New insight into 4-nitrobenzene diazonium reduction process: Evidence for a grafting step distinct from NO2 electrochemical reactivity

Electrochemical and spectroscopic investigations were performed in order to clarify the mechanism of 4-nitrobenzene diazonium reduction on glassy carbon in protic medium. The number and nature of the electron transfer processes were found to be strongly correlated to the electrode surface state. On polished electrode two different reduction peaks were observed. Selective electrolyses realized at the corresponding potential definitely proved that the grafting process actually occurs at a potential distinct from NO2 electroreduction, this latter inducing the presence of the quasi-reversible NO/NHOH redox couple at the electrode surface. These results were confirmed by XPS analyses. Furthermore, voltammetric experiments using Fe(CN)63- showed that the electrochemical properties of the modified electrode strongly depend on the potential applied for grafting, which modulates the nitro group oxidation state. All the results suggested that the electrode functionalization was more efficient when grafting and NO2 reduction were performed separately

Evidence of an EC' mechanism occurring during the simultaneous assay of ascorbic and uric acids on poly(3,4-ethylenedioxythiophene) modified gold microsensor.

A voltammetric microsensor has been developed for the simultaneous assay of ascorbic (AA) and uric (UA) acids in aq. soln. The electrode surface has been modified by means of electropolymd. conductive poly(3,4-ethylenedioxythiophene) (PEDOT) org. films. The anodic peak potential sepn. between both acids was more than 300 mV. The sensitivity of the microsensor for UA was found to be dependent on the presence of AA in the mixt. By using square wave voltammetry (SWV), it increased from 77.5 mA mM-1 cm-2 without AA to 86.2 mA mM-1 cm-2 with AA 1 mM. An EC' catalytic mechanism was highlighted, inducing the regeneration of reduced UA by AA at the vicinity of the electrode surface

Rattraper ou devancer l’Europe? Politiques françaises des énergies renouvelables et dynamiques d’européanisation

La France a échoué de façon répétée à atteindre ses objectifs européens en matière de consommation d’électricité d’origine renouvelable. Quant au rapide développement des agrocarburants, il tient d’abord au poids et à l’influence du secteur agricole domestique. Cela ne signifie pas pour autant que la construction européenne a été sans influence sur les politiques françaises de soutien aux énergies renouvelables, mais pas nécessairement sur un mode hiérarchique. Afin de rendre compte des interactions entre politiques françaises et européennes, cet article s’inscrit dans une approche de sociologie politique attentive à la diversité des pratiques et « usages de l’Europe », en explorant les dynamiques verticales et horizontales de l’européanisation. France has repeatedly failed to reach its European objectives in terms of renewable electricity consumption. As for the rapid growth of biofuels, it results mainly from the weight and influence of the domestic agriculture sector. Yet, this does not mean that the European integration process has had no influence on French renewable energy policies, although not necessarily in a top-down fashion. In order to account for the interactions between French and European policies, this paper develops an approach centered on the practices and usages of Europe, and explores vertical and horizontal dynamics of Europeanization

Hg(II) trace electrochemical detection on gold electrode: Evidence for chloride adsorption as the responsible for the broad baseline

Investigations were performed in order to clarify the origin of the broad baseline observed during Hg(II) trace electrochemical detection on gold electrode in the presence of Cl- anions. The influence of Cl- concentration on the shape of the voltammograms was studied in the presence and in the absence of Bovine Serum Albumin (BSA) in order to bring out adsorption/desorption processes. On the basis of these experiments, and contrary to what has been proposed by several authors in the literature, it was proved that the broad baseline does not result from calomel (Hg2Cl2) formation but is rather related to an interaction between Cl- and polycrystalline Au electrode surface. The evolution of the shape of the baseline was also studied in the presence of other halide anions, namely F-, Br-, and I-. The latter two were found to induce a broad baseline similar to that recorded in the presence of Cl-. Finally, it was shown that BSA addition is not suitable for Hg(II) detection since it prevents Hg(0) deposition onto the electrode surface

Influence of the gold nanoparticles electrodeposition method on Hg(II) trace electrochemical detection

Gold nanoparticles (AuNPs) were deposited on Glassy Carbon (GC) substrate by using three electrochemical techniques: Cyclic Voltammetry (CV), Chronoamperometry (CA) and Potentiostatic Double-Pulse (PDP). For each electrodeposition method, the resulting AuNPs-modified electrodes were characterized by CV in H2SO4 and Field Emission Gun Scanning Electron Microscopy (FEG-SEM). CA was found to be the best electrodeposition mode for controlling the morphology and the density of AuNPs. The modified electrodes were used for low Hg(II) concentration detection using Square Wave Anodic Stripping Voltammetry (SWASV). AuNPs obtained by CA afforded the best amperometric response while involving the lowest amount of charge during the electrodeposition step (QAu(III)). This analytical response is correlated to both the smallest particle size (ca. 17 nm in diameter) and the highest particle density (332 particles μm−2), thus displaying high electrode effective surface area. In these optimal conditions, using a Hg(II) preconcentration time of 300 s, the nanosensor array exhibited a linearity range from 0.80 to 9.9 nM with a sensitivity of 1.16 μA nM−1. A detection limit of 0.40 nM (s/n = 3) was reached

Aproximació a la definició de Cinema negre (VII)

Abstract not availabl

Electrodeposited gold nanoparticles on glassy carbon: Correlation between nanoparticles characteristics and oxygen reduction kinetics in neutral media

Gold nanoparticles (AuNPs) were deposited onto glassy carbon (GC) by constant potential electrolysis (CPE) using various sets of potential and duration from -0.3 to 0.7 V and 10 to 1800 s, respectively. The physico-chemical characteristics of the as-obtained deposits were investigated by cyclic voltammetry (CV) in H2SO4, field emission gun scanning electron microscopy (FEG-SEM), and Pb underpotential deposition (UPD). Their performances towards the oxygen reduction reaction (ORR) in a NaCl-NaHCO3 (0.15 M / 0.028 M, pH 7.4) neutral solution were examined and correlated to AuNPs size and density. The best results were obtained using the deposits which exhibited a high density (555 +/- 49 µm-2) of relatively small AuNPs (25 +/- 12 nm). The Koutecky-Levich treatment was systematically applied to all the deposits in order to determine the number of electrons n exchanged for the ORR in the potential range from 0.1 to -1 V. The values of the cathodic transfer coefficients Beta n were also extracted and compared to the values reported for unmodified GC and bulk Au. A map of the Beta n values as a function of AuNPs electrodeposition potential and duration was also provided

Kinetics of dioxygen reduction on gold and glassy carbon electrodes in neutral media

The electrochemical reduction of dioxygen (O₂) has been studied on bulk gold (Au) and glassy carbon (GC) electrodes in aqueous neutral solution close to blood ionic composition. The mechanism was found to involve two successive bielectronic steps with hydrogen peroxide (H₂O₂) as the reaction intermediate whatever the electrode material used. On Au, O₂ and H₂O₂ were reduced at close potentials. The determination of the kinetic parameters of O₂ electroreduction was thus achieved after removing the cathodic current corresponding to H₂O₂ reduction. Cyclic voltammograms exhibited one cathodic peak whose both current density (jp) and potential (Ep) evolution as a function of potential scan rate (r) was in accordance with Randles Sevcik and Nicholson-Shain equations, respectively. Rotating disk electrode (RDE) voltammetry was also performed and the data were analyzed using the Koutecky-Levich relationship. The effective number of electrons (n) was found to be roughly independent of the potential and close to n = 2 when removing H₂O₂ reduction current whereas it gradually increased up to n = 4 while considering the total current. The Tafel slopes allowed the cathodic transfer coefficients (Beta n) to be calculated in several neutral aqueous electrolytes. Values varied from 0.25 to 0.49 and were systematically higher on Au than on GC electrode. Similar results were obtained with Tafel slopes deduced from Butler Volmer exploitation of the current-potential curves