سال:1397 | دوره: | شماره: |تعداد مقالات:10

In this research, grain refinement process of AISI 304 stainless steel (304 SS) was successfully performed by an advanced thermomechanical operation. Then, the role of grain refinement on the electrochemical response of 304 SS in an acidic solution (0. 1 M HNO3 solution) was investigated. Microstructural observations depicted that thermomechanical operation resulted in reduction in the grain size from about 37 μ m to about 380 nm by a factor of ~100. All the electrochemical experiments concerning the passive and semiconducting properties evaluated by potentiodynamic polarization (PDP), electrochemical impedance spectroscopy (EIS) and Mott– Schottky (M– S) measurements. PDP and EIS plots revealed that grain refinement led to superior conditions for forming the passive layers. M– S tests showed that grain-refining process cannot change the semiconductor properties (n-and p-type semiconductors) of the passive layers. Moreover, M– S tests depicted that the calculated acceptor and donor densities (NA and ND) declined with grain refinement. These responses were consistent with the observations of the PDP and EIS tests, evidencing that the passive response enhanced with decreasing the grain size. In conclusion, all the electrochemical experiments depicted that the grain refinement in micro-scales can significantly enhance the passive and semiconducting properties of 304 SS by creation of more stable and compact passive layer.

In this paper, a new stable and sensitive electrochemical sensor was prepared by two-fold modification of glassy carbon electrode (GCE) with poly-alizarin red S (AzrS) and multiwalled carbon nanotubes (MWCNTs). The fabricated poly-AzrS/MWCNTs/GCE modified chemical sensor was employed towards the investigation of electrocatalytic oxidation of serotonin in 0. 1 mol/dm3 phosphate buffer (PBS) solution of pH 6. 0 with the help of voltammetric techniques such as cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS). The developed electrochemical sensor exhibited a potent and persistent electron mediating behaviour towards the serotonin determination and also lavishly resolved oxidation peaks for serotonin and epinephrine (EP) simultaneously. The effect of experimental variables, such as potential scan rate, solution pH, simultaneous determination, accumulation time, impedance and concentration were examined. The limit of detection (LOD) and limit of quantification (LOQ) were found to be as 1. 8×10-7 mol/dm3 and 17. 52×10-7 mol/dm3, respectively with a dynamic range from 0. 5×10-6 to 1. 1×10-5 mol/dm3. The fabricated electrochemical sensor was applied for the direct determination of serotonin in blood serum samples. Further the fabricated two-fold modified electrochemical sensor exhibited good sensitivity, stability and reproducibility in comparison with bare GCE towards the determination of serotonin.

The graphene quantum dots (GQDs) were prepared by tuning the carbonization degree of citric acid and graphite screen-printed electrode modified with graphene quantum dots (GQDs/SPE) was constructed and used for the sensitive voltammetric determination of isoproterenol. In comparison with unmodified electrode, the presence of the GQD/ SPE resulted in a remarkable increase in the peak currents. The electrochemical response characteristics of the modified electrode toward isoproterenol were studied by means of cyclic voltammetry (CV), differential pulse voltammetry (DPV) and chronoamperometry. It was demonstrated that the modified electrode presents good electrical conductivity and has favorable electrochemical response to isoproterenol. The (GQDs/SPE) displays a linear range from 1. 0 to 900. 0 μ M and a detection limit of 0. 6 μ M (S/N=3) to isoproterenol.

Poly (nicotinamide) modified carbon paste electrode (poly-NA MCPE) was fabricated for the electrocatalytic determination of acetaminophen (AC) and folic acid (FA) by using cyclic voltammetric method. Compared to bare carbon paste electrode (BCPE) the poly-NA MCPE showed better electrocatalytic performance towards the oxidation of AC in phosphate buffer solution (PBS) of pH 7. 4. Under the optimized experimental conditions, the influence of scan rate and concentration were studied. The detection limit of AC was calculated to be 0. 072 mM by CV technique, in a linear concentration range of 20. 66 to 119. 04 μ M. The poly-NA MCPE was used for the simultaneous determination of AC and FA in a binary mixture by CV and differential pulse voltammetric (DPV) technique.

In this study, fabrication of carbon paste electrode amplified with CdO/CNTs nanocomposite and 1-ethyl-3-methylimidazolium tetrafluoroborate (CdO/CNTs/1-E-3-MITFBr/CPE) for determination of carmoisine was investigated. The electro-oxidation of carmoisine occurs at a potential about 680 mV at a surface of CdO/CNTs/1-E-3-MITFBr/CPE and this mount is less positive than the bare carbon paste electrode at the optimized condition. The square wave voltammograms (SWV) peak currents of carmoisine show good linear dynamic range (0. 1-700 μ M) with a detection limit of 40. 0 nM. Finally, the CdO/CNTs/1-E-3-MITFBr/CPE was used as highly selective sensor for determination of carmoisine in real samples.

Salbutamol is a short-acting, selective beta2-adrenergic receptor agonist used in the treatment of asthma and chronic obstructive pulmonary disease (COPD). In this work a salbutamol selective nanocomposite sensor based on ion-pair as a sensing element, multi-walled carbon nanotubes (MWCNTs), graphite powder and paraffin oil is constructed. The optimized composition of 7% MWCNTs, 20% Ionophore, 20% paraffin oil and 53% graphite powder shows a Nernestian response of 29. 1± 0. 4 in the range of 5×10-6-1×10-2 mol L-1. Multi-walled carbon nanotubes are used because of electrical conductivity and remarkable mechanical strength. The proposed carbon paste electrode can be used over the pH range of 3. 5– 10 and has a detection limit of 3. 0×10-6 mol L-1. This method is used to salbutamol recognition in pure solutions and pharmaceutical preparations with high accuracy and precision.

A novel electrochemical sensor consisting of Mn3O4 nanoparticles modified graphite screen printed electrode (Mn3O4 NPs/SPE) was fabricated and applied for the determination of norepinephrine (NEP). Electroanalytical measurements including cyclic voltammetry (CV) and differential pulse voltammetry (DPV) were used. The optimum buffer of pH 7. 0, the norepinephrine oxidation peak current enhanced linearly with concentration ranging from 0. 7 to 400. 0 μ M (R2 of 0. 9994) with a detection limit of 0. 1 μ M. The proposed sensor was used for determination of norepinephrine in real samples.

The comparative study of the inhibition and adsorption properties of extract of Coriandrum Sativum seeds (CSE) as a new eco-friendly corrosion inhibition in 1. 0 M hydrochloric and 0. 5 M sulfuric solutions was investigated using several methods such as polarization curves, Bode plots, electrochemical impedance spectroscopy (EIS) and scanning electron microscopy (SEM). All results demonstrated that CSE suppressed the corrosion reaction in both acids medium (93. 7% in 1. 0 M HCl, 96. 7% in 0. 5 M H2SO4). Adsorption characteristics of the extract were approximated by various adsorption isotherm models (Langmuir, Freundlich and Temkin) and were in a good agreement with the Fourier Transformed Infrared spectroscopy (FTIR) results, they have shown that CSE contains Functional groups responsible of corrosion inhibition and other methods results. The inhibition mechanisms, estimated from the temperature dependence of inhibition efficiency as well from kinetic and activation parameters show that the extract functioned via mixed inhibition mechanism. It is suggested that molecular as well as protonated organic species in the extract contribute to the observed inhibiting action.

Cerium oxide possess various applications including waste refiner, catalyst, electrolyte in solid state fuel cell, glass decoloring and materials polishing. The use of this material in nanosized form, with high surface area improves its functionality significantly. In this study, ultrafine CeO2 nano-particles were prepared by a simple electrochemical platform. The synthesis experiments were performed from 0. 01 M cerium nitrate aqueous electrolyte in the presence of H2O2 and PVP. The as-deposited powder was also calcined 400 ° C for 2 h. The morphologies and crystal structures of the prepared powders were examined by means of scanning and transmission electron microcopies (SEM and TEM) as well as X-ray diffraction (XRD), FT-IR and DSC-TGA. These analysis results proved the electro-synthesis of pure crystalline cerium oxide final particles. The high surface area (184. 8 m2 g– 1) of the prepared nanoparticles was also confirmed through BET analysis. A possible mechanism of CeO2 deposition on the cathode surface was proposed, when the hydrogen peroxide additive played an important role in the formation of hydrous cerium oxide. In final, this simple electrochemical procedure is proposed for mass production of high surface area ultrafine nanoparticles of cerium oxide.

A novel Ni2+ ion-imprinted polymer (IIP) was synthesized through a precipitation polymerization technique using itaconic acid (as functional monomer) and ethylene glycol dimethacrylate (as cross-linking agent). NIP was next used to construct a Ni2+ ion-selective membrane electrode through dispersing its particles in a poly (vinyl chloride)(PVC) based membrane plasticized with dibutylphthalate. The electrode revealed a Nernstian response of 24. 2± 0. 5 mV decade-1 to Ni2+ from 1. 0×10-5 to 1. 0×10-1 mol L-1 and had a lower detection limit of 5. 0×10-6 mol L-1. A control electrode based on non-imprinted polymer (NIP) was also prepared and evaluated, and found to be insensitive to the analyte ions in aqueous media. The satisfactory qualities of the developed IIP sensor make it a suitable candidate for the determination of Ni2+ ions.