Extrapolated long-term stability of titanium dioxide nanoparticles and multi-walled carbon nanotubes in artificial freshwater

  • Andrea Brunelli
  • Alex Zabeo
  • Elena Semenzin
  • Danail Hristozov
  • Antonio Marcomini
Research Paper


Long-term stability of two engineered nanomaterials (ENMs), i.e., the inorganic n-TiO2 and the organic Multi-Walled Carbon Nanotubes (MWCNTs), dispersed in artificial freshwater (5–100 mg l−1), was investigated from short-term settling velocity, particle size distribution, and surface charge. Hydrodynamic diameter and ζ-pot, calculated by means of dynamic and electrophoretic light scattering, respectively, qualitatively indicated a general ENMs dispersion instability over 1 h time. Sedimentation results, obtained by centrifugal separation analysis using the LUMiSizer over approx. 30 min analysis time, allowed to estimate the quantitative long-term (over 30 days) stability of ENMs. Settling data fitted satisfactorily with a first-order kinetic equation (R 2 in the range of 0.918–0.989). The settling rate constant k values extrapolated at gravity spanned one order of magnitude, i.e., from 7.21 × 10−5 to 4.12 × 10−4 s−1, and with the increasing of initial ENMs concentration. Sedimentation velocities were in good agreement with short- to long-term literature data (7.8 × 10−2–1.7 × 101 m day−1 vs. 5 × 10−4–3 × 10−1 m day−1 for n-TiO2 and 5.9 × 10−2–3.4 × 10−1 m day−1 vs. 2 × 10−1–1.2 m day−1 for MWCNTs). n-TiO2 showed a higher long-term stability with respect to MWCNTs (average: 1 × 10−1 ± 3.4 × 10−2 m day−1 instead of 1.7 × 10−1 ± 1.1 × 10−1 m day−1, respectively).


Engineered nanomaterials Environmental exposure Sedimentation kinetics Long-term stability estimation Centrifugal separation analysis 



This research was partially founded by the European Commission within the Seventh Framework Program (FP7; SUN project - Grant Agreement n° 604305). The authors thankfully acknowledge VenetoNanotech for providing TEM images of MWCNT and Riccardo Cossi (Qi srl, Pomezia, Italy) and Andrea Scandella (University Ca’ Foscari of Venice) for their valuable technical support.

Compliance with ethical standards

Conflict of Interest

The authors declare that they have no conflict of interest.

Supplementary material

11051_2016_3412_MOESM1_ESM.docx (3.8 mb)
Supplementary material 1 (DOCX 3938 kb)


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Copyright information

© Springer Science+Business Media Dordrecht 2016

Authors and Affiliations

  • Andrea Brunelli
    • 1
  • Alex Zabeo
    • 1
  • Elena Semenzin
    • 1
  • Danail Hristozov
    • 1
  • Antonio Marcomini
    • 1
  1. 1.Department of Environmental Sciences, Informatics and StatisticsUniversity Ca’ Foscari of VeniceVeniceItaly

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