Yuwen Liu

New approximate formula for Arrhenius temperature integral

Abstract In this paper a more precise approximate formula for Arrhenius temperature integral, i.e., − ln P(u)=0.37773896+1.89466100 ln u+1.00145033u , is proposed, by using two-step linearly fitting process: (i) the linear dependence of d ln p(u)/ d u on 1/u and (ii) the linear dependence of ( ln p(u)−c ln u ) on u. Values of p(u) at different u were directly obtained from numerical integration of temperature integral without derivation from any approximating infinite series, and values of d ln p(u)/ d u were obtained by numerical differentiating. New equation for the evaluation of non-isothermal kinetic parameters has been obtained from the above dependence, which can be put in the form ln g(α) T 1.89466100 = ln AE βR +3.63504095−1.89466100 ln E −1.00145033 E RT The validity of this formula was confirmed and its deviation from the values of numerical integrating was discussed. Compared with some previously published approximate formulae, our formula has the best result in the kinetics analysis of non-isothermal process.

Graphene Nanoelectrodes: Fabrication and Size-Dependent Electrochemistry

The fabrication and electrochemistry of a new class of graphene electrodes are presented. Through high-temperature annealing of hydrazine-reduced graphene oxides followed by high-speed centrifugation and size-selected ultrafiltration, flakes of reduced graphene oxides (r-GOs) of nanometer and submicrometer dimensions, respectively, are obtained and separated from the larger ones. Using n-dodecanethiol-modified Au ultramicroelectrodes of appropriately small sizes, quick dipping in dilute suspensions of these small r-GOs allows attachment of only a single flake on the thiol monolayer. The electrodes thus fabricated are used to study the heterogeneous electron transfer (ET) kinetics at r-GOs and the nanoscopic charge transport dynamics at electrochemical interfaces. The r-GOs are found to exhibit similarly high activity for electrochemical ET reactions to metal electrodes. Voltammetric analysis for the relatively slow ET reaction of Fe(CN)6(3-) reduction produces slightly higher ET rate constants at r-GOs of nanometer sizes than at large ones. These ET kinetic features are in accordance with the defect-dominant nature of the r-GOs and the increased defect density in the nanometer-sized flakes as revealed by Raman spectroscopic measurements. The voltammetric enhancement and inhibition for the reduction of Ru(NH3)6(3+) and Fe(CN)6(3-), respectively, at r-GO flakes of submicrometer and nanometer dimensions upon removal of supporting electrolyte are found to significantly deviate in magnitude from those predicted by the electroneutrality-based electromigration theory, which may evidence the increased penetration of the diffuse double layer into the mass transport layer at nanoscopic electrochemical interfaces.

Electron-Transfer Kinetics and Electric Double Layer Effects in Nanometer-Wide Thin-Layer Cells

Redox cycling in nanometer-wide thin-layer cells holds great promise in ultrasensitive voltammetric detection and in probing fast heterogeneous electron-transfer kinetics. Quantitative understanding of the influence of the nanometer gap distance on the redox processes in the thin-layer cells is of crucial importance for reliable data analysis. We present theoretical consideration on the voltammetric behaviors associated with redox cycling of electroactive molecules between two electrodes separated by nanometer widths. Emphasis is placed on the weakness of the commonly used Butler-Volmer theory and the classic Marcus-Hush theory in describing the electrochemical heterogeneous electron-transfer kinetics at potentials significantly removed from the formal potential of redox moieties and, in addition, the effect of the electric-double-layer on the electron-transfer kinetics and mass transport dynamics of charged redox species. The steady-state voltammetric responses, obtained by using the Butler-Volmer and Marcus-Hush models and that predicted by the more realistic electron-transfer kinetics formulism, which is based on the alignments of the density of states between the electrode continuum and the Gaussian distribution of redox agents, and by inclusion of the electric-double-layer effect, are compared through systematic finite element simulations. The effect of the gap width between the electrodes, the standard rate constant and reorganization energy for the electron-transfer reactions, and the charges of the redox moieties are considered. On the basis of the simulation results, the reliability of the conventional voltammetric analysis based on the Butler-Volmer kinetic model and diffusion transport equations is discussed for nanometer-wide thin-layer cells.

Microcalorimetric studies of the synergistic effects of copper-1,10-phenanthroline combined with hyperthermia on a liver hepatoma cell line Bel-7402

The effects of copper-1,10-phenanthroline combined with hyperthermia on human liver hepatoma cell line, Bel-7402 were studied. The effect was evaluated by the mean thermal power of the cells and total energy Q produced during the measurement period (35 h). It was found that the energy produced reduced after the treatment. Condensation of nuclear chromatin and apoptotic bodies can be observed from fluorescence microscope, which showed apoptosis occurs under the action of copper-1,10-phenanthroline combined with hyperthermia. The analysis by flow cytometry showed the proportion of apoptotic cells in the cell population increased. It indicates that the combination of hyperthermia and copper-1,10-phenanthroline has a synergetic effect on Bel-7402.

Theoretical Analysis of Electrochemical Formation and Phase Transition of Oxygenated Adsorbates on Pt(111)

The electrochemical oxygenation processes of Pt(111) surface are investigated by combining density functional theory (DFT) calculations and Monto Carlo (MC) simulations. DFT calculations are performed to construct force-field parameters for computing the energy of (√3 × √3)R30°-structured OH*-H2O* hydrogen-bonding networks (differently dissociated water bilayer) on the Pt(111) surface, with which MC simulations are conducted to probe the reversible H2O* ↔ OH* conversion in OH*-H2O* networks. The simulated isotherm (relation between electrode potential and OH* coverage) agrees well with that predicted by the experimental cyclic voltammetry (CV) in the potential region of 0.55-0.85 V (vs RHE). It is suggested that the butterfly shape of CV in this region is due to different variation trends of Pt-H2O* distance in low and high OH* coverages. DFT calculation results indicate that the oxidative voltammetry in the potential region from 0.85 V to ca. 1.07 V is associated with the dissociation of OH* to O*, which yields surface structures consisting of OH*-H2O* networks and (√3 × √3)-structured O* clusters. The high stability of the half-dissociated water bilayer (OH*-H2O* hydrogen-bonding network with equal OH* and H2O* coverages) formed in the butterfly region makes OH* dissociation initially very difficult in energetics, but become facile once starts due to the destabilization of OH* by the formed O* nearby. This explains the experimentally observed nucleation and growth behavior of O* phase formation and the high asymmetry of oxidation-reduction voltammetry in this potential region.