Sharif Digital Repository

The voltammetric performance of edge-plane pyrolytic graphite (EPG) electrode via adsorptive stripping voltammetry was investigated for study of the electrochemical behavior of omeprazole (OMZ) in aqueous solution. The results revealed that the oxidation of OMZ is an irreversible pH-dependent process that proceeds with the transfer of one electron and one proton in an adsorption-controlled mechanism. The determination conditions, such as the pH values of the supporting electrolyte, accumulation time and scan rate were optimized. Simplicity, high reproducibility and low detection limit (3 nM) of the electrode response as well as wide linear range (0.01 to 4.0 µM) can be stated as significant... 

A new micro-solid phase extraction method was developed by combining solid-phase extraction and stir bar sorptive extraction to benefit from the advantages of both techniques. A polypyrrole coating was electrochemically synthesized on the surface of an already used graphite furnace, employed in electro-thermal atomic absorption spectroscopy. The cylindrical geometry of the graphite tube provided a rather huge surface area, suitable for sorptive extraction. The novel sorbent coating was examined as an extracting medium to isolate malathion. Effects of different parameters such as extraction time, salt concentration, sample volume, desorption solvent and time were investigated and optimized.... 

A simple modified TiO2 nanotubes electrode was fabricated by electrodeposition of Pd, Pt and Au nanoparticles. The TiO2 nanotubes electrode was prepared using the anodizing method, followed by modifying Pd nanoparticles onto the tubes surface, offering a uniform conductive surface for electrodeposition of Pt and Au. The performance of the modified electrode was characterized by cyclic voltammetry and differential pulse voltammetry methods. The Au/Pt/Pd/TiO2 NTs modified electrode represented a high sensitivity towards individual detection of dopamine as well as simultaneous detection of dopamine and uric acid using 0.1 M phosphate buffer solution (pH 7.00) as the base solution. In both case,... 

Three new chromophores based on the triphenylamine (MM, DM, DN) with various novel electron withdrawing anchoring groups have been synthesized for use in dye-sensitized solar cells (DSSCs). The sensitizers were characterized by 1H and 13C NMR, Mass, UV–Vis, and electrochemical analysis. The HOMO and LUMO electron distributions of the sensitizers were calculated using density functional theory on a B3LYP level for geometry optimization. The DSSC device based on DM dye showed the best photovoltaic performance among MM and DN dyes: maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 98 %, short circuit current (JSC) of 4.58 mA/cm2, open circuit voltage (VOC) of... 

Sol composition and ripening conditions are two important parameters in silica fiber production through the conventional sol-gel process. In the current study, silica nanofibers were successfully obtained via the electrospinning technique, and sol-gel formation occurred during this process. Based on previous reports, with the aim of increasing the selectivity, we used the molecular imprinted methodology to produce a selective medium via sol-gel electrospinning. In this process, sol-gel was formed during electrospinning and then, the backbone polymer was removed by heating. To obtain a thin layer of silica nanofibers, the influencing parameters such as backbone polymer types, imprinting time... 

Due to its high discharge capacity, low cost, and good safety, LiNi0.5Co0.2Mn0.3O2 (NCM 523) is regarded as a promising cathode material for the next-generation of lithium-ion batteries. However, poor cycling stability and rate capability are the main disadvantages of the NCM 523 cathode material. In this work, SiO2 single layer-coated and reduced graphene oxide (outer)/SiO2 (inner) double layer-coated NCM 523 have been prepared by a facile wet chemical method. Field emission scanning electron microscopy (FESEM), energy dispersive X-ray (EDX) analysis, transmission electron microscopy (TEM), Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy results confirm that NCM 523... 

In this work, cycling-induced aging occurring in 18650-type LiFePO4/graphite full cells at different C-rates is studied extensively. The mechanism of performance degradation is investigated using a combination of electrochemical and microstructural analyses. Half-cell studies are carried out after dismantling the full cells, using fresh and cycled LiFePO4 cathode and graphite anode to independently study them. The results show that the capacity of LiFePO4 electrodes is significantly recovered. The rate of capacity fading in the discharge state considered as irreversible capacity in the graphite is higher than LiFePO4 half cells, indicating a greater degradation in the performance of this... 

Pyrrole was electro-polymerized on the surface of the glassy carbon electrode (GCE) coated with a thin film of carbon nanomaterials, including carbon nanotubes (CNTs), carbon nanoparticles (CNPs), nanodiamond-graphite (NDG) or graphite nanopowder (GNP). Morphology, thickness, stability and loading of the polypyrrole (PPY) film were significantly affected by the structure and morphology of the sub-layer of carbon nanomaterials. Electrochemical oxidation of atorvastatin (ATOR) was investigated. Under the optimized conditions, a significant increase in the peak current (compared to other modified electrodes and bare GCE) and a negative shift in the peak potential (compared to bare GCE) were... 

Ruthenium oxide was coated on multiwalled carbon nanotubes (MWCNTs) to obtain nanocomposite electrode which has a good response to the pH. To synthesize this electrode, gold and cobalt were coated on a stainless steel 304 substrates, respectively, and then, vertically aligned carbon nanotubes were grown on the prepared substrates by chemical vapor deposition. Gold reduced activity of the stainless steel, while cobalt served as a catalyst for growth of the carbon nanotube. Ruthenium oxide was then coated on MWCNTs via sol-gel method. At last, different techniques were used to characterize the properties of synthesized electrode including scanning electron microscopy (SEM), transmission... 

A simple electrodeposition method is employed to construct a thin film modifier of palladium-gold nanoparticles (Pd-AuNPs) decorated multi-walled carbon nanotube (MWCNT) on the surface of glassy carbon electrode (GCE). Morphology and property of Pd-AuNPs-MWCNT have been examined by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). Electrochemical performance of Pd-AuNPs-MWCNT/GCE for detection of ceftazidime (CFZ) has been investigated by cyclic voltammetry (CV). This nanostructured film modified electrode effectively exhibited enhanced properties for detection of ceftazidime (CFZ). The effects of various experimental variables such as, the amount of casted MWCNT,... 

Electrochemical deposition, as a well-controlled synthesis procedure, has been used for subsequently layer-by-layer preparation of nickel hydroxide nanoparticle-reduced graphene oxide nanosheets (Ni(OH)2-RGO) on a graphene oxide (GO) film pre-cast on a glassy carbon electrode surface. The surface morphology and nature of the nano-hybrid film (Ni(OH)2-RGO) was thoroughly characterized by scanning electron and atomic force microscopy, spectroscopy and electrochemical techniques. The modified electrode appeared as an effective electro-catalytic model for analysis of rifampicin (RIF) by using linear sweep voltammetry (LSV). The prepared modified electrode exhibited a distinctly higher activity... 

The effects of various ratios of Fe/Ni/MgO and growth temperatures on yield, diameter and quality of multi-walled carbon nanotubes (MWCNTs) were studied. Thermal gravimetric analysis (TGA) confirmed that the MWCNT yield depends on Fe/Ni ratio with the following order; Fe0.5 Ni0.5 > Fe > Fe0.75 Ni0.25 > Fe0.25 Ni0.75 > Ni. The results indicated that there is an optimum temperature (940 °C) for the MWCNT growth both from quality and quantity (yield) aspects as compared to other temperatures. Moreover, the changes on Fe/Ni to MgO ratio for the MWCNT growth revealed that Fe/Ni/MgO with the ratio of 17.5/17.5/65 had the highest quality and surface area as compared to the other ratios. The... 

By using graphene nanosheets decorated with Ag nanoparticles (AgNPs-G) as an effective approach for the surface modification of pyrolytic graphite electrode (PGE), a sensing platform was fabricated for the sensitive voltammetric determination of Azathioprine (Aza). The prepared AgNPs-G nanosheets were characterized using transmission electron microscopy (TEM), X-ray diffraction (XRD), UV-vis and Raman spectroscopy techniques. The electrochemical behavior of Aza was investigated by means of cyclic voltammetry. Comparing to the bare PGE, a remarkable enhancement was observed in the response characteristics of Aza on the surface of the modified electrode (AgNPs-G/PGE) as well as a noticeable... 

So-called negative capacitance seems to remain an obscure feature in the analysis of the frequency-dependent impedance of perovskite solar cells. It belongs to one of the puzzling peculiarities arising from the mixed ionic-electronic conductivity of this class of semiconductor. Here we show that apparently high capacitances in general (positive and negative) are not related to any capacitive feature in the sense of a corresponding charge accumulation. Instead, they are a natural consequence of slow transients mainly in forward current of the diode upon ion displacement when changing voltage. The transient current leads to a positive or negative ‘capacitance’ dependent on the sign of its... 

Artificial neural networks were used to predict the oxidation peaks potentials of 7 monosaccharides under linear sweep voltammetry regime. Two sets of descriptors, one based on molecular properties calculated through DFT and another based on simple geometric distributions of hydroxyl groups and asymmetric carbon atoms along molecular chains, were employed to introduce the molecules to networks. Relatively, simple networks of (3,3,1) and (3,3,3,1) structures with the number of epochs not exceeding 15 through training process were capable of correctly predicting the peaks positions with R values in the range of 0.97-0.99. © 2008 Elsevier Ltd. All rights reserved  

Solid-phase microextraction (SPME) coupled to gas chromatography (GC) was applied to the extraction of phenol and some of its volatile derivatives in water samples. The SPME fiber consisted of a thin layer of polyaniline, which was electrochemically coated on a fine Pt wire. The stability of the coating was such that it could be used at temperatures as high as 325 °C, without any deterioration. The effects of various parameters affecting the extraction efficiency were studied, simultaneously. From these, optimization of the extraction temperature, extraction time, coating thickness, sample pH, salt concentration and desorption time was carried out by means of a (26-2) fractional factorial... 

Evolution of renewable energies in the era of the modernized world has been strongly tied up to the incessant development of high-performance energy storage systems benefiting from both high energy and power densities. In the present work, binder-free positive electrodes are fabricated via a facile electrochemical deposition route in which copper oxide nanorods (CuO NRs) directly grown onto the copper foam (CF) are decorated with bimetallic cobalt-zinc sulfide nanoarrays (Co-Zn-S NAs). The fabricated Co-Zn-S@CuO-CFs represent promising specific capacity of 317.03 C.g−1 at 1.76 A.g−1, along with superior cyclic stability (113% retention after 4500 cycles). Negative electrodes were further... 

In this work, cycling-induced aging occurring in 18650-type LiFePO4/graphite full cells at different C-rates is studied extensively. The mechanism of performance degradation is investigated using a combination of electrochemical and microstructural analyses. Half-cell studies are carried out after dismantling the full cells, using fresh and cycled LiFePO4 cathode and graphite anode to independently study them. The results show that the capacity of LiFePO4 electrodes is significantly recovered. The rate of capacity fading in the discharge state considered as irreversible capacity in the graphite is higher than LiFePO4 half cells, indicating a greater degradation in the performance of this... 

Herein, MIL-101(Fe), CoFe2O4, novel binary (MIL-101(Fe)/CoFe2O4, MIL-101(Fe)/GO and CoFe2O4/GO), and ternary (MIL-101(Fe)/CoFe2O4/(3%)GO and MIL-101(Fe)/CoFe2O4/(7%)GO) magnetic composites based upon the MIL-101(Fe) were synthesized. The XRD, FESEM, TEM, EDX, BET-BJH, FTIR, VSM, DRS, PL, EIS and other electrochemical analyses were applied to characterize samples. The MIL/CoFe2O4/(3%)GO demonstrated the best performance compared to other samples for visible light photocatalytic and photo-Fenton-like degradation of Direct Red 23 (DtR-23), Reactive Red 198 (ReR-198) dyes as well as Tetracycline Hydrochloride (TC-H) antibiotic. Degradation of dyes using the ternary composite after 70 min of...