Sharif Digital Repository

The first usage of dihexadecyl hydrogen phosphate (DHP)-modified highly oriented multi-walled carbon nanotube (MWCNTs) forests in a sensor configuration was developed to investigate the electrochemical oxidation and determination of simvastatin (SV) in pharmaceutical dosage forms. Synthesis of well-aligned MWCNTs on a conductive Ta substrate by catalytic vapor deposition technique using a common chemical, ethylenediamine, and without being plasma-aided was reported. The electrochemical behavior and oxidation of SV at the aligned MWCNTs/DHP/Ta electrode were discussed in detail through cyclic voltammetry and differential pulse voltammetry. This modified electrode showed considerably higher... 

Free-standing TiO2 nanotube array (TNA) films were fabricated via two-step anodization of a titanium sheet. The X-ray diffraction pattern indicated amorphous TNAs were transformed into anatase after annealing the films at 500 °C in air. The surface of TNA was modified by a sequential-chemical bath deposition (S-CBD) method to fabricate Ag2S nanoparticles and forming TNA/Ag2S-n nanostructure, by varying the number of cycles (n). Based on SEM observations, the produced films consisted of vertically ordered tubular structure arrays, each with 125 nm in diameter and 4.1 μm in length containing silver sulphide nanoparticles of ∼12 nm diameter. X-Ray photoelectron spectroscopy (XPS) confirmed the... 

Anatase and amorphous TiO2 nanoparticles were used to improve recovery of heavy oil from sandstone cores. Before performing core floods, the stability of nanoparticles at different salinities was tested using ζ potential and ultraviolet-visible (UV-vis) methods. While water recovered only 49% of the oil in the core flood experiments, 0.01% anatase structure solution recovered 80% of the oil after injecting two pore volumes at optimum conditions. To understand the mechanism responsible for improved recovery, contact angle measurements were performed on the rock surface before and after treatment with the nanoparticle solution. Contact angle measurements showed that the rock wettability... 

The effect of pulse reverse current (PRC) method on Ni-Mo coatings electroplated from chloride solution was investigated by various plating parameters such as plating duration, the anodic duty cycle, the anodic current density and the cathodic current density. By increasing the anodic duty cycle and anodic current density, the Mo content of coatings reached 68wt.% and 78wt.%, respectively at cathodic current densities of 500 and 300mAcm-2. The Mo content of coatings increases by the preferential dissolution of Ni on the anodic pulse and also by the replenishment of Mo complexes in the diffusion layer near the substrate surface during the anodic pulse. In comparison with the direct current... 

To the best of our knowledge, this work presents the first successful effort to fabricate and study nanostructured Ni-based composite coatings using the electrophoretic deposition method with nanostructured SiO2 particles. In this work, Ni/SiO2 nanoparticle composite coatings were prepared by electrophoretic deposition (EPD) [1] and their hardness, wear and corrosion resistances [2] were examined. After studying the morphology of the coatings and finding the optimum conditions for uniform coating, in order to improve the mechanical properties as well as resistance to corrosion, sintering was performed. The Ni/SiO2 nanocomposite coatings show excellent hardness (∼376 HV), reduced Young's... 

The diffusion and deposition of TiO2 nanoparticles in EOR application was investigated in this paper. TEM image of nanoparticles showed that the particles are elongated with average long and short axis sizes of 54 and 15 nm. Water flooding tests showed that the recovery factor can be improved from 49% to 80% using TiO2 nanoparticles. Viscosity and interfacial tension measurements showed that by using TiO2 nanoparticles the viscosity of injected fluid and interfacial tension do not change significantly and can not explain the change in recovery factor. Contact angle measurements showed that nanoparticles deposition changed the wettability of the rock surface from oil-wet to water-wet. SEM... 

In this research, a finite element model was developed in order to simulate the two-step residual stress distribution of a thermal barrier coating system, considered to be used in diesel engine cylinder head, with a real roughness and real porosity. Two steps including the bond coat and the top coat deposition processes were taken into account. The real geometry of coating layers, including the roughness and the porosity, was also considered based on a scanning electron microscopy image. Then, effects of the convective heat transfer coefficient and initial substrate and substrate/bond coat preheating temperatures on the residual stress were studied. Obtained results illustrate that the... 

In this paper, particle deposition in the upper airways and five lobes of a human lung is simulated. The simulation is based on a stochastic lung model, derived from detailed morphometric measurements. Pathways are simulated using Monte Carlo methods consequently the whole structure changes both stochastically and statistically in each simulation. In this investigation the termination phenomena is a function of each daughter's diameter which best satisfies the lung's morphometry. Complementary to the previous available assumptions, i.e. flow divisions according to the ratio of daughter's cross sections or distal volumes, in this investigation flow rates are computed in an upward manner... 

This paper describes the designing and evaluation of an alternative energy system which consists of PEMFC, PV, PEM electrolyser, methane reformer and hydrogen tank. In order to find out the minimum capacity of the components, a system sizing model is developed in MATLAB based on meteorological and electrical demand data. Three scenarios are considered based on different combinations of solar energy and fossil fuel energy as energy resources. The heating energy produced by the fuel cell is recovered for supplying domestic hot water while the system would supply electrical energy. Results show that system sizing strongly depends on scenarios and unit cost of electricity decreases through the... 

We present a new TiO2 morphology, featuring high surface area and open structure, synthesized by a two-step chemical route for the manufacture of dye-sensitized solar cells (DSSCs). This construct is sets of intertwined one-dimensional (1D) nanostructures (i.e., nanotubes), so-called skein-like nanotubes (NTs). Such morphology is produced by a combination of TiC oxidation and hydrothermal processes. The mesoporous TiO2 nanoparticles, as the product of TiC oxidation operation, is used as the precursor of hydrothermal process to grow the skein-like NTs. The effect of processing parameters of TiC oxidation and hydrothermal processes is studied. The skein-like morphology enables to eliminate the... 

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... 

Zinc-TiO2 nano-composite coatings were synthesized by Direct Current (DC) and Pulse Current (PC) electrodeposition techniques. The effects of the plating parameters on the microstructure, codeposition percentage of TiO2 and corrosion behavior were investigated. The coatings morphology presents hexagonal grains perpendicularly oriented to the surface. Under DC conditions, TiO2 content of the coatings decreased with increasing TiO2 concentration of the electrolyte. Increasing applied current and TiO2 concentration in the bath leads to a fine microstructure with corrosion currents as low as 2.7 μA/cm2. Under PC conditions, incorporation rate of nanoparticles tends to increase with increasing... 

In this research, we have used glancing angle deposition (GLAD) RF sputtering technique with various angular speeds ranging from 5 to 30 RPM to fabricate polytetrafluoroethylene (PTFE, Teflon) coated Tungsten on glass substrate for producing hydrophobic surface. According to scanning electron microscopy (SEM) observations, Tungsten nanorods were formed on the substrate with average diameter and length of about ∼50 nm and 300 nm, respectively. Hydrophobic property of W/Glass and PTFE/W/Glass systems was investigated by water contact angle measurements and we have found that the contact angle varied with the substrate angular speed. Maximum contact angle of 121 was measured for the... 

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... 

Indium tin oxide (ITO) thin films have been deposited using RF sputtering technique at different pressures, RF powers, and substrate temperatures. Variations in surface morphology, optical properties, and film resistances were measured and analyzed. It is shown that a very low value of sheet resistance (1.96 ω/sq.) can be achieved with suitable arrangement of the deposition experiments. First, at constant RF power, deposition at different pressure values is done, and the condition for achieving minimum sheet resistance (26.43 ω/sq.) is found. In the next step, different values of RF powers are tried, while keeping the pressure fixed on the previously found minimum point (1-2 Pa). Finally,... 

In this research TiO2 hollow spheres with different diameters were prepared using titanium tetraisopropoxide (TTIP) as the TiO2 precursor. Carbon spheres with average sizes of 230, 325 and 450 nm were prepared as the templates by hydrothermal method. Then TiO2 was deposited on the surface of the carbon spheres through a liquid phase deposition (LPD) process. This two dimensional growth was performed in an appropriate concentration of TTIP and different LPD times. Finally the TiO2 hollow spheres were achieved for specific LPD times by burning the carbon templates. Two kinds of TiO2 nanocrystals with sizes around 20 nm were hydrothermally grown in acidic (pH = 1.5) and basic (pH = 10)... 

Nickel modified graphite electrodes (G/Ni) prepared by galvanostatic deposition were examined for their redox process and electrocatalytic activities towards the oxidation of methanol, ethanol, 1-propanol and 2-propanol in alkaline solutions. The methods of cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS) were employed. In CV studies, the electrochemical response, peak current varied in the order of MeOH > EtOH > 1-PrOH > 2-PrOH. Under the CA regime, a higher catalytic rate constant obtained for methanol oxidation was in agreement with CV measurements. Lower charge transfer resistance was obtained for low carbon alcohols oxidation and significantly higher... 

In this work, ultraviolet photodetectors based on electrodeposited ZnO sheet thin films were fabricated on a glass substrate. Before electrodeposition, a thin buffer layer of ZnO was deposited on the glass by pulsed laser deposition method. This layer not only acted as a nucleation site for ZnO sheet growth, but also made it possible to use cheap glass substrate instead of conventional fluorine-doped tin oxide (FTO) substrate. Our results showed that photoresponse properties of the photodetectors strongly depend on the sheet sizes. The smaller sheets exhibited enhanced photosensitivity, shortened fall times and decreased gain compared to larger ones. We showed that photodetectors based on... 

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 morphological characteristics and electronic structure of the BaTiO 3 films grown by pulsed-laser deposition technique have been investigated. AFM and FE-SEM images reveal columnar growth characteristic of these films. Utilizing spectrophotometer, optical band gap of the films were reckoned to be about 3.76 eV. Both dα/dE and PL vs. E plots reveal numerous luminance states in the gap. Despite the presence of many luminance faults in the gap, cations manage to preserve their electronic states