Silver/silver bromide/polypyrrole nanoparticles obtained by microemulsion photopolymerization in the presence of a cationic surfactant

Conductive silver/silver bromide/polypyrrole nanoparticles were obtained by photopolymerization in o/w microemulsions of pyrrole monomer in the presence of silver nitrate as electron acceptor and dopant under UV light irradiation. The microemulsions were prepared using cetyltrimethylammonium bromide (CTAB) as cationic surfactant. The particles were analyzed by scanning electron microscopy (SEM), UV/Vis, Fourier transform infrared spectroscopy, cyclic voltammetry, and X-ray diffraction (XRD). It was observed from SEM analysis that spherical particles can be obtained by this procedure with relatively narrow particles sizes distributions and average particle diameters of the silver cores (Dp) between 39 and 46 nm, which decreases as the surfactant concentration is increased. The conductivities of the resulting materials were between 0.12 and 0.40 S/m. Formation of cores of Ag and AgBr were observed from the XRD analysis, which was ascribed to the reduction of Ag⁺ to Ag⁰ and to reaction of Ag⁺ with the counterion of CTAB surfactant, respectively.     

Immobilization of silver nanoparticles obtained by electric discharge method on a track membrane surface

Composite poly(ethylene terephthalate) track membranes containing immobilized silver nanoparticles with the aim of using them for surface-enhanced Raman scattering spectroscopy have been obtained and studied. A dispersion of negatively charged silver nanoparticles has been synthesizes by the method of pulsed electrical discharge between silver electrodes immersed in distilled water. To ensure the electrostatic deposition of nanoparticles onto the track membrane surface, it has been modified with polyethyleneimine. The composition and morphology of the surface of the obtained composite membranes have been studied by X-ray photoelectron spectroscopy and scanning electron microscopy. Aggregation of nanoparticles on the surface has been analyzed. The coefficient of Raman-scattering enhancement has been determined by the example of rhodamine 6G molecules adsorbed on a membrane with immobilized silver nanoparticles.     

Synthesis of ZrB2 nanoparticles by sol-gel method

Zirconium diboride (ZrB₂) nanoparticles were synthesized by sol-gel method using zirconium n-propoxide (Zr(OPr)₄), boric acid (H₃BO₃), and sucrose (C₁₂H₂₂O₁₁). Additionally, acetylacetone (acac) was used as chemical modifier in a neutral condition to stabilize Zr(OPr)₄ which hydrolyzes easily. Here, C₁₂H₂₂O₁₁ was used since it can be completely decomposed to carbon. Thus, carbon might be accounted precisely for the carbothermal reduction reaction. A single phase ZrB₂ without residual ZrO₂ was obtained with a molar ratio of B/Zr = 2.3 for the starting materials at 1,550 °C and the average grain size of ZrB₂ nanoparticles was ca. 50 nm. The photomicrograph revealed a spherical round shape morphology of the ZrB₂ nanoparticles with an uniform size distribution. On the other hand, in the case of either B/Zr (mol.) = 2.0 or pyrolyzing temperature below 1,550 °C for B/Zr (mol.) = 2.3, there existed both m-ZrO₂ and t-ZrO₂ phases besides ZrB₂.     

Porosity of aluminium oxide-based binary systems obtained by sol-gel method

A comparative study of binary oxide systems Al₂O₃-SnO₂; Al₂O₃-GeO₂ and Al₂O₃-B₂O₃ obtained by the sol-gel method has been made. Particular attention was paid to changes in the texture as a function of the type of the second component and its concentration in the binary system. Additionally, we describe changes in the porosity of the above systems after annealing in hydrogen atmosphere. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the nature of decrease in the particles size of nanostructured nickel oxide obtained by the sol-gel method in the presence of surfactants

A processes of formation of nanostructured powders of nickel oxide by annealing in the temperature range of 200–700°C of the nickel hydroxide obtained by the sol-gel method at 80°C from solutions of nickel nitrate by precipitation with alkali in the presence of surfactant AF-12 (polyethylene oxide alkylphenyl ether) was investigated. The formation of nanostructured powders of nickel oxide in the presence of a surfactant reduces the size of nanoparticles to 20–25 nm, which is 1.5 times smaller than the particles obtained without a surfactant. The effective influence of surfactant on the particle size begins in the temperature range of its decomposition and evaporation equal 350–400°C.     

Biodegradation of flax fibers in the presence of silver nanoparticles

Biodegradation of flax fibers differing in the chemical composition, structure of cellulose, and content of concomitant natural impurities (pectin compounds, lignin, hemicellulose) was studied. The effect exerted on the biodegradation by silver nanoparticles immobilized in the fiber was evaluated.     

Structural features of finely dispersed pseudoboehmite obtained by a sol-gel method

Simulation of diffraction patterns, radial distribution function analysis, and electron microscopy are applied to study the features of the structure of nanosized pseudoboehmite obtained by the sol-gel method. It is found to consist of plate-like particles with a thickness of one lattice constant in the [010] direction. Such a structure of the pseudoboehmite particles results in the absence of the 020 diffraction peak in the diffraction pattern.     

A simple method to synthesize triangular silver nanoparticles by light irradiation

We describe a simple method to synthesize triangular silver nanoparticles by photoreducing the silver ions by citrate. A noteworthy difference of the present method as compared with the previous photo-induced methods is that good shape control over the nanoparticles can be realized in the absence of soft templates or polymer directing agents. The formation process of the silver nanoparticles was investigated by UV-vis spectroscopy and transmission electron microscopy (TEM). It was found that the concentration of reactant plays important role in the morphology control of produced silver nanoparticles. As one of the applications of these nanoparticles, they were used as surface-enhanced Raman scattering substrates and 1,4-bis[2-(4-pyridyl)ethenyl]-benzene (BVPP) was used as a Raman probe to evaluate the enhancement ability of the triangular silver nanoparticles.     

Luminescent nanocomposite synthesized by sol-gel method in micellar solution of alkyl-polyglycoside with solubilized luminol

It is shown that micellar surfactant solution with solubilized luminophore dye luminol can be used to synthesize silicate nanocomposite with luminescent properties. In the course of its synthesis, micelles perform a dual role, i.e., they solubilize luminol in neutral media, in which it is poorly soluble, and catalyze the sol-gel process, as well act as a template for the silicate forming in situ. It is established that, upon the incorporation of dye into the silicate matrix, its luminescent properties not only retained, but the intensity of fluorescence increases substantially. It is suggested that the approach developed can be used to produce biosencors since, along with dye, it permits us to immobilize enzymes.     

Fluorescence of pyrene in the presence of silver nanoparticles on cellulose modified by surface-active substances

Luminescent properties of pyrene in the ordered structure formed by the molecules of a surface-active substance represented by cetyltrimethylammonium bromide on a cellulose matrix preliminarily modified with silver nanoparticles are studied. Elevated intensity of fluorescence in the violet range of the spectrum of pyrene molecules solubilized in these structures is observed. This phenomenon is rationalized by the resonance of electron transitions of monomeric pyrene molecules in this range with plasmonic vibrations in silver nanoparticles.

     

Thermostability of glucose oxidase in silica gel obtained by sol-gel method and in solution studied by fluorimetric method

The thermostability of glucose oxidase entrapped in silica gel obtained by sol-gel method was studied by thermostimulated fluorescence of FAD at pH 5 and 7 and compared with that of the native enzyme in the solution and at the presence of ethanol. The unfolding temperatures were found to be lower for the enzyme immobilised in gel as compared with the native enzyme but higher as for the enzyme at the presence of ethanol. In gel, the thermal denaturation of glucose oxidase is independent on pH while in solution the enzyme is more stable at pH 5. The investigation the enzyme in different environment by steady-state fluorescence of FAD and tryptophan, synchronous fluorescence and time-resolved fluorescence of tryptophan indicates that the state of the molecule (tertiary structure and molecular dynamics) is different in gel and in solution. The ethanol produced during gel precursor hydrolysis is not the main factor influencing the thermostability of the enzyme but more important are interactions of the protein with the gel lattice.     

Preparation and characterization of silver nanoparticles by chemical reduction method

Silver nanoparticles were prepared by the reduction of AgNO(3) with aniline in dilute aqueous solutions containing cetyltrimethlyammonium bromide, CTAB. Nanoparticles growth was assessed by UV-vis spectroscopy and the average particle size and the size distribution were determined from transmission electron microscopy, TEM. As the reaction proceeds, a typical plasmon absorption band at 390-450nm appears for the silver nanoparticles and the intensities increase with the time. Effects of [aniline], [CTAB] and [Ag(+)] on the particle formation rate were analyzed. The apparent rate constants for the formation of silver nanoparticles first increased until it reached a maximum then decreased with [aniline]. TEM photographs indicate that the silver sol consist of well dispersed agglomerates of spherical shape nanoparticles with particle size range from 10 to 30nm. Aniline concentrations have no significant effect on the shape, size and the size distribution of Ag-nanoparticles. Aniline acts as a reducing as well as adsorbing agent in the preparation of roughly spherical, agglomerated and face-centered-cubic silver nanoparticles.     

Preparation and characterization of a novel nanocomposite: silver nanoparticles decorated cerasome

In this study, a novel artificial hybrid vesicle, nano silver particles decorated cerasome were fabricated through sol–gel and self-assemble methods as well as in situ reduction. Samples were characterized in terms of hydrodynamic size and surface morphology via dynamic light scattering as well as scanning and transmission electron microscopies. Analysis through energy dispersive X-ray spectrometer proved the existence of silver particles. Due to the high morphological stability of cerasome, Silver nanoparticles with a size of about 5–10 nm can be deposited on the surface without any stabilizers. The UV spectra revealed a single symmetric extinction peak at 406 nm, confirming the spherical shape of the synthesized silver nanoparticles. Several reducing agents were screened before confirming sodium borohydride (NaBH₄). Comparison of different NaBH₄/lipid ratios (K_{NaBH4/cerasome-forming lipid}) was then carried out in order to ascertain its effect. Investigation of the stability of this hybrid vesicles was carried out, indicating that it can be stored at 4 °C for at least 3 months without any morphological change. Results demonstrated that this hybrid vesicle has excellent morphological stability, which impart it significant potential for various applications such as being an antibacterial material and a radio sensitization agent.     

Facile size-regulated synthesis of silver nanoparticles by controlled thermolysis of silver alkylcarboxylates in the presence of alkylamines with different chain lengths

Controlled thermolysis of silver alkylcarboxylates with primary alkylamines was investigated as a facile synthetic method of silver nanoparticles. A series of silver alkylcarboxylates, C(7)H(15)COOAg, C(13)H(27)COOAg, and C(17)H(35)COOAg, have been prepared and the thermolysis of those silver alkylcarboxylates in the presence of various alkylamines, C(8)H(17)NH(2), C(12)H(25)NH(2), and C(18)H(37)NH(2), with no use of solvent was conducted at 120 or 180 degrees C for 5 h, providing spherical silver nanoparticles stabilized by alkylcarboxylates and alkylamines. The size and dispersibility of nanoparticles depend on the alkyl chain length of the precursors, alkylcarboxylates and alkylamines.     

Preparation,structure and properties of silicate-phosphate glasses obtained by means of sol-gel method

Gels, densified amorphous materials and thin layers in SiO₂-P₂O₅, SiO₂-P₂O₅-Al₂O₃ and SiO₂-P₂O₅-Na₂O systems were obtained from alcohol solutions. Detailed DTA, XRD and FTIR investigations were carried out for dried gels and heat-treated samples. It has been found, among others, that the addition of aluminium to the silicate-phosphate glasses eliminates the doubly bonded oxygen (P=O) and leads to the formation of a continuous framework connected with [SiO₄], [PO₄] and [AlO₄] tetrahedra.There were measured the chemical and electrical properties of glasses covered with silicatephosphate gel layers. It has been found that the chemical resistance of the covered glasses is higher than that of the basic, sodium-calcium-silicate glass. Moreover, the silicate-phosphate layers modify the surface electrical conduction of the basic glasses. The layers of systems SiO₂-P₂O₅ and SiO₂-P₂O₅-Al₂O₃ show the electrical conduction considerable higher than the basic glass. The layers containing sodium, depending on its concentration, behave similarly to the basic glass or show lower electrical conductivity.     

ZnSe colloidal nanoparticles synthesized by solvothermal method in the presence of ZrCl4

The nanocrystalline ZnSe was synthesized from precursors of zinc acetate and Se powder in a high boiling trioctylphosphine (TOP), oleic acid, and ZrCl(4) by solvothermal method. The produced ZnSe nanoparticles showed gradual absorption edge shifting towards blue wavelength region as well as transformation of crystal phase from cubic to hexagonal with increasing ZrCl(4) concentrations in precursor solutions. The particle size calculated from XRD measurements for ZnSe nanoparticles was decreased with increasing ZrCl(4) concentrations for a reaction time of 240 min, from 6.5 nm to 5.1 nm whereas from TEM measurements it was 7.0 to 6.1 nm at 0.0 and 22.5 mol% of ZrCl(4), respectively. No trace of zirconium was found in solid ZnSe nanoparticles by SEM-EDS analysis but the atomic percentage of Se with respective to Zn was decreased with increasing ZrCl(4). The absorption edge blue shifting was explained on the basis of decreased particle size. The crystal phase transformation may be due to the combined effect of small internal energy difference between the two phases and the decrease of crystallite size.     

Polyacrylate/silica nanocomposite materials prepared by sol-gel process

Polyacrylate/silica nanocomposite was prepared by sol-gel process via in situ emulsion polymerization. The influence of the synthetic conditions, such as the ratio of different monomers and the contents of tetraethoxysilane (TEOS), γ-methacryloxypropyltrimethoxysilane (Z-6030), diethanolamine (DAM) and ammonium persulfate (APS) on the physical mechanical properties of polyacrylate/silica nanocomposite was investigated in details. Dynamics Laser Scattering (DLS) indicated that the average diameter of the polyacrylate/silica latex particles (177 nm) was bigger than that of the pure polyacrylate latex particles (105.3 nm), but the ζ potential of polyacrylate/silica was decreased respectively in contrast to that of the polyacrylate. Differential Scanning Calorimeters (DSC) analysis confirmed that the glass transition temperature of polyacrylate/nano-SiO₂ (T_g = −24 °C) was higher than that of polyacrylate (T_g = −36 °C). UV analysis showed that the UV absorbency of polyacrylate/silica was improved evidently in contrast to that of polyacrylate.     

Morphology evolution of ZrB2 nanoparticles synthesized by sol-gel method

Zirconium diboride (ZrB₂) nanoparticles were synthesized by sol-gel method using zirconium n-propoxide (Zr(OPr)₄), boric acid (H₃BO₃), sucrose (C₁₂H₂₂O₁₁), and acetic acid (AcOH). Clearly, it was a non-aqueous solution system at the very beginning of the reactions. Here, AcOH was used as both chemical modifier and solvent to control Zr(OPr)₄ hydrolysis. Actually, AcOH could dominate the hydrolysis by self-produced water of the chemical propulsion, rather than the help of outer water. C₁₂H₂₂O₁₁ was selected, since it can be completely decomposed to carbon. Thus, carbon might be accounted precisely for the carbothermal reduction reaction. Furthermore, we investigated the influence of the gelation temperature on the morphology of ZrB₂ particles. Increasing the gelation temperature, the particle shapes changed from sphere-like particles at 65 °C to a particle chain at 75 °C, and then form rod-like particles at 85 °C. An in-depth HRTEM observation revealed that the nanoparticles of ZrB₂ were gradually fused together to evolve into a particle chain, finally into a rod-like shape. These crystalline nature of ZrB₂ related to the gelation temperature obeyed the “oriented attachment mechanism” of crystallography.