One-step preparation and characterization of PDDA-protected gold nanoparticles

Poly(diallyl dimethylammonium) chloride (PDDA), an ordinary and watersoluble, cationic polyelectrolyte, was investigated for its ability to generate and stabilize gold colloids from a chloroauric acid precursor. In this reaction, PDDA acted as both reducing and stabilizing agents for gold nanoparticles (AuNPs). More importantly, PDDA is a quaternary ammonium polyelectrolyte, which shows that the scope of the reducing and stabilizing agents for metal nanoparticles can be extended from the amine-containing molecules to quaternary ammonium polyelectrolytes or salts. UV-vis spectroscopy, transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS) and Fourier transform infrared (FTIR) were used to characterize the synthetic AuNPs. The PDDA-protected AuNPs obtained are very stable and have relative narrow size distribution.

Synergistic effect of supported nickel catalyst with intumescent flame-retardants on flame retardancy and thermal stability of polypropylene

Supported nickel catalyst (Ni-Cat) was used as a catalyst to improve the flame retarclancy of intumescent flame-retardants (IFR) systems based on ammonium polyphosphate and pentaerythritol (PETOL) in polypropylene (PP) matrix. Limited oxygen index (LOI), UL-94 rating, and thermogravimetric analysis were used to characterize the flame retardancy and thermal stability of the PP systems, and field emission scanning electron microscopy (FE-SEM) and Fourier transformed infrared spectroscopy (FTIR) were used to analyze the microstructure and composition of the chars formed during measuring LOI value and after combustion at 800 degrees C. The catalytic effect of NiCat was shown in an increase of LOI, a change in the char microstructure, and improvement of the thermal stability in the PP systems, which result from the synergistic effect of Ni-Cat and IFR. The results from FE-SEM and FTIR spectra of the char can explain how this synergistic effect happened.

Synthesis and fluorescence properties of Eu2+-doped KMgF3 nanoparticles

The phase diagram of a cetyltrimethyl ammonium bromide( CTAB)/n-butanol/n-octane/KNO3-Mg( NO3)(2) system was drawn. Nanoparticles of Eu2+-doped KMgF3 were prepared from the quaternary microemulsions of cetyltrimethyl ammonium bromide(CTAB), n-butanol, n-octane and water. The X-ray diffraction(XRD) patterns were indexed to a pure KMgF3 cubic phase. The environmental scanning electron microscopic (ESEM) images show the presence of spherical Eu2+-doped KMgF3 nanoparticles with a diameter of ca. 20 nm. The emission of KMgF3: Eu2+ nanoparticles peaks at 360 mn. The excitation band was observed at 250 nm with a blue shift of ca. 70 nm compared with that of KMgF3: Eu2+ single crystal. The preparation method of nano-KMgF3: Eu2+/PMMA composite films was inquired into.

Nitrate-citrate combustion synthesis and properties of Ce1-xSmxO2-x/2 solid solutions

A nitrate-citrate combustion route to synthesize nanocrystalline samarium-doped ceria powders for solid electrolyte ceramics is presented. This route is based on the gelling of nitrate solutions by the addition of citric acid and ammonium hydroxide, followed by an intense combustion process due to an exothermic redox reaction between nitrate and citrate ions. The influence of ignition temperature on the characteristics of the powders was studied. The change of the crystal structure with the content of doped Sm was investigated. High temperature X-ray, and Raman scattering were used to characterize the sample. The lattice constant and unit volume increase with doping level and increasing temperature. Dense ceramic samples prepared by uniaxial pressing and sintering in air were also studied.

Synergistic extraction of zinc(II) by mixtures of primary amine N1923 and Cyanex272

The extraction of zinc(II) and cadmium(II) from chloride solution by mixtures of primary amine N1923 and Cyanex272 (HA) was studied. The synergistic effect was observed for the extraction of zinc(II) while no synergistic effect for cadmium(II), which makes it possible to separate zine(II) and cadmium(II) with the mixtures. The results showed that zinc(II) was extracted as (RNH3Cl)(3) . ZnCIA instead of ZnA(2) . 2HA which was extracted by Cyanex272 alone. The extraction mechanism was discussed and the formation constants and thermodynamic functions were determined. The separation factors between zinc(II) and cadmium(II) were calculated.

Charge transfer across the water/nitrobenzene interface by three-electrode system

A droplet of aqueous solution containing a certain molar ratio of redox couple is first attached onto a platinum electrode surface, then the resulting drop electrode is immersed into the organic solution containing very hydrophobic electrolyte. Combined with reference and counter electrodes, a classical three-electrode system has been constructed, Ion transfer (IT) and electron transfer (ET) are investigated systematically using three-electrode voltammetry. Potassium ion transfer and electron transfer between potassium ferricyanide in the aqueous phase and ferrocene in nitrobenzene are observed with potassium ferricyanide/potassium ferrocyanide as the redox couple. Meanwhile, the transfer reactions of lithium, sodium, potassium, proton and ammonium ions are obtained with ferric sulfate/ferrous sulfate as the redox couple. The formal transfer potentials and the standard Gibbs transfer energy of these ions are evaluated and consistent with the results obtained by a four-electrode system and other methods.

The effect of pH difference between two phases on the partition of lysozyme in aqueous two-phase system

In the investigation of effect of KSCN on the partitioning of lysozyme in PEG2000/ammonium sulfate aqueous two-phase system, it was found that the KSCN could alter the pH difference between the two phases. and thus affect the partition of lysozyme. The relationship between partition coefficients of lysozyme and pH differences between two phases was discussed.

Chlorohydrin water swellable rubber compatibilized by an amphiphilic craft copolymer. I. Synthesis and characterization of compatibilizer PVA-g-PBA

The graft copolymerization of butyl acrylate onto poly(vinyl alcohol) with eerie ammonium nitrate as redox initiator in a aqueous medium has been investigated. The formation of graft copolymer was confirmed by means of IR, scanning electron microscopy (SEM), and wide-angle X-ray diffraction (WAXD). The percentage of mononer conversion and percentage of grafting varied with concentrations of initiator, nitric acid, monomer, macromolecular backbone (X-n = 1750, M = 80 000), reaction temperature and reaction time. Some inorganic salts and organic solvents have a great influence upon grafting. The reaction mechanism has been explored, and rate equations for the reaction are established. (C) 2000 John Wiley & Sons, Inc.

Synthesis and structure of a novel mononuclear tungsten (VI) citrato complex, (NH4)(3)[Li(H2O)(3)WO3(C6H4O7)]

The first mononuclear tungsten-citrato complex, (NH4)(3)[Li(H2O)(3)WO3(C6H4O7)] (1) has been prepared by the reaction of ammonium tetrathio tungstate and lithium citrate in CH3OH - H2O solution at pH 8.2. There are two crystallographically independent anions in the asymmetric crystallographic unit. The crystal structure of the title compound (triclinic, space group P (1) over bar, a = 6.901(1), b = 15.136(3), c = 16.107(3) Angstrom, alpha = 75.85(3), beta = 89.89(3), gamma = 89.97(3), V = 1631.4(6) Angstrom (3), R = 0.068, R-w = 0.1674 for 3878 reflections with I > 2 sigma (1)), reveals that in the compound a tungsten atom is coordinated to a fully deprotonated citrate as a tridentate ligand and three terminal oxygen atoms to form a distorted coordination octahedron.

The effect of KSCN on the partition of proteins in polyethylene glycol/(NH4)(2)SO4 aqueous two-phase system

The effect of potassium thiocyanate on the partitioning of lysozyme and BSA in polyethylene glycol 2000/ammonium sulfate aqueous two-phase system has been investigated. As a result of the addition of potassium thiocyanate to the PEG/ammonium sulfate system, the PEG/mixed salts aqueous two-phase system was formed. It was found that the potassium thiocyanate could alter the pH difference between the two phases, and, thus, influence the partition coefficients of the differently charged proteins. The relationship between partition coefficient of the proteins and pH difference between two phases has been discussed. It was proposed that the pH difference between two phases could be employed as the measurement of electrostatic driving force for the partitioning of charged proteins in polyethylene glycol 2000/ammonium sulfate aqueous two-phase system.

Facile synthesis of phenyl-capped oligoanilines using pseudo-high dilution technique

Monodispersed phenyl-capped trianiline and tetraaniline were successfully synthesized by the reactions of diphenylamine with acetaldehyde-based Sckiff's bases of N-phenyl-1,4-phenylenediamine and 1,4-phenylenediamine, respectively, in the presence of ammonium persulfate and hydrochloric acid, subsequent deprotonation and reduction with phenylhydrazine. The reaction mechanism probably involves the slow hydrolysis of the Sckiff's bases and subsequent oxidative coupling reactions of the formed ammonium salts with diphenylamine at pseudo-high dilution condition of the salts.

Electrospray ionization mass spectrometry of cyclodextrin complexes with amino acids in incubated solutions and in eluates of gel permeation chromatography

1:1 complexes of beta-cyclodextrin (CD) with three amino acids (Gly, Phe and Trp) have been detected as ions in the gas phase using infusion positive and negative ion electrospray ionization mass spectrometry (ESI-MS). In contrast with the positive ion ESI mass spectra of simple aqueous solutions, the aggregates and adducts usually formed in the ESI process did not appear in the positive ion ESI spectra of solutions buffered with ammonium acetate (NH4Ac), even at higher analyte concentrations, These studies suggest that addition of buffer and/or use of a low analyte concentration should be used to overcome formation of aggregates and metal ion adducts in such mass spectrometry studies. Also, the deprotonated complexes are dissociated by collision induced dissociation (CID) to form an abundant product ion, the deprotonated CD, requiring transfer of a proton to the amino acid carboxyl group, To understand formation of complexes in the gas phase, gel permeation chromatography (GPC) was used to separate free amino acids (AAs) from complexes in an incubated solution. The ESI mass spectra of the GPC fractions show the presence of 1:1 complexes of both CD-aromatic amino acids and CD-aliphatic amino acids. Compared with CD-aliphatic amino acid complexes, CD-aromatic amino acid complexes appear to be destabilized in the gas phase, possibly because the hydrophobic interaction which binds the aromatic group of amino acids in the CD cavity in solution may become repulsive when solvent evaporates from the droplets during the electrospray process, whereas those complex ions formed as proton bound dimers are stabilized by electrostatic forces, the major binding force for such complexes in the gas phase. In addition, the GPC technique coupled with off-line ESI-MS can rapidly separate CD complexes by size, and provides some information on the character of the complexes in solution. (C) 1998 John Wiley & Sons, Ltd.

Synthesis and structure of [NH4](4)H[(PMo8V4V2O42)-V-IV-O-V].24H(2)O

[NH4](4)H[(PMo8V4V2O42)-V-IV-O-V] . 24H(2)O has been hydrothermally synthesized from ammonium vanadate and sodium molybdate in aqueous solution by adding phosphorous acid, and its structure determined by single crystal X-ray analysis. The heteropoly molybdovanadophosphate anion is a bicapped 'pseudo-Keggin' polyanion, two vanadium atoms are distributed at two 'capping' metal atom positions and other four vanadium atoms randomly distributed at eight metal atom positions. (C) 1998 Elsevier Science Ltd. All rights reserved.

Probe beam deflection combined with cyclic voltammetry studies of C-60-modified electrode film

C-60 films, prepared by solution casting, were studied by means of in situ probe beam deflection (PBD) combined with cyclic voltammetry (CV). PBD is a powerful technique for investigation of phenomena at the electrode/electrolyte interface in acetonitrile with quaternary ammonium and alkali metal salts as supporting electrolytes. In tetra-n-butylammonium (TBA(+)) salt solution, a stable CV can be obtained during the first two reduction/reoxidation waves. On reduction, injection of cations to maintain charge balance and dissolution of small amount of C-60(-) (TEA(+)) and/or C-60(2-) (TBA(+))(2) are detected. During the reoxidation process ejection of cations and injection of anions occur simultaneously, especially for the second reoxidation wave. In the case where TBABr is the supporting electrolyte, the accompanied behavior is more complicated than in TBABF(4), TBAClO(4), and TBAPF(6) solutions. A small pair of prewaves in CV are proposed due to oxidation/reduction of C-60 domains but not dissolution/redeposition of C-60 film. Extending the potential scan range to the third reduction wave, no apparent corresponding reoxidation wave is related to the third reduction wave, the electroactivity of the film disappears rapidly and dissolution of C-60 film is observed. In tetraethylammonium (TEA(+)) and NAClO(4) solutions, the electrochemistry of the C-60 films is unstable, and potential scans lead to dissolution of flaking of the film.

WATER-SOLUBLE AND AMPHIPHILIC POLYMERS .11. GRAFT-POLYMERIZATION OF ACRYLIC-ACID ON POLY(VINYL ALCOHOL)

The graft polymerization of acrylic acid(AA) on poly(vinyl alcohol) (PVAL) has been investigated by using either potassium persulfate (KPS) or ceric ammonium nitrate(CAN) as an initiator. In the case of KPS initiation, the formation of the graft polymer always lags behind the homopolymer formation. The graft polymer is separated by acetone, and the increase of reaction temperature favors the homopolymer formation at the early stage. In the case of CAN initiation, graft polymers with a high PAA content can hardly be obtained when the polymerization is performed under nitrogen and at < 0.06 mol/L HNO3 concentration. It has been found that incorporation of a small amount of oxygen in a protective nitrogen gas accelerates markedly the graft polymerization, and that the resulting graft polymers can not be separated by acetone precipitation technique in most cases. The Dalian nitrogen(containing 0.7% oxygen) is a good protective gas for CAN-initiated PVAL-AA graft polymerization.