Mikolaj Donten

Electrodeposition and properties of NiW, FeW and FeNiW amorphous alloys. A comparative study

Thin, micrometre-thick layers of a new amorphous alloy, FeNiW, have been obtained by electrodeposition. The iron mole fraction, [Fe]/([Fe]+[Ni]), can be changed from 0 to 1, however, the best properties under constant current deposition are obtained for the mole fraction near 0.5. The key, needed properties of the FeW and NiW alloys were transferred to the FeNiW alloy, while the unwanted properties of the two-component alloys were eliminated. The new alloy is hard (1040 HV, for equal percentage of Fe and Ni), smooth, of nice appearance, and of good adherence to both steel and copper. Pulse electroplating further improves the smoothness and uniformity of the electrodeposited layers and allows one to obtain higher tungsten content of up to 35 at.%. X-ray diffractometry, EDX, and chronopotentiometry were used to characterise the new material. The influence of pH and the ratio of concentrations of Fe and Ni in the plating solution was examined.

Selective Knockout of Gold Active Sites

It has long been known that defects on a gold surface play an important role in electrocatalysis, but the precise mechanism has always been unclear. This work indicates that the defect sites provide partially filled d-orbitals that stabilize freeradical intermediates. Strong evidence for this hypothesis is that the sites can be selectively knocked out by treatment with OH• radicals generated by Fentons reagent. The knockout effect is demonstrated using oxygen reduction, hydrogen reduction, and the redox electrochemistry of hydroquinone.

Electron transfer – ion insertion electrochemistry at an immobilised droplet: probing the three-phase electrode-reaction zone with a Pt disk microelectrode

A four-electrode setup was used to study the following system: a nitrobenzene (NB) drop containing no added supporting electrolyte and either ferrocene or decamethylferrocene was placed on a glassy carbon disk and surrounded by an aqueous solution of supporting electrolyte. The glassy carbon electrode was polarised appropriately to generate either the ferrocenium or the decamethylferrocenium cations. A very thin conical-body Pt microdisk electrode was placed inside the NB drop to detect the product cations. The relation between the time of appearance of the reduction current at the microelectrode and the distance from the three-phase junction indicates that the electrode reaction starts at this junction where both the electron transfer and the ion transfer can take place.

Formation of Nanofibers in Thin Layers of Amorphous W Alloys with Ni, Co, and Fe Obtained by Electrodeposition

Scanning tunneling microscopy (STM) experiments supported by scanning electron microscopy (SEM) pictures and X-ray diffractometry indicate that all electrodeposited amorphous alloys of tungsten with the iron-group metals are in fact of nanofibrous structure. It has been shown that the nanofibers grow perpendicularly to the copper support and, as the thickness of the alloy microlayer grows, group into well-packed bundles. The thickness of the fibers, for 79:21 Ni-W and 75:25 Co-W determined from the STM images, equals 50 A. This number correlates well with the average grain size (40-55 A) calculated, using the Scherrer formula, from the peak broadening seen at the X-ray spectrograms.

Gold Electrocrystallization on Carbon and Highly Oriented Pyrolytic Graphite from Concentrated Solutions of LiCl

The early stages of the electrolytic deposition of gold on carbon electrodes from concentrated LiCl electrolytes have been investigated by voltammetry, chronoamperometry, and microscopy. The analysis of current-time transients according to existing theories indicates that this process occurs by multiple three-dimensional nucleation, followed by diffusion-controlled growth of nuclei. Diffusion coefficients calculated on the basis of nucleation theory were found to be higher than those Irom rotating disk experiments (RDE), suggesting that gold species are adsorbed on the electrode surface. Gold nucleation from 6 M LiCl cannot be classified as either instantaneous or progressive nucleation. The kinetic parameters for nucleation, aN o (nucleation rate) and N o (number density of active sites on the substrate surface), were estimated by using a general Poisson nucleation law. Both quantities were found to vary with potential and with concentration of gold. The potential dependence of the nucleation rate, aN o , was interpreted according to classical and atomistic theory. For low gold concentrations, where adsorption of AuCl or AuCl 3 might occur prior to nucleation, the number of atoms in the critical nucleus (N c ) was less than unity over the entire potential range analyzed. For high gold concentrations the number of atoms forming the critical nucleus depends on overpotential. In all solutions studied nucleation takes place on a limited number of active sites

Tannic acid modified silver nanoparticles show antiviral activity in herpes simplex virus type 2 infection.

The interaction between silver nanoparticles and herpesviruses is attracting great interest due to their antiviral activity and possibility to use as microbicides for oral and anogenital herpes. In this work, we demonstrate that tannic acid modified silver nanoparticles sized 13 nm, 33 nm and 46 nm are capable of reducing HSV-2 infectivity both in vitro and in vivo. The antiviral activity of tannic acid modified silver nanoparticles was size-related, required direct interaction and blocked virus attachment, penetration and further spread. All tested tannic acid modified silver nanoparticles reduced both infection and inflammatory reaction in the mouse model of HSV-2 infection when used at infection or for a post-infection treatment. Smaller-sized nanoparticles induced production of cytokines and chemokines important for anti-viral response. The corresponding control buffers with tannic acid showed inferior antiviral effects in vitro and were ineffective in blocking in vivo infection. Our results show that tannic acid modified silver nanoparticles are good candidates for microbicides used in treatment of herpesvirus infections.

Progress in Targeting Tumor Cells by Using Drug-Magnetic Nanoparticles Conjugate

To limit cytotoxicity of anticancer drugs against healthy cells, an appropriate carrier should be synthesized to deliver the drug to the tumor tissue only. A good solution is to anchor a magnetic nanoparticle to the molecule of the drug and to use a properly directed external magnetic field. The synthesis of the conjugate of doxorubicin with magnetic nanoparticles (iron oxide) modified by us resulted in a substantial depression of the aggregation process of the nanoparticles and therefore allowed the correct examination of cytotoxicity of the modified drug. It has been shown, by performing the electrochemical microbalance measurements, that the use of magnetic field guaranteed the efficient delivery of the drug to the desired place. The change in the synthesis procedure led to an increase in the number of DOX molecules attached to one magnetic nanoparticle. The release of the drug took place at pH 5.8 (and below it), which pH characterizes the cancer cells. It has also been found that while the iron oxide magnetic nanoparticles were not cytotoxic toward human urinary bladder carcinoma cells UM-UC-3, the tumor cell sensitivity of the DOX-Np complex was slightly higher in comparison to the identical concentration of doxorubicin alone.

The interface between metallic substrates and layers of electrodeposited Co–W amorphous alloys

Abstract The process of formation of deposits of Co–W amorphous alloys on copper and mild steel substrates has been studied. For the alloy layers plated on copper, the content of Co and W in the amorphous coverage has been examined and found to be a function of the distance from the substrate surface. The examination was based on the quantitative EDS and WDS analysis of the cross-sections of the alloy layers. It has been found that an intermediate inner layer is formed on the copper substrate, and the adhesion of the alloy to this substrate is very good. The adhesion of the alloy layers to steel was much weaker compared to copper. We relate this difference to the absence of the interface layer between the alloy and steel. The difference found for the two substrates correlates well with the differences in the crystal structures of the substrates and the deposited metals.

A novel type of electrochemical sensor based on ferromagnetic carbon-encapsulated iron nanoparticles for direct determination of hemoglobin in blood samples

An effective, fast, facile and direct electrochemical method of determination of hemoglobin (Hb) in blood sample without any sample preparation is described. The method is accomplished by using the ferromagnetic electrode modifier (carbon-encapsulated iron nanoparticles) and an external magnetic field. The successful voltammetric determination of hemoglobin is achieved in PBS buffer as well as in the whole blood sample. The obtained results show the excellent electroactivity of Hb. The measurements are of high sensitivity and good reproducibility. The detection limit is estimated to be 0.7 pM. The electrochemical determination data were compared with the gravimetric data obtained with a quartz crystal microbalance. The agreement between these results is very good. The changes of the electrode surface morphology before and after Hb detection are monitored by electron microscopy. The functionality of the electrochemical sensor is tested with human and rat blood samples. The concentration of hemoglobin in the blood samples determined by using voltammetric/gravimetric detection is in perfect agreement with the data obtained from typical clinical analysis.

Conditions of Strict Voltammetric Reversibility of the H+/H2 Couple at Platinum Electrodes

Cyclic voltammetric curves obtained at Pt electrodes for the hydrogen couple, H(+)/H(2), fit very well the Shuman theory, as corrected, for reversible electrode processes of other than 1:1 stoichiometry. Good agreement was obtained for acid concentrations in the millimolar range and for normal scan rates, which minimize the effect of the adsorption peaks. An error in Shumans equation for potential is corrected. Voltammograms obtained at Pt microelectrodes fit well the theoretical simulated data.