Jolanta Nieszporek

The Influence of Thiourea on the Two-Step Electroreduction of Zn(II) Ions

Summary. The two-step reduction of Zn(II) ions at a dropping mercury electrode in 1 M NaClO4/0.001 M HClO4 in the presence of thiourea was examined in wide potential and frequency ranges using the impedance method. The catalytic activity of thiourea concerns both electron transfer steps. It was found that the acceleration of the electroreduction process depends on the surface concentration of thiourea.Zusammenfassung. Die zweistufige Reduktion von Zn(II)-Ionen an einer Quecksilbertropfelektrode in 1 M NaClO4/0.001 M HClO4 in Gegenwart von Thioharnstoff wurde in einem breiten Potential- und Frequenzbereich mittels der Impedanzmethode untersucht. Die katalytische Aktivität von Thioharnstoff betrifft beide Elektronenübertragungsschritte. Es wurde beobachtet, daß die Beschleunigung der Elektroreduktion von der Oberflächenkonzentration des Thioharnstoffs abhängt.

Mixed adsorption layers of 0.1 M tert-butanol-tetramethylthiourea at the interface of Hg/aqueous perchlorate solutions.

The electrosorption behavior of tetramethylthiourea (TMTU) on a mercury electrode from 1.0, 0.5, and 0.1 M NaClO(4) solutions containing 0.1 M tert-butanol (TB) is described by means of adsorption isotherm constants. The adsorption parameters for the double layer were calculated from a double-layer differential capacity measurement extrapolated to zero frequency. The values of the relative surface excess increase along with the concentration of NaClO(4). It seems that the adsorption of TMTU is determined by an interaction between adsorbed molecules. The presence of TB in the adsorption layer distinctly influences the parameters of the inner layer.

Adsorption of tert-butanol at the electrode from concentrated NaClO4 solutions

The parameters of the double layer for tert-butanol adsorption determined in the supporting electrolytes: 2 mol dm−3, 3 mol dm−3 and 4 mol dm−3 NaClO4, show an increase of tert-butanol adsorption on the mercury electrode together with the increase of NaClO4 concentration. The adsorption of tert-butanol on the electrode takes place via the −CH3 group which is shown by the changes in the values of zero charge potentials, Ez. On the basis of the analysis of the changes of relative surface excess values, Γ′, and the parameters determining the maximum adsorption, the process of adsorption in the discussed systems can be recognized as a physical process. Besides, it can be said that a major drawback in the process of adsorption of the organic substance on the electrode is to remove water from the electrode surface.

The inhibition effect of water on the purification of natural gas with nanoporous graphene membranes

Molecular dynamics simulations are used to investigate the inhibiting effect of water on the natural gas separation with nanoporous graphene. The membrane separation process involves CH4 + N2 mixtures with and without the addition of water. The results show that water is able to form hydrogen bonds with nitrogen atoms located in a nanopore rim. This effect causes a decrease of separation selectivity as well as a reduction of gas permeation. In the extreme case, when the nanopore rim contains only nitrogen atoms, water agglomerates at the center of the nanopore and effectively closes down the permeation path. The conclusions are confirmed by the analysis of stability and kinetics of hydrogen bonds.

Multi-centred hydrogen bonds between water and perchlorate anion

ABSTRACT Results of classical molecular dynamics simulations are presented for the re-orientational dynamics of water hydrogen bonded to perchlorate anion. Different mechanisms of bond formation are presented. Due to its regular tetrahedron geometry the perchlorate anion can make classical as well as bifurcated and trifurcated hydrogen bonds. The angular variation of water in the first solvation shell of perchlorate suggests the transitional character of multi-centred hydrogen bonds. As a result water molecules can slide around the anion.