Showing papers on "Enthalpy published in 2009"
TL;DR: In this paper, it was shown that for a dilute solution of charged adsorbates or for a solution of uncharged adsorates at any concentration, the thermodynamic equilibrium constant of adsorption would be reasonably approximated by the Langmuir equilibrium constant.
Abstract: In the study of adsorption, changes in free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) have been most frequently calculated from the Langmuir equilibrium constant. In a strict theoretical sense, the Langmuir equilibrium constant with units of liters per mole and the thermodynamic equilibrium constant without units are not the same. Moreover, the equilibrium constants for thermodynamic calculation have also been derived in different ways in the literature, for example, Frumkin isotherm, Flory−Huggins isotherm, distribution constants, and so on. As a result, values of ΔG°, ΔH°, and ΔS° of adsorption reported in the literature are very confusing. This study shows that for a dilute solution of charged adsorbates or for a solution of uncharged adsorbates at any concentration, the thermodynamic equilibrium constant of adsorption would be reasonably approximated by the Langmuir equilibrium constant, and thus the use of the Langmuir equilibrium constant for calculation of ΔG° and subsequent determination of ...
900 citations
01 Apr 2009
TL;DR: The results indicate that montmorillonite clay adsorbs MB efficiently and could be employed as a low-cost alternative in wastewater treatment for the removal of cationic dyes.
Abstract: In this study, montmorillonite clay (MC) has been utilized as the adsorbent for the removal of a cationic dye, methylene blue (MB), from aqueous solution by the batch adsorption technique under different conditions of initial dye concentration, adsorbent concentration, contact time, solution pH, and temperature. Attempts were made to fit the isothermal data using Langmuir and Freundlich equations. The experimental results have demonstrated that the equilibrium data are fitted well by a Langmuir isotherm equation. Thermodynamic parameters such as the changes in enthalpy, entropy, and Gibbs' free energy were determined, showing adsorption to be an endothermic yet spontaneous process. Pseudo-first-order, pseudo-second-order, and intraparticle diffusion models were considered to evaluate the rate parameters. The experimental data fitted the pseudo-second-order kinetic model, with an activation energy of +28.5 kJ mol(-1). The results indicate that MC adsorbs MB efficiently and could be employed as a low-cost alternative in wastewater treatment for the removal of cationic dyes.
617 citations
TL;DR: Kinetic studies showed that the kinetic data were well described by the pseudo-second-order kinetic model and significant increases in initial adsorption rate were observed with the increase in temperature followed by pH and initial MB concentration.
503 citations
TL;DR: Thermodynamic parameters indicated that adsorption of phenol onto organobentonite was feasible, spontaneous and exothermic in the temperature range of 0-40 degrees C.
349 citations
TL;DR: In this paper, a kinetic and thermodynamic study of the adsorption of azo-dye Orange II from aqueous solutions onto titania aerogels was performed.
284 citations
TL;DR: Results suggest that the adsorption process of nitrate by chitosan hydrobeads is a spontaneous, exothermic process that has positive entropy.
266 citations
TL;DR: Peanut hull, an agricultural by-product abundant in China, was used as adsorbent for the removal of Cu(II) from aqueous solutions and the negative DeltaG(0) values at various temperatures confirm the biosorption processes are spontaneous.
228 citations
TL;DR: In this article, the molar heat capacities of rutile and anatase were measured from 0.5 K to about 380 K, and fits of the resulting data set were used to generate C P,m°, ΔT S m° and ΔT H m° values at smoothed temperatures between 0 and 1300 K.
Abstract: At high temperature, coarse-grained (bulk) rutile is well established as the stable phase of TiO2, and nanophase anatase, thermodynamically stable relative to nanophase rutile, transforms irreversibly to rutile as it coarsens. The lack of experimental heat-capacity data for bulk anatase below 52 K lends uncertainty to its standard entropy and leaves open a slight possibility that anatase may have a thermodynamic stability field at low temperature, as suggested by some theoretical calculations. In the present study, the molar heat capacities of rutile and anatase were measured from 0.5 K to about 380 K. These data were combined with previously measured high-temperature heat capacities, and fits of the resulting data set were used to generate C P ,m°, ΔT S m°, ΔT H m°, and ΔT G m ° values at smoothed temperatures between 0.5 and 1300 K for anatase and 0.5 and 1800 K for rutile. Using these new data and the enthalpy of transformation between anatase and rutile at 298 K, the change in Gibbs free energy for the transition between anatase and rutile from 0 to 1300 K was calculated. These calculations reveal that the transformation from bulk anatase to bulk rutile is thermodynamically favorable at all temperatures between 0 and 1300 K, confirming that bulk anatase does not have a thermodynamic stability field. Implications for the natural occurrence of these two minerals in terrestrial, lunar, and planetary settings are discussed. In particular, anatase requires low-temperature aqueous conditions for its formation and may be a reliable indicator of such conditions in both terrestrial and extraterrestrial settings.
223 citations
TL;DR: In this article, the electrical conductivity of San Carlos olivine aggregate of various water content was measured at a pressure of 10 GPa in a Kawai-type multi-anvil apparatus.
217 citations
TL;DR: In this article, experimental measurements of excess molar enthalpy, density, and isobaric molar heat capacity are presented for a set of binary systems ionic liquid+water as a function of temperature at atmospheric pressure.
173 citations
TL;DR: It is found that the oxygen-carbon bond dissociation enthalpy is substantially lowered by oxygen substituents situated at the phenyl ring adjacent to the ether oxygen, which could be a competitive initial reaction under high-temperature pyrolysis conditions.
Abstract: Lignin is an abundant natural resource that is a potential source of valuable chemicals. Improved understanding of the pyrolysis of lignin occurs through the study of model compounds for which phenethyl phenyl ether (PhCH2CH2OPh, PPE) is the simplest example representing the dominant β-O-4 ether linkage. The initial step in the thermal decomposition of PPE is the homolytic cleavage of the oxygen−carbon bond. The rate of this key step will depend on the bond dissociation enthalpy, which in turn will depend on the nature and location of relevant substituents. We used modern density functional methods to calculate the oxygen−carbon bond dissociation enthalpies for PPE and several oxygen-substituted derivatives. Since carbon−carbon bond cleavage in PPE could be a competitive initial reaction under high-temperature pyrolysis conditions, we also calculated substituent effects on these bond dissociation enthalpies. We found that the oxygen−carbon bond dissociation enthalpy is substantially lowered by oxygen subs...
TL;DR: The results show that TAB samples can be an alternative low cost adsorbent for removing U(VI) ions from aqueous solutions.
TL;DR: In this article, the solubility of hydrogen sulfide in three ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1- butyl- 3methyloride tetrafluoroborate (BF4), and 1-Butyl 3 methylimide bis(trifluoromethylsulfonyl)imide (Tf2N), at temperatures ranging from (303.15 to 343.15) K and pressures up to 1
TL;DR: In this article, the adsorption behavior of Cu 2+ and Cd 2+ onto bentonite was studied as a function of temperature under optimized conditions of amount of adsorbent, particle size, pH, concentration of metals, and shaking time.
TL;DR: The results indicate that a-WM can be used as an effective and no-cost adsorbent for the treatment of industrial wastewaters contaminated with Pb(II) ions.
TL;DR: ZnAl-NO(3) LDHs have been employed to remove chloride ion from aqueous solution in a batch mode and it was found from kinetics test that the pseudo-second order kinetics model could be used to well describe the uptake process.
TL;DR: In this paper, the Gibbs-Helmholtz equation was used to predict enthalpies of absorption of CO 2 in aqueous solutions of 2-aminoethanol (MEA) and N-methyldiethanolamine.
TL;DR: Insight is provided into the previously reported dependence of the transfection efficiency of DNA/chitosan complexes on ch itosan DDA and molecular weight, where complex stability and chitOSan-DNA binding strength play a critical role.
TL;DR: Among the tested methods, B97-D and the M06 series of functionals best reproduce the experimental binding enthalpy value of Sponsler et al.
Abstract: The binding enthalpy of a triphenylphosphine ligand in Ru(CO)Cl(PPh3)3(CH═CHPh) is studied with “standard” (BP86 and B3LYP), dispersion-corrected (B3LYP-D and B97-D), and highly parametrized (M05 a...
TL;DR: In this paper, the phase equilibria of quaternary CO 2 + H 2 + cyclopentane (CP ) + water systems containing gas hydrates were determined by using a high-pressure differential scanning calorimeter (DSC).
TL;DR: It could be shown that below T(g) no clear relationship between the various factors determined and physical stability exists, indicating that stability predictions on the basis of relaxation time alone may be inadequate.
TL;DR: The results showed that temperature, pH and mass of adsorbent affected boron removal by adsorption, and Boron removal increased with increasing pH and advertisersorbent dosage, but decreased with increasing temperature.
TL;DR: Theoretical work was essentially focused on the evaluation of the Nonrandom Two-Liquid Segment Activity Coefficient (NRTL-SAC) model, which has been referred as a simple and practical thermodynamic framework for drug solubility estimation.
TL;DR: FTIR and (13)C NMR study revealed that the amino and isocyanate groups present on the surface of the adsorbent were involved in chemical interaction with 2-nitroaniline, indicating that the adsorption was a spontaneous and endothermic process.
TL;DR: In this article, the authors used Clausius-Clapeyron (CC) equation to estimate the isosteric heat of adsorption and desorption isotherm at two different temperatures.
TL;DR: In this paper, the properties of Ni-based superalloys have been measured and relationships between properties and the γ′ phase content (which can be represented by mass% Al in the alloy) have been identified.
Abstract: Thermophysical properties for the solid and liquid phases of several Ni based superalloys (CMSX-4, CMSX-10, CM186LC, IN 738 and Rene 80) have been measured. The following properties were measured: heat capacity and enthalpy, thermal expansion coefficient and density, thermal diffusivity, viscosity and surface tension. Analysis of these measurements showed that that γ′ phase (Ni3Al) affected the values for the following properties; C p, enthalpy, electrical resistivity, thermal diffusivity and conductivity. Relationships have been identified between properties and the γ′ phase content (which can be represented by mass% Al in the alloy). These relations were then used to calculate property values of the alloys from chemical composition. Other relations were developed to estimate the viscosities and surface tensions of Ni based superalloys. The predicted property values were found to be in good agreement with the measured values.
TL;DR: In this paper, the ERAS-model was applied in order to study the microscopic mechanisms involved in the mixing process of binary systems ionic liquid + n-nitromethane.
TL;DR: In this article, a new formulation of the garnet-clinopyroxene geothermometer was developed based on the published experimental data including graphite capsules, and a published subregular-solution model was adopted to express the nonideality of garnet.
Abstract: Published experimental data including garnet and clinopyroxene as run products were used to develop a new formulation of the garnet–clinopyroxene geothermometer based on 333 garnet–clinopyroxene pairs. Only experiments with graphite capsules were selected because of difficulty in estimating the Fe3+ content of clinopyroxene. For the calibration, a published subregular-solution model was adopted to express the non-ideality of garnet. The magnitude of the Fe–Mg excess interaction parameter for clinopyroxene (WFeMgCpx), and differences in enthalpy and entropy of the Fe–Mg exchange reaction were regressed from the accumulated experimental data set. As a result, a markedly negative value was obtained for the Fe–Mg excess interaction parameter of clinopyroxene (WFeMgCpx = − 3843 J mol−1). The pressure correction is simply treated as linear, and the difference in volume of the Fe–Mg exchange reaction was calculated from a published thermodynamic data set and fixed to be −120.72 (J kbar−1 mol−1). The regressed and obtained thermometer formulation is as follows:
where T = temperature, P = pressure (kbar), A = 0.5 Xgrs (Xprp − Xalm − Xsps), B = 0.5 Xgrs (Xprp − Xalm + Xsps), C = 0.5 (Xgrs + Xsps) (Xprp − Xalm), Xprp = Mg/(Fe2+ + Mn + Mg + Ca)Grt, Xalm = Fe/(Fe2+ + Mn + Mg + Ca)Grt, Xsps = Mn/(Fe2+ + Mn + Mg + Ca)Grt, Xgrs = Ca/(Fe2+ + Mn + Mg + Ca)Grt, XMgCpx = Mg/(Al + Fetotal + Mg)Cpx, XFeCpx = Fe2+/(Al + Fetotal + Mg)Cpx, KD = (Fe2+/Mg)Grt/(Fe2+/Mg)Cpx, Grt = garnet, Cpx = clinopyroxene. A test of this new formulation to the accumulated data gave results that are concordant with the experimental temperatures over the whole range of the experimental temperatures (800–1820 °C), with a standard deviation (1 sigma) of 74 °C. Previous formulations of the thermometer are inconsistent with the accumulated data set; they underestimate temperatures by about 100 °C at >1300 °C and overestimate by 100–200 °C at <1300 °C. In addition, they tend to overestimate temperatures for high-Ca garnet (Xgrs ≈ 0.30–0.50). This new formulation has been tested against previous formulations of the thermometer by application to natural eclogites. This gave temperatures some 20–100 °C lower than previous formulations.
TL;DR: In this article, the electrical conductivity of wadsleyite aggregates has been determined under a broad range of thermodynamic conditions using the impedance spectroscopy for a frequency range of 10 − 2 to 10 6 ǫ.
TL;DR: In this paper, the ability of original waste mud and different types of activated waste mud which are acid-activated (a-WM) and precipitated waste mud (p-WM), in removing excess of fluoride from aqueous solution by using batch technique was assessed.