Electrochemical study of the Nd1.95NiO4 + δ/oxide electrolyte interface

Nickelate-based oxides are potential cathodes in Solid Oxide Fuel Cells operating at intermediate temperatures. The chemical compatibility between apatite electrolyte, i.e., La₉Sr₁Si₆O_26.5, and Nd-deficient nickelate, i.e., Nd_1.95NiO_4 + δ, has been characterized. The equilibrium between the nickelate material and the gas phase has been studied as functions of temperature and oxygen partial pressure, using potentiometric measurements with microelectrodes, i.e., metallic or ceramic point electrodes. Two solid electrolytes were used, i.e., apatite and yttria-stabilized zirconia. The response of the nickelate is discussed in terms of oxygen stoichiometry.     

Study of the Interaction of Methylene Violet with Calf Thymus DNA Using an SPR-Based DNA Sensor

Electrochemical and surface plasmon resonance technologies were combined to detect binding of low-molecular-weight compounds to DNA. First, zirconia thin films were electrochemically deposited onto bare gold electrodes. Second, calf thymus DNA was attached onto the zirconia thin films. Finally, the interaction of methylene violet with the DNA-modified surface was tested. The binding isotherm gave a K_D of 2.21 × 10^?5 M. Fluorescence quenching experiments were performed to confirm the interaction. Regenerating surfaces with 1 mM NaOH provided reusable surfaces. This study provides a generic platform which can be tailored for the study of interactions of small molecules with DNA.     

Zirconia-supported phosphotungstic acid as catalyst for alkylation of phenol with benzyl alcohol

The liquid-phase alkylation of phenol with benzyl alcohol was carried out using zirconia-supported phosphotungstic acid (PTA) as catalyst. The catalysts with different PTA loadings (5–20 wt.% calcined at 750 °C) and calcination temperature (15 wt.% calcined from 650 to 850 °C) were prepared and characterized by ³¹P MAS NMR and FT-IR pyridine adsorption spectroscopy. The catalyst with optimum PTA loading (15%) and calcination temperature (750 °C) was prepared in different solvents. ³¹P MAS NMR spectra of the catalysts showed two types of phosphorous species, one is the Keggin unit and the other is the decomposition product of PTA and the relative amount of each depends on PTA loading, calcination temperature and the solvent used for the catalyst preparation. The catalysts with 15% PTA on zirconia calcined at 750 °C showed the highest Brönsted acidity. At 130 °C and phenol/benzyl alcohol molar ratio of 2 (time, 1 h), the most active catalyst, 15% PTA calcined at 750 °C gave 98% benzyl alcohol conversion with 83% benzyl phenol selectivity.     

Preparation of Al2O3–ZrO2 mixed supports; their characteristics and hydrothermal stability

Al₂O₃–ZrO₂ mixed supports have been synthesised using a colloidal solution of ZrO(OH)₂ or a Zr(IV) propoxide solution in organic medium. Zirconia content in these samples was about 10% (36% of the theoretic monolayer). The hydrothermal stability (alumina→boehmite transformation at 230 °C, about 10 bar pressure, in the presence of water vapour) of these supports was then investigated by XRD. The presence of the zirconia over the alumina decrease the quantity of boehmite formed after the hydrothermal treatment. The dispersion of zirconia and the stability in hydrothermal conditions of the final support are function of the preparation method.     

Local atomic structure of a zirconia-based americium transmutation fuel

(Zr,Y,Am)O₂ with 6 and 19 mol% Am were prepared by infiltration of americium in porous yttria-stabilised zirconia (YSZ) beads. Samples were sintered at 1600 °C in Ar/H₂ to yield Am(III). By annealing them at 1000 °C in flowing air, the Am is oxidised to Am(IV). Both Am(III) and Am(IV) samples exhibit the presence of a single (Zr,Y,Am)O₂ phase with fluorite structure. The local atomic structure around the Zr, Y, and Am atoms is determined by EXAFS analysis. The Zr-O bond distance decreases from 2.15 to 2.12 Å with increasing Am(III) content, whereas the Y-O bond distance is independent of Am content and oxidation state. The Am(III)-O bond distance is 2.37 Å for both Am concentrations, while oxidation to Am(IV) decreases the Am(IV)-O distance to 2.28 Å, with a simultaneous expansion of the environment around the Zr atoms. The Am-O bond distances are contracted compared with the compounds Am₂Zr₂O₇ and AmO₂ and the distances expected from the ionic radii.     

ZrO2-Graphene-Chitosan nanocomposite modified carbon paste sensor for sensitive and selective determination of dopamine

A sensitive and stable electrochemical sensor was developed by modification of carbon paste electrode with ZrO₂/graphene/chitosan nanocomposite. The modified sensor served as a potential electrocatalytic platform for dopamine. Electrochemical impedance spectroscopy studies indicated reduction of charge transfer resistance at the modified electrode surface thereby facilitating the electron transfer process which resulted in higher current response to dopamine. The electrochemical behavior of dopamine at the modified electrode was studied using cyclic and square wave voltammetry. The maximum current response for the electro-oxidation of dopamine was observed at pH 7.4 and the process was realized to be diffusion controlled. The modified sensor demonstrated linearity in the range 1000–5000 nM, with high sensitivity (22 nA/nM), detection limit of 11.3 nM and selectivity for dopamine in the presence of ascorbic and uric acid which are found to co-exist with dopamine in physiological media. The method was employed for quantification of dopamine in a pharmaceutical formulation.     

Characterization of plasma fluorinated zirconia for dental applications by X-ray photoelectron spectroscopy

This paper discusses fluorination of biomedical-grade yttria-stabilized zirconia (YSZ) by sulfur hexafluoride plasma treatment and characterization of near-surface chemistry products by X-ray photoelectron spectroscopy (XPS). Deconvolution of the Zr 3d and Y 3d XPS core level spectra revealed formation of both ZrF₄ and YF₃. In addition, seven-coordinate ZrO₂F₅ and/or ZrO₃F₄ phases were deconvolved, retaining similar atomic coordination as the parent oxide and believed to have formed by substitutional displacement of oxygen by fluorine. No additional components attributed to yttria oxyfluoride were deconvolved. Argon ion sputter depth profiling determined the overlayer to be ∼4.0 nm in thickness, and angle resolved XPS showed no angle dependence on component percentages likely due to fluorination extending into the grain boundaries of the polycrystalline substrates. Importantly, the conversion layer did not induce any apparent change in zirconia crystallinity by inspection of Zr-O 3d_5/2,3/2 peak positions and full-width-at-half-maximum values, important for retaining its desirable mechanical properties.     

钾助剂对Cu/ZrO2合成甲醇催化剂活性的影响

考察了钾助剂对Ｃｕ／ＺｒＯ２合成甲醇催化剂活性的影响，发现添加适量的钾可以显著提高对ＣＯ／２Ｈ２合成甲醇反应的活性，同时使生成ＣＯ２的选择性略有提高。ＸＰＳ和ＴＰＲ结果显示，钾呈现出给电子效应，钾的助剂作用可能是通过调节反应气体中ＣＯ２的含量而实现的。     

Butane isomerization over platinum promoted sulfated zirconia catalysts

The isomerization of n-butane to i-butane has been studied at 11 bar in a microflow reactor over sulfated zirconia (SZ) and platinum containing sulfated zirconia (Pt-SZ) catalysts. In the presence of H₂ a significantly higher temperature is required for isomerization over SZ than in its absence. The rate over SZ is higher with n-butane containing 33 ppm butene as an impurity than with a feed that is pre-equilibrated over a Pt/SiO₂ catalyst to a much lower butene content. Over Pt-SZ the reaction rate is higher, because any butene consumed is rapidly regenerated; the conversion is perfectly stable in 83 h runs, selectivity to i-butane is 95%; i-pentane and propane are the main byproducts. The activation energy is 53 kJ mol⁻¹. Upon increasing the pressure of H₂ from 1.1 to 6.6 bar, the reaction rate was found to decrease in a perfectly reversible fashion. Kinetic analysis reveals that the reaction order is negative in H₂ (−1.1 to −1.3 depending on the temperature) and positive in n-butane (+ 1.3 to +1.6), indicating that the mechanism of this isomerization is intermolecular: butene is formed and reacts with adsorbed C₄-carbenium ions to adsorbed C₈ intermediates which isomerize and undergo β-fission to fragments with i-C₄ structure. This mechanism is confirmed over Pt-SZ by isotopic labelling experiments, though at much lower pressure, using double labelled ¹³CH₃---CH₂---CH₂---¹³CH₃. The primary reaction product consists of i-butane molecules, containing zero, one, two, three and four ¹³C atoms in a binomial distribution.