ANALYTICAL AND BIOANALYTICAL ELECTROCHEMISTRY
Year:2019 | Volume:11 | Issue:11|Papers Count:10

The present work continues to focus on expanding the use of plant extracts to combat metal corrosion and reports on the inhibiting effect of Hammada Scoparia (HS) extract on the corrosion of carbon steel in 1 M hydrochloric acid. Electrochemical impedance spectroscopy (EIS), potentiodynamic polarization and gravimetric methods were utilized to examine the metal corrosion behavior without and with inhibitor. Polarization studies show that the Hammada Scoparia (HS) extract acts as a mixed inhibitor in acidic electrolyte and its inhibitory effectiveness rise with Hammada Scoparia (HS) extract concentration reaches a maximum of 93% for 0. 6 g/L. The obtained Nyquist plots showed depressed semicircles and their diameter enhanced with rising HS extract concentration. The inhibiting capacity of HS extract for carbon steel in hydrochloric acid at diverse temperatures (303-333 K) was reduced somewhat. The adsorption of the HS extract on carbon steel follows the Langmuir isotherm. SEM and EDX observations confirmed the existence of protective film on the metal surface. A good agreement was obtained between various used technical.

The extracts of Thapsia garganica (Apiaceae) were used as green corrosion inhibitors to protect A 106 Gr B carbon steel against 1 M HCl solution. The inhibition effect of extracts methanolic (extract I) and ethyl acetate (extract II), were examined on carbon steel A 106 Gr B in hydrochloric acid with potentiodynamic polarization and electrochemical impedance spectroscopic technical. These measurements were made in an environment contains HCl alone and HCl plus the addition of different concentrations of the inhibitor (5; 10; 20; 30; 40 ppm), after 30 min of immersion, and taken at a temperature of (298± 1) K. The inhibition efficiency of 96% was achieved with the addition of 40 ppm of me thanolic extract and 95% with ethyl acetate extract in 298 K. The extracts behaves are a mixed type corrosion inhibitors and is spontaneously adsorbed on the steel surface. Physisorption of two extracts is best described by the Langmuir adsorption model. Mechanism of inhibition was also investigated by calculating the thermodynamic and activation parameters like (Δ G), (Ea), (Δ Ha) and (Δ Sa). The originality of this work is the discovery of another safe, eco-friendly and non-toxic inhibitor from natural plants.

In order to improve the electrochemical performances of solid oxide fuel cells (SOFC), La2Ni1-xO4± δ (0. 01≤ x≤ 0. 1) materials were prepared by citrate route and then used as cathodes for oxygen reduction reaction (ORR). Their microstructure and morphology were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The excess of the oxygen contents and the electrical conductivities were performed by iodometric titration and 4-point probs method respectively. The electrochemical performances were subsequently studied by impedance spectroscopy and the results obtained are promising which confirm the good electrochemical performance of most of the analyzed compositions. It has been shown that, the electrical conductivity increases with increasing of the excess oxygen content. The morphology of such cathode materials has a significant influence on the electrochemical behavior of the studied electrode materials. Accordingly, among the studied materials, the Ni-10% deficient material (symbolised by LN10O) shows the best electrochemical properties with respect to oxygen reduction reaction. Such sample is the most porous one, conducing to an easy diffusion of oxygen and, consequently, favouring the ORR phenomenon.

A carbon paste electrode (CPE) modified by natural phosphate (NP) has been evaluated using the electrochemical detector in the analysis of N, N’-ethylene-2, 2’-bipyridinium (DQ). The working electrode was obtained by depositing the NP on the surface of the CPE. The optimal potential window from-1. 2 V to 1. 6 V has been selected. DQ has been pre-concentrated on the surface of the CPE-NP in 0. 1 M K2SO4 (pH 3). The reactivity of DQ on the electroanalysis detector was characterized by the appearance of the anodic peak at 0. 7 V and the cathodic peak at 0. 25 V. The influence of parameters such as pH, scan rate, accumulation time and concentration were studied by cyclic voltammetry. The optimal preconcentration time is 16 min. The kinetics of electron transfer on the CPE-NP in the detection of analyte was found using the scan rate effect. The concentration variation was studied. The scan rate effect has been showed the electrode process is adsorption controlled. The redox peak currents indicated a linear dependence with the DQ concentrations (1×10-5 mol. L-1-6×10-5 mol. L-1). The results have been showed that the CPE-NP exhibited an excellent electro-catalytic activity for the DQ analysis. The calculated limits of detection and quantification have been 9. 24×10-8 and 3. 08×10-7 mol. L-1, respectively. The present electrochemical detector shows excellent performance in detecting the DQ. The proposed method has been applied to the determination of DQ concentration in a real sample of river water with satisfying results.

The presence of heavy metals in the environment, resulting from industrial wastewater discharges, causes considerable damage to the natural balance of the aquatic ecosystem when they exceed certain concentrations. During this study, we were able to eliminate the content of Ni2+ ions contained in synthetic wastewater samples by the adsorption technique on a hull substrate taken from the beaches of Mehdia in Morocco. The present study indicates that the envisaged adsorption decreased the efficiency of the retention of Ni2+ ions from 91. 03% (6. 5 ppm) to 52. 36 (250 ppm) and the adsorption capacity of 13. 67%. mg / g for 200 ppm. The mass effect of the adsorbent was of the order of 84. 8% for a value of 2 g, the temperature was of the order of 95% for 328± 2 K. and a yield of 89. 15% for a pH of between 6 and 7 and of the order of 93. 5% for a contact time of 180 min.

In this research work, montmorillonite/polyaniline/chitosan/platinum (MMT/PANI/CS/Pt) nanocomposite is used as an effective and novel catalyst for electrooxidation of ethanol. The glassy carbon electrode surface is coated with MMT/PANI and chitosan by applying a constant potential. Thereafter, the surface of the GCE is potentiostatically coated with platinum nanoparticles. The constructed electrode is referred to as: GCE/MMT/PANI/CS/Pt. The electrooxidation of ethanol molecules on the surface of MMT/PANI/CS/Pt electrode is studied using various electrochemical methods such as cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy (EIS). The experimental results, indicate that the GCE/MMT/PANI/CS/Pt electrode possess a higher catalytic activity for ethanol electrooxidation compared to the GCE/Pt electrode. The Tafel plots indicate a better kinetic for ethanol electrooxidation in the presence of MMT/PANI/CS. The effect of various parameters on electrocatalytic oxidation of the ethanol molecules, such as the amount of platinum nanoparticles, MMT/PANI and ethanol concentration on the modified electrodes is investigated for electrooxidation of ethanol molecules using the GCE/MMT/PANI/CS/Pt electrode. The optimum conditions are obtained with 0. 011 mg cm-2 Pt nanoparticle, 0. 08 w/v% MMT/PANI and 1 M ethanol.

In present work, a cardiovascular drug, propranolol (PROP) has been investigated using reduced graphene oxide modified carbon paste electrode (rGO-CPE). A simple, selective and sensitive method has been developed using cyclic voltammetry (CV), differential pulse voltammetry (DPV), square wave voltammetry (SWV) and electrochemical impedance spectroscopy (EIS). At pH-7. 0 in 0. 1 M phosphate buffer solution (PBS) PROP shows excellent electrooxidation process on rGO-CPE. The EIS data provides charge transfer resistance behaviour at carbon paste electrode (CPE, 96. 6 kΩ ) and rGO-CPE (46. 7 kΩ ), which shows the increased electron transfer process at rGO-CPE. The linear calibration curves were obtained in the concentration range of 0. 1– 2. 5 μ M (for DPV) and 0. 1– 5. 0 μ M (for SWV), respectively. The lower limits of detection values were found to be 0. 4×10-8 M and 0. 2×10-9 M, respectively. The effect of pH, scan rate, electrode kinetics, electroactive surface area, sensitivity and selectivity on the determination of PROP has been studied. The modified electrode rGO-CPE has been successfully employed for the determination of PROP present in pharmaceutical sample.

A modified carbon paste electrode with Fe3O4 nanoparticles/multi-walled carbon nanotubes nanocomposite (Fe3O4/MWCNTs/CPE) was developed as an efficient sensor for simultaneous determination of acetaminophen (AC) and theophylline (TP). The Fe3O4/MWCNTs nanocomposite was characterized by scanning electron microscopy (SEM), X-Ray diffraction (XRD), and Fourier transform infrared spectroscopy (FT-IR). Also, electron transfer rate of [Fe(CN)6]3-/4-as a redox couple probe on the surface of the Fe3O4/MWCNTs/CPE was studied using electrochemical impedance spectroscopy (EIS). The modified electrode preserved and combined the properties of the individual modifiers synergistically. The anodic peak currents of AC and TP were increased at the nanocomposite modified electrode compared to the bare electrode. Under the optimal experimental pH, the linear analytical curves were obtained in the range of 2-1000 μ M with a limit of detection (LOD) (S/N=3. 0) of 1. 68 μ M for AC and in the range of 3-1000 μ M and with a detection limit of 2. 48 μ M for TP using the differential pulse voltammetry (DPV) results. The applicability of the proposed method was successfully proved for simultaneous determination of these compounds in drug samples.

A chemically modified carbon paste electrode (CPE) founded on electrospun manganese oxide (Mn3O4) nanofibers (MONFs) was constructed as a new simple electrochemical sensor for a sensitive simultaneous determination of dopamine (DA) and tyrosine (Tyr). To investigate their electrochemical behavior several methods like differential pulse voltammetry (DPV) and cyclic voltammetry (CV) methods were used. MONFs were fabricated by an electrospinning process by manganese acetate stabilized with polyvinyl alcohol (PVA) as the precursors. In order to characterize MONFs several techniques such as field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) technique and energy dispersive X-ray spectroscopy (EDX) were used. Application of MONFs as the modifier of the CPE (MONFs/CPE) showed high oxidation peak currents for determination of DA and Tyr due to its catalytic effect and its surface area. Optimization of experimental parameters, by DPV method, showed the best sensitivity in determination of DA and Tyr in phosphate buffer solution (PBS) at pH of 7 with accumulation time of 20 s. Using DPV technique, the sensor revealed broad linear ranges of 0. 05-180 μ M and 0. 1-270 μ M with detection limits of 49 nM and 56 nM toward DA and Tyr, respectively. The fabricated sensor exposed excellent sensitivity, simplicity and high selectivity toward simultaneous determination of DA and Tyr. The analytical application of the sensor has been assessed for analysis of DA and Tyr in human blood serum and urine with acceptable results.

A genosensor was fabricated for detecting a fragment of Apolipoprotein E gene (ApoE). The sensor was made of a nanocomposite of reduced graphene oxide (rGO) and cerium oxide (CeO2) nanoparticles. For this purpose, surface of a glassy carbon electrode was first modified by polyaniline (PANI) and then rGO-CeO2 nanocomposite. It was next characterized through scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. A 23-base oligonucleotide sequences previously reported as a fragment of Apolipoprotein E gene (ApoE) which has a point mutation occurred in the progression of Alzheimer’ s disease was selected as a target molecule. Its ssDNA probe was immobilized on the modified surface via a strong interactions between CeO2 nanoparticles and the phosphate groups in the ssDNA. Detection of the biosensor signal was performed by square wave voltammetry (SWV) and Ru(bpy)3]2+/3+ as an electrochemical probe. In presence and absence of the target sequence, the electrochemical probe showed a different behaviour on the electrode surface. The developed genosensor could detect the ApoE gene sequence high selectively and sensitively, with in a good linear range of 10 fM to 10 nM.