نانوساختارها
سال:1391 | دوره:1 | شماره:1 |تعداد مقالات:19

The silica supported platinum nanoparticles was synthesized by using the sol-gel method. The possibility of using diamminedinitro platinum (II) as Pt precursor and effect of metal precursor concentration on the final Pt nanoparticle size was investigated. A stable silica sol was prepared via hydrolysis of tetraethyl orthosilicate (TEOS) as a metal alchoxide and condensation reaction. Subsequently, diamminedinitro platinum (II) was added to sol to form the Pt/silica sol. After drying and calcination of the sol, the Pt/SiO2 nanocpmposite has been obtained. Crystallographic information and crystalline size of the synthesized Pt/SiO2 were determined by X-ray diffraction (XRD) method. Morphology of the nanoparticles and hydrogen-bonding interaction between silanol groups and amine ligands were characterized by SEM and Fourier transform infrared (FTIR) spectra, respectively. Transmission Electron Microscopy (TEM) was employed in evaluating the distribution and size of the platinum nanoparticles in the silica.

The synthesis of nanostructures cobalt through a controlled chemical process followed by heat treating at various temperatures is studied. The product is characterized by ICP, XRD, FESEM, and TEM, indicating that the as- synthesized particles have an amorphous structure with 1.76 for Co/B ratio, an average size of 50 nm. The transformation of intermediate phases into single phase nanocrystalline metallic cobalt during the heat treatment is investigated by DSC analysis. The mean crystallite size of obtained cobalt was 30 nm. The decrease in coercivity (4344.93A/mf) with the sharp increase in saturation magnetization (1.41×10-4 Am2/kg) presents excellent ferromagnetic properties for nano- crystallite cobalt.

Covalent grafting of MCM-41 with 3-chloropropyl trimethoxysilane and subsequent reaction respectively with acacdien and complexation with MoO2 (acac)2 afforded MoO2acacdien@MCM-41. X-ray diffraction and nitrogen sorption analyses revealed the preservation of the textural properties of the support as well as accessibility of the channel system despite sequential reduction in surface area, pore volume and pore size. Elemental analyses showed nearly complete complexation of the supported ligands and the presence of 0.24 mmol molybdenum per gram of the catalyst. Epoxidation of cyclooctene, 1-hexene and 1-octene in the presence of MoO2acacdien@MCM-41 with tert -butyl hydroperoxide (TBHP) were carried out with relatively good conversion in the mild reaction conditions.

A new efficient and practical method for the room-temperature reduction of aromatic nitro compounds employing FeSO4. 7H2O, NaBH4, H3PW12O40 system in H2O under mild conditions is reported. The method is simple, inexpensive, easily scaled-up and applicable for the large scale preparation of different substituted anilines.

In this article, thermo-elastic-behavior of a thick-walled cylinder made from a polystyrene nanocomposite reinforced with functionally graded (FG) single-walled carbon nanotubes (SWCNTs) was carried out in radial direction while subjected to a steady state thermal field. The SWCNTs were assumed aligned, straight with infinite length and a uniform layout. Two types of variations in the volume fraction of SWCNTs were considered in the structure of the FG cylinder along the radius from inner to outer surface, namely: incrementally increasing (Inc Inc) and incrementally decreasing (Inc Dec). These are compared with uniformly distributed (UD) structure. Mori-Tanaka method was used for stress-strain analysis. Using equations of motion, stress-strain and their corresponding constitutive correlations of a polystyrene vessel, a second order ordinary differential equation was proposed based on the radial displacement which was solved in order to obtain the distribution of displacement and radial, circumferential and axial stresses. For constant temperatures at the inner and outer surfaces of the FG cylinder considered here, results in this work indicate that radial and circumferential stresses and displacement are lower for the Inc Inc FG cylinder, and the axial stresses are higher irrespective of the structure of the FG material.

The preparation of nanostructure type manganese oxide and cobalt oxide materials with the smallest particle size is reported here. The nanorod manganese oxide and cobalt oxide nanotube were prepared via a sol-gel reaction in reverse micelles from KMnO4 and CoCl2 with respectively source at room-temperature. The structure and surface morphology of the obtained manganese oxide were studied by means of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM) and transmission electron microscopy.

The fluid flow and heat transfer in lid-driven enclosures filled with Cu-water nanofluid is numerically investigated. The moving vertical walls of the enclosure are maintained in a constant temperature, while the horizontal walls are insulated. The hybrid scheme is used to discretize the convection terms and SIMPLER algorithm is adopted to couple the velocity field and pressure in the momentum equations. The effect of moving direction of walls on mixed convection is studied for various Ri numbers, aspect ratios and volume fractions of nanoparticles. For this purpose, vertical walls are moved in two directions: one, force convection aids to free convection and two, it interacts to free convection. It is observed that the direction of moving wall mainly affected the flow field, temperature gradient and heat transfer. In addition, by increasing the volume fraction of nanoparticles, the variation of average Nusselt number on the hot wall, as an index of heat transfer rate, is linear in two cases.

As a new precursor, [tris (2-hydroxyacetophenato) triaqua (III)], [Y (HAP)3 (H2O)3]; complex was used in thermal decomposition process for the synthesis of rod-like high-temperature ceramic YBCO with length of about 320-350 nm and diameters 60–90 nm.The as-synthesized products were characterized by XRD, FT-IR, TEM, SEM and EDX analyses. The results showed that by using fine raw materials, the calcination temperature can be reduced to 870oC. It was found that this type of precursor have clearly effects on the size and morphology of product because the organic ligands around yttrium center act like a protecting agent to prevent agglomeration.

Vanadium supported on highly ordered nanoporous silica (VOx-LUS-1) was synthesized and characterized by XRD, Nitrogen adsorption desorption isotherms and UV-visible spectrophotometer. Direct oxidation of benzene to phenol in liquid phase by H2O2 peroxide was examined by using various solvents (methanol, acetone, acetic acid, acetonitryl). The maximum yield (25%) and selectivity (73%) of the phenol produced were obtained in the presence of acetic acid. The catalyst can be reused for several times without any appreciable loss of activity.