Silver nanoparticles aggregative behavior at low concentrations in aqueous solutions

Abstract

This study describes aggregation kinetics of silver nanoparticles (AgNPs) and particle size distribution (PSD) of silver aggregates at concentrations ranging from 10 mgAg.L−1 to 10 μgAg.L−1. Aggregation kinetics were conducted at different NaCl concentrations for 2 h and at three environmentally NaCl concentrations (9, 86 and 428 mM) for 12 h to determine the critical coagulation concentration (CCC) and PSD. At mgAg.L−1 level, CCC was near 70 mM, and near 150 mM at μgAg.L−1 level. Furthermore, PSD was strongly affected by AgNPs concentration. At 10 and 1 mgAg.L−1, more than 80 % of aggregates had a hydrodynamic diameter (Dh) higher than 200 nm after 2 h, and more than 95 % after 12 h. At 100 and 10 μgAg.L−1, the main aggregate population had a Dh smaller than 200 nm. At mgAg.L−1 level, particle concentration remained high enough to promote interactions between AgNPs and aggregates, favoring the formation of large aggregates, although it was not the case at μgAg.L−1 level. Moreover, at 106 particles. mL−1, AgNPs aggregation was strongly reduced and could cause the presence of a plateau in aggregation kinetics. Evolution of silver aggregates PSD may increase their residence time in the water column and promotes their exportation to the ocean.