Study on complexation adsorption behavior of dibenzo-18-crown-6 immobilized on CPVA microspheres for metal ions

Dibenzo-18-crown-6 (DBC) was immobilized on crosslinked polyvinyl alcohol (CPVA) microspheres, resulting in polymer-supported crown ether DBC–CPVA. The complexation adsorption behaviors of DBC–CPVA microspheres towards diverse metal ions were investigated. The experimental results show that among alkali metal ions, the complexation adsorption ability of DBC–CPVA for K⁺ ion is the strongest, and crown ether-metal complex in 1:1 ratio is formed, exhibiting a high adsorption capacity. The adsorption capacities of alkali metal ions on DBC–CPVA are in the order: K⁺ ? Na⁺ > LI⁺ > Rb⁺ > Cs⁺. Among several divalent metal ions, DBC–CPVA exhibits stronger adsorption ability towards Zn²⁺ and Co²⁺ ions, and a “sandwich”-type complex is formed probably in a molar ratio of 2:1 between the immobilized DBC and Zn²⁺ ion as well as between the immobilized DBC and Co²⁺ ion. The adsorption capacities of the several divalent metal ions on DBC–CPVA are in the order: Zn²⁺ > Co²⁺ ? Cd²⁺ > Cu²⁺ > Ni²⁺ > Pb²⁺. The complexation adsorption is exothermic physical physisorption process, and raising temperature leads to the decrease of the adsorption capacity. At the same time, the entropy during the complexation adsorption decreases, so the adsorption process is driven by the decrease of enthalpy.     

Material Balance Study of Adsorption of Organic Compounds

It was shown that the structure of a surface complex and the nature of an adsorption bond can be determined from the material balance of adsorption of H⁺and OH^–ions and organic compound. A calculation procedure was considered using adsorption of benzoic acid on silica gel and zirconia as examples. It was established that adsorption of benzoic acid on silica gel was accompanied by the release of H⁺ions resulted from the formation of surface hydrogen bonds, whereas adsorption on zirconia, by the substitution of OH^–ions in coordination sphere of Zr(IV).     

Specific adsorption of anions preceding the dissolution of CuO in acidic solution

The specific adsorption of sulfate and chloride ions on powdered CuO was studied by radiotracer techniques in acidified of 0.5 mol dm^–3 NaClO₄ supporting electrolyte. It was found that the pH and concentration dependence of the adsorption of labelled sulfates could be determined over a wide pH range (2.0≤pH≤7.0), despite the gradual dissolution of the copper oxide. No specific adsorption was found at pH≥7.0. It was postulated that the specific adsorption was preceded by the protonation of the CuO surface. No reliable relationships were found for labelled chlorides, owing to the relatively high desorption rate of the surface complexes formed in the sorption process. The apparent adsorbability of sulfate ions was significantly higher than that of the chloride ions, as shown by the results of competitive adsorption of the two species. This observation was in agreement with the postulated lower desorption rate of the surface complex formed with sulfates than that of species formed with chlorides. Electronic Publication     

Study on the sensitive and selective adsorption voltammetry of vanadium with antipyrylazo III (APA III)

The sensitive and selective adsorption voltammetric determination of the vanadium(V)-antipyrylazoIII complex in HAc-NaAc solution is investigated. The V-complex is strongly adsorbed onto a stationary Hg-electrode and is reduced at a potential more negative than that corresponding to the reduction of its ligand. The conditions for determining vanadium are investigated and the mechanism of the reduction peak of the vanadium complex is discussed, as also the influence of foreign ions on the determination of vanadium. An at least 20-fold excess of foreign ions does not cause any interference. The detection limit is 4×10^–10 mol/l V with 3 min enrichment time.     

Specific Features of Glucoamylase Immobilization by Adsorption on Fibrous Polyelectrolytes

Some fundamental aspects of the immobilization of a hydrolytic enzyme glucoamylase via adsorption on aminocarboxylic ion-exchangers with fibrous structure were considered. The sorption capacity of amphoteric supports for the enzyme was studied in relation to the time of immobilization, concentration of hydrogen ions and the protein, and the ionic form of a polyelectrolyte. The catalytic properties of free and immobilized enzymes were compared.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005, pp. 1003–1005.Original Russian Text Copyright © 2005 by Shkutina, Stoyanova, Selemenev.     

Structure and Electrosurface Properties of Porous Glasses with Different Compositions in KCl and NaCl Solutions

For porous glasses with and without small amounts of fluorine and phosphorus, structural (specific surface area, structure resistance coefficient, and mean pore radius) and electrosurface characteristics (adsorption of potential-determining ions, conductivity, counterion transport numbers, and electrokinetic potential) in sodium and potassium chloride solutions are compared. Results of measuring the equilibrium and transport characteristics of membranes are used to calculate the constants of surface reactions and adsorption potentials of ions within the framework of the 2-pK model of oxide surface charging. Within the framework of the homogeneous model, electrochemical characteristics of porous glasses, namely, concentrations of co- and counterions in a pore-confined liquid, Donnan potentials, convective component of the conductivity of a pore-confined solution, and mobility of counterions in the membranes, are calculated.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 3, 2005, pp. 342–351.Original Russian Text Copyright © 2005 by Ermakova, Medvedeva, Volkova, Sidorova, Antropova.     

A quantum mechanics/molecular mechanics (QM/MM) investigation on the mechanism of adsorptive removal of heavy metal ions by lignin: single and competitive ion adsorption

In this paper, an adsorption removal mechanism of heavy metal ions (Pb, Cu, Cd, Zn, and Ni) by lignin is investigated by molecular and quantum chemical modeling. First, the lowest energy sites of lignin for heavy metal ions were investigated using a Metropolis Monte Carlo search and simulated annealing. Then, equilibrium adsorption capacities of lignin for heavy metal ions were calculated with conductor-like screening models with a segmented activity coefficients, together with generalized gradient approximation and Volsko–Wilk–Nusair density functional functional theory. These calculations followed the local pseudo-thermodynamic equilibrium at the interface of lignin and ion-containing effluent. Several kinetic Monte Carlo simulations were performed to analyze the surface kinetics of ion adsorption. The affinity of lignin for metal ions follows the order: Pb > Cu > Cd > Zn > Ni which is in agreement with experimental observations. The stability of ions follows the order: Pb > Cd > Zn > Ni > Cu, indicating that the adsorption affinity does not demand the same order of stability on ions. In addition, it was found that while the adsorption of heavy metal ions on the lignin is accessible, the adsorbed heavy metal ions, however, are less stable than the adsorbed water molecules. As such, the used lignin must be replaced by fresh lignin in a cyclic manner. While lignin provides desirable adsorption performance for single ion removal, it failed in processing of practical heavy metal ion solutions expected in environmental issues.     

Green,ultrafine cellulose-based porous nanofibrous membranes for efficient heavy metal removal through incorporation of chitosan by various electrospinning ways

Rapid global industrialization has worsened the heavy metal contamination of aquatic ecosystems globally. In this study, green, ultrafine cellulose-based porous nanofibrous membranes for efficient heavy metal removal were obtained by incorporating chitosan (CS) and using conventional and core–shell electrospinning ways. The relationship between the parameters of the electrospinning solution, the micro-morphology and porosity, the chemically active sites, the thermal stability, and the adsorption performance of the biocomposite nanofibrous membranes were analyzed. The adsorption effects of the copper ions, including the initial concentration, solution pH, and interaction time, were investigated. The results show that the average diameters of the conventional and core–shell ultrafine nanofibers with 50% and 30% CS loading are 56.22 nm and 37.28 nm, respectively. The core–shell cellulose acetate (CA)/CS biocomposite nanofibrous membranes showed the weaker thermal stability with a 48.2 °C lower maximum thermal decomposition temperature and induced the surface aggregation of more copper ions compared to the conventional one. A more uniform distribution of the chemical adsorption sites is obtained by conventional single-nozzle electrospinning than by core–shell electrospinning, which effectively promotes the adsorption performance of copper ions and decreases the surface shrinkage of the nanofibrous membranes during adsorption. The 30% CS conventional nanofibrous membranes at an aqueous solution pH of 5 showed the optimum adsorption capacity of copper ions (86.4 mg/g). The smart combination of renewable biomass with effective chemical adsorption sites, electrospinning technology that produces an interwoven porous structure, and an adsorption method with low cost and facile operation shows a promising prospect for water treatment.

     

A Radiochemical Study of Reactions of Diethylsilylium Ions with Trimethyl(<Emphasis Type="Italic">tert</Emphasis>-butylamino)silane in Gas and Liquid Phases

The reaction of diethylsilylium ions with trimethyl(tert-butylamino)silane in gas and liquid phases was studied radiochemically. In contrast to the reactions of carbocations with amines, with diethylsilylium ions the proton transfer channel is not realized at all. As in the reactions of diethylsilylium ions with benzene, alcohols, and ethers, the reaction with the aminosilane is accompanied by rearrangement of the silylium ion. Formation of the condensation complex with trimethyl(tert-butylamino)silane is complicated by both its geometry and electron density distribution, despite the fact that formation of the condensation complex in this case is more exothermic than with the nucleophiles studied previously (benzene, alcohol, ether).__________Translated from Zhurnal Obshchei Khimii, Vol. 75, No. 1, 2005, pp. 77–81.Original Russian Text Copyright © 2005 by Kochina, Vrazhnov, Sinotova, Ignat’ev.     

A study of the factors affecting the adsorption of cobalt ions onto Pakistani coal powder from solutions

Large deposits of coal are abundantly available in Pakistan. An attempt has been made to check its efficacy for the cobalt ions from aqueous solutions in order to exploit the locally available naturally occurring cheaper material for the decontamination/removal of metal ions from nuclear and industrial effluents. The adsorption behavior of cobalt ions on coal powder has been studied as a function of various physicochemical parameters i.e., stirring speed, shaking time, pH, concentration of cobalt ions, temperature, etc. Conditions for the uptake of cobalt ions were established. Adsorption dynamics models such as intra-particle diffusion model, pseudo-first order kinetic model (Lagergren’s equation) and pseudo-second order kinetic model were applied to the adsorption data to elucidate the adsorption process and its mechanism. Results reveal that the adsorption mechanism is predominantly diffusion and both intra-particle and boundary layer diffusion seem significant in the rate controlling step. The adsorption process is best accounted for using pseudo second order kinetic model and the overall rate of adsorption process appears to be controlled by more than one step, namely the external mass transfer and intra-particle diffusion mechanism. The existence of two slopes in the Freundlich plot also confirms the surface diffusion and intra-particle diffusion modes of adsorption. The Langmuir isotherm equation was obeyed well in the whole range of cobalt ions concentration with high value of correlation coefficient (r ²  = 0.999). The adsorption energy (E _a) calculated from D–R isotherm was 6.756 kJ/mol indicating physical nature of adsorption. The adsorption of cobalt ions increased with the increase of temperature and thermodynamic parameters such as ΔH, ΔS and ΔG were calculated. Results suggested that the cobalt ions adsorption on coal powder is endothermic (ΔH 33.90 kJ/mol) and spontaneous (negative ΔG values) process. The adsorption of other metal ions on coal powder was studied at optimized condition for cobalt ions to check its selectivity. Consequently, cobalt ions can be removed from Zr, Ru Eu, Er, Sm, Gd, Dy, Ce, U, and Th ions, where as Cs, Cr and Sr ions reduces the adsorption of cobalt ions by co-adsorption and their reducing affect is in the order of Sr > Cr > Cs.     

Role of the diffuse layer of the ionic charge on the impedance spectroscopy of a cell of liquid

We investigate the role of the diffuse layer of the ionic cloud on impedance spectroscopy measurements. The analysis is performed assuming that the ions have equal mobility, the electrodes are perfectly blocking and adsorption phenomenon can be neglected. We find that the dielectric permittivity, in the limit of high frequency ω, tends to the dielectric permittivity of the pure liquid as ω^-3/2. The relationship between the detected equivalent permittivity and conductivity of the cell with the real and imaginary part of the complex dielectric constant is discussed. We show also that the presence of the ions is responsible for a distribution of relaxation times. An application to nematic liquid crystals is presented.     

The sorption of uranyl ions on silica-titania mixed-hydroxide gels

SiO₂–TiO₂ mixed hydroxide gels were prepared and the apparent adsorption capacity for Na⁺ (1.30–1.60 mmol/g dry sample) determined by pH titration. The effect of solution pH on the sorption ability of the binary gels was studied. It is found that: (1) the sorption mechanism depends upon the pH, and the two most important factors are the nature of both counter ions in bulk solution and the surface of silica-titania gels, (2) the best pH range for the sorption of uranyl ions is 4–7. The thermodynamic functions were evaluated, suggesting that the reaction is chiefly attributed to physical adsorption rather than chemical one, and the opposite is the case of the reaction.     

钇(III)离子印迹聚合物的制备及性能研究

以钇(III)离子作为模板, 以4-乙烯吡啶(4-VP)、乙酰丙酮(Hacac)和钇(III)形成的三元配合物为功能单体、乙二醇二甲基丙烯酸酯(EDMA)为交联剂, 采用本体聚合法合成了钇(III)离子配位分子印迹聚合物. 系统研究了印迹聚合物对钇(III)离子的吸附性和选择性. 结果表明, 印迹聚合物对钇(III)离子有很好的亲和性, 达到吸附平衡的时间为60 min, 最大吸附量为12.4 mg&#8226;g&#8722;1, 重复使用时性能稳定, 而且印迹聚合物对钇(III)离子具有较强的选择性识别能力.     

Investigation of ion adsorption on silver sulfide,iodide and bromide precipitates by the radioactive tracer technique

The radioactive tracer method was used to investigate the adsorption of iodide and europium ions from aqueous solution on dried isoelectric precipitates of silver sulfide, silver iodide and silver bromide. The relationship between the amount of iodide ions adsorbed on Ag₂S and the iodide ion and HNO₃ concentrations in the solution was determined. It was shown that the iodide ions adsorbed on Ag₂S could be desorbed with sulfide ions. Using Ag₂S, AgI and AgBr precipitates, a relationship between the europium ion adsorption and Eu(NO₃)₃, H₂S, NaI, NaBr and NaCl concentration in solution was established. The adsorption of europium ions was also assessed in respect to the presence of lanthanum and barium ions. For adsorption measurement iodide and europium ions were labeled with their radioactive isotopes and the amounts adsorbed were determined from the measured radioactivities of the precipitates after reaching the equilibrium between the solid phase and the solution.     

Laterite clay-based geopolymer as a potential adsorbent for the heavy metals removal from aqueous solutions

This study is focused on the investigation of low iron lateritic clay-based geopolymer as a potential adsorbent for the higher uptake of Ni(II) and Co(II) ions from aqueous solutions. BET analysis revealed that the sieved geopolymer sample (SGS) was characterized by 17.441 m²/g of surface area, 0.005 cm³/g of pore volume, and 13.549 Å of pore diameter. SEM investigation confirmed the presence of pores and cavities onto the surface of SGS. XRD analysis showed that the geopolymer is semi-crystalline in nature. It was found that the adsorption ability of SGS remained 520 mg/g for Ni(II) ions and 500 mg/g for Co(II) ions when 0.5 M solutions were stirred with SGS for 60 min. The temperature and pH of the solution were maintained at 60 °C and 7.0, respectively. The adsorption data of both heavy metal (HM) ions fitted best in the pseudo-second-order kinetic model. The low activation energy value i.e. 2.507 kJ/mol for Ni(II) ions and 2.286 kJ/mol for Co(II) ions confirmed adsorption is physisorption. Adsorption data were tested with Langmuir and Freundlich models, the data showed comparatively better fitting in the Freundlich model. The greater value of monolayer adsorption capacity (Xm) for Ni(II) ions was found 1.77 × 10⁻² mol/g while for Co(II) ions it remained 1.69 × 10⁻² mol/g confirming the better interaction of metal ions with the adsorbent surface. Negative values of ΔG° confirmed the spontaneity of the process while the positive value of ΔS° showed the randomness of adsorbate particles. The positive value of ΔH° showed that the adsorption process remained endothermic for both HM ions. The experimental results confirmed the ability of laterite clay-based geopolymer for better removal of HM ions and hence can be employed for the wastewater treatment processes at low-cost adsorbent.     

To Interpretation of the EPR Parameters of Nitrosyl Complexes of Transition Metal Ions

Interpretation of the EPR parameters of low-spin nitrosyl complexes of d ⁵ transition metal ions was illustrated with a pentacyanonitrosyl complex of Cr⁺. The bond covalence in the antibonding and bonding states of this complex was determined from EPR and optical spectroscopic data. The reasons for the observed abnormal value of the Zeeman splitting parameter were analyzed. The contributions to the components of the A and HFC tensors at the N atom of the nitrosyl group were calculated.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 6, 2005, pp. 423–426.Original Russian Text Copyright © 2005 by Murav’ev.     

Coupled radiotracer and voltammetric study of the adsorption of 1-hydroxy-ethane-1,1-diphosphonic acid on polycrystalline gold

Coupled application of a version of the in-situ radiotracer ‘foil’ method and voltammetry provided information on the time-, potential-, concentration- and pH-dependent adsorption of 1-hydroxy-ethane-1,1-diphosphonic acid (HEDP) on a polycrystalline gold electrode, and on the effect of Zn²⁺ ions on the adsorption phenomena. Adsorption processes on the oxide-free surface of gold were observed to be potential-dependent in the potential range 0.05–1.00 V (versus RHE), while formation and irreversible accumulation of oxidation products of HEDP could be detected at E>1.00 V. The relative adsorption strength of HEDP (its dissociation and/or oxidation products) was found to be higher on an oxide-free gold surface than on an oxide-covered one. The surface excess of HEDP increased with increasing pH. Addition of Zn²⁺ ions to the solution exerted a substantial effect on the HEDP accumulation. Namely, significant differences in the surface coverage, as well as in the kinetics and mechanism of HEDP adsorption could be detected in the potential regions below and above E=0.2 V. Reduction of Zn(II) species at E≤0.1 V is probably coupled with the induced adsorption of HEDP on an Au electrode, leading to the formation of a polymolecular HEDP–Zn surface complex layer.     

Ion-exchange studies of <Superscript>110m</Superscript>Ag(I) using synthetic inorganic ion-exchanger

In the present investigation, the selective adsorption of silver on synthetic inorganic ion exchanger, zinc(II) ferrocyanide, has been established by batch method, under specific conditions, using ^110mAg as a tracer. The efficiency of adsorption has been determined by γ-ray spectrometry and was found to be greater than 96%. The Ag(I) uptake by the exchanger has also been evaluated. The selectivity of the method was checked by studying the adsorption of Ag(I) in the presence of a number of foreign ions using their corresponding tracers. The interfering ions were removed by washing the ion-exchanger with appropriate reagents, so that it could be applied for the determination of trace amount of Ag(I) in complex matrices, containing trace amount of other metal ions.     

The effect of solvent nature on the adsorption interaction between cinnamic acid and silicon dioxide

It is established that the adsorbability of cinnamic acid from solutions on the surface of highly dispersed silica decreases with an increase in the polarity and electron-donor ability of a solvent. The adsorption process is considerably affected by the hydrophobization of the surface. The adsorption curve passes through a maximum when methyl groups are substituted for 40–55% of the total number of hydroxyls on the silica surface. Probable structures of adsorption complexes are suggested.__________Translated from Kolloidnyi Zhurnal, Vol. 67, No. 2, 2005, pp. 201–205.Original Russian Text Copyright © 2005 by Pogorelyi, Barvinchenko, Pakhlov, Smirnova.     

Adsorption of the fluoride ion on the surface of various faces of a single crystal of silver: a quantum-chemical study

The fluoride ion adsorption from a gas phase on various faces of a single crystal of silver is studied by a density functional method within a cluster model for metal. The adsorption bond energy is found to increase in the series Ag(100) < Ag(111) < Ag(311) < Ag(110). A substantial structural and energetic heterogeneity of various adsorption sites is revealed. The results are utilized to simulate the electrochemical interface between individual faces of a single crystal of silver and aqueous solutions containing the fluoride ion. It is assumed that the adsorption potential may be represented as the sum of two contributions, one of which describes the metal–ion interaction and the other, the ion solvation energy. The plotted adsorption terms take into account partial degradation of the fluoride ion when adsorbed from an aqueous solution. Estimates of discreteness of the electrical double layer are presented. A conclusion on the maximum manifestation of specific adsorption of the fluoride ion for the Ag(100) face is made.Translated from Elektrokhimiya, Vol. 41, No. 2, 2005, pp. 232–238.Original Russian Text Copyright © 2005 by Nazmutdinov, Zinkicheva.This revised version was published online in April 2005 with corrections to the article note and article title and cover date.