Aureole nanofibers by electrospinning of PAMAM‐PEO solution

Poly(amido amine) (PAMAM) dendrimer‐polyethylene oxide (PEO) nanofibers as dendrimeric‐polymeric composite nanofibers were prepared via electrospinning of PEO solution containing PAMAM dendrimer. The resultant fibers were characterized by means of transmission electron microscopy (TEM), differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The morphology and thermal properties of PEO nanofibers with and without PAMAM dendrimer were compared and the effect of PAMAM concentration on morphology and thermal properties of the resultant fibers was studied. The fibers had a size range of about 400–1300 nanometer in diameter with aureole morphology in most regions. The phase change temperature, phase transition heat, and the crystallinity of the produced composite fibers were determined by DSC analyses. TGA was also used to confirm the presence of PAMAM and to determine the amount of it within the fibers. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Exopolysaccharide from Pantoea sp. BCCS 001 GH isolated from nectarine fruit: production in submerged culture and preliminary physicochemical characterizations

Food Science and Biotechnology - Exopolysaccharide (EPS), as potential microbial base polysaccharide source, has plenty of applications due to its unique physicochemical structure. A Pantoea sp....     

Synthesis and photocatalytic activity of WO(3) nanoparticles prepared by the arc discharge method in deionized water

In this paper, we discuss the synthesis and characterization of tungsten trioxide nanoparticles prepared by the arc discharge method in deionized (DI) water. The size and morphology of WO(3) nanoparticles prepared using different arc currents (25, 35 and 45?A) were studied. Dynamic light scattering (DLS) and scanning electron microscopy (SEM) results indicate that at an arc current of 25?A, the size of the particles is about 30?nm, and this increases to 64?nm by increasing the arc current. This size increase caused a decrease of optical band gap from 2.9 to 2.6?eV. X-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) spectra demonstrate the formation of the WO(3) phase. Photodegradation of Rhodamine B shows that samples prepared at the lowest current have more photocatalytic activity due to having the smallest particle size and highest surface area. The results demonstrate the ability of the arc discharge method for direct formation of WO(3) nanoparticles in DI?water medium.     

Thermochemical growth of Mn-doped CdS nanoparticles and study of luminescence evolution

We report a new method of growing Mn-doped CdS (CdS:Mn) nanoparticles in an aqueous solution at boiling temperature. The idea is to use precursors that react only at high temperature, in order to gain crystalline luminescent nanoparticles. CdSO(4), Mn(NO(3))(2) and Na(2)S(2)O(3) were used as the precursors, and thioglycerol was employed as the capping agent and also the reaction catalyst. Na(2)S(2)O(3) is thermally sensitive and it releases S(2-) ions upon heating. The CdS:Mn nanoparticles obtained are about 4?nm in size and show both cubic and hexagonal crystalline phases with a ratio of 35% to 65%. The luminescence of nanoparticles contains a peak at 580?nm, which is related to Mn(2+) ions. Prolonged reaction time results in a decrease of the Mn luminescence peak to about 35% of the maximum value. We discuss the possible causes of the Mn peak reduction and attribute it to preferential dissolution of Mn ions into the solution due to shape reconfiguration of the nanoparticles.     

One step electrodeposition of V2O5/polypyrrole/graphene oxide ternary nanocomposite for preparation of a high performance supercapacitor

A new ternary nanocomposite based on graphene oxide (GO), polypyrrole (PPy) and vanadium pentoxide (V₂O₅) is obtained via one-step electrochemical deposition process. Electrochemical deposition of V₂O₅, PPy and GO on a stainless steel (SS) substrate is conducted from an aqueous solution containing vanadyl acetate, pyrrole and GO to get V₂O₅/PPy/GO nanocomposite. Characterization of the electrode material is carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and atomic force microscopy (AFM). The electrochemical performance of the as-prepared nanocomposite is evaluated by different electrochemical methods including cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy (EIS) in 0.5 M Na₂SO₄ solution. Remarkably, V₂O₅/PPy/GO nanocomposite shows a specific capacitance of 750 F g^?1 at a current density of 5 A g^?1, which is far better than PPy (59.5 F g^?1), V₂O₅/PPy (81.5 F g^?1) and PPy/GO (344.5 F g^?1). Furthermore, V₂O₅/PPy/GO maintains 83% of its initial value after 3000 cycles, which demonstrates good electrochemical stability of the electrode during repeated cycling. These results demonstrate that the combination of electrical double layer capacitance of GO and pseudocapacitive behavior of the PPy and V₂O₅ can effectively increase the specific capacitance and cycling stability of the prepared electrode. Also, a symmetric supercapacitor device assembled by V₂O₅/PPy/GO nanocomposite yielded a maximum energy density of 27.6 W h kg^?1 at a power density of 3600 W kg^?1, and a maximum power density of 13680 W kg^?1 at an energy density of 22.8 W h kg^?1.     

Synthesis and characterization of alumina flakes/polymer composites

Alumina flakes were prepared by solution combustion method and milled to provide powder. XRD and SEM data exhibited microsized flakes with 100 nm thickness and nanosized grains. Then the powders were dispersed in polystyrene (PS) and poly methyl methacrylate (PMMA) matrixes and thin sheets of composites were produced by solution method. Mechanical properties of the composites were characterized using tensile test and their fracture surfaces, elemental composition and hydrophobic property were tested by SEM, EDX and contact angle techniques, respectively. The results exhibited better mechanical properties compared to pure polymer samples i.e. the elastic modulus in PMMA and PS composites, were increased about 107 and 109%, respectively. In addition the composite surfaces became more hydrophobic than pure polymer systems. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A photochemical method for controlling the size of CdS nanoparticles

The optical and electrical properties of semiconductor nanoparticles are strongly dependent on their size. A flexible control of the size of the nanoparticles is of interest for tuning their properties for different applications. Here we use a coupled method to control the size of CdS nanoparticles. The method involves the photochemical growth of CdS nanoparticles together with the use of a capping agent as an inhibiting factor. CdS nanoparticles were formed through a photoinduced reaction of CdSO(4) and Na(2)S(2)O(3) in an aqueous solution. Mercaptoethanol (C(2)H(6)OS) was used as the capping agent, and we investigated the effect of illumination time, illumination intensity and the concentration of capping agent on the nanoparticle size. Transmission electron microscopy (TEM) shows crystalline nanoparticles with relatively low dispersion. Optical absorption spectroscopy was mainly used to measure the band gap and size of the nanoparticles. Increasing the illumination time or illumination intensity increases the nanoparticle size, while higher capping agent concentration leads to smaller nanoparticle size. A band gap range of 2.75-3.4?eV was possible with our experimental conditions, corresponding to a 3.2-6.0?nm size range.     

Pd doped WO3 films prepared by sol–gel process for hydrogen sensing

The sol gel method was employed to prepare peroxopolytungstic acid (P-PTA). Palladium chloride salt was dissolved in the sol with different Pd:W molar ratios and coated on Al₂O₃ substrates by spin coating method. XRD and XPS techniques were used to analyze the crystal structure and chemical composition of the films before and after heat treatment at 500 °C. We observed that Pd can modify the growth kinetic of tungsten trioxide nanoparticles by reducing the crystallite size and as a result can improve hydrogen sensitivity. Resistance-sensing measurements indicated sensitivity of about 2.5 × 10⁴ at room temperature in hydrogen concentration of 0.1% in air. Considering all sensing parameters, an optimum working temperature of 100 °C was obtained.