HCl nanoscience at copper and copper/gold alloy surfaces

Abstract The reaction of HCl with clean, Cu(100) and (111), and Au/ Cu(100) surfaces was investigated using x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) under ultra high vacuum (UHV) conditions. Exposure of the Cu(100) and (111) samples to HCl at room temperature leads to the formation of a saturated copper chloride monolayer. In the case of Cu(100), the saturated coverage was half monolayer corresponding to a c(2x2)-Cl reconstruction (half monolayer is 7.25x1014 cm-2) while for Cu(111) it was one third monolayer consistent with the reconstruction of (√3x√3)R30o (one third monolayer 5.9x1014 cm-2). The interaction of HCl with preoxidised Cu(100) and (111) showed different behaviour from those of clean copper surface depending on the way of interaction of oxygen with copper surface. Interaction of HCl with peroxidised Cu(111) at saturation oxygen coverage leads to the adsorption of chlorine on top of the copper surface with one third coverage. In contrast, presence of oxygen on Cu(100) surface at saturation coverage or less leads to adsorb chlorine but with an excess in chlorine concentration (more than the expected c(2x2) coverage). Oxidized Cu(100) and (111) surface at elevated temperature leads to the formation multi oxide layer. The two oxide surfaces („‟44‟‟ and „‟29‟‟) observed at the Cu(111) depend on the temperature of the substrate at the time of oxidation. The (√2x2√2)R45o structure was observed on the Cu(100) surface on heating which is the same structure formed at saturation coverage at room temperature. Interaction of HCl with Cu(100) and (111) surfaces covered by multilayers of oxide lead to adsorption of chlorine on top of the copper surface with a coverage more than more than the saturation coverage. Interaction of HCl with Au/Cu(100) showed two different behaviour depending on the gold coverage. Au/Cu(100) alloy formed at half monolayer of gold coverage, forming c(2x2) structure. Exposure of the Au/Cu(100) alloy at half monolayer of gold coverage to HCl leads to the formation of c(2x2)-Cl structure with saturation coverage of half monolayer in similar manner of interaction of HCl with the clean cu(100) surface. Interaction of HCl with Au/Cu(100) surface at gold coverage more than half monolayer leads to a dealloying of the gold from the copper surface and forming the Au(111) surface. Cu-Cl formed underneath the Au(111) surface with excess of chlorine concentration

XPS and STM studies of the oxidation of hydrogen chloride at Cu(100) surfaces

The dissociative chemisorption of HCl on clean and oxidized Cu(100) surfaces has been investigated using x-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM). Whereas the dissociation of HCl at the clean surface is limited to the formation of a (√ 2 × √ 2)-R45° Cl(a) monolayer, the presence of surface oxygen removes this barrier, leading to chlorine coverages up to twice that obtained at the clean surface. Additional features in the STM images that appear at these coverages are tentatively assigned to the nucleation of CuCl islands. The rate of reaction of the HCl was slightly higher on the oxidized surface but unaffected by the initial oxygen concentration or the availability of clean copper sites. Of the two distinct domains of adsorbed oxygen identified at room temperature on the Cu(100) surfaces, the (√ 2 × √ 2)-R45° structure reacts slightly faster with HCl than the missing row (√ 2 × 2 √ 2)-R45° O(a) structure. The results address the first stages in the formation of a copper chloride and present an interesting comparison with the HCl/O(a) reaction at Cu(110) surfaces, where oxygen also increased the extent of HCl reactions. The results emphasize the importance of the exothermic reaction to form water in the HCl/O(a) reaction on copper

Enhancing surface reactivity with a noble metal

Gold, the archetypal noble metal, is usually associated with an inhibition of surface reactivity by site blocking. In this paper however, we show that on Cu(100) surfaces a gold adlayer can actually increase the extent of reaction with the substrate

Copper(II) catalysis for oxidation of l-tryptophan by hexacyanoferrate(III) in alkaline medium: A kinetic and mechanistic approach

The catalytic effect of copper(II) catalyst on the oxidation of l-tryptophan (Trp) by hexacyanoferrate(III) (HCF), has been investigated spectrophotometrically in an aqueous alkaline medium at a constant ionic strength of 0.5 mol dmâ3 and at 25 °C. The stoichiometry for both the uncatalyzed and catalyzed reactions was 1:2 (Trp:HCF). The reactions exhibited first order kinetics with respect to [HCF] and less than unit orders with respect to [Trp] and [OHâ]. The catalyzed reaction exhibited fractional-first order kinetics with respect to [CuII]. The reaction rates were found to increase as the ionic strength and dielectric constant of the reaction medium increase. The effect of temperature on the rates of reactions has also been studied, and the activation parameters associated with the rate-determining steps of the reactions have been evaluated and discussed. Addition of the reaction product HCF(II) to the reaction mixture did not affect the rates. Plausible mechanistic schemes for uncatalyzed and catalyzed reactions explaining all of the observed kinetic results have been proposed. In both cases, the final oxidation products are identified as indole-3-acetaldehyde, ammonia, and carbon dioxide. The rate laws associated with the reactionsâ mechanisms are derived. The rate constants of the slow steps of the reactions along with the equilibrium constants are also calculated. Keywords: Oxidation, Kinetics, l-Tryptophan, Hexacyanoferrate(III), Copper(II), Catalysi

Catalytic oxidation of carbon monoxide over of gold-supported iron oxide catalyst

<p>In this work, a series of gold nanoparticles deposited on α-FeOOH nanorods were studied in relation to their performance in the low-temperature oxidation of CO. The catalysts were characterised by different techniques such as, Fourier transform infrared (FTIR), X-ray diffraction (XRD), N₂ adsorption/desorption, hydrogen temperature programmed reduction (H₂-TPR) and transmission electron microscope (TEM) images. The XRD proved the formation of α-FeOOH crystalline structure and also showed small diffraction peaks for Au-agglomerated particles on the surface. While TEM images revealed the formation of α-FeOOH with nanorod structure with different dimensions, TEM also showed some agglomerations of Au particles on the support surface. The H₂-TPR experiments the enhancement of Au/α-FeOOH reducibility. The performance of Au/α-FeOOH in the CO oxidation was greatly affected by Au content and α-FeOOH preparation method.</p

Some natural aqueous extracts of plants as green inhibitor for carbon steel corrosion in 0.5 M sulfuric acid

The inhibiting impact of natural aqueous extracts of some plants such as curcumin, parsley and cassia bark extracts for the corrosion of carbon steel (C-steel) in 0.5 M H2SO4 solution was inspected utilizing some techniques such as galvanostatic and potentiodynamic anodic polarization and weight loss measurements. Outcomes indicated that the percentage inhibition efficiency increases with increasing the concentration of the extract due to its horizontal adsorption on the C-steel surface. The process of adsorption is followed by the Temkin isotherm. These natural extracts acted as pitting corrosion inhibitors by shifting the pitting potential to more noble values. The sequence of inhibition efficiency of the natural extracts decreases in the following order: cassia bark extract > parsley extract > curcumin extract. This arrangement is related to the molecular size of the major components of the three natural extracts used

Enhancing surface reactivity with a noble metal

Gold, the archetypal noble metal, is usually associated with an inhibition of surface reactivity by site blocking. In this paper however, we show that on Cu(100) surfaces a gold adlayer can actually increase the extent of reaction with the substrate

Large scale validation of a new non-invasive and non-contact bilirubinometer in neonates with risk factors

Abstract The study was aimed to evaluate the performance of a newly developed non-invasive and non-contact bilirubin measurement device (AJO-Neo) as an alternative to the conventional invasive biochemical method of total serum bilirubin (TSB) estimation in preterm and term neonates suffering from hyperbilirubinemia associated with risk factors, and/or undergoing phototherapy. The safety and efficacy of the device were assessed in 1968 neonates with gestational ages ranging from 28 to 41 weeks and suffering from incidences of hyperbilirubinemia. Linear regression analysis showed a good correlation between AJO-Neo and the conventional method of TSB (Pearson’s coefficient, r = 0.79). The small bias (0.27 mg/dL) and limits of agreements (− 3.44 to 3.99 mg/dL) were within the range of clinical acceptance. The device was also precise in the measurement of bilirubin levels in all subgroups of the study. The receiver operator curve (ROC), that takes account of both sensitivity and specificity of a device showed high efficacy of the device (area under the curve, AUC = 0.83) in the detection of bilirubin. While monitoring the bilirubin level during phototherapy, the device indicated promising results showing good agreement with TSB. Specificities and sensitivities of the device indicated a much higher accuracy in neonates with associated risk factors for hyperbilirubinemia. Hence, the newly developed device (AJO-Neo) is reliable in measuring bilirubin level in preterm, and term neonates irrespective of gestational or postnatal age, sex, risk factors, feeding behavior or skin color