Showing papers in "Portugaliae Electrochimica Acta in 2009"
TL;DR: In this paper, the corrosion inhibition of mild steel in H 2SO 4 in the presence of methocarbamol was studied using thermometric and gasometric (hydrogen evolution) methods.
Abstract: The corrosion inhibition of mild steel in H 2SO 4 in the presence of methocarbamol was studied using thermometric and gasometric (hydrogen evolution) methods. The study revealed that the corrosion rate increases with temperature, time and concentration of H2SO 4. Addition of methocarbamol to the corrodent solution lowered the corrosion rate of mild steel. Inhibition efficiency (%I) of methocarbamol was found to increase with concentration and decreased with temperature. Adsorption of methocarbamol molecule on mild steel surface was found to obey the Langmuir adsorption isotherm. The phenomenon of physical adsorption is proposed from the obtained thermodynamic parameters.
97 citations
TL;DR: In this article, the effect of phenylthiourea as a corrosion inhibitor for low carbon steel at different hydrochloric acid concentrations, different temperatures and fixed speed of electrode rotation was addressed.
Abstract: The effect of phenylthiourea as a corrosion inhibitor for low carbon steel at different hydrochloric acid concentrations, different temperatures and fixed speed of electrode rotation, were addressed in this work. Polarization technique was used to evaluate the corrosion rates parameters. The corrosion rate of low carbon steel increases with temperature and follows Arrhenius equation in all acid concentrations in presence and absence of the inhibitor. Detailed thermodynamic parameters of activation ( �Hact and �Sact ) for the corrosion reaction were obtained using nonlinear estimation method, while
88 citations
TL;DR: In this paper, the adsorption properties of ethanol extract of vernonia amygdalina for the corrosion of mild steel were studied using weight loss, thermometric, gasometric and IR methods of monitoring corrosion.
Abstract: Inhibitive and adsorption properties of ethanol extract of vernonia amygdalina for the corrosion of mild steel were studied using weight loss, thermometric, gasometric and IR methods of monitoring corrosion. The results revealed that ethanol extract of Vernonia amygdalina inhibited the corrosion of mild steel. The inhibition efficiency of the extract increased as the concentration of the extract increases. The inhibitor was found to function by being adsorbed on the surface of mild steel. The adsorption of the inhibitor followed the Langmuir adsorption isotherm. IR spectra of the corrosion product (without inhibitor), the extract and the corrosion product (with the inhibitor) confirmed that ethanol extract of vernonia amygdalina is an adsorption inhibitor. Phytochemical studies also revealed that ethanol vernonia amygdalina contains tannin, saponnins, flavanoid and anthraquinone, all of them contributing to the corrosion inhibition. Physical adsorption mechanism has been proposed from the values of some of the thermodynamic parameters obtained.
81 citations
TL;DR: In this article, an aqueous extract of beet root extract was used to control corrosion of carbon steel in well water in the absence and presence of Zn 2+ has been evaluated by mass loss method.
Abstract: The inhibition efficiency (IE) of an aqueous extract of beet root (BR) in controlling corrosion of carbon steel in well water in the absence and presence of Zn 2+ has been evaluated by mass loss method The formulation consisting of 4 mL of BR extract and 50 ppm Zn 2+ offers 98% inhibition efficiency to carbon steel immersed in well water A synergistic effect exists between BR extract and Zn 2+ Addition of N-Cetyl-N,N,N – trimethylammonium bromide (CTAB) does not change the excellent inhibition efficiency of the BR – Zn 2+ system The BR – Zn 2+ system shows excellent IE up to 7 days Polarization study reveals that this formulation controls the cathodic reaction predominantly AC impedance spectra reveal that a protective film is formed on the metal surface FTIR spectra reveal that the protective film consists of Fe 2+ - betanin complex and Zn(OH) 2 The film is found to be UV - fluorescent
73 citations
TL;DR: In this paper, the adsorption properties of ethanol extract of Phyllanthus amarus leaves for the corrosion of mild steel in H 2SO 4 were investigated using gravimetric, thermometric and gasometric methods.
Abstract: Inhibitive and adsorption properties of ethanol extract of Phyllanthus amarus for the corrosion of mild steel in H 2SO 4 were investigated using gravimetric, thermometric and gasometric methods. Ethanol extract of Phyllanthus amarus leaves is a good adsorption inhibitor for the corrosion of mild steel in H 2SO 4. Thermodynamic consideration indicates that the adsorption of the extract is exothermic and spontaneous. Also, the adsorption characteristic of the inhibitor is consistent with the assumptions of Langmuir adsorption isotherm. From the results and findings of the study, a physical adsorption mechanism is proposed for the adsorption of ethanol extract of Phyllanthus amarus on mild steel surface. The inhibition potentials of ethanol extract of Phyllanthus amarus leaves are enhanced by its phytochemical constituents.
58 citations
TL;DR: In this paper, the corrosion inhibition of aluminium by Ipomoea involcrata (IP) in 1 M NaOH was rapidly assessed using the gasometric technique at 30 and 60 o C.
Abstract: The corrosion inhibition of aluminium by Ipomoea involcrata (IP) in 1 M NaOH was rapidly assessed using the gasometric technique at 30 and 60 o C . Results obtained showed that Ipomoea involcrata acts as an inhibitor for aluminium corrosion in 1 M NaOH. Inhibition efficiency increased with increase in concentration of IP up to 55.0 % at 50 v/v% and decreased with increase in temperature. The adsorption of IP was in accord with Langmuir adsorption isotherm at the studied temperatures. A mechanism of physical adsorption is proposed from the calculated values of a E , ads Q and ads G Δ .
54 citations
TL;DR: In this article, the authors used gravimetric, gasometric and IR methods to study the corrosion of mild steel in H 2SO 4 using Azadirachta indica extracts.
Abstract: The corrosion of mild steel in H 2SO 4 was studied using gravimetric, gasometric and IR methods. The results indicate that the rate of corrosion of mild steel in H 2SO 4 increases with increase in the concentration of the acid and that ethanol extracts of the seeds and leaves of Azadirachta indica inhibit the corrosion of mild steel in H 2SO 4. Inhibition efficiencies of the leaves and seeds extract range from 82.62 to 94.24% and from 60.55 to 84.78%, respectively. The inhibition potential of these extracts is attributed to the presence of tannin, saponin, glycoside, anthraquinone, flavonone and other phytochemicals in the extracts. IR study confirms that the inhibitors are adsorption inhibitors and the adsorption of the inhibitors on mild steel surface is exothermic, spontaneous and consistent with the assumptions of Flory-Huggins adsorption isotherm. Based on the values of the activation, free energy of adsorption and the variation of inhibition efficiency with temperature, a physical adsorption mechanism is proposed for the adsorption of ethanol extract of leaves and seeds of Azadirachta indica on the surface of mild steel.
52 citations
TL;DR: In this article, the authors measured the corrosion rates in the presence of nizoral (NZR), an antifungal drug, as mild steel corrosion inhibitor in 0.1 M H 2SO 4 was measured by the weight loss method in the temperature range from 30 − 50 o C. Results revealed that NZR acts as an inhibitor for mild steel in sulphuric acid solution.
Abstract: The corrosion rates in the presence of nizoral (NZR), an antifungal drug, as mild steel corrosion inhibitor in 0.1 M H 2SO 4 was measured by the weight loss method in the temperature range from 30 – 50 o C. Results obtained revealed that NZR acts as an inhibitor for mild steel in sulphuric acid solution. Inhibition efficiency increased with increase in concentration of the inhibitor but decreased with increase in temperature. The addition of KI increased the inhibition of NZR to a considerable extent. The experimental results suggest that the presence of iodide ions in the solution stabilized the adsorption of Nizoral molecules on the mild steel surface thereby improving the inhibition efficiency of Nizoral. The adsorption characteristics of the inhibitor were approximated by Langmuir adsorption isotherm and kinetic/thermodynamic adsorption model of El-Awady et al. Mechanism of physical adsorption is proposed from the activation and thermodynamic parameters calculated.
48 citations
TL;DR: In this article, the results obtained indicate that clarithromycin is a good adsorption inhibitor for the corrosion of zinc in H 2SO 4, but the inhibition efficiency increases with increasing concentration but decreases with increasing temperature.
Abstract: The corrosion of zinc in 0.01 to 0.04 M H 2SO 4 was studied using gravimetric and gasometric methods of monitoring corrosion. The results obtained indicate that clarithromycin is a good adsorption inhibitor for the corrosion of zinc in H 2SO 4. The inhibition efficiency of clarithromycin increases with increasing concentration but decreases with increasing temperature. There was no significant difference between the inhibition efficiencies of clarithromycin obtained at various concentrations of H 2SO 4 (P>0.5), but values of inhibition efficiency tend to decrease with increasing concentration of the acid. The adsorption of clarithromycin on zinc surface is endothermic, spontaneous and is best described by Langmuir adsorption isotherm. Calculated values of activation energies and free energies of adsorption indicate that the adsorption of clarithromycin on zinc surface supports the mechanism of physical adsorption.
40 citations
TL;DR: In this paper, an attempt is made to machine the A356/SiC p composite work material using Electro Chemical Machining process and the results showed that all the four selected factors are significant and from the S/N graph the optimum level of each factor is chosen.
Abstract: Aluminium metal matrix composites (AMMCs) are now gaining their usage in aerospace and automotive industries. Because of their inherent nature, difficult to machine, they find very little applications in other sectors. Even non traditional processes like Laser Jet Machining and Electro Discharge Machining result in significant sub surface damage to the work. In this paper, an attempt is made to machine the A356/SiC p composite work material using Electro Chemical Machining process. Silicon carbide with an average particle size of 40 microns is tried in three different proportions, namely 5%, 10% and 15% by weight. Taguchi’s L 27 orthogonal array is chosen to design the experiments and 54 trials are conducted to study the effect of various parameters like applied voltage, electrolyte concentration, feed rate and percentage reinforcement on maximizing the material removal rate. ANOVA results have shown that all the four selected factors are significant and from the S/N graph the optimum level of each factor is chosen. A mathematical model is also developed using the regression method. Confirmation experiment is conducted and found that the data obtained have close match with the data predicted using the model.
39 citations
TL;DR: In this paper, the effect of iodide ion on the corrosion inhibition of aluminium in NaOH in the presence of Gum Arabic (GA) was studied using weight loss and hydrogen evolution techniques at 303 and 313 K.
Abstract: The effect of iodide ion on the corrosion inhibition of aluminium in NaOH in the presence of Gum Arabic (GA) was studied using weight loss and hydrogen evolution techniques at 303 and 313 K. The results obtained showed that inhibition efficiency increased with increasing GA concentration. The inhibiting action of GA was considerably enhanced by the addition of KI. The adsorption of KI, GA alone and in combination with iodide ion was found to obey Temkin adsorption isotherm. The inhibiting effect of GA and (GA+KI) increased with increase in temperature of the corrosion medium, indicating chemical adsorption mechanism. Synergism parameter evaluated was found to be greater than unity for the different concentrations of GA, which shows that the enhanced inhibition of GA caused by the addition of iodide ion is due to synergistic effect. It could be deduced from the thermodynamic parameters obtained that adsorption of GA alone and in combination with KI onto the metal surface is spontaneous.
TL;DR: In this paper, the authors studied the effect of azithromycin on the corrosion of zinc in H 2SO 4 at different temperatures (303 to 333 K) and found that the concentration of H 2 SO 4 did not have a significant impact on the inhibition efficiency of the inhibitor.
Abstract: Inhibition of the corrosion of zinc in various concentrations (0.01 to 0.05 M) of H 2SO 4 was studied using weight loss and hydrogen evolution methods of monitoring corrosion. The results revealed that various concentrations of azithromycin (0.0001 to 0.0005 M) inhibited the corrosion of zinc in H 2SO 4 at different temperatures (303 to 333 K). The concentration of H 2SO 4 did not exert significant impact on the inhibition efficiency of azithromycin, but inhibition efficiencies were found to decrease with increase in the concentration of the inhibitor. Values of inhibition efficiency obtained from the weight loss measurements correlated strongly with those obtained from the hydrogen evolution measurements. The activation energies for the corrosion of zinc inhibited by azithromycin were higher than the values obtained for the blank. Thermodynamic data revealed that the adsorption of azithromycin on the surface of zinc was endothermic (values of enthalpies of adsorption were positive), spontaneous (values of free energies of adsorption were negative) and was consistent with the adsorption model of Langmuir.
TL;DR: In this paper, the degradation of atrazine in aqueous solution using current controlled electrolysis at a platinum electrode was studied, and the effects of pH, current magnitude and direction, and temperature, were evaluated.
Abstract: Atrazine is a highly used herbicide and it has been found in both deep and superficial waters. Its solubility in water is reduced and is relatively stable in humid environments, where it has a half-life of one hundred days. Atrazine can be degraded by oxidative photolysis or by microorganisms. It is moderately toxic in humans, animals and plants, because it can be absorbed by inhalation, ingestion or through the skin. In this work, we study the degradation of atrazine in aqueous solution using current controlled electrolysis at a platinum electrode. The effects of pH, current magnitude and direction, and temperature, were evaluated. The atrazine decomposition was monitored during electrolysis by UV-Vis spectrophotometry; quantification of atrazine was done by GC/MS, and quantification of cyanuric acid was done by HPLC. It was found that at 25 oC in acid media, atrazine is degraded partially to cyanuric acid with formation of persistent intermediate compounds, but at 60 oC atrazine is completely degraded to cyanuric acid. The TOC results indicate no electrochemical combustion and no mineralization was observed under the experimental conditions studied.
TL;DR: In this paper, the voltammetric behavior of quetiapine (QTP) was studied using direct current (DC t), differential pulse (DPP) and alternating current (AC t) polarography.
Abstract: The voltammetric behaviour of quetiapine (QTP) was studied using direct current (DC t), differential pulse (DPP) and alternating current (AC t) polarography. The drug manifests cathodic waves over the pH range of 6 – 11.8. The waves were characterized as being irreversible, diffusion-controlled with limited adsorption properties. At pH 8, the diffusion current-concentration relationship was rectilinear over the range of 8 – 44 µg/mL and 4 – 44 µg/mL using DC t and DPP modes, respectively, with minimum detection limits (LOD) of 0.06 µg/mL and 0.04 µg/mL using the DC t and DPP modes, respectively. The diffusion-current constant (I d) is 1.36 ± 0.04 (n = 10). The proposed method was successfully applied to the determination of the studied compound both in pure form and in formulations. The results obtained were favourably compared with those obtained using a reference method. A pathway for the electrode reaction was postulated.
TL;DR: In this paper, the inhibition efficiency of an aqueous extract of Hibiscus rosa-sinensis (white) in controlling corrosion of aluminium at pH 12 has been evaluated by weight loss method in the absence and presence of Zn 2+.
Abstract: The inhibition efficiency (IE) of an aqueous extract of Hibiscus rosa-sinensis (white) in controlling corrosion of aluminium at pH 12 has been evaluated by weight loss method in the absence and presence of Zn 2+ . The formulation consisting of 8 mL flower extract (FE) and 50 ppm of Zn 2+ had 98% inhibition efficiency. Polarization study revealed that this formulation functioned as cathodic inhibitor. AC impedance spectra revealed the presence of a protective film formed on the metal surface. FTIR spectra revealed that the protective film consisted of a complex formed between the active principle of the flower extract and Al 3+ .
TL;DR: In this paper, 1 4H-1,4-benzothiazin-2-yl)ethanone (1 4-BT) was synthesized via a new mechanism.
Abstract: methyl-4H-1,4-benzothiazin-2-yl)ethanone (1,4-BT) was synthesised via a new mechanism. 1,4-BT was thereafter tested as corrosion inhibitor of mild steel in hydrochloric solution at 293 K by weight loss measurements and electrochemical techniques (potentiodynamic polarisation, polarisation resistance, impedance spectroscopy (EIS)). Inhibiting efficiency (E%) increased with concentration and reached highest values up to 98% even at low concentration with changing the mechanism of the corrosion process. Results obtained showed that the inhibitor studied was an efficient inhibitor, especially in cathodic domain. The temperature effect on the corrosion behaviour of mild steel in 1 M HCl with and without 1,4-BT at 5 10 -3 M was studied in the temperature range from 293 to 333 K. E% remains the same even at high temperature. The adsorption free energy and activation parameters for the mild steel dissolution reaction, in the presence of 1,4-BT, were determined. 1,4-BT is adsorbed on the mild steel surface according to a Langmuir isotherm adsorption model.
TL;DR: It was found that the immobilized glucose oxidase conserves its substrate specificity in the presence of a number of glucides (galactose, maltose, fructose, and saccharose) in 100 fold higher concentrations.
Abstract: The goal of this work is the evaluation of the analytical characteristics of the determinations performed using glucose oxidase and acetylcholinesterase based electrochemical sensors, developed applying original or optimized conventional methods of enzyme immobilization. It was found that the sensitivity of glucose determination, for example, varies from 0.048 to 3.36 mA L mol -1 cm -2 and the response time of the glucose oxidase based sensors – from 5 to 30 s, according to the method of the bioreceptor immobilization. The sensitivity of the analysis is affected from the activity of the immobilized biocomponent, from the composition of the solution (concentration of the substrate, of the mediator and of the inhibitor), and from the experimental conditions (pH, temperature, agitation), as well as from the kinetic parameters of the studied process. It was found that the immobilized glucose oxidase conserves its substrate specificity in the presence of a number of glucides (galactose, maltose, fructose, and saccharose) in 100 fold higher concentrations. The selectivity of glucose analysis is ensured applying a suitable potential. Interferences free glucose amperometric determination was performed at 0.00 V/SCE, in the presence of ascorbates and urates. The electrochemical quantification of enzyme inhibitors allows reaching particularly low limits of detection (10 -9 -10 -14 mol L -1 ).
TL;DR: In this article, a cyclic voltammetric study on the electrooxidation of methanol on 30 % Pt and 20 % Pt + 10 % Ru catalysts supported on Vulcan XC-72 was carried out in 0.5 M H 2SO 4.
Abstract: The cyclic voltammetric study on the electro-oxidation of methanol on 30 % Pt and 20 % Pt +10 % Ru catalysts supported on Vulcan XC-72 was carried out in 0.5 M H 2SO 4. Kinetic parameters such as exchange current density, Tafel slope and heterogeneous rate constants were calculated. The 30 % Pt showed a higher apparent catalytic activity for the electro-oxidation of methanol as compared with 20 % Pt + 10 % Ru catalyst. The presence of Ru did not contribute significantly towards the apparent catalytic activity of a catalyst for the electro-oxidation of methanol but it may be useful to prevent the
TL;DR: In this article, the authors used reticulated vitreous carbon (RVC) and graphite felt (GF) as porous electrode for the removal of 20 ppm Cu(II) in 0.5 mol dm -3 Na2SO4 at pH 2.
Abstract: This paper deals with the use of reticulated vitreous carbon (RVC) and graphite felt (GF) as porous electrode for the removal of 20 ppm Cu(II) in 0.5 mol dm -3 Na2SO4 at pH 2 (which resembles a rinsing wastewater generated by a plating industry). The experimental mass transport characterization (kma = bu c ) showed that for 100 ppi (RVC), the value of the coefficient b, associated with magnitude of porous electrode, is 0.88, while for (GF) is 3.38. On the other hand, c value for 100 ppi (RVC) is 0.06, while for (GF) is 0.62, indicating that the flow pattern is a complex function of the shape of the electrode. The experimental potential drop for 100 ppi (RVC) and (GF) (1.2 cm thick), indicated the absence of hydrogen evolution. Current efficiencies for RVC and GF were function of convection, giving values comprised between 45 ≤ φ ≤ 68% and 51 ≤ φ ≤ 73%, respectively, and energy consumption values of 0.3 < Econs < 1.7 and 0.4 < Ec < 1.1 kWh m -3 , respectively. Theoretical number of identical cells in the stack (N) necessary to the cupric depletion from 20 to 1 ppm, for 100 ppi (RVC) and (GF) were calculated.
TL;DR: In this paper, the effect of phenyl phthalimide derivatives on the corrosion of carbon steel in 0.5 M H 2SO 4 solution was studied using weight loss and galvanostatic polarization techniques.
Abstract: The effect of some phenyl phthalimide derivatives on the corrosion of carbon steel in 0.5 M H 2SO 4 solution was studied using weight loss and galvanostatic polarization techniques. The percentage inhibition efficiency was found to increase with increasing concentration of inhibitor and with decreasing temperature. Inhibition was explained by adsorption of these compounds on the metal surface. The adsorption follows Freundlich adsorption isotherms. Some thermodynamic functions were computed and discussed.
TL;DR: In this paper, the inhibition efficiency of K 3[Fe(CN) 6] in controlling corrosion of carbon steel in aqueous solution containing 60 ppm Cl - in the presence and absence of Zn 2+ has been evaluated by weight loss method.
Abstract: The inhibition efficiency (IE) of K 3[Fe(CN) 6] in controlling corrosion of carbon steel in aqueous solution containing 60 ppm of Cl - in the presence and absence of Zn 2+ has been evaluated by weight loss method. The formulation consisting of 100 ppm K 3[Fe(CN) 6] and 50 ppm Zn 2+ offers 98% inhibition efficiency to carbon steel immersed in aqueous solution containing 60 ppm Cl - . A synergistic effect exists between K 3[Fe(CN) 6] and Zn 2+ . As immersion period increases, the inhibition efficiency of K 3[Fe(CN) 6]� Zn 2+ system decreases. Polarization study reveals that this formulation controls the cathodic reaction predominantly. AC impedance spectra reveal that a protective film is formed on the metal surface. FTIR spectra reveal that the protective film consists of Prussian blue and Zn(OH) 2. The film is found to be UV fluorescent.
TL;DR: In this paper, a laccase-based polyphenolic biosensor was applied on polyether sulphone membranes and applied on an Universal Sensors (US) electrode base system containing a platinum working electrode and silver, silver chloride electrode.
Abstract: New developments in the utilization of a laccase based polyphenolic biosensor were done in order to optimize its application in wines. Laccase was immobilized on polyether sulphone membranes and applied on an Universal Sensors (US) electrode base system containing a platinum working electrode and silver, silver chloride electrode. Caffeic acid was dissolved either in tartarate standard buffer solution at pH 3.5 or in 12% ethanol tartarate standard buffer solution at pH 3.5. The referred values of pH and ethanol percentage are the average values of table wines. Wines from different regions of Portugal, namely Grao Vasco (Dao), A P_Cabernet (Setubal), C P_Castelo de Syrah (Setubal), Ol (Alentejo), A P (Alentejo) and Quinta dos Pocos (Douro), were studied. Grao Vasco was taken as a reference. It was observed that Grao Vasco (Dao) wine presented a caffeic acid equivalent concentration superior to the other studied wines, followed by a Douro wine: Quinta dos Pocos (values of 17.00 and 12.18 mg/L, respectively, were found). It was also possible to verify that the two latter referred wines did not inhibit the biosensor, which could be reused after having been dipped in those wines. However, the wines from Setubal and Alentejo, studied in this work, have a caffeic acid equivalent concentration lower than the other two mentioned before and seemed to inhibit the system, since the biosensor response decreased after being used in them. It was, thus, not possible to do several assays with the same membrane, when those wines were used. Reproducibilities were better for caffeic acid standard solutions, Grao Vasco and Quinta dos Pocos wines, than for the other wines. In fact RSDs (Relative standard deviations) of the order of 1.1, 1.4 and 5.0% were obtained for caffeic acid standard solution, Grao Vasco and Quinta dos Pocos wines, whereas 20% was found in the Setubal and Alentejo studied wines. Two particular wines, A P_Cabernet and A P, were studied in more detail. Cyclic voltammograms and biosensor responses of these two wines indicate that A P has more caffeic acid equivalents than the A P_Cabernet.
TL;DR: In this article, an Artificial Neural Networks (ANN) model was used to obtain electrodeposits of copper-tin over mild steel substrate and a model for the plating parameters were developed using ANN.
Abstract: The aim of this research is to obtain electrodeposits of copper-tin over mild steel substrate The plating parameters were studied and a model is developed using Artificial Neural Networks (ANN) The electrodeposition of copper-tin was carried out from an alkaline cyanide bath Copper content of coatings in alloy deposition was determined by using X-ray fluorescence spectroscopy The results were used to create a model for the plating characteristics and also for studies using ANN The ANN model is compared with the conventional mathematical regression model for analysis
TL;DR: In this article, the effect of some amidopoly ethylamine, with different numbers of units, on the corrosion of zinc electrode in ZnCl 2, NH 4Cl and (ZnCl2 + NH 4CL) electrolytes has been studied using galvanostatic polarization measurements.
Abstract: The effect of some amidopoly ethylamine, with different numbers of ethylamine units, on the corrosion of zinc electrode in ZnCl 2, NH 4Cl and (ZnCl 2 + NH 4Cl) electrolytes has been studied using galvanostatic polarization measurements. The inhibition efficiency was found to increase with increasing concentration, number of ethylamine units per molecule and with decreasing the temperature. Inhibition is explained on the basis of adsorption of amidopoly ethylamine molecules on the zinc electrode surface through their ethylamine groups. The inhibitors are adsorbed on the zinc electrode surface according to Langmuir adsorption isotherm. Some thermodynamic parameters are calculated and explained for the tested systems from the data obtained at different temperatures.
TL;DR: A carbon paste biosensor modified with a crude enzymatic extract of the Pycnoporus sanguineus fungi as a lacase source is proposed for catechol determination and other phenolic compounds, presenting better response forcatechol, hydroquinone and resorcine.
Abstract: Laccase is a poliphenoloxidase enzyme that catalyzes the oxidation of catechol compounds in the corresponding quinones. The current obtained in this redox process can be used for quantitative analysis. In this work, a carbon paste biosensor modified with a crude enzymatic extract of the Pycnoporus sanguineus fungi as a lacase source is proposed for catechol determination and other phenolic compounds. The effect of carbon paste and electrolyte composition, pH from 3.0 to 8.0, scan rate from 10 to 40 mVs -1 and potential pulse amplitude from 10 to 60 mV on the differential pulse voltammetric response was investigated. The analytical curves were linear in the catechol concentration range from 2.0 x 10 -5 to 7.0 x 10 -4 molL -1 , with detection limits of 4,5 x 10 -6 molL -1 . This biosensor was used for the determination of different kind of phenolic compounds, presenting better response for catechol, hydroquinone and resorcine.
TL;DR: In this paper, a multi-walled carbon nanotubes (MWCNTs)-modified edge plane pyrolytic graphite (EPPG) electrode using cyclic voltammetry (CV) in three kinds of room temperature ionic liquids (RTILs) was investigated.
Abstract: Oxygen reduction reaction (ORR) was investigated on a multi-walled carbon nanotubes (MWCNTs)-modified edge plane pyrolytic graphite (EPPG) electrode using cyclic voltammetry (CV) in three kinds of room temperature ionic liquids (RTILs), i.e., 1ethyl-3-methylimidazolium tetrafluoroborate (EMIBF 4), 1-n-propyl-3-methylimidazolium tetrafluoroborate (PMIBF 4), and 1-n-butyl-3-methylimidazolium tetrafluoroborate (BMIBF 4). The results demonstrated that, after being modified by MWCNTs on the EPPG electrode, both the reduction peak current of oxygen and the oxidation peak current of superoxide anion were all dramatically increased, and the values of standard rate constant, �s, corresponding to ORR, were greatly enhanced. Under the same condition, in PMIBF 4, MWCNTs-modified EPPG electrode exhibited the most satisfied electrocatalysis for ORR, in which standard rate constant, �s, was improved from 2.9 × 10 -3 cm s -1 on a EPPG electrode, to 10.4 × 10 -3 cm s -1 . While in EMIBF 4 and BMIBF 4,
TL;DR: In this paper, square wave voltammetry was used to explore the adsorption property of cefadroxil complex with copper ions on the hanging mercury drop electrode (HMDE).
Abstract: Square-wave voltammetry was used to explore the adsorption property of cefadroxil complex with copper ions on the hanging mercury drop electrode (HMDE). By employing the adsorptive stripping voltammetric approach, a sensitive electroanalytical method for the quantitative analysis of cefadroxil antibiotic was achieved. A welldeveloped voltammetric peak was obtained in pH 10 Britton-Robinson buffer (B-R buffer) at -650 mV. The cyclic voltammetric studies indicated that the reduction process was irreversible and primarily controlled by adsorption. An investigation of the variation of adsorptive voltammetric peak current with supporting electrolyte, pH, accumulation time, accumulation potential, scan rate, pulse amplitude, SW frequency, working electrode area and convection rate has resulted in the recognition of optimal experimental conditions for cefadroxil analysis. The studied electroanalytical signal showed a linear response for cefadroxil in the concentration range 6 ×10 -7 - 2 ×10 -6 mol L -1 (r = 0.999). A limit of detection of 2 ×10 -9 mol L -1 with relative standard deviation of 2.783 RSD% and mean recovery of 99% was obtained. Possible interferences by several substances usually present in pharmaceutical formulation were also evaluated. The analytical quantification of cefadroxil in commercially available pharmaceutical formulation was performed and compared with data from HPLC technique.
Abstract: Corrosion of the embedded steel reinforcements (rebars) in concrete is the major reason for the deterioration of concrete structures. One of the effective methods of overcoming this serious problem is by applying a barrier coating to the steel rebars. The barrier coating on steel rebars isolates the steel from the immediate environment and also acts as an insulator to prevent the corrosion. Four different coatings have been formulated using resins such as epoxy silicone-polyamide, polyester polyol-aromatic isocyanate, and acrylic polyol-aromatic isocyanate. These formulations consist of either ordinary portland cement (OPC) or fly ash as extender (pozzolanic pigments) and titanium dioxide (TiO 2) and zinc phosphate as the main pigment. All these coatings have been studied for their barrier protection and other mechanical properties. Evaluation study of these coatings include Electrochemical Impedance Spectroscopy (EIS), chemical resistance tests and mechanical tests such as flexibility, impact resistance, adhesion, hardness and abrasion resistance, etc., as per ASTM standards and the results are discussed elaborately. It has been concluded from this study that the epoxy siliconepolyamide resin based coating formulation shows good mechanical properties in addition to the barrier protection to the steel rebars from the corrosive environments.
TL;DR: In this article, the free energy of adsorption of [(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-(4-methoxy-phenyl)methyl]-urea on iron in phosphoric media was studied by using electrochemical technique.
Abstract: The adsorption of [(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-(4-methoxy-phenyl)methyl]-urea on iron in phosphoric media was studied by using electrochemical technique. The adsorption mechanism was investigated using adsorption isotherms. The experimental data fit localized adsorption models. The values for free energy of adsorption, o ads G Δ , were also calculated at each surface coverage, �, of the studied compound by applying the mathematical model of Bockris – Swinkels adsorption isotherm. The variation of free energy of adsorption o ads G Δ with surface coverage, �, was interpreted in terms of deviation from ideal condition assumed in Langmuir model. A possible adsorption model of HPU2 molecules on to the metal surface was suggested.
TL;DR: In this article, azo-dye derived from sulfonamide was synthesized and the elucidation of ligand and complex structures were studied by electronic, infrared and 1H NMR spectroscopies.
Abstract: Molecular structure of the azo-dye derived from sulfonamide was synthesized. The elucidation of ligand and complex structures were studied by electronic, infrared and 1H NMR spectroscopies. Proton-ligand constants of sulphonamid azo-derivatives and the stability constant of Mo (III), VO (II), UO2 (II) and Co (II) metal ions with sulfonamide azodye derivatives have been determined potentiometrically in 0.1 M KCl and 30% (v/v) ethanol-water mixture. The data are discussed in terms of the electronic character of the substituents and of the change in temperature. The pK 1-H values have been found to increase with increasing electron donating nature of the subsituents. The evaluated dissociation processes are non spontaneous, endothermic and entropically unfavourable. The order of the stability constants of the formed complexes was found to be Mo 3+ > VO 2+ > UO2 2+ > Co 2+ . The influence of substituents on the stability of the complexes was examined on the basis of an electron repelling property of the substituent. The effect of temperature on the stability of the formed complexes was studied and the corresponding thermodynamic parameters (∆G, ∆H and ∆S) were evaluated and discussed. The stoichiometries of these complexes were determined conductometrically and indicated the formation of 1:1 and 1:2 (metal:ligand) complexes.