highlights: • The behaviour of AgNPs upon discharge into natural waters is not yet fully understood. • Aggregation kinetics of AgNPs followed by DLS in NaCl and seawaters were confronted. • CCC, D_f and k were obtained in NaCl for ± charged and non-ionic polymer coatings. • Only specific coated-AgNPs behave in seawater as expected from experiments in NaCl. • Coating size/charge and DOM are critical to infer behaviour in seawater from NaCl. The aggregation behaviour of polymer-coated silver nanoparticles (AgNPs) was characterized in NaCl solutions, and in two seawaters of different salinities and dissolved organic matter (DOM) contents. Representative organic coatings i.e. tannic acid (TA), alginic acid (ALG), two gum Arabic samples (GAL and GAH), branched polyethylenimine (BPEI), and non-ionic surfactants (reference material NM-300K) were selected to cover a wide range of zeta-potentials. The stability in NaCl solutions, as determined from the rate of variation in hydrodynamic size within a timeframe of one hour, followed the order BPEI ≫ NM-300K ≈ GAL ≫ ALG ≈ TA ≫ GAH. In the seawater samples the order was NM-300K ≈ GAL ≫ ALG > GAH > TA ≈ BPEI, and only TA, GAL and NM-300K batches behaved as expected from the NaCl experiments. Remarkably, the BPEI sample showed the largest aggregation rate in the seawater sample with the highest DOM concentration (277 μM C). The GAH sample displayed a non-monotonic variation in aggregation rate with NaCl concentration, apparently due to concomitant precipitation of AgCl. The results indicate that non-electrostatic stabilization mechanisms and DOM-coating interactions are important for the prediction of stability and persistence of polymer-coated AgNPs in seawater.