Catherine Debiemme-Chouvy

Antimicrobial N-halamine polymers and coatings: a review of their synthesis, characterization, and applications.

Antimicrobial N-halamine polymers and coatings have been studied extensively over the past decade thanks to their numerous qualities such as effectiveness toward a broad spectrum of microorganisms, long-term stability, regenerability, safety to humans and environment and low cost. In this review, recent developments are described by emphasizing the synthesis of polymers and/or coatings having N-halamine moieties. Actually, three main approaches of preparation are given in detail: polymerization, generation by electrochemical route with proteins as monomers and grafting with precursor monomers. Identification and characterization of the formation of the N-halamine bonds (>N-X with X = Cl or Br or I) by physical techniques such as Fourier transform infrared spectroscopy (FTIR), nuclear magnetic resonance spectroscopy (NMR), energy-dispersive X-ray spectroscopy (EDX), X-ray photoelectron spectroscopy (XPS), and by chemical reactions are described. In order to check the antimicrobial activity of the N-halamine compounds, bacterial tests are also described. Finally, some examples of application of these N-halamines in the water treatment, paints, healthcare equipment, and textile industries are presented and discussed.

Amorphous carbon nitride as an alternative electrode material in electroanalysis: Simultaneous determination of dopamine and ascorbic acid

Boron-doped diamond (BDD) films are excellent electrode materials, whose electrochemical activity for some analytes can be tuned by controlling their surface termination, most commonly either to predominantly hydrogen or oxygen. This tuning can be accomplished by e.g. suitable cathodic or anodic electrochemical pretreatments. Recently, it has been shown that amorphous carbon nitride (a-CNx) films may present electrochemical characteristics similar to those of BDD, including the influence of surface termination on their electrochemical activity toward some analytes. In this work, we report for the first time a complete electroanalytical method using an a-CNx electrode. Thus, an a-CNx film deposited on a stainless steel foil by DC magnetron sputtering is proposed as an alternative electrode for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) in synthetic biological samples by square-wave voltammetry. The obtained results are compared with those attained using a BDD electrode. For both electrodes, a same anodic pretreatment in 0.1 mol L(-1) KOH was necessary to attain an adequate and equivalent separation of the DA and AA oxidation potential peaks of about 330 mV. The detection limits obtained for the simultaneous determination of these analytes using the a-CNx electrode were 0.0656 μmol L(-1) for DA and 1.05 μmol L(-1) for AA, whereas with the BDD electrode these values were 0.283 μmol L(-1) and 0.968 μmol L(-1), respectively. Furthermore, the results obtained in the analysis of the analytes in synthetic biological samples were satisfactory, attesting the potential application of the a-CNx electrode in electroanalysis.

A very thin overoxidized polypyrrole membrane as coating for fast time response and selective H2O2 amperometric sensor

Pyrrole electrooxidation in the presence of weak-acidic anions allows one to locally, rapidly and in single step form on the electrode a pinhole-free very thin layer of overoxidized polypyrrole (OPPy). This membrane could be really useful for the design of amperometric biosensor based on oxidation of H(2)O(2) generated by an oxidase. Indeed, using rotation disk electrode, the apparent diffusion coefficient of H(2)O(2) within this OPPy film was found to be 10(-8)cm(2)s(-1), which corresponds to a fast response time of 0.1 ms. Moreover, it is shown that with this system, platinum electrode coated with the very thin OPPy membrane, the H(2)O(2) sensitivity is excellent (700 nA microM(-1)cm(-2)) and the H(2)O(2) selectivity relative to potentially interfering species present in biological fluids, such as ascorbate and dopamine, is very good. Thus, this OPPy membrane which can be locally electrodeposited is ideal for the construction of oxidase-based microbiosensors.

Nanocomposite systems based on gold nanoparticles and thiometalates. From colloids to networks

A new nanocomposite system based on gold nanoparticles and thiometalates is described. According to the metalate species, WS42¬ or WS2O22¬, and to the experimental conditions, two sizes of particles are obtained (d = 2 or 5 nm). These particles lead either to stable colloidal solutions or irreversible micrometric spherical aggregates of nanoparticles cemented by WS42¬. Energy dispersive spectrometry (EDS), transmission electron microscopy (TEM), scanning electron microscopy (SEM), UV-vis spectroscopy and X-ray photoelectron spectroscopy (XPS) have been used to fully characterize the different composite systems.

Contribution to the understanding of the CdTe and Cd1-yZnyTe surface chemistry

Abstract X-ray photoelectron spectroscopy (XPS) and X-ray Auger electron spectroscopy (X-AES) measurements coupled with electrochemical characterizations are used to study the chemical surface modifications of CdTe (or CZT) immersed in acidic and basic solutions. Te- or Cd-enriched surfaces are obtained depending on the nature of the oxidation bath.

One-Step Electrochemical Synthesis of a Very Thin Overoxidized Polypyrrole Film

Generally, the electrochemical oxidation of pyrrole results in polypyrrole film in its doped conducting form. In this paper, it is shown that, in the presence of weak-acidic anions, pyrrole electro-oxidation leads to the formation of a very thin nonconducting overoxidized polypyrrole film. This phenomenon is due to the release of protons at the electrode/electrolyte interface during pyrrole oxidation. XPS analyses confirm (i) the film does not contain doping anions and (ii) the presence of carbonyl bonds; both features are characteristic of overoxidized polypyrrole.

Templateless electrogeneration of polypyrrole nanostructures: impact of the anionic composition and pH of the monomer solution

Different superhydrophilic polypyrrole nanostructures can be electrosynthezised in the presence of anions of weak acid (monohydrogenophosphate) and non-acidic anions (perchlorate) without the need for templates. Actually the type of nanostructures formed depends both on the concentration of anions at the electrode and on the interfacial pH. Depending on the anion composition of the pyrrole aqueous solution the film electrogenerated under a given applied potential is either a very thin membrane (10–20 nm) consisting of overoxidized polypyrrole or a tridimensional film with oriented nanowire array or a network of more or less interconnected nanofibers. The formation of such nanostructures is explained by a side reaction which is water oxidation. Since this reaction is pH-dependent, the pH of the pyrrole solution is one of the key parameter for the synthesis of such nanostructures. The reaction mechanism is discussed and compared to those proposed in the literature for nanofiber network electrosynthesis. Actually in the monomer solution, the role of the anions of weak acid is twofold. On the one hand they allow to limit the decrease of the interfacial pH during pyrrole oxidation and on the other hand to decrease the interfacial anion concentration, so that water oxidation takes place with formation of hydroxyl radicals and dioxygen nanobubbles.

Determination of the diffusion coefficient of protons in Nafion thin films by ac-electrogravimetry.

This letter deals with an adaptation of the ac-electrogravimetry technique to extract separately the dynamic properties of H(+) and water in Nafion nanometric thin films (average thickness of 400 nm). An original theoretical approach was developed to extract the representative parameters from ac-electrogravimetry data. The concentration change of the exchanged species and the diffusion coefficient of the protons in a Nafion nanometric thin film (D = 0.5 × 10(-6) cm(2) s(-1) at 0.3 V vs SCE) were estimated for the first time according to the applied potential. The conductivity value of Nafion thin films was calculated from the Nernst-Einstein equation using diffusion coefficients and concentration values extracted from ac-electrogravimetry data. The calculated conductivity results agree well with the experimental proton conductivity values of Nafion thin films.

Local oxide growth on the n-GaAs surface studied by small area XPS

The photoanodic dissolution of n-GaAs was investigated in a buffered solution at an intermediate pH (pH 9). At this pH, the GaAs dissolution rate was limited by the growth of an anodic oxide film. A laser illumination leads to a local oxide growth only in the illuminated part on to GaAs. Transient photocurrent and capacitance measurements clearly show dissolution kinetics in two steps: the first step is about a few tens of seconds and is correlated with gallium oxide dissolution, and the second step is greater than a few minutes, indicating the origin of at least two surface films onto GaAs. A parallel approach using in-situ electrochemistry and ex-situ surface analysis (XPS) was performed to characterise the growth of an anodic film on to GaAs. A gallium enrichment was detected on this oxide film. The arsenic deficiency in this oxide results from a higher arsenic oxide solubility. The limitation of the GaAs dissolution is due to the dissolution of gallium oxide at pH 9.

X‐ray photoelectron spectroscopy study of GaAs surface exposed to a rf hydrogen plasma

Using x‐ray photoelectron spectroscopy analysis, it is shown that hydrogen plasma treatment of the gallium arsenide surface induces a modification of the superficial stoichiometry. The resulting surface composition presents a gallium enrichment and is the same whatever the initial composition. The departure from the stoichiometry increases with the plasma power. After the plasma treatment, the absence of arsenic oxidation and an abnormal gallium suboxidation state is observed. Moreover, these new gallium and arsenic oxidation states are stable when the sample is left in the air.