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Manilo M.V.,Ukrainian Academy of Sciences | Netreba S.V.,Ukrainian Academy of Sciences | Prokopenko V.A.,Ukrainian Academy of Sciences | Lebovka N.I.,Ukrainian Academy of Sciences | And 3 more authors.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2016

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. © 2016 Elsevier B.V. Source


Manilo M.,Ukrainian Academy of Sciences | Lebovka N.,Ukrainian Academy of Sciences | Lebovka N.,CNRS Integrated Transformations of Renewable Matter | Barany S.,Hungarian Academy of Sciences | Barany S.,The Transcarpathian Ii Ferenc Rakoczi Hungarian Institute
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2014

To characterize the electric double layers (EDLs) of multi-walled carbon nanotubes (NTs), laponite clay disks and NT+laponite hybrid particles, their electrophoretic mobility was investigated as a function of pH and concentration of electrolytes (KCl, CaCl2 and AlCl3). The electrokinetic behaviour of NTs resembles that of the lyophobic colloids. An increase in pH from 2 to 12 resulted in substantial increase of the absolute (negative) values of the electrophoretic mobility of NTs due to dissociation of surface hydroxyl and carbonyl groups, which was identified by infra-red (IR) spectroscopy. The observed attraction between similarly charged colloidal particles of NTs and laponite was explained by the highly heterogeneous distribution of negatively charged functional groups on the surface of NTs and difference in electrophoretic mobility of NT and laponite particles. © 2014 Elsevier B.V. Source


Manilo M.V.,Ukrainian Academy of Sciences | Lebovka N.I.,Ukrainian Academy of Sciences | Lebovka N.I.,CNRS Integrated Transformations of Renewable Matter | Barany S.,University of Miskolc | Barany S.,The Transcarpathian Ii Ferenc Rakoczi Hungarian Institute
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2015

Aggregation of multi-walled carbon nanotube (NT)+laponite hybrid particles in aqueous suspensions under continuous stirring at different values of mass ratio of laponite and NTs, X=mL/mNT, was investigated using Photometric Dispersion Analyser. It has been found that NTs+laponite suspension at X=1 is the most stable in respect to variation of pH and electrolytes concentration. Addition of electrolytes (KCl, CaCl2 and AlCl3) destabilized the suspension with formation of large quickly sedimenting flocs. Also the strength of flocs and the reversibility of aggregation of NT+laponite nanoparticles as a function of the shear rate have been determined. From time dependencies of the degree of aggregation in hybrid NTs+laponite suspensions, the critical coagulation concentrations (CCC) for KCl (CCC1=5×10-3M), CaCl2 (CCC2=10-3M) and AlCl3 (CCC3=10-5M) for the NTs+laponite complex suspension were estimated. The ratio of CCC1/CCC2≈5 is very close to the CCCz2.5=5.66 criterion. It is an evidence of aggregation of NT+laponite hybrid particles in the secondary minimum. © 2015. Source


Manilo M.,Ukrainian Academy of Sciences | Lebovka N.,Ukrainian Academy of Sciences | Barany S.,University of Miskolc | Barany S.,The Transcarpathian Ii Ferenc Rakoczi Hungarian Institute
Journal of Environmental Sciences (China) | Year: 2015

The kinetics of adsorption and parameters of equilibrium adsorption of Methylene Blue (MB) on hybrid laponite-multi-walled carbon nanotube (NT) particles in aqueous suspensions were determined. The laponite platelets were used in order to facilitate disaggregation of NTs in aqueous suspensions and enhance the adsorption capacity of hybrid particles for MB. Experiments were performed at room temperature (298K), and the laponite/NT ratio (X l) was varied in the range of 0-0.5. For elucidation of the mechanism of MB adsorption on hybrid particles, the electrical conductivity of the system as well as the electrokinetic potential of laponite-NT hybrid particles were measured. Three different stages in the kinetics of adsorption of MB on the surface of NTs or hybrid laponite-NT particles were discovered to be a fast initial stage I (adsorption time t =0-10min), a slower intermediate stage II (up to t =120min) and a long-lasting final stage III (up to t =24hr). The presence of these stages was explained accounting for different types of interactions between MB and adsorbent particles, as well as for the changes in the structure of aggregates of NT particles and the long-range processes of restructuring of laponite platelets on the surface of NTs. The analysis of experimental data on specific surface area versus the value of X l evidenced in favor of the model with linear contacts between rigid laponite platelets and NTs. It was also concluded that electrostatic interactions control the first stage of adsorption at low MB concentrations. © 2015. Source

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