Iodide adsorption on the surface of chemically pretreated clinoptilolite

The possibility to use the monoionic Ag⁺-form (eventually Hg⁺- and Hg²⁺- forms) of clinoptilolite of domestic origin for radioactive iodide elimination from waters has been studied. The capacity of the monoforms of clinoptilolite towards iodide exceeds many times that of the capacity of clinoptilolite in natural form. Due to the low solubility product of AgI, Hg₂I₂ and HgI₂ iodides generate precipitates on the zeolite surface. Rtg analyses of the silver form of clinoptilolite after sorption of iodide demonstrate the formation of new crystals on the zeolite surface. The influence of interfering anions on the adsorption capacity of silver clinoptilolite towards iodide was investigated, too. Kinetic curves of iodide desorption from the surface of silver and mercury clinoptilolite were compared. Simultaneously, adsorption isotherms for the systems aqueous iodide solution/Ag^–, Hg-clinoptilolite were determined.     

Adsorption of51Cr(VI) on manganese dioxide from aqueous solution

Sorption of⁵¹Cr(VI) by MnO₂ has been studied as a function of pH and ionic concentration in the presence of certain added cations and anions. The findings are explained in the light of deprotonation/hydroxyl ion association reaction on oxide surface and its subsequent interaction with the tracer. Infrared spectroscopy has shown the chemical interaction of Cr(VI) on the surface of MnO₂. The influence of certain interfering ions has been shown on the sorption of⁵¹Cr(VI) on MnO₂ surface. An attempt has been made to concentrate traces of⁵¹Cr under optimum experimental conditions. The experimental observation shows that the activity sorbed under specified conditions can be recovered appreciably by leaching the pre-adsorbed carrier.     

Gold sorption on weak base anion exchangers with aminoguanidyl groups

Two resins with different matrices, both bearing aminoguanidyl ligands, were obtained and used for gold sorption from hydrochloric acidic and from alkali solutions. Resin 1 was a aminoguanidine derivative of poly(acrylonitril-co-vinyl acetat-co-divinyl benzene) terpolymer (AN/VA/DVB), (67:27:10 wt.%), and Resin 2 the same derivative of gel expanded poly(vinylbenzyl chloride-co-divinylbenzene) copolymer (VBC/DVB). The resins sorption capacity and sorption isotherms of both resins were determined for AuCl₄⁻ and Au(CN)₂⁻ anions. Resin 2 revealed the best sorption of gold from acidic and alkali solutions: 68 and 23 mg/g, respectively. The effect of the HCl concentration on AuCl₄⁻ removal from solution was investigated. Gold was recovered quantitatively from both resins using a 5% thiourea solution in 0.1 HCl. Both resins remained ability of multiple gold sorption and desorption under acidic conditions.     

Sorption of plutonium from low level liquid waste using nano MnO2

Nano-crystalline MnO₂ has been synthesized by the method of alcoholic hydrolysis of KMnO₄ and its potential as a sorbent for plutonium present in the low level liquid waste (LLW) solutions was investigated. The kinetic studies on the sorption of Pu by MnO₂ reveal the attainment of equilibrium sorption in 15 h, however 90 % of sorption could be achieved within an hour. In the studies on optimization of the solution conditions for sorption, it was observed that the sorption increases with the pH of the aqueous solution, attains the maximum value of 100 % at pH = 3 and remains constant thereafter. The sorption was found to be nearly independent of the ionic strength (0.01–1.0 M) of the aqueous solutions maintained using NaClO₄, indicating the inner sphere complexation between the Pu⁴⁺ ions and the surface sites on MnO₂. Interference studies with different fission products, viz., Cs⁺, Sr²⁺ and Nd³⁺, revealed decrease in the percentage sorption with increasing pH of the suspension indicating the competition between the metal ions. However, at the metal ion concentrations prevalent in the low level liquid waste solutions, the decrease in the Pu sorption was only marginally decreased to 90 % at pH = 3, the decrease being more in the case of Nd³⁺ than that in the case of Cs⁺. This study, therefore, shows nano-crystalline MnO₂ can be used as a sorbent for separation of Pu from LLW solutions.     

Formation and redox behaviour of polycarbazole prepared by electropolymerization of solid carbazole crystals immobilized on an electrode surface

Carbazole solid crystals have been mechanically attached to platinum or gold electrodes by two different methods and investigated by cyclic electrochemical quartz crystal microbalance measurements in the presence of aqueous acidic media. It was demonstrated that oxidative dimerization and polymerization can also be accomplished under such conditions. During electropolymerization, anions and water molecules enter the surface layer; however, these species leave the film after the reduction of the polymer formed. The mass changes observed in the course of the redox transformations of polycarbazole film can be explained by potential- and time-dependent sorption/desorption of H⁺ and ClO₄ ⁻ ions. The electroactivity of the polymer diminishes in more dilute acid media; however, it is recovered again in concentrated HClO₄ solutions. In more dilute acid solution the extent of the water sorption (film swelling) increases.     

EQCM study of redox properties of PEDOT/MnO<Subscript>2</Subscript> composite films in aqueous electrolytes

Electrochemical behavior of poly-3,4-ethylenedioxythiophene composites with manganese dioxide (PEDOT/MnO₂) has been investigated by cyclic voltammetry and electrochemical quartz crystal microbalance at various component ratios and in different electrolyte solutions. The electrochemical formation of PEDOT film on the electrode surface and PEDOT/MnO₂ composite film during the electrochemical deposition of manganese dioxide into the polymer matrix was gravimetrically monitored. The mass of manganese dioxide deposited into PEDOT at different time of electrodeposition and apparent molar mass values of species involved into mass transfer during redox cycling of PEDOT/MnO₂ composites were evaluated. It was found that during the redox cycling of PEDOT/MnO₂ composite films with various MnO₂ content, the oppositely directed fluxes of counterions (anions and cations) occur, resulting in a change of the slope of linear parts of the Δf–E plots with changing the mass fraction of MnO₂ in the composite film.Rectangular shape of cyclic voltammograms of PEDOT/MnO₂ composites with different loadings of manganese dioxide was observed, which is characteristic of the pseudocapacitive behavior of the composite material. Specific capacity values of PEDOT/MnO₂ composites obtained from cyclic voltammograms were about 169 F g^?1. The specific capacity, related to the contribution of manganese dioxide component, was about 240 F g^?1.     

Effect of environmental conditions on 109Cd(II) sorption to MnO2

The sorption of Cd(II) from aqueous solution on MnO₂ was investigated under ambient conditions. Experiments were carried out as a function of contact time, solid content, pH, ionic strength, foreign ions, fulvic acid and temperature. The results indicated that the sorption of Cd(II) was strongly dependent on pH and ionic strength. At low pH, the sorption of Cd(II) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on MnO₂ surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The Langmuir, Freundlich and Dubinin–Radushkevich models were used to simulate the sorption isotherms at three different temperatures. The thermodynamic data (ΔG ⁰, ΔS ⁰, ΔH ⁰) calculated from the temperature dependent sorption isotherms suggested that the sorption of Cd(II) on MnO₂ was an spontaneous and endothermic process.     

Decomposition and Detection of Hydrogen Peroxide Using δ‐MnO2 Thin Film Electrode with Self‐Healing Property

A thin film of δ‐type MnO₂ grown cathodically has been investigated with respect to the ability toward anodic decomposition of H₂O₂ and durability. With polarization at less positive potentials than +0.4 V vs. Ag/AgCl, the film was dissolved exclusively as a result of reduction of Mn⁴⁺ sites in the oxide by H₂O₂ to soluble Mn²⁺. At +0.9 V, MnO₂ remained unchanged and decomposed H₂O₂ in solution. At +0.8 V, the film was once dissolved in the initial stage; however, it was self‐healed via reoxidation of the liberated Mn²⁺ ions. Amperometric flow‐injection analysis of H₂O₂ was carried out with the δ‐MnO₂ film.     

Impact of environmental conditions on the sorption behavior of radionuclide <Superscript>60</Superscript>Co(II) on MnO<Subscript>2</Subscript>

The fate and transport of toxic metal ions and radionuclides in the environment is generally controlled by sorption reactions. The removal of ⁶⁰Co(II) from wastewaters by MnO₂ was studied as a function of various environmental parameters such as shaking time, pH, ionic strength, foreign ions, and humic substances under ambient conditions. The results indicated that the sorption of ⁶⁰Co(II) on MnO₂ was strongly dependent on pH and ionic strength. At low pH, the sorption of ⁶⁰Co(II) was dominated by outer-sphere surface complexation and ion exchange with Na⁺/H⁺ on MnO₂ surfaces, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of HA/FA enhances ⁶⁰Co(II) sorption at low pH values, whereas reduces ⁶⁰Co(II) sorption at high pH values. The Langmuir and Freundlich models were used to simulate the sorption isotherms of ⁶⁰Co(II) at three different temperatures of 298.15, 318.15 and 338.15 K. The thermodynamic parameters (ΔH ⁰, ΔS ⁰ and ΔG ⁰) calculated from the temperature dependent sorption isotherms indicated that the sorption process of ⁶⁰Co(II) on MnO₂ was endothermic and spontaneous.     

The inhibition mechanism of pitting corrosion of pure aluminum by nitrate and sulfate ions in neutral chloride solution

The inhibition mechanism of pitting corrosion of natural oxide film-covered pure aluminum by NO⁻ ₃ and SO²⁻ ₄ ions has been examined in 0.1 M NaCl solution using potentiodynamic polarization experiments, a.c. impedance spectroscopy, Auger electron spectroscopy and a combination of the potentiostatic current transient method and optical microscopy. It was found that NO⁻ ₃ ions can be incorporated into the natural oxide film on pure aluminum at open-circuit potential, but the incorporation of SO²⁻ ₄ ions into the film hardly occurs. The incorporation of NO⁻ ₃ ions lowered the pitting susceptibility of pure aluminum in 0.1 M NaCl solution. Based upon the experimental results, it is suggested that the pitting corrosion inhibition mechanism by anions can be classified into two different groups: inhibition by competitive adsorption of anions (SO²⁻ ₄) with Cl⁻ ions and inhibition by the incorporation of anions (NO⁻ ₃) into the film rather than competitive adsorption. Both cases may impede the incorporation of Cl⁻ ions into the film, thus inhibiting pitting corrosion of natural oxide film-covered pure aluminum in chloride solutions. Received: 16 October 1998 / Accepted: 6 January 1999     

Sorption properties of oxides IX: Effect of anions on the sorption of uranium (VI) on hydrous oxides

Effect of anions such as nitrate, chloride, sulphate and carbonate on the sorption of U(VI), from aqueous solutions on hydrous oxides of Ti(IV), Ce(IV) Zr(IV) and Th(IV) has been studied. The sorption of U(VI) is markedly reduced in the presence of anions, like carbonate, whichform strong complexes with UO ₂ ^{2 +} in solution. The results are explained in terms of a competition for free UO ₂ ^{2 +} between surface hydroxyl groups and ligands (anions) present in solution. The sorption of U(VI) on these hydrous oxides was also studied from a bicarbonatecarbonate mixture. Sorption was less under conditions when tricarbonate complex of U(VI) was formed, but increased at higher pH values (>9), presumably due to the formation and sorption of hydroxo complexes of U(VI).     

Synthesis, Spectral, Thermal and CO2 Absorption Studies on Birnessites Type Layered MnO6 Oxide

Birnessite type layered MnO₆ oxides with increased crystallinity were synthesized from six carbohydrates and three dihydric phenols viz., dextrose, starch, fructose, galactose, maltose, lactose, catechol, resorcinol, quinol and KMnO₄ through the formation of a sol–gel. All of the MnO₆ oxides were characterized by powder XRD. The strong signal at 2θ ~ 12° corresponding to 7.4 Å refers to the Mn–Mn distance between the adjacent layers. The interlayer volume is dispersed with K⁺ ions and H₂O molecules. The presence of interlayer K⁺ ions is indicated by a signal at 25°, corresponding to a distance of 3.5 Å. IR spectra of the oxides show signature bands at ca. 500 cm^?1 due to the stretching modes occurring for MnO₆ entity. A broad band observed at ca. 3300 cm^?1 is due to interlayer water molecules. Thermal analysis indicated three stage decomposition with the formation of MnO₂ at ca. 600 °C through the intermediate formation of Mn(OH) _n . The MnO₆ exhibited a remarkable CO₂ scrubbing ability, which has also been investigated.     

Adsorption of 99TcO4 − onto hydrotalcite and calcined hydrotalcite under basic conditions: influence of humic acids and anions

The remediation of technetium-99 (⁹⁹Tc) at contaminated sites remains a major challenge, as Tc high solubility and anionic nature under oxic conditions lead to high contaminant mobility. Hydrotalcite, a form of anionic clay, can strongly retain anions, especially upon mineral calcination. However, naturally occurring humic acids can also sorb onto hydrotalcite, therefore competing with TcO₄ ^? for sorption sites. This work explores the ability of hydrotalcite to retain TcO₄ ^? in presence of humic substances to evaluate the efficacy of hydrotalcite for Tc remediation in natural environment. Results show that calcined hydrotalcite can immobilize TcO₄ ^?, while the presence of 23 ppm humic acids has little influence on TcO₄ ^? uptake. However, additional monatomic and polyatomic anions in solution can compete with TcO₄ ^? for sorption sites on hydrotalcite.     

Iodide‐Selective Electrodes Based on Bis[N(2‐methyl‐phenyl) 4‐Nitro‐thiobenzamidato]mercury(II) and Bis[N‐phenyl 3,5‐Dinitro‐thiobenzamidato]mercury(II) Carriers

Highly selective poly(vinyl chloride) (PVC) membrane electrodes based on recently synthesized mercury complexes including Hg(Nmpntb)₂ and Hg(Npdntb)₂ as new carriers for iodide‐selective electrodes by incorporating the membrane ingredients on the surface of graphite electrodes are reported. The effect of various parameters including the membrane composition, pH and possible interfering anions were investigated on the response properties of the electrodes. Both sensors exhibited Nernstian responses toward iodide over a wide concentration range of 7×10^?7 to 0.1 M and 1×10^?6 to 0.1 M, with slopes of 59.6±0.8 and 58.9±0.9 mV per decade of iodide concentration and detection limit of 3×10^?7 M and 7×10^?7 for Hg(Npdntb)₂ and Hg(Nmpntb)₂, respectively, over a wide pH range of 3–11. The sensors have response times of ≤5 s and can be used for at least 2 months without any considerable divergence in their potential response. The proposed electrodes show good ability to discriminate iodide over several inorganic and organic anions. The electrodes were successfully applied to direct determination of iodide in synthetic mixture, waste water and drinking water and as indicator electrodes in precipitation titrations.     

Surfactant-assisted electrodeposition and improved electrochemical capacitance of silver-doped manganese oxide pseudocapacitor electrodes

Ag-doped MnO₂ pseudocapacitor electrodes with dendrite and foam-like structures were successfully produced for the first time using an electrodeposition method employing structure-directing agents, i.e., sodium dodecyl sulfate (SDS) and cetyltrimethylammonium bromide (CTAB) acting through micelle formation at solid–liquid interfaces. Doping silver with MnO₂ enhanced their electronic conductance. Controlling pseudocapacitor electrode morphologies with surfactants accelerated ion transport. The specific capacitance values of the Ag-doped MnO₂ films produced with SDS and CTAB, measured in 0.5?M Na₂SO₄ at a scan rate of 5?mV?s^?1 were 551 and 557?F?g^?1, respectively. These values are about 2.7-fold higher than that of the pure MnO₂ film and about 1.4-fold higher than that of the Ag-doped MnO₂ film made without using surfactants.     

Preparation and properties of the layered organic derivatives of γ-zirconium phosphate,Zr(CH3−(OCH2CH2)n−OPO3) (HPO4) (n=1–3)

New kinds of organic derivatives of layer structured -zirconium phosphate Zr(HPO₄)₂·2H₂O are prepared by the exchange of the interlayer phosphate groups with phosphoric ester groups having oxyethylene chains, CH₃–(OCH₂CH₂)_n–OPO₃ ^2– (n=1–3). Half of the interlayer phosphate groups are exchanged topochemically, the oxyethylene chains being grafted onto the phosphate layers through the ester bonds in the resulting derivatives. The derivatives behave like crown ethers, and form complexes with alkali salts of soft base anions such as SCN^– and I^–. Alkali salts of hard base anions such as Br^– and NO₃ ^– do not form complexes with the derivatives. The alkali iodide complexes of the organic derivatives can be used for the halogen exchange reaction. n-Butyl bromide is converted into n-butyl iodide in the presence of the alkali iodide complexes. The reactivities for the halogen exchange reaction increase with the number of the oxyethylene units.     

Electrochemical quartz crystal microbalance study for vanadium hexacyanoferrates: monitoring of film growth and ion effects during redox reactions

An electrochemical quartz crystal microbalance was employed to monitor directly the growth of vanadium hexacyanoferrate (VHF) films on platinum substrates during electrodeposition and interfacial coagulation in the solution containing sulfuric acid electrolyte, vanadium(IV) and hexacyanoferrate(III). Mass changes of the gold/crystal working electrode were correlated with cyclic voltammetry data. Effects of cations (NH₄⁺, Li⁺, Na⁺ and K⁺), anions (SO₄²⁻ and NO₃⁻) and solvent during redox reactions of the films were studied. The results show that cations were incorporated into the film during reduction and expelled from the film during oxidation. Solvent also participates in VHF electrochemistry, and its role cannot be neglected. Anions play no role in VHF electrochemistry.     

Preparation and characterization of polyaniline/manganese dioxide composites via oxidative polymerization: Effect of acids

Polyaniline/manganese dioxide (PANI/MnO₂) composites have been chemically prepared by oxidative polymerization of aniline in acidic medium containing MnO₂ as an oxidant. The acids used were; H₂SO₄, HNO₃, HCl, and H₃PO₄ The prepared composites were characterized by SEM, elemental analysis, FT-IR, XRD, TGA, and magnetic susceptibility. XRD measurements of the composites revealed that the crystal structure of incorporated MnO₂ undergone a distortion and converted into amorphous. Thus, the XRD pattern of PANI was predominate. The degree of crystallinity of the prepared composites is depended on the type of compensated acid anions and has the order; . This order is agrees with the order of crystallographic radii and the shape of the corresponding acid anions. From the value of point zero charge of MnO₂ (pzc at pH ≈7.5) and FT-IR spectra, it was concluded that adsorbed acids anions on the oxide surface works as the charge compensator for positively charge PANI in the formation of PANI/MnO₂. The content of PANI in the composite was depended on the type of acid used. Thermogravimetric study exhibited that the composite with low content of PANI has a higher thermal stability. Magnetic susceptibility measurements revealed that the composites has a diamagnetic properties. A schematic composition of the composites has been suggested.     

Formation of platinum sites on layered double hydroxide type basic supports: II. Effect of the nature of the interlayer anion of the layered aluminum-magnesium hydroxides on platinum binding and Pt/MgAlO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> formation

The interaction of aqueous H₂PtCl₆ solutions with hydrotalcite-type aluminum-magnesium hydroxides differing in the nature of their interlayer anion is reported. In the case of CO₃²⁻ as the interlayer anion, the introduction of the platinum(IV) chloro complex does exerts no significant effect on the structural properties of the support, on its thermal decomposition dynamics, and on the textural characteristics of the resulting oxide phase. The binding of the platinum complexes to “activated hydrotalcite” with interlayer OH⁻ anions increases the interplanar spacing and enhances the thermal stability of the layered structure. This is accompanied by marked changes in textural characteristics of the material, leading to the formation of a nearly monodisperse mixed oxide phase. In the Pt/MgAlO _x samples obtained by reductive treatment, a considerable proportion of platinum is in the form of planar particles, and this corroborates the hypothesis that the metal complex at the sorption stage is mainly localized in the interlayer space of this support. Platinum binds to the support as chloro complexes via rapid anion exchange, and these bound platinum species are characterized by a higher reduction temperature.     

Adsorption of strontium ions from aqueous solution using hydrous,amorphous MnO2–ZrO2 composite: a new inorganic ion exchanger

Hydrous, amorphous MnO₂–ZrO₂ composite was prepared as a new inorganic composite material under various conditions for removal of Sr²⁺ ion from aqueous solutions. The physico-chemical characterization was carried out by Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron microscopy and thermogravimetry. The maximum sorption capacity for synthesized composite was evaluated as 1.5 meq/g sorbent and batch experiments were carried out as a function of contact time, aqueous phase pH, temperature and initial metal ions concentration of adsorptive solution. The results indicated that under optimal conditions, Sr²⁺ ions could be efficiently removed using MnO₂–ZrO₂ composite from aqueous solutions when pH > 5. The equilibrium isotherms were determined and the sorption data were successfully modeled using Langmuir model. Kinetics of the process was studied by considering a pseudo second-order model. This model predicted chemisorption as the adsorption mechanism. The results of thermodynamic investigation reveal that the adsorption process of the studied ion is entropy driven.