Sharif Digital Repository

In this thesis, we study the application of graph theory in chemistry. Such as, molecular graphs, modeling, algorithms, topologicalindicesandsoon. Themaingoalinthisresearchis collecting problems in chemistry which have mathematical models, specially in graph theory. Also we study the methods applied to them by considering the problems in chemistry with mathematical approach. In particular case, dendrimers and other structures of chemistry have been attributed to some graphs, where by studying their graphical parameters, like connectivity, independent sets, perfect matchings, isomorphism and topological indices and other parameters, we obtain some results in chemistry  

H2S is a toxic gas used in chemical laboratories and industries. H2S is also liberated in nature due to biological processes and also from mines and petroleum fields. At some threshold level, exposure to concentrations over 10 ppm can result in headaches, irritability, dizziness and in some case leads to death. So that introducing sensors which sense H2S at ppm level with the low response time is so essential. The present work emphasizes on H2S resistance-sensing properties of pure and Pd doped WO3 films prepared by Arc discharge method. XRD, SEM, EDAX and XPS were applied to analyze crystal structure, morphology and chemical composition of the films. The analyzes results showed that films... 

The aim of this research is preparation of tungsten trioxide nanoparticles film for hydrogen sulfide gas sensing. These nanoparticles were made by simple and inexpensive sol-gel method. To improve gas sensing properties, various precursors of copper and copper oxides were added to the sol. This solution was coated on alumina substrate by spin coating method. After annealing, sensing properties of samples were studied by measuring the electrical resistance. Best precursor and its molar percentage of copper to tungsten were selected (WO3-Cu2O (1%)). All tests for this sample were done in temperatures below 100 °C and gas concentration lower than 10 ppm. Sensitivity of WO3-Cu2O (1%) to 1 ppm... 

The purpose of this project is to construct a gas sensor based on one-dimensional nanostructured electrodes of copper oxide. By creating of these nanostructures, can be reduced breakdown voltage of gases, including flammable, to a few hundred volts. The CuO nanowires were grown by thermal oxidation on copper substrate to form self-assembled. In this method, by heating the copper foil,Cu2O also was formed on substrate. Effects of surface tension of substrate and oxidation temperature on surface density and structure of the nanowires were studied. SEM images taken from the samples showed that the surface tensions increases the density of nanowires and increasing the oxidation temperature leads... 

Graphene oxide is a single sheet of Carbon atoms which has been arranged on a two-dimensional honeycomb lattice. Functional groups such as epoxy, carboxyl and carbonyl are located on basal plane and at the edges of graphene oxide and they localize electrons on the surface of graphene oxide and open band gap in its band structure. Pure graphene has zero band gap, so existence of fluorescence properties is unlikely; but graphene oxide has fluorescence properties due to band gap in its band structure. Fluorescence properties of graphene have been used in live cell imaging and drug delivery, so study and increasing of fluorescence properties is significantly important. The purpose of this... 

The 21st century is facing two major obstacles on the way of accessing clean and renewable energies: first, the rapidly increasing need to the energy resources; and second, the limitations - as well as side-effects - of the conventional fossil fuels. Meanwhile, the production of the solar hydrogen, through water splitting, has been proposed as a promising solution to find a clean and effective source of energy. This process occurs in photo-electro-chemical systems with the activation energy that lies within the range of visible light. One approach that herewith comes to mind, is to start the process by utilizing semiconductors to absorb the sunlight. In order to overcome the overpotential... 

In this thesis, graphene/titanium oxide and graphene/tungsten oxide composites were synthesized using arc discharge in liquid and their photocatalytic behavior was studied. Based on physical principles of the arc discharge in liquid, geometry of point-point was used for metallic Ti and W electrodes. TiO2 and WO3 nanoparticles and their nanocomposites with graphene and graphene oxide (GO) were studies using DLS, UV-vis, PL, ICP, FTIR, XRD, Raman and TEM characterization. The concentration of aqueous solution of Rhodamine B mixed with graphene/WO3 and GO/WO3 composites and WO3 nanoparticles under ultraviolet light was measured versus time and reached to 0.1, 0.6 and 0.6 of the initial value... 

Transparent conductive materials have been widely used in semiconductor technology. Among them all, Indium tin oxide (ITO) has been utilized as electrodes in liquid crystal displays, solar cells, heat reflecting films and gas sensors.In general, the desired properties of transparent conductive oxides are high conductance and transmission. However, due to the complexity of ITO molecular structure, the film properties strongly depend on the depositon parameters.In first part of this thesis, physical properties and electrical characteristic of ITO films, different deposition techniques, and effects of deposition parameters (substrate temperature, pressure, power, etc. ) on film properties are... 

In this thesis, the thermal and thermoelectric properties of graphene-based nanostructures are numerically investigated. The transport parameters, including Seebeck coefficient, electrical conductance, and thermal conductance are obtained as well as the thermoelectric figure of merit. The Hamiltonian matrix is set up using a third nearestneighbor atomistic tight-binding approximation and the dynamical matrix using a 4th nearest neighbor force constant approximation. Both ballistic and diffusive regimes are considered in this work. For transport investigation, the Landauer formula and the nonequilibrium Green’s function techniques are used. The role of temperature, geometrical parameters,... 

The need for better characterization systems (electron microscopes) and high resolution lithography systems, have made electron beams systems an interesting choice for research and development. In fact, all of the above applications require ideal electron beams (beams with minimum energy spread, maximum current density, and minimum spotsize), and electron-optic lenses (simple lenses with minimum aberration). In this research, theoretical aspects of electron emission and lens systems are reviewed. Field emission array (FEA) electron guns are introduced as electron sources with minimum energy spread, and a new simulation method is presented in order to minimize the complexity, and reduce the... 

For realization of nanosale photonic device required by the future system, electron beams, and scanning probe microscopes have been used to control the site on the subtrate. However, these techniques have a fatal disadvantage because they cannot deal with insulators and Diffraction of light, limiting their application.To overcome this difficulties, we design and implement near-field optical chemical vapor deposition, which enables the fabrication of nanometer-scale structure, while controlling their position. To guarantee that an optical near field is generated sufficiently, we fabricated a sharped W-tip by electrochemical etching. The separation between the W-tip and the substrate was kept... 

Some widely used drugs such as paclitaxel (PTX) are poorly water soluble. The clinical use of PTX with solubilizer causes side effects. These problems limited its application in treatments. In this work has been studied the effect of β-CD-g-PG (HPCD) hybrid nanomaterials, conjugated PG branches onto β-CD core, on the water solubility of PTX. First HPCD has been synthesized. Then the inclusion complex of PTX with HPCD was prepared. The inclusion complex efficiency for PTX:HPCD complex in 1:25 mole ratio was 87%. Then solubility of PTX with HPCD in water has been determined, showing Ap type phase solubility diagram. Then stability constants were calculated. The first order and second order... 

Paclitaxel is using as a drug against breast and ovary cancers. Although paclitaxel has high biologic activity, it has very poor solubility in water the same as some other drugs. Since drugs should be solved in water to be absorbed by the body, for absorb enhancement, we should use carriers which includes both polar and non polar sites.
Beta-Cyclodextrin which has this feature is capable for producing inclusion complex in its hydrophobic pores with non polar materials. In this project, by adding polymeric polyglycerol branches on Beta-Cyclodextrin, a polymeric nanostructure has been developed to enhance water solubility in comparison with pure Beta-Cyclodextrin.
Study on producing... 

Paclitaxel is used as a drug against breast and ovarian cancers. Although paclitaxel has high biologic activity, it has very pour solubility in water like some other drugs. Since drugs should be solved in water to be absorbed by the body, for absorb enhancement, we should use carriers which includes both polar and non polar sites. eta-Cyclodextrin which has this feature is capable for producing inclusion complex in its hydrophobic pores with non polar materials. In this project by adding polymeric polyacrylamide branches on beta-Cyclodextrin, polymeric nano structure has been developed to enhance water solubility in comparison with pure beta-Cyclodextrin. Study on producing polymeric nano... 

A series of V2O5 catalysts supported on multiwall carbon nanotube (MWCNT), single wall carbon nanotube (SWCNT) and graphene were synthesized by hydrothermal and reflux methods for oxidative dehydrogenation of propane (ODHP) to propylene. The catalysts were characterized by techniques including the BET surface area measurements, XRD, FTIR, H2-TPR, NH3-TPD, FESEM and UV-vis diffuse reflectance. The performance of the catalysts and the supports were subsequently examined in a fixed bed reactor. The vanadium catalyst supported on graphene with C/V molar ratio of 1:1 synthesized through the hydrothermal method had the best performance under the reactor test conditions of 450°C, feed C3H8/Air... 

In this study, the effect of nano-structure mesoporous supports on the performance of the nickel catalysts in the combined reforming process was investigated. In the first part, magnesium aluminate spinel was prepared using a sol-gel method and employed as a catalyst support for the preparation of nickel catalysts with various nickel contents. The samples were characterized using BET, XRD, TPR, TPO, CO chemisorption and SEM techniques. The results showed that increasing the nickel content up to 7.5 wt.% improved the catalytic activity, but further increase in nickel content decreased the activity due to the decrease in the nickel dispersion. The catalysts except of the sample with 2.5 wt.%... 

TiO2 is one of the most frequently used photocatalyst materials. Porous TiO2 nanostructure has drawn much attention recently due to high decomposition rate of organic pollutants. In this thesis, TiO2 nanoparticles were synthesized via sol-gel method and were coated on cotton and jute fiber separately; besides, the impregnated fibers were heat treated to eliminate cellulose. Titanium tetraisopropoxide (TTIP) was used as a precursor and two solutions, acidic and alcoholic, were used as the primary solutions for synthesis. In acidic solution, the crystalline phase and size distribution of TiO2 nanoparticles were evaluated with changing pH.Then, the appropriate pH was chosen for coating. In... 

Polypropylene/clay nanocomposites are considered as a group of widely used nanocomposites in industrial applications due to their desired properties, yet reasonable cost. However, dissimmilar chemical nature of polypropylene and clay do not allow perfect dispersion of silicate layeres in the matrix and thus restricts full advantages of these composites.An earlier investigation in this group considered solving this shortcoming through incorporation of PA6 as an intermediate phase to enhance clay platelets dispersion. The current project follows this route via studing the influence of molecular weight of the PP matrix, compatibilzer and the mixing procedure of the compound. To investigate the... 

Considering that automobile weigth reduction in industry is important, improvement the strength of low carbon steel sheets is important. These sheets can be supported the service condition in lower thicknesses. Bulk nano-structured materials have been mostly attracted in materials science due to their unique physical and mechanical properties. Severe plastic deformation (SPD) is one of the most efficient methods to produce ultra fine grained or nano-structured materials. Materials produced by SPD are of great importance because of (1) non-porous structure, (2) great mechanical properties such as high strength and toughness and (3) proper dimension for mechanical and physical testing. ... 

Recently, synthesis of nanostructured CdTe of II-VI semiconductors has caused much attention due to their great potential in many optoelectronic applications such as solar cells and detectors. Among different synthesis methods, solvothermal process is a suitable method due to low temperature synthesis. In this work CdTe nanoparticles, nanowires, nanorods and nanobelts with cubic structure (zincblende) were synthesized via a simple solvothermal method at a moderate temprature. The effect of processing parameters on some properties sush as crystal structure, morphology, crystallite size chemical bond configuration and optical properties of synthesized CdTe were investigated. It was found that,...