Dispersion copolymerization of acrylamide with acrylic acid in an aqueous solution of ammonium sulfate: Synthesis and characterization

Dispersion copolymerization of acrylamide with acrylic acid in an aqueous solution of ammonium sulfate using poly(2-acrylamido-2-methylpropanesulfonic acid sodium) as the stabilizer and ammonium persulfate (APS) as the initiator was investigated. The influence of initiator concentration, stabilizer concentration, ammonium sulfate concentration, chain-transfer agent concentration, and polymerization temperature on the copolymerization was discussed. The results showed that varying the ammonium sulfate concentration could affect the particle size and the intrinsic viscosity of the copolymer significantly. With increasing the stabilizer concentration, the particle size of the copolymer decreased first, and then increased, meanwhile the intrinsic viscosity of the copolymer decreased. The increase of initiator concentration, chain-transfer agent concentration, and polymerization temperature resulted in the increase in the particle size. Polydisperse spherical particles were formed in the system, and the kinetics for the dispersion copolymerization were discussed.

Synergistic extraction of rare earths(III) from chloride medium with mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 and di-(2-ethylhexyl)-2-ethylhexylphosphonate

The synergistic effect of 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 (HPMBP, HA) and di-(2ethylhexyl)-2-ethylhexylphosphonate (DEHEHP, B) in the extraction of rare earths (RE) from chloride solutions has been investigated. Under the experimental conditions used, there was no detectable extraction when DEHEHP was used as a single extractant while the amount of RE(III) extracted by HPMBP alone was also low. But mixtures of the two extractants at a certain ratio had very high extractability for all the RE (III). For example, the synergistic enhancement coefficient was calculated to be 9.35 for Y3+, and taking Yb3+ and Y3+ as examples, RE3+ is extracted as RE(OH)A(2).B. The stoichiometry, extraction constants and thermodynamic functions such as Gibbs free energy change Delta G (-17.06kJmol(-1)), enthalpy change Delta H (-35.08kjmol(-1)) and entropy change Delta S (-60.47JK(-1)mol(-1)) for Y3+ at 298 K were determined. The separation factors (SF) for adjacent pairs of rare earths were calculated. Studies show that the binary extraction system not only enhances the extraction efficiency of RE(III) but also improves the selectivity, especially between La(III) and the other rare earth elements.

Kinetics of cerium(IV) extraction with DEHEHP from HNO3-HF medium using a constant interfacial cell with laminar flow

Studies of the extraction kinetics of cerium(IV) into n-heptane solutions of di(2-ethylhexyl)-2-ethylhexyl phosphonate DEHEHP from HNO3-HF solutions have been carried out using a constant interfacial cell with laminar flow. The experimental hydrodynamic conditions were chosen so that the contribution of diffusion to the measured rate of reaction was minimized. The data were analyzed in terms of pseudo-first order constants. The effects of the stirring rate, specific interfacial area, and temperature on the extraction rate showed that the most probable reaction zone is in the aqueous homogeneous phase. The results were compared with those of the system without HF. It was concluded that the presence of HF decreases the extraction rate of cerium. The addition of HF increases the activation energy for the forward reaction from 21.2 to 55.3 kJ/mol and for the reverse process from 57.9 to 79.0 kJ/mol. According to the experimental data correlated as a function of the concentration of the relevant species involved in the extraction reaction, the corresponding rate equation was deduced as follows:-d[Ce]/dt = k[Ce] center dot B-0.62 center dot HF-0.58 center dot [NO3-](0.57)

Extraction of rare earths(III) from nitrate medium with di-(2-ethylhexyl) 2-ethylhexyl phosphonate and synergistic extraction combined with 1-phenyl-3-methyl-4-benzoy l-pyrazolone-5

The extraction of trivalent rare earths ( RE) from nitrate solutions with di-(2-ethylhexyl) 2-ethylhexyl phosphonate (DEHEHP, B) and synergistic extraction combined with 1-phenyl-3-methyl-4-benzoyl-pyrazolone-5 (HPMBP, HA) were investigated. The extraction distribution ratios demonstrate a distinct "tetra effect," and Y lies between Tb and Dy when DEHEHP is used as a single extractant for RE. According to the corresponding separation factors (SF12) for adjacent pairs of rare earths, it could be concluded that DEHEHP could be employed for the separation of La from the other rare earths, and Y from light rare earths. The present work has also found that mixtures of HPMBP and DEHEHP have an evident synergistic effect for RE(III). Taking Y( III) as an example, a possible synergistic extraction mechanism is proposed. The enhancement of extraction in the binary system can be explained due to the species Y(NO3) (.) A(2) (.) HA (.) B formed. The synergistic enhancement coefficients ( R), extraction constants, formation constants and thermodynamic functions of the reaction were calculated.

Extraction and stripping of ytterbium (III) from H2SO4 medium by Cyanex 923

The extraction and stripping of ytterbium (III) from sulfuric acid medium using Cyanex 923 in heptane solution was investigated. The effects of extractant concentration, pH and sulfate ion as well as stripping agents, acidity and temperature on the extraction and stripping were studied. The equilibrium constants and thermodynamic parameters, such as Delta H (10.76 kJ(.)mol(-1)), Delta G (-79.26 kJ(.)mol(-1)) and Delta S (292.41 J(.)K(-1.)mol(-1)), were calculated. The extraction mechanism and the complex species extracted were determined by slope analysis and FrIR spectra. Furthermore, it was found that the extraction of Yb (III) from sulfuric acid medium by Cyanex 923 increased with pH, concentration of SO42-, HSO4-, and extractant concentration, and approximately a quantitative extraction of Yb (III) was achieved at an equilibrium pH near 3.0, and the extracted complex was YbSO4(HSO4)(.)2Cyanex923((o)).

Effects of surfactant loadings on the dispersion of clays in maleated polypropylene

A series of organically modified clays (OMCs) with a surfactant loading range from 0.625 to 2.5 times the cation exchange capacity (CEC) were melt-mixed with maleated polypropylene (PPMA). Wide-angle X-ray diffraction and transmission electron microscopy results of these narrocomposites show that dispersion of clays becomes unfavorable in the PPMA matrix during melt intercalation as the surfactant loading increases in the process of modifying clays, though larger interlayer distances are obtained in their corresponding OMCs. It is even important that clays uniformly disperse at the nanoscale level in the PPMA matrix when the surfactant loadings are below the CEC, which implies that incomplete exchange of inorganic cations in the process of modifying clay benefits the dispersion of clays in the PPMA matrix.

Synergistic extraction of lanthanum(III) from chloride medium by mixtures of 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 and triisobutylphosphine sulphide

The synergistic effect of 1-phenyl-3-methyl-4-benzoyl-pyrazalone-5 (HPMBP) and triisobutylphosphine sulphide (TIBPS, B) is investigated in the extraction of lanthanum(III) from chloride solution. Lanthanum(III) is extracted by the mixture as LaCl2.PMBP.B-0.5 instead of La(PMBP)(3).(HPMBP) which is extracted by HPMBP alone. The equilibrium constants and thermodynamic functions such as DeltaG, DeltaH and DeltaS are determined. The extraction of other rare earth ions by mixtures of HPMBP and TIBPS is also studied and the possibility of separating rare earth ions is discussed.

Kinetics of cerium(IV) extraction from H2SO4-HF medium with Cyanex 923

Studies of the extraction kinetics of cerium(IV) from H2SO4-HF solutions with Cyanex 923 in n-heptane have been carried out using a constant interfacial area cell with laminar flow. The experimental hydrodynamic conditions were chosen so that the contribution of diffusion to the measured rate of reaction was minimized. The data were analyzed in terms of pseudo-first order constants. The results were compared with those of the system without HF. It was concluded that the addition of HF reduces the activation energy for the forward rate from 46.2 to 36.5 U mol(-1) while it has an opposite effect on the activation energy for the reverse process(the activation energy increased from 23.3 to 90.8 U mol(-1)). Thus, HF can accelerate the rate of cerium(IV) extraction. At the same time, the extraction rate is controlled by a mixed chemical reaction-diffusion rather than by a chemical reaction alone. A rate equation has also been obtained.

Preparation of polyimide-BaTiO3 hybrid films by a dispersion process and their microstructure

Barium titanate (BaTiO3) powders with particle sizes of 30 similar to 50 nm were prepared from barium stearate, titanium alkoxides and stearic acid by stearic acid-gel method. Dispersing the agglomerate of BaTiO3 nanoparticles into poly(amic acid) solution followed by curing led to the formation of polyimide hybrid films. The hybrid films were transparent and well distributed with BaTiO3 nanoparticles when the BaTiO3 content was less than 1 wt%. Highly loaded hybrid film containing 30 wit % BaTiO3 was tough, had a smooth surface and possessed much higher dielectric and piezoelectric constants than the parent polyimide.

Sol-gel thin-film immobilized soybean peroxidase biosensor for the amperometric determination of hydrogen peroxide in acid medium

An acid-stable soybean-peroxidase biosensor was devel oped by immobilizing the enzyme in a sol-gel thin film. Methylene blue was used as a mediator because of its high electron-transfer efficiency. The sol-gel thin film and enzyme membrane were characterized by FT-IR, and the effects of pH, operating potential, and temperature were explored for optimum analytical performance by using the amperometric method. The H2O2 sensor exhibited a fast response (5 s), high sensitivity (27.5 mu A/mM), as well as good thermostability and long-term stability. In addition, the performance of the biosensor was investigated using flow-injection analysis (FIA).

Catalytic oxidation of cyclohexene to cyclohexanone by a triple system in acidic aqueous acetonitrile medium

The catalytic oxidation of cyclohexene to cyclohexanone using Pd(OAc)(2)/HQ/FePc was investigated in an acidic aqueous solution of acetonitrile. The role of each component of this system in the oxidation of cyclohexene was explored by means of UV-VIS, IR, XPS spectroscopy and. cyclic voltammetry, respectively. Based on the experimental results, the mechanism of the oxidation of cyclohexene catalyzed by Pd(OAc)(2)/HQ/FePc was elucidated.

A study of the dependence of ferrocene diffusion on electrolyte concentration and size in a polymer medium using non-steady-state chronoamperometry

This article describes a quantitative study of the diffusion rate of ferrocene(Fc) dissolved in ploy(ethylene glycol)(PEG) medium containing MClO(4)(M = Li+, Na+, Bu(4)N(+), Hx(4)N(+)). The apparent diffusion coefficient D-app and the active concentration c(a) of Fc were simultaneously measured by using non-steady-state chronoamperometry. The D-app and c(a) of Fc have been estimated in PEG containing different concentrations and sizes of supporting electrolyte, and the dependence of D-app on ferrocene concentrations has been observed. The values of D-app decrease with increasing concentrations of Fc, increasing concentrations of LiClO4 or the ratio (O:Li) and also with 4 decreasing cation radius of the electrolyte. The temperature dependencies conform to a simple free volume model. The concentration and size of the counterion dependencies of the diffusion rate are similar to the behavior of their dependencies of ionic conductivity in polyelectrolyte.

KINETIC-STUDY OF ELECTROCATALYTIC REDUCTION OF HYDROGEN-PEROXIDE AT IRON(III) PORPHYRIN MODIFIED GLASSY-CARBON ELECTRODE IN ALKALINE-MEDIUM USING THE ROTATION-SCAN METHOD

Reduction of hydrogen peroxide at a glassy carbon (GC) electrode modified with sigma-bonded pyrrole iron(III) octaethylporphyrin complex, (OEP)Fe(Pyr), was studied by cyclic voltammetry and a rotating disk electrode. In 0.1N NaOH solution, it is shown that such an (OEP)Fe(Pyr)/GC electrode has a significant catalytic activity towards hydrogen peroxide reduction (E(D) = -0.80 V, k = 0.066 cm s(-1)); however, the electrode stability is low. The deactivation is observed when the reaction charge (Q) is passing through the (OEP)Fe(Pyr)/GC disk electrode. A linear rotation scan method is applied to study the kinetic process by determining the disk electrochemical response (i(D)) to rotation rate (omega) at a definite disk potential (E(D)). Considering that the number of adsorbed electroreduced catalyst molecules (Red) varies according to the disk potential, a factor theta(= Gamma(Red)/(Gamma(Red) + Gamma(Ox))) is introduced to describe the electrode surface area fraction for electroreduced species. The obtained Koutecky-Levich equation is applicable whatever the potential is.

Studies on hybridization effects of different geographic populations of Chlamys farreri - II. The medium-term growth and development of Chlamys farreri populations from China and Russia and their reciprocal crosses

Based on the research of juvenile (2, 3, 4 months) growth and survival of three populations of two different geographic areas in Chlamys farreri from Russian and China and their F, hybrids derived from Chinese cultural population (CC) female x Russian population (RW) male, Chinese wild population (CW) female x Russian population (RW) male, Russian population (RW) female x Chinese wild population (CW) the study of the medium-term (6, 8, 10, 12 months) growth and development of Chlamys farreri was carried out. The four determined results indicated that there existed different extent heterosis (3% similar to 52 %) for the growth in three types of F-1 hybrids, and the offspring derived from CC female X Rmale had a stronger heterosis among the crosses at the medium-term; the uptrend among traits are wet weight > shell width > shell length > shell height, Chinese cultural population could be recognized as excellent parent, and seasonal variations influence very much on the daily increment and growth rate of each trait of Chlamys farreri and it is only able to survive and could barely grow in winter (6 similar to 8 months), but grows fast in temperate season (10similar to12 months).

Chandrananimycins A-C: Production of novel anticancer antibiotics from a marine Actinomadura sp isolate M048 by variation of medium composition and growth conditions

In our screening of marine actinomycetes for bioactive principles, three novel antibiotics designated as chandrananimycin A (3c), B (3d) and C (4) were isolated from the culture broth of a marine Actinomadura sp. isolate M045. The structures of the new antibiotics were determined by detailed interpretation of mass, 1 D and 2 D NMR spectra.