Boualem Saidani

Amorphous carbon nitride as an alternative electrode material in electroanalysis: Simultaneous determination of dopamine and ascorbic acid

Boron-doped diamond (BDD) films are excellent electrode materials, whose electrochemical activity for some analytes can be tuned by controlling their surface termination, most commonly either to predominantly hydrogen or oxygen. This tuning can be accomplished by e.g. suitable cathodic or anodic electrochemical pretreatments. Recently, it has been shown that amorphous carbon nitride (a-CNx) films may present electrochemical characteristics similar to those of BDD, including the influence of surface termination on their electrochemical activity toward some analytes. In this work, we report for the first time a complete electroanalytical method using an a-CNx electrode. Thus, an a-CNx film deposited on a stainless steel foil by DC magnetron sputtering is proposed as an alternative electrode for the simultaneous determination of dopamine (DA) and ascorbic acid (AA) in synthetic biological samples by square-wave voltammetry. The obtained results are compared with those attained using a BDD electrode. For both electrodes, a same anodic pretreatment in 0.1 mol L(-1) KOH was necessary to attain an adequate and equivalent separation of the DA and AA oxidation potential peaks of about 330 mV. The detection limits obtained for the simultaneous determination of these analytes using the a-CNx electrode were 0.0656 μmol L(-1) for DA and 1.05 μmol L(-1) for AA, whereas with the BDD electrode these values were 0.283 μmol L(-1) and 0.968 μmol L(-1), respectively. Furthermore, the results obtained in the analysis of the analytes in synthetic biological samples were satisfactory, attesting the potential application of the a-CNx electrode in electroanalysis.

Inhibition of acid corrosion of mild steel by aqueous nettle extracts

Purpose – The aim of this research was to investigate the use of aqueous extracts of nettle plant (NE) as a green corrosion inhibitor of mild steel in hydrochloric acid solution. Design/methodology/approach – The inhibition efficiency was investigated by weight loss measurements, potentiodynamic polarizations, electrochemical impedance spectroscopy, SEM observations and EDX analysis. Findings – The inhibition efficiency increased with an increase in concentration of NE up to a critical concentration of 1.5×10−3 g · cm−3 where the highest inhibition efficiency of 97 percent was obtained. The adsorption of the inhibitor was spontaneous (reflected by the negative value of ΔGads0), supported the mechanism of physical adsorption and obeyed to the Langmuir adsorption isotherm. The inhibition action of the extracts was independent on the storage time; it could be conserved without any specific conditions of time and temperature. Research limitations/implications – The anticorrosion effect can be better understoo...

Free Contact Microchannel Impedance Through Two Antiparallel Planar Microelectrodes

The present work describes new results using a contact free impedance device, which permits to reach a best understanding of the free contact transduction. Measurements were carried out through a polyethylene terephthalate (PET) microchannel photoablated. Impedance measurement of empty microchannel at different PET thickness separating the two electrodes demonstrate that the recorded impedance is not changed whatever the PET thickness. The result shows that the polyethylene (PE) film lamination has an effect on the impedance measurement in empty microchannel. Then impedances diagrams in the filled microchannel were plotted by subtracting impedance contribution in empty microchannel from the global microdevice response. The Nyquist diagram of filled microchannel exhibits a loop diameter from high to medium frequencies, and a capacitive behavior at low frequencies. The loop diameter obtained is inversely proportional to the microchannel conductivity. Modeling impedance of microsystem highlighted the effect of microchannel rough surface phenomena.

Structural, Viscoelastic, and Electrochemical Characteristics of Self-Assembled Amphiphilic Comblike Copolymers in Aqueous Solutions

Self-assembly in aqueous solutions of an amphiphilic comblike polyelectrolyte (80C12) that consists of a polystyrene (PS) backbone onto which quaternary ammonium pendant moieties have been grafted has been investigated by light scattering and cryo-transmission electron microscopy measurements in the presence of KCl and methylviologen dication (MV2+) under conditions mimicking those for electrochemical measurements. Polymer chains self-assemble within branched cylindrical micelles that display viscoelastic properties, characterized by a relaxation time of 4 s. To tune this time, 80C12 was mixed with a polyoxyethylene nonionic surfactant (Brij C12E10). Relatively increasing the amount of the latter leads to a decrease in the relaxation time of the 80C12 solution. Correlatively, electrochemical experiments with a rotating disk electrode show a transition of the mass transport rate, which deviates from the classical Newtonian behavior in the same velocity domain. This result generalizes what has been already observed with solutions of linear polymers of high molecular weight and wormlike micelles based on surfactants subjected to elongational deformations. Moreover, the critical times derived from rheological and electrochemical experiments display the same trend.