Effect of the Synthesis Route and Fe Presence on the Redox Activity of Ni in Layered Double Hydroxides
ChemElectroChem, 2016
Pt electrodes coated with a Ni/Al or Ni/Fe layered double hydroxide (LDH) were studied to investi... more Pt electrodes coated with a Ni/Al or Ni/Fe layered double hydroxide (LDH) were studied to investigate whether the presence of Fe and the extent of crystallinity affect the performance of the Ni centers as redox mediators for oxidizable compounds. The LDHs were synthesized by both a chemical and an electrochemical method, which allowed the obtainment of thin and well-adherent LDH films having similar morphology but a different crystallinity degree. Fe centers were not electroactive but they influenced the electroactivity of Ni, shifting the redox potential to less anodic values and increasing the percentage of the electroactive Ni sites. The LDHs prepared by electrodeposition were more conductive than the chemically synthesized LDHs, and, when Fe was the trivalent metal, the electronic conductivity was further increased. The highest electrocatalytic efficiency, evaluated taking glucose as model compound, was obtained for the electrodes coated with the electrochemically synthesized LDHs.
Iron vs Aluminum Based Layered Double Hydroxides as Water Splitting Catalysts
Electrochimica Acta, 2016
This paper describes the electrosynthesis, characterization and electrocatalytic properties towar... more This paper describes the electrosynthesis, characterization and electrocatalytic properties towards oxygen evolution reaction (OER) of four layered double hydroxides (LDHs) containing cobalt or nickel as divalent cation and aluminum or iron as trivalent metal. The electrochemical behaviour of the LDH modified electrodes was studied by cyclic voltammetry (CV), and the LDHs were characterized by XRD and SEM/EDS. Two materials, i.e., platinum and glassy carbon (GC), were investigated as electrode supports recording polarization and chronopotentiometric curves, with a rotating disk electrode in alkaline solutions. LDHs containing iron exhibited higher activity for OER and all the materials showed a good stability and durability in alkaline media. When GC was used as electrode support the performances of the OER catalysts resulted to be even better than those exhibited by the same LDHs electrodeposited on Pt.
ÐThe electronic effect of some meta-or para-substituents on the reduction of the title compounds ... more ÐThe electronic effect of some meta-or para-substituents on the reduction of the title compounds has been investigated. The reversible reduction potential values of these compounds have been evaluated by cyclic voltammetry at a mercury electrode in 0.1 M tetraethylammoniumtetra¯uoroborate, dimethylsulfoxide solutions. The substituent effect depends on both its nature and its position. The reduction potential values of the derivatives studied have been correlated with the Hammett substituent constants.
Polypyrrole was used as sensitive material in the development of a new device employed for the in... more Polypyrrole was used as sensitive material in the development of a new device employed for the indirect detection of OH radicals. The polypyrrole film was electrosynthesized on glassy carbon. The modified electrode was exposed to the OH radicals generated by Fenton reaction. As a result of the overoxidation the conductivity of the polymer diminished very much. The over-oxidation (%) was directly proportional to the COH amount that reached the electrode surface. ABTSC + , superoxide and alkylperoxy radicals did not interfere in the determination. The applicability of the device was demonstrated by estimating the COH scavenging ability of ascorbic acid.
The use of scanning electrochemical microscopy for the characterisation of patinas on copper alloys
Electrochimica Acta, 2011
The scanning electrochemical microscopy (SECM) was employed in the feedback mode for the visualis... more The scanning electrochemical microscopy (SECM) was employed in the feedback mode for the visualisation of the local changes of morphology and reactivity, occurring on the surface of a quaternary copper-based alloy, due to exposure to environment. First, samples artificially aged by exposure to leaching acid rain were tested. The layer of corrosion products (“patina”) was investigated by performing SECM scans and approach curves, and the information provided by this electrochemical technique was compared with SEM–EDX–Raman characterisation. Successively, to highlight the early stages of localised corrosion processes, in situ examination of the surface exposed to an acidic environment was performed. The results show that SECM is a powerful characterisation tool of the deterioration process and is able to map the precursor sites of corrosion on the bronze surface.
Copper hexacyanoferrate thin films were potentiodynamically deposited on glassy carbon electrodes... more Copper hexacyanoferrate thin films were potentiodynamically deposited on glassy carbon electrodes and employed for the chronoamperometric detection of hydrogen peroxide at 0.0 V vs. SCE. A new experimental procedure based on the intercalation of copper ions inside the structure of the films led to sensors with improved performances. The modified electrode displayed an increased sensitivity to hydrogen peroxide detection together with a wider linear response range and a lower detection limit. Furthermore, even if the electrode response decreased with use, the initial activity could be restored by performing a new intercalation procedure.
Novel Poly(ethylene glycol)s Bearing Tributyltin Carboxylate End Groups as Ionophores in the Development of Chloride Ion‐Selective Electrodes
Electroanalysis, 2006
The potentiometric response characteristics of electrodes based on PVC membranes containing novel... more The potentiometric response characteristics of electrodes based on PVC membranes containing novel polyethylene glycols (PEGs) with tributyltin carboxylate end groups as ionophores for chloride ions were studied in 0.1 M HEPES solution, at the spontaneous pH. The effects of solvent mediator, amount of cationic additive, amount of ionophore and PEG chain length on the behavior of the sensors were investigated. The membranes with the best composition responded to chloride concentration in a linear range from 10−4 to 10−1 M Cl− with a nearly Nernstian slope and a detection limit of 6.5×10−5 M. The sensor showed a short response time (<25 s) in the whole concentration range and an operational lifetime of about one week for the most performing PVC membranes. In comparison with ISEs based on anion exchangers the interferences from the more lipophilic anions were greatly reduced, as inferable by the selectivity coefficients determined with the matched potential method at chloride concent...
A study on the performances of mixed hexacyanoferrates of Cu and Pd (CuPdHCFs), potentiodynamical... more A study on the performances of mixed hexacyanoferrates of Cu and Pd (CuPdHCFs), potentiodynamically grown on glassy carbon surfaces, was carried out. Morphological (SEM‐EDX analysis) and electrochemical characterizations were performed, and the electrocatalytic ability of films with various compositions was tested by chronoamperometry. CuPdHCFs were found to display good electrocatalytic performances, with a maximum sensitivity of 45.3 mA M−1 cm−2 at 0.0 V vs. SCE (depending on the Cu and Pd ratio), against the value of 9.1 mA M−1 cm−2 obtained with pure copper hexacyanoferrate (CuHCF). Additionally, mixed hexacyanoferrates showed a higher pH and operational stability. The key role of Cu in Cu‐based hexacyanoferrates was investigated and highlighted.
Dye-coated stationary-phases: A retention model for anions in ion-interaction chromatography
Chromatographia, 1998
ABSTRACT The separation of inorganic anions (NO3 −, NO2 −, Cl−, Br−, I−, SO4 2−, S2O3 2−) by ion-... more ABSTRACT The separation of inorganic anions (NO3 −, NO2 −, Cl−, Br−, I−, SO4 2−, S2O3 2−) by ion-interaction chromatography mediated with a specific dye has been investigated. Chromatography was performed on a LiChrospher RP-18 colum dynamically coated with crystal violet, using acetonitrile-water buffered with phthalate as the mobile phase. The presence of the dye in the eluent enabled indirect spectrophotometric detection of the analytes, which have no significant UV absorption. Retention data were collected for the different anions by varying the composition of the mobile phase according to a full factorial experimental design. A theoretical model for the retention of singly- and doubly-charged analytes, on the basis of the two main processes of ion-exchange and ion-pair formation, has been proposed and validated with the experimental data.
Thin films of pure-nickel-based hydrotalcite-like compounds have been deposited on a Pt electrode... more Thin films of pure-nickel-based hydrotalcite-like compounds have been deposited on a Pt electrode by electrosynthesis. The best films have been obtained by cathodic reduction of a 0.03 M solution of Ni and Al nitrates in different molar ratios. The films, obtained in different experimental conditions, have been characterized by different techniques, such as SEM, AFM, and XRD. Particular attention has been devoted to understanding the mechanism of their growth. The electrochemical properties of the films obtained for different deposition times and Ni/Al ratios have been studied in basic solution (NaOH) by cyclic voltammetry and AC impedance spectroscopy.
Cerium-doped zirconium oxide (Ce/ZrO 2) was introduced as a highly efficient electrocatalyst for ... more Cerium-doped zirconium oxide (Ce/ZrO 2) was introduced as a highly efficient electrocatalyst for electrooxidation of salicylic acid (SA). The electrocatalyst material was synthesized via co-precipitation of cerium and zirconium ions, and then the resulting solid was heat-treated at high temperature to create crystallized cerium-doped zirconium oxide nanoparticles. The obtained material was characterized by scanning electron microscopy and X-ray diffraction methods. The Ce/ZrO 2-modified carbon paste electrode (Ce/ZrO 2-CPE) exhibited a distinct oxidative peak for SA, whereas no signal was observed for SA at unmodified carbon paste electrode at the same experimental conditions. Cyclic voltammetry and electrochemical impedance spectroscopy were applied to investigate the electrocatalytic performance of the electrode and SA electrooxidation mechanism. Square wave voltammetry was used to capture the analytical signal of SA. The electrode composition was optimized to increase the SA signal. Using the optimized electrode, it became possible to determine SA in the concentration range of 5.0-1000.0 μM with detection limit of 1.1 μM (3S b /m). The electrode showed very high sensitivity of 1013.5 μA mM −1 cm −2 which is remarkably better than the previously reported SA sensors. The proposed method was successfully applied for the determination of SA in human serum, milk, and pharmaceutical samples.
A home-made microelectrode array, based on reticulated vitreous carbon, was used as working elect... more A home-made microelectrode array, based on reticulated vitreous carbon, was used as working electrode in square wave voltammetry experiments to quantify the bacterial load of Escherichia coli ATCC 13706 and Pseudomonas aeruginosa ATCC 27853, chosen as test microorganisms, in synthetic samples similar to drinking water (phosphate buffer). Raw electrochemical signals were analysed with partial least squares regression coupled to variable selection in order to correlate these values with the bacterial load estimated by aerobic plate counting. The results demonstrated the ability of the method to detect even low loads of microorganisms in synthetic water samples. In particular, the model detects the bacterial load in the range 3-2,020 CFU ml −1 for E. coli and in the range 76-155,556 CFU ml −1 for P. aeruginosa.
Simple TLC systems capable of separating the most important fractions of the radiopharmaceuticals... more Simple TLC systems capable of separating the most important fractions of the radiopharmaceuticals %"Tc-MAG3, 99mTccMDP, WmTc-DPD and 99mTc~HM-PA0 were developed for measurements of radiochemical purity. Silica gel or cellulose layers were used for chromatography and the radioactivity distribution in the developed radiochromatograms was obtained with a TLC linear analyser. The chromatographic procedures proposed are suitable also for studies of kinetic instability.
Electrodes modified by One-Step Electrosynthesis of Ni/Al-NO
ABSTRACT Electrodes modified with films of the Ni/Al-NO3 double layered hydroxide have been obtai... more ABSTRACT Electrodes modified with films of the Ni/Al-NO3 double layered hydroxide have been obtained by one-step electrosynthesis. The electrosynthesis has been carried out by cathodic reduction of nitrate solutions of nickel and aluminium, investigating several operative parameters. The materials investigated as electrode supports were: Pt, Au, Ag, glassy carbon, reticulated vitreous carbon, colloidal graphite, and Boron doped diamond. The films have been characterised by CV, XRD, FT-IR spectroscopy, optical microscopy, AFM, and EQCM. For Pt and Au the best deposits were obtained at -0.9 V or at 3 mA cm -2 (deposition time: 10 s). For glassy carbon and colloidal graphite the best deposits were obtained at -1.2 V or at 30 mA cm-2 (deposition time: 10 s). The repeatability and the reproducibility of the modification procedure have been verified to propose the modified electrodes as amperometric sensors. The electrocatalytic properties of Ni/Al-NO3 films electrosynthesised on Pt or Au in the optimal conditions (E = -0.9 V and t = 10 s) have been investigated taking into account methanol and glucose as analytes. The sensitivity of the calibration graphs was very similar to that obtained when electrodes were modified with the HT synthesised by chemical methods. The major advantage of the novel procedure is the very short time to carry out the deposition and the longer lifetime of the electrodes.
Combined Use of Synchrotron‐Radiation‐Based Imaging Techniques for the Characterization of Structured Catalysts
Advanced Functional Materials, 2010
Active‐phase‐coated metallic supports as structured catalysts are gaining attention in endothermi... more Active‐phase‐coated metallic supports as structured catalysts are gaining attention in endothermic and exothermic processes because they improve heat transfer. The deposition of a well‐adhered and stable catalyst layer on the metallic support constitutes an important feature for the successful application of the final material. In this work, coating of FeCrAlY foams is performed by a one‐step electrosynthesis‐deposition of hydrotalcite‐type compounds, precursors of catalysts active in endothermic steam methane reforming. The catalysts are studied at different length scales by using, for the first time, a combination of several techniques: SEM/EDS and X‐ray fluorescence, X‐ray powder diffraction and absorption‐tomography experiments on the micro‐ and nanoscales at a synchrotron facility. The results show that the morphology of the coating depends on the synthesis conditions and that the catalyst may be described as Ni metal crystallites dispersed on γ‐Al2O3, homogeneously coating the...
An ion-selective electrode (ISE) for sulfate based on a dispersion of hydrotalcite particles into... more An ion-selective electrode (ISE) for sulfate based on a dispersion of hydrotalcite particles into a polymeric membrane using coated-wire (CW) configuration is described. Membranes, based both on poly(vinyl chloride) (PVC) containing different plasticizers and poly(dimethylsiloxane) (PDMS) were studied. The best performance in terms of slope (−29.6 ± 0.8 mV per decade) and response time (<1 min) was displayed by the PDMS based membrane whereas the linearity range (4.0×10 −5 to 4.0×10 −2 M) was practically the same for all the developed ISEs. The interference of hydrophobic inorganic anions was very low in comparison with the conventional ion-exchanger based electrodes, as shown by the selectivity coefficients determined by the matched potential method (MPM). The selectivity was also good towards the most common univalent and divalent anions and improved in the presence of 2-[4-(2-Hydroxyethyl)-1-piperarazinyl]ethanesulfonic acid (HEPES). The potentiometric response was practically constant in the pH range 4-7. A successful application of sulfate determination in commercial mineral waters, using direct potentiometry, is presented.
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