posted on 2016-01-13, 12:50authored byRonald
D. Kent, Peter J. Vikesland
Dissolution
of copper-based nanoparticles (NPs) can control their environmental
persistence and toxicity. Previous research has generally reported
limited dissolution of Cu-based NPs at circumneutral pH, but the environmentally
important case of dissolution in solutions that are undersaturated
with respect to copper mineral phases has not been investigated thoroughly.
In this study, immobilized Cu-based NPs were fabricated on solid supports.
Metallic copper (Cu), cupric oxide/hydroxide (Cuox), and
copper sulfide (CuxS) NPs were investigated.
Dissolution rate constants were measured in situ by
an atomic force microscope equipped with a flow-through cell. A mass-balance
model indicated that the flowing solution was consistently undersaturated
with respect to cupric solid phases. Based on the measured rate constants,
Cuox NPs are expected to dissolve completely in these undersaturated
conditions within a matter of hours, even at neutral to basic pH.
The expected persistence of metallic Cu NPs ranges from a few hours
to days, whereas CuxS NPs showed no significant
dissolution over the time scales studied. Field deployment of Cu-based
NP samples in a freshwater stream confirmed these conclusions for
a natural aquatic system. These results suggest that Cu and Cuox NPs will be short-lived in the environment unless dissolution
is hindered by a competing process, such as sulfidation.