Electrochemical scanning tunneling microscopic observation of the preoxidation process of CO on Pt(111) electrode surface

Presented are sequential images of CO on Pt(111), observed with electrochemical scanning tunneling microscopy, during its electrochemical preoxidation process. In the course of the well-known phase transition from the (2 x 2)-3CO-alpha structure to the (radical 19 x radical 19)R23.4 degrees-13CO structure, various structures were observed: (2 x 2)-3CO-beta (Chem. Comm. 2006, 2191-2193), (1 x 1)-CO, and (radical 13 x radical 13)R46.1 degrees-9CO. Based on an analysis of the populations of the structures averaged over imaging time and imaged location at the preoxidation potential range (0-0.25 V vs Ag/AgCl), the structures of CO domains changed sequentially in the order of (2 x 2)-3CO-alpha, (2 x 2)-3CO-beta, (1 x 1)-CO, (radical 13 x radical 13)R46.1 degrees-9CO, and (radical 19 x radical 19)R23.4 degrees-13CO as the potential shifted from 0 to 0.25 V. Such a sequential structural change demonstrates that the structures of (2 x 2)-3CO-beta, (1 x 1)-CO, and (radical 13 x radical 13)R46.1 degrees-9CO are transient ones during the preoxidation of CO on Pt(111). Discussed are the transient structures in terms of various aspects, such as the absence of CO in solution and the origin of compressed structures.     

Preparation of a nanoporous CaCO3-coated TiO2 electrode and its application to a dye-sensitized solar cell

A nanoporous CaCO3 overlayer-coated TiO2 thick film was prepared by the topotactic thermal decomposition of Ca(OH)2, and its performance as an electrode of a dye-sensitized solar cell was investigated. As compared to bare TiO2, nanoporous CaCO3-coated TiO2 provided higher specific surface area and, subsequently, a larger amount of dye adsorption; this in turn increased short-circuit current (Jsc). Furthermore, the CaCO3 coating demonstrated increased impedance at the TiO2/dye/electrolyte interface and increased the lifetime of the photoelectrons, indicating the improved retardation of the back electron transfer, which increases Jsc, open-circuit voltage (Voc), and fill factor (ff). Thereby, the energy conversion efficiency (eta) of the solar cell improved from 7.8 to 9.7% (an improvement of 24.4%) as the nanoporous CaCO3 layer was coated onto TiO2 thick films.     

15N/14N Analysis of Amino Acids with GC-C-IRMS - Methodical Investigations and Ecotoxicological Applications

Abstract

In order to perform the ¹⁵N/¹⁴N analysis of amino acids using a gas chromatograph and isotope ratio mass spectrometer linked up via a combustion interface (GC-C-IRMS), the amino acids must be derivatized. Tert-butyldimethylsilylation is examined using various techniques (direct conversion to nitrogen gas, ConFlo-IRMS [1], GC-C-IRMS [2]) and subsequently applied to isotopic characterization of amino acids from wheat protein hydrolyzate obtained from plants exposed to ozone. The method provides a reliable tool for studying ecotoxicological effects on plants at a molecular level in addition to the investigation of the natural variations of different N fractions.     

Modeling of Ethylene Polymerization Kinetics over Supported Chromium Oxide Catalysts

Summary: Silica supported chromium oxide catalysts have been used for many years to manufacture polyethylene and they still account for more than 50% of world production of high‐density polyethylene. Along with its commercial success, the catalytic mechanism and polymerization kinetics of silica supported chromium oxide catalysts have been the subject of intense research. However, there is a lack of modeling effort for the quantitative prediction of polymerization rate and polymer molecular weight properties. The chromium oxide catalyzed ethylene polymerization is often characterized by the presence of an induction period followed by a steady increase in polymerization rate. The molecular weight distribution is also quite broad. In this paper, a two‐site kinetic model is developed for the modeling of ethylene polymerization over supported chromium oxide catalyst. To model the induction period, it is proposed that divalent chromium sites are deactivated by catalyst poison and the reactivation of the deactivated chromium sites is slow and rate controlling. To model the molecular weight distribution broadening, each active chromium site is assumed to have different monomer chain transfer ability. The experimental data of semibatch liquid slurry polymerization of ethylene is compared with the model simulations and a quite satisfactory agreement has been obtained for the polymerization conditions employed.

Polymerization rates at different reaction temperatures: symbols – data, lines – model simulations.     

Preparation and Antibacterial Activity of Thermo-Responsive Nanohydrogels from Qiai Essential Oil and Pluronic F108

Essential oils (EOs) have been used in cosmetics and food due to their antimicrobial and antiviral effects. However, the applications of EOs are compromised because of their poor aqueous solubility and high volatility. Qiai (Artemisia argyi Levl. et Van. var. argyi cv. Qiai) is a traditional Chinese herb and possesses strong antibacterial activity. Herein, we report an innovative formulation of EO as nanohydrogels, which were prepared through co-assembly of Qiai EO (QEO) and Pluronic F108 (PEG-b-PPG-b-PEG, or PF108) in aqueous solution. QEO was efficiently loaded in the PF108 micelles and formed nanohydrogels by heating the QEO/PF108 mixture solution to 37 °C, by the innate thermo-responsive property of PF108. The encapsulation efficiency and loading capacity of QEO reached 80.2% and 6.8%, respectively. QEO nanohydrogels were more stable than the free QEO with respect to volatilization. Sustained QEO release was achieved at body temperature using the QEO nanohydrogels, with the cumulative release rate reaching 95% in 35 h. In vitro antibacterial test indicated that the QEO nanohydrogels showed stronger antimicrobial activity against S. aureus and E. coli than the free QEO due to the enhanced stability and sustained-release characteristics. It has been attested that thermo-responsive QEO nanohydrogels have good potential as antibacterial cosmetics.     

The role of resolved virtual photons in the production of forward jets at HERA

The measurement of forward jet cross sections has been suggested as a promising probe of new small x parton dynamics and the question is whether the new HERA data provide an indication of this. In this paper the influence of resolved photon processes has been investigated and it has been studied to what extent the inclusion of such processes in addition to normal deep inelastic scattering leads to agreement with data. It is shown that two DGLAP evolution chains from the hard scattering process towards the proton and the photon respectively, are sufficient to describe effects observed in the HERA data, which have been attributed to BFKL dynamics. Received: 11 March 1999 / Published online: 18 June 1999     

Optical and Electrical Properties of the PLT Films with Various Compositions Deposited by Sol-Gel Process

In order to study optical and electrical properties of (Pb_1-xLa_x)TiO₃ (PLT) films with varying La concentration, the PLT films were deposited by sol-gel process. X-ray diffraction revealed that a pseudocubic phase of the PLT film became dominant with increasing La concentration due to decrease of lattice constant of c-axis. Three-dimensional atomic force microscopy images showed that the grain size and root mean square surface roughness decreased by addition of La. The optical band gap of the PLT films became wider when Pb was substituted with La. The addition of La increased the transparency of the PbTiO₃ film and shifted the threshold for initiation of absorption to shorter wavelength. Hysteresis loops of the PLT films showed that remanent polarization and coercive field decreased with increasing La concentration. In addition, we modified the surface of the PLT film with La concentration of 5% using a keV oxygen ion beam at different doses. The optical band gap of the PLT film was changed by the oxygen ion beam irradiation although the XRD patterns and the transmittance values were not significantly changed. In measuring AFM images of the surface of modified PLT film, significant changes of the grain shape and size were not found. Moreover, polarization and dielectric constant were not changed after oxygen ion irradiation. These results suggested that addition of La could affect the optical and electrical properties of the PbTiO₃ and PLT films and that surface modification by oxygen ion beam modification with 1 keV energy can change the surface property but not bulk property.     

MULTIPLICITY OF SOLUTIONS AND SOURCE TERMS IN A FOURTH ORDER NONLINEAR ELLIPTIC EQUATION

0Introducti0nWeinvestigatetheexistellce0fs0lutiolls0fthef0urthordernonlillearellipticb0undaryvalueproblemwhereu =max{u,0},sisreal,andcisn0taneigenvalue0f-A11llderDirichletb0undarycondition.Hereweassumethatflisab0unded0pensetinR"withsmootl1b0undaryOn.The0perat0rA2denotesthebihalm0nic0perat0r.Weassumethatbisllotancigenvalue0fAa cAunderDirichletb0undaryc0llditi0n.Theno11lillcarequati0uwithjumpillgn0l1lillearityhavebeenextcllsivclystudi(}dbymany.uth.rs[3'4'6'7'8].Theyst11dicdtheexistence()fs0l…     

Solvent-Processible Polymer Membrane-Based Reference Electrodes for Miniature Chemical Sensors

We have recently developed a new type of liquid junction-free reference electrode that is suited for fabrication of miniature ion sensor devices. The proposed reference electrode system employs a solvent-processible polymer membrane, and the best performance membrane so far is formulated with an aromatic type polyurethane,synthesized with 4,4'- methylenebis(phenyl isocyanate) and poly(tetramethylene ether glycol).     

Electron-ion Coulomb Bremsstrahlung in nonideal plasmas

The classical electron-ion Coulomb Bremsstrahlung process is investigated in nonideal plasmas. An effective pseudopotential model taking into account the plasma screening and collective effects is applied to describe the electron-ion interaction potential in a classical nonideal plasma. The classical straight-line trajectory method is applied to the motion of the projectile electron in order to visualize the variation of the differential Bremsstrahlung radiation cross-section (DBRCS) as a function of the scaled impact parameter, nonideal plasma parameter, projectile energy, photon energy, and Debye length. The results show that the DBRCS in ideal plasmas described by the Debye-Hückel potential is always greater than that in nonideal plasmas, i.e., the collective effects reduce the DBRCS for both the soft and hard photon cases. For large impact parameters, the DBRCS for the soft photon case is found to be always greater than that for the hard photon case. Received 1st December 1999