Cathodic modifications of platinum surfaces in organic solvent: reversibility and cation type effects

Cathodic modification of platinum surfaces leads to the formation of iono-platinic phases ([Pt(n-), M+, MX]), which involves the insertion of cations and salts into the platinum electrode. This process was investigated at the local scale by in situ observation of surface electrochemical processes by atomic force microscopy (EC-AFM) techniques as a function of the salt and the injected charge, with special attention about the process reversibility. AFM images recorded in solution after the cathodic modifications of well-defined platinum surfaces [epitaxial platinum deposit on (100) MgO substrate] show drastic modification on the morphology of the surface, confirming previous ex situ studies. The amplitude of the modifications directly depends on both the nature of supporting electrolyte and the quantity of charge injected into the platinum. As long as the injected charge remains small enough to maintain the adhesion of the Pt deposit onto the MgO substrate, the process was found to be fully reversible. Indeed, impressive morphology changes occur under the cathodic treatment (formation of [Pt(n-), M+, MX]) but the initial geometry is totally recovered after reoxidation of the iono-platinic phase. This cycle of reduction-reoxidation can be performed several times without any significant alteration of the recovered surface and of its structural characteristics. It is suggested that the modification starts at the interface solution platinum surface and then its insertion into the platinum surface.     

Functionalization of silicon surfaces with Si-C linked beta-cyclodextrin monolayers

Vinyl-terminated heptapodyl beta-cyclodextrins react with hydrogenated silicon surfaces to generate covalently-bound molecular recognition devices.     

Indirect reduction of aryldiazonium salts onto cathodically activated platinum surfaces: formation of metal-organic structures

Platinum phases of general formula [Pt(n-), M+, MX] can be electrogenerated from cathodic polarization in dry dimethylformamide containing a supporting electrolyte, MX. The reaction of these electrogenerated Pt phases as reducing agent with aryldiazonium salts was investigated for preparing controlled metal-organic interfaces and characterizing the reactivity of the "reduced platinum phases". In a two-step process, the "reduced platinum phase" locally reacts with aryldiazonium salts, leading to the attachment of aryl groups onto the metal surface in the previously modified areas. Detailed experiments using cyclic voltammetry, X-ray photoelectron spectroscopy (XPS), and in situ electrochemical atomic force microscopy (EC-AFM) were carried out to follow the reaction in solution with the example of NaI as supporting electrolyte (MX = NaI). These studies demonstrate the irreversible attachment of aryl groups onto the platinum electrode. Comparison between the direct electroreduction of aryldiazonium compounds (4-nitrophenyl- and 4-bromophenyldiazonium) on a platinum electrode and their reaction with [Pt2-, Na+, NaI] suggests that a similar general mechanism is responsible for the grafting. However in the second case, no applied potential is required to stimulate the binding thanks to the reductive properties of [Pt2-, Na+, NaI]. Competitive reduction of the organic layer and growth of the layer were observed and analyzed as a function of the injected charge used to initially produce [Pt2-, Na+, NaI]. Similar reactions are highly probable with other MX salts owing to the redox properties observed for this type of platinum phase ([Pt(n-), M+, MX]).     

Direct Electron Transfer of Hemoglobin and Myoglobin at the Bare Glassy Carbon Electrode in an Aqueous BMI.BF4 Ionic‐Liquid Mixture

Direct and remarkably fast electron transfers between a bare glassy carbon electrode and heme proteins (hemoglobin or myoglobin) are obtained by using an aqueous 1‐butyl‐3‐methyl imidazolium tetrafluoroborate (BMI.BF₄) ionic‐liquid mixture as electrolyte. The ionic liquid is observed to play a key role in the achievement of the electron transfer. The experimental data show that the proteins are not strongly adsorbed onto the electrode surface while giving rise to sharp and well‐defined redox responses. Such a finding contrasts with most of the reported works found in literature and—beyond the fundamental aspect—it may be of interest in applications where adsorption is critical. Moreover, the electrocatalytic activity of the proteins toward the reduction of oxygen and nitrite in the aqueous BMI.BF₄ mixture is evidenced, showing the potential of this simple approach for bioelectroanalytical devices.     

Controlling the Stepwise Closing of Identical DTE Photochromic Units with Electrochemical and Optical Stimuli

The full or stepwise controlled closing of identical photochromic dithienylethene units in the same molecule was addressed with a combination of electrochemical and optical stimuli in a trimetallic carbon-rich ruthenium complex.     

Highly sensitive and rapid determination of sunset yellow in drinks using a low-cost carbon material-based electrochemical sensor

Starting from simple graphite flakes, an electrochemical sensor for sunset yellow monitoring is developed by using a very simple and effective strategy. The direct electrochemical reduction of a suspension of exfoliated graphene oxide (GO) onto a glassy carbon electrode (GCE) surface leads to the electrodeposition of electrochemically reduced oxide at the surface, obtaining GCE/ERGO-modified electrodes. They are characterized by cyclic voltammetry (CV) measurements and field emission scanning electron spectroscopy (FE-SEM). The GCE/ERGO electrode has a high electrochemically active surface allowing efficient adsorption of SY. Using differential pulse voltammetry (DPV) technique with only 2 min accumulation, the GCE/ERGO sensor exhibits good performance to SY detection with a good linear calibration for concentration range varying 50–1000 nM (R² = 0.996) and limit of detection (LOD) estimated to 19.2 nM (equivalent to 8.9 μg L⁻¹). The developed sensor possesses a very high sensitivity of 9 μA/μM while fabricated with only one component. This electrochemical sensor also displays a good reliability with RSD value of 2.13% (n = 7) and excellent reusability (signal response change < 3.5% after 6 measuring/cleaning cycles). The GCE/ERGO demonstrates a successful practical application for determination of sunset yellow in commercial soft drinks.

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Electron-transfer mediation on poly-aryl dendrimer-modified electrodes

Electrochemical properties of a dendrimer-modified electrode that was prepared by immobilization of ferrocenyl-terminated dendrimers on a poly-phenyl acetate anchoring layer were investigated in CH₂Cl₂. The anchoring layer was made by electro-grafting of the corresponding diazonium salt on a glassy carbon surface. The method allows the fabrication of a robust interface where the properties of the dendrimers are well-preserved. Moreover, the control of the layer properties as the permeation of molecules from the solution to the surface could be tuned up from only limited to totally blocked through the electrochemical conditions used during the electro-grafting of the anchoring layer. Detailed investigations performed with cyclic voltammetry and on different types of layers show that the modified electrode catalyses the oxidation of redox substrates. The process depends on the standard potential of the redox couple compared to that of the adsorbed dendrimer molecules. Experiments indicate that the electron exchange with molecules in solution takes place mainly at the dendrimer film–solution interface as the dendrimers inside the film permit the charge-transfer through the modified film to the carbon substrate. The interest of using robust electrode dendrimer relies on the possibility of large structural variations allowing the careful introduction of specific properties in the layer.