1,721,018 research outputs found
Nucleation and Growth of Copper particles on Pt and Pt/Poly-3-Methylthiophene Modified Electrode in Presence of Cl- Complexing Agent
No full textThe kinetics of electrochemical deposition of copper particles from Cu2+ solution on platinum and poly-3-
methylthiophene modified platinum electrode was studied in potentiostatic conditions in presence of Cl−
anions. The complex behavior of current transients suggests that the deposition process involves several
stages with different kinetics. Results obtained on platinum show that after an initial adsorption process,
the copper deposition is accomplished through two different models: a three-dimensional nucleation
and growth under diffusive control (3DPD model) and a progressive nucleation and two-dimensional
growth (2DP model). The analysis of current transients recorded on platinum poly-3-methylthiophene
modified electrode (Pt/PMT) shows a very different behavior. On Pt modified electrode a process of growth
related to a semi-infinite diffusion to a planar surface was accompanied by two different mechanisms
of nucleation and growth: a three-dimensional nucleation and growth with no diffusive control (3DP
model) and an instantaneous nucleation with two-dimensional growth (2DP model)
ELECTROCHEMICAL PREPARATION OF A COMPOSITE GOLD-COBALT ELECTRODE AND ITS ELECTROCATALYTIC ACTIVITY IN ALKALINE MEDIUM.
No full textA chemically modified electrode composed of cobalt(III) oxyhydroxide film dispersed on the gold substrate (Au-Co) was characterised by cyclic voltammetry. Electrochemical deposition of the cobalt film was accomplished by cycling the potential between 0.0 V and 1.1 V (vs. saturated calomel electrode (SCE)) in 0.1 M acetate solution (at pH 7.3) containing 10 mM CoCl2. The effects of several experimental parameters (pH, applied potentials, etc.) on the film formation and growth were evaluated. The electrochemical behaviour of the Au-Co composite electrode was investigated in alkaline medium. The film appears uniform and compact and shows good electrical conductivity and electrochemical activity towards the oxidation of several scarcely electroactive organic molecules. The concomitant presence on the electrode surface of both active catalysts leads to a wide range of potential applications where a significant electrochemical activity towards the electrooxidation of several classes of organic compounds is observed. (C) 1999 Elsevier Science Ltd. All rights reserved.
Accession Number: WOS
ANODIC ELECTRODEPOSITION OF CONDUCTING COBALT OXYHYDROXIDE FILMS ON A GOLD SURFACE. XPS STUDY AND ELECTROCHEMICAL BEHAVIOUR IN NEUTRAL AND ALKALINE SOLUTION.
No full textA novel chemically modified electrode prepared by anodic electrodeposition of cobalt (III) film on the gold electrode substrate (Au-Co) was characterised by cyclic voltammetry and XPS techniques in both neutral and alkaline medium. Cobalt oxyhydroxide film was deposited by cycling the potential between 0.0 and 1.1 V versus SCE in 0.1 M sodium acetate solutions containing 10 mM CoCl2. The electrocatalytic properties of the Au-Co electrode were investigated in alkaline medium using glucose as a model compound. A comparative XPS study of bare gold, bare cobalt and Au-Co electrodes after electrochemical treatment in neutral and alkaline solutions has been carried out. A detailed XPS analysis of the Au4f(7.2), Co2p(3.2), O1s and C1s regions was performed to check the chemical composition of the Au-Co electrode upon electrochemical treatments. Film deposition is attributed to growth of conducting and compact CoOOH oxyhydroxide with significant insertion of carbonyl groups within the electrodeposited layer. The prolonged electrochemical treatment in alkaline medium produces a good stabilization of the Co-III oxyhydroxide film, with a dominant O1s feature at about 532.4 eV of BE corresponding to a non-stoichiometric surface oxygen. The absence of CoO species proves good conducting properties of the cobalt film and the absence of any passivation effects on the catalytic performance
ELECTROCATALYSIS OF ASCORBIC ACID ON THE GLASSY CARBON ELECTRODE CHEMICALLY MODIFIED WITH POLYANILINE FILMS.
No full textChemically modified electrodes prepared by electropolymerization of aniline on glassy carbon electrodes, exhibited good electrocatalytic properties towards ascorbic acid oxidation. The electrocatalytic response was evaluated by cyclic voltammetry with regard to pH, Blm thickness, ascorbic acid concentration, scan rate, electrolyte composition, rotation speeds of the electrode, and other variables. The location of the reactions taking place was discussed with experimental evidence that the cross-exchange reaction is the rate-determining step. Experiments in flowing streams were performed to characterize the electrode as an amperometric sensor for the determination of ascorbic acid. The electrode stability, precision, limit of detection and linear range were evaluated at a constant potential of 0.350 V (vs. Ag/AgCl). The limit of detection was 1.0 mu M (i.e., 1.76 ng injected), and the calibration plot was linear in the range 1.0 mu M-0.7 mM (correlation coefficient 0.999). The resulting modified electrode was found to retain 80 % of its initial response in flowing streams for 8 h of operating time
Chemical characterization of red cells from the black sea urchinArbacia lixulaby X-ray photoelectron spectroscopy
No full textRed spherula cells (RSC) from sea urchin coelomic fluid have attracted great interest for their specific and intriguing properties, such as for example antimicrobial activities and immune response, that probably tie in with their red characteristic pigments. Although to date different studies have been reported aimed to chemically characterize their pigments extracted from the cells, few data are available about the chemical characterization of the cell surface. In this work, a systematic chemical characterization of the RSC surface by X-ray photoelectron spectroscopy (XPS) analysis is described. The results were compared with data on colorless cells from the same coelomic fluid sample. Our observations evidenced that the two cell types were characterized by the presence of different chemical functional groups. In particular, the colorless cells are dominated by the presence of alkyl, alcohol, amide, and carboxyl groups in accordance with other similar cell types, enriched in Na+and Cl−ions. Traces of elements like S (sulphonates) and P (phosphates) are also present. On the other hand, the RSC in addition to the alkyl groups show a reduction in the content of amide groups, accompanied by the anomalous presence of keto-enolic groups that probably can be associated with the presence of quinones/hydro-quinones from red pigments. A chemical enrichment in elements such as Cl−and Mg2+and sulphate groups (-R-O-SO3−), as well as the presence of sulphides and phosphates traces, is evident. The absence of carbonate groups is also observed in both cell populations, confirming the absence of sodium and magnesium carbonate salts. No traces of toxic elements (i.e., heavy metals) have been revealed
Oxidative potential of atmospheric aerosols
Full text linkAtmospheric particulate matter (PM) is one of the leading health risks worldwide [1,2].
Several epidemiological studies have provided evidence of the association between exposure
to PM and the onset of cardiovascular and respiratory diseases [3], as well as
cardiopulmonary diseases and other adverse health effects [4]. The exact mechanisms leading
to PM toxicity are not fully known, however, several studies suggest that the generation
of reactive oxygen species (ROS) could be a major mechanism by which PM leads to both
chronic and acute adverse health effects [5,6]. For this reason, in recent years, the oxidative
potential (OP) of PM, defined as its ability to generate oxidative stress in biological systems,
has been proposed as a relevant metric for addressing PM exposure [7,8]. However, the
link between OP and adverse health effects is still uncertain [9–11], and contrasting results
have been obtained when PM oxidative potential has been compared with the results of
in-vivo and in-vitro toxicological tests or the outcomes of epidemiological studies [12].
The OP can be evaluated through several in vitro assays, but protocols employing
chemical (acellular) assays have become common as well. Acellular assays can be useful for
investigating the PM properties which are responsible for oxidative stress: ROS compounds
can either be carried by components of the aerosol itself (particle-bound ROS) or induced
by the catalytic activity exerted by aerosol constituents (PM-induced ROS). The diverse
OP assays developed so far have certainly improved our knowledge of the mechanisms
underlying PM oxidative stress. At the same time, they pose the issue of comparability
between the different assays and protocols, as well as problems surrounding the actual
correlation between acellular OP and in vitro (or in vivo) toxicity. Measurements of PM
oxidative potential are influenced by the chemical composition of the aerosol, by its size
distribution, and by the weight of different natural and anthropogenic sources of PM
leading to temporal and spatial variabilities that need investigation in current research.
Moreover, recent studies show that photochemical aging increases the oxidative potential
of atmospheric aerosols. However, several aspects regarding the specific chemical species,
aerosol sources, and atmospheric processes that affect OP are not well established, and
further research is needed [13–15]. Another topic that needs extensive research is the
characterization of the OP of indoor aerosols.
This special issue includes five research papers and two review papers discussing
recent advances in the studies of the oxidative potential of atmospheric particulate matter
ELECTROCATALYSIS AND AMPEROMETRIC DETECTION OF ALDITOLS AND SUGARS AT A GOLD-NICKEL COMPOSITE ELECTRODE IN ANION-EXCHANGE CHROMATOGRAPHY.
No full textA novel Au-Ni composite electrode prepared by cathodic precipitation/deposition of nickel hydroxide on the gold surface was characterised. The resulting composite electrode was evaluated as an amperometric sensor in flow injection analysis and anion-exchange chromatography for the quantitation of alditols and simple carbohydrates. Constant potential detection at +0.6V vs Ag/AgCl and a pulsed detection mode were employed, and their applicability and usefulness discussed. The detection Limits (S/N = 3) for all investigated compounds, in both modes of detection, ranged between 1.5 and 7.5 pmol injected. Linear dynamic ranges spanned over four and three orders of magnitude when the composite electrode was used in the DC or pulsed mode. The main advantage of the Au-Ni composite electrode is that detection selectivity can be tailored by the choice of the detection mode and by the polarisation potential. As an example, we show how to detect common carbohydrates in tea powder using the constant potential detection mode
VOLTAMMETRIC AND XPS INVESTIGATION OF NICKEL HYDROXIDE ELECTROCHEMICALLY DISPERSED ON GOLD SURFACE ELECTRODES.
No full textA chemically modified electrode composed of mixed hydroxide and oxyhydroxide nickel film (6-8 nmol cm(-2)) on the gold substrate (Au \ Ni) was characterized by cyclic voltammetry and XPS techniques. The gold substrate electrodes were firstly electrochemically conditioned in 0.2 M NaOH by cycling the potential between -0.25 and 0.6 V versus SCE, then modified by cathodic electrodeposition of nickel hydroxide films. These nickel films were obtained either by voltage cycling (50 mV s(-1)) between 0.0 and -0.5 V (SCE) or at constant potential of -0.3 or -0.5 V using non-deaerated 50 mM Ni(NO3)(2) solutions. X-ray photoelectron spectroscopy (XPS) characterisation and voltammetric behaviour of Au \ Ni electrodes in alkaline solutions are described. Continuous electrochemical cycling of the Au \ Ni electrodes induces significant changes of the nickel films in terms of crystallographic structures and chemical composition. Combination of XPS and electrochemical methodologies have demonstrated the ability to follow the morphological and chemical changes in alkaline solutions upon cycling potentials. Angular-dependent XPS measurements have demonstrated that electrochemical treatment induces the formation of a uniform film layer with the following chemical distribution: Au \ Ni(OH)(2) \ NiOOH. The electrocatalytic activity of the Au \ Ni electrodes is investigated in alkaline medium using glucose as a model compound. The favourable combination of active species such as gold and nickel leads to a sensing electrode with strong catalytic activity over a wide range of applied potentials
ELECTROOXIDATION OF THIOCYANATE ON THE COPPER-MODIFIED GOLD ELECTRODE AND ITS AMPEROMETRIC DETERMINATION BY ION CHROMATOGRAPHY
No full textCyclic voltammetry was used to investigate the electrochemical behavior of an Au/Cu electrode towards the electrooxidation of thiocyanate ion in alkaline medium, The effects of pH, copper loading, scan rate and applied potential on the electrocatalytic oxidation of thiocyanate have been investigated. Flow injection experiments and ion-chromatography (IC) were performed to characterise the electrode as an amperometric sensor for the thiocyanate determination. The effects of carbonate concentration and common interferents on the retention time were also estimated, The electrode stability, precision, limit of detection and linear range were evaluated at a constant applied potential of 0.7 V vs. Ag/AgCl. Calibration plots, obtained in IC, were linear from 1.0 to 195 mu M (correlation coefficient of 0.9984), The detection limit (LOD) was 0.5 mu M (29 ppb) in a 50 mu l injection. An example of analytical application, which includes the IC separation and detection of thiocyanate ion present in human urine, is given.
Accession Number: WO
Surface characterization of ancient pottery by X-Ray Phptoelectron Spectroscopy. Part II. Analysis of a red-coloured pigment
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