Stability of silver nanoparticles (nAg) in aqueous solution: the role of particle size and water ionic strength

Abstract

Silver nanoparticles (nAg) are currently some of the widely produced and applied in commercial products. Their high usage translates to an increased potential to environmental release, and more concerning is their complex toxicity towards aquatic biota which can arise from the particulates, dissolved species or both forms. However, there is limited and contradicting information on how the nanoparticle and aqueous solution characteristics influence nanoparticle stability and toxicity. This study investigates the influence of particle size of silver (nAg) on nanoparticle dissolution and agglomeration dynamics using citrate capped 10nm and 40nm Ag particles in Hoagland¿s nutrient medium (HM), of different strength's 50% and 100%, to additionally investigate the influence of ionic strength at 100µg nAg/L concentration over 10 days. Agglomeration dynamics were monitored using TEM and zetasizer. The results indicate that at all time periods the smaller 10-nAg underwent higher dissolution rates relative to larger 40-nAg, this presents a definite effect of particle size influence on nAg dissolution.The quantity of dissolved Ag was notably lower by 10days relative to 2hrs, possible result of re-agglomeration of dissolved Ag and adsorption to other media electrolytes; although such a trend was notably higher on 10-nAg exposures. The re-agglomeration hypothesis is yet to be confirmed with Nanoparticle Tracking Analysis (NTA). The effect of water hardness was observed; nAg underwent notably higher dissolution in 50%HM, this was more defined for 10-nAg (Figure 2) whilst for 40-nAg after 10 days was not the case.Water hardness as CaCO3 was on average 2-folds lower in 50%HM than in 100%HM, suggesting the shielding effect of electrolytes is altering nanoparticle stability. The hypothesis was confirmed by quantification of Ca and Mg electrolytes, which were also on average 2-fold less in 50%HM than in 100%HM.