نانوساختارها
سال:1392 | دوره:3 | شماره:3 |تعداد مقالات:25

In this work, sol-gel method was used tosynthesize titanium dioxide nanoparticles (TiO2). The TiO2 nanoparticles was characterized by Scanning Electron Microscopy (SEM), x-ray diffraction (XRD) and BET technique. The TiO2 and coumarin derivative (7- (1, 3-dithiolan-2-yl) -9, 10-dihydroxy-6H-benzofuro [3, 2-c] chromen-6-on) were incorporated in a graphite composite electrode. The resulting modified electrode displayed a good electrocatalytic activity for the oxidation of hydroxylamine, which leads to a reduction in its overpotential by more than 520 mV. Differential pulse voltammetry (DPV) of hydroxylamine at the modified electrode exhibited a linear dynamic range (between 0.5 and 500.0 mM) with a detection limit (3s) of 0.133 mM. The high sensitivity, ease of fabrication and low cost of this modified electrode for the detection of hydroxylamine demonstrate its potential sensing applications.

In this research, tellurium (Te) film with thicknesses of 100-250 nm were deposited on ceramic substrates by thermal evaporation at 373 K. The thickness of the film was determined by Rutherford backscattering spectroscopy. The influence of the thickness on the structural, morphological and molecular bonds was characterized using XRD, scanning electron microscope, and Raman spectroscopy. The XRD results confirmed that increasing the thickness, increased the intensity of the peaks, indicating increased crystallinity. SEM images indicated that the density of the film and holes in the film decreased as thickness increased. The Raman spectrum revealed that the TeO2 molecular bond formed on the surface only at room temperature up to 100 nm in thickness; as thickness increased, this bond was observed at 323 K.

Protein aggregation is a problem in biotechnology. High temperature is one of the most important reasons to enhance enzyme inactivation and aggregation in industrial systems. This work focuses on the effect of TiO2 and SiO2 nanoparticles on refolding and reactivation of lysozyme. In the presence of TiO2 and SiO2 nanoparticles, after enzyme heat treatment at 98oC for 30 min, not only aggregates were observed, but the amount of those increased. Hence the residual activity of lysozyme (without additives) and even in the presence of TiO2 and SiO2 nanoparticles after heat treatment was very low (<5%). Tm of the aggregated lysozyme after this heat treatment was decreased with increasing concentrations of TiO2 and SiO2 nanoparticles from 0 to 0.02 mg/ml in neutral pH, Whether the Tm of natural enzyme was above 373 (K) or 100oC. these nanoparticles help enzyme denaturation and misfolding in heating.

In this study, two-dimensional pulsating unsteady flow of nanofluid through a rectangular channel with isothermal walls is investigated numerically. The set of resultant algebraic equations is solved simultaneously using SIMPLE algorithm to obtain the velocity and pressure distribution within the channel. The effects of several parameters, such as volume fraction of different nanoparticles, Reynolds number, and the amplitude and frequency of pulsation flow, on the rate of heat transfer and pressure drop are examined. The results show that the heat transfer enhancement on the target surface obtained by the flow pulsation highly depends on pulsating velocity. It can also be seen that total Nusselt number increases significantly due to increase in amplitude of pulsation and volume fraction of nanoparticles. Analysis also reveals that pressure drop for the alumina nanoparticles is much greater than that of the base fluid.

Despite its numerous potential applications, two-dimensional monolayer graphyne, a novel form of carbon allotropes with sp and sp2 carbon atoms, has received little attention so far, perhaps as a result of its unknown properties. Especially, determination of the exact values of its elastic properties can pave the way for future studies on this nanostructure. Hence, this article describes a density functional theory (DFT) investigation into elastic properties of graphyne including surface Young’s modulus and Poisson’s ratio. The DFT analyses are performed within the framework of generalized gradient approximation (GGA), and the Perdew–Burke–Ernzerhof (PBE) exchange correlation is adopted. This study indicates that the elastic modulus of graphyne is approximately half of that of graphene due to its lower number of bonds.

The BFT approach is used to formulate the electronic states in graphene through a non-commutative space in the presence of a constant magnetic field B for the first time. In this regard, we introduce a second class of constrained system, which is not gauge symmetric but by applying BFT method and extending phase space, the second class constraints converts to the first class constraints so the system becomes a gauge symmetric.

Poly (ethylene adipte) and poly (ethylene adipate) /silica nanocomposite (PEAd/SiO2) containing 3 wt.% SiO2 were prepared by an in situ method. The examinations on the nonisothermal crystallization kinetic behavior have been conducted by means of differential scanning calorimeter (DSC). The Avrami, Ozawa, and combined Avrami and Ozawa equations were applied to describe the crystallization kinetics and to determine the crystallization parameters of the prepared PEAd/SiO2 nanocomposites. It is found that the inclusion of the silica nanoparticles can accelerate the nucleation rate due to heterogeneous nucleation effect of silica on the polymer matrix. According to the obtained results, the combined Avrami and Ozawa equation shown that the better model for examination of this system.

Monometallic and bimetallic Ni and Co catalytic nanoparticles supported on Titanium dioxide (rutile phase) substrate were prepared by wet impregnation method. These nanoparicles were used as catalysts for synthesis of multiwalled carbon nanotubes (MWCNTs) from acetylene decomposition at 700oC by the catalytic chemical vapor deposition (CCVD) technique. The nanomaterials (catalyst and CNTs) were characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Raman spectroscopy. In this paper, the usage of TiO2 powder as catalyst support was examined and the effect of applied catalyst type on characteristics of grown CNTs was investigated. The results showed that the rutile phase of TiO2 powder can be applied as a suitable catalyst support in CNT growth process. Furthermore, it was observed that the CNTs synthesized on Ni-Co bimetallic catalyst possess smaller average diameters, better quality and less amorphous carbon compared to Ni and Co monometallic catalyst types.

The purpose of the current research is investigating the phenylalanine removal by using magnetic nanoparticles (Fe3O4) from water samples. The effect of pH, contact time and phenylalanine concentration on phenylalanine adsorption efficiency by magnetite nanoparticles are studied in a batch system. Transmission electron microscopy (TEM), X-ray Diffraction Patterns (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) were used to characterize the synthesized magnetite nanoparticles.

The combined effect of hydrostatic pressure and temperature on correlation energy in a triplet state of two electron spherical quantum dot with square well potential is computed. The result is presented taking GaAs dot as an example. Our result shows the correlation energies are i) negative in the triplet state contrast to the singlet state ii) it increases with increase in pressure iii) further decreases due to the application of temperature iv) it approaches zero as dot size approaches infinity and v) it contribute 10% decrement in total confined energy to the narrow dots. All the calculations have been carried out with finite models and the results are compared with existing literature.

Ultra-short pulse is a promising technology for achieving ultrahigh data rate transmission which is required to follow the increased demand of data transport over an optical communication system. Therefore, the propagation of such type of pulses and the effects that it may suffer during its transmission through an optical waveguide has received a great deal of attention in the recent years. We provide an overview of recent theoretical developments in a numerical modeling of Maxwell's equations to analyze the propagation of short laser pulses in photonic structures. The process of short light pulse propagation through 2D periodic and quasi-periodic photonic structures is simulated based on Finite-Difference Time-Domain calculations of Maxwell’s equations.

The effect of single and double-layer anti-reflective coatings on efficiency enhancement of silicon solar cells was investigated. The reflectance of different anti-reflection structures were calculated using the transfer matrix method and then to predict the performance of solar cells coated by these structures, the weighted average reflectance curves were used as an input of a PC1D simulation. In contrast to the single-layer anti-reflection coating that has not significant contribution to efficiency enhancement, the double-layer was obtained to be practical to improve the efficiency of Si solar cells. Considerable enhancement in the conversion efficiency (Eff) and short-circuit current density (Jsc) were obtained for TiO2/ SiO2 doublelayer anti-reflective coating.