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Electrochemical and electrocatalytic properties of thin films Au(111-25 nm), which are quasi-single-crystal electrodes 25
nm thick made of gold with the (111) preferential orientation, and same electrodes modified with a monolayer (ML) of palladium
are studied in 0.1 M solutions of HClO4 and H2SO4 employing voltammetric techniques and surface enhanced infrared reflection absorption spectroscopy (ATR-SEIRAS). Spectroscopic
experiments demonstrate strong adsorption of electrolyte species (H2O, OHads, anions) on the Pd surface. The weak and reversible adsorption of CO on Au(111-25 nm) does not change the interfacial-water
structure. Adsorption of CO on the Pd-modified film results in an irreversibly adsorbed CO adlayer stabilized by co-adsorbed
isolated water species. Various electrooxidation mechanisms are discussed. Electrochemical and spectroscopic investigations
on the adsorption and electrooxidation of HCOOH on bare and 1 ML Pd-Au(111-25 nm) electrodes reveal that electrooxidation
proceeds in both cases via a direct or dehydrogenation pathway. This mechanism involves the formation of formate as intermediate,
which is detected by in situ ATR-SEIRAS. The reactivity on Pd-modified surfaces is higher than on bare gold. The specifically
adsorbed anions (sulfate/bisulfate) and the oxide formation on the substrate surface lower the reactivity for CO and HCOOH
on both surfaces.
Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 11, pp. 1312–1329.
Based on the report delivered at the 8th International Frumkin Symposium “Kinetics of the Electrode Processes,” October 18–22,
2005, Moscow.
The text was submitted by the authors in English. 相似文献
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V. A. Keskinov A. K. Pyartman N. A. Charykov O. V. Arapov A. A. Pronkin V. V. Lishchuk V. V. Leonov 《Russian Journal of Physical Chemistry A, Focus on Chemistry》2008,82(3):329-331
The phase diagram of the hexane-o-xylene-dimethylformamide ternary liquid system was studied at T= 298.15 K. The diagram contained the regions of homogeneous solutions and two-phase liquid systems (systems with stratification), phase I being enriched in dimethylformamide and phase II, in hexane. The distribution of fullerenes C60 and C70 was considered at various concentrations and simultaneous presence in sections at variable phase compositions. The extraction isotherms of fullerenes C60 and C70 under various conditions were found to be close to linear, and the C70/C60 separation factor depended on the composition of the coexisting phases and ranged from 1.25 to 1.8. Fullerene C70 was predominantly distributed in phase I. 相似文献
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M. Yu. Anikovsky A. S. Tatikolov P. G. Pronkin P. P. Levin V. I. Sklyarenko V. A. Kuzmin 《High Energy Chemistry》2003,37(6):398-404
The influence of DNA on the cis–trans equilibrium and fluorescent properties of 3,3-diethyl-9-thiomethylthiacarbocyanine iodide (DTTC) in a phosphate buffer (pH 7) was studied by various photochemical techniques. The interaction of dye molecules with DNA leads to the formation of stable noncovalently bonded complexes. Data obtained from DTTC absorption and fluorescence spectra suggest that complexation proceeds primarily through the cis-form of the dye. Complexation with DNA leads to a substantial increase in the quantum yield of the triplet state of DTTC molecules. The rate constant for quenching the dye triplet state by oxygen turned out to be significantly lower than the diffusion-controlled value. 相似文献
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P. G. Pronkin A. S. Tatikolov V. I. Sklyarenko V. A. Kuz’min 《High Energy Chemistry》2006,40(4):252-258
The processes of cis-trans photoisomerization and thermal back isomerization as well as the effect of DNA on the spectral and kinetic characteristics of the triplet state of a number of meso-substituted thiacarbocyanine dyes: 3,3’-diethyl-9-methoxythiacarbocyanine iodide (K1), 3,3’,9-triethylthiacarbocyanine iodide (K2), 3,3’-diethyl-9-methylthiacarbocyanine iodide (K3), and 3,3’-diethyl-9-chlorothiacarbocyanine perchlorate (K4), were studied by the flash photolysis method. Upon flash photoexcitation, the processes of trans-cis and cis-trans photoisomerization were observed for dye K1; the data on the structure of the absorption bands of the photoisomers were obtained. Complexation with DNA leads to an increase in the quantum yield of the triplet state of the dyes, which is explained by growing rigidity of the bound molecules. In the presence of DNA, triplet state deactivation follows the two-exponential law, thus showing that the dyes form complexes of two different types. The processes of quenching of the dye triplet state by oxygen were studied in solutions and in complexes with DNA. The rate constants for oxygen quenching of the triplet state of the dyes in complexes with DNA were found to be much lower than the values expected for the diffusion-controlled reactions (with allowance for the spin statistical factor, $k_{qO_2 } < 1/9k_{dif} $ ), which is explained by the steric factor of the complexation. 相似文献
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Cis-trans equilibrium for a number of meso-substituted oxacarbocyanine dyes, 3,3′-diethyloxacarbocyanine iodide (K1), 3,3′-diethyl-9-methyloxacarbocyanine iodide (K2),
3,3′-dimethyl-9-ethyloxacarbocyanine iodide (K3), 3,3′,9-triethyl-6,6′-dimethoxyoxacarbocyanine iodide (K4), and 3,3′,9-triethyl-5,5′-dimethyloxacarbocyanine
iodide (K5), has been studied in solutions and in a complex with DNA by spectral and fluorescent methods. A shift of the cis-trans isomer equilibrium toward the formation of the trans-isomer was observed in the presence of DNA, which determined in many respects the spectral effects observed upon the complexation
of the oxacarbocyanine dyes. A steep rise of fluorescence (due to binding of the trans-isomer) in a complex with DNA is favorable for using oxacarbocyanine dyes to determine DNA. 相似文献
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S. Pronkin 《Surface science》2004,573(1):109-127
Quasi-single crystalline gold films of 20 nm thickness and preferential (1 1 1) orientation on Si hemispheres were modified by controlled potentiostatic deposition of Pd (sub-ML, ML, multi-L) from sulphate and/or chloride-containing electrolyte. The electrochemical properties of these model electrodes were characterised for hydrogen and (hydrogen-) sulphate adsorption as well as for surface oxide formation by cyclic voltammetry. Conditions were developed to fabricate defined and stable Pd monolayers. In situ ATR-SEIRAS (Attenuated Total Reflection Surface Enhanced Infrared Reflection Absorption Spectroscopy) experiments were carried out to describe the electrochemical double layer of Pd modified gold film electrodes in contact with aqueous 0.1 M H2SO4 with focus on interfacial water and anion adsorption. Based on an analysis of the non-resonant IR background signal the potential of zero charge is estimated to 0.10-0.20 V (vs. RHE). CO was found to be weakly physisorbed in atop sites on Au(1 1 1-20 nm)/0.1 M H2SO4 only in CO saturated electrolyte. CO, deposited on a quasi-single crystal gold film modified with 1 ML Pd, is chemisorbed with preferential occupation of bridge sites and atop positions at step edges. Saturated CO adlayers, as obtained by deposition at 0.10 V, contain isolated water species and are covered by a second layer of hydrogen bonded water. Potentiodynamic SEIRAS experiments of CO electro-oxidation on Pd-modified gold film electrodes demonstrate clearly the existence of a “pre-oxidation” region. They also provide spectroscopic evidence that isolated water and weakly hydrogen bonded water are consumed during the reaction and that atop CO on defect sites is a preferential reactant. The simultaneous in situ monitoring of the potential- and time-dependent evolution of characteristic vibrational modes in the OH- and CO-stretching regions are in agreement with the Gilman (“reactant pair”) mechanism of CO oxidation. 相似文献
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P. G. Pronkin A. S. Tatikolov V. I. Sklyarenko V. A. Kuz’min 《High Energy Chemistry》2006,40(6):403-409
Using the flash photolysis method, the spectral and kinetic characteristics of triplet states of a number of meso-substituted thiacarbocyanine dyes (3,3′-diethyl-9-methoxythiacarbocyanine iodide, 3,3′,9-triethylthiacarbocyanine iodide, 3,3′-diethyl-9-methylthiacarbocyanine iodide, and 3,3′-diethyl-9-thiomethylthiacarbocyanine iodide) were studied, and the rate constants of triplet quenching by a stable nitroxyl radical, iodide ion, and oxygen were determined in solutions and in complexes with DNA. The results obtained show the formation of two types of dye-DNA complexes: formed by binding of the dye in the groove of a DNA molecule and by intercalation of the dye between base pairs. The complexation creates steric hindrances upon quenching of the triplet states of the ligands and causes great differences between the rate constants of the quenching processes. 相似文献