Zbigniew Stojek

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.

A comparative study of Prussian-Blue-modified graphite paste electrodes and solid graphite electrodes with mechanically immobilized Prussian Blue

Abstract The cyclic voltammetry of Prussian Blue was studied using two different types of electrodes. In one case microcrystalline particles of Prussian Blue were mechanically immobilized on the surface of a paraffin-impregnated solid graphite electrode, whereas in the other the Prussian Blue was added to a paste of graphite and silicone oil. The overall behaviour of Prussian Blue in both electrodes is very similar to the well-known behaviour for electrodes with an electrochemically synthesized Prussian Blue film. Differences were observed for the modified paste electrode, particularly in acid-containing solutions. Prussian Blue exhibits pronounced ion-exchange properties in acid solutions. New voltammetric peaks are observed which are clearly related to an exchange of protons between Prussian Blue and the solution. In mixed solutions containing potassium ions and protons competition between these cations is visible. Scanning electron microscopy in conjunction with energy dispersive X-ray analysis supports a reaction scheme which includes both cations. This study provides evidence for the ability of protons to undergo a chemically reversible intercalation in the Prussian Blue lattice. An additional aim of this study was to assess the reliability of experiments using graphite paste electrodes with an organic binder. The results show that the binder affects the electrochemistry of Prussian Blue, but the similarities between “pure” Prussian Blue and that in the paste electrode are clearly dominant.

Voltammetry in solutions of low ionic strength. Electrochemical and analytical aspects

Recent progress in microelectrode voltammetry in solutions without or with low concentrations of supporting electrolyte is reviewed. The following points are addressed: mathematical treatment of transport, experimental setup, steady state and non steady state transport, migration coupled with homogeneous equilibrium, voltammetry in undiluted redox liquids, studies on the mechanism of the electrode processes, transport of ions in solutions of polyelectrolytes and colloids, and analytical applications.

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.

Graphite multi-micro-disc based mercury film electrode. Comparison of experimental and theoretical anodic stripping results

Abstract an ensemble of properly distanced micro mercury film electrodes (MMFE) was used in cyclic and anodic stripping voltammetry. the experimental results were compared with the anodic stripping theory, and the agreement was found to be satisfactory. The MMFE peaks (calculated per unit area) were higher, thinner and shifted towards more negative potentials compared with the large area mercury film electrode (LAMFE) peaks. The initial graphite electrode consisted of 65 independent micro-discs forming a circle, and was prepared from carbon fibres 4.66 μm in radius. The graphite multi-micro-disc electrode was quantitatively checked in a Fe(CN) 6 3− solution under both chronoamperometric and voltammetric conditions. The deposition and oxidation of mercury is discussed also.

Analytical application of submicroelectrodes in solutions containing little or no supporting electrolyte

Abstract Carbon submicroelectrodes of radius 4 μm were used in highly resistive water and chlorobenzene (BCl) solutions. Various uncharged and charged substrates (O 2 , Fe(CN) 3− 6 , phenol, anthracene and phenanthrene) were examined. In aqueous solutions the wave heights were practically independent of the concentration of the supporting electrolyte and linearly dependent on the substrate concentration. In BCl medium, a certain level of electrolyte was necessary to observe the waves. Determination of phenol in water without added electrolyte, phenol in BCl, and anthracene in phenanthrene in BCl solution containing 5 × 10 −2 mol dm −3 TBAP was found to be possible.

Silver based mercury film electrode: I. General characteristics and stability of the electrode

Summary The influence of the manner of preparation of a MFE with silver substrate and aging of these electrodes was investigated on voltammetric curves recorded for 10 different electrolyte solutions. A procedure for estimation of the moment of transformation of the fluid mercury into solid silver amalgam was proposed. It was established that after this transformation the residual currents rose and useful potential ranges diminished. The procedure of preparation of silver based mercury film electrode with prolonged “life-time” was worked out.

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.

Thermoresponsive poly(N-isopropylacrylamide) gel for immobilization of laccase on indium tin oxide electrodes.

We report on the properties of hydrogel matrix for the immobilization of laccase on conductive supports. The poly(N-isopropylacrylamide) gel is attached firmly to the indium-tin oxide (ITO) electrode, following its silanization with dimethylethoxyvinylsilane. The enzyme entrapped in the gel structure remained active longer than in the solution, and its redox and catalytic properties could be investigated by voltammetric methods. The reduction signals of the active sites, T1 and T2, of the Cerrena unicolor laccase were determined to be 0.79 and 0.38 V, respectively. The laccase catalytic activity toward oxygen in poly(N-isopropylacrylamide) was found to depend strongly on temperature. Reversible swelling/shrinking of the matrix was studied at 30 and 35 degrees C. Shrinking of the gel at higher temperature considerably decreased the efficiency of the catalytic reaction, however, interestingly, did not lead to irreversible changes in the enzyme structure. At temperatures below that corresponding to volume phase transition, the catalytic properties of the film were fully restored. High catalytic efficiency of the gel immobilized enzyme made it possible to employ the gel covered electrode for monitoring oxygen in solutions.

Nanogravimetric and voltammetric DNA-hybridization biosensors for studies of DNA damage by common toxicants and pollutants

Electrochemical and nanogravimetric DNA-hybridization biosensors have been developed for sensing single mismatches in the probe-target ssDNA sequences. The voltammetric transduction was achieved by coupling ferrocene moiety to streptavidin linked to biotinylated tDNA. The mass-related frequency transduction was implemented by immobilizing the sensory pDNA on a gold-coated quartz crystal piezoresonators oscillating in the 10MHz band. The high sensitivity of these sensors enabled us to study DNA damage caused by representative toxicants and environmental pollutants, including Cr(VI) species, common pesticides and herbicides. We have found that the sensor responds rapidly to any damage caused by Cr(VI) species, with more severe DNA damage observed for Cr(2)O(7)(2-) and for CrO(4)(2-) in the presence of H(2)O(2) as compared to CrO(4)(2-) alone. All herbicides and pesticides examined caused DNA damage or structural alterations leading to the double-helix unwinding. Among these compounds, paraoxon-ethyl and atrazine caused the fastest and most severe damage to DNA. The physico-chemical mechanism of damaging interactions between toxicants and DNA has been proposed. The methodology of testing voltammetric and nanogravimetric DNA-hybridization biosensors developed in this work can be employed as a simple protocol to obtain rapid comparative data concerning DNA damage caused by herbicide, pesticides and other toxic pollutants. The DNA-hybridization biosensor can, therefore, be utilized as a rapid screening device for classifying environmental pollutants and to evaluate DNA damage induced by these compounds.