Sharif Digital Repository

Effect of cathodic enzymatic decolorization of reactive blue 221 (RB221) on the performance of a dual-chamber microbial fuel cell (MFC) was investigated. Immobilized laccase on the surface of a modified graphite electrode was used in the cathode compartment in order to decolorize the azo dye and enhance the oxygen reduction reaction. First, methylene blue which is an electroactive polymer was electropolymerized on the surface of a graphite bar to prepare the modified electrode. Utilization of the modified electrode with no enzyme in the MFC increased the power density up to 57% due to the reduction of internal resistance from 1000 to 750 Ω. Using the electropolymerized-enzymatic cathode... 

Graphene oxide nanowalls with extremely sharp edges and preferred vertical orientation were deposited on a graphite electrode by using electrophoretic deposition in an Mg 2+-GO electrolyte. Using differential pulse voltammetry (DPV), reduced graphene nanowalls (RGNWs) were applied for the first time, in developing an ultra-high-resolution electrochemical biosensor for detection of the four bases of DNA (G, A, T, and C) by monitoring the oxidation signals of the individual nucleotide bases. The extremely enhanced electrochemical reactivity of the four free bases of DNA, single-stranded DNA, and double-stranded DNA (dsDNA) at the surface of the RGNW electrode was compared to electrochemical... 

Solid-phase microextraction (SPME) is a fast, solvent-free technique, which, since its introduction in the 1990s, has been increasingly applied to sample preparation in analytical chemistry. Conventional SPME fibers are fabricated by making a physical bond between the usual silica substrate and the polymeric coatings. However, some applications are limited, as the lifetime and the stability of conventional SPME fibers cannot meet the demands of analyzing relatively non-volatile compounds with more polar moieties. There have been attempts to analyze less volatile compounds by increasing the thermal, physical and chemical stability of the fibers. In this review, we present some new... 

The electrochemical behavior of lamotrigine (LMT) at the pyrolytic graphite electrode (PGE) is investigated in detail by the means of cyclic voltammetry. During the electrochemical reduction of LMT, an irreversible cathodic peak appeared. Cyclic voltammetric studies indicated that the reduction process has an irreversible and adsorption-like behavior. The observed reduction peak is attributed to a two-electron process referring to the reduction of azo group. The electrode showed an excellent electrochemical activity toward the electro-reduction of LMT, leading to a significant improvement in sensitivity as compared to the glassy carbon electrode. The results of electrochemical impedance... 

The particlehole continuum in the Dirac sea of graphene has a unique window underneath, which in principle leaves room for bound state formation in the triplet particlehole channel (Baskaran and Jafari 2002 Phys. Rev. Lett. 89 016402). In this work, we construct appropriate triplet particlehole operators and, using a repulsive Hubbard-type effective interaction, we employ equations of motion to derive approximate eigenvalue equations for such triplet operators. While the secular equation for the spin density fluctuations gives rise to an equation which is second order in the strength of the short range interaction, the explicit construction of the triplet operators obtained here shows that,... 

In this study the effect of deposition temperature and thickness on the physical properties of carbon films deposited by magnetron sputtering PVD was investigated. The results of Raman spectra and grazing incidence XRD (GIXRD) patterns show that the graphitization increases by increasing the deposition temperature. There is a change in deposition mechanism at 400 °C from amorphous carbon deposition to nano-structured graphite deposition. Also by increasing substrate temperature the electrical resistance of carbon films reduces significantly up to 300 °C and then remains largely constant. High intrinsic compressive stress in low temperature deposited carbon films causes cracks and... 

CeO 2-TiO 2 nanoparticles were prepared by the sol-gel process using 2-hydroxylethylammonium formate as room-temperature ionic liquid and calcined at different temperatures (500-700°C). CeO 2-TiO 2-graphene nanocomposites were prepared by hydrothermal reaction of graphene oxide with CeO 2-TiO 2 nanoparticles in aqueous solution of ethanol. The photocatalysts were characterized by X-ray diffraction, BET surface area, diffuse reflectance spectroscopy, scanning electron microscopy, and Fourier transformed infrared techniques. The results demonstrate that the room-temperature ionic liquid inhibits the anatase-rutile phase transformation. This effect was promoted by addition of CeO 2 to TiO 2.... 

An artificial neural network (ANN) model was used to predict the weight loss of MgO-C composites at different temperatures and graphite contents. The general idea of ANN modeling was presented and after that the empirical weight loss data were used for both model verification and assessment of the oxidation rate predictions. The model was proved to have an astounding power in predicting kinetic parameters of the oxidation process. Graphite oxidation was, for example, found to be controlled by alternative diffusion steps. Plotting the Arrhenius law curves for graphite oxidation indicated a distinguishable slope change at a critical temperature which is related to the graphite content. This... 

In this paper, Ti-6Al-4V/TiC composite was fabricated by VIM furnace and graphite crucible. X-ray diffraction analysis and EDS techniques were used to identify the phases in the material. Microstructure characteristics of the Ti-6Al-4V/TiC composite were evaluated by means of optical microscopy. The tensile test was performed at room temperature after hot-rolling of the samples in the beta phase field. The results revealed that at different melting times, three kinds of precipitates are formed in the microstructure including grain boundary, eutectic and transgranular precipitates. The size of transgranular precipitates was significantly larger than that of the other two types of carbides and... 

The effect of mould preheating temperature, casting modulus and graphite addition method on surface decarburisation during lost wax casting of CK 45 steel has been investigated. For this purpose, a novel image analysis program was developed to determine the carbon concentration profile. It was observed that on increasing the preheating temperature and casting modulus, the depth of decarburisation increases significantly. This behaviour was related to the decreased cooling rate of the samples which enhances the loss of carbon by reaction with the surrounding atmosphere. It was also found that the distribution of graphite in different layers of the mould and the distance of these layers from... 

A new polymer with C 4H stoichiometry based on graphene is synthesized in situ using template-induced polymerization of self-organizing hydrogen adsorbates on graphene. The polymerization is observed "live" on the surface of graphene by photoemission spectroscopy. Photoemission spectroscopy allows for an accurate determination of the carbon/hydrogen stoichiometry, an aspect that is extremely important for understanding functionalized graphene  

We have prepared a pyrolytic graphite electrode (PGE) whose surface is covered with a thin film of a nano-mixture of graphite/diamond (NGD). The electrode is shown to be capable of electrochemically sensing of tryptophan (TRP) and 5-hydroxytryptophan (HTRP). The presence of the NGD film resulted in a remarkable increase in the peak currents and sharpness of the waves so that submicromolar concentrations of TRP and HTRP become detectable. Potential scan rates, the pH of the solution, the accumulation conditions and the amount of the modifier were optimized via cyclic voltammetry. Linear sweep voltammetry, under optimized accumulation time and in open circuit operation, was applied to the... 

The electrochemical response of sodium levo-thyroxin (T4) at the surface of an edge plane pyrolytic graphite (EPPG) electrode is investigated using cyclic voltammetric technique in the presence of 0.1M HCl as supporting electrolyte. T4 underwent totally irreversible oxidation at this system and a well-defined peak at 821mV was obtained. Compared to the signals obtained in the optimized conditions at bare glassy carbon and carbon paste electrodes, the oxidation current of T4 at an EPPG electrode was greatly enhanced. The electrochemical process of T4 was explored and the experimental conditions were optimized. The oxidation peak current represented a linear dependence on T4 concentration from... 

This paper addresses the fabrication of bronze-nano-graphite coatings containing 30. nm sized graphite particles. Addition of Poly Vinyl Pyrrolidone (PVP) and dispersing the suspension by ultrasound was utilized to stabilize the electroplating solution. Pulsed current electrodeposition was used and the deposits were characterized in terms of graphite content, particle dispersion in coating and morphology. The wear behavior of the coating was compared to bronze-micro-graphite coatings prepared with the same experimental conditions. The present coating showed improved wear resistance in comparison to bronze-micro-graphite coatings at the same graphite content  

Single-walled carbon nanotubes (SWCNTs) and multiwalled carbon nanotubes (MWCNTs) were synthesized in aqueous solutions containing FeCl2, FeCl3, FeSO4 and Fe2(SO4) 3. The effects of iron charge and the counter ions on the formation of carbon nanotubes (CNTs) were investigated. Thermogravimetric (TG) analysis indicated that carbon multilayer structures including CNTs and multishell graphite particles were formed in deionized (DI) water without the iron precursor. SWCNTs were also synthesized in the presence of the iron ions. It was also found that the mole ratio of [Fe2+]/[Fe3+] in the solution has a significant influence on the purity of CNTs and the process yield. The highest yield was... 

The effect of mold hardness on the microstructure of ductile iron and the contraction porosity was investigated. Molds with different hardnesses (0.41, 0.48, 0.55, 0.62 MPa) and a sand mold prepared by Co2 method were used. The influence of silicon content on the induced expansion pressure owing to the formation of graphite was also investigated. The contraction during solidification can be compensated by an induced expansion owing to the graphite relief when the hardness of mold increases; therefore, the possibility of achieving a sound product without using any riser increases  

Electro-oxidation of alcohols (methanol, ethanol, 1-propanol and 2-propanol) on nickel dispersed into a thick layer of poly-o-aminophenol on graphite electrode (GE/POAP-SDS/Ni) was investigated. Ni-doping into the polymeric film was achieved chemically followed by enrichment of Ni(III) through cycling the potential. The electro-oxidation of alcohols on GE/POAP-SDS/Ni were found to be dominated by direct electro-oxidation with some contribution from Ni(II)/Ni(III) couple. Rate constants for the electro-oxidation of methanol, ethanol, 1-propanol and 2-propanol as derived by chronoamperometry were 1.65 × 105, 1.31 × 105, 2.53 × 104 and 1.40 × 104 cm3 mol-1 s-1, respectively. Impedance... 

Models capable of accurate simulation of microcantilever dynamics coupled with complex tip-sample interactions are essential for interpretation and prediction of the imaging results in amplitude modulation or tapping-mode atomic-force microscopy (AM-AFM or TM-AFM). In this paper, four approaches based on combinations of lumped and finite element methods for modelling of cantilever dynamics, and van derWaals and molecular dynamics for modelling of tip-sample interactions, are used to simulate the precise imaging by AM-AFM. Based on the simulated imaging and force determination, the efficiency of different modelling schemes is evaluated. This comparison is performed considering their...