Papers by Keyword: Core-Shell Nanoparticle

Abstract: Core–shell Fe₂O₃@C nanoparticles are very studied due to its biocompatibility with plant and animals cells and due its special properties of chemical adsorption. Thus, the definition of an easy synthesis method of these nanoparticles is very important to the scientific studies and to future applications of these materials. For example, the properties of these nanoparticles depend of the combination between some processing parameters, as the temperature, time, chemical composition, atmosphere and others. The mass yield of the synthesis processes depend of these parameters and are important information. In this work the effect of temperature and of the concentration of the iron precursor were evaluated on the characteristics of the proposed nanoparticles. The nanostructures of Fe₂O₃ coated with carbon (Fe₂O₃@C) were synthetized by adapted co-precipitation hydrothermal rote. In 40.0 ml of distilled water was added 1.800 g of glucose, 6.006 g of urea, 0.500 g of polyethylene Glycol (PEG 1500) and different concentrations of iron nitrate Fe (NO₂)₃.9H₂O and different temperature values were applied. The Fe₂O₃@C core-shell were characterized by scanning electron microscopy (SEM/FEG), Energy Dispersive Scanning (EDS) and X-ray Diffractions (XRD). Results showed that nanoparticles form clusters with different sizes that are dependent on the temperature values and Fe (NO₃)₃.9H₂O concentration. The core-shell mass has a linear relation with the iron precursor mass and the reaction temperatures influences the microstructure of the core-shell nanoparticles.

Abstract: Core/shell type nanoparticles with an average diameter of 20nm were synthesized by chemical precipitation method. Firstly, Monodisperse Fe₃O₄ nanoparticles were synthesized by solvethermal method. FeSO₄ž7H₂O and NaBH₄ were respectively dissolved in distilled water, then moderated Fe₃O₄ particles and surfactant(PVP) were ultrasonic dispersed into the FeSO₄ž7H₂O solution. The resulting solution was stirred 2 h at room temperature. Fe could be deposited on the surface of monodispersed Fe₃O4 nanoparticles to form core-shell particles. The particles were characterized by using various experimental techniques, such as transmission electron microscopy (TEM), X-ray diffraction (XRD), AGM and DTA. The results suggest that the saturation magnetization of the nanocomposites is 100 emu/g. The composition of the samples show monodisperse and the sides of the core/shell nanoparticles are 20-30nm. It is noted that the formation of Fe₃O₄/Fe nanocomposites magnetite nanoparticles possess superparamagnetic property.

Abstract: Composites have achieved much attention because of their excellent qualities. Core-shell γ-Fe₂O₃/Au nanoparticles were prepared by chemical reduction. Their optical properties and morphology were characterized by UV-visible spectrum (UV-vis), X-ray diffraction (XRD) and Transmission Electronic Microscopy (TEM). Furthermore, the average particle size and interface structure were also analyzed using small angle X-ray scattering (SAXS).

Abstract: Spherical α-Fe2O3/Ag core/shell nanoparticles were prepared by reducing Ag(NH3)2+ with formaldehyde using the seeding method. 3- Aminopropyltriethoxysilane (APS) acts as a “bridge” to link between α-Fe2O3 core and Ag shell. The obtained nanoparticles were characterized by XRD, TEM, SEM, EDS, and Roman. The results show thatα-Fe2O3 cores are coated by Ag shell completely. The average size of α-Fe2O3/Ag nanoparticles is 95 nm and the thicknesses of Ag shell are 15nm in 3.7% HCHO and 1.0M AgNO3. The thickness of Ag shell can be tunable by changing reaction conditions, such as the concentration of AgNO3, reduction reaction rate. The surface-enhanced Raman scattering (SERS) effect of the core/shell particles are measured with Pyridine (Py) as molecule probe. SERS indicate that the Raman signals of Py adsorbed on α-Fe2O3/Ag nanoparticles exhibit large enhancement at 1010 and 1038 cm-1 respectively. And the intensity of signals is enhanced with the increase of the thickness of Ag shell. The uniform and rough surface of α-Fe2O3/Ag particles exhibits strong SERS activity in 3.7% HCHO and 1.0M AgNO3. The spherical α-Fe2O3/Ag core/shell nanoparticles exhibit SERS activity.

Abstract: The adhesion enhancement effect of tetraethoxysilane (TEOS) addition to a silica-polyaniline composite film on ITO glass substrate was studied. The composite film was prepared with the silica-polyaniline core-shell composite nanoparticles which were synthesized by a chemical polymerization of polyaniline in a colloidal solution of silica. A small amount of TEOS and acidic water was added to the dispersion solution of composite nanoparticles. The addition of TEOS was intended to increase the adhesion of electrochromic film to substrate without a deterioration of the electrochromic properties such as response time and cycle life. The adhesion of the films was tested by a tape test, and the composite film with TEOS showed a dramatic increase in adhesion to the ITO glass substrate when compared with the film deposited without TEOS. The electrochromic properties of the films were also characterized using the cyclic voltammetry and the optical response measurement.

Abstract: This paper reports the silica density, surface structures and optical properties of gold nanoparticles coated with different thickness of silica shells. The gold nanoparticles encapsulated with amorphous silica shells were prepared in a slight modification of Stǒber method. The silica-shell thickness could be varied from 20 to 50 nm by controlling the experimental conditions, such as reaction time. Transmission Electron Microscopy (TEM) and UV-Visible absorption spectroscopy were employed to characterize the size, shell density, surface structures and the optical properties of these silica-coated gold nanoparticles. The TEM images demonstrated that the density of the silica shell were depended on the reaction time, and the surface morphology was changed from porous structures in the initial coating to the final continuous and smooth silica surface. With the increasing of the reaction time, the silica-coated gold nanoparticles became more and more round and monodispersed. UV-Vis spectra showed that surface plasmon absorption peak had a red-shifted of 3~12 nm on increasing the thickness of silica shell from 20 to 50 nm. A possible mechanism of silica formation on gold nanoparticles was proposed on the basis of silica shell density and the shift of absorption peak of coated gold nanoparticles.

Abstract: We performed first-principles calculations using the projector augmented-wave (PAW) method for Au/Pd slab interface models. The calculations of relaxed configurations and energies for the thin Pd layers (3 layers) stacking on Au (111) and Au (100) slabs with an epitaxial relationship represent that Pd overlayers have a lateral expansion in both cases. This trend is in good agreement with experimental results for Pd/Au slabs and Au-Pd core-shell nanoparticles, obtained by electron microscopy, X-ray diffraction, and positron annihilation. In addition, an intermixing configuration near the Au-Pd interface was shown to be more stable than the binary separated one.

Abstract: Experimental results are presented on the ablation of copper and brass targets in a liquid environment: ethanol, acetone, or water by irradiation with either a pulsed copper vapour laser (0.51 μm) or a pulsed Nd:YAG laser (1.06 μm). The ablated material was ejected into the surrounding liquid as nanoparticles of average size 20 nm. The nanoparticle composition depends on the nature of the liquid. Ablation of 60%Cu, 40%Zn brass in ethanol results in formation of core-shell nanoparticles. Brass nanoparticles were characterized by a well-defined plasmon peak at 510-520 nm.