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排序方式: 共有174条查询结果,搜索用时 31 毫秒
51.
S. Despond E. Espuche N. Cartier A. Domard 《Journal of Polymer Science.Polymer Physics》2005,43(1):48-58
Water sorption was studied at 20 °C on films composed of different natural polymers. Three polysaccharides were investigated: chitosan, cellulose, and alginate. The major differences between these polymers, from a structural point of view, lay in the substitution of an OH group by an NH2 function for chitosan and by an ionic COO?Na+ group for alginate. An analysis of the experimental water sorption isotherms, expressed as the number of water molecules sorbed per repeating unit in the amorphous phase, associated with an analysis of the enthalpy profile related to the water sorption allowed us to propose a water sorption mechanism in two steps for all the polymers: water sorption on polymer‐specific sites in the first step and water clustering around the first sorbed water molecules in the second step. It was determined that two water molecules interacted with the polymer chains for cellulose and chitosan, whereas four water molecules were bonded to alginate chains. The specific sorption sites were identified as OH groups for cellulose, OH and NH2 groups for chitosan, and ionic and OH groups for alginate. A systematic reduction of the half‐sorption time was observed in the activity range corresponding to this first sorption step, and it was explained by a water plasticization effect. On the other hand, an increase in the half‐sorption time was observed in the second sorption step, at a high activity (>0.8), for chitosan and alginate. A modelization associating the Guggenheim–Anderson–de Boer model and the clustering theory, applied to our systems, allowed us to relate the occurrence of this last phenomenon to the formation of water clusters containing more than two water molecules. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 48–58, 2005 相似文献
52.
Eliane P. Oliveira Ricardo E. Santelli Ricardo J. Cassella 《Microchemical Journal》2008,89(2):116-122
This work reports the evaluation of the combined use of Pd and HF as chemical modifiers for the direct determination of total chromium in waters derived from petroleum exploration employing electrothermal atomic absorption spectrometry (ET AAS). Such waters, usually called as produced waters, have complex composition presenting a number of organic and inorganic substances. When obtained from offshore operations they also present high salinity. In order establish conditions for chromium measurement pyrolysis and atomization curves were built up in different media and employing Pd and HF as chemical modifiers. Also, a detailed study about calibration strategy was performed. At best conditions, pyrolysis and atomization temperatures were 1200 °C and 2600 °C, respectively, and 10 μL of a 500 mg L− 1 Pd solution was added together with 10 μL of a 50% (v/v) HF solution on 20 μL of sample. Obtained results indicate that, in this kind of sample, chromium can be determined by standard addition method or employing external calibration with standard solutions prepared in 0.8 mol L− 1 NaCl medium. In order to evaluate the accuracy of the procedure, a recovery test was performed with seven spiked samples of produced waters. The detection limit, quantification limit and the relative standard deviation in 0.8 mol L− 1 NaCl were also calculated and the values found were 0.45 μg L− 1, 1.5 μg L− 1 and 6.0% (at 2.5 μg L− 1 level), respectively. 相似文献
53.
Picard E Gauthier H Gérard JF Espuche E 《Journal of colloid and interface science》2007,307(2):364-376
Organically modified montmorillonites obtained by cation exchange from the same natural layered silicate were studied. The surface properties of the pristine and a series of organically modified clays were determined by inverse gas chromatography and the water adsorption mechanisms were studied by a gravimetric technique coupled with a microcalorimeter. A significant increase of the specific surface area, a decrease of the water adsorption, and a decrease of the dispersive component of the surface energy were observed when the sodium cations of the natural montmorillonite were exchanged for a quaternary ammonium. Slighter differences in surface properties were observed, on the other hand, between the different types of organically modified montmorillonites. Indeed, similar dispersive components of the surface energy were determined on the organoclays. Nevertheless, the specific surface area increased in the range 48-80 m(2)/g with increasing d-spacing values and the presence of specific groups attached to the quaternary ammonium, such as phenyl rings or hydroxyl groups, led to some specific behaviors, i.e., a more pronounced base character and a higher water adsorption at high activity, respectively. Differences in interlayer cation chain organization, denoted as crystallinity, were also observed as a function of the nature of the chains borne by the quaternary ammonium. In a later step, polyethylene-based nanocomposites were prepared with those organically modified montmorillonites. The clay dispersion and the barrier properties of the nanocomposites were discussed as a function of the montmorillonite characteristics and of the matrix/montmorillonite interactions expected from surface energy characterization. 相似文献
54.
Ana Cláudia M. Oliveira Marluce S. Santos Luma M. S. Brandão R. M. Navarro Yerga J. L. G. Fierro Manuela S. Leite Eliane B. Cavalcantia Renan Tavares Figueiredo 《Chemical Papers》2017,71(6):1129-1141
This work reports the reforming of bio-ethanol on chitosan–TiO2 hybrid photocatalysts at ambient temperature. The influence of chitosan composition on the photocatalytic performance of chitosan–TiO2 hybrid was studied. The hybrids were characterized by CHN elemental analysis, nitrogen adsorption–desorption isotherms, thermogravimetric analysis, diffuse reflectance spectroscopy, X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results showed that the preparation variables used for the incorporation of chitosan on TiO2 promoted changes in the morphology, superficial area, crystal size and porosity of the photocatalyst, affecting the band gap of this semiconductor and consequently the reactivity of the chitosan–TiO2 hybrids. The catalysts were evaluated for hydrogen production from ethanol under visible light. It was demonstrated that the calcination temperature of 623 K and a chitosan content of 20% were the most appropriate preparation conditions and the resulting product displays a pore size of 1.9 nm, crystal size of 11.3 nm, BET area of 178 m2 g?1 and band gap of 2.92 eV. The calcination temperature of 623 K and incorporation of 20% of chitosan obtained the same results in the conversion rate of hydrogen in comparison to the pure TiO2 P25. 相似文献
55.
[reaction: see text] A new approach for the synthesis of (+/-)-indatraline, which is a 3-phenyl-1-indanamine that displays several biological activities, is described. The strategy features as the key step a diastereoselective ring contraction of a 1,2-dihydronaphthalene promoted by PhI(OTs)OH, to construct the indan ring system. The oxidative rearrangement of other 1,2-dihydronaphthalenes was also investigated, generalizing this method to obtain indans. 相似文献
56.
Eliane Trovatti Susana C. M. Fernandes Laurent Rubatat Carmen S. R. Freire Armando J. D. Silvestre Carlos Pascoal Neto 《Cellulose (London, England)》2012,19(3):729-737
Bionanocomposites with improved properties based on two microbial polysaccharides, pullulan and bacterial cellulose, were
prepared and characterized. The novel materials were obtained through a simple green approach by casting water-based suspensions
of pullulan and bacterial cellulose and characterized by TGA, RDX, tensile assays, SEM and AFM. The effect of the addition
of glycerol, as a plasticizer, on the properties of the materials was also evaluated. All bionanocomposites showed considerable
improvement in thermal stability and mechanical properties, compared to the unfilled pullulan films, evidenced by the significant
increase in the degradation temperature (up to 40 °C) and on both Young’s modulus and tensile strength (increments of up to
100 and 50%, for films without glycerol and up to 8,000 and 7,000% for those plasticized with glycerol). Moreover, these bionanocomposite
films are highly translucent and could be labelled as sustainable materials since they were prepared entirely from renewable
resources and could find applications in areas as organic electronics, dry food packaging and in the biomedical field. 相似文献
57.
Force constants and dipole moment derivatives have been computed for the molecules CH3 X(X=F, Cl, Br, I) using MO wavefunctions with pseudo-potentials for the interaction between the inner shell and valence electrons. The values obtained at the SCF approximation level from a set of gaussian valence orbitals contracted in double-zeta form and enriched with polarization functions compare well with experimental assignments of force and interaction constants, as well as integrated intensities from infrared data. The transferability of atomic force fields and polar tensors (second derivatives of total energies and first derivatives of dipole moments with respect to atomic displacements in cartesian coordinates) is discussed. 相似文献
58.
Eliane M.Z. Michielin Sibele R. Rosso Elton Franceschi Gustavo R. Borges Marcos L. Corazza J. Vladimir Oliveira Sandra R.S. Ferreira 《The Journal of chemical thermodynamics》2009,41(1):130-137
The aim of this work is to report phase equilibrium data for the binary systems (CO2 + α-humulene) and (CO2 + trans-caryophyllene), and for the ternary system (CO2 + α-humulene + trans-caryophyllene). Results from literature show that α-humulene and trans-caryophyllene are the main compounds responsible for the anti-inflammatory and anti-allergic characteristics attributed to the medicinal plant Cordia verbenacea D.C., hence giving importance to the phase behaviour investigation performed in this work. Phase equilibrium experiments were performed in a high-pressure, variable-volume view cell over the temperature range of T = (303 to 343) K and pressures up to 20 MPa. (Liquid + liquid) and (vapour + liquid + liquid) equilibrium were observed at T = 303 K, while (vapour + liquid) phase transitions were verified to occur from T = (313 to 343) K, for all systems studied. Thermodynamic modelling was performed using the Peng–Robinson equation of state and the classical quadratic mixing rules, with a satisfactory agreement between experimental and calculated values. 相似文献
59.
An electroanalytical method for the determination of morpholine, a corrosion inhibitor, was developed at a cathodically pretreated boron-doped diamond electrode (BDDE). The voltammetric response of morpholine at the BDDE in 0.1?mol L?1 KCl (pH 10) shows an irreversible oxidation process at approximately 1.3?V vs. Ag/AgCl in 3.0?mol L?1 KCl. Using cyclic voltammetry, the number of electrons involved in the morpholine electroxidation mechanism was found to be 1. The application of chronoamperometry showed that the apparent diffusion coefficient (D0) was 2.99?×?10?6 cm2 s?1. Using square wave voltammetry under the optimized conditions (frequency of 30.0?Hz, pulse amplitude of 100?mV and step potential of 20?mV at pH 10.0), the developed method provided limits of detection and quantification of 2.1 and 6.9?mg L?1, respectively, with a linear range from 5.0 to 100.0?mg L?1 (r?=?0.991). Intraday (n?=?10) and interday (two consecutive day) precision values assessed as the relative standard deviation for solutions containing 30.0, 60.0, and 90.0?mg L?1 of morpholine were from 0.41 to 5.86% and 0.92 to 3.19%, respectively. The feasibility of the method for the interference-free determination of morpholine was verified by the analysis of synthetic boiler water samples containing CaCO3, Na2SO3, Na3PO4, FeCl3, and humic acid as organic matter. In addition, hydrazine was added as a possible interfering compound because of its widespread use in corrosion inhibition. Recovery values from 90.9 to 109.4% were obtained in the synthetic boiler water, thereby attesting to the accuracy of the method. 相似文献
60.
Martina Costa Cerqueira Pinto Nathany Lisbôa de Souza e Castro Eliane Pereira Cipolatti Roberto Fernandez‐Lafuente Evelin Andrade Manoel Denise Maria Guimarães Freire José Carlos Pinto 《大分子反应工程》2019,13(1)
Core–shell polymer supports with different morphological features and compositions are prepared through combined suspension and emulsion polymerizations. It is shown that proper manipulation of the divinylbenzene (DVB) feed content allows for maximization of specific areas, porosities, and mechanical resistances. Additionally, it is shown that feeding of previously prepared miniemulsions leads to core–shell particles with smaller specific areas, due to less efficient coating of the cores. Particularly, the combined manipulation of polymerization times and DVB feed compositions allows for production of particles with pronounced specific area (50 m2 g?1) and porosity (0.30 cm3 g?1). Produced core–shell polymer particles are employed as supports for the immobilization of lipase B from Candida antarctica, and the obtained enzymatic activities for both hydrolysis (A hyd) and esterification (A est) reactions are very high (A hyd = 34.7 ± 3.8 U/g; A est = 3564.6 ± 581 U/g), even when compared to activities obtained using the reference commercial biocatalyst Novozym 435 (A hyd = 7.6 ± 1.8 U/g, A est = 2384.7 ± 307.2 U/g). Finally, biocatalysts prepared with the core–shell supports present higher enzymatic activities than biocatalysts prepared with supports of higher specific area obtained through conventional emulsion polymerizations, indicating that the porous structure of the shell can be beneficial for the immobilization and activity of the enzymes. 相似文献