Search Results
Abstract
Thermal decomposition of various synthetic manganese oxides (MnO, Mn3O4, Mn2O3, MnOOH) and a natural manganese dioxide (MnO2) from Gabon was studied with the help of termogravimetry in inert, oxidizing and reducing atmospheres. The compounds were characterized by XRD and electrochemical activity was tested by cyclic voltammetry using a carbon paste electrode. The natural manganese dioxide showed the best oxidizing and reducing capacity, confirmed by the lower temperatures of the transitions, the extent of the reactions and electrochemical performance in cyclic voltammograms.
Abstract
Thermogravimetry (TG), cyclic voltammetry (CV) and other analytical techniques were used to study the reactions of mercury with Pt–30% Ir alloy. The results allowed to suggest that an electrodeposited mercury film interacts with the substrate and when subjected to heat or electrochemical removal at least four mass loss steps or five peaks appeared during the mercury desorption process. The first two steps were attributed to Hg(0) removal probably from the bulk and from the adsorbed monolayer which wets the electrode surface. These two processes are responsible for peaks D and F in the cyclic voltammograms. The last two peaks (G, H) in CV were ascribed to the intermetallic compound decomposition. In TG curves, the last two steps were attributed to the PtHg4 (third step), and PtHg2 decomposition followed by Hg removal from the subsurface. The PtHg2 was formed by an eutectoide reaction: PtHg→PtHg2+Hg(Pt–Ir). The Hg diffused to the subsurface was not detectable by cyclic voltammetry.
Abstract
Thermogravimetry, cyclic voltammetry and other analytical techniques were used to study the reactions of mercury with pure iridium. The results allowed to suggest when subjected to heat or anodic stripping voltammetry an electrodeposited mercury film reacts with Ir substrate and at least three mass loss steps and three peaks appear in the mercury desorption process. The first two were attributed to Hg(0)species removal like a mercury bulk and a mercury monolayer. The last can be ascribed to the mercury removal from a solid solution with iridium.
Abstract
Striking similarities and differences in the behaviour of two-dimensional (2D) self-assembled monolayers (SAMs) on gold and corresponding three-dimensional (3D) SAMs on gold of two alkanethiols of different chain lengths, hexadecanethiol (HDM) and octadecanethiol (ODM) were investigated as a function of temperature. Cyclic Voltammetry (CV) of the 2D SAMs and Differential Scanning Calorimetry (DSC) of the 3D SAMs were used to study previously unexplained behaviour. CV revealed two transition temperatures in both the HDM and ODM 2D systems. In the DSC studies, both a lower and higher temperature transition was observed in the 3D SAMs of HDM but only one temperature transition was observed in the 3D SAMs of ODM. It was deduced that the lower temperature transitions in the gold-alkanoate nanoparticles were related to interaction between the methyl group chain ends. The lower temperature transition was observed in the 3D system of HDM but not that of ODM because the curvature in the 3D system that is absent in the 2D system reduces the interaction between the alkyl chain ends due to a longer chain resulting in an increased distance between the end groups. It was concluded that the lower transition temperature was attributed to the disordering of the alkyl chains starting from the end closest to the terminal groups.
The Folin-Ciocalteu (FC) test and cyclic voltammetry (CV) at a glassy carbon electrode were used to quantify phenolic antioxidants in a set of 17 Croatian wines and express them in gallic acid (GAE) and catechin equivalents (CE). The total phenolic index (TPI) values for red wines expressed in GAE ranged from 18.851 to 26.905 mM, while TPI for white wines ranged from 1.722 to 2.869 mM. The levels of phenolics derived from CV measurements were markedly lower than those of TPI, since these values include only those phenolic compounds that get oxidised up to 500 mV and contain ortho -diphenol and triphenol groups.The free radical scavenging ability of the same set of wines was evaluated according to the Brand-Williams assay and expressed in equivalents of catechin, gallic acid, vitamin C and Trolox. Ivan Dolac barrique 2002 exhibited the highest antioxidant activity. The DPPH radical scavenging ability of the wines was also evaluated and correlated to the TPI values. Better correlation was observed between the TPI and the antioxidant activity for red wines (r 2 =0.826) as opposed to white wines (r 2 =0.686). The highest correlation (r 2 =0.970) was found between the TPI and the antioxidant activity measured when the whole set of samples was considered.
Abstract
Electronic interaction between two iron atoms was studied in the ferrocene-arene binuclear complexes ([Fc(CH2)nPhFeCp]+PF6 -) by using 57Fe Mössbauer spectroscopy and cyclic voltammetry(CV). By comparing the CV data between Fc(CH2)nPh and its arene complexes it was revealed that the considerable electronic interaction between two iron atoms exists in the n = 0 complex and a slight interaction in the n = 1 complex, while no significant interaction exists in n = 2, 3, 4, and 6 complexes. These results were discussed by using MO calculations.
Abstract
The heavy use of99mTc in nuclear medicine and the recent development of188Re radiopharmaceuticals have encouraged the comparative study of Tc and Re coordination compounds. In this work, the electrochemistry of [MVO2 (amine)2]+ (M=Tc, Re; amine = ethylenediamine, 1,3-diaminopropane, diethylenetriamine, triethylenetetramine) complexes is studied by cyclic voltammetry and the results are compared. The voltammograms of these compounds, obtained at different pH values, show that [ReO2(amine)2]+ cations are thermodynamically stable even when protonated. On the other hand, analogous Tc compounds are not so stable and easily decompose if existing as [TcO(OH) (amine)2]2+.
Abstract
The electrochemical behaviour of uranium has been studied in basic, NaCl-saturated NaAlCl4 melts at 175°C. Solutions of UO3 exhibit two oxidation/reduction waves (cyclic voltammetry). The first wave corresponds to the U(VI)/U(IV) redox couple and is irreversible (slow electron transfer). The second wave corresponds to the deposition and stripping of an insoluble U(III) compound (U(IV)/U(III)). Solutions of UO2 or UCl4 and U(IV) solutions prepared by exhaustive electrolysis of UO3 behave identically. The cyclic voltammograms of U(IV) solutions are the same as those of UO3, but they show additional anodic peaks. Analysis of the peak currents (cyclic voltammetry), the limiting currents (pulse polarography) and the non-linear log i-t curves (anodic controlled potential coulometry) leads to the conclusion that uranium (IV) in the basic chloroaluminate melt exists as two different species in slow equilibrium with one another, of which only one species can be oxidized to U(VI). E.m.f. measurements of U(VI)-U(IV) mixtures indicate that the electron transfer process involves the formation of an intermediate U(V) species in a disproportionation equilibrium.
Abstract
In the first part, LiCl-KCl-UCl3 and LiCl-KCl-UCl3-UCl4 molten salts were prepared, which were studied employing cyclic voltammetry and chronopotentiometry techniques, respectively. It was determined that the reduction of U(IV) to uranium metal takes two steps. Firstly, U(IV) is reduced to U(III). Then, the reduction of U(III) to uranium metal occurs in a step with a global exchange of three electrons. Cyclic voltammetry studies indicated that at low sweep rates, the reduction of U(III) to uranium is reversible. However, a mixed control of both diffusion and electrontransfer is observed as the sweep rate increases. The diffusion coefficient of U(III) and the formal potential of U(III)/U versus Ag/AgCl reference electrode in these two salt systems were calculated respectively. In second part, based on the data of the electrode processes of uranium ions, electrodeposition of uranium metal was carried out. Uranium deposits were prepared adopting a 304 stainless steel electrode in the molten LiCl-KCl-UCl3 and LiCl-KCl-UCl3-UCl4, respectively by employing suitable electrolytic techniques. The morphology of the deposits and the cross-section of the cathode were investigated by SEM. It was determined that at the beginning of the deposition process, uranium product alloys with stainless steel and forms a thin layer, and then uranium begins to grow adhering to the layer.
