Non-isothermal reduction of silica-supported nickel catalyst precursors in hydrogen atmosphere: a kinetic study and statistical interpretation

A series of silica-supported nickel catalyst precursors was synthesized with different SiO₂/Ni mole ratios (0.20, 0.80 and 1.15). Non-isothermal reduction of Ni catalyst precursors was investigated by temperature-programmed reduction at four different heating rates (2, 5, 10 and 20 °C min^?1), in a hydrogen atmosphere. Kinetic parameters (E _a, A) were determined using Friedman isoconversional method. It was found that for all mole ratios, apparent activation energy is practically constant in conversion range of α = 30–70 %. In considered conversion range, the following values of apparent activation energy were found: E _a = 129.5 kJ mol^?1 (SiO₂/Ni = 0.20), E _a = 133.8 kJ mol^?1 (SiO₂/Ni = 0.80) and E _a = 125.0 kJ mol^?1 (SiO₂/Ni = 1.15). Using two special functions (y(α) and z(α)), the kinetic model was determined. It was established that reduction of Ni catalyst precursors with different SiO₂/Ni mole ratios is a complex process and can be described by two-parameter ?esták–Berggren (SB) autocatalytic model. Based on established values of SB parameters for each mole ratio, the possible mechanism was discussed. It was found that for all investigated ratios, the Weibull distribution function fits very well the experimental data, in the wide range of conversions (α = 5–95 %). Based on obtained values of Weibull shape parameter (θ), it was found that experimentally evaluated density distribution functions of the apparent activation energies can be approximated by the unbalanced peaked normal distribution.     

Estimation of kinetic parameters for the phase change memory materials by DSC measurements

The non-isothermal method for estimating the kinetic parameters of crystallization for the phase change memory (PCM) materials was discussed. This method was applied to the perspective PCM material of Ge₂Sb₂Te₅ with different Bi contents (0, 0.5, 1, 3 mass%) for defining the kinetic triplet. Rutherford backscattering spectroscopy and X-ray diffraction were used to carry out elemental and phase analysis of the deposited films. Differential scanning calorimetry at eight different heating rates was used to investigate kinetics of thermally induced transformations in materials. Dependences of activation energies of crystallization (E _a) on the degree of conversion were estimated by model-free Ozawa–Flynn–Wall, Kissinger–Akahira–Sunose, Tang and Starink methods. The obtained values of E _a were quite close for all of these methods. The reaction models of the phase transitions were derived with using of the model-fitting Coats–Redfern method. In order to find pre-exponential factor A at progressive conversion values, we used values of E _a already estimated by the model-free isoconversional method. It was established that the crystallization processes in thin films investigated are most likely describes by the second and third-order reactions models. Obtained kinetic triplet allowed predicting transition and storage times of the PCM cells. It was found that thin films of Ge₂Sb₂Te₅ + 0.5 mass% Bi composition can provide the switching time of the phase change memory cell less than 1 ns. At the same time, at room temperature this material has a maximum storage time among the studied compositions.     

Alignment of Ar+ (2p −1 2 P 3/2) ions after electron impact ionisation in the range 1 keV to 268 eV

We have measured the alignmentA ₂₀ of Ar⁺(2p ^{?1 2} P _3/2) ions after electron impact ionization in the range of primary electron energyE ₀=1000...268 eV (range of excess energyE ₁=750...19.5 eV) via the anisotropic angular distribution ofL ₃?M _2,3 M _2,3(¹ S ₀) Auger electrons. On decomposing the Auger spectra into their components special care was taken by including the effect of the postcollision interaction on the shape of Auger lines. The present alignment values forE ₀≧350 eV agree well with previously existing experimental values of DuBois and Rodbro and with theoretical DWBA results of Berezkho and Kabachnik, but forE ₀<350 eV they deviate systematically from the DWBA values. For the lowest impact energyE ₀, which is only 19.5 eV above threshold, we obtainedA ₂₀=+0.09(16). This value clearly indicates that in the ionisation process near threshold the two low-energy electrons escape not only with a two-electron partial waveL=0, according to Wannier's original assumption, but also with partial wavesL>0.     

Corrosion inhibition investigations of 3-acetylpyridine semicarbazone on carbon steel in hydrochloric acid medium

The corrosion inhibition efficiency of 3-acetylpyridine-semicarbazide (3APSC) on carbon steel (CS) in 1.0 M HCl solution has been investigated using weight loss measurements, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies. The results show that inhibition efficiency on metal increases with the inhibitor concentration. 3APSC exhibited marked inhibition towards carbon steel in HCl medium even at low concentrations. The adsorption of inhibitor on the surfaces of the corroding metal obeys the Langmiur isotherm and thermodynamic parameters (K _ads, ?G _ads ⁰ ) were calculated. Activation parameters of the corrosion process (E _a, ?H* and ?S*) were also calculated from the corrosion rates. Polarization studies revealed that 3APSC act as a mixed-type inhibitor. Surface analysis of the metal specimens was performed by scanning electron microscopy.     

Effects of Cu addition on the structure and magnetic properties of L10-FePt nanoparticles prepared by sol–gel method

(FePt)₁₀₀Cu₀, (FePt)₉₅Cu₅ and (FePt)₉₀Cu₁₀ nanoparticles (NPs) were successfully synthesized by the sol–gel method. The relationship between Cu doping and structure and magnetic properties of L1₀-FePt NPs was studied. The results indicated that all three samples originated a L1₀-FePt structure and Cu doping did not destroy the ordered structure of L1₀-FePt. By increasing the Cu content, c/a ratio of the FePtCu NPs linearly decreased. Pawley refinement showed symmetry of (FePt)₉₅Cu₅ NPs was still tetragonal. When the Cu concentration increased from 0 to 10 %, coercivity increased from 7,050 to 11,250 Oe. This result confirms that the prepared alloys can be promising candidates for magnetic storage applications.     

KL 2,3 ionization in neon by electron impact in the range 1.5–50 keV: cross sections and alignment

We have measured the ratio of cross sections σ(KL _2,3)/σ(K) for neon for electron impact in the energy range ofE ₀=1.5 ... 50 keV via the intensity ofKL _2,3?LLL _2,3 Auger satellite lines relative to the intensity ofKL ₁ L _2,3 (³ P) diagram line. The experimental ratio decreases over the full range of energyE ₀ which is contrary to an earlier result by Carlson et al. We have also measured the alignment ofKL _2,3 ¹ P and³ P states via the angular distribution of Auger satellite intensity for the energy rangeE ₀=1.5 ... 4 keV, within experimental error we have found a zero alignment. The totalK Auger spectrum, measured forE ₀=40 keV and at the magic angle of emission ?=54.7°, has been decomposed into its components by using appropriate line shapes distorted by postcollision interaction. Finally, we discussed whether the lines observed at the high-energy side ofKL _2,3?LLL _2,3 Auger satellite lines can be interpreted as structures caused by an angular momentum exchange in the postcollision interaction predicted by Niehaus and Zwakhals.     

Weak acid–base interaction induced assembly for the formation of rambutan-like poly(styrene-alt-maleic anhydride)/silica composite microspheres

To investigate the effect of surface functionality on the morphology of polymer/silica composite, poly(styrene-alt-maleic anhydride) (SMA) spheres prepared via precipitation polymerization method was employed. In water/ethanol solution, diethanolamine (DEA) was used to catalyze the hydrolysis reaction of tetraethoxysilane (TEOS), and rambutan-like poly(styrene-alt-maleic anhydride)/silica (SMA/SiO₂) microspheres were synthesized through in situ sol–gel process. The obtained structure and morphology were characterized by FTIR, NMR, TEM, SEM, and TGA. The results showed that the hydrolyzed SMA chains on the surface was crucial to the nucleation and growth of silica, and the morphologies of SMA/SiO₂ composite microspheres can be controlled by the amount of DEA and the ratio of SMA/TEOS. In addition, the SMA/SiO₂ microspheres were used to prepare hierarchical structure of SMA/SiO₂/Ag particles, which were utilized for the construction of surface-enhanced Raman scattering substrate (SERS).     

Polymer–filler interactions in sol–gel derived polymer/silica hybrid nanocomposites

The effect of polymer–filler interaction on solvent swelling and dynamic mechanical properties of the sol–gel derived acrylic rubber (ACM)/silica, epoxidized natural rubber (ENR)/silica, and poly (vinyl alcohol) (PVA)/silica hybrid nanocomposites has been described for the first time. Tetraethoxysilane (TEOS) at three different concentrations (10, 30, and 50 wt %) was used as the precursor for in situ silica generation. Equilibrium swelling of the hybrid nanocomposites in respective solvents at ambient condition showed highest volume fraction of the polymer in the swollen gel in PVA/silica system and least in ACM/silica, with ENR/silica recording an intermediate value. The Kraus constant (C) also followed a similar trend. In dynamic mechanical analysis, the storage modulus dropped at higher strain (>1%), which indicated disengagement of polymer segments from the filler surfaces. This drop was maximum in ACM/silica, intermediate in ENR/silica, and minimum in PVA/silica, both at 50 and 70 °C. The drop in modulus with theoretical volume fraction of silica (ϕ) was interpreted with the help of a Power law model ΔE′ = a₁ϕ, where a₁ was a constant and b₁ was primarily a filler attachment parameter. Strain dependence of loss modulus was observed in ACM/silica hybrid nanocomposites, while ENR/silica and PVA/silica nanocomposites showed almost strain‐independent behavior. The storage modulus showed sharp increase with increasing frequency in ACM/silica system, while that was lower in both ENR/silica (at higher frequency) and PVA/silica systems (in the entire frequency spectrum). The increase in modulus with ϕ also followed similar model ΔE′ = a₂ϕ proposed in the strain sweep mode. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2399–2412, 2005     

Adsorption and inhibition effect of curcumin on mild steel corrosion in hydrochloric acid

The inhibition effect of curcumin on the corrosion of mild steel in 1.0 M HCl solution was studied by weight loss, potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) methods. The experimental results suggest that this compound is an efficient corrosion inhibitor and the inhibition efficiency increases with the increase in inhibitor concentration. Adsorption of this compound on mild steel surface obeys Langmuir isotherm. Also the objective of this work is to attempt to find relationships between electronic structure and inhibition efficiency. The structural parameters, such as the frontier molecular orbital energies (E _HOMO and E _LUMO), gap of energy ΔE, from the molecule to iron as well as electronic parameters such as Mulliken atomic populations were calculated and discussed using the Density Functional Theory method (DFT).     

Polyluminol/hydrogel composites as new electrochemiluminescent-active sensing layers

This paper reports on electrochemiluminescent sensors and biosensors based on polyluminol/hydrogel composite sensing layers using chemical or biological membranes as hydrogel matrices. In this work, luminol is electropolymerized under near-neutral conditions onto screen-printed electrode (SPE)-supported hydrogel films. The working electrode coated with a hydrogel film is soaked in a solution containing monomeric luminol units, allowing the monomeric luminol units to diffuse inside the porous matrix to the electrode surface where they are electropolymerized by cyclic voltammetry (CV). Sensors and enzymatic biosensors for H₂O₂ and choline detection, respectively, have been developed, using choline oxidase (ChOD) as a model enzyme. In this case, hydrogel is used both as the enzymatic immobilization matrix and as a template for the electrosynthesis of polyluminol. The enzyme was immobilized by entrapment in the gel matrix during its formation before electropolymerization of the monomer. Several parameters have been optimized in terms of polymerization conditions, enzyme loading, and average pore size. Using calcium alginate or tetramethoxysilane (TMOS)-based silica as porous matrix, H₂O₂ and choline detection are reported down to micromolar concentrations with three orders of magnitude wide dynamic ranges starting from 4?×?10^?7 M. Polyluminol/hydrogel composites appear as suitable electrochemiluminescence (ECL)-active sensing layers for the design of new reagentless and disposable easy-to-use optical sensors and biosensors, using conventional TMOS-based silica gel or the more original and easier to handle calcium alginate, reported here for the first time in such a configuration, as the biocompatible hydrogel matrix. Figure

Elaboration of electrochemiluminent polyluminol/hydrogel composite sensing layers     

Characteristics of the 5S rRNA from cotton seeds

The individuality of the 5S rRNA from cotton seeds has been determined by the production of a single narrow band on gel electrophoresis and by the characteristic UV spectrum with values of the ratios E₂₆₀/E₂₃₀ and E₂₆₀/E₂₈₀ of 2.03–2.1 and 2.08–2.14, respectively. The melting curve of the 5S rRNA has been obtained and a total hyperchromic effect of 25% has been calculated. The nucleotide composition of the 5S rRNA has been established by determining the amount of nucleotides in an alkaline hydrolysate (22.6% of AMP; 30.2% of GMP; 22.6% of UMP; and 24.6% of CMP). The nucleotides were identified from the position of their appearance in the elution profile, from their UV spectra in 0.1 N HC1 and 0.1 KOH, and also by one- and two-dimensional chromatography of the nucleotides obtained, in the presence of markers.     

Structural and thermal properties of HDPE/n-AlN polymer nanocomposites

High-density polyethylene (HDPE) containing various volume fractions (0–20 vol%) of aluminum nitride nanoparticles (n-AlN) is prepared by melt mixing. Structural and morphological characterizations of the prepared composites are carried out by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM), and atomic force microscopy (AFM). Thermal stability and degradation kinetics of HDPE/AlN (nano) composites are investigated by Thermogravimetric analysis (TG). HR-TEM micrographs confirm fairly uniform dispersion of AlN nanoparticles, as well as the existence of long interconnected chain-like aggregates. AFM images also confirm homogeneous dispersion of n-AlN in the polymer matrix. Roughness analysis from the AFM data indicates the presence of substantial undulation from the mean surface level. Thermogravimetric data indicate small improvement in the thermal stability of the composites. Kinetic parameters, viz., the activation energy (E _a), frequency factor (A), and reaction order (n) are estimated using the isoconversional methods of Kissinger, Flynn–Wall–Ozawa (FWO), KAS, and Friedman. Activation energies (E _a) calculated by the above four models display nearly similar features and are enhanced by the presence of AlN nanoparticles. Kinetics of degradation of HDPE-AlN (nano) composites follows a first-order reaction.     

TiO2 and Al2O3 nanoporous oxide layers decorated with silver nanoparticles—active substrates for SERS measurements

Self-organized nanoporous oxide layers (TiO₂, Al₂O₃) exhibiting specific properties, obtained by anodic oxidation at a constant voltage in neutral electrolyte, may serve as attractive SERS substrates for investigating the interactions between an adsorbate and adsorbent, or as a stable platform for detecting various organic compounds. This paper presents the influence of the size of the nanotubes/nanopores and the structure of the porous oxide layers on the SERS enhancement factor, E _F. We used pyridine and mercaptobenzoic acid as probe molecules, since they have a large cross-section for Raman scattering. To characterize the morphology and structure of the oxide layer substrates, before and after vacuum vapor deposition of silver nanoparticles, we applied scanning electron microscopy, X-ray diffraction and surface analytical techniques: AES, XPS and SERS. The results obtained show that for the same amount of Ag (0.02 mg/cm²) the size of the nanopores significantly affects the E _F, which reaches, at a properly chosen nanopore size, distinctly higher values than that characteristic of a standard silver surface roughened by electrochemical cycling, i.e. E _F?>?10⁶. The new Ag/MeO _x –NT composites layer, ensure a good reproducibility of the SERS measurements and exhibit stability over a limited period of time.     

Crystal and molecular structure of <Emphasis Type="Italic">E</Emphasis>-3-(1,3-dimethylindol-2-yl)methylene-4-isopropylidenetetrahydrofuran-2,5-dione

The crystal and molecular structure of E-3-(1,3-dimethylindol-2-yl)methylene-4-isopropylidenetetrahydrofuran-2,5-dione, C₁₈H₁₇NO₃ (I), was investigated by XRD. The monoclinic structure of I (space group P2₁/c, a = 12.411(2) Å, b = 7.586(1) Å, c = 16.107(3) Å, β = 96.90(2)°, Z = 4) was solved by direct methods and refined by the full-matrix least squares in an anisotropic approximation to R = 0.044 for all 2842 independent reflections collected (CAD-4 automatic diffractometer, λCuK _α). The geometric parameters of sterically strained molecule I were determined with a high accuracy.     

Solvation of ions. XXVII. Comparison of methods to calculate single ion free energies of transfer in mixed solvents

Free energies of transfer of ions from water to mixtures of water with acetonitrile (AN), with dimethylformamide (DMF), with dimethylsulfoxide (DMSO), and with ethylene glycol have been determined using both the tetraphenylarsonium tetraphenylboride [TATB] and the negligible liquid junction potential [E _j ] assumptions. By making use of ΔG _tr (Ag⁺)[TATB]=12 kJ-mol^?1 for transfer from DMSO to AN and by assuming negligible liquid junction potential in the cell $${\text{Ag|AgNO}}_{\text{3}} {\text{(0}}{\text{.01}}M{\text{),S}}\parallel {\text{Et}}_{\text{4}} {\text{NPic(0}}{\text{.1}}M{\text{),AN}}\parallel {\text{AgNO}}_{\text{3}} {\text{(0}}{\text{.01}}M{\text{),AN|Ag}}$$ single ion free energies of transfer of silver ion ΔG _tr (Ag⁺)[E _j ] from DMSO to 35 pure and mixed solvents show a standard deviation of only 2 kJ-mol^?1 when compared with ΔG _tr (Ag⁺) calculated from the TATB assumption that ΔG _tr (Ph ₄ As⁺)=ΔG _tr (Ph ₄ B^?). The ferrocene assumption [Fc] also gives acceptable agreement with ΔG _tr (Ag⁺)[TATB] provided that the solvents are not highly aqueous. Other cells with other junctions give less acceptable agreement between the E _j and TATB assumptions. It is essential that the salt bridge is always tetraethylammonium picrate in AN, if the E _j assumption is assumed. Because of the ease of making potentiometric measurements compared with the difficulty of measurements required for the TATB assumption, the negligible liquid junction potential method in the cell shown is recommended for estimating transfer free energies of single ions. The ferrocene assumption is acceptable only for non-structured aprotic solvents.     

An efficient synthesis of 1-thioamidoalkyl-2-naphthol derivatives

The discovery and development of phosphorus pentoxide supported on silica gel (P₂O₅–SiO₂) as an efficient catalyst has led to an efficient method for the direct preparation of 1-thioamidoalkyl-2-naphthol derivatives in high yields by one-pot, three-component reaction of β-naphthol, aryl aldehydes, and thiourea or N-phenylthiourea at 100 °C under solvent-free conditions. In addition to its simplicity, this method has the ability to prepare a wide variety of the desired products.     

Application of thermal analysis for determination of film pressure and film surface energy on silica gel surface

The results of dynamic and quasi-isothermal thermodesorption of water from a silica gel surface at low furnace heating rates in the temperature range 20–125° are presented. From the experimental results, the water film pressure π on silica gel surface, the activation energy ΔE and the evaporation heat ΔH were calculated. An interpretation of π changes in relation to the film thickness and wetting process has been proposed. It is concluded that the characteristic film pressure values correspond to the work of spreading, and immersional, adhesional and adhesional-cohesional wetting. From the determined film pressure values, the average value of the silica gel polar component, γ _s ^P , was calculated to be 114.67 mJ/m².     

Formation of the active surface of Ag/SiO2 catalysts in the presence of FeO x additives

Supported FeO _x -modified silver catalysts based on commercial silica gel and prepared via impregnation with a solution of Fe- and Ag-containing salts while varying the amount of modifier from 1 to 10 wt % are studied. It is found that the introduction of Fe-containing compounds leads to the distribution of silver in the form of clusters/ions on the surface of SiO₂, improving the reducibility of the systems in the H₂ TPR mode. After reduction at 800°C, the catalysts containing 10 wt % iron and 5 wt % silver comprise a Fe₂SiO₄ iron silicate phase.     

Preparation of Cu (II)/PEI–QPEI/SiO2 nanopowder as antibacterial material

The silica nanoparticles were prepared by the sol–gel process, and then twice modified and grafted by polyethylenimine (PEI) on their surface. After quaternary ammonium reaction and chelated copper reaction, the PEI/SiO₂, QPEI/SiO₂, PEI–QPEI/SiO₂ and Cu (II)/PEI–QPEI/SiO₂ nanopowders were obtained in turn. The morphology and structure of the products were characterized through SEM, EDX, HRTEM, FTIR and element analysis. At the same time, the antibacterial activity of the products to E. coli and Candida were evaluated through quantification and qualitative ways, e.g. microcalorimetric method and culture dish method. The results suggested that the Cu (II)/PEI–QPEI/SiO₂, a novel three-component functional nanopowder, presented the best antibacterial activity to both E. coli and Candida duo to the synergistic sterilization capability of the ammonium salt and copper ions, compared with other products. It indicated that the Cu (II)/PEI–QPEI/SiO₂ nanopowder could be a novel antibacterial nanomaterial to widely application in preventing and minimizing bacteria of the organism and environment in future.     

Keggin-type phosphotungstic acid supported on mesoporous SiO2–Al2O3 aerogel like beads and their application in the isopropylation of naphthalene

Spherical mesoporous silica–alumina aerogel like beads based on sol–gel technology and the drop wise addition have been synthesized and used as catalyst support for phosphotungstic acid (PWA). Their catalytic performances in the isopropylation of naphthalene with isopropanol were investigated in a batch reactor. It was found that PWA was highly dispersed on the silica–alumina support and their Keggin structure can be retained. In addition, PWA/SiO₂–Al₂O₃ catalyst showed high surface area, both of Lewis acid sites and Brönsted acid sites. Because of having more Brönsted acid sites, silica–alumina supported acid catalysts showed much higher conversion (87.97 %) and selectivity to diisopropylnaphthalenes (41.41 %) and β,β-products (59.82 %) than pure acid and reactive supports in the isopropylation of naphthalene. The catalytic behavior has been discussed in relation with the physical chemical properties of catalysts, reaction and activation temperature and reaction time.