Absolute Aggregation Rate Constants of Hematite Particles in Aqueous Suspensions: A Comparison of Two Different Surface Morphologies

Schudel, M.; Behrens, Sven H.; Holthoff, Helmut; Kretzschmar, Ruben; Borkovec, Michal

doi:10.1006/jcis.1997.5207

Cited by 202 publications

(243 citation statements)

References 55 publications

(46 reference statements)

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“…The coagulation rate was calculated from the slope of kinetic curves as explained before [7,12]. The stability ratio (W) was calculated from the initial slopes of kinetic curves belonging to the slow and fast coagulation as suggested in literature [20,21]. To ensure the onset of fast coagulation regime, at least three different, instantly coagulating concentrations of NaCl were applied.…”

Section: Coagulation Kinetic Measurementmentioning

confidence: 99%

Adsorption of organic acids on magnetite nanoparticles, pH-dependent colloidal stability and salt tolerance

Tombácz

Tóth

Nesztor

et al. 2013

Colloids and Surfaces A: Physicochemical and Engineering Aspect

111

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Graphical abstractH-type isotherms HA, PAM, GA, and CA Highlights  Organic acids either stabilize or destabilize oxide nanoparticles in natural waters.  The stabilizing/destabilizing effect depends on pH, salinity and organic concentration.  Specific configuration of carboxylic groups is necessary to surface complexation.  Surface complexation leads to high affinity adsorption isotherms.  Higher molecular weight organic acids provide better stability than smaller ones. AbstractThe adsorption of different organic acids and their influence on the pH-dependent charging, salt tolerance and so the colloidal stability of magnetite nanoparticles are compared. Adsorption isotherms of citric acid -CA, gallic acid -GA, poly(acrylic acid) -PAA, poly(acrylic-co-maleic acid) -PAM and humic acid -HA were measured. The pH-dependent charge state of MNPs was characterized by electrophoretic mobility and their aggregation by dynamic light scattering. The salt tolerance was tested in coagulation kinetic experiments. Although the adsorption capacities, the type of bonding (either H-bonds or metal ioncarboxylate complexes) and so the bond strengths are significantly different, the following general trends have been found. Small amount of organic acids at pH < ~8 (the pH of PZC of magnetite) -relevant condition in natural waters -only neutralizes the positive charges, and so promotes the aggregation and sedimentation of nanoparticles. Greater amounts of organic acid, above the charge neutralization, cause the sign reversal of particle charge, and at high

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Section: Coagulation Kinetic Measurementmentioning

confidence: 99%

Adsorption of organic acids on magnetite nanoparticles, pH-dependent colloidal stability and salt tolerance

Tombácz

Tóth

Nesztor

et al. 2013

Colloids and Surfaces A: Physicochemical and Engineering Aspect

111

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“…The coagulation rate was calculated from the slope of the kinetic curves as explained before [8]. The stability ratio (W) was calculated from the initial slopes of kinetic curves belonging to the slow and fast coagulation ranges as given in literature [15,16,17]. To determine the onset of fast coagulation regime, at least three different NaCl concentrations were used within the range of instant coagulation.…”

Section: Coagulation Kinetic Experimentsmentioning

confidence: 99%

Colloidal stability of carboxylated iron oxide nanomagnets for biomedical use

Tombácz¹,

Szekeres²,

Hajdú³

et al. 2014

Period. Polytech. Chem. Eng.

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“…The coagulation rate was calculated from the slope of kinetic curves as explained before [5,8]. The stability ratio (W) was calculated from the initial slopes of kinetic curves belonging to the slow and fast coagulation as suggested in the literature [15,16]. The critical coagulation concentration (CCC) is usually determined from the log 10 W versus log 10 electrolyte concentration function.…”

Section: Coagulation Kinetic Measurementmentioning

confidence: 99%

“…In parallel, the pH-dependent particle aggregation was measured by dynamic light scattering, which can be used even in coagulating system [15,16] and particle size data provide information on the colloidal stability of systems. In the pure magnetite sols, only the electric double layer exists far from the PZC, which is able to stabilize particles at low salt concentration, so the measured average hydrodynamic sizes remained below 100 nm (Fig.…”

Section: The Effect Of Ha and Ca Presence On The Ph-dependent Charge mentioning

confidence: 99%

Surface charging, polyanionic coating and colloid stability of magnetite nanoparticles

Hajdú

Illés

Tombácz

et al. 2009

Colloids and Surfaces A: Physicochemical and Engineering Aspect

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a b s t r a c tThe formation of small and large molecular polyanionic coating on the surface of magnetite (Fe 3 O 4 ) 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 pHdependent 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.

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Absolute Aggregation Rate Constants of Hematite Particles in Aqueous Suspensions: A Comparison of Two Different Surface Morphologies

Cited by 202 publications

References 55 publications

Adsorption of organic acids on magnetite nanoparticles, pH-dependent colloidal stability and salt tolerance

Adsorption of organic acids on magnetite nanoparticles, pH-dependent colloidal stability and salt tolerance

Colloidal stability of carboxylated iron oxide nanomagnets for biomedical use

Surface charging, polyanionic coating and colloid stability of magnetite nanoparticles

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