Barbara Ballarin

Electrocatalytic properties of nickel(II) hydrotalcite-type anionic clay: application to methanol and ethanol oxidation

Abstract Glassy carbon electrodes modified with a [Ni/Al–Cl] hydrotalcite-type anionic clay have been studied with respect to the electrochemical oxidation of the Ni(II) centres. The oxidation of Ni(II) is quasi-reversible and the presence in the hydrotalcite lattice of nickel with mixed oxidation states increases the conductivity of the coverage strongly. It has been verified that these nickel redox systems may act as redox mediators for the oxidation of alcohol substrates (methanol and ethanol have been tested) which are not oxidised at the bare electrode in the potential window available. For both alcohols the height of the current responses in linear sweep voltammetry is roughly linear with varying concentration in solution up to a limit of ca. 3000 ppm, with a detection limit of 3–4 ppm.

Thermal Inkjet Technology for the Microdeposition of Biological Molecules as a Viable Route for the Realization of Biosensors

Abstract Recent progress in inkjet printing of parts of biosensors are highlighted, with particular reference to the printing of biologically active molecules. We describe a system constituted by a thermal inkjet printer, adapted to layering a bidimensional array of dots [701 × 701 dots per inch] on solid supports. The printer was used to depose a β‐galactosidase (GAL)‐containing ink on a polyester sheet, with dots obtained from 10 pL drops, each drop containing in turn 6 pg of enzyme. The activity of GAL after the preparation was determined using a colorimetric probe (Brilliant Blue FCF). The activity loss of the microdeposed enzymes was found to be around 15%, showing that the 2 µsec‐lasting thermal shock experienced by the biomolecule into the printhead nozzle affects to a lesser extent the activity of the thermal inkjet deposited enzyme. In conclusion, the most recent findings of our group in this line are depicted, and a view of possible future developments of the “biopolytronics” field is outlined.

Electrodes coated by hydrotalcite-like clays. Effect of the metals and the intercalated anions on ion accumulation and retention capability

The influence of the nature of the di- and trivalent metals and of the interlayer anion of different hydrotalcite-like (HT) clays on the anion-exchange ability is investigated. In view of the application of similar clays as electrode coatings in electroanalysis and electrocatalysis, the responses of electrodes modified with the different HT to electroactive species in solution constitute the primary source of information. However, XRD measurements have proved to be invaluable tools when coupled with the electrochemical data. Two organic and one inorganic anion with reversible redox behaviour, i.e. anthraquinone mono- and disulphonates and hexacyanoferrate(II), have been chosen as electroactive species.

Glyphosate and glufosinate detection at electrogenerated NiAl-LDH thin films.

An amperometric sensor based on Ni(1-x)Al(x)(OH)(2)NO(3x).nH(2)O layered double hydroxide (LDH) has been developed for the electrochemical analysis in one step of two herbicides: glyphosate (N-(phosphonomethyl)glycine, Glyp) and glufosinate ((DL-homoalanine-4-yl)-methylphosphinic acid, Gluf). NiAl-LDH was prepared by coprecipitation or by electrodeposition at the Pt electrode surface. Inorganic films were fully characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Adsorption isotherms of Glyp onto this inorganic lamellar material have been established. Electrocatalytic oxidation of Glyp and Gluf is possible at the Ni(3+) centres of the structure. The electrochemical responses of the NiAl-LDH modified electrode were obtained by cyclic voltammetry and chronoamperometry at 0.49V/SCE as a function of herbicide concentration in 0.1M NaOH solution. The electrocatalytic response showed a linear dependence on the Glyp concentration ranging between 0.01 and 0.9mM with a detection limit of 1muM and sensitivity 287mA/Mcm(2). The sensitivity found for Gluf was lower (178mA/Mcm(2)).

Modification of electrodes with porphyrin-functionalised conductive polymers

A new thiophene derivative has been synthesised, in which a porphyrin moiety has been inserted in the β position of the heterocyclic ring. The homopolymer deriving from this monomer has been prepared by chemical oxidation and subsequently deposited on a glassy carbon electrode, while the copolymer with dithiophene has been generated electrochemically directly on the electrode surface. Both materials have been characterised by SEM, and by UV-visible and IR spectroscopies. The electrochemical behaviour of the relevant coatings has been studied and the complexing ability of the polymer chains has been investigated with respect to the Ni(II) ion.

Synthesis Route to Supported Gold Nanoparticle Layered Double Hydroxides as Efficient Catalysts in the Electrooxidation of Methanol

This work describes a new one-step method for the preparation of AuNP/LDH nanocomposites via the polyol route. The novelty of this facile, simple synthesis is the absence of additional reactants such as reductive agents or stabilizer, which gives the possibility to obtain phase-pure systems free of undesiderable effect. The AuNP formation is confirmed by SEM, TEM, PXRD, and XAS; moreover, the electrochemical characterization is also reported. The electrocatalytic behavior of AuNP/LDH nanocomposites has been investigated with respect to the oxidation of methanol in basic media and compared with that of pristine NiAl-Ac. The 4-fold highest catalytic efficiency observed with AuNP/LDH nanocomposites suggests the presence of a synergic effect between Ni and AuNP sites. The combination of these experimental findings with the low-cost synthesis procedure paves the way for the exploitation of the presented nanocomposites materials as catalysts for methanol fuel cells.

Electrochemical behaviour and preconcentration of uranyl(VI) at Nafion-coated glassy carbon electrodes

Abstract The electrochemical behaviour of UO 2 2+ solutions at Nafion ® -coated glassy carbon electrodes has been examined and compared with the behaviour observed at uncoated electrodes. At pH 2.4, two reduction processes are always observed at both electrodes; however, the mechanism involved in the first process is affected strongly by the presence of the polymeric coating. While in homogeneous solution the first reduction product UO 2 + is quite stable and reacts only with electrogenerated U III , in the presence of Nafion the local high concentration of H + inside the coating causes it to disproportionate. The relevance of the ion exchange competition between H + and Na + to this reaction is proved. The influence of the applied potential on the rate and extent of incorporation was also studied. The ion exchange characteristics of Nafion for the different oxidation states generated by reducing UO 2 2+ have been compared qualitatively and the selectivity coefficients for U IV and U VI determined. The values obtained indicate a selectivity of Nafion for U IV about 20 times higher than that for U VI , so that preconcentration from UO 2 2+ dilute solutions can be achieved by applying a suitable reducing potential at the modified electrode.

Determination of trace amounts of Eu3+ and Yb3+ ions at nafion-coated thin mercury film electrodes

Abstract The use of Nafion-coated thin mercury film electrodes (NCTMFE) for determining trace amounts of Eu3+ and Yb3+ ions was examined. Ion-exchange preconcentration of submicromolar levels of the two rare earths was achieved efficiently at a rotating NCTMFE, while the use of “classical” Nafion-coated glassy carbon electrodes is restricted to the determination of Eu3+ alone. Differential-pulse voltammetry was used to quantify the accumulated ions. The influence of variables such as rotation rate, preconcentration time and scan parameters was assessed. A preconcentration -voltammetry-regeneration scheme suitable for multiple analysis with the same modified electrode was developed. Calibration graphs with a linearity range extending up to 2 μM and detection limits of 0.03 and 0.08 μM for Eu3+ and Yb3+, respectively, were obtained. For Yb3+, the detection limit can be lowered to 0.02 μM by electrocatalytic amplification of the signals achieved by operating in the presence of ammonium nitrate as supporting electrolyte. However, in this instance a more restricted linearity range is observed. The effect of competing incorporation caused by the presence in solution of an excess of La3+ is also discussed, together with the competition between Eu3+ and Yb3+ when one of the two is present in large excess over the other.

Electrochemical synthesis and characterisation of polythiophene conducting polymers functionalised by metal-containing porphyrin residue

Abstract Two different copolymers of 2,2′-bithiophene and of new thiophene derivatives, bearing in the β position a porphyrin macrocycle, either free or complexed with Ni(II), have been electrogenerated and studied. The electrochemical behaviour of the relevant coatings has been compared, and the complexing ability of the macrocycle with respect to Ni(II) ion has been investigated. Moreover, the possibility of growing the metal-containing polymer on a micro Pt disk has been checked. The resulting modified microelectrode has been characterised and tested.

Electrochemistry of Yb3+ and Eu3+ at Nafion modified electrodes

Abstract The influence of the electrodeposition of a thin mercury film on the voltammetric behaviour of Yb3+ and Eu3+ incorporated by ion-exchange in Nation® coated glassy carbon electrodes is examined. A significant role of the nature of the electrode material is observed only in the case of Yb3+ and the improvement in the reversibility and reproducibility of the voltammograms observed after mercury deposition is attributed to the higher overpotential required for hydrogen evolution on mercury. No such effect is observed in fact in the case of Eu3+, which is reduced at far less negative potential values than Yb3+ and, in this case, reversible and reproducible voltammetric patterns are obtained at both modified electrodes. The detailed analysis of the ion-exchange process demonstrates that mercury deposition does not cause deterioration of the ion-exchange properties of the Nation coating, while the nature of the supporting electrolyte cations examined (Li+, Na+, K+, Rb+, NH+4, tetraethylammonium) proves to influence significantly both the extent and rate of incorporation. The ion-exchange distribution and selectivity coefficients of Nation for the two rare earth cations studied are also reported together with the relevant apparent diffusion coefficients.