Sharif Digital Repository

At the first part of this thesis, a pyrolitic graphite electrode (PGE) modified with graphite/nanodiamond film (GND) was applied as a sensitive electrochemical sensor for determination and study of electrochemical behavior of tryptophan (Trp) and 5-hydroxytryptophan (5-HTP) in aqueous solutions. The results showed that GND caused a remarkable increase in the peak currents so the GND/PGE electrode surface was more sensitive to the concentration of Trp and 5-HTP than the PGE surface. The determination of Trp and 5-HTP were investigated by stripping voltammetry. Experimental parameters such as scan rate, pH, accumulation conditions and amount of the modifier used on the PGE surface were... 

Part 1: A novel modified pyrolytic graphite electrode with nanodiamond/graphite was fabricated. The electrochemical response characteristics of the modified electrode toward the epinephrine (EN) and uric acid (UA) are studied by means of cyclic and linear sweep voltammetry. The structural morphology and thickness of the film was characterized by SEM technique.The prepared electrode shows an excellent catalytic activity in the electrochemical oxidation of EN and UA, leading to remarkable enhancements in the corresponding peak currents and lowering the peak potentials. The prepared modified electrode acts as a highly sensitive sensor for simultaneous determination of EN and UA in the presence... 

In this research, the instability analysis of single-walled carbon nanotubes (SWCNTs) and graphitic shells conveying fluid is investigated based on the molecular structural mechanics. Using the reduced order models for fluid and structure, the dynamic behavior of carbon nanotubes (CNTs) conveying fluid is accurately modeled via a few number of lowest flow modes and natural frequencies and mode shapes of CNTs structure. In addition, the boundary element method (BEM) is used to model the potential flow. The molecular mechanics (MM) model is applied to modal analysis and driving the natural frequencies and mode shapes of SWCNTs. The effect of chirality on flow-induced instability is taken into... 

Nowadays, replacement of traditional cast iron shoes with composite brake blocks is a main project in railway systems. The main purpose of this replacement is noise reduction( for example by about 10dB for a 100km/h freight train). One of the main sources of noise emission is the rolling sound of the wheel on the rail. The rougher and more out-of-round wheel surface, the greater the noise produced. Cast iron brake shoes, still widely used on freight wagons, make the wheel surface much rougher than composite brake blocks due to the fusing of minute metal particles into the tread surface during braking. It is therefore necessary to replace the current cast iron brake shoe with a synthetic... 

Composite coatings including self-lubricant particles such as graphite, MoS2, Al2O3 and SiC are extensively used to decrease the coefficient of friction of tribo-surfaces. Adding lubricant particles to an appropriate metallic matrix like copper, nickel, lead and their alloys is a suitable option in severe condition –for instance high temperature and low pressure- which liquid lubricants will be failed. Bronze can give various properties such as wear resistance, corrosion and oxidation protection, However cyanide solutions for electroplating process have environmentally limited for plating of Cu-Sn. In this research, a chloride electrolyte for bronze electroplating was developed and effect of... 

Fuel system is one of the most important parts of pulse detonation engine which has the responsibility of fuel, oxidizer and also purge gas in the different operational frequencies of engine. Although pulse detonation engines are sort of air breathing engines and purge gas and oxidizer one in the same unit in their structure, due to existence idea in the pulse detonation rocket engines coverage of functional condition, fuel, oxidizer and purge gas, will study it in three different structures.
In this study purpose is improvement of the pulse detonation engine of Sharif University which will provide as the possibility of safe functional condition and high operational frequency in... 

Because of the working conditions of semiconductors at ambient temperature and pressure, degradation of organic pollutants through semiconductors photocatalysis has attracted the interest of many researchers. Because of its large exciton binding energy,high chemical and physical stability,high electron and hole mobility, and low cost; zinc oxide, an n-type semiconductor with 3.2 eV direct band gap, is widely used in applications such as photocatalysts, solar cells, and light-emitting diodes. Among various morphologies of ZnO, 1D nanostructures such as nanowires and nanorods have recieved much attention due to their high surface to volume ratio. However, the application of ZnO as a... 

In this study, the aging of the LiFePO4/graphite cell was investigated in two different types of 18650 Li-ion batteries during cycling at various C-rates (0.5, 1, 2, 3, 4C) and high temperature under long-term cycling. An amount of 20% Capacity loss was considered as the end of the cycling. Batteries with a capacity of 1500 mAh after this capacity drop, experience 60, 120, 1502, and 2155 cycles, at the rates of 4, 3, 2, and 1C , and batteries with capacity of 1400 mAh was also 60, 360, 1100, 1000, and 805 cycles at a rate of 0.5C. Capacity decrease of the cell is in linear relationship with cycle number and the slope of the capacity-fading line increases with elevating current rate. Aging... 

Due to the increasing spread of metal industries and the need for raw material as feed for electric furnaces in order to produce cast iron and steel, as well as scrap deficiency and rising prices, the use of sponge iron as a substitute for scrap was considered in this project Therefore, in order to achieve the chemical analysis of the sorel ingot that is special for spherical graphite cast iron production with low manganese and chromium content, the direct reduction process was carried out using tunnel kiln method on low-manganese iron ore concentrate.After the investigation on direct reduction parameters including the saggers and coal grading,the produced sponge iron has melted in... 

One of the remarkable subject in advanced electrochemistry is, design and architecting new advanced materials with new electrochemical capabilities. One of the notable capabilities is electrocatalysis. Extensive researches are carrying out into the design and preparation of electrocatalyst materials to take advantage of these materials in fabrication of electrochemical sensors and storage/conversion devices. In this field nonoporous materials attracted a lot of attentions due to their unique features. In order to make use of the nanoporous materials as the electrocatalysts, these materials must be fabricated into continuous supported thin films on the electrode surface, which is the... 

One of the most important factors affecting the performance of the vehicle's brake disc is its stiffening coefficient. To improve this feature, many researches have been carried out by leading automotive companies, whose scientific aspects have not yet been widely disseminated. Brake discs are often made of cast iron and are more likely to produce gray iron with type A graphite. However, according to available resources, factors such as graphite morphology, their length-to-thickness ratios, cast iron and heat treatment on the piece affect this important feature. One of the most important factors that make changes in the above mentioned cases is the chemical composition and freezing rate. In... 

Carbon nanostructures are of great importance in scientific and industrial research. Two case of the important two-dimensional carbon nanostructures are graphitic carbon nitride (g-C3N4) and graphene. In the first part of this work, adsorption of important heavy metal cations including Hg+2, Ag+, Cr+3, Pb+2, Cu+2, Ni+2, Cd+2, Tl+, Sb+3, Zn+2 and As+3 on the surface of (g-C3N4) was investigated by density functional theory (DFT). The main purpose of this theoretical study is to evaluate the ability of g-C3N4 to adsorb pollutant cations. The most prominent result of this work was the ability of g-C3N4 for effective adsorption of As+3 and Sb+3 ions from aqeous solutions. Also, another... 

Because of low friction coefficient, Copper-Graphite and Copper-Babbitt composites can be used as brushes and bearing materials instead of materials containing lead which cause environmental problems. So far, many methods such as powder metallurgy and centrifugal casting have been used to fabricate Copper-Graphite composites. The most important problem of these methods is agglomeration of Graphite particles. Simultaneous stirring of samples during fabrication process which is one of the features of friction stir processing (FSP), can solve the problem. Recently, FSP has been used for fabricating surface composite for the purpose of producing hard and wear resistance layers on ductile... 

well known metal-free nanostructure carbon-based catalyst, mesoporous graphitic carbon nitride, with diverse morphologies were synthesized by using ethylendiamine/carbontetrachloride as a precursor, SBA-15 and SBA-15 nanorod as hard templates. We have investigated morphology effect on the catalytic performance. The catalysts were characterized by means of low angle and wide angle XRD, BET, FT-IR, CHNOS, FE-SEM analysis. Because of high surface area, pore volume and high nitrogen content, which acts as lewis basic site, for the first time, carbon nitride is chosen for selective catalytic oxidation of hydrogen sulfide to sulfure. Reaction was taken place in a fixed-bed reactor and at... 

At the first part of this thesis, a pyrolitic graphite electrode (PGE) modified with new coccine/multi-walled carbon nanotubes film (NC/MWCNT) was applied as a sensitive electrochemical sensor for determination and study of electrochemical behavior of tyrosine (Tyr) in aqueous solutions. The results showed that NC/MWCNT caused a remarkable increase in the peak current so the NC/MWCNT/PGE electrode surface was far more sensitive to the concentration of Tyr than the PGE surface. The determination of Tyr was investigated by linear sweep voltammetry (LSV). Experimental parameters, such as scan rate, pH and amount of the modifier used on the PGE surface were optimized by monitoring the LSV... 

In the first part, preparation of different kinds of polypyrrole/carbon composites and their application for drug analysis are described. In the first work, A very sensitive electrochemical sensor constructed from a glassy carbon electrode modified with a layer-by-layer MWCNT/doped overoxidized polypyrrole (oppy/MWCNT /GCE) was used for the determination of acetaminophen (AC) in the presence of codeine and ascorbic acid (AA). In comparison to the bare glassy carbon electrode, a considerable shift in the peak potential together with an increase in the peak current was observed for AC on the surface of oppy/MWCNT/GCE, which can be related to the enlarged microscopic surface area of the... 

In the first work, the method of direct growth was used to grew MOFs based on cobalt, as electroactive centers, for preparing electrochemical sensors for the determination of glucose. In comparison to most of the electrochemical sensing platforms based on MOFs for determining glucose, which suffer from some disadvantages like time-consuming synthesis procedures and using hazardous organic solvents, the proposed in situ growth method is much faster and no need to toxic organic solvents. Herein, cobalt-based MOFs were grown on the surface of the reduced graphene oxide modified glassy carbon electrode by the direct and rapid conversion of cobalt hydroxide nanosheets intermediates. The... 

The g-C3N4/Fe2O3 nanocomposite was produced by the combustion synthesis. The product was characterized by x-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), Fourier-transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller study (BET), Ultraviolet-visible analysis (UV-vis) and photoluminescence measurement (PL). Effect of iron nitrate on stability and photocurrent density under simulated visible-light irradiation was determined. The highest photocurrent density obtained (4.25 μA/Cm2) was twelve times the pure g-C3N4. This improvement was due to a bandgap decrease, the specific surface area increase, reduction of the electron-hole recombination, and... 

Herein, cupric oxide (CuO)/graphitic carbon nitride (g-C3N4) is synthesized under microwave irradiation for enhanced photoelectrochemical (PEC) performance and photostability. A facile, one-pot method was utilized to directly deposit the nanocomposite onto FTO from a solution containing copper precursor and urea. Possible mechanisms of CuO/g-C3N4 formation and PEC performance improvement were examined via XRD, FTIR, FESEM, XPS, UV-Vis, and PL. Controlled amounts of urea determined the morphological evolution of CuO and the formation of a protective carbon layer, while its excess quantity converted to g-C3N4 in the presence of CuO. Through heat treatment of the nanocomposite, carbon-doped... 

Octahedral crystals of Fe-Metal-organic frameworks like Fe-MIL-101, which is the most stable and active metal-organic frameworks; in combination with graphitic carbon nitride nanosheets could significantly enhance the photocatalytic activity of g-C3N4 for inorganic dye degradation under the irradiation of visible light application. This appropriate cocatalyst modifies the performance of semiconductor via suppressing the recombination of photo-induced carriers and since the synthesized composite prepared by in-situ procedure possesses close contact between each other, the migration of electrons in the photocatalytic reaction will be continued, so the degradation process via the active species...