Radioactive Tracer Study of the Displacement of Iodine Adatoms from Platinized Platinum Electrode by Carbon Monoxide

Radioactive tracer studies confirm the earlier electrochemical results that carbon monoxide can virtually completely displace iodine adatoms. For the first time, it is found that iodine adatoms are not displaced by carbon monoxide when iodide anions are adsorbed in the presence of an upd silver monolayer. The possible reasons for the effect observed are discussed.     

Effect of treatment in supercritical CO<Subscript>2</Subscript> on the composition and structure of tealeaf and cellulose

The influence of the pretreatment procedures with supercritical CO₂ (SC-CO₂) on the elemental composition of tealeaf is studied. Fourier-transform infrared absorption spectroscopy is used to examine the effect of SC-CO₂ on the structure of Chinese green tea and cellulose.     

The influence of optical activity on optimal conditions of focusing of one- and two-dimensional light beams of different profiles in a cubic photorefractive crystal

We compare regular features of propagation of one- and two-dimensional light beams in an optically active photorefractive crystal placed in an external electric field. We show that there exist ranges of the crystal thickness in which the optical activity can lead to an increase in the relative intensity of either beam. We have found that, taking into account the optical activity, an optimal orientation angle at which a maximal self-focusing of light beams is observed differs from commonly used values of 35.3° and 90° for the x and y polarized beams, respectively.     

Variations in the Charge and Open-Circuit Potential of a Platinum Electrode during Adsorption of Iodine and Iodide Ions

The adsorption of iodine and iodide anions on a Pt/Pt electrode (0.5 M H₂SO₄ as a supporting solution) is compared using potentiodynamic and galvanostatic charging curves, transients of the current and open-circuit potential (OCP), and analytical measurements. Variations in the charge and OCP during the adsorption obey relationships derived for strong adsorption of neutral species and ions on a hydrogen electrode with the formation of irreversibly adsorbed atoms. The main product of the I₂ and I^– chemisorption in acid solutions is adsorbed iodine atoms. However, adsorption of iodine occurs in noticeable amounts and above a monolayer in the form of species that undergo electrodesorption during a cathodic polarization to potentials of the beginning of hydrogen adsorption. In the presence of a monolayer of adsorbed iodine atoms, potential of the zero total charge of a Pt/Pt electrode is in the oxygen adsorption region.     

A study of local crankshaft-type mobility in vitreous polyvinyl chloride and polyacrylonitrile by the method of conformational probes

Secondary relaxation transitions and local conformational dynamics in polyacrylonitrile and polyvinyl chloride were studied by the method of conformational probes. Relaxation transitions at 210 and 260 K (polyvinyl chloride) and 165 K (polyacrylonitrile) were explained by freezing of “crankshaft-type” motions.     

Adsorption of Carbon Monoxide on Platinized Platinum Electrode with Preadsorbed Iodine and Iodide Anions

Adsorption of carbon monoxide in the presence of adlayers formed upon exposure of Pt/Pt to I^– anions and I₂ (0.5 M ₂SO₄ as the supporting electrolyte) is studied using the method of electrode washing. Transients of current and potentiodynamic curves show that the displacement of iodine adatoms from the Pt/Pt surface by CO is virtually complete when CO is adsorbed in the range of hydrogen adsorption potentials (E 0.35 V (RHE)) and incomplete at higher potentials. It is concluded that the bond formed by iodine adatoms with the surface strengthens with an increase in the potential. Possible reasons for the striking difference in the behavior of adatomic monolayers formed from KI and I₂ solutions is discussed. The surface charge of Pt/Pt is observed to drastically change as a result of the displacement of iodine adatoms by carbon monoxide.     

Electrocatalytic activity of platinum—polyaniline and palladium—polyaniline systems obtained by cycling the electrode potential

Steady-state current densities of electrooxidation of CH₃OH, HCOOH, and CO at the Pt-PAN-GC electrodes (where PAN and GC stand for polyaniline and glassy carbon, respectively) and those of electrooxidation of HCOOH at the Pd-PAN-GC electrodes are measured (per cm₂ of the true metal-catalyst surface area). The found higher activity of Pt and Pd particles incorporated in PAN, as compared with Pt/Pt and Pd/Pt, is attributed to interaction between metal-catalyst particles and the polymeric matrix. The activation effect is the most pronounced for the HCOOH electrooxidation at Pd-PAN-GC. The data concerning hydrogen evolution testify in favor of a decrease in exchange currents of this reaction upon going from Pt to Pt-PAN-GC electrodes     

Electrocatalytic Behavior of a Palladium–Polyaniline System Obtained by Electrodepositing Palladium into a Preliminarily Formed Polyaniline Film

The electrochemical behavior of Pd–PAN systems, where PAN stands for polyaniline, is studied. The systems are formed by electrodepositing palladium onto a PAN–GC electrode (GC, for glassy carbon). It is shown by atomic force microscopy that some palladium particles are deposited directly on the PAN surface even at potentials of low electroconductivity of PAN. Properties of Pd–PAN coatings formed by this technique are compared to those of Pd–PAN systems formed by cycling the potential of a GC electrode in a PdSO₄+ aniline solution, which were studied earlier. Redox characteristics of PAN and the degrees of the promotion of the electrocatalytic activity in the HCOOH oxidation reaction differ in the two systems. The differences are attributed to specific features inherent in the formation of the mixed coating, in particular, to differences in the degree of contact of palladium crystallites with PAN. The PAN degradation in the Pd–PAN systems is shown to be linked mainly to the PAN oxidation, which is catalyzed by the incorporated palladium particles.     

Variations in the Overall Charge and Open-Circuit Potential of a Palladium Electrode during the Adsorption of Iodine and Iodide Anions

Transients of the current and the open-circuit potential during the adsorption of I^– and I₂ on Pd/Pt (supporting electrolyte 0.5 M H₂SO₄) are measured and so are potentiodynamic and galvanostatic charging curves, in the presence and absence of adlayers. Dependences of the overall electrode charge on potential are constructed. After the adsorption of both I^– and I₂, values of the electrode surface charges at potentials of the double-layer region turn negative and considerably differ in their magnitude. The latter is connected with different character of adlayers, which is shown by experiments on the adsorption of silver atoms at underpotentials after a preliminary adsorption of I^– and I₂ on the electrode surface. Certain discrepancies between experimentally-found and theoretically-expected values of transients are attributed to a substantial increase in the irreversibility of sorption and desorption of hydrogen and oxygen in the presence of iodine atoms adsorbed on the surface.     

The local dynamics of polyetherimides: Conformational probes, IR Fourier transform spectra, and quantum-chemical calculations

The IR Fourier transform absorption spectra were used to study the rotational mobility of macromolecule fragments (local dynamics) of several vitreous polyetherimides by the method of conformational probes. The temperatures of the freezing of conformational equilibria of probes were determined. The IR spectra of diphenyl ether, 2,2-diphenylpropane, phthalimide, and N-phthalimide were studied; these molecules were used as models of fragments of monomeric units of polyetherimides. Quantum-chemical calculations of the energies and vibrational spectra of these molecules were performed by the B3LYP method with the 6–31G(d,p) basis set. The rotational mobility of benzene rings in the main chain of polyetherimide macromolecules was estimated, and the nature of secondary relaxation transitions was determined. The IR spectra of polyetherimides were interpreted. The rotational mobility of the CH₃ and CF₃ groups of polyetherimides was estimated from the temperature dependence of absorption band contours of these groups.