Increase In Surface Concentration Research Articles

Influence of wet oxidation of herringbone carbon nanofibers on the pseudocapacitance effect

Herringbone carbon nanofibers (CNFs) were treated with concentrated HNO3 and a mixture of diluted HNO3/H2SO4 to obtain a series of oxygen enriched CNF with different oxygen group distribution, but with a similar porous texture. Oxygen functional groups were determined by X-ray photoelectron spectroscopy. CNFs with a very high relative concentration of carbonyl and/or quinone groups and hydroxyl groups were obtained by adjusting the suitable temperature and time of oxidation with HNO3 and HNO3/H2SO4, respectively. The electrochemical behavior of the samples was studied in three- and two-electrode cells. The performance of oxidized CNFs-based supercapacitors working in 1molL−1 H2SO4 and 6molL−1 KOH was analyzed using cyclic voltammetry and galvanostatic charging/discharging. The specific capacitance of the oxidized CNFs was more than twice enhanced in acidic and alkaline media compared to the pristine CNFs due to the pseudocapacitance effect. It was revealed that not only quinone groups but also hydroxyl groups contribute into the overall capacitance through the pseudocapacitance effect. With increasing surface concentration of the CO and C–OH groups, the capacitance values increase for the capacitors operating in both media.

Kinetics of electrochromic process in thin films of cathodically deposited nickel hydroxide

Ni(OH)2 films have been obtained by cathodic deposition from 1 M Ni(NO3)2 on a glass with a current-conducting SnO2 layer. The films have a porous structure and consist of chaotically joined formations of 100–150 nm in size. They contain a considerable amount of adsorbed water, because of which their refraction index was n = ~1.5, whereas for crystalline nickel hydroxide, it was n = 2.37. It has been shown that in the course of discoloration of films through a shift of their potential towards more negative values, an electric field is formed in the bulk of film, which accelerates the entry of cations into it (protons as [H3O]+) from the electrolyte and electrons from ohmic contact. In this case, the initial dependence i(t), where i ~ t−1/4, is bound up with gradual increase in proton surface concentration. It is proposed to determine separately the dependence of the effective codiffusion coefficient of charge carriers (protons and electrons) on decoloration potential by the analysis of plots of current, injected charge, and luminous transmittance of films against time. This procedure involves a series of periodic stops of potential during the recording of current–potential curves for an electrochromic electrode and allows one to monitor the ratio of the film forms NiOOH and Ni(OH)2 in the course of film reduction.

Preparation and characterization of planar Ni–Au bimetallic model catalysts

Ni–Au bimetallic model catalysts were prepared as thin films on Re(0001) or Ru(0001) single crystal substrates. Surface compositions and electronic structures of the Ni–Au thin films were characterized by low energy ion scattering spectroscopy and X-ray photoelectron spectroscopy, respectively. Surface alloys were prepared by annealing Ni–Au thin films from 500 to 800K, resulting in substantial surface enrichment of Au. Annealing a Ni–Au thin film with a 1:1 bulk composition ratio at 700K for 10min resulted in a surface alloy with 84% (atomic concentration) of Au in the outermost surface layer. The surface atomic structure was investigated using CO as probe molecules, which exclusively adsorbs on the Ni atoms rather than on the Au atoms at room temperature. Polarization modulation infrared reflection absorption spectroscopy of CO adsorption on Ni–Au surface alloys showed that CO adsorption on two-fold bridge sites decreased and finally disappeared with an increase of Au surface concentration. The absence of Ni bridge site CO adsorption indicated that Ni atoms were isolated by Au atoms on Ni–Au alloyed surface.

Reduction of CeO2 in composites with transition metal complex oxides under hydrogen containing atmosphere and its correlation with catalytic activity

Reduction behavior of pure and doped CeO2, the multi-phase La0.6Sr0.4CoO3·xCeO2, La0.8Sr0.2MnO3·xCeO2, and La0.95Ni0.6Fe0.4O3·xCeO2 composites, was studied under hydrogen containing atmosphere to address issues related to the improvement of electrochemical and catalytic performance of electrodes in fuel cells. The enhanced reduction of cerium oxide was observed initially at 800°C in all composites in spite of the presence of highly reducible transition metal cations that could lead to the increase in surface concentration of oxygen vacancies and generation of the electron enriched surface. Due to continuous reduction of cerium oxide in La0.6Sr0.4CoO3·x-CeO2 and La0.8Sr0.2MnO3·xCeO2 (up to 10 h) composites the redox activity of the Ce4+/Ce3+ pair could be suppressed and additional measures are required for reversible spontaneous regeneration of Ce4+. After 3 h exposure to H2-Ar at 800°C the reduction of cerium oxides and perovskite phases in La0.95Ni0.6Fe0.4O3·xCeO2 composites was diminished. The extent of cerium oxide involvement in the reduction process varies with time, and depends on its initial deviation from oxygen stoichiometry (that results in the larger lattice parameter and the longer pathway for O2− transport through the fluorite lattice), chemical origin of transition metal cations in the perovskite, and phase diversity in multi-phase composites.

Micro- to nanostructured poly(pyrrole-nitrilotriacetic acid) films via nanosphere templates: applications to 3D enzyme attachment by affinity interactions

We report the combination of latex nanosphere lithography with electropolymerization of N-substituted pyrrole monomer bearing a nitrilotriacetic acid (NTA) moiety for the template-assisted nanostructuration of poly(pyrrole-NTA) films and their application for biomolecule immobilization. The electrodes were modified by casting latex beads (100 or 900 nm in diameter) on their surface followed by electropolymerization of the pyrrole-NTA monomer and the subsequent chelation of Cu(2+) ions. The dissolution of the nanobeads leads then to a nanostructured polymer film with increased surface. Thanks to the versatile affinity interactions between the (NTA)Cu(2+) complex and histidine- or biotin-tagged proteins, both tyrosinase and glucose oxidase were immobilized on the modified electrode. Nanostructuration of the polypyrrole via nanosphere lithography (NSL) using 900- and 100-nm latex beads allows an increase in surface concentration of enzymes anchored on the functionalized polypyrrole electrode. The nanostructured enzyme electrodes were characterized by fluorescence microscopy, 3D laser scanning confocal microscopy, and scanning electron microscopy. Electrochemical studies demonstrate the increase in the amount of immobilized biomolecules and associated biosensor performances when achieving NSL compared to conventional polymer formation without bead template. In addition, the decrease in nanobead diameter from 900 to 100 nm provides an enhancement in biosensor performance. Between biosensors based on films polymerized without nanobeads and with 100-nm nanobeads, maximum current density values increase from 4 to 56 μA cm(-2) and from 7 to 45 μA cm(-2) for biosensors based on tyrosinase and glucose oxidase, respectively.

Mechanical and compositional characteristics of steam-treated Douglas fir (Pseudotsuga menziesii L.) during pelletization

Rheological properties of pelletizing steam-treated Douglas fir at four different severities were investigated. Steam-treated wood pellets exhibited three compression regions that became more distinct with increasing treatment severity. Hydrolysis of hemicelluloses and condensations of lignin led to an increase in elasticity of pellets made from steam treated feedstock. The increased treatment duration improved the dimensional stability of pellets. The increase in particle surface roughness and concentration of mono-sugars and extractives contributed to the increase in required energy for extruding steam treated pellets from the die. The maximum breaking force, Meyer hardness and the hardness modulus increased with steam treatment. The increased hardness and dimensional stability of steam-treated pellets can be attributed to the binding role of mono-sugars released from Douglas fir during steam treatment.

Surface ozone values in anomalous summer 2010 measured in Obninsk

Given and analyzed are the results of the measuring of concentration of ozone O3, nitrogen oxides NOx, and carbon monoxide CO at the surface as well as the sum of hydrocarbons and the aerosol optical depth in Obninsk (Kaluga oblast) during the warm period 2010 and 2011. The relationship between the air temperature and the maximum daily ozone values in May–September 2010 are characterized by the higher correlation coefficient than in May–September 2011: 0.82 ± 0.05 versus 0.64 ± 0.07. Increased concentration of surface ozone in Obninsk in July–August 2010 as compared to the similar period in 2011 were caused by the higher concentrations of the compounds-predecessors of ozone. The concentration of O3 in August 2010 exceeded 200μg/m3 and was never registered in Obninsk during the observation period of 2004–2011. This is associated with the air masses that came to Obninsk from the areas with peat and forest fires that resulted in the dramatic increase in surface concentrations of NOx, CO, and hydrocarbons.

Excitation energy migration and trapping on the surface of fluorescent poly(acrylic acid)-grafted polymer particles

The surface of poly(methyl methacrylate) particles with different amounts of a grafted layer of poly(acrylic acid) was labeled with varying degrees of an amino derivative of fluorescein isothiocyanate. The resulting fluorescent polymer particles were analyzed by absorption spectroscopy and by steady-state and time-resolved fluorescence spectroscopy including measurements of the fluorescence anisotropy. The combined results indicate that the overall decrease in fluorescence intensity with increasing surface concentrations of the fluorophore can be traced back to the formation of non-fluorescent aggregates. A mechanism is proposed, in which the excitation energy migrates between identical fluorophores until it is transferred to non-fluorescent aggregates acting as an energy trap. Increases in the surface fluorophore concentration increase both the probability for energy transfer between identical fluorophores and the probability for energy transfer to non-fluorescent aggregates. Furthermore, we suggest that this mechanism also applies to fluorescent protein conjugates and rationalizes the nonlinear dependence of the fluorescence emission on the labeling density.

Characteristics of airborne radionuclides concentration in a coastal environment

Airborne radionuclides from the Fukushima nuclear power plant accident in 2011 were measured in 12 regional monitoring stations in Korea. The Gangneung (GN) monitoring station located in a coastal region almost always has a higher radioactivity concentration of airborne radionuclides than any other station. The possible cause of this higher concentration was analysed in terms of the local meteorology and topography. The increase in surface concentrations of radionuclides at the GN region might be attributed to the downslope windstorm, temperature inversion and coupled sea breeze and mountain flows.

Study of the nanosized Li2MnO3: Electrochemical behavior, structure, magnetic properties, and vibrational modes

In this work, we synthesized nano-particles (20–80nm) of Li2MnO3 using the self-combustion reaction and studied the electrochemical activity of electrodes prepared from this nano-material at 30, 45, and 60°C. It was shown that the first Li-extraction from nano-Li2MnO3 occurs at much lower potentials (by 180–360mV) in comparison with micron-sized Li2MnO3 electrodes. This can be associated with the higher surface-to-volume ratio, much shorter the diffusion path and the increased surface concentration of the electrochemically active sites. On the basis of magnetic susceptibility studies of nano-Li2MnO3 we proposed a model of disordered surface layer, containing Mn3+ or Mn2+ ions, both at low spin state, at the surface of these nano-particles. From the results of structural analysis (by X-ray and electron diffraction and vibrational Raman spectroscopy) of galvanostatically cycled nano-Li2MnO3 electrodes in Li-cells we came to a conclusion of partial transition of layered LiMO2 to spinel-type ordering.

Water Oxidation at Hematite Photoelectrodes with an Iridium-Based Catalyst

The iridium complex [Cp*Ir(H2O)3](SO4) was used as an organometallic source for the electrodeposition of iridium oxide onto Fe2O3. The new iridium-containing electrode allowed us to study the coupling between the photocatalytic properties of hematite and the electrocatalytic properties of the iridium-based material. A cathodic shift of the photocurrent for water oxidation upon electrodeposition of the iridium complex was observed, which increased with increasing surface concentration of IrOx on Fe2O3. The shift for the highest surface concentration of iridium tested amounts to 300 mV at 200 μA·cm–2 current density. The catalytic mechanism of the IrOx layer was unveiled by impedance spectroscopy measurements fitted to a physical model and can be explained on the basis of a highly capacitive layer, which enhances charge separation and stores photogenerated holes at Fe2O3, subsequently oxidizing water. These findings improve our understanding of the mechanism of water oxidation by heterogeneous Ir-based cata...

A coarse-grained model for polyethylene glycol in bulk water and at a water/air interface

A coarse-grained model for polyethylene glycol (PEG) in water has been developed using a combination of the iterative Boltzmann inversion (IBI) methodology and a suitable coarse-grained water potential. The combined coarse-grained model is shown to be effective in reproducing the properties of single chains in bulk water and multiple chains across a series of chain lengths and concentrations, and is transferable to PEG chains at a water/air interface. Good agreement is achieved with both experiment and reference atomistic simulations in an explicit solvent. Simulations of a single chain in aqueous solution yield a molecular weight (MW)-radius of gyration (Rg) relation that compares favourably with the reported scaling law from experiment. Simulations of multiple chains across a wide concentration range show no concentration dependence of Rg, in agreement with previous atomistic simulations. The model we develop is shown to be transferable between polymer in bulk water and at a water/air interface. For interfacial simulations, PEG chains are found to spontaneously migrate to the surface and adsorb to form a thin surface layer, which thickens with increasing surface concentration. The point at which the surface is fully saturated with polymer, and the polymer layer thicknesses obtained from simulations, are both in good agreement with experimental findings. At high surface concentrations, when the surface is fully saturated with polymer, ethylene oxide (EO) segments are found to extend into the water subphase as loop and tail conformations, with this extension increasing with further increases in the surface concentration. The coarse-grained model is noted to provide very large increases in simulation speed, with equilibration times of <1000× the reference atomistic models. We also consider a number of different coarse-grained models for water in this study, showing that the CSJ model adopted in this work [Chiu et al., J. Chem. Theory Comput., 2010, 6, 851] is far superior for studying water at a water/air surface, than many of the previous coarse-grained models of water.

IBS, NERD and functional dyspepsia are immuno–neuronal disorders of mucosal cytokine imbalances clinically reversible with high potency sucralfate

Irritable bowel syndrome (IBS), non-erosive reflux disorder (NERD), and functional dyspepsia (FD) are best classified as immuno–neuronal disorders of the mucosa or functional mucosal syndromes (FMS). Each appears to be clinically reversible using high potency sucralfate (HPS). In FMS of the GI tract, postprandial nausea, altered motility, discordant peristalsis, vomiting, diarrhea, and hyperalgesia are the clinical expressions of a mucosal imbalance between pro-inflammatory cytokines of up-regulated intra-epithelial lymphocytes (IELs) and feedback anti-inflammatory cytokines tasked with moderating the antigenic response of IELs. Normal functioning GI tract requires an operative balance between pro-inflammatory and anti-inflammatrory cytokines, a balance governed by locally expressed growth factors. The surface concentration of sucralfate can be enhanced 7–23-fold by suspending it in a select concentration of cations and multi-dentate cationic chelators. Increased surface concentration of sucralfate facilitates novel dose effects which include efficient activation of growth factors, quiescence of gated-nociceptor firing and resultant restoration of normal GI function.

Adsorption and diffusion of strontium in simulated rock fractures quantified via ion beam analysis

AbstractAn experimental technique has been developed and applied to the problem of determining effective diffusion coefficients and partition coefficients of Sr in low permeability geological materials. This technique, the micro-reactor simulated channel method (MRSC), allows rapid determination of contaminant transport parameters with resulting values comparable to those determined by more traditional methods and also creates product surfaces that are amenable for direct chemical analysis. An attempt to further constrain mass flux was completed by detailed ion beam analysis of polished tuff surfaces (tuff is a polycrystalline polyminerallic aggregate dominated by silicate phases) that had been reacted with Sr solutions at concentrations of 10−5, 10−3 and 10−1 mol l−1. Ion beam analysis was carried out using beams of both protons (using particle induced X-ray emission and elastic backscattering spectrometry or EBS) and alpha-particles (using Rutherford backscattering spectrometry). The ion beam analyses showed that increased solution concentrations resulted in increased surface concentrations and that in the highest concentration experiment, Sr penetrated to at least 4 μm below the primary interface. The Sr surface concentrations determined by EBS were 0.06 (±0.05), 0.87 (±0.30) and 2.40 (±1.0) atomic weight % in the experiments with starting solution concentrations of 10−5, 10−3, and 10−1 mol l−1, respectively.

Increase of secondary electron yield of amorphous carbon coatings under high vacuum conditions

Electron cloud (e-cloud) is one of the major limitations for beam quality in modern particle accelerators. The macroscopic property which governs this phenomenon is the secondary electron yield (SEY) of a surface, defined as the number of emitted electrons per incident electron. SEY of inner surface walls must be less than 1.3 to prevent the formation of an e-cloud. Although most pure metals possess an SEY within this range, technical surfaces (i.e. those resulting from the necessary machining to produce vacuum parts) typically display much higher SEY. An elegant and effective solution to this problem is to deposit the carbon coating on these surfaces by magnetron sputtering. However, the first measurements performed at CERN revealed an increase of the SEY as a function of long term air exposure. Furthermore, we observed a rapid increase of the SEY of these samples whilst under high vacuum conditions. In order to determine the contaminant responsible for the observed ageing, as well as the ageing mechanism, the samples were exposed to various gases and vapours such as water vapour, H2, rotary pump oil vapour, etc. The results confirm that the vapour of rotary pump oils is responsible for exceptionally fast sample ageing. We also observed that high SEY samples usually have an increased surface concentration of oxygen. The possible ageing mechanisms are discussed.

Self-segregating hyperbranched polymer/silver nanoparticle hybrids in thermoplastic polyurethane films

Self-segregating hyperbranched polymer (HBP) additives have been utilized to concentrate silver nanoparticles (AgNPs) at the air interface of polyurethane films. The limited spontaneous surface migration of the AgNPs was enhanced through the addition of appropriately functionalized HBPs. Both amine and thiol terminated additives were employed to allow interaction of the HBP with the nanoparticles. Both types of additives increased surface concentration of silver modestly, though the thiol-terminated HBPs demonstrated nearly a seven-fold enhancement of surface migration. It was also found that wholly-aliphatic HBPs demonstrated only slightly reduced ability to bias AgNP concentration as compared to HBPs functionalized with perfluorinated chains. In addition, films containing 1% total silver concentration were tested for antimicrobial activity using the ASTM-E 2180 protocol. Significant reduction of the microorganisms was observed for all samples, 6-log reduction was achieved for the gram-negative bacteria P. aeruginosa, the gram-positive bacteria S. aureus, and the fungi C. albicans. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

Hydrogen Permeation and Corrosion Fatigue Crack Growth Rates of X65 Pipeline Steel Exposed to Acid Brines Containing Thiosulfate or Hydrogen Sulfide

Corrosion fatigue crack growth rates were obtained for X65 pipeline steel in acid brines containing thiosulfate (S2O32−) or hydrogen sulfide (H2S). Samples were exposed for 72 h at the open-circuit potential to allow bulk hydrogen charging. The corrosion fatigue crack growth rate increased with partial pressure of H2S and correlated with the steady-state flux of hydrogen permeation during corrosion in the same solutions. The rate of hydrogen absorption increased with increasing S2O32− concentration to a maximum at 10−3 M S2O32−, owing to a competition between increased surface concentration of H2S from S2O32− reduction and increased rate of iron sulfide film formation. Corrosion fatigue behavior in S2O32−-containing acidified brines is the same as in solutions with low partial pressures of H2S, in accordance with predictions from the hydrogen permeation results. This suggests that, for corrosion fatigue studies, S2O32− solutions are possible candidates for replacement of H2S gas, as long as the H2S partial pressure of interest is low. Also, the expected concentration of hydrogen inside the metal specimen at the end of the exposure period correlates with the rate of corrosion fatigue crack growth, suggesting that hydrogen charged during the pre-charging period controls corrosion fatigue crack growth.

Aluminum oxide and systems based on it: Properties and applications

The metastable forms of aluminum oxide that exist in the range of 300–800°C are characterized; differences in the microstructures of homogeneous γ-, η-, and χ-Al2O3 are demonstrated; and the acid-base properties of the above modifications are compared. The catalytic properties of aluminum oxide in ethanol dehydration and propionitrile ammonolysis were studied. It was found that an increased surface concentration of Lewis acid sites, including strong acid sites (ν(CO) = 2237 cm−1), is required for preparing an effective catalyst for the dehydration of ethanol, whereas the rate of propionitrile conversion increased proportionally to the surface concentration of Bronsted acid sites. γ-Aluminum oxide was used to prepare catalysts for carbon monoxide oxidation. It was found that the supporting of Pd on γ-Al2O3 did not change the support structure. Palladium on the surface of γ-Al2O3-550 (Tcalcin = 550°C, SBET = 300 m2/g) occurred as single particles (2–3 nm) and aggregates (∼100 nm). The single particles were almost completely covered with a layer of aluminum oxide to form core-shell structures. According to XPS data, they were in atypical states (BE(Pd 3d5/2) = 336.0 and 338.0 eV), which were not reduced by hydrogen in the range of 15–450°C and were resistant to the action of the reaction mixture. Palladium on the surface of γ-Al2O3-800 (SBET = 160 m2/g) was in the states Pd0 and PdO, which are typical of Pd/Al2O3, and the proportions of these states can change under the action of the reaction mixture. An increase in the Tcalcin of the Pd/Al2O3(800)-450 catalyst from 450 to 800 → 1000 → 1200°C led to the agglomeration of palladium particles and to an increase in the temperature of 50% CO conversion from 145 to 152 → 169 → 189°C, respectively. α-Aluminum oxide was used in the preparation of an effective Mn-Bi-O/α-Al2O3 supported catalyst for the synthesis of nitrous oxide by the oxidation of ammonia with oxygen: the NH3 conversion was 95–97% at 84.4% N2O selectivity.

Electrochemical immunosensor for label free epidermal growth factor receptor (EGFR) detection

This paper presents an electrochemical immune sensor for label free detection of epidermal growth factor receptor (EGFR) by immobilizing anti-EGFR antibody (Anti-EGFRab) on dithiobissuccinimidyl propionate (DTSP) self-assembled monolayer (SAM) on gold (Au) electrode. Electrochemical studies show that increased surface concentration of redox moieties onto Anti-EGFRab/DTSP immuno-electrode leads to high electron transport and improved sensing performance. The antigen–antibody complex demonstrates a high association constant (5×1012L/mol) that results in high affinity of Anti-EGFRab to EGFR, confirming that the DTSP–SAM provides a conducive environment for anti-EGFR immobilization. The electrochemical response of EA/Anti-EGFRab/DTSP/Au electrode as a function of EGFR concentrations exhibits a linear range from 1pg/mL to 100ng/mL, a detection limit of 1pg/mL at a sensitivity of 2.02μAM−1at a regression coefficient of 0.99.

Controls on dissolved cobalt in surface waters of the Sargasso Sea: Comparisons with iron and aluminum

Dissolved cobalt (dCo), iron (dFe) and aluminum (dAl) were determined in water column samples along a meridional transect (∼31°N to 24°N) south of Bermuda in June 2008. A general north‐to‐south increase in surface concentrations of dFe (0.3–1.6 nM) and dAl (14–42 nM) was observed, suggesting that aerosol deposition is a significant source of dFe and dAl, whereas no clear trend was observed for near‐surface dCo concentrations. Shipboard aerosol samples indicate fractional solubility values of 8–100% for aerosol Co, which are significantly higher than corresponding estimates of the solubility of aerosol Fe (0.44–45%). Hydrographic observations and analysis of time series rain samples from Bermuda indicate that wet deposition accounts for most (&gt;80%) of the total aeolian flux of Co, and hence a significant proportion of the atmospheric input of dCo to our study region. Our aerosol data imply that the atmospheric input of dCo to the Sargasso Sea is modest, although this flux may be more significant in late summer. The water column dCo profiles reveal a vertical distribution that predominantly reflects ‘nutrient‐type’ behavior, versus scavenged‐type behavior for dAl, and a hybrid of nutrient‐ and scavenged‐type behavior for dFe. Mesoscale eddies also appear to impact on the vertical distribution of dCo. The effects of biological removal of dCo from the upper water column were apparent as pronounced sub‐surface minima (21 ± 4 pM dCo), coincident with maxima in Prochlorococcus abundance. These observations imply that Prochlorococcus plays a major role in removing dCo from the euphotic zone, and that the availability of dCo may regulate Prochlorococcus growth in the Sargasso Sea.