Jiří Škvarla

Enhancement of the bentonite sorption properties

The almost monomineral fraction of bentonite rock-montmorillonite was modified by magnetic particles to enhance its sorption properties. The method of clay modification consists in the precipitation of magnetic nanoparticles, often used in preparing of ferrofluids, on the surface of clay. The influence of the synthesis temperature (20 and 85 degrees C) and the weight ratio of bentonite/iron oxides (1:1 and 5:1) on the composite materials properties were investigated. The obtained materials were characterized by the X-ray diffraction method and Mössbauer spectroscopy. Changes in the surface and pore properties of the magnetic composites were studied by the low nitrogen adsorption method and the electrokinetic measurements. The natural bentonite and magnetic composites were used in sorption experiments. The sorption of toxic metals (zinc, cadmium and nickel) from the model solutions was well described by the linearized Langmuir and Freundlich sorption model. The results show that the magnetic bentonite is better sorbent than the unmodified bentonite if the initial concentration of studied metals is very low.

Cytochrome c conjugated to ZnO-MAA nanoparticles: the study of interaction and influence on protein structure.

Nanoparticle-protein conjugates have potential for numerous applications due to the combination of the properties of both components. In this paper we studied the conjugation of horse heart cytochrome c with ZnO nanoparticles modified by mercaptoacetic acid (MAA) which may be a material with great potential in anticancer therapy as a consequence of synergic effect of both components. Cyt c adsorption to the ZnO-MAA NPs surface was studied by UV-vis spectroscopy and by a dynamic light scattering in various pH. The results indicate that the optimal pH for the association of protein with modified nanoparticles is in range 5.8-8.5 where 90-96% of cytochrome c was assembled on ZnO-MAA nanoparticles. The interaction of proteins with nanoparticles often results in denaturation or loss of protein function. Our observations from UV-vis spectroscopy and circular dichroism performed preserved protein structure after the interaction with modified nanoparticles.

Magnetic–hydrophobic coagulation of paramagnetic minerals: a correlation of theory with experiments

Abstract A simple theoretical model of magnetic–hydrophobic coagulation considering the total interaction potential energy between two spheres exposed to an external magnetic field as a sum of the van der Waals, electrostatic, magnetic, and hydrophobic components is proposed. The model was used to interpret experiments on coagulation of fine siderite particles in distilled water and 10−2 M KCl, hydrophobized by sodium oleate. In the experiments, a relative extent of the coagulation/stability equilibrium of the siderite suspension was evaluated photoelectrically. To estimate the model parameters, the ζ-potential and hydrophobicity of siderite particles were measured. A qualitative agreement was obtained between the model predictions (energy maximum and secondary minimum) and the experimental results (voltage changes after a selected interval of sedimentation) of the siderite suspensions. Moreover, a statistically significant correlation was found between the experimental voltages and the calculated energy maximum (a crucial factor of theories on the fine particle coagulation kinetics), which can be represented by a linear regression equation with the correlation coefficient of 0.979.

Evaluation of mutual interactions in binary mineral suspensions by means of electrophoretic light scattering (ELS)

Abstract The effect of mutual interaction (heteroaggregation and dissolution interference) between different fine mineral particles in their multi-component suspensions complicate the possibility of selective separation. Presenting results obtained on three two-component mixtures (silicasilica/ aminopropyl, hematite-quartz, and magnesite-quartz) it has been shown that this effect can be evaluated with the ELS technique by comparing zeta potential distributions determined prior to and after mixing the individual components. A theoretical interpretation of evaluated heteroaggregation was introduced.

A Simple Interaction Model of Particles Covered With Polyelectrolyte Brush Layers in the Strong Charging and Strong Screening Regime with Implications to Microbial Aggregation and Adhesion

In order to better understand and predict the influence of main solution parameters (pH and ionic strength) on aggregation/adhesion of “hairy” colloids mimicking bacteria, a simple interaction model is proposed. In this model, the van der Waals interaction energy between two spheres is combined with the electrosteric interaction energy between brush layers of flexible polyelectrolyte chains end-grafted on the spheres. The latter interaction energy component is expressed using simple asymptotic scaling approximations (omitting their numerical prefactors) derived earlier (Pincus, P.: Colloid stabilization with grafted polyelectrolytes, Macromolecules, 1991, 24, 2912-2919) for the mean thickness L and interaction force P of planar polyelectrolyte brushes in the so-called strong charging limit (SCL) and the strong screening limit (SSL) on the assumption that the distribution of monomers throughout the brushes is uniform. Any other interaction components (double-layer, structural or acid-base, hydrophobic, bridging, etc.) are neglected. The nonelectrostatic (excluded volume) interactions are also omitted. Both quenched and annealed polyelectrolyte types (with the constant and pH-dependent charge, respectively) of brushes are considered. The number of monomers per chain N, grafting density σ and the monomer size a* are proposed as brush parameters. The fraction of elementary charged monomers f is the next parameter which however may depend on the solution conditions for annealed brushes. The above parameters can be estimated by identifying them with the known molecular parameters and/or from the fixed charge density — a parameter obtainable from the soft particle electrophoretic analysis (Ohshima, H.: Electrophoretic mobility of soft particles, J. Colloid Interface Sci., 1994, 163, 474-483). Three sets of the brush parameters are used to model the effect of ionic strength and/on the interaction energy between Gram-negative bacteria in the SSL regime where the quenched and annealed polyelectrolyte brushes are expected to behave identically. Generally, a step-like interaction energy-vs-separation profile is obtained with a pseudosecondary minimum (no maximum), being in line with the conception of secondary minimum aggregation and adhesion of bacteria. An opposite influence of increasing/ and ionic strentgh on the pseudosecondary minimum depth (decrease and increase, respectively) is found which is expected but not predictable by the DLVO-based or steric interaction models. Dramatic changes in the position and depth of that minimum also indicate a necessity of proper evaluation of the brush parameters but, at the same time, reveal a possibility of accounting the wide variability in the bacterial cell wall structures (also inferred from the soft-particle electrophoretic analysis).