Showing papers on "Standard molar entropy published in 2014"

Removal of Cu(II) ions from aqueous solutions by low-cost natural hydroxyapatite/chitosan composite: Equilibrium, kinetic and thermodynamic studies

Abstract: In this study, a simple method for providing natural hydroxyapatite/chitosan (N-HAP/chitosan) composite is introduced and adsorption suitability of this composite for treating the solutions containing Cu(II) ions has been studied. Kinetic and isotherm studies were carried out by studying the effects of parameters such as adsorbent particle size, temperature and pH. The equilibrium data at different temperatures were analyzed by Langmuir and Freundlich isotherms. Equilibrium data agreed well with Langmuir isotherm, based on this model the maximum adsorption capacity of N-HAP/chitosan composite for Cu(II) was found to be 1.776 mmol/g at pH 7.50 and 25 °C for 47.6 nm adsorbent particle size. A pseudo-second order kinetic model has been proposed to correlate the experimental data. The thermodynamic parameters such as standard Gibb's free energy (ΔG°), standard enthalpy (ΔH°), standard entropy (ΔS°) and activation energy (Ea) were evaluated by applying the Van’t Hoff and Arrhenius equations. The results reveal Cu(II) adsorption onto N-HAP/chitosan is spontaneous, has endothermic nature and is followed by physisorption.

Synthesis and characterization of a starch–AlOOH–FeS2 nanocomposite for the adsorption of congo red dye from aqueous solution

Abstract: This work described the synthesis and characterization of a starch–AlOOH–FeS2 nanocomposite for the adsorption of congo red (CR) dye from aqueous solution. The morphology of the starch–AlOOH–FeS2 was characterized by using scanning and transmission electron microscopy, N2 adsorption–desorption isotherms, X-ray photoelectron spectroscopy, and fourier transform-infrared spectroscopy. The adsorption of CR onto starch–AlOOH–FeS2 was evaluated as a function of contact time, solution pH, concentration and temperature. The adsorption results demonstrate that the maximum removal of CR was found to be at pH 5. The adsorption kinetics data fitted well to the pseudo first-order equation whereas the Freundlich equation exhibits better correlation to the experimental data. Thermodynamic parameters, such as the standard free energy change (ΔG°), the standard entropy change (ΔS°) and the standard enthalpy change (ΔH°), were also evaluated. The results suggested that starch–AlOOH–FeS2 is a potential adsorbent for CR dye removal from aqueous solution.

Interaction of the dietary pigment curcumin with hemoglobin: energetics of the complexation.

Abstract: Thermodynamics of the interaction of the chemotherapeutic and chemopreventive dietary pigment, curcumin, with hemoglobin was studied by isothermal titration calorimetry. The binding was characterized to be exothermic. At 293.15 K, the equilibrium constant for curcumin-Hb complexation was found to be (4.88 ± 0.06) × 10(5) M(-1). The binding stoichiometry was calculated to be 1.08 ± 0.05, confirming a 1:1 complexation. The binding was driven by a large negative standard molar enthalpy change (ΔH(0) = -118.45 ± 0.05 kJ mol(-1)) and an unfavorable standard molar entropy change (TΔS(0) = -86.53 ± 0.01 kJ mol(-1)) at 293.15 K. Increasing the temperature favoured the binding, and the magnitude of the negative standard molar heat capacity change suggested the involvement of significant hydrophobic forces in the binding process. With increasing salt concentration, the magnitude of the equilibrium constant decreased slightly; and the complexation mostly involved non-polyelectrolytic forces contributing about 92-94% of the standard molar Gibbs energy change. DSC studies revealed that curcumin binding caused a partial unfolding of the protein.

Vesicle Formation by l-Cysteine-Derived Unconventional Single-Tailed Amphiphiles in Water: A Fluorescence, Microscopy, and Calorimetric Investigation

Abstract: Two new l-cysteine-derived zwitterionic amphiphiles with poly(ethylene glycol) methyl ether (mPEG) tail of different chain lengths were synthesized and their surface activity and self-assembly properties were investigated. In aqueous phosphate buffered solution of pH 7.0, the amphiphiles were observed to form stable unilamellar vesicles, the bilayer membrane of which is constituted by the mPEG chains. The vesicle phase was characterized by a number of methods including fluorescence spectroscopy, dynamic light scattering, and transmission electron microscopy. The thermodynamics of self-assembly was also studied by isothermal titration calorimetry through measurements of the standard Gibbs free energy change (ΔG°m), standard enthalpy change (ΔH°m) and standard entropy change (ΔS°m) of micellization. The self-assembly process was found to be entropy-driven, which implies that the mPEG chain behaves like a hydrocarbon tail of conventional surfactants. The effects of pH, temperature, salt, and aging time on th...

Quadrupole terms in the Maxwell equations: Born energy, partial molar volume, and entropy of ions

Abstract: A new equation of state relating the macroscopic quadrupole moment density Q to the gradient of the field ∇E in an isotropic fluid is derived: Q = αQ(∇E - U∇·E/3), where the quadrupolarizability αQ is proportional to the squared molecular quadrupole moment. Using this equation of state, a generalized expression for the Born energy of an ion dissolved in quadrupolar solvent is obtained. It turns out that the potential and the energy of a point charge in a quadrupolar medium are finite. From the obtained Born energy, the partial molar volume and the partial molar entropy of a dissolved ion follow. Both are compared to experimental data for a large number of simple ions in aqueous solutions. From the comparison the value of the quadrupolar length LQ is determined, LQ = (αQ/3ɛ)(1/2) = 1-4 A. Data for ion transfer from aqueous to polar oil solution are analyzed, which allowed for the determination of the quadrupolarizability of nitrobenzene.

Decontamination of 4-chloro-2-nitrophenol from aqueous solution by graphene adsorption: equilibrium, kinetic, and thermodynamic studies

Abstract: Chloro-2-nitrophenol (4C2NP) is an important chemical widely used in the pharmaceuticals, herbi- cide, and pesticide industries. The ability of graphene to remove 4C2NP from aqueous solutions was per- formed as a function of contact time, amounts of adsorbent, pH, initial 4C2NP concentrations, and tempera- tures using a batch technique. Based on the results, the amount of 4C2NP adsorption increased with increas- ing initial concentration, whereas the alkaline pH range, higher graphene dosage, and higher temperature were unfavorable. Non-linear regression methods suggest that the isotherm data can be well described by the Freundlich isotherm equation. The adsorption kinetic data were analyzed using the non-linear rate equations of pseudo-first and pseudo-second order. It was found that the pseudo-second-order kinetic model was the most appropriate model, describing the adsorption kinetics. The observed changes in the standard Gibbs free energy (ΔGo), standard enthalpy (ΔHo), and standard entropy (ΔSo) show that the adsorption of 4C2NP by graphene is feasible, spontaneous, and exothermic in the temperature range 298-328 K.

Physical–chemical properties of nickel analogs ionic liquid based on choline chloride

Abstract: In this paper, a homogeneous, green analogs ionic liquid containing choline chloride and nickel chloride hexahydrate is formed. The structure of the analogs ionic liquid is preliminary investigated by Fourier transform infrared spectroscopy. It is shown that the nickel chloride hexahydrate bond via hydrogen bonds with choline chloride and urea. The physico-chemical properties of the analogs ionic liquid such as viscosity, conductivity, density, and thermal stability are measured as a function of temperature and composition. The thermal expansion coefficients (r), the molar Gibbs energy of activation (ΔG*) for viscous flow, the molar enthalpy of activation (ΔH*), and the molar entropy of activation (ΔS*) for viscous flow have been calculated. A straight-line equation is used to fit the density data while the Arrhenius equation is used to fit both viscosity and conductivity. Thermal stability of analogs ionic liquid was carried out from room temperature to 973.15 K. It indicates that analogs ionic liquid is stable from room temperature to 488.2 K.

Experimental Investigation on the Solubility of Oxygen in Toluene and Acetic Acid

Abstract: By using the dual vessel equilibrium method, the solubility of oxygen in toluene and acetic acid was experimentally investigated with pressure ranging from 0.1 to 1.0 MPa at temperatures from 293.1 to 383.1 K. The results show that the oxygen solubility either in toluene or in acetic acid increases with a rise in temperature. On the basis of the experimental data, Henry coefficients were derived and expressed as a function of temperature. At the same temperature, Henry coefficient for the oxygen–toluene system is lower than that for the oxygen–acetic acid system. Through analysis of the Gibbs energy (ΔG0), partial molar enthalpy (ΔH0), and the partial molar entropy (ΔS0) of the solvation, we can know that solubilization of oxygen either in toluene or in acetic acid is an endothermic process. To correlate the experimental data, the Peng–Robinson equation of state with the quadratic mixing rule was used for the two systems.

Synthesis and Physicochemical Properties of Two SO3H-Functionalized Ionic Liquids with Hydrogen Sulfate Anion

Abstract: Two SO3H-functionalized ionic liquids (ILs), N-isobutyl-3-sulfopropan-1-aminium hydrogen sulfate [IBAC3S]HSO4 and N-isobutyl-4-sulfobutan-1-aminium hydrogen sulfate [IBAC4S]HSO4, were synthesized and characterized by NMR and HR-MS. The thermal properties and acidities were analyzed. Density, dynamic viscosity, surface tension, conductivity, and refractive index of the IL were studied as a function of temperature. The physicochemical properties, namely molecular volume, isobaric coefficients of thermal expansion, standard entropy, critical temperature, molar free volume, interstice volume, etc. of the IL were estimated according to the reported empirical and thermodynamic equations. On the basis of the Walden rule, the ionicty of the two SO3H-functionalized ionic liquids was assessed by the product of molar conductivity and viscosity.

Oxygen non-stoichiometry and thermodynamic properties of Bi2Sr2CoO6+δ ceramics

Abstract: In the literature the structure Bi 2 Sr 2 CoO 6+ δ has been described with a variable oxygen nonstoichiometry δ . We identified δ parameter by thermogravimetric measurements and determined thermodynamic properties of Bi 2 Sr 2 CoO 6+ δ . The heat capacity and enthalpy increments of Bi 2 Sr 2 CoO 6+ δ were measured by the relaxation time method (PPMS) from 2 to 256 K, by differential scanning calorimetry (DSC) from 258 to 355 K and by drop calorimetry from 573 to 1123 K. Above-room temperature, the dependence of molar heat capacity under isodynamical (constant p O 2 ) and conventional isoplethal conditions (constant composition) was derived from the experimental data by the least-squares method. The low temperature heat capacity was analyzed in terms of a combined Debye–Einstein model. The molar entropy S m ∘ ( 298.15 ) = 318.9 J K − 1 mol − 1 was evaluated from the low-temperature heat-capacity measurements.

Thermodynamic and magnetic properties of knorringite garnet (Mg 3 Cr 2 Si 3 O 12 ) based on low-temperature calorimetry and magnetic susceptibility measurements

Abstract: The low-temperature heat capacity of knorringite garnet (Mg3Cr2Si3O12) was measured between 2 and 300 K, and thermochemical functions were derived from the results. The measured heat capacity curves show a sharp lambda-shaped anomaly peaking at around 5.1 K. Magnetic susceptibility data show that the transition is caused by antiferromagnetic ordering. From the C p data, we suggest a standard entropy (298.15 K) of 301 ± 2.5 J mol−1 K−1 for Mg3Cr2Si3O12. The new data are also used in conjunction with previous experimental results to constrain ∆H f ° for knorringite.

Studying different methods to determine the thermo kinetic constants in the adsorption of Pb2+ on an activated carbon from Bois carré seeds

Abstract: The effect of temperature on the adsorption of lead by an activated carbon from Bois carre seeds is investigated. The pseudo second order equation is applied to the kinetic data obtained at different temperatures in order to determine the adsorption rate constants at these temperatures. Then, the Arrhenius equation is applied to these rate constants to determine the activation energy of the sorption reaction and the pre-exponential factor. They are equal to 37 kJ mol −1 and 6.1 × 10 3 mol −1 kg s −1 , respectively. By applying the Eyring equation to the rate constants, the standard thermodynamic activation parameters of the sorption reaction can also be calculated. In addition, the isotherms of lead adsorption on the activated carbon from Bois carre seeds, at different temperatures, are determined and fitted by the Freundlich equation. The Niwas and the classical methods are applied to the equilibrium data obtained at these different temperatures in order to determine the equilibrium constants. Then, the Van’t Hoff equation is applied to the equilibrium constants in order to determine the standard enthalpy of the sorption reaction. The standard sorption enthalpy is also determined using a new method suggested by the authors, the value is equal to −53.2 kJ mol −1 . The other standard thermodynamic parameters (free standard enthalpy and standard entropy) are deduced. The thermodynamic study shows that rate sorption of the activated carbon from Bois carre seeds increases with the temperature contrarily to the quantity of lead sorbed at equilibrium.

Adsorption thermodynamic and desorption studies of U(VI) on modified silica gel (SiAPMS-HL)

Abstract: In this study, the adsorption process was examined by various isotherm models Langmuir, Freundlich and Dubinin–Radushkevich and equilibrium data were successfully described by Langmuir model. Adsorption thermodynamics of uranium (VI) on modified silica gel (SiAPMS-HL) has been studied within a temperature range from 293 to 333 K and the thermodynamic parameters, such as equilibrium constant (K D), standard free energy changes (ΔG°), standard enthalpy change (ΔH°) and standard entropy change (ΔS°), have been obtained. The desorption studies were conducted in batch system to investigate the kind, concentration and volume of the eluent.