Surface charging, polyanionic coating and colloid stability of magnetite nanoparticles

A. Hajdú, E. Illés, E. Tombácz, I. Borbáth

Research output: Contribution to journalArticle

64 Citations (Scopus)

Abstract

The formation of small and large molecular polyanionic coating on the surface of magnetite (Fe3O4) nanoparticles and their role in the stability enhancement of aqueous magnetic fluids are compared. Magnetite was synthesized and stabilized with citric (CA) and humic (HA) acids. The macromolecular HA, a notable fraction of the natural organic matter (NOM), contains mainly carboxylic groups similarly to the CA, and both acids are able to form surface complexes on the ≡Fe-OH sites of iron oxides. The pH-dependent charge state of particles and their aggregation were quantified, and the enhanced salt tolerance of stabilized systems was studied. The dynamic light scattering (DLS) method was used to characterize colloidal stability under different conditions. The average particle size and electrophoretic mobility were measured, and the electrolyte tolerance was tested in coagulation kinetic measurements. The colloidal stability of magnetite dispersions depends sensitively on the pH and the concentration of organic acids present. The trace amount of HA neutralizes the positive charges on magnetite surface under acidic condition only in part, and so it promotes the aggregation between the particles having both positive sites and negative humate patches on the surface. Above the adsorption saturation, the surface becomes completely covered causing the reversal of charge sign and overcharging of nanoparticles. The magnetite nanoparticles become stabilized in a way of combined steric and electrostatic effects. The thicker layer of macromolecular HA provides better electrosteric stability than that of CA coating. However, in the presence of either CA or HA, the dissolution of magnetite is enhanced due to the complexation of iron ions in the aqueous medium.

Original languageEnglish
Pages (from-to)104-108
Number of pages5
JournalColloids and Surfaces A: Physicochemical and Engineering Aspects
Volume347
Issue number1-3
DOIs
Publication statusPublished - Sep 5 2009

Fingerprint

Magnetite Nanoparticles
Magnetite nanoparticles
Ferrosoferric Oxide
Colloids
magnetite
charging
colloids
Magnetite
coatings
Coatings
nanoparticles
Agglomeration
acids
Electrophoretic mobility
Magnetic fluids
Organic acids
Dynamic light scattering
Coagulation
Complexation
Dispersions

Keywords

  • Adsorption
  • Citric acid
  • Colloidal stability
  • Humic acid
  • Magnetic fluids
  • Magnetite

ASJC Scopus subject areas

  • Colloid and Surface Chemistry

Cite this

Surface charging, polyanionic coating and colloid stability of magnetite nanoparticles. / Hajdú, A.; Illés, E.; Tombácz, E.; Borbáth, I.

In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, Vol. 347, No. 1-3, 05.09.2009, p. 104-108.

Research output: Contribution to journalArticle

@article{e93fcb899beb4d23bd6ab8e265403eb6,
title = "Surface charging, polyanionic coating and colloid stability of magnetite nanoparticles",
abstract = "The formation of small and large molecular polyanionic coating on the surface of magnetite (Fe3O4) nanoparticles and their role in the stability enhancement of aqueous magnetic fluids are compared. Magnetite was synthesized and stabilized with citric (CA) and humic (HA) acids. The macromolecular HA, a notable fraction of the natural organic matter (NOM), contains mainly carboxylic groups similarly to the CA, and both acids are able to form surface complexes on the ≡Fe-OH sites of iron oxides. The pH-dependent charge state of particles and their aggregation were quantified, and the enhanced salt tolerance of stabilized systems was studied. The dynamic light scattering (DLS) method was used to characterize colloidal stability under different conditions. The average particle size and electrophoretic mobility were measured, and the electrolyte tolerance was tested in coagulation kinetic measurements. The colloidal stability of magnetite dispersions depends sensitively on the pH and the concentration of organic acids present. The trace amount of HA neutralizes the positive charges on magnetite surface under acidic condition only in part, and so it promotes the aggregation between the particles having both positive sites and negative humate patches on the surface. Above the adsorption saturation, the surface becomes completely covered causing the reversal of charge sign and overcharging of nanoparticles. The magnetite nanoparticles become stabilized in a way of combined steric and electrostatic effects. The thicker layer of macromolecular HA provides better electrosteric stability than that of CA coating. However, in the presence of either CA or HA, the dissolution of magnetite is enhanced due to the complexation of iron ions in the aqueous medium.",
keywords = "Adsorption, Citric acid, Colloidal stability, Humic acid, Magnetic fluids, Magnetite",
author = "A. Hajd{\'u} and E. Ill{\'e}s and E. Tomb{\'a}cz and I. Borb{\'a}th",
year = "2009",
month = "9",
day = "5",
doi = "10.1016/j.colsurfa.2008.12.039",
language = "English",
volume = "347",
pages = "104--108",
journal = "Colloids and Surfaces A: Physicochemical and Engineering Aspects",
issn = "0927-7757",
publisher = "Elsevier",
number = "1-3",

}

TY - JOUR

T1 - Surface charging, polyanionic coating and colloid stability of magnetite nanoparticles

AU - Hajdú, A.

AU - Illés, E.

AU - Tombácz, E.

AU - Borbáth, I.

PY - 2009/9/5

Y1 - 2009/9/5

N2 - The formation of small and large molecular polyanionic coating on the surface of magnetite (Fe3O4) nanoparticles and their role in the stability enhancement of aqueous magnetic fluids are compared. Magnetite was synthesized and stabilized with citric (CA) and humic (HA) acids. The macromolecular HA, a notable fraction of the natural organic matter (NOM), contains mainly carboxylic groups similarly to the CA, and both acids are able to form surface complexes on the ≡Fe-OH sites of iron oxides. The pH-dependent charge state of particles and their aggregation were quantified, and the enhanced salt tolerance of stabilized systems was studied. The dynamic light scattering (DLS) method was used to characterize colloidal stability under different conditions. The average particle size and electrophoretic mobility were measured, and the electrolyte tolerance was tested in coagulation kinetic measurements. The colloidal stability of magnetite dispersions depends sensitively on the pH and the concentration of organic acids present. The trace amount of HA neutralizes the positive charges on magnetite surface under acidic condition only in part, and so it promotes the aggregation between the particles having both positive sites and negative humate patches on the surface. Above the adsorption saturation, the surface becomes completely covered causing the reversal of charge sign and overcharging of nanoparticles. The magnetite nanoparticles become stabilized in a way of combined steric and electrostatic effects. The thicker layer of macromolecular HA provides better electrosteric stability than that of CA coating. However, in the presence of either CA or HA, the dissolution of magnetite is enhanced due to the complexation of iron ions in the aqueous medium.

AB - The formation of small and large molecular polyanionic coating on the surface of magnetite (Fe3O4) nanoparticles and their role in the stability enhancement of aqueous magnetic fluids are compared. Magnetite was synthesized and stabilized with citric (CA) and humic (HA) acids. The macromolecular HA, a notable fraction of the natural organic matter (NOM), contains mainly carboxylic groups similarly to the CA, and both acids are able to form surface complexes on the ≡Fe-OH sites of iron oxides. The pH-dependent charge state of particles and their aggregation were quantified, and the enhanced salt tolerance of stabilized systems was studied. The dynamic light scattering (DLS) method was used to characterize colloidal stability under different conditions. The average particle size and electrophoretic mobility were measured, and the electrolyte tolerance was tested in coagulation kinetic measurements. The colloidal stability of magnetite dispersions depends sensitively on the pH and the concentration of organic acids present. The trace amount of HA neutralizes the positive charges on magnetite surface under acidic condition only in part, and so it promotes the aggregation between the particles having both positive sites and negative humate patches on the surface. Above the adsorption saturation, the surface becomes completely covered causing the reversal of charge sign and overcharging of nanoparticles. The magnetite nanoparticles become stabilized in a way of combined steric and electrostatic effects. The thicker layer of macromolecular HA provides better electrosteric stability than that of CA coating. However, in the presence of either CA or HA, the dissolution of magnetite is enhanced due to the complexation of iron ions in the aqueous medium.

KW - Adsorption

KW - Citric acid

KW - Colloidal stability

KW - Humic acid

KW - Magnetic fluids

KW - Magnetite

UR - http://www.scopus.com/inward/record.url?scp=69249232415&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=69249232415&partnerID=8YFLogxK

U2 - 10.1016/j.colsurfa.2008.12.039

DO - 10.1016/j.colsurfa.2008.12.039

M3 - Article

AN - SCOPUS:69249232415

VL - 347

SP - 104

EP - 108

JO - Colloids and Surfaces A: Physicochemical and Engineering Aspects

JF - Colloids and Surfaces A: Physicochemical and Engineering Aspects

SN - 0927-7757

IS - 1-3

ER -