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Autor/a:
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David, Calin; Galceran i Nogués, Josep; Rey Castro, Carlos; Puy Llorens, Jaume; Companys Ferran, Encarnació; Salvador, José; Monné Esquerda, Josep; Wallace, Rachel; Vakourov, Alex
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Notas:
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There is a current debate on whether the toxicity of
engineered ZnO nanoparticles (NPs) can be traced back to their
nanoscale properties or rather to the simple fact of their relatively high
solubility and consequent release of Zn2+ ions. In this work, the
emerging electroanalytical technique AGNES (Absence of Gradients
and Nernstian Equilibrium Stripping), which is specially designed to
determine free metal ion concentration, is shown to be able to
measure the Zn2+ concentration resulting from dissolution of ZnO
nanoparticles dispersed in aqueous salt solutions. Three NP samples
from different sources (having average primary particle diameters of 6, 20, and 71 nm) were tested and compared with bulk ZnO
material. The enhanced solubility of the nanoparticles with decreasing primary radius allows for an estimation of the surface
energy of 0.32 J/m2
. AGNES also allows the study of the kinetics of Zn2+ release as a response to a change in the solution
parameters (e.g., pH, ZnO concentration). A physicochemical model has been developed to account for the observed kinetic
behavior. With this model, only one kinetic parameter is required to describe the time dependence of the free Zn2+ concentration
in solution. Good agreement with this prediction is obtained when, starting from an equilibrated NP dispersion, the pH of the
medium is lowered. Also, the independence of this parameter from pH, as expected from the model, is obtained at least in the pH
range 7−9. When dissolution is studied by dispersing ZnO nanoparticles in the medium, the kinetic parameter initially decreases
with time. This decrease can be interpreted as resulting from the increase of the radius of the clusters due to the agglomeration/
aggregation phenomena (independently confirmed). For the larger assayed NPs (i.e., 20 and 71 nm), a sufficiently large pH
increase leads to a metastable solubility state, suggesting formation of a hydroxide interfacial layer.
Research leading to these results received funding from the European Union Seventh Framework Programme (FP7/2007- 2013) under grant agreement no. 229244 (ENNSATOX), from the Spanish Ministry of Education and Innovation (Projects CTQ2009-07831 and CTM2009-14612), and from the “Comissionat per a Universitats i Recerca del Departament d’Innovacio, Universitats i Empresa de la Generalitat de Catalunya”. |
