Dissolution and Phosphate-Induced Transformation of ZnO Nanoparticles in Synthetic Saliva Probed by AGNES without Previous Solid–Liquid Separation. Comparison with UF-ICP-MS

The variation over time of free Zn2+ ion concentration in stirred dispersions of ZnO nanoparticles (ZnO NPs) prepared in synthetic saliva at pH 6.80 and 37 °C was followed in situ (without solid–liquid separation step) with the electroanalytical technique AGNES (Absence of Gradients and Nernstian Eq...

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Bibliographic Details
Published in:Environmental science & technology 2019-04, Vol.53 (7), p.3823-3831
Main Authors: David, Calin A, Galceran, Josep, Quattrini, Federico, Puy, Jaume, Rey-Castro, Carlos
Format: Article
Language:English
Subjects:
Decay rate
Genetic transformation
Inductively coupled plasma mass spectrometry
Ion concentration
Ionic strength
Mass spectrometry
Mass spectroscopy
Nanoparticles
Organic chemistry
pH effects
Phosphates
Reproducibility
Saliva
Separation
Speciation
Stability constants
Ultrafiltration
Zinc
Zinc oxide
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Summary:The variation over time of free Zn2+ ion concentration in stirred dispersions of ZnO nanoparticles (ZnO NPs) prepared in synthetic saliva at pH 6.80 and 37 °C was followed in situ (without solid–liquid separation step) with the electroanalytical technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping). Under these conditions, ZnO NPs are chemically unstable due to their reaction with phosphates. The initial stage of transformation (around 5–10 h) involves the formation of a metastable solid (presumably ZnHPO4), which later evolves into the more stable hopeite phase. The overall decay rate of ZnO NPs is significantly reduced in comparison with phosphate-free background solutions of the same ionic strength and pH. The effective equilibrium solubilities of ZnO (0.29–0.47 mg·L–1), as well as conditional excess-ligand stability constants and fractional distributions of soluble Zn species, were determined in the absence and presence of organic components. The results were compared with the conventional ultrafiltration and inductively coupled plasma-mass spectrometry (UF-ICP-MS) methodology. AGNES proves to be advantageous in terms of speed, reproducibility, and access to speciation information.
ISSN:0013-936X
1520-5851
DOI:10.1021/acs.est.8b06531