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![The differencial capacity curves of double layer interface Hg/1 mol dm -3 NaClO 4 (•) and Hg/1 mol dm -3 NaClO 4 in the presence of 3×10 -3 mol dm -3 TU (◊) [33], MTU (♦), ATU (Δ) [35] and DMTU (▲) [34]](publication/225249602/figure/fig1/AS:11431281117789752@1675549616134/The-differencial-capacity-curves-of-double-layer-interface-Hg-1-mol-dm-3-NaClO-4-and.png)
The differencial capacity curves of double layer interface Hg/1 mol dm -3 NaClO 4 (•) and Hg/1 mol dm -3 NaClO 4 in the presence of 3×10 -3 mol dm -3 TU (◊) [33], MTU (♦), ATU (Δ) [35] and DMTU (▲) [34]
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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 electrod...
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... were carried out at frequencies of 200 Hz, 400 Hz, 600 Hz, 800 Hz 1200 Hz and amplitude 5 mV. In all of the systems studied the frequency dispersion was observed and therefore the differential capacity values obtained were extrapolated to zero frequency from linear dependence C d =f( ω), where (w) is angular frequency, w = 2pf [rad s -1 ]. Fig. 1 presents the differential capacity curves of the double layer on the interface Hg/1 mol dm -3 NaClO 4 and in the presence of 3×10 -3 mol dm -3 TU, MTU, DMTU or ...
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Citations
... [8,9] The susceptibility of ClO 4 À ions to the destruction of the water structure and the fact that they only slightly adsorb on the electrode surface is an added value and very relevant to the phenomena occurring at the electrode/solution interface. The previous studies have shown a significant effect of changes in water activity [10] and the presence of organic substances on the mechanism and kinetics of electroreduction of Bi(III) ions, [11][12][13][14][15][16] which has advanced the interpretation of the mechanism of the "cap-pair" effect. [15] The aim of the present study was to investigate the electroreduction process of In(III) ions and in the presence of acetazolamide as a function of changes in water activity. ...
... Active complexes also participate in the passage of subsequent electrons .It should be noted, however, that the composition of the active complexes changes after the transition of successive electrons, as suggested by Markus' theory. [11] This was the mechanism indicated by earlier studies. [13] Above 4 mol · dm À 3 chlorates(VII) concentration, however, the relationship ln kf = f(E) becomes linear, confirming the already noted regularity, according to which the process mechanism changes with changing water activity. ...
The influence of acetazolamide (ACT) on the kinetics and the mechanism of electroreduction of In(III) ions as a function of changes of the water activity was investigated using electrochemical methods (DC, SWV, CV and EIS, CV). The multi‐step mechanism of the electroreduction process should take into account the dehydration step of indium ions and the presence of In‐ACT (,,cap‐pair” effect) active complexes, mediating electron transfer, located in the adsorption layer. Differences in the electrode mechanism in the presence of ACT were observed for higher chlorates(VII) concentrations (above 4 mol ⋅ dm⁻³ chlorates(VII)) reflected by a lack of step wise nature of the electrode process. The highest catalytic activity was observed in 4 mol ⋅ dm⁻³ chlorates(VII).
... It is also important to note the different character of the dependence = ( ) (Figure 7) above ACT concentration of 1 × 10 −4 mol·dm −3 , which may suggest changes in the electrode mechanism [24]. A similar effect was observed for In(III) in the presence of higher concentrations of thiourea and its selected derivatives [25] and for Bi(III) in the presence of amino acids [26] or for Zn(II) in the presence anionic surfactant sodium 1-decanesulfonate [27]. ...
... The acceleration effect of the In(III) ions electroreduction by acetazolamide (as theoretically inferred) is due to the lowering of the activation barrier. It is caused by a more efficient interpenetration of the orbital of In-acetazolamide complexes compared to the A similar effect was observed for In(III) in the presence of higher concentrations of thiourea and its selected derivatives [25] and for Bi(III) in the presence of amino acids [26] or for Zn(II) in the presence anionic surfactant sodium 1-decanesulfonate [27]. ...
The results of kinetic measurements revealed an accelerating effect of acetazolamide (ACT) on the multistep In(III) ions electroreduction in chlorates(VII) on a novel, cyclically renewable liquid silver amalgam film electrode (R–AgLAFE). The kinetic and thermodynamic parameters were determined by applying the DC polarography, square-wave (SWV) and cyclic voltammetry (CV), as well as electrochemical impedance spectroscopy (EIS). It was shown that ACT catalyzed the electrode reaction (“cap-pair” effect) by adsorbing on the surface of the R–AgLAFE electrode. The catalytic activity of ACT was explained as related to its ability to form active In(III)- acetazolamide complexes on the electrode surface, facilitating the electron transfer process. The active complexes constitute a substrate in the electroreduction process and their different structures and properties are responsible for differences in the catalytic activity. The determined values of the activation energy ΔH≠ point to the catalytic activity of ACT in the In(III) ions electroreduction process in chlorates(VII). Analysis of the standard entropy values ΔS0 confirm changes in the dynamics of the electrode process.
... Supporting electrolytes can be acidic, neutral, or are many a times subsidized with organic substances which can act as catalysts or inhibitors of the electrode processes. The "cap-pair" rule [3] determines the conditions that indicate the catalytic activity of a substance [4][5][6][7][8][9][10] developed and used for electrode processes. It has been well known that a major role in accelerating the process is played by the ability of the organic substance to form complexes with the depolarizer and to locate the depolarizer reduction potential in the area of labile adsorption equilibrium of the organic substance. ...
The cyclically refreshable liquid silver amalgam film silver based electrode (R-AgLAFE) to study of electrode processes under the “cap-pair” conditions was used. The catalytic effect of cysteine on the Bi(III) ions electroreduction processes has been demonstrated. The magnitude of the catalytic effect is related to the formation of the Bi(III) – Hg(SR)2 active complexes mediating electron transfer equilibrium
... The catalytic effect of metal cation reduction according to the "cap-pair" mechanism includes both chemical reactions and heterogeneous charge transfer processes of active complexes on the electrode surface. The surface formation of active complexes within the electrode double layer with the studied metal cations is a plausible mechanism for zinc(II) [2,3], cadmium [4], indium(III) [5] and bismuth(III) ion reduction [6,7], while the complexation of europium(III) ions is assumed to proceed in the bulk of the solution as well [8]. ...
The catalytic influence of methionine (Mt) on the electroreduction of Bi(III) ions on the novel, cyclically renewable liquid silver amalgam film electrode (R–AgLAFE) in a non-complexing electrolyte solution was examined. The presence of methionine leads to a multistep reaction mechanism, where the transfer of the first electron is the rate limiting step, which is the subject of catalytic augmentation. The catalytic activity of methionine is a consequence of its ability to remove water molecules from the bismuth ion coordination sphere, as well as to form active complexes on the electrode surface, facilitating the electron transfer process.
... The mechanism for the catalytic effect of metal cations electroreduction under "cap-pair" conditions, includes both chemical reactions and heterogeneous processes of charge transfer between the electro-active particle of the complex and the depolarised working electrode. The formation of electroactive complexes with depolarisers is possible both in the adsorption layer for zinc(II) ions [18][19][20], cadmium [21] indu(III) [22,23] and bismuth(III) [24][25][26][27][28][29], and outside the layer for europium(III) ions [30]. The goal of this current paper was to collect and summarise studies on the kinetics and mechanism of action for selected organic substances on the electroreduction of Bi(III) ions in chlorate(VII) solutions in terms of expanding the interpretation of the "cap-pair" effect mechanism. ...
The paper discusses the electroreduction of Bi(III) ions in the aspect of expanding the ”cap – pair” effect. The ”cap – pair” rule is associated with the acceleration of the electrode’s processes by organic substances. The interpretation of the ”cap – pair” effect mechanism was expanded to include the effect of supporting electrolyte concentration on the acceleration process and the type of electrochemical active as well as used protonated organic substances. It has also been shown that the phenomena occurring at the electrode/solution interface can influence a change in the dynamics of the electrode’s process according to the ”cap – pair” rule.
... To understand these fluxes from the anthroposphere to the hydrosphere, lithosphere and biosphere, the relevant chemical properties of this poorly-studied element have to be adequately elucidated. For instance, the large hydrolysis processes of indium (e.g. an increase by 0.1 units in the pH of a solution in equilibrium with precipitated In(OH) 3 decreases the free concentration by a factor of 2) are key to explain the transfer from some natural waters to the sediments (Nosal-Wiercinska, 2010;White et al., 2017). Moreover, hydrolysis also hinders the accurate study of its speciation with most conventional techniques and, so, there are many unresolved aspects of the behaviour of indium in a number of systems (Chung and Lee, 2012;Tuck, 1983). ...
... This is the first application of AGNES to a trivalent ion. pH 3 is chosen here to avoid any complication from hydrolysis (Nosal-Wiercinska, 2010;White et al., 2017), for which conflicting formation constants have been reported (Alekseev et al., 2013;Tuck, 1983). This pH is relevant for acid mine drainages where high In concentrations have been reported (Nosal-Wiercinska, 2010;White et al., 2017). ...
... pH 3 is chosen here to avoid any complication from hydrolysis (Nosal-Wiercinska, 2010;White et al., 2017), for which conflicting formation constants have been reported (Alekseev et al., 2013;Tuck, 1983). This pH is relevant for acid mine drainages where high In concentrations have been reported (Nosal-Wiercinska, 2010;White et al., 2017). Speciation capability will be assessed with a ligand (NTA, nitrilotriacetic acid) forming a relatively inert complex and another one (oxalate) forming a labile one. ...
Indium is increasingly used in electronic devices, from which it can be mobilized towards environmental compartments. Speciation of In in waters is important for its direct ecotoxicological effects, as well as for the fate of this element in the environment (e.g. fluxes from or towards sediments). Free indium concentrations in the environment can be extremely low due to hydrolysis, especially important in trivalent cations, to precipitation and to complexation with different ligands. In this work, the free indium concentration (which is a toxicologically and geochemically relevant fraction) in aqueous solutions at pH3 has been measured with an adapted version of the electroanalytical technique AGNES (Absence of Gradients and Nernstian Equilibrium Stripping). Speciation measurements in mixtures of indium with the ligands NTA (nitrilotriacetic acid) and oxalate indicate that the values of their stability constants in the NIST46.6 database are less adequate than those published in some more recent literature. The extraordinary lability and mobility of In-oxalate complexes allow the measuring of free indium concentrations below nmol/L in just 25s of deposition time.
... [10] The study of adsorption of organic substances at electrodes attracts wide interest as it relates to understanding the electrical double layer structure, [11,12] the kinetics of electron transfer [13,14] and the mechanism of electrode processes. [15][16][17][18][19][20][21] The thermodynamic analysis of surface concentrations is still the most frequently used route to gain an insight into the mode of organic compounds adsorption. [22] This entails the description of experimental data by means of an adsorption isotherm, and the construction of an adsorption model based on the derived adsorption parameters. ...
The electrosorption behaviour of non-ionic surfactant: N-decanoyl-N-methylglucamine on mercury electrode in 1 mol dm−3 NaClO4 solution was determined. The values of the relative surface excess were determined on the basis of double layer differential capacity. A set of parameters of maximal adsorption and the constants of Frumkin, modified Flory-Huggins and virial adsorption isotherms were obtained. It was stated that the adsorption of this surfactant is determined by the adsorption energy, however here is no simple relation between a surface excess and the values of repulsive interactions parameter A. Adsorption properties of three surfactants: cationic, anionic and non-ionic were compared.
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... The adsorption process of various substances (simple ions, organic compounds, natural and synthetic polymers) on the solid surface is very important due to both theoretical and practical aspects (Nosal-Wiercińska, 2010a, 2010b, 2012Nosal-Wiercińska and Dalmata, 2010). Adsorbed polymers exhibit stabilization-flocculation properties, and hence they are widely used in many industries including chemical, pharmaceutical, automotive technologies, food processing and electrical engineering (Ross, 1995;Shahidi et al., 1999;Kadajji and Betageri, 2011;Jin et al., 2003;Moody, 1992;Duro et al., 1999;Farrokhpay, 2009). ...
Adsorbed polymers show stabilization- flocculation properties of colloidal suspension and they are widely used in technological applications (chemical and pharmaceutical industries, food processing, drinking water purification and wastewater treatment). Thus, the influence of polyacrylic acid (PAA) addition on the stability of synthesized alumina suspension as a function of solution pH was studied. The changes of the examined systems stability in time were monitored using the turbidimetry method. It was shown that the alumina suspension without the polymer is the most stable at pH 3 (electrostatic stabilization), whereas at the pH values 6 and 9 the systems are unstable (coagulation). The addition of PAA with the lowest molecular weight (i.e. 2 000) at pH 3 causes large deterioration of the system stability (destabilization by charge neutralization), whereas at the pH values 6 and 9 significant improvement of analogous system stability is observed (electrosteric stabilization). PAAs with higher molecular weights (100 000 and 240 000) cause stabilization of the alumina suspension in the whole range of studied pH. At pH 3 it is rather steric stabilization. On the other hand, at the pH values 6 and 9 the steric mechanism of stabilization is combined with the electric one, leading to electrosteric interactions.
The nanostructured cyclically refreshable liquid amalgam film silver-based electrode (R-AgLAFE) was applied to study of the Bi(III) electrode process in the presence of 2-thiocytosine and selected ionic surfactants. The application of voltammetrictechniques (SWV, CV, DC), as well as electrochemical impedance spectroscopy (EIS) allowed the determination of the kinetic which in turn, defined the 2-thiocytosine catalytic effect and also their correlation in the presence of surfactants. The presence of mixed 2-thiocytosine-CTAB and 2-thiocytosine-SDS adsorption layers affects the mechanism and kinetics of Bi(III) ions electro-reduction process in chlorate(VII). CTAB and SDS change the dynamics of the catalytic impact of 2-thiocytosine on Bi(III) ions electro reduction. In both cases, the Bi–(RS–Hg) complex plays a key role, as it is the 2-thiocytosine that dominates in the establishment of the adsorption equilibria of the studied mixed adsorption layers.
The paper discusses the electroreduction of Bi(III) ions in the aspect of expanding the “ cap-pair ” effect.
The “ cap-pair ” rule is associated with the acceleration of the electrode’s processes by organic substances. The interpretation of the “ cap-pair ” effect mechanism was expanded to include the effect of supporting electrolyte concentration on the acceleration process and the type of electrochemical active as well as used protonated organic substances. It has also been shown that the phenomena occurring at the electrode/solution interface can influence a change in the dynamics of the electrode’s process according to the “ cap-pair ” rule.
