سال:1396 | دوره: | شماره: |تعداد مقالات:10

Cobalt-decorated graphene nanocomposite electrode was prepared via an electrochemical strategy and utilized for phosphate sensing. Electrochemical approach has found to be a simple, cheap, and green method for this purpose. The composite electrode was also characterized with scanning electron microscopy and cyclic voltammetry. Characteristics such as potentiometric response, calibration curve, response time, effects of dissolved oxygen, interfering ions, and pH were also evaluated. The potentiometric response for the range of 10-6 to 10-2 M showed a good linear relationship with the logarithm of phosphate concentrations with a slope of-31. 6 mV per decade change of concentration.

In this study, SiO2@Fe3O4/GR nanocomposite, ionic liguid and 2-(ferrocenylethynyl)fluoren-9-one (2FE) modified carbon paste electrode (SiO2@Fe3O4/GR/2FE/IL/CPE) was used for the determination of levodopa. The electrochemical behavior of levodopa was investigated using cyclic voltammetry (CV), chronoamperometry (CHA) and differential pulse voltammetry (DPV) techniques. Due to the fine characteristics of modified electrode, a good linear relationship between the anodic peak current and levodopa concentration in the range 0. 1– 500. 0 μ M was observed. The detection limit (3σ ) obtained by DPV was 6. 0×10-8 M (S/N=3). Here, a new sensor is introduced that is simple, rapid, sensitive, selective and cost-effective for quantitation of levodopa in real samples.

The poly (congo red) film was developed on the surface of carbon paste electrode by electrochemical method. The fabricated poly (congo red) modified carbon paste electrode exhibited excellent electrocatalytic activity towards the oxidation of catechol (CC) and hydroquinone (HQ) in a binary mixture by cyclic voltammetric (CV) and differential pulse voltammetric (DPV) techniques. The scan rate effect was found to be adsorption controlled electrode process. The interference study was done by varying the concentration of one species while other kept constant. Overall a sensitive and selective method was developed for the electroanalysis of CC and HQ.

A novel anion-selective electrode for salicylate ion with new ionophore was designed based on modified carbon paste electrode with multi walled carbon nanotubes (MWCNTs). Electrode made was evaluated for electrochemical studies using potentiometric and impedance techniques and results compared with together. The results of the potentiometric method using modified carbon paste electrode showed that the prepared electrode has a Nernstian slope 60. 1± 0. 1 mV in concentrations measurement range 1. 0×10-7-1. 0×10-1 M, the detection limit 5. 4×10-8, with pH range of 3. 5-9. 3, while using the impedance technique, the concentration measurement range increased to 1. 0×10-9-1. 0×10-1 M, pH range increased to 3. 8-10. 7 and the detection limit decreased to 4. 3×10-10 M.

Poly 4-aminobenzene sulfonic acid modified glassy carbon electrode (poly(4-ABSA/GCE)) was prepared with electrochemical polymerization technique in phosphate buffer solution (PBS) (pH 7. 0). The modified glassy carbon electrode (GCE), which has high electrooxidation ability in the pH range of 5-10 with cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques, was successfully developed for the electrochemical determination of quercetin (QR). However, the QR or the products of the oxidation reaction are adsorbed strongly on the modified glassy carbon surface. Therefore, when subsequent sweeps of the CV and DPV voltammograms were recorded, a decrease was observed at the peak current and at peak potential there was a shift to a lower positive potential. The best results for the quantitative determination of QR were obtained by DPV technique in 0. 1 M PBS (pH 8. 0). A linear calibration curve for DPV analysis was constructed in the QR concentration range of 7×10-5 to 9×10-4 M. The method was applied for the analysis of QR in onion peel.

This work describes a novel thrombin admittance biosensor based on self-assembled anti-thrombin-aptamer. The biosensor was constructed by modification of glassy carbon electrode by using of MWCNT-1-butyl-3-methylimidazolium hexafluorophosphate, electro-deposition of gold nanoparticles and finally loading DNA aptamer on the electrode surface. The electrochemical response of thrombin (in form of coulometric admittance) was obtained by coulometric FFT admittance voltammetry (CFFTAV). The analyte signal was established on the decrease of the admittance related to the redox couple of probe (Fe(CN)6]3− /4− ). The influences of important parameters in the determination process were investigated, and optimized. The change in the analyte response was proportional to the concentrations in range of 0. 03 to 18 nM, with a detection limit of 8×10-12 M. Moreover, the proposed biosensor exhibited high sensitivity and long-term stability. The biosensor was successfully used to the determination of thrombin content in the biological samples.

The electro-oxidation of Catechol in presence of L-Glutamine has been investigated in aqueous solution with various pH values, different electrodes and different concentration of L-Glutamine by using cyclic voltammetry, differential pulse voltammetry and controlled potential coulometry. Electrochemically generated o-benzoquinone (Michael acceptor) from oxidation of Catechol reacts with lower concentration of L-Glutamine as nucleophiles in the second scan of potential. The products obtained from the reaction are assumed to be 2-amino-5-((3, 4-dihydroxoyphenyl)amino)-5-oxopentanoic acid that undergo electron transfer at more negative potentials than the Catechol. The effect of pH of Catechol in presence of L-Glutamine has been studied by varying pH from 5 to 11. The slope of the plots of anodic peak current, Ep against pH of Catechol-Glutamine adduct is 25. 6 mV, indicates that the oxidation proceeded via the 2e− /2H+ processes. The concentration effect of L-Glutamine with the fixed concentration of Catechol (2 mM) was measured from 10 mM to 100 mM. The reaction was strongly influenced by the pH as well as concentration of L-Glutamine and electrode materials. The reaction is mostly favorable in 50 mM of L-Glutamine and 2 mM of Catechol at pH 7. The behavior of the reaction is diffusion controlled followed by ECE mechanism.

An ion-selective electrode for mercury (II) ion is fabricated based on primarily electrodeposition of polypyrrole on the surface of stainless steel electrode, followed by coating with multiwall carbon nanotubes (MWCNTs), poly (vinyl chloride) (PVC) composite membrane which is modified with a new enamine ionophore. Polypyrrole film because of its good stability and conductivity was prepared as an intermediate layer of solid contact electrode. The combination of conducting polymers with those of MWCNTs leads to an improved performance of the resulting sensing devices. The electrode showed a Nernstian slope of 29. 34± 0. 25 mV decade-1 over a wide concentration range of 5. 0×10-7 to 1. 0×10-2 M with the detection limit of 1. 4×10-7 M of Hg(NO3)2. The proposed electrode exhibited a very good selectivity toward Hg (II) ion over a variety of metal ions. The response of this nanocomposite membrane electrode remains stable for at least two months without observing any considerable deviation. The practical applicability of this sensor as an indicator electrode in potentiometric titration of Hg (II) ions with EDTA and in titration of mixed halides are demonstrated. This electrode was also successfully applied for the determination of mercury ions in river water samples.

The active cauliflower-like LiFePO4 (LFP/Cin) material was synthesized with hydrothermal process in the presence of glucose and then calcined at 600 ° C. The physical properties, particle size and morphology of obtained samples were investigated with the X-ray diffraction (XRD), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The electrochemical performance of nano-composites was studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic cycling performance. The CV curves show that LFP/Cin has higher electrochemical reactivity for lithium insertion and extraction than the LFP conventional cathode material. EIS measurements demonstrated that Rct for LFP/Cin is 70 and 50 percent lower compared to LFP and LFP/Cex respectively. The initial discharge capacity of LiFePO4/Cin cathode material delivers about 133. 92 mAh g− 1 (82% of theoretical capacity) at 0. 1 C and cycling stability with 96. 3% of capacity retention after 40 cycles at 0. 1 C. Electrochemical tests demonstrate that in-situ carbon coating play an important role in the improvement of battery performance with increasing the conductivity, reduce the particles size and unique structure.

The present study aims at investigating the corrosion inhibition performance of a new triazole inhibitor namely (Z)-4-((2, 4-dihydroxybenzylidene) amino)-5-methy-2, 4-dihydro-3H-1, 2, 4-triazole-3-thione on mild steel corrosion in 1. 0 M HCl solution using weight loss, electrochemical impedance spectroscopy, potentiodynamic polarization measurements and density functional (DFT) methods. The results show that inhibition efficiency increases with increase in the inhibitor concentration and maximum inhibition efficiency of 80. 74% was obtained at a concentration of 10-3 M. The corrosion behavior was also studied in the absence and presence of inhibitor at various concentrations in the temperature range of 318-348 K. Potentiodynamic polarization results showed that the inhibitor is mixed-type. The Nyquist plots showed that on increasing the inhibitor concentration charge-transfer resistance increased and double-layer capacitance values decreased thereby suggesting that corrosion inhibition is charge transfer controlled process and inhibition occurs due to the adsorption of inhibitor molecules on the metal surface. The adsorption of inhibitors followed Langmuir a isotherm Quantum chemical calculations very well supported the experimental results.