共查询到20条相似文献,搜索用时 31 毫秒
1.
J. C. Alexandre de Oliveira R. H. López J. P. Toso Sebastião M. P. Lucena C. L. CavalcanteJr. D. C. S. Azevedo G. Zgrablich 《Adsorption》2011,17(5):845-851
We model carbon-based microporous materials, such as activated carbons, taking into account surface defects in the form of
geometrical rugosity in the inner surface of each graphitic slit pore. The used model is a simplified variation of the randomly
etched graphite (REG) pore model (Seaton et al., Langmuir 13:1199–1204, 1997). 相似文献
2.
To understand the thermodynamic characteristics of cationic surfactants in binary mixtures, the aggregation behavior of hexadecyltrimethylammonium
chloride (CTAC) has been investigated in ethylene glycol (EG) + water solvent mixtures at different temperatures and EG to
water ratios. The critical micelle concentration (CMC) and degree of counter ion bonding (β) were calculated from electrical conductivity measurements. An equilibrium model for micelle formation was applied to obtain
the thermodynamic parameters for micellization, including the standard Gibbs energies of micellization (DGmico)\Delta G_{\mathrm{mic}}^{\mathrm{o}}), standard enthalpies of micelle formation (DHmico)\Delta H_{\mathrm{mic}}^{\mathrm{o}}) and standard entropies of micellization (DSmico)\Delta S_{\mathrm{mic}}^{\mathrm{o}}). Our results show that DGmico\Delta G_{\mathrm{mic}}^{\mathrm{o}} is always negative and slightly dependent on temperature. The process of micellization is entropy driven in pure water, whereas
in EG + water mixtures the micellization is enthalpy driven. 相似文献
3.
Raphael da C. Cruz Rosana J. Martins Márcio J. E. de M. Cardoso Oswaldo E. Barcia 《Journal of solution chemistry》2009,38(8):957-981
Density measurements were made for binary aqueous solutions of polyethylene glycol at seven temperatures: 283.15, 288.15,
293.15, 298.15, 303.15, 308.15, and 313.15 K. Polyethylene glycol samples with nominal average molar masses of 3000 g⋅mol−1 (PEG 3000), 6000 g⋅mol−1 (PEG 6000), 10000 g⋅mol−1 (PEG 10000) and 20000 g⋅mol−1 (PEG 20000) were used. These results were used to determine the specific volumes of solutions with solute-to-solvent mass
ratios (mass of the solute/mass of the solvent) in the range 0.0546 to 1.4932 for PEG 3000, from 0.0553 to 1.4986 for PEG
6000, from 0.0552 to 1.2241 for PEG 10000, and from 0.0530 to 1.2264 for PEG 20000. The differences between the specific volume
of a solution and the specific volume of the pure solvent, at a given temperature, were represented by a virial-type equation
in terms of solute concentration. The first-order coefficient of the expansion is the partial specific volume of the solute
at infinite dilution. The higher-order coefficients are related to the contribution of pairs, triplets, and higher-order solute
aggregates, according to the Constant-Pressure Solution Theory. The functional dependence of the virial coefficients upon
temperature is discussed in terms of solute-solute and solute-solvent interactions. The effect of the PEG molar mass on the
partial specific volume of solute at infinite dilution, as well as the contributions of pairs of solute molecules to the solution
volume, are also investigated. The apparent specific volume, apparent specific expansibility, apparent specific expansibility
at infinite dilution and virial coefficients of the apparent specific expansibility are also presented. 相似文献
4.
The aim of this work was to study the effect of the metal loading on the structure of two series of cobalt and manganese pillared
clay-supported catalysts. For this purpose, equilibrium data for CO2 adsorption at 273 K were analysed using Freundlich, Langmuir and Toth isotherm models, in order to estimate the adsorption
parameters and to relate them with the metal loading of the catalysts. The metal distributions on the porous structure of
the catalysts were studied using the temperature programmed reduction results combined with information from the nitrogen
physisorption data. Comparison of all results reveals that up to a certain metal loading, about 0.5 wt% of Co and 2 wt% of
Mn, the metal oxide is well dispersed into the porous structure of the pillared clay. At higher metal loadings, bulk-metal
oxide particles are formed on the external surface. 相似文献
5.
6.
A new method of synthesis 2,2-dimethylolpropionic acid from 2,2-dimethylolpropionaldehyde was put forward. The electrochemical
oxidation behavior of 2,2-dimethylolpropionaldehyde has been investigated on a Ti/SnO2 + Sb2O4/PbO2 electrode by cyclic voltammetry (CV) and stable polarization curves in sulfuric acid. The results showed that it was an irreversible
reaction controlled by diffusion. The formation mechanism of 2,2-dimethylolpropionic acid in the sulfuric acid was then proposed
and the transfer coefficients of the reaction were calculated. It was concluded that RCHO+ỌHads→RCHOỌHads was the rate-determining step in the electrolysis process. The rate of this step obtained from the assumed process agrees
well with experiment. 相似文献
7.
Spectroscopic and spectrofluorimetric studies were made of the interaction between the drug atenolol and iodine. The interaction
was found to proceed through the initial formation of a charge transfer (CT) complex as an intermediate species. The product
of this interaction has been isolated and characterized using UV-Vis, FT-IR and Raman spectroscopic techniques. Formation
of the triodide
I3-\mathrm{I}_{3}^{-}
species was confirmed by its electronic and Raman spectra. Peaks appeared in Raman spectrum of the isolated product at 153,
102 and 85 cm−1 that are assigned to ν
as(I-I), ν
s(I-I) and
d(I3-)\delta(\mathrm{I}_{3}^{-})
respectively, which confirmed the presence of the
I3-\mathrm{I}_{3}^{-}
ion. The stoichiometry of the complex was found to be 1:2. The rate of their reaction has been measured as a function of time
and solvent. Pseudo-first-order rate constants for the reaction were measured at various temperatures and the thermodynamic
activation parameters (ΔG
#,ΔS
# and ΔH
#) were computed. Preliminary fluorescence quenching studies indicated that the interaction between atenolol and iodine is
spontaneous and proceeds through a CT complex, and the quenching of fluorescence of atenolol by iodine increases as the extent
of such complexation increases 相似文献
8.
Pasquale Crea Concetta De Stefano Mutsa Kambarami Frank J. Millero Virender K. Sharma 《Journal of solution chemistry》2008,37(9):1245-1259
The protonation constants for oxidized glutathione, H
i−1L(4−i+1)−, K
i
H=[H
i
L(4−i)−]/[H
i−1L(4−i+1)−][H+] i=1,2,…,6 have been measured at 5, 25 and 45 °C as a function of the ionic strength (0.1 to 5.4 mol⋅[kg(H2O)]−1) in NaCl solutions. The effect of ionic strength on the measured protonation constants has been used to determine the thermodynamic
values (K
i
H0) and the enthalpy (ΔH
i
) for the dissociation reaction using the SIT model and Pitzer equations. The SIT (ε) and Pitzer parameters (β
(0), β
(1) and C) for the dissociation products (L4−, HL3−, H2L2−, H3L−, H4L, H5L+, H6L2+) have been determined as a function of temperature. These results can be used to examine the effect of ionic strength and
temperature on glutathione in aqueous solutions with NaCl as the major component (body fluids, seawater and brines). 相似文献
9.
The well-known adsorption integral equation (AIE) for calculating pore size and adsorption energy distributions from adsorption isotherms on porous solids is, from the mathematical point of view, a linear Fredholm integral equation of the first kind and therefore an ill-posed problem. What can we realistically expect from the solution of such an ill-posed problem by regularization? Does it make sense to restrict the number of possible solutions by the so-called ansatz method? In this paper, the two methods for solving ill-posed problems are from scratch explained and illuminated by concrete examples. Their relevance and fundamental limitations are discussed. 相似文献
10.
M. Sundar D. Easwaramoorthy S. Kutti Rani M. Palanichamy 《Journal of solution chemistry》2007,36(9):1129-1137
The kinetics and mechanism of oxidation of lysine, a basic α-amino acid, by oxone in an acetic acid/sodium acetate buffered medium (pH = 3.6–5.2) at 308 K has been investigated. The
rate of disappearance of oxone at constant [lysine] and pH follows the equation:
The experimental results rule out autocatalysis of the aldehyde product which was observed in other neutral α-amino acids reactions under the same kinetic conditions. The different behavior of lysine is due to the formation of the
product, 6-amino-2-oxo hexanoic acid, which does not initiate the autocatalysis. 相似文献
11.
Artemis P. Guimarães Andreas Möller Reiner Staudt Diana C. S. de Azevedo Sebastião M. P. Lucena Célio L. Cavalcante Jr. 《Adsorption》2010,16(1-2):29-36
The diffusion behavior of C4–C10 n-alkanes in silicalite-1 has been investigated by using the Zero Length Column method. The diffusivities derived from measurements at different purge rates with different purge gases confirming intracrystalline diffusion control. Data are compared with results reported in the literature for MFI zeolites. The diffusivities were found to be consistent and agree well with data previous obtained by ZLC. However, these data showed a remarkable disagreement with other reported techniques (PFG-NMR, QENS and Permeation). The eventual influence of carbon dioxide (CO2) adsorption on diffusion properties of n-alkanes in silicalite was also investigated. For this purpose, a series of experiments was performed involving hydrocarbons mixed with CO2. Data were obtained at 303 K and flow rates between 20 and 80 mL/min. The presence of CO2 does not seem to influence the intracrystalline transport rate of the investigated light hydrocarbons (n-C4 and n-C6). On the other hand, the situation for n-C8 and n-C10 is more complex. The diffusivity values are higher compared to the previously reported values. 相似文献
12.
Nemanja Trišović Nebojša Banjac Nataša Valentić Gordana Ušćumlić 《Journal of solution chemistry》2009,38(2):199-208
The absorption spectra of nine compounds structurally related to phenytoin (5,5-diphenylhydantoin) were recorded in twelve
solvents over the range of 200 to 400 nm. The effects of solvent dipolarity/polarizability and solvent/solute hydrogen bonding
interactions were analyzed by means of the linear solvation energy relationship (LSER) concept proposed by Kamlet and Taft.
The lipophilic activity of the investigated hydantoins was estimated by calculation of their log 10
P values. The calculated values of log 10
P were correlated with the ratio of the contributions of specific and non-specific solute/solvent interactions. The correlation
equations were combined with the corresponding ED50 values to generate new equations that demonstrate exact relationship between solute/solvent interactions and the structure-activity
parameters. 相似文献
13.
Adduct formation in the binary systems of O-phospho-L-serine with biogenic amines (putrescine, spermidine or spermine) has
been investigated. The overall stability constants of the adducts and the equilibrium constants of their formation have been
determined using computer analysis of potentiometric data. Ion-ion interactions have been established to occur in the identified
molecular complexes. The potential reaction centers are phosphate, carboxylate and amine groups from phosphorylated serine
as well as the –NH3+ and –NH2+– groups from polyamine. The pH range of adduct formation is found to coincide with that in which the polyamine is protonated
(positive reaction center) and the phosphoserine is partly or totally deprotonated (negative reaction center). The stability
of the molecular complexes formed in the studied systems depends on the acid-base character of the substrates and on the structure
of the reacting molecules. Sites of interactions in the bioligands have been deduced on the basis of the results of the equilibrium
study and analysis of the changes in the positions of signals in the 13C and 31P NMR spectra. 相似文献
14.
Crown-Ether Type Podands as Alkali Metal Cation Extractants: Influence of the Number of Oxygens in the Chain 总被引:1,自引:0,他引:1
Mário Valente Sérgio Filipe Sousa Alexandre Lopes Magalhães Cristina Freire 《Journal of solution chemistry》2010,39(8):1230-1242
Several polyether-type podands were synthesized that contained a variable number of potential donor oxygen atoms (four to
twelve) and an aromatic ring in the chain. Extraction experiments were performed to elucidate the influence of the number
of oxygen atoms on the extraction selectivity towards alkali metal picrates, from aqueous to dichloromethane phases. The results
show that the extraction efficiency for lithium picrate is almost independent of the number of oxygen atoms in the podand.
The extraction efficiency for sodium picrate was found to increase significantly with the number of oxygen atoms up to about
seven, but for the potassium to cesium picrates the extraction efficiency increased up to about eight oxygen atoms. The increase
in extraction efficiency may be rationalized in terms of the saturation of the cation’s first coordination sphere: after a
critical number of oxygen atoms is reached and the first coordination sphere is saturated, the much smaller detected increases
in the extraction efficiency may be seen as a statistical effect. The discrimination between sodium and potassium pirates
is only achieved when the podands possess seven or more oxygen atoms. Under the experimental conditions used, the podands
studied are unable to discriminate between potassium, rubidium and cesium picrates. 相似文献
15.
Solution densities over the temperature range 288.15 to 328.15 K have been measured for aqueous solutions of N-acetylarginamide monotrifluoroacetate and sodium trifluoroacetate, from which the partial molar volumes at infinite dilution,
V2oV_{2}^{\mathrm{o}}, were determined. The partial molar heat capacities at infinite dilution, Cp,2oC_{p,2}^{\mathrm{o}}, were also determined for these solutes over the same temperature range. These V2oV_{2}^{\mathrm{o}} and Cp,2oC_{p,2}^{\mathrm{o}} results, along with relevant data taken from the literature, have been used to calculate the contributions of the protonated
arginyl side-chain to the thermodynamic properties. These new side-chain values were critically compared with those obtained
previously using alternative side-chain model compounds. 相似文献
16.
Shekappa D. Lamani Praveen N. Naik Sharanappa T. Nandibewoor 《Journal of solution chemistry》2010,39(9):1291-1310
The kinetics of the osmium(VIII) (Os(VIII)) catalyzed oxidation of diclofenac sodium (DFS) by diperiodatocuprate(III) (DPC)
in aqueous alkaline medium has been studied spectrophotometrically at a constant ionic strength of 1.0 mol⋅dm−3. The reaction showed first order kinetics in [Os(VIII)] and [DPC] and less than unit order with respect to [DFS] and [alkali].
The rate decreased with increase in [periodate]. The reaction between DFS and DPC in alkaline medium exhibits 1:2 [DFS]:[DPC]
stoichiometry. However, the order in [DFS] and [OH−] changes from first order to zero order as their concentration increases. Changes in the ionic strength and dielectric constant
did not affect the rate of reaction. The oxidation products were identified by LC-ESI-MS, NMR, and IR spectroscopic studies.
A possible mechanism is proposed. The reaction constants involved in the different steps of the mechanism were calculated.
The catalytic constant (K
C) was also calculated for Os(VIII) catalysis at the studied temperatures. From plots of log 10
K
C versus 1/T, values of activation parameters have been evaluated with respect to the catalytic reaction. The activation parameters with
respect to the slow step of the mechanism were computed and discussed, and thermodynamic quantities were also determined.
The active osmium(VIII) and copper(III) periodate species have been identified. 相似文献
17.
Solvent extraction of the trivalent lanthanoids (except Pm) with mixtures of a chelating extractant, either 1-(2-thienyl)-4,4,4-trifluoro-1,3-butanedione
(thenoyltrifluoro-acetone, HTTA) or 4-benzoyl-3-methyl-1-phenyl-2-pyrazolin-5-one (HP) and diphenylsulphoxide (S), from chloride
solutions has been studied in C6H6. It was found that, in the presence of a diphenylsulfoxide, the lanthanoids were extracted as Ln(TTA)3⋅S and LnP3⋅S. The extraction data have been analyzed by a graphical method taking into account aqueous phase speciation and the plausible
complex extracted into the organic phase. On the basis of the experimental data, values of the equilibrium constants have
been calculated. Positive values of the synergistic coefficients show that all lanthanoids are extracted synergistically upon
the addition of compound S to the chelating extractant. The separation of the lanthanoids with synergistic mixtures was, in
most cases, a little higher than those obtained using HTTA or HP alone. 相似文献
18.
Yonit Sembira-Nahum Alexander Apelblat Emanuel Manzurola 《Journal of solution chemistry》2008,37(3):391-401
Densities of aqueous solutions of L-glutamic acid and magnesium-L-glutamate were determined from T=288.15 to 333.15 K at 5 K temperature intervals. The measured densities were used to evaluate the apparent molar volumes,
V
2,φ
(m,T), the cubic expansion coefficients, α(m,T), and the changes of isobaric heat capacities with respect to pressure, (∂
C
p
/∂
p)
T,m
. They were qualitatively correlated with changes in the structure of water that occur when L-glutamic acid or magnesium-L-glutamate
are present. 相似文献
19.
Thangavelu Jayabalan Pascaline Pré Valérie Héquet Pierre Le Cloirec 《Adsorption》2008,14(4-5):679-686
The influence of material properties on the reactivities of activated carbon materials have been studied on a laboratory scale. Carbon samples having diversified origin and properties were characterized using a thermogravimetry (TG) coupled with a differential scanning calorimetry (DSC). Reactivity parameters like the Point of Initial Oxidation (PIO) representing the beginning of the oxidation reactions and the Spontaneous Ignition Temperature (SIT) where the bed combustion takes place in a self sustaining manner were experimentally determined. The intrinsic properties of the activated carbons influencing oxidation and ignition were examined qualitatively followed by quantitative statistical correlations. Results from both qualitative and statistical correlations showed that increase in the oxygen content in the form of surface oxygenated groups increased the reactivity of activated carbons. It was by far the single most influential property discriminated from the analysis. The porosity characteristics like the specific surface area and pore volume did show some vague trends but could not be validated like that of the oxygen content. The effects of these individual properties on the oxidation and ignition reactivity are discussed. 相似文献
20.
Pascale Bénézeth David J. Wesolowski Donald A. Palmer Michael L. Machesky 《Journal of solution chemistry》2009,38(7):925-945
Specific studies detailing the effects of amines, used as pH control agents for corrosion inhibition in power plants, on the
surface charge of iron oxides provide data to assess the mechanism of how these amines impact deposition rate. The current
study was undertaken in order to determine accurately the dissociation constants of the relevant amines at Pressurized Water
Reactor (PWR) operating conditions and to investigate the effect of sorption of two of these amines (morpholine and dimethylamine)
by magnetite. The acid-dissociation equilibria of morpholine (MOR), dimethylamine (DMA) and ethanolamine (ETA) were measured
potentiometrically with a hydrogen-electrode concentration cell (HECC) from 0 to 290 °C in sodium trifluoromethanesulfonate
(NaTr) solutions at ionic strengths up to 1 mol⋅kg−1. Magnetite surface titrations were performed at an ionic strength of 0.03 mol⋅kg−1 (NaTr medium) in the presence or absence of morpholine and dimethylamine buffers over a wide range of pH and total amine
concentrations at 150–250 °C.
D.A. Palmer is retired. 相似文献