Portugaliae
Electrochimica Acta

Special Issue Dedicated to the XII Iberian Meeting of Electrochemistry & XVI Meeting of the Portuguese Electrochemical Society

Metal carbonyl clusters are molecules or molecular ions perfectly defined in size, composition and structural details, which belong by size to the field of nanomaterials. Their molecular structures result from subtle balances between the metal-metal and metal-carbonyl interactions and usually adopt close-packed structures in which a chunk of cubic or hexagonal metal lattice is surrounded by a shell of CO ligands. Very often, such derivatives display extended redox activity affording reversible electron cascades. In many cases such activity increases if interstitial or semi-interstitial atoms of the main group elements (C, N, P, etc.) are inserted in their frames. This in fact triggers establishment of further metal-to-interstitial atom(s) interactions which not only contribute to the number of cluster valence electrons, but also modifies the bonding character of the frontier molecular orbitals.

The electrochemical properties of the one-dimensional coordination polymers [{CuX}2(YNC10H14O)]n (X=Cl: Y=NMe2 1a, Y=NHMe 1b, Y=NH2 1c; X=Br: Y=NH2 2c) and dimers [{Cu(YNC10H14O)}2(μ-X)2] (X=Cl: Y=NMe2 3a; Y=NHMe 3b; X=Br: Y=NMe2 4a; Y=NHMe 4b) were studied by cyclic voltammetry (CV) and controlled potential electrolysis (CPE). All complexes display anodic and cathodic processes. The anodic processes involve the oxidation of the metal site (Cu(I)Cu(II)), while the cathodic processes are based on the ligand. The substituent (Y) at the camphor hydrazones (YNC10H14O) plays a relevant role in the electrochemical properties and reactivity of Cu(I) coordination polymers and Cu(I) dimmers, as corroborated by CPE.

In this work LaNiO3 oxide was prepared by a self-combustion method using citric acid. The electrodes were obtained by coating a nickel foam support with the oxide suspension. Optical microscopy and cyclic voltammetry were used on the electrodes characterization. The evaluation of the electrodes electrocatalytic activity, towards the oxygen evolution reaction in alkaline medium, was performed by means of steady state measurements. The reaction follows a first order kinetics, with respect to OH- concentration, with Tafel slopes close to 40 mV, for low overpotentials. Based on the apparent and real current densities it was possible to conclude that the increase on the electrode activity, when compared with the published data, is mostly related to geometric factors. This fact has been associated with the high electrode/electrolyte contact area provided by the foam nickel substrate. Synergetic effects between the Ni foam and the perovskite oxide cannot be discarded.

The influence of the hydrodynamics of the system on the extent of the electrochemical degradation of phenol, using a boron doped diamond (BDD) anode was investigated. Two different electrochemical cells were used: a batch stirred cell (A), with a volume of 200 mL and a BDD anode of 17.5 cm2, and a batch with recirculation cell (B), with a BDD anode of 70 cm2 and connected to a tank of 30 L. Assays were performed at different stirring speeds and applied current density of 300 A m-2, for cell A, and various flow rates, with an imposed current density of 100 A m-2, for cell B. Chemical oxygen demand (COD) and total organic carbon (TOC) tests were performed to the samples collected throughout the assays, as well as UV-Vis spectrophotometric measurements. For cell A, after 2 h assay, COD removals between 84 and 94% and TOC removals ranging from 54 and 86 % were attained. For the assays run with cell B, during 10 h, COD and TOC removals varied from 27 to 51% and from 23 to 46%, respectively. The influence of the turbulence near the electrode’s surface in the combustion efficiency was also analysed.

Metal recovery by reduction of metal ions present in model solutions, containing one or more heavy metals, was performed. To prepare the model solutions, sulfates and/or chlorides of Cu(II), Cd(II), Pb(II) and Zn(II) were used, at pH 3.5. Assays were run in a one or two compartments cell, at different applied potentials, using a steel plate as cathode, a platinum plate as anode and an Ag/AgCl, KClsat as reference electrode. The metal recovery yield was determined by atomic absorption spectroscopy. The phases corresponding to the metallic deposits were identified by X-ray diffraction. For the solutions containing just one metal ion, the best metal recoveries and the corresponding applied potentials, obtained in a one cell compartment, were the following: Cu(II) 99% at E = - 100 mV; Pb(II) 99% at E = - 800 mV; Cd(II) 93% at E = - 900 mV; and Zn(II) 38% at E = - 1300 mV. The metal removals from the mixed solution of four heavy metals, after 4 consecutive chronoamperometries, performed in a one compartment cell, at the best applied potentials determined with the solutions containing only one metal ion, were the following: Cu(II) 99%; Pb(II) 68%; Cd(II) 92%; and Zn(II) 10%.

The present work reports the results concerning the development and implementation of the first electrochemical biosensor for acrylamide determination, based on a direct biochemical interaction between the analyte and intact bacterial cells, with intracellular enzymatic activity. The biological recognition element consisted of whole cells of Pseudomonas aeruginosa containing intracellular amidase activity, which catalyses the hydrolysis of acrylamide producing ammonium ion (NH4+) and acrylic acid. The transduction process was accomplished by means of an ammonium ion selective electrode. Whole cells were firstly immobilized on single discs of polymeric membranes, such as polyethersulphone, nylon and polycarbonate, which were, then, attached to the surface of the selective electrode. However, it was observed a significant loss of cells each time the biosensor was used, namely at the beginning of the assay, when the membranes were attached to the ammonium electrode, and after the assay, when removed for storage purposes. This evidence determined a premature decrease in the biosensor’s stability. Instead of using single membrane discs, a “sandwich” design, with two membrane discs was considered. This way the cells remain contained between the membranes, never contacting the electrode’s surface, preventing their premature loss. Consequently, the activity of the biosensor could be maintained for longer periods of time. The analytical performance of the biosensor was evaluated. The best results were obtained when polyethersulphone double membranes were used. A typical response of 120 mV (after 6 min reaction time), a Nernstian slope of 48 mV/decade, a limit of detection of 6.31×10-4 M and a half-life time of 27 days, are examples of some figures of merit observed for this biosensor.