Dissolution and aggregation kinetics of zero valent copper nanoparticles in (simulated) natural surface waters:...

The combined effects of pH, dissolved organic carbon (DOC) and Ca²⁺/Mg²⁺ on the dissolution and aggregation kinetics of zero valent copper engineered nanoparticles (Cu⁰ ENPs) were investigated. The dissolution and aggregation of the particles were studied in (a) synthetic aqueous media, similar in chemistry to natural surface waters, and (b) natural surface waters samples, for up to 32 or 24 h. The DOC stabilized the particles and prevented aggregation, and thus increased the available surface area. The higher available surface area in turn accelerated the dissolution of the particles. The presence of Ca²⁺/Mg²⁺, however, changed the aggregation and the dissolution of the DOC-stabilized particles. The influence of Ca²⁺/Mg²⁺ on DOC-stabilized particles was different at different pH's. In the absence of DOC, 10 mM of Ca²⁺/Mg²⁺ induced charge reversal on the particles and caused particle stability against aggregation. This subsequently increased particles dissolution. The results obtained with regard to dissolution and aggregation of the particles in natural surface waters were compared with those determined for the synthetic waters. This comparison showed that the behavior of the particles in the natural surface waters was mostly similar to the behavior determined for media at pH 9. Overall, the current study provides some novel insights into the simultaneous effects of physicochemical parameters of water on particle stability against aggregation and dissolution, and provides data about how the processes of aggregation and dissolution of Cu⁰ ENPs interact and jointly determine the overall particle fate.