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1.
J. E. Vargas L. Giraldo J. C. Moreno-Piraján 《Journal of Thermal Analysis and Calorimetry》2010,102(3):1105-1109
Immersion enthalpies of activated carbon samples obtained by activation with steam at temperatures between 600 and 900 °C
and activation times between 1 and 10 h were determined. The calorimetric liquids of immersion are CCl4, water, NaOH, and HCl 2 M solutions, and the values of the immersion enthalpies are related to other properties of the activated
carbons such as the surface area B.E.T., the micropore volume, the content of acid, and basic surface groups. The highest
values for the immersion enthalpies take place for the polar solvent CCl4 and for HCl solution, with values between 4.0 and 75.2 J g−1 and 9.15 and 48.3 J g−1, respectively. 相似文献
2.
Liliana Giraldo J. C. Moreno-Piraján 《Journal of Thermal Analysis and Calorimetry》2007,89(2):589-594
The interactions among five samples of activated carbons, obtained from different lignocellulosic materials with different
degrees of activation of approximately 20% and aqueous solutions of phenol and 4-nitro phenol are studied by means of the
determination of immersion enthalpies.
It is established that the obtained activated carbons are of a basic character and show values for the pH at the point of
zero charge, pHPZC, that range from 7.4 to 9.7 and, in all cases, higher total basicity contents than the values obtained for total acidity.
The immersion heat of the activated carbons in CCl4 and water is determined obtaining values which are higher for CCl4 immersion and vary from 31.4 to 48.6 J g−1. The hydrophobic factor, hf, it is calculated from the relation between of the immersion heat of the activated carbons in CCl4 and the immersion heat in water, the obtained values were 2.98 and 6.75, which are greater than 1 due to the greater values
obtained in CCl4 when compared to the values obtained in water.
Immersion enthalpies in phenol solution range from 7.6 to 13.9 J g−1 and for the case of 4-nitro phenol such enthalpies range from 12.7 to 20.5 J g−1; all the 5 samples studied showed a higher value for the heat of immersion in aqueous solutions of 4-nitro phenol. 相似文献
3.
D. Diana Paola Vargas G. Liliana Giraldo P. Juan Carlos Moreno 《Journal of Thermal Analysis and Calorimetry》2013,111(2):1067-1072
In this study, energetic interactions between activated carbon monoliths and various liquids were evaluated by determining immersion enthalpies in C6H6, H2O and aqueous solutions of NaOH and HCl. Immersion enthalpies depend on both the surface chemistry and the interactions between specific groups, and were compared with results from volumetric titrations. Immersion enthalpies of activated carbon monoliths were between ?95.85 and ?176.5 J g?1 for C6H6 and between ?11.19 and ?68.31 J g?1 for H2O; whereas immersion enthalpies in NaOH and HCl solutions were between ?20.36 and ?82.25 J g?1 and ?18.81 and ?96.16 J g?1, respectively. In support of these results, a high level of acidic groups was found on the surface of the activated carbon monoliths by Boehm volumetric titrations, with values between 719 and 1,290 g mol?1, in agreement with the higher immersion enthalpies observed in NaOH. Correlations were established between immersion enthalpies in the liquids and the surface chemistry properties of the activated carbon monoliths determined by volumetric titrations, demonstrating that immersion enthalpy is a useful parameter for characterisation of these materials in specific liquids. 相似文献
4.
Marylin Betancourt Liliana Giraldo Sonia Moreno R. Molina J. C. Moreno 《Journal of Thermal Analysis and Calorimetry》2008,92(3):899-904
Total acidity for a series of modified clays obtained from a natural vermiculite is determined through temperature programmed
desorption (TPD) using ammonia as probe molecule. Results obtained for the acidity range from 15.1 to 68.5 meq/100 g.
Immersion enthalpies of the clays in benzene, water and aqueous solutions of NH3 0.058 M and NaHCO3 0.053 M are determined. The results obtained show that immersion enthalpies in benzene and water are between −6.26 and −25.6
J g−1 and −2.10 and 5.55 J g−1, respectively and are smaller than the values obtained for the immersion enthalpies in the solutions.
Immersion enthalpy values in NH3 solution are greater than the obtained using NaHCO3. Linear relations between the total acidity of the clays and the immersion enthalpies in the basic solutions are determined.
An interaction factor using ammonia is calculated since the relation between the immersion enthalpy in ammonia solution and
in water and it may be deduced that the relation with the total acidity is of second order tendency between them. 相似文献
5.
Y. S. Murillo L. Giraldo J. C. Moreno-Piraján 《Journal of Thermal Analysis and Calorimetry》2011,104(2):555-559
A way to calculate the enthalpic contributions of each component of the mixture of activated carbon and water to the immersion
enthalpy using the concepts of the solution enthalpies is presented. By determining the immersion enthalpies of a microporous
activated carbon in water, with values that are between –18.97 and −27.21 Jg−1, from these and the mass ratio of activated carbon and water, differential enthalpies for the activated carbon,
ΔHDIFacH_{{\rm DIF}_{\rm ac}} and water, ΔHDIFwH_{{\rm DIF}_{\rm w}} are calculated, and values between –15.95 and –26.81 Jg−1 and between –19.14 and –42.45 Jg−1, respectively are obtained. For low ratios of the mixture, the components’ contributions to the immersion enthalpy of activated
carbon and water differ by 3.20 Jg−1. 相似文献
6.
N. K. Tunali H. N. Erten S. Kinikoğlu Ş. Gümüş 《Journal of Radioanalytical and Nuclear Chemistry》1979,49(2):225-237
The extraction of iodine and bromine under various conditions from their saturated aqueous solutions by CCl4, C6H6 and o-xylene has been studied. The data obtained from the experiments carried out at various temperatures, for H2O(I2)−CCl4 and H2O(I2)−C6H6 systems, exhibit an Arrhenius behaviour. The overall activation energy calculated for the extraction in the H2O(I2)−CCl4 system, 650±50 cal·mol−1 is lower than that of H2O(I2)−C6H6, 3600±300 cal·mol−1. The use of the solubility parameter for the interpretation of the data in the extraction of iodine is investigated. The
data obtained in multiple extractions are treated by using the analogy between extraction and radioactive decay. The half
number of extraction for each system is determined. The complex curves obtained in the H2O(I2)−CCl4 and H2O(I2) −Br2)−CCl4 systems are resolved into two components. 相似文献
7.
Diego A. Blanco-Martínez Liliana Giraldo Juan C. Moreno-Piraján 《Journal of Thermal Analysis and Calorimetry》2009,96(3):853-857
The immersion enthalpies of modified activated carbons were determined, with commercial CarbochemTM–PS230 (CAG) as the initial activated carbon, which was modified by: chemical treatment with HNO3 7 mol L−1 (CAO) and thermal treatment under flow of H2 (CAR) in function of the adsorbed quantity of monohydroxilated phenols, catechol, resorcinol and hydroquinone at a pH of
7 in aqueous dissolutions in order to characterize the solid–solution interaction and evaluate the influence of the chemical
characteristics of the activated carbon in the phenol adsorption. The results show a variation in the immersion enthalpy in
function of the adsorbed quantity of phenol and the initial dissolution concentration; which shows that the intensity of the
interaction changes in function of the composition of the liquid phase. The immersion enthalpies present the following arrangement:
catechol > resorcinol > hydroquinone, with a −ΔHinm of 35.7; 30.8 and 24.6 Jg−1, respectively, at a pH of 7 for a 100 mg L−1 phenol monohydroxilated solution. 相似文献
8.
The adsorption process of 3-chloro phenol from aqueous solution on a activated carbon prepared from African palm stone and
which presents a specific surface area of 685 m2 g−1, a greater quantity of total acid groups and a pHPZC of 6.8 is studied. The adsorption isotherms are determined at pH values of 3, 5, 7, 9 and 11. The adsorption isotherms are
fitted to the Langmuir model and the values of the maximum quantity adsorbed that are between 96.2 and 46.4 mg g−1 are obtained along with the constant KL with values between 0.422 and 0.965 L mg−1. The maximum quantity adsorbed diminishes with the pH and the maximum value for this is a pH of 5. The immersion enthalpies
of the activated carbon in a 3-chloro phenol solution of constant concentration, of 100 mg L−1, are determined for the different pH levels, with results between 37.6 and 21.2 J g−1. Immersion enthalpies of the activated carbon in function of 3-chloro phenol solution concentration are determined to pH
5, of maximum adsorption, with values between 28.3 and 38.4 J g−1, and by means of linearization, the maximum immersion enthalpy is calculated, with a value of 41.67 J g−1. With the results of the immersion enthalpy, maximum quantity adsorbed and the constant KL, establish relations that describe the adsorption process of 3-chloro phenol from aqueous solution on activated carbon. 相似文献
9.
G. J. De Jong U. A. Th. Brinkman 《Journal of Radioanalytical and Nuclear Chemistry》1977,35(1):223-232
For the system liquid anion-exchanger—Cr(III)−NCS−, an investigation has been made of the dependence of the percentage extraction of Cr(III) on parameters such as standing
time of the Cr(III)−NCS− solution, temperature, pH and type of exchanger. Quantitative extraction of e.g. 4·10−4 M Cr(III) by 0.1M Aliquat in CCl4 is easily achieved at room temperature, using 4.75M KNCS−0.05N HCl as aqueous phase. At high Cr(III) concentrations, the
complex anion present in the organic phase is Cr(NCS)
6
3−
; when working with dilute metal ion solutions, the species extracted is Cr(NCS)4 (H2O)
2
−
. Separations of mixtures containing 10−2−10−4 M Co(II), Ni(II) and Cr(III) have successfully been accomplished. 相似文献
10.
Rima Tarozaitė Loreta Tamašauskaitė Tamašiūnaitė Vitalija Jasulaitienė 《Journal of Solid State Electrochemistry》2009,13(5):721-731
Platinum–tin complexes were prepared by the reduction of Pt(IV) with Sn(II) in HCl media and studied by light absorption spectrometry,
X-ray photoelectron spectroscopy (XPS), and electron microscopy. The formation of three complexes, H3[Pt(SnCl3)5], H2[Pt(SnCl3)2Cl2], and H2[Pt3(SnCl3)8], depending on HCl and SnCl2 concentrations, has been shown. The glassy carbon (GC) electrode modified in the complexes solutions was found to be an electrocatalyst
for borohydride oxidation in a 1.0-M NaOH solution. Comparison of BH4
− electrooxidation on Pt and on GC modified with platinum–tin complexes has shown that catalytic hydrolysis of BH4
− did not proceed in the latter case in contrast to its oxidation on the Pt electrode, and only direct BH4
− oxidation has been observed in the positive potentials scan. The activity of Pt–Sn complexes for BH4
− oxidation changes with time and eventually decreases due to Sn(II), bound in the complex with Pt(II), oxidation by atmospheric
oxygen. The complexes may be renewed by addition of missing amounts of SnCl2 and HCl. 相似文献
11.
Summary. Calcium sulfate occurs in nature in form of three different minerals distinguished by the degree of hydration: gypsum (CaSO4·2H2O), hemihydrate (CaSO4·0.5H2O) and anhydrite (CaSO4). On the one hand the conversion of these phases into each other takes place in nature and on the other hand it represents
the basis of gypsum-based building materials. The present paper reviews available phase diagram and crystallization kinetics
information on the formation of calcium sulfate phases, including CaSO4-based double salts and solid solutions.
Uncertainties in the solubility diagram CaSO4–H2O due to slow crystallization kinetics particularly of anhydrite cause uncertainties in the stable branch of crystallization.
Despite several attempts to fix the transition temperatures of gypsum–anhydrite and gypsum–hemihydrate by especially designed
experiments or thermodynamic data analysis, they still vary within a range from 42–60°C and 80–110°C. Electrolyte solutions
decrease the transition temperatures in dependence on water activity.
Dry or wet dehydration of gypsum yields hemihydrates (α-, β-) with different thermal and re-hydration behaviour, the reason
of which is still unclear. However, crystal morphology has a strong influence.
Gypsum forms solid solutions by incorporating the ions HPO4
2−, HAsO4
2−, SeO4
2−, CrO4
2−, as well as ion combinations Na+(H2PO4)− and Ln3+(PO4)3−. The channel structure of calcium sulfate hemihydrate allows for more flexible ion substitutions. Its ion substituted phases
and certain double salts of calcium sulfate seem to play an important role as intermediates in the conversion kinetics of
gypsum into anhydrite or other anhydrous double salts in aqueous solutions. The same is true for the opposite process of anhydrite
hydration to gypsum. Knowledge about stability ranges (temperature, composition) of double salts with alkaline and alkaline
earth sulfates (esp. Na2SO4, K2SO4, MgSO4, SrSO4) under anhydrous and aqueous conditions is still very incomplete, despite some progress made for the systems Na2SO4–CaSO4 and K2SO4–CaSO4–H2O.
Corresponding author. E-mail: daniela.freyer@chemie.tu-freiberg.de
Received December 17, 2002; accepted January 10, 2003
Published online April 3, 2003 相似文献
12.
We have studied the basicity of 2-phenyl-5-R-1,3,4-oxadiazoles (R = H, Me, CH2Ph, t-Bu, CH2Cl, CCl3, CF3) in aqueous sulfuric acid solutions. These compounds are weak organic bases (pKBH
+ is −1.8 to −5.2). The values of pKBH
+ determined on the H0 and X acidity function scales agree well with each other. The substituent at the 5 position has a substantial effect on the
basicity of the 1,3,4-oxadiazole ring.
__________
Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 748–756, May, 2006. 相似文献
13.
G. Bognár Cs. Pintér B. Horváth T. Sydo E. Ligeti J. Pulai D. Lőrinczy 《Journal of Thermal Analysis and Calorimetry》2009,95(3):769-774
Osteonecrosis (ON) of the femoral frequently occurs after steroid medication. One of the final pathways leading to steroid
induced ON is thought to be pathologic fat metabolism. The pathobiological mechanism underlying the induction of fat metabolism
outslides by steroids leading to ON has not been fully elucidated. The purpose of this study was to examine the intraoperative
obtained gluteal fat tissue from ON patients with histology, gas chromatography (GC) and differential scanning calorimetry
(DSC) and to compare them with otherwise healthy patient’s samples. The histological sections showed no significant differences
compared with the control group. GC revealed that fraction of saturated fatty acids decreased in ON samples from mean values
of controls of 24% to 21, the polyunsaturated fraction from 20 to 14%. The monounsaturated acids showed an increase from mean
rate of 52% of the controls to 65% of steroid treated samples. DSC curves correlate with chromatographic analysis of the tissue
fatty acids (Steroid treated, heating between 0–100°C: T
m=5.7°C, ΔH= −15.8J/g−1; heating between −20–100°C: Tm= −9.96 and 5.85°C, ΔH= −59.17 and −16.2 J g−1. Non-necrotic, heating between 0–100°C: two separable transition with Tm=5.7 and 9.9°C, total ΔH= −20.8 J g−1; heating between −20–100°C: Tm= −10.9 and 4.95°C, total ΔH= −75.8 J g−1.)
Our preliminary findings are rather tendentious. Further investigations are needed with higher sample rate and under other
anamnestic circumstances too. 相似文献
14.
Xian-Ming Zhang Yu-Feng Hu Xiao-Ming Peng Wen-Jia Yue 《Journal of solution chemistry》2009,38(10):1295-1306
Conductivities were measured for the ternary systems NaNO3–KNO3–H2O, NaCl–BaCl2–H2O, NaCl–LaCl3–H2O, and their binary subsystems NaNO3–H2O, KNO3–H2O, NaCl–H2O, BaCl2–H2O, and LaCl3–H2O at (293.15, 298.15 and 303.15) K. The results were used to verify the generalized Young’s rule and the semi-ideal solution
theory. Comparison of the results shows that the average relative differences between the predicted and measured conductivities
are ≤4.2×10−3 for NaNO3–KNO3–H2O, ≤4.6×10−3 for NaCl–BaCl2–H2O, and ≤8.9×10−3 for NaCl–LaCl3–H2O, indicating that the generalized Young’s rule and the semi-ideal solution theory can provide good predictions for the conductivity
of mixed electrolyte solutions in terms of the data from their binary subsystems. 相似文献
15.
S. Hegstad E. Lundanes R. Reistad L. S. Haug G. Becher J. Alexander 《Chromatographia》2000,52(7-8):499-504
Summary A method for the determination of the food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) in human hair has been developed and validated. Hair samples (200 mg) were dissolved in NaOH (1 M) and PhIP
was isolated by successive solid-phase extraction on a polystyrene-divinylbenzene column and on a silica-based mixed-mode
column with C8 and-SO3
− functional groups. Quantification was performed by gas chromatography-electron-impact ionization high-resolution mass spectrometry
in selected-ion-monitoring mode. The method was validated for determination of PhIP in the concentration range 0.5–25 ng g−1 hair with [2H3]PhIP as internal standard. The limit of quantification was 0.26 ng g−1 hair. Within-day and between-day precision were in the ranges 1–27% and 2–15% relative standard deviation, respectively.
The hair sample used for method validation was found to contain 0.26 ng PhIP g−1 hair. 相似文献
16.
Efficient uranium(VI) biosorption on grapefruit peel: kinetic study and thermodynamic parameters 总被引:3,自引:0,他引:3
The uranium(VI) biosorption by grapefruit peel was studied from aqueous solutions. Batch experiments was conducted to evaluate
the effect of contact time, initial uranium(VI) concentration, initial pH, adsorbent dose, salt concentration and temperature.
The equilibrium process was well described by the Langmuir, Redlich–Peterson and Koble–Corrigan isotherm models, with maximum
sorption capacity of 140.79 mg g−1 at 298 K. The pseudo second order model and Elovish model adequately describe the kinetic data in comparison to the pseudo
first order model and the process involving rate-controlling step is much complex involving both boundary layer and intra-particle
diffusion processes. The effective diffusion parameter D
i and D
f values were estimated at different initial concentration and the average values were determined to be 1.167 × 10−7 and 4.078 × 10−8 cm2 s−1. Thermodynamic parameters showed that the biosorption of uranium(VI) onto grapefruit peel biomass was feasible, spontaneous
and endothermic under studied conditions. The physical and chemical properties of the adsorbent were determined by SEM, TG-DSC,
XRD and elemental analysis and the nature of biomass–uranium (VI) interactions was evaluated by FTIR analysis, which showed
the participation of COOH, OH and NH2 groups in the biosorption process. Adsorbents could be regenerated using 0.05 mol L−1 HCl solution at least three cycles, with up to 80% recovery. Thus, the biomass used in this work proved to be effective materials
for the treatment of uranium (VI) bearing aqueous solutions. 相似文献
17.
Yoshio Kobayashi Takuya Nozawa Tomohiko Nakagawa Kohsuke Gonda Motohiro Takeda Noriaki Ohuchi Atsuo Kasuya 《Journal of Sol-Gel Science and Technology》2010,55(1):79-85
This paper describes a method for direct coating of fluorescent semiconductor nanoparticles with silica shell. The fluorescent
semiconductor nanoparticles used were CdSe
x
Te1–x
nanoparticles coated with ZnS and succeedingly surface-modified with carboxyl groups, or quantum dots (Q-dots). The Q-dots
were silica-coated by performing sol–gel reaction of tetraethyl orthosilicate (TEOS) using NaOH as a catalyst in the presence
of the Q-dots. Quasi-perfect Q-dots/silica core-shell particles were formed at 5.0 M H2O and 4.0 × 10−4 M NaOH. Under these concentrations of H2O and NaOH, the particle size of Q-dots/silica particles could be varied from 20.1 to 38.1 nm as the TEOS concentration increased
from 2.5 × 10−4 to 50 × 10−4 M. The Q-dots/silica particles showed fluorescence as well as the uncoated Q-dots. 相似文献
18.
R. A. Pacer 《Journal of Radioanalytical and Nuclear Chemistry》1983,77(1):19-28
Using as eluent a sequence of 3M HCl, 12M HCl, and 8M HNO3, a mixture of210Pb,210Bi, and210Po may be clearly separated on a column of Dowex 1×2−100 anion exchange resin. A Cherenkov count in H2O and the variation in count rate with time confirm that the nuclides emerge in the order210Pb→210Bi→210Po. If 12M HCl is replaced by 1.5M H2SO4/2.3 M Na2SO4, a clean separation also results, but recovery of210Po becomes considerably more difficult. All three nuclides are readily detectable by liquid scintillation counting, with the
efficiency for210Pb in the 60–70% range. The Cherenkov aqueous counting efficiency for210Bi is ∼14–15%. 相似文献
19.
V. A. Demin A. I. Kamenev N. P. Zveryak V. I. Zarembo 《Journal of Analytical Chemistry》2010,65(1):87-90
The behavior of Cd(II), Pb(II), Cu(II), and I− in the aqueous solutions of sodium chloride is studied by stripping voltammetry. A new version of using an indicator electrode
from carbon glass ceramics modified with mercury for the consecutive stripping determination of Cd(II), Pb(II), Cu(II), and
iodide is proposed. The mercury-graphite electrode was formed in the solution of a supporting electrolyte based on NH4Cl, HCl, 0.05 M potassium tetraoxalate (KH3C4O3 · 2H2O), and 5 × 10−5 M mercury(II). At first, Cd(II), Pb(II), Cu(II), and then iodide were determined by anodic-cathodic stripping voltammetry
after adding a sample solution (table salt, 10–100 mg/mL NaCl). 相似文献
20.
Mariano Velázquez-Rivera Donald A. Palmer Richard M. Kettler 《Journal of solution chemistry》2006,35(12):1699-1730
This study measures the osmotic coefficients of {xH2SO4 + (1−x)Fe2(SO4)3}(aq) solutions at 298.15 and 323.15 K that have ionic strengths as great as 19.3 mol,kg−1, using the isopiestic method. Experiments utilized both aqueous NaCl and H2SO4 as reference solutions. Equilibrium values of the osmotic coefficient obtained using the two different reference solutions
were in satisfactory internal agreement. The solutions follow generally the Zdanovskii empirical linear relationship and yield
values of a
w for the Fe2(SO4)3–H2O binary system at 298.15 K that are in good agreement with recent work and are consistent with other M2(SO4)3–H2O binary systems. 相似文献