J.P. Correia

On the Mechanism of Electroless Ni‐P Plating

The electroless deposition mechanism of nickel, in a chloride‐based solution, using hypophosphite ion as reducing agent was examined using potentiodynamic method and open‐circuit potential measurements. The results indicate that the mixed potential theory is unable to describe this system. This is due to the nature of the involved mechanism. It is assumed that the process is initialized by adsorption of hypophosphite ions, followed by the homolysis of primary reductant species, resulting in the formation of atomic and ionic radicals which promote nickel and hypophosphorous acid reduction to originate the Ni‐P deposit. The initial deposition stages of Ni‐P were observed, revealing that the substrate induction, which leads to an increase in the catalytic activity, is not related to a galvanic displacement process, but rather to the establishment of the electrochemical conditions which allow the adsorption/breakdown of the hypophosphite ions. The experimental results are in good agreement with the proposed mechanism.

Electronically conductive polymer grafted with oligonucleotides as electrosensors of DNA: Preliminary study of real time monitoring by in situ techniques

Polypyrrole bearing covalently linked oligonucleotide (ODN) probes has been used for electrode modification through one-step electrosynthesis. The biofilms obtained were employed for the direct and real-time detection of DNA hybridisation by using photocurrent spectroscopy and a quartz crystal microbalance (QCM). The photoelectrochemical properties of polypyrrole appear to be influenced by the presence of ODN allowing the transduction of the hybridisation event into a measurable photocurrent. The operational parameters of the biosensor (film thickness, ODN load, …) were assessed to optimise the response to DNA hybridisation. In addition, QCM detection, which is based on the monitoring of the biofilm mass uptake generated by molecular recognition, has been used as a validation technique. The sensors obtained have been demonstrated to be fully reusable. They have also shown a suitable sensitivity and a good reproducibility in terms of kinetic behaviour and intensity of the measured signal. Finally, this study considers the pertinence of both techniques regarding DNA hybridisation detection.

On the initiation and growth of polymer films onto electrode surfaces

Abstract The probe beam deflection technique (PBD) has been successfully used to detect in situ the influence of electrochemical mode and conditions on the initial stages of poly-3-methylthiophene formation. The interpretation of the results is coherent with the previously reported oligomer formation in solution prior to deposition. The effect of the initial polymerization steps in the subsequent stages of the polymer growth has also been investigated, analysing the redox behaviours along with the correspondent deflectograms obtained for thin films synthesized under different deposition charges. The data indicate that up to a given thickness the polymer responses reflect the nature of the first deposited layer. The electropolymerization behaviour of methylthiophene has also been contrasted to that of pyrrole under the same experimental conditions (solvent, monomer concentration, anionic and cationic components of the electrolyte). The results clearly reveal an earlier deposition process and that oligomer formation, if any, is not determinant for polypyrrole deposition.

Study of DNA hybridization on polypyrrole grafted with oligonucleotides by photocurrent spectroscopy

Recognition of DNA sequences by biochemical sensor is generally performed by analysis after completion of hybridization. Using a technique able to directly translate the biological event into an electrical signal allows the in situ monitoring of the hybridization kinetics. In this aim, the photoelectrochemical behavior of one electroactive polymeric sensor based on a copolymer of polypyrrole and polypyrrole-oligonucleotide has been investigated in aqueous solution. This sensor has been studied as such (i) and in two other situations: (ii) when the copolymer is in presence of non-complementary oligonucleotides; and (iii) when the copolymer is in presence of complementary oligonucleotides. From the photocurrent spectra obtained at -0.6 V/SCE versus incident energy the allowed direct and indirect transitions for each polymer have been evidenced. The photocurrent evolution during hybridization and adsorption processes has been recorded in real time and the hybridization kinetics has revealed to be comparable with mass variations obtained by quartz crystal microbalance under the same experimental conditions.

Polypyrrole incorporating electroless nickel

Abstract The electroless deposition of Ni–P (phosphorus content about 20 at.%) into polypyrrole (PPy) film is described and conditions for achieving good dispersions of small particles discussed. The influence of the loading level/particle size on the electrocatalytic properties of these new electrodes is illustrated by the study of the hydrogen evolution reaction (HER). The usefulness of electrochemical treatments, not only in overcoming the loss of catalyst at anodic potentials but also in promoting the formation of a catalytic nickel oxide phase is demonstrated. The performance towards nitrite ion oxidation reveals that electroless deposition on conductive polymers can be envisaged as an attractive method for the fabrication of good electrocatalytic materials with application in a wide range of potentials.

Electrochemical mineralization of anaerobically digested olive mill wastewater

A novel approach was developed for the energetic valorisation and treatment of olive mill wastewater (OMW), combining anaerobic digestion and electrochemical oxidation. The electrochemical treatment was proposed as the final step to mineralize the remaining OMW fraction from the anaerobic reactor. The electrooxidation of anaerobically digested OMW was investigated over dimensionally stable anodes (DSAs). RuO(2) based anode was significantly more efficient than IrO(2)-type DSA, mainly for the COD removal. IrO(2) based anode promoted a selective oxidation of phenols and colour removal. For instance, after an electrolysis charge of 10.4 × 10(4) C L(-1), COD removals of 14 and 99%, phenols removals of 91 and 100% and colour removals of 85 and 100% were obtained for IrO(2) and RuO(2) DSAs-type, respectively. The electrochemical post-treatment was effectively performed without using a supporting electrolyte and in the presence of the solids that remained from the anaerobic process. The achievement of the required effluent quality for sewer systems disposal depends on the operating conditions of the anaerobic process. Consequently, special care must be taken with the chloride and nitrogen levels that may surpass the legal discharge limits. The electrochemical oxidation over RuO(2) based DSA is an appropriate second-step treatment for OMW disposal, after the recovery of its energetic potential.

Photoelectrochemical studies of polymer films: Poly(3-methylthiophene) and poly(3-methylthiophene)/Cu systems

Abstract In this work, the behaviour of P3MeTh films in aqueous solutions is characterized by cyclic voltammetry under chopped light in the potential domain where the polymer is oxidized, as well in its reduced state. The photocurrent observed in the negative potential region is enhanced by the incorporation of copper particles in the polymer matrix and subsequent oxidation, resulting in a P3MeTh Cu 2 O photosensitive composite. The electrochemical photocurrent displayed by the polymer and by the composite are discussed under the light of classic formalisms derived from solid state theory and of a recent model proposed by Semenikhin et al . which appears to describe well this type of modified electrodes.

Structural modifications during conducting polymer formation — an ellipsometric study

Polyaniline films potentiodynamically synthesised on gold substrates are analysed ex situ by conventional and imaging ellipsometry (at constant wavelength). Polymers grown up to 50 cycles appear to be homogeneous, whereas different structures are displayed by thicker layers. The memory effect, induced by the polymer electrochemical characterisation, in subsequent polymer growth, is demonstrated. In the case of thin films, a reliable methodology has been successfully employed to obtain, from the ellipsometric parameters Delta and psi, the refractive index, the extinction coefficient and the thickness of polymer layers. This approach also allowed us to quantitatively evaluate the magnitude of polymer swelling upon oxidation (11 - 22%). Furthermore, the surface morphology is well evidenced by the results obtained by imaging ellipsometry.

In situ IR study of the electrooxidation of hypophosphite on a polycrystalline nickel electrode

Electrooxidation of the hypophosphite ions on polycrystalline nickel in alkaline solutions has been investigated using cyclic voltammetry, chronoamperometry and in situ IR spectroscopy (SNIFTIRS). A spectroelectrochemical flow cell was used in order to keep the composition of the thin layer constant. The spectra were analysed as a function of the electrode potential during the anodic, cathodic scans and at open-circuit potential as a function of time. On the assumption that solvent bands are independent of applied potential, there is some evidence at open circuit for hypophosphite ions adsorbing to the nickel surface through the hydrogen atoms; this orientation persists until oxidation takes place. Phosphite ions were the only oxidation product to be detected.

Poly(3-methylthiophene) incorporating electrolessly deposited Ni–P particles

Abstract In this work, the incorporation of Ni–P particles in poly(3-methylthiophene) films by electroless deposition is investigated. It is possible to observe the autocatalytic deposition in polymers containing a few nickel nuclei created by short potential step experiments. The polymer synthesis conditions were found to play an important role in the amount and dispersion of the metal particles. The electrocatalytic properties of the modified electrodes are analysed and compared with those of pristine polymer and bare nickel electrodes. It is concluded that they present good catalytic activity for the hydrogen evolution reaction (HER).