Search Results
Abstract
A novel solid complex, formulated as Ho(PDC)3 (o-phen), has been obtained from the reaction of hydrate holmium chloride, ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phenH2O) in absolute ethanol, which was characterized by elemental analysis, TG-DTG and IR spectrum. The enthalpy change of the reaction of complex formation from a solution of the reagents, Δr H m θ (sol), and the molar heat capacity of the complex, c m, were determined as being –19.1610.051 kJ mol–1 and 79.2641.218 J mol–1 K–1 at 298.15 K by using an RD-496 III heat conduction microcalorimeter. The enthalpy change of complex formation from the reaction of the reagents in the solid phase, Δr H m θ(s), was calculated as being (23.9810.339) kJ mol–1 on the basis of an appropriate thermochemical cycle and other auxiliary thermodynamic data. The thermodynamics of reaction of formation of the complex was investigated by the reaction in solution at the temperature range of 292.15–301.15 K. The constant-volume combustion energy of the complex, Δc U, was determined as being –16788.467.74 kJ mol–1 by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δc H m θ, and standard enthalpy of formation, Δf H m θ, were calculated to be –16803.957.74 and –1115.428.94 kJ mol–1, respectively.
Abstract
Sorption of Th(IV) on Zr2O(PO4)2 as a function of contact time, reaction temperature, pH, ionic strength and solid-to-liquid ratio (m/V) is studied under ambient condition by using batch technique. Effects of fulvic acid (FA), phosphate, sulfate and citrate on Th(IV) sorption are investigated in detail. A pseudo-second-order rate equation is used to simulate the kinetic sorption. The removal of Th(IV) increases with increasing pH and hardly depends on ionic strength. Sorption of Th(IV) increases with increasing m/V and reaction temperature. The presence of FA and phosphate enhances the sorption of Th(IV) on Zr2O(PO4)2 while sulfate and citrate decrease the sorption. The Langmuir and Freundlich models are used to simulate the sorption isotherm of Th(IV) on Zr2O(PO4)2 at different temperatures. The thermodynamic data (i.e., ∆H 0, ∆S 0, ∆G 0) are calculated from temperature dependent sorption isotherms. The results suggest that the sorption process of Th(IV) on Zr2O(PO4)2 is spontaneous and endothermic.
Abstract
This work contributed to the adsorption of radiocobalt on goethite as a function of contact time, pH, ionic strength and foreign ions in the absence and presence of fulvic acid (FA) under ambient conditions. The results indicated that adsorption of Co(II) was dependent on ionic strength and foreign ions at low pH values (pH < 7.8), and independent of ionic strength and foreign ions at high pH values (pH > 7.8). Outer-sphere surface complexation and/or ion exchange were the main mechanisms of Co(II) adsorption on goethite at low pH values, whereas inner-sphere surface complexation was the main adsorption mechanism at high pH values. The presence of FA enhanced Co(II) adsorption at low pH values, but reduced Co(II) adsorption at high pH values. The thermodynamic data (ΔH 0, ΔS 0, ΔG 0) were calculated from the temperature dependent adsorption isotherms, and the results suggested that adsorption process of Co(II) on goethite was spontaneous and endothermic. The results are crucial to understand the physicochemical behavior of Co(II) in the nature environment.
Inorganic particulates in removal of toxic heavy metal ions
Part X: Removal behavior of aluminum hydroxide for Hg(II): A radiotracer study
Abstract
The removal behavior of amorphous aluminum hydroxide for Hg(II) ions from aqueous solutions was investigated by employing a radiotracer technique at micro down to trace level concentrations. The batch type experiments were performed to obtain various physico-chemical parameters, viz., effect of sorptive concentration, temperature and pH. It was observed that the increase in sorptive concentration (from 1·10−8 to 1·10−2 mol·dm−3), temperature (from 303 to 333K) and pH (from 3.4 to 10.3) apparently favored the uptake of Hg(II) by this solid. Similarly, the presence of anions (six fold) viz., oxalate, phosphate, glycine and EDTA also enhanced the uptake behavior of aluminum hydroxide for Hg(II). Whereas, the added cations viz., Na+, K+, Ba2+, Sr2+, Mg2+, Cd2+ and Fe3+ more or less suppressed the removal behavior of the adsorbent. Further, the adsorption process followed the classical Freundlich adsorption isotherm and deductions of various thermodynamic data revealed that the uptake of Hg(II) on aluminum hydroxide followed the ion-exchange type mechanism and thermodynamically it was found to be endothermic in nature.
Low-temperature heat capacities and standard molar enthalpy of formation of the complex
Zn(Val)SO4·H2O(s) (Val=L-α-valine)
Abstract
Low-temperature heat capacities of a solid complex Zn(Val)SO4·H2O(s) were measured by a precision automated adiabatic calorimeter over the temperature range between 78 and 373 K. The initial dehydration temperature of the coordination compound was determined to be, T D=327.05 K, by analysis of the heat-capacity curve. The experimental values of molar heat capacities were fitted to a polynomial equation of heat capacities (C p,m) with the reduced temperatures (x), [x=f (T)], by least square method. The polynomial fitted values of the molar heat capacities and fundamental thermodynamic functions of the complex relative to the standard reference temperature 298.15 K were given with the interval of 5 K.
Enthalpies of dissolution of the [ZnSO4·7H2O(s)+Val(s)] (Δsol H m,l 0) and the Zn(Val)SO4·H2O(s) (Δsol H m,2 0) in 100.00 mL of 2 mol dm−3 HCl(aq) at T=298.15 K were determined to be, Δsol H m,l 0=(94.588±0.025) kJ mol−1 and Δsol H m,2 0=–(46.118±0.055) kJ mol−1, by means of a homemade isoperibol solution–reaction calorimeter. The standard molar enthalpy of formation of the compound was determined as: Δf H m 0 (Zn(Val)SO4·H2O(s), 298.15 K)=–(1850.97±1.92) kJ mol−1, from the enthalpies of dissolution and other auxiliary thermodynamic data through a Hess thermochemical cycle. Furthermore, the reliability of the Hess thermochemical cycle was verified by comparing UV/Vis spectra and the refractive indexes of solution A (from dissolution of the [ZnSO4·7H2O(s)+Val(s)] mixture in 2 mol dm−3 hydrochloric acid) and solution A’ (from dissolution of the complex Zn(Val)SO4·H2O(s) in 2 mol dm−3 hydrochloric acid).
Abstract
Uranium oxides are known as nonstoichiometric compounds whose composition changes according to external conditions such as temperature and oxygen partial pressure. The change of composition caused by the formation of defect structure results in a change of their properties. In this paper, the compositional changes of UO2 and doped UO2 [(U, M)O2; M=La, Ti, Pu, Th, Nb, Cr, etc.] and also those of other uranium oxides (U4O9, U3O8) are shown against oxygen partial pressure. From the results of doped UO2, it is concluded that the valence control rule holds to a first approximation. The defect structures are estimated both from log x vs. log Po2 (x: deviation from the stoichiometric composition and Po2: oxygen partial pressure) and log 
vs. log Po2 (: electrical conductivity) relations. The defect structures of UO2 and doped UO2 are derived based on the Willis model for UO2+x. The detect structure of U4O9 phase is similar to that of UO2+x, but the defect structures of U3O8 phase are complicated due to the existence of many higher-order phase transitions. The thermodynamic data such as the partial molar enthalpy and entropy and the heat capacity are important to characterize the defect structure. The high temperature heat capacities of UO2 doped with Gd show pronounced increases at high temperatures the onset temperature decreases as the dopant content increases. The increase of heat capacity is interpreted to be due to the formation of lattice defects. The heat capacity measurements on U4O9 and U3O8 clucidate the presence of the phase transition. The mechanisms of these phase transitions are discussed.
Prostaglandins are biological lipid mediators that control a variety of physiological and pathophysiological processes. They function as locally acting hormones and are continuously synthesized and inactivated in target tissues by respective biosynthetic and metabolic enzymes. The separation of prostaglandins and their metabolites is crucial for study of their roles in biological systems. In this article, we describe systematic studies of the retention and separation of prostaglandin E 2 (PGE 2 ) from its inactive metabolites 15-keto-PGE 2 and 13,14-dihydro-15-keto-PGE 2 . We also describe the separation of a second prostaglandin species, PGF 2α , from its metabolites 15-keto-PGF 2α and 13,14-dihydro-15-keto-PGF 2α . Chromatography was performed on RP-18W high-performance thin-layer chromatographic plates with binary mobile phases comprising water and an organic modifier (methanol, ethanol, acetonitrile, acetone, or tetrahydrofuran). The experimental data revealed that at constant temperature, plots of the retention, R M , of the prostaglandins against the mole fraction of organic modifier in the water ( X S ) were nonlinear. By use of mobile phases of similar eluent strength the effect of temperature on the retention and separation of the solutes was examined. Thermodynamic data, calculated from linear Van’t Hoff plots, indicated that the mechanism of retention for each prostaglandin compound was consistent for the different mobile phases. The separation of PGE 2 and PGF 2α from each other and from their respective metabolites was rapid and robust in acetonitrile and in acetonitrile-water mobile phases. Interestingly, with 100% acetonitrile as the mobile phase the reversed-phase system apparently performed as a normal-phase system. The chromatographic system described here is applicable to the rapid processing of a large number of samples, which is a requirement for determining the biological metabolism of PGE 2 and PGF 2α and for studying the kinetics of prostaglandin-inactivating enzymes. The system is also suitable for the prepurification of complex biological samples for subsequent quantification of individual prostaglandins.
Abstract
The injection moulding of semi-crystalline thermoplastic polymers requires an exact knowledge of the thermodynamic data and of the crystallization kinetics. The behaviour of the polymer melt during rapid cooling in the mould determines, to a great extent, the quality and usability of a final product. Technical raw materials are often equipped with nucleating agents in order to obtain crystallization within the desired temperature range and at the required rate. The use of recycled material (regranulate) shows an analogous effect such as the addition of nucleating agents, i.e. crystallization begins at a higher temperature and a higher crystallization rate is detected compared to materials without added regranulate. Heat flux DSC was used to study the crystallization of polyamides, polyolefins and polyoxymethylene during cooling at various cooling rates. Although the temperature gradients and pressures which occur in the proceesing machine cannot be realised in DSC tests, the DSC results reproduce the direction of influence of the regranulate additive very clearly.
-consistent thermodynamic data for minerals in the system Na2OK2O-Berman, R.G. 1988: Internally-consistent thermodynamic data for minerals in the system Na2OK2O-CaO-MgO-FeO-Fe2O3-Al2O3-TiO2-H2O-CO2. J. Petrol. , 29 , pp. 445-522. Internally
) Table 1 Maximum number of moles adsorbed, N s , equilibrium constant, K and thermodynamic data, Δ H , Δ G , and ΔS for interaction between divalent cations and SiHa
