Overcharging of magnetite nanoparticles in electrolyte solutions

Maryna V. Manilo, Svitlana V. Netreba, Vitaliy A. Prokopenko, Nikolai I. Lebovka, S. Bárány

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The effect of electrolytes with mono-, bi-, and trivalent anions on the surface charge (ζ-potential) of magnetite nanoparticles was investigated. The nanoparticles of magnetite, Fe3O4, were synthesised using different methods: a) coprecipitation of bivalent and trivalent iron sulphates at temperature T = 25 °C (sample NM1) and b) oxidation of rotating steel disk in distilled water at T = 25 °C (sample NM2) and at T = 50 °C (sample NM3). All samples were characterized using transmission electron microscopy, infra-red spectroscopy, by measurements of electrophoretic mobility and particle size distribution. Transmission electron microscopy data evidenced that primary particles in dried powder samples have quasi-spherical shape with mean diameters of ≈15 nm (NМ1), ≈80 nm (NМ2) and ≈70 nm (NМ3). From other hand data of particle size distribution analysis in aqueous suspensions at pH 6 indicated formation of aggregates of size of ≈30 nm (NМ1), ≈1200 nm (NМ2) and ≈520 nm (NМ3). Infra-red data also evidenced the presence of different functional groups in dependence on the protocol of synthesis. In presence of background electrolyte KCl (1 mM) the isoelectric point for all particles was in the interval рН 6.0–8.0. Adding of electrolytes with mono- (Cl), bi- (SO4 2−), and trivalent (PO4 3−) anions resulted in noticeable differences in behaviour of the ζ-potential and position of the isoelectric point for particles NМ1, NМ2 and NМ3. An increase of concentration of electrolytes always resulted in overcharging (changing from positive to negative charge) of particles NМ1 and NM3, whereas for particle NМ2 the overcharging was observed for both bivalent (SO4 2−) and trivalent (PO4 3−) anions. This behaviour cannot be explained by changes in the structure of electric double layer. The observed shifts of the isoelectric point and changes in the pH values in the presence of electrolytes reflected the impact of specific adsorption of anions on the ζ-potential of magnetite nanoparticles. Differences in pH values at which overcharging of nanoparticles took place can be explained by diverse structure of the surfaces of particles NМ1, NМ2 and NМ3.

Original languageEnglish
Pages (from-to)291-297
Number of pages7
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Publication statusPublished - Oct 5 2016



  • Characterization
  • Electrolytes
  • Nanomagnetite
  • pH
  • Synthesis
  • Zeta-potential

ASJC Scopus subject areas

  • Colloid and Surface Chemistry

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