Agnieszka Nosal-Wiercińska

Adsorption of cystine at mercury/ aqueous solution of chlorate (VII) interface in solutions of different water activity

Abstract

Comparison of stability properties of poly(acrylic acid) adsorbed on the surface of silica, alumina and mixed silica-alumina nanoparticles — application of turbidimetry method

The influence of anionic poly(acrylic acid) — PAA addition on the stability of synthesized silica, alumina and mixed silica-alumina suspensions as a function of solution pH was studied. The turbidimetry method was used to monitor the changes of the examined systems stability over time. The calculated stability coefficients enabled estimation of polymer adsorption influence on stability of metal oxide suspension. It was shown that the alumina suspension without the polymer is the most unstable at the pH values 6 and 9, whereas the silica polymer was most unstable at pH 3. PAA with higher molecular weight (240 000) is a relatively effective stabilizer of all investigated adsorbents (except silica at pH 3). These properties of poly(acrylic acid) are highly desirable in many branches of industry (e.g. production of cosmetics, pharmaceuticals, paints) where polymers are widely used as effective stabilizers of colloidal suspensions.

The Influence of Protonation on the Electroreduction of Bi (III) Ions in Chlorates (VII) Solutions of Different Water Activity

We examined the electroreduction of Bi (III) ions in chlorate (VII) solutions under varied protonation conditions of the depolariser using voltammetric and impedance methods. The results of the kinetic parameter correlation lead to the statement that the changes in the amount of chloric (VII) acid against the amount of its sodium salt in the supporting electrolytes of the low water activity have a significant influence on the rate of Bi (III) ion electroreduction. The increase of the concentration of chloric acid sodium salt, as well as the chloric (VII) acid alone within the particular concentration of the supporting electrolyte, inhibits the process of Bi (III) ion electroreduction. It should be associated with the reorganisation of the structure of the double layer connected with the slow dehydration inhibited by ClO 4− ions. The standard rate constants ks values with the increase of the chlorate (VII) concentrations for all the solutions examined of chlorates (VII) confirms the catalytic influence of the decrease of water activity on the process of Bi (III) ion electroreduction. The multistage process is confirmed by the non-rectilinear 1nkf = f(E) dependences.

β–Cyclodextrins incorporated multi-walled carbon nanotubes modified electrode for the voltammetric determination of the pesticide dichlorophen

In this work, a glassy carbon electrode modified with β-cyclodextrins and multi-walled carbon nanotubes (β-CDs/MWCNTs/GCE) was constructed and applied for the square-wave adsorptive stripping voltammetric (SWAdSV) determination of the pesticide dichlorophen (Dcp). For the first time, this compound was electrochemically investigated. The voltammetric measurements were conducted in phosphate buffer (PBS) at pH 6.5 as a supporting electrolyte, and SWAdSV technique parameters were optimized. A linear calibration curve in the wide concentration range from 5.0 × 10-8molL-1 to 2.9 × 10-6molL-1 was obtained. Excellent analytical performance in terms of limit of detection (LOD) of 1.4 × 10-8molL-1 was achieved. The utility of the proposed method was verified by the quantitative analysis of Dcp in Pilica River water samples with satisfactory results. The characterization of modified electrodes was conducted by means of atomic force microscopy (AFM), electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV). Moreover, in this work, the dissociation constants (pKa) of Dcp using potentiometric pH titration were estimated. The stoichiometry of the Dcp-β-CDs inclusion complex formed in solution was determined by proton nuclear magnetic resonance (1H NMR) spectroscopy, and a binding constant (β2) was estimated from NMR titration studies.

Catalytic activity of thiourea and its selected derivatives on electroreduction of In(III) in chlorates(VII)

It was found that thiourea, N-methylthiourea, N,N′-dimethylthiourea and N-allylthiourea accelerate the electroreduction process of In(III) ions in chlorates(VII). These substances are adsorbed on mercury from chlorates(VII). The relative surface excesses of thiourea and its derivatives increase with the increase of their concentrations and electrode charge. After adding thiourea, N-methylthiourea, N,N′-dimethylthiourea and N-allylthiourea to the solution an acceleration of the electroreduction process of In(III) ions occurs. This process depends on two factors: the adsorption of an accelerating substance on mercury and on the formation of complexes between a depolarizer and an accelerating substance on the electrode surface. The equilibrium of this complexing reaction determines the magnitude of the catalytic effect.

Studies of the Effect of Thiourea on the Electroreduction of In(III) Ions in Perchloric Acid

The influence of thiourea on the electroreduction of In(III) ions on mercury electrode in perchloric acid solution was examined. It was observed, that thiourea can catalyze the electroreduction of In(III) ions. The presence of thiourea leads to multistage reaction where transfer of the first electron is principally catalyzed. Catalytic activity of thiourea is connected with its ability to remove molecules of coordinated water as well as with forming of active complexes of indium ions on the surface of electrode, facilitating transfer of electrons.

Electrochemical study of the fungicide acibenzolar-s-methyl and its voltammetric determination in environmental samples

The electrochemical behavior of new generation fungicide acibenzolar-s-methyl (S-methyl 1,2,3-benzothiadiazole-7-carbothioate, ASM) on the hanging mercury drop electrode (HMDE) was investigated using square wave adsorptive stripping voltammetry. This method of determination is based on the irreversible reduction of ASM at the HMDE. The well-defined ASM peak was observed at −0.4 V (vs. Ag/AgCl) in BR buffer at pH 2.2. The reduction peak current was proportional to concentration of ASM from 1.0 × 10−8 to 6.0 × 10−8 mol L−1 with detection and quantification limit 3.0 × 10−9 and 1.0 × 10−8 mol L−1, respectively. The applicability of the developed method for analysis of spiked samples of tap water, river water, and soil is illustrated. The effect of adsorption on the mercury electrode was studied in detail using the AC impedance method. Possible interferences with other common pesticides and heavy metal ions were examined. Clarification of the electrode mechanism was made using cyclic voltammetry (CV) technique.

Application of the catalytic properties of methionine to the determination of Bi(III) as well in the presence of Cu(II) ions at low levels by square wave voltammetry

ABSTRACT A simple and fast method for the determination of Bi(III) in the presence Cu(II) in non-complexing solution was proposed. The catalytic activity of L-methionine on Bi(III) ions electroreduction as well as lack of this amino acid influence on Cu(II) ions electroreduction process were utilised. The calibration graph of Bi(III) in 4 mol dm−3 chlorate (VII) in the presence of 5 × 10−2 mol dm−3 methionine is linear in the range of concentrations of Bi(III) from 3 × 10−7 to 1 × 10−4 mol dm−3. The detection and quantification limits were found to be 1.53 × 10−7 and 5.12 × 10−7 mol dm−3, respectively. Precision and recovery of the method were investigated by determination of Bi(III).

Adsorption and Stability Properties of Aqueous Suspension of Chromium (III) Oxide in the Presence of Synthetic and Natural Polymers: Possibilities of Solid Removal

The effects of type and content of polymer functional groups on the adsorption mechanism on the chromium (III) oxide surface were studied. Both synthetic [poly(acrylic acid) (PAA), anionic polyacrylamide (PAM), poly(aspartic acid) (ASP), block co-polymer of ASP with poly(ethylene glycol) (ASP-b-PEG)] and natural [bovine serum albumin, ovalbumin, human serum albumin, bacterial polysaccharide (exopolysaccharide EPS)] polymers were applied. For this purpose, adsorption, surface charge, zeta potential and stability measurements were carried out. The largest adsorption was found for the ASP-b-PEG (synthetic polymer) and EPS (natural polymer). The most effective destabilizers for Cr2O3 removal from the aqueous suspension were PAA 240,000 and ASP 6800.

Influence of temperature on the reduction kinetics of Bi(III) ion in the presence of cystine in chlorate (VII) solutions of decreased water activity

AbstractThe results of the kinetic measurements of Bi(III) electroreduction on a mercury electrode in 1–8 mol dm−3 chlorate (VII) solutions and in the presence of cystine demonstrate a dependence of the process on the temperature. The applied electrochemical techniques (DC polarography, cyclic and SWV voltammetry) allowed for the determination of the kinetic and thermodynamic parameters and their correlation with water activity. The catalytic activity of cystine was confirmed by the decrease in overall enthalpies of activation. The changes in the values of ΔH≠ and ΔS0 for Bi(III) electroreduction in the presence of cystine with the increase of chlorate (VII) concentration showed that the mechanism is different in solutions with low water activity as compared to those with high water activity. Probably it is connected with a different structure of the activated complexes (Bi-Hg(SR)2), mediating electron transfer.