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

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

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

Oxygen reduction reaction features in neutral media on glassy carbon electrode functionalized by chemically prepared gold nanoparticles

Gold nanoparticles (AuNPs) were prepared by chemical route using 4 different protocols by varying reducer, stabilizing agent and solvent mixture. The obtained AuNPs were characterized by transmission electronic microscopy (TEM), UV-Visible and zeta potential measurements. From these latter surface charge densities were calculated to evidence the effect of the solvent mixture on AuNPs stability. The AuNPs were then deposited onto glassy carbon (GC) electrodes by drop-casting and the resulting deposits were characterized by cyclic voltammetry (CV) in H2SO4 and field emission gun scanning electron microscopy (FEG-SEM). The electrochemical kinetic parameters of the 4 different modified electrodes towards oxygen reduction reaction (ORR) in neutral NaCl-NaHCO3 media (0.15 M / 0.028 M, pH 7.4) were evaluated by rotating disk electrode voltammetry and subsequent Koutecky-Levich treatment. Contrary to what we previously obtained with electrodeposited AuNPs [Gotti et al., Electrochim. Acta 2014], the highest cathodic transfer coefficients were not obtained on the smallest particles, highlighting the influence of the stabilizing ligand together with the deposits morphology on the ORR kinetics

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Wet oxidation of phenol by hydrogen peroxide using heterogeneous catalysis Fe-ZSM-5: a promising catalyst

International audienceThis letter presents an original approach to the treatment of phenolic aqueous wastes using H2O2 with heterogeneous catalysts. The experimental results indicate that the system using Fe-ZSM-5 zeolite with MFI structure is promising since it allows total elimination of phenol and significant total organic carbon (TOC) removal under mild working conditions. Moreover, Fe-ZSM-5 remains active after after successive runs. Compared with processes using homogeneous catalysis, the possibility of induced pollution caused by the metal ions in the solution is avoided

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Nanoparticules d’or pour susciter des rencontres entre science et société

International audienceEn raison de sa couleur et de ses propriétés de métal noble, l’or a depuis toujours été un élément de fascination et de convoitise. Des démonstrations avec des nanoparticules d’or se prêtent bien aux actions de formation et de dissémination des sciences. Des expériences faciles et ludiques peuvent montrer au grand public comment les propriétés changent à l’échelle nanométrique avec la taille et la forme et expliquer les applications des nanoparticules d’or dans plusieurs domaines. Différentes actions ont été menées par des scientifiques de la Société Chimique de France, de la Société Française de Physique, des C’Nano ou du GDR Or-Nano pour proposer des ateliers destinés à présenter les nanoparticules d’or et introduire les nanosciences au sein des lycées ou des universités, dans des expositions ou des musées. Ce partage de connaissances permet d’informer le grand public, de susciter des curiosités et parfois même des vocations chez les plus jeunes. Pour le chercheur, les actions de dissémination lui permettent à travers la communication et les échanges d’aller au-delà de ses propres recherches, et l’amènent parfois à de nouvelles interrogations

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Des capteurs pour la qualité de l’eau Que ce soit pour une meilleure connaissance et compréhension du cycle de l’eau et des chemins de l’eau dans la zone superficielle de l’écorce terrestre ou pour une gestion plus « intelligente » de la qualité des eaux naturelles ou potables et des effluents urbains, industriels et agroalimentaires, la mise au point de capteurs en continu et, si possible, à faible coût, est un des défis du XXIe siècle. Si les procédés de traitement des eaux et d’épu..

From Organometallic Chemistry to Multifunctional Nanoparticle-Based Devices for Gas Detection and Degradation of Air Pollutants

This article was presented at the International Conference EcoBalt 2023 “Chemicals & Environment”, Tallinn, Estonia, 9–11 October 2023, and belongs to the Proceedings of International Conference EcoBalt 2023 "Chemicals & Environment")