A study of cetylpyridinium cation sorption on Na-vermiculite

The sorption of cetylpyridinium on Na-vermiculite has been studied by the adsorption, calorimetry, and X-ray diffraction methods. The ion-exchange component of cetylpyridinium sorption on Na-vermiculite has been distinguished and analyzed. Variations in the integral heat of ion exchange of cetylpyridinium cations on Na-vermiculite have been determined as depending on the amount of absorbed cetylpyridinium by the calorimetry method. X-ray diffraction analysis of cetylpyridinium-Na-vermiculite organomineral complexes with different contents of exchange cations has been carried out in parallel. The formation of monolayer (interlayer spacing Δd = 20.25 Å) and bilayer (Δd = 37.27 Å) intercalation structures with a tilt angle of cetylpyridinium ions to the silicate basal surface of ≈57° has been revealed.     

Radiochemical study of Co2+ sorption on chlorite and kaolinite

In this work, the sorption behavior of Co(II) ions on natural chlorite and kaolinite as a function of time, concentration and temperature was studied.⁶⁰Co radiotracer method and the batch technique were used. The kinetic results indicated that about one day of contact time was enough to achieve equilibrium. The sorption process was described by Freundlich type isotherms. Sorption of Co(II) ions on both clays was found to be endothermic with ΔH ⁰ (kJ/mol) and ΔS ⁰ (kJ/mol·K) being 33 and 0.14 for kaolinite and 17 and 0.102 for chlorite, respectively. The magnitudes of the corresponding ΔG ⁰ values suggest that sorption occur mainly via an ion exchange mechanism on both clays.     

Study of NaOH-treated clinoptilolites and their physical and ion-exchange characteristics with regard to Cs+ and Co2+

The ion-exchange ability of NaOH-treated clinoptilolites with regard to Cs⁺ and Co²⁺ have been studied by a radiochemical method, enabling to calculate the sorption coefficient. The surface characteristics, total cation exchange capacity and X-ray structural analysis were measured as well. The measurements were done on Slovak clinoptilolite. Comment are made on a possible explanation of increasing sorption coefficient.     

Thermodynamic parameters of Cs+ sorption on natural clays

Electrochemical properties of hexavalent and tetravalent uranium were investigated in various molten organic ionic mixtures. Kinetic parameters and reaction mechanisms were defined by voltammetry, chronoamperometry and sampled polarography. Long-term electrolyses in the mixture phenanthrene/TBABF4 allowed the preparation of both metallic uranium and crystallized uranium dioxide.     

Thermodynamic aspects of sorption of Fe2+ onto unbleached Kraft fibres

The sorption of Fe(2+) onto unbleached kraft fibre was investigated at different conditions such as pH, temperature, and concentrations. The sorption, which increased with concentration and temperature, followed the Langmuir isotherm. Thermodynamically, the process was spontaneous and endothermic. It was found that the precipitation of Fe(2+) was highly dependent on pH and reached 100% when pH exceeded approximately 8.     

Optical properties of a perfluorosulfonic membrane modified with Co2+ cations

A perfluorosulfonic membrane was modified with Co²⁺ cations. A comparative study of the thermal stabilities of the starting (hydrogen) and cobalt(II)-containing forms of the membrane was carried out. Optical electronic spectroscopy was used to characterize color transformations accompanying sorption-desorption of water by the modified membrane.     

DTG-DTA study of sewage sludge used in the sorption of Cd2+ and Co2+

The present study was carried out for evaluating the retention behavior of sanitary sewage in relation to cadmium and cobalt ions in an ascendant continuous-flow reactor. It was found that the studied sludge presented a high assimilation of the metals, probably due to the presence of anionic groups, which favors adsorption and complexation processes. Thermal analyses of the samples showed a shift in the thermal decomposition of the ‘in natura’ sludge, when compared with those of the samples spiked with the metals, confirming the possibility of interactions between the heavy metals and the anionic groups present in the sludge.     

UO 2 2+ sorption on bentonite

The capacity of bentonite and purified bentonite to remove UO ₂ ²⁺ ions from aqueous solutions has been investigated. The UO ₂ ²⁺ uptake in these clays was determined for 0.2 and 0.002M uranyl nitrate solutions. It was found that under these conditions (0.2M) the maximum UO ₂ ²⁺ uptake was 1.010±0.070 meq UO ₂ ²⁺ /g of bentonite and 0.787±0.020 meq UO ₂ ²⁺ /g of purified bentonite. In purified bentonite UO ₂ ²⁺ sorption is irreversible up to 50 hours as no desorption was observed. Such is not the case in the natural bentonite. X-ray diffraction, thermal analyses, and transmission electron microscopy were used to characterize the solids. The uranium content was determined by neutron activation analysis.     

Isotherm sorption of Cd2+, Co2+, and Ni2+ onto high-yield kraft fibers

The sorption capacity of high-yield kraft fibers for Cd2+, Co2+, and Ni2+ increased with pH and concentration of the cations in the liquid phase. Within the concentration range for the experiments, which was less than 2 mM, the experimental results fitted the Langmuir, Freundlich, and Sips models with regression coefficient greater than 0.97. Of the three cations investigated, Ni2+ had the highest sorption affinity, followed by Cd2+ and Co2+. The effect of the hydrated radius on the sorption affinity was discussed. Thermodynamically, the sorption was spontaneous and exothermic in the temperature range 283-308 K.     

Qualitative analysis of Cu2+, Co2+, and Ni2+ cations using thin-layer chromatography

The M(DEDTC)2 (M = Cu, Co, or Ni) and M(PyDTC)2 (M = Cu or Co) complexes prepared by reactions of sodium diethyldithiocarbamate and ammonium pyrollidinedithiocarbamate with metal (II) nitrates are examined for qualitative analysis and separation using thin-layer chromatography systems. These complexes and their mixtures are spotted to the activated thin layers of silica gel 60GF254 (Si-60GF254) with a 250-microm thickness. Pure toluene and a toluene-cyclohexane mixture (3:1, v/v) are used as mobile phases for running of the complexes. These chromatographic systems are successfully used for qualitative analysis of corresponding metal cations and separation of components in both M(DEDTC)2 and M(PyDTC)2 complex mixtures.     

Thermodynamic characteristics of the sorption of glycerol ethers on stationary phase OV-101

Retention characteristics, temperature dependences of the retention characteristics, and thermodynamic characteristics of sorption on the nonpolar OV-101 phase are determined for 33 glycerol mono-, di-, and triethers with linear and branched monobasic alcohols containing one to five carbon atoms in the temperature range of 100–180°C.     

Thermodynamic characteristics of sorption of heterocyclic compounds m capillary gas chromatography

Dependences of sorption energies of sulfur-, oxygen-, and nitrogen-containing heterocyclic compounds on the nature of heteroatoms, structure of substituents and their position in the ring were studied. The contributions of heteroatoms, functional and alkyl groups to the energy of dispersive interaction of position isomers with nonpolar stationary phases were determined for imidazoles, piperidines, morpholines, thiomorpholines, dioxalanes, oxathiolanes, dithiolanes, thiophenes, and furans. The nonequivalence of contributions of the same substituents to the sorption energy of each of the heterocyclic compounds, depending on the nature of the heteroatom and position of the substituent, was shown. The obtained values of contributions of heteroatoms and substituents can be used for apriori calculation of retention indices of position isomers of five- and six-membered heterocycles containing one or two heteroatoms in the ring.Translated from lzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 2033–2038, August, 1996.     

Monitoring 60Co activity for the characterization of the sorption process of Co2+ ions in municipal activated sludge

In large volumes produced activated sludges from wastewater treatment plants (WWTPs) with low concentrations of heavy metals can be utilized as agricultural fertilizers and soil conditioners. Increased contents of toxic xenobiotics are limiting factors that affect the utilization of these heterogeneous wastes. The main aim of our paper was to show the utilization of dried activated sludge (DAS) from municipal WWTP as potential Co²⁺ ions sorbent i.e. for non-agricultural purposes. The radio indicator method by radionuclide ⁶⁰Co and γ-spectrometry for characterization DAS sorption properties was used. DAS soluble and solid fractions were characterized by biochemical, ETAAS and CEC analysis. The sorption of Co²⁺ ions by DAS was rapid process and equilibrium was reached within 2 h. Sorption capacity of DAS (Q) increased with the initial concentration of CoCl₂ in the range from 100 to 4,000 μmol l^?1, reaching 20 and 160 μmol g^?1. Obtained Q values were depent on pH value from 2.0 to 8.0. The maximum sorption capacity (Q _max) of DAS at pH 6 calculated from mathematical model of Langmuir adsorption isotherm was 175 ± 9 μmol g^?1. FT-IR analyses showed the crucial role of carboxyl functional groups of DAS surfaces on cobalt uptake. For confirmation ion-exchange mechanism in sorption process of Co²⁺ ions by DAS scanning electron microscopy and EDX analysis were used.     

Thermodynamic study of complex formation between Ni2+ and Co2+ cations and 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix 5) in binary mixed nonaqueous solutions

Conductometric titrations were performed in pure and binary solvent solutions of ethyl acetate (EtOAc), methyl acetate (MeOAc) and methanol (MeOH) with acetonitrile (AN) at 288, 298, 308, and 318 K to determine the stoichiometry, the complex stability constants and the standard thermodynamic parameters for the complexation of nickel(II) and cobalt(II) cations with 1,13-bis(8-quinolyl)-1,4,7,10,13-pentaoxatridecane (kryptofix 5). The stability constants of the resulting 1:1 complexes formed between the metal cations and the ligand in different solvent mixtures were determined by computer fitting of the conductance-mole ratio data. The results revealed that the stability order of (kryptofix 5)-Ni²⁺ and (kryptofix 5)-Co²⁺ complexes changes with nature and composition of the solvent system. There is a non-linear relationship between the logK _f values of complexes and the mole fraction of acetonitrile in the mixed solvent system. In addition, the conductometric data show that the stoichiometry of the complexes formed between the nickel(II) and cobalt(II) cations with the acyclic ligand changes with the nature of the solvent. The enthalpy and entropy values for the 1: 1 [ML] complexation reactions were evaluated from the temperature dependence of the formation constants. Thermodynamically, in most of systems, the complexation processes of nickel(II) and cobalt(II) cations with kryptofix 5, are both enthalpy and entropy stabilized and the values of these parameters are influenced by the nature and composition of the binary mixed solvent solutions.     

Investigation of the sorption of water vapor on cation-substituted vermiculite. 2. Thermodynamic description of sorption equilibria

The changes in the thermodynamic functions of the sorbents were calculated for the first time from measurements of the deformations of vermiculite during the sorption of water vapor and adsorption-calorimetric data.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Institute of Colloid Chemistry and the Chemistry of Water, Academy of Sciences of the Ukraine, 252180 Kiev. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 6, pp. 1270–1275, June, 1992.     

Theoretical sstudy on the Co2+OH2+/Co3+OH2+ electron transfer reactivity

This paper presents a contact distance dependence analysis scheme and an abinitio calculation application for the electron transfer (ET) reactivity of Co²⁺OH₂/Co³⁺OH² reacting pair. The applicability of these schemes and the corresponding models has been discussed. The contact distance (R _CoCo) dependence of the relevant quantities has been analyzed. The results indicate that the activation energy from the accurate PES method agrees well with that from the anharmonic potential method, and they are obviously better than that from the harmonic potential method. The pair distribution function varies from 10^?2 to 10^?5 along withR _CoCo changing from 1.20 to 0.35 nm. The coupling matrix element exponentially decays along with the increase ofR _CoCo, and the effective electronic coupling requiresR _CoCo smaller than 0.75 nm. In the range from 0.50 to 0.75 nm forR _CoCo, the corresponding electronic transmission coefficient falls within 1.0—10^?6. The local ET rate also exponentially decays along with the increase ofR _CoCo due to the electronic factor. Since the contribution from the pair distribution function to the total ET rate is an inverse measure of that from the electronic factor, the variation of the spherically averaged local ET rate along withR _CoCo exhibits a parabola with a maximum at 0.50 nm ofR _CoCo. This maximum is close to the overall observed ET rate value. For this mono-hydrated transition metal ionic system, the ET rate generally is about 10⁶ L·mol^?1·s^?1 in gaseous process. Further, since it is impossible to experimentally determine the structures and their PESs of these hydrated systems, especially for the unstable intermediate species,ab initio calculations can play an effective auxiliary role in discussing the ET reactivities of these kinds of reacting systems.     

Identification of selective ion-exchange resin for fluoride sorption

The defluoridation capacity (DC) of a chelating resin, namely Indion FR 10 (IND), and Ceralite IRA 400 (CER), an anion-exchange resin, were compared under various equilibrating conditions for the identification of selective sorbent. The results showed that chelating resin is more selective than an anion-exchange resin for fluoride removal. The fluoride sorption was reasonably explained using Freundlich and Langmuir isotherms. The surface morphology of resins before and after fluoride sorption was observed using scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) was used for the determination of functional groups responsible for fluoride sorption. Various thermodynamic parameters such as DeltaG0, DeltaH0, DeltaS0, and Ea have been calculated to understand the nature of sorption. The sorption kinetic mechanism was studied with reaction-based and diffusion-based models. The sorption process was found to be controlled by pseudo-second-order and particle diffusion models. The performance of the resins studied has been tested with field samples collected from a fluoride-endemic area.     

Nitrogen heteroaromatic cations by [2+2+2] cycloaddition

A modular approach to the construction of monocationic quaternary N-heteroaromatic frameworks was developed capitalizing on a direct pyridine-type nitrogen quaternization followed by metal-catalyzed [2+2+2] cycloaddition with gaseous acetylene. The flexibility of the route is demonstrated on 12 diverse scaffolds based on pyridinium, quinolinium, thiazolium, benzothiazolium, imidazolium, and pyrimidinium. Electrochemical study revealed a quinolinium redox system with two electrochemically distinct forms that are interconverted by a homogeneous chemical reaction triggered by fast electron transfers (reduction at -0.7 V and oxidation at -0.05 V).