Cobalt Exchange Research Articles

Conductivity and Hygroscopic Expansion of Ionomer Thin Films: Effect of Cobalt Exchange and Thermal/Aqueous Treatment

The replacement of pure Pt catalysts with Pt–Co and Pt–Ni alloy catalysts has helped reduce the cost of polymer electrolyte fuel cells but has also introduced long-term performance degradation due to leaching out of cobalt and nickel into the catalyst layer ionomer and polymer electrolyte membrane. This work reports the impact of exchange of protons with cobalt ions on the humidity-dependent (0–90% RH) hydration and conductivity of ∼30 nm thin ionomer films at a fuel cell-relevant temperature (80 °C) for seven different ionomers varying in equivalent weight from 620 to 1100 g/mol of sulfonic acid. A significant suppression (up to 2 orders of magnitude at low RH) in ionic conductivity was observed for all ionomers upon exchange of protons with cobalt ions, consistent with prior studies. From a corresponding measurement of film swelling characteristics of H+-form and Co2+-exchanged ionomers, not reported earlier, the present study provides a clear piece of evidence that the water content of the ionomer films decreases upon Co2+ exchange. This suppression in water uptake is the dominant cause of the reduction in ionic conductivity of ionomer films upon Co2+ exchange. The most interesting finding of the study is that a large variation in conductivity between the H+ form and Co2+ form of ionomer films at a given RH is significantly minimized when conductivity is correlated with the water content (λ = number of water molecules per protogenic group). Accordingly, the work introduces a new universal relationship for ionic conductivity and water content of the ionomer films.

Exchange of zinc, cobalt and selenium in highly productive cows in the first 100 days of lactation when feeding them mixed ligand complexes

Exchange of zinc, cobalt and selenium in highly productive cows in the first 100 days of lactation when feeding them mixed ligand complexes

ЕЛЕКТРОХІМІЧНЕ ДОСЛІДЖЕННЯ ПРОЦЕСІВ ПОГЛИНАННЯ КОБАЛЬТУ ҐРУНТАМИ УКРАЇНИ

In this paper, the processes of cobalt absorption by soils of Ukraine are investigated by using the electrochemical method of pulsed inversion chronopotentiometry. It has been established that the absorption capacity of cobalt by soil varieties from complexing media is 64–98 %. In solutions of KNO3, NH4OH and CSN2H4 mobile compounds of cobalt are part of [Co(H2O)n]2+, [Co(NH3)n]2+,[Co(CSN2H4)n]2+, and in solutions of Na4P2O7, Na5P3O10 and ЕДТА4– anionic complexes [Co(P2O7)n]2–4n, [Co(P3O10)n]2–5n ³ [CoЕДТА]2– are formed. The cobalt cationic complexes [Co(H2O)n]2+, [Co(NH3)n]2+, [Co(CSN2H4)n]2+ are almost completely absorbed by the soils. Anionic complexes – [Co(P2O7) n] 2–4n, [Co(P3O10) n]2–5n ³ [CoЕДТА]2– largely remain mobile in the soil profile. The sorption effect depends on the charge of the complex ions, their strength and on the steriîìåtric parameters of the complex ions. A close positive relationship was established between the cobalt absorption by soils and the cation exchange capacity of soils, the correlation coefficient was 0,7976, and between the cobalt absorption by soils and the humus content (0,7034). In the study of biohumus, it was found that cobalt goes into the solution of 0,02M ЕДТАNa2 + 0,09M NH4Cl by the mechanism of competitive complexation, its transition to the HCl solution occurs due to the protonization of the functional groups of biohumus with which the metal is bound. Biohumus has rather high sorption properties of cobalt and may be promising for its use as an effective carrier matrix in various combinations with basic fertilizers. Isotherms of sorption or exchange of cobalt for exchange ions of biohumus in various solutions correspond to isotherms of Langmuir single layer adsorption. The method of IIHP analysis is important to use to control the content of trace elements at the level of their trace concentrations necessary for plant development.

Effect of Cobalt Ion Exchange and Thermal Pretreatment of Ionomer Thin Films on Conductivity, Water Uptake and Swelling

It is known that Cobalt (Co) can leach out from the Pt-Co alloy catalysts causing degradation of long-term fuel cell performance. Although the fundamental mechanism of performance loss is not fully understood, it has been hypothesized that the Co ion interacts with the nanothin ionomer films in the fuel cell catalyst layer by exchanging with the protons and thereby adversely affecting the performance. However, the effect of Cobalt ion, specifically and the transport properties of nanothin fluorinated ionomers films, in general is not fully known. We have studied the effect of cation(Cobalt) on spin-coated nanothin ionomers on its key properties – (i) proton conduction and water uptake which directly affects the electrochemical performance of fuel cell catalyst layers, and (ii) swelling behavior, which is an indicator of mechanical strength and thereby the durability of the ionomer. Electrochemical impedance spectroscopy (EIS) of films on interdigitated elecrodes for conductivity measurements, quartz crystal microbalance (QCM) for water uptake, and environmental ellipsometry for swelling measurement was employed, Quantification of exchanged Cobalt in nanothin films is non-trivial problem and we have used a set of x-ray techniques (EDX, XPS) for determination of cobalt in the cation exchanged films. In this work conductivity of the different ionomer thin film (~ 30 nm) were tested before and after Cobalt exchange at different temperatures (30-80 °C) and humidity (40-90 % RH) conditions. It was seen that the conductivity of the ionomer thin films decreased after Cobalt exchanged but the proton conduction of some of the non-commercial ionomers is not as strongly affected by Co ion exchange as that of the state-of-the-art Nafion ionomer. We also investigated the effect of ionomer thin film pretreatment on the conductivity of the cobalt exchanged ionomer. It was found that the the samples annealed at 160 °C and then cation exchanged by exposure to cobalt solution showed less reduction in conductivity than unannealed cation exchanged ionomer films. The presentation will share the details of the film preparation and characterization as well as the results for the conductivity, water uptake and swelling of the ionomer films. Figure 1

Synthesis of Zeolite NaA at Low Temperatures: Characterization, Cobalt Exchange and Enhanced Catalytic Activity of Styrene Epoxidation

Zeolites NaA were synthesized with the crystallization temperatures of 25, 40, 60, and 95°C, then converted into Co2+–NaA catalysts by an ion-exchange method. The samples were characterized and the results revealed that the higher the reaction temperature, the shorter the crystallization time and the bigger the particle size of zeolite NaA will be. Zeolite NaA kept its crystal structure before and after cobalt exchange. However, the introduction of cobalt ions into zeolite would result in a decrease in the intensity of all crystallographic reflexes. Furthermore, Co2+–NaA (25°C zeolite sample) was shown to exhibit better catalytic activity of styrene epoxidation as compared with that of Co2+–NaA (40, 60, and 95° zeolite sample) catalysts, which may be ascribed to its short diffusion path and enhanced physical transport of reactant and product.

Hydrogen sulfide adsorption by thermally treated cobalt (II)-exchanged NaX zeolite

The faujasite framework structure and the morphological properties of Co2+-exchanged NaX zeolite were maintained when samples were treated at a temperature ≤600℃, but were distorted at higher temperature. The cobalt (II) exchange and thermal treatment processes significantly improved the H2S adsorption capacity of the NaX zeolite and the highest values were 4.24 mg g−1 for 0.10-CoX-600 and 4.42 mg g−1 for 0.15-CoX-600. Moreover, the first-order adsorption kinetic showed a relatively good fit when applied to the experimental data for the H2S adsorption process.

Study on Modification of NaX Zeolites: The Cobalt (II)-Exchange Kinetics and Surface Property Changes under Thermal Treatment

The cobalt (II) ion-exchange process followed the Freundlich and Langmuir adsorption models as well as the pseudo-second-order kinetic model. The cobalt-exchanged contents increased when the initial Co(NO3)2solution concentration increased up to 0.14 mol L−1at the optimal pH of 6.05. The N2adsorption isotherms are mixed types I/II isotherms and H3 type hysteresis. Both the micropore and mesopore adsorptions occurred during the adsorption process. The modification, which is both the cobalt (II) exchange and thermal treatment, significantly improved the surface properties of NaX zeolites. Accordingly, the optimal temperature range is 500 to 600°C for a thermal treatment. This is consistent with the results of XRD analysis.

Synthesis of zeolite NaX at 25 °C and 95 °C: Characterization, cobalt exchange and catalytic performance in epoxidation of styrene

Zeolites NaX were synthesized with the crystallization temperatures of 25°C and 95°C and converted into cobalt-exchanged catalysts (Co2+–NaX) by an ion-exchange method. The results indicated that zeolites synthesized at 25°C were composed of many closely packed nanocrystals with the average size of around 30nm, while the samples obtained at 95°C were big single crystals. Zeolite NaX before and after the cobalt exchange kept pure faujasite structure, however, the introduction of cobalt ions into zeolite would lead to a decrease in the intensity of all crystallographic reflexes. Moreover, Co2+–NaX (25°C zeolite sample) exhibited higher catalytic performances in epoxidation of styrene as compared with that of Co2+–NaX (95°C zeolite sample) catalysts, which may be attributed to their short diffusion path and enhanced physical transport of reactants and products.

Kinetics and Equilibrium Studies for the Removal of Cobalt, Manganese, and Silver in Ethanol using Dowex 50W-x8 Cation Exchange Resin

Organic solvents such as ethanol, find a wide range of applications in fuel, pharmaceutical industries, food industries, and paint formulations, among others. The removal of Ag(I), Co(II), and Mn(II) ions in ethanol by cation exchange resin, Dowex 50W-x8, was investigated. The adsorption characteristics of metal ions onto Dowex 50W-x8 resin were described by Langmuir isotherms. The maximum sorption exchange capacities at 298 K were obtained as 47.4 mg g−1, 52.6 mg g−1, and 58.5 mg g−1 for Ag(I), Co(II), and Mn(II), respectively. The data was also fitted to Temkin and Dubinin-Radushkevich adsorption isotherm models to evaluate other adsorption properties. The ion exchange of silver, cobalt, and manganese on cation exchange resin followed pseudo-second-order kinetics, and the intraparticle diffusion was rate-determining step. The thermodynamic parameters indicated that the sorption of metal ions onto Dowex 50W-x8 resin was spontaneous (negative ΔG°) and endothermic in nature (positive ΔH°) implying that the adsorption capacity increased with increasing temperature. The resin can be regenerated by eluting metal ions with 3.0 mol L−1 HNO3 followed by washing it with 10 mL of Millipore water and 10 mL of 2.0 M NaOH, respectively. The proposed method was applied for metal ion removal in real ethanol samples.

Brillouin light scattering study of spin waves in NiFe/Co exchange spring bilayer films

Spin waves are investigated in Permalloy(Ni80Fe20)/Cobalt(Co) exchange spring bilayer thin films using Brillouin light scattering (BLS) experiment. The magnetic hysteresis loops measured by magneto-optical Kerr effect show a monotonic decrease in coercivity of the bilayer films with increasing Py thickness. BLS study shows two distinct modes, which are modelled as Damon-Eshbach and perpendicular standing wave modes. Linewidths of the frequency peaks are found to increase significantly with decreasing Py layer thickness. Interfacial roughness causes to fluctuate exchange coupling at the nanoscale regimes and the effect is stronger for thinner Py films. A quantitative analysis of the magnon linewidths shows the presence of strong local exchange coupling field which is much larger compared to macroscopic exchange field.

HUMAN ELEMENTAL PORTRAIT: MORBIDITY, DEMOGRAPHY AND PROBLEM OF NATION HEALTH MANAGEMENT

The negative effects of anthropogenic factors (excessive intake of heavy metals, deficit of essential chemicals, adverse climatic and geographical conditions) contribute to reduction of health at individual and population levels. There is a relationship between the basic demographic indices of population of some regions and countries and provision with some essential macro- and trace elements. Moreover, not only the absolute population indices of chemical elements content in hair, but also the relative indices (frequency deviation from the norm) are important biomarkers of demographic status. In the article, a relationship between an exchange of macro-and trace elements and a number of demographic indices has been shown. For example, it has been shown that an increase in prevalence among the population of Fe, Al, K excessive accumulation in men and Cu, Co deficit in women with Mn imbalance at the background can be considered as a negative demographic prognostic factor. Furthermore, calcium-phosphorus metabolism as well as exchange of cobalt correlates with the level of fertility.

UZM-9 제올라이트에서 메탄올의 올레핀으로 전환반응: 전이금속 이온 교환이 촉매의 활성저하에 미치는 영향

구리, 코발트, 니켈, 철의 전이금속 이온을 교환한 LTA 골격구조의 UZM-9 제올라이트에서 메탄올이 저급올레핀으로 전환(Methanol-to-Olefin: MTO)되는 반응을 조사하여 전이금속 이온 교환이 촉매의 활성저하에 미치는 영향을 고찰하였다. 전이금속 이온 교환에 따른 UZM-9의 결정구조, 결정 모양, 세공구조, 산성도 변화는 크지 않았다. UZM-9은 둥지 입구가 작아 MTO 반응에서 저급올레핀에 대한 선택도가 높지만, 둥지가 커서 활성중간체인 헥사메틸벤젠 등 폴리메틸벤젠이 쉽게 고리화축합되어 다고리 방향족화합물이 많이 생성되므로 활성저하가 빠르다. 그러나 구리와 코발트 이온을 교환하면 MTO 반응에서 UZM-9의 활성저하가 느려졌다. MTO 반응 중 생성되는 폴리메틸벤젠 양이온 라디칼과 전이금속 이온의 상호작용으로 활성중간체가 안정화되어 활성저하가 느려졌다. The effect of transition metal ion exchange into UZM-9 zeolite with LTA framework on its deactivation in methanol-to-olefin (MTO) conversion was discussed. The ion exchange of copper, cobalt, nickel, and iron did not induce any notable change in the crystallinity, crystal morphology, and acidity of UZM-9. The small cage entrance of UZM-9 caused the high selectivity to lower olefins in the MTO conversion, while its large cages allowed the rapid further cyclecondensation of active intermediates, polymethylbenzenes including hexamethylbenzene, resulting in a rapid deactivation. The UZM-9 containing copper and cobalt ions showed considerably slow deactivations. The interaction between transition metal ions and polymethylbenzene cation radicals, the active intermediates, generated in the MTO conversion stabilized the radicals and slowed down the deactivation of UZM-9.

Selective Cobalt (II) Exchange Properties of Na-2-Mica and Na-ETS-4

Co2+ exchange isotherms and Kielland plots were determined for highly-charged sodium swelling mica (Na-2-mica) and sodium Engelhard Titano-Silicate-4 (Na-ETS-4). The results showed that both Na-2-mica and Na-ETS-4 were highly selective for Co2+ at (equivalent fraction) of < 0.3. X-ray diffraction (XRD) patterns after 2Na+ → Co2+ exchange process were examined to check for change in d001-spacing of Na-2-mica. As the uptake of Co ions increased, strong ∼14 Å phase (two-layer hydrate) of Na-2-mica increased, while the ∼12 Å phase (one-layer hydrate) decreased. These synthetic ion exchangers have a great potential for decontamination of radioactive or stable cobalt from waste water and soils.

Determination of the maximum retention of cobalt by ion exchange in h-zeolites

This work aimed to determine the maximum content of cobalt that can be incorporated by ion exchange in zeolites H-USY, H-Beta, H-Mordenite, and H-ZSM-5. To reach this goal, batch isotherms at 75ºC were constructed after addition of zeolite samples in flasks filled with cobalt nitrate solution. The equilibrium data were fitted to Langmuir, Freundlich, and Tóth adsorption isotherm models. Langmuir was the best model for zeolites H-Beta, H-Mordenite, and H-ZSM-5, whereas experimental data for H-USY were better fitted to the Freundlich isotherm model. From the isotherms, it was possible to determine the maximum cobalt exchange level (q max) that can be incorporated in each zeolite through ion exchange. In this sense, H-USY presented the highest q max value (2.40 meq/g zeol), while H-ZSM-5 showed the lowest one (0.64 meq/g zeol). These results also show the influence of the zeolite framework related to the channel system, pore opening, presence of cavities and secondary porosity and SiO2/Al2O3 ratio (SAR) on the maximum capacity and behavior of cobalt ion exchange in protonic zeolites.

Batch and column studies on heavy metal removal using a local zeolitic tuff

Ion exchange is considered to be one of the most cost effective methods if low cost ion exchangers such as natural zeolites are used in waste water treatment. In this study, a zeolitic tuff rich in clinoptilolite from Gördes Manisa Turkey was examined to evaluate its ion exchange performance for the removal of copper, nickel and cobalt ions from metal (II) nitrate solutions at various concentrations by performing both batch and packed column experiments. A clinoptilolite tuff with purity around 60% was used in ion exchange experiments. Copper, nickel and cobalt exchange capacities of the tuff were determined as 8.3 mg (0.26 meq) Cu 2+/g, 6.6 mg (0.23 meq) Ni 2+/g and 4.5 mg (0.15 meq) Co 2+/g, respectively. The equilibrium behavior of the system was best described by classical Langmuir model. The experimental breakthrough curves from the column experiments were fitted to solid diffusion control model. The study showed that efficient metal ion removal can be done by using the local clinoptilolite rich tuff.

Adsorption of Nitrogen, Oxygen, and Argon in Cobalt(II)-Exchanged Zeolite X

Adsorption of nitrogen, oxygen, and argon on cobalt(II)-exchanged zeolite X at 288.2 and 303.0 K was studied. The nitrogen and oxygen adsorption capacities increase upon cobalt ion exchange up to 71%, beyond which it shows a decreasing trend because of the partial degradation of the zeolite structure during the cation exchange and high-temperature vacuum dehydration processes. The magnitude of the increase in the adsorption capacities for nitrogen is much higher than that of oxygen. The nitrogen/oxygen as well as nitrogen/argon selectivities in the low-pressure region increase with an increase in cobalt exchange. Marginal oxygen selectivity over argon is observed for zeolite samples with higher cobalt exchange. The heats of adsorption values for nitrogen and oxygen increase and that for argon remain unaffected by cobalt exchange in zeolite X. The very high nitrogen adsorption capacity, selectivity, and heat of adsorption in the low-pressure region for cobalt-exchanged zeolite X compared to the parent sodium form of the zeolite show stronger interaction between nitrogen molecules with the extraframework cobalt cations of the zeolite. This stronger interaction has been explained in terms of the pi-complexation between nitrogen molecules and cobalt cations of the zeolites, as confirmed by diffuse reflectance infrared Fourier transform spectroscopy, wherein the N[triple bond]N stretching frequency at 2099 cm(-1) is observed for N2 molecules adsorbed in NaCoX.

63Ni and 57Co Uptake and Selectivity of Tin Antimonates of Different Structure

Tin antimonates of different structure were studied for their uptake of cobalt and nickel in the decontamination of floor drain water and neutral bond water simulates. Selectivity was observed to vary with the structures and degree of crystallinity of the tin antimonates (pyrochlore, rutile, and mixed metal oxides). High selectivity for cobalt of exchangers with pyrochlore structure is attributed to ion exchange of cobalt inside the tunnel structure; nickel uptake evidently took place mostly at the outer surfaces of the materials. Electrostatic forces governed the ion exchange of rutile tin antimonates owing to their particle hydrate structure. With some limitation, the prediction of nickel uptake on tin antimonates from the more abundant cobalt uptake data is considered possible.

Octahedral-tetrahedral equilibrium and solvent exchange of cobalt(II) ions in primary alkylamines.

The enthalpy differences (Delta H degrees ) of the equilibrium between the octahedral and tetrahedral solvated cobalt(II) complexes were obtained in some primary alkylamines such as propylamine (pa, 36.1 +/- 2.3 kJ mol(-1)), n-hexylamine (ha, 34.9 +/- 1.0 kJ mol(-1)), 2-methoxyethylamine (meea, 44.8 +/- 3.1 kJ mol(-1)), and benzylamine (ba, 50.1 +/- 3.6 kJ mol(-1)) by the spectrophotometric method. The differences in the energy levels between the two geometries of the cobalt(II) complexes in the spherically symmetric field (Delta E(spher)) were estimated from the values of Delta H degrees by offsetting the ligand field stabilization energies. It was indicated that the value of Delta E(spher) is the decisive factor in determining the value of Delta H degrees and is largely dependent on the electronic repulsion between the d-electrons and the donor atoms and the interelectronic repulsion in the d orbitals. The comparison between activation enthalpies (Delta H(++)) for the solvent exchange reactions of octahedral cobalt(II) ions in pa and meea revealed that the unexpectedly large rate constant and small Delta H(++) in pa are attributed to the strong electronic repulsion in the ground state and removal of the electronic repulsion in the dissociative transition state, which can give the small Delta E(spher) between the ground and transition states. Differences in the solvent exchange rates and the DeltaH(++) values of the octahedral metal(II) ions in some other solvents are discussed in connection with the electronic repulsive factors.

The promotion of cobalt mordenite by palladium for the lean CH 4-SCR of NO x in moist streams

The promotional effect of palladium on the catalytic performance of cobalt ion exchanged mordenite (Co-HMOR) for the lean NO x reduction with methane in a wet reaction stream was evaluated. The addition of 0.1–0.15 wt.% Pd to Co-HMOR samples containing high Co 2+ levels lead to a material that can convert 60% NO to N 2 and 60% CH 4 to CO 2 at 500 °C in a reaction mixture containing 1000 ppm NO, 2700 ppm CH 4, 6% O 2, and 8% H 2O, at GHSV=30 000 h −1. NO reduction over Pd/Co-HMOR increases with Co loading up to about 90% cobalt exchange. The increase of Pd loading to Co-HMOR favors methane combustion instead of NO reduction. Experiments of NO oxidation to NO 2 in the presence of 2% water vapor show that the addition of Pd to Co under-exchanged samples produces much less NO 2 than was found under the same conditions on cobalt over-exchanged samples loaded with small amounts of Pd. On the other hand, almost total NO reduction to nitrogen was obtained between 500 and 550 °C in the oxygen free feed (CH 4+NO+H 2O). The nature of the active species was investigated by XPS and TPR. Results from XPS reveal that cobalt is uniformly distributed as Co 2+ in fresh Pd/Co-HMOR samples but, Pd exists as Pd 0 and Pd 2+ on the surface. The addition of Pd to Co-HMOR shifts the maxima in the temperature-programmed reduction profiles to lower temperatures and increases the reducibility of Co 2+ cations at exchange positions.

Ion Exchange of Divalent Cobalt and Iron with Na–Y Zeolite: Binary and Ternary Exchange Equilibria

Divalent cobalt and iron removal from aqueous solutions by batch ion exchange with a synthetic Na–Y zeolite has been studied under competitive and noncompetitive conditions. The binary Co/Na and Fe/Na ion-exchange equilibrium isotherms, constructed at 291±2 K and a total solution positive charge concentration of 0.1 eq dm−3, exhibited sigmoidal shapes that are attributed to an exchange site heterogeneity. The solution pH and the ratio of sorbate to sorbent are identified for which minimal imbibition of metal hydroxide and maintenance of zeolite structural integrity are ensured. An increase in Fe and Co concentration over the range 0.005–0.05 mol dm−3 lowered the removal efficiency but the external Fe was preferred to the indigenous sodium over the entire concentration range; there was a switch in preference from Co to Na at [Co] in excess of 0.034 mol dm−3. Exchange data for Cu2+/Na+ and Ni2+/Na+ binary systems are included for comparative purposes, and ion exchange affinity and Na–Y exchange capacity are discussed in terms of metal ion hydration and ion location. The effect of exchange temperature has been considered where the maximal Fe exchange was temperature independent while Co exchange was promoted with increasing temperature. A Co/Fe/Na–Y ternary exchange isotherm was constructed from 20 pairs of experimental points and is treated quantitatively in terms of ternary and pseudo-binary separation factors. The preference of the zeolite for exchange with iron over cobalt under noncompetitive conditions also extended to solutions containing both metals.