Local order around rare earth ions during the devitrification of oxyfluoride glasses

Erbium L(3)-edge extended x-ray absorption fine structure (EXAFS) measurements were performed on rare earth doped fluorosilicate and fluoroborate glasses and glass ceramics. The well known nucleating effects of erbium ions for the crystallization of cubic lead fluoride (based on x-ray diffraction measurements) and the fact that the rare earth ions are present in the crystalline phase (as indicated by Er(3+) emission spectra) seem in contradiction with the present EXAFS analysis, which indicates a lack of medium range structural ordering around the Er(3+) ions and suggests that the lead fluoride crystallization does not occur in the nearest neighbor distance of the rare earth ion. Molecular dynamics simulations of the devitrification process of a lead fluoride glass doped with Er(3+) ions were performed, and results indicate that Er(3+) ions lower the devitrification temperature of PbF(2), in good agreement with the experimental results. The genuine role of Er(3+) ions in the devitrification process of PbF(2) has been investigated. Although Er(3+) ions could indeed act as seeds for crystallization, as experiments suggest, molecular dynamics simulation results corroborate the experimental EXAFS observation that the devitrification does not occur at its nearest neighbor distance.     

Hydrogen and higher shell contributions in Zn2+, Ni2+, and Co2+ aqueous solutions: an X-ray absorption fine structure and molecular dynamics study

A detailed investigation of the hydration structure of Zn2+, Ni2+, and Co2+ in water solutions has been carried out combining X-ray absorption fine structure (EXAFS) spectroscopy and Molecular Dynamics (MD) simulations. The first quantitative analysis of EXAFS from hydrogen atoms in 3d transition metal ions in aqueous solutions has been carried out and the ion-hydrogen interactions have been found to provide a detectable contribution to the EXAFS spectra. An accurate determination of the structural parameters associated with the first hydration shell has been performed and compared with previous experimental results. No evidence of significant contributions from the second hydration shell to the EXAFS signal has been found for these solutions, while the inclusion of the hydrogen signal has been found to be important in performing a quantitative analysis of the experimental data. The high-frequency contribution present in the EXAFS spectra has been found to be due to multiple scattering (MS) effects inside the ion-oxygen first coordination shell. MD has been used to generate three-body distribution functions from which a reliable analysis of the MS contributions to the EXAFS spectra of these systems has been carried out.     

Investigation of the charge compensation mechanism on the electrochemically Li-ion deintercalated Li1-xCo1/3Ni1/3Mn1/3O2 electrode system by combination of soft and hard X-ray absorption spectroscopy

In situ hard X-ray absorption spectroscopy (XAS) at metal K-edges and soft XAS at O K-edge and metal L-edges have been carried out during the first charging process for the layered Li1-xCo1/3Ni1/3Mn1/3O2 cathode material. The metal K-edge XANES results show that the major charge compensation at the metal site during Li-ion deintercalation is achieved by the oxidation of Ni2+ ions, while the manganese ions and the cobalt ions remain mostly unchanged in the Mn4+ and Co3+ state. These conclusions are in good agreement with the results of the metal K-edge EXAFS data. Metal L-edge XAS results at different charge states in both the FY and PEY modes show that, unlike Mn and Co ions, Ni ions at the surface are oxidized to Ni3+ during charge, whereas Ni ions in the bulk are further oxidized to Ni4+ during charge. From the observation of O K-edge XAS results, we can conclude that a large portion of the charge compensation during Li-ion deintercalation is achieved in the oxygen site. By comparison to our earlier results on the Li1-xNi0.5Mn0.5O2 system, we attribute the active participation of oxygen in the redox process in Li1-xCo1/3Ni1/3Mn1/3O2 to be related to the presence of Co in this system.     

The stability of the SEI layer, surface composition and the oxidation state of transition metals at the electrolyte-cathode interface impacted by the electrochemical cycling: X-ray photoelectron spectroscopy investigation

The stability of the valence state of the 3d transition metal ions and the stoichiometry of LiMO(2) (M = Co, Ni, Mn) layered oxides at the surface-electrolyte interface plays a crucial role in energy storage applications. The surface oxidation/reduction of the cations caused by the contact of the solids to air or to the electrolyte results in the blocking of the Li-transport through the interface that leads to the fast batteries deterioration. The influence of the end-of-charge voltage on the chemical composition and the oxidation state of 3d transition metal ions, as well as the stability of the solid-electrolyte interface formed during the electrochemical Li-deintercalation/intercalation of the LiCoO(2) and Li(Ni,Mn,Co)O(2), have been investigated by X-ray photoelectron spectroscopy. While the chemical composition of the solid-electrolyte interface is similar for both layered oxide surfaces, the electrochemical cycling to some critical voltage values leads to the disappearance of the interface. By the analysis of the shape of the 2p and 3s photoelectron emissions we show that the formation of the solid-electrolyte interface layer correlates with the partial reduction of the trivalent Co ions at the electrolyte-LiCoO(2) interface and the amount of the Co(2+) ions is increased as the solid-electrolyte interface vanishes. In contrast, the Mn(4+), Co(3+) and Ni(2+) ions of the Li(Ni,Mn,Co)O(2) are stable at the interface under the electrochemical cycling to higher end-of-charge voltage. A correlation between deterioration of the LiCoO(2) and Li(Ni,Mn,Co)O(2) batteries and the change of electronic structure at the surface/interface after the electrochemical cycling has been found. The dissolution of the solid-electrolyte interface layer might be the reason for the fast deterioration of the Li-ion batteries.     

ToF-SIMS depth profiling analysis of the uptake of Ba2+ and Co2+ ions by natural kaolinite clay

The sorption behavior of Ba(2+) and Co(2+) ions on a natural clay sample rich in kaolinite was studied using time-of-flight secondary ion mass spectrometry (ToF-SIMS). Depth profiling at 10-A steps was performed up to a 70-A matrix depth of the clay prior to and following sorption. The results showed that Co(2+) is sorbed in slightly larger quantities than Ba(2+), with significant numbers of ions fixed on the outermost surface of the clay. Depletion of the ions K(+), Mg(2+), and Ca(2+) from the clay lattice was observed to accompany enrichment with Co(2+) and Ba(2+) ions. The data obtained using X-ray powder diffraction (XRPD) and scanning electron microscopy (SEM) indicated insignificant structural and morphological changes in the lattice of the clay upon sorption of both Ba(2+) and Co(2+) ions. Analysis using energy dispersive X-ray spectroscopy (EDS) showed that the average atomic percentage (+/-S.D.) of Ba and Co on kaolinite surface were 0.49 +/- 0.11 and 0.61 +/- 0.19 , respectively, indicating a limited uptake capacity of natural kaolinite for both ions.     

High-nuclearity 3d-4f clusters as enhanced magnetic coolers and molecular magnets

Four 52-metal-ion 3d-4f cluster complexes featuring a common core of Ln(42)M(10) (Ln = Gd(3+), Dy(3+); M = Co(2+/3+), Ni(2+)) were obtained through self-assembly of the metal ions templated by mixed anions (ClO(4)(-) and CO(3)(2-)). Magnetic studies revealed that the Gd(42)Co(10) and Gd(42)Ni(10) clusters exhibit the largest magnetocaloric effect (MCE) among any known 3d-4f complexes. Replacement of Gd(3+) ions with anisotropic Dy(3+) ions caused significant changes in the magnetic behavior of the clusters; both Dy(42)Co(10) and Dy(42)Ni(10) displayed slow relaxation of the magnetization.     

Water exchange dynamics of manganese(II), cobalt(II), and nickel(II) ions in aqueous solution

The first row transition metal ions Mn(2+), Co(2+), and Ni(2+) have been studied by classical umbrella sampling molecular dynamics simulations. The water exchange mechanisms, estimates of reaction rates, as well as structural changes during the activation process are discussed. Mn(2+) was found to react via an I(A) mechanism, whereas Co(2+) and Ni(2+) both proceed via I(D). Reaction rate constants are generally higher than those obtained by experiment but the simply constructed metal(II) ion-water potential reproduces the relative order quite well.     

Colorimetric assay for parallel detection of Cd2+, Ni2+ and Co2+ using peptide-modified gold nanoparticles

A colorimetric assay has been developed for parallel detection of Cd(2+), Ni(2+) and Co(2+) utilizing peptide-modified gold nanoparticles (P-AuNPs) as a sensing element based on its unique surface plasmon resonance properties. The functional peptide ligand, CALNNDHHHHHH, was self-assembled on gold nanoparticles (AuNPs) to produce P-AuNPs probe. The P-AuNPs probe could be used to simultaneously detect and showed different responses to the three ions Cd(2+), Ni(2+) and Co(2+) in an aqueous solution based on the aggregation-induced color change of AuNPs. The method showed good selectivity for Cd(2+), Ni(2+) and Co(2+) over other metal ions, and detection limit as low as 0.05 μM Cd(2+), 0.3 μM Ni(2+) or 2 μM Co(2+). To simultaneously (or parallel) detect the three metal ions coexisting in a sample, EDTA and imidazole were applied to mask Co(2+) and Ni(2+) for detecting Cd(2+), glutathione and EDTA were applied to mask Cd(2+) and Co(2+) for detecting Ni(2+), and glutathione and imidazole were applied to mask Cd(2+) and Ni(2+) for detecting Co(2+). Finally, the simple and cost-effective probe could be successfully applied for simultaneously detecting Cd(2+), Ni(2+), and Co(2+) in river water. Because this novel P-AgNPs-based probe design offers many advantages, including simplicity of preparation and manipulation compared with other methods that employ specific strategies, the sensing system shows potential application in the developing region for monitoring water quality.     

Spectrophotometric study of complex formations between 1-(2-pyridylazo)-2-naphthol (PAN) and some metal ions in organic solvents and the determination of thermodynamic parameters

The complexation reactions between Ni(2+), Co(2+) and Zn(2+) metal ions with PAN in methanol (MeOH), acetonitrile (AN) and dimethyl sulfoxide (DMSO) were studied using a spectrophotometric method. The stability constants of the resulting complexes were determined from computer fitting absorbance mole-ratio data. The results revealed that the stability constants of complexes are varying in order of Ni(2+)相似文献   

Spectrophotometric and conductometric study of complexation of salophen and some transition metal ions in nonaqueous polar solvents

The complexation reaction between Cu(2+), Co(2+) and Ni(2+) metal cations with N,N'-bis(salicylidene)-1,2-phenylenediamine (salophen), in three nonaqueous polar solvents such as: acetonitrile (AN), dimethyl sulfoxide (DMSO), methanol (MeOH) and two binary mixtures of AN:DMSO and AN:MeOH at 25 degrees C were studied by spectrophotometric and conductometric methods. All investigated metal ions form 1:1 ML complex which their stability constants were determined and increase as Irving-Williams stability order of Co(2+)相似文献   

Determination of CoSi2 self-aligned nanostructures with grazing incidence X-ray absorption spectroscopy

Self-aligned nanostructures (SAN) made by reacting Co nanoparticles with crystalline Si substrates at high temperatures were studied with grazing incidence X-ray absorption spectroscopy (GI-XAS). The results from extended X-ray absorption fine structure (EXAFS) analysis and X-ray absorption near-edge spectroscopy (XANES) were used to identify SAN as crystalline CoSi2. Theoretical calculations of EXAFS and XANES spectra of several crystalline cobalt silicides were performed with the FEFF8 package. On the basis of these studies, the SAN samples were determined to contain nearly pure CoSi2.     

Selective sensors for Zn2+ cations based on new green fluorescent poly(amidoamine) dendrimers peripherally modified with 1,8-naphthalimides

The paper reports on the spectral photophysical characteristics of two new fluorescent PAMAM dendrimers of zero and second generation decoreted with 1,8-naphthalimide units, designed for ionic detection. The dendrimers were studied by (1)H NMR, (13)C NMR, FT-IR spectroscopy and elemental analysis. Their ability to detect ions has been evaluated in acetonitrile by monitoring the quenching of the fluoresence intensity. Different ions have been tested: Zn(2+), Co(2+), Ni(2+), Cu(2+) and Fe(3+) for the purpose. The results have shown clearly that only Zn(2+) could be efficiently detected using the dendrimer of second generation. In addition, it has been shown that for both dendrimers in a acetonitrile-water solution, the fluoresence intensity is pH dependant, hence could find application as a detector of harmful pH changes in the environment.     

A comparative study on textural characterization: cation-exchange and sorption properties of crystalline alpha-zirconium(IV), tin(IV), and titanium(IV) phosphates

Tetravalent metal phosphates (M=Zr, Ti, and Sn) were prepared and characterized by XRD, surface properties, and TG-DTA. The cation exchange and sorption behavior of these metal phosphates toward transition metal ions such as Cu(2+), Co(2+), and Ni(2+) have been studied comparatively as a function of temperature and concentration. The adsorption process was found to increases with increase in temperature and concentration. The selectivity order for alpha-titanium and alpha-tin phosphates is Cu(2+)>Co(2+)>Ni(2+), whereas for alpha-zirconium phosphate it is Cu(2+)>Ni(2+)>Co(2+). The ion exchange capacity of alpha-titanium phosphate is greater than those of other phosphates, which is explained on the basis of the surface behavior, disorderness of the system, degree of hydrolysis of incoming guest adsorbate metal ions, and structural steric hindrance of the exchangers during adsorption and sorption. The distribution coefficient, Gibbs free energy, enthalpy, and entropy values indicate that the ion-exchange processes are spontaneous.     

Structural and electronic characterization of the complexes obtained by the interaction between bare and hydrated first-row transition-metal ions (Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+)) and glycine

The complexes formed by the simplest amino acid, glycine, with different bare and hydrated metal ions (Mn(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+)) were studied in the gas phase and in solvent in order to give better insight into the field of the metal ion-biological ligand interactions. The effects of the size and charge of each cation on the organization of the surrounding water molecules were analyzed. Results in the gas phase showed that the zwitterion of glycine is the form present in the most stable complexes of all ions and that it usually gives rise to an eta(2)O,O coordination type. After the addition of solvation sphere, a resulting octahedral arrangement was found around Ni(2+), Co(2+), and Fe(2+), ions in their high-spin states, whereas the bipyramidal-trigonal (Mn(2+) and Zn(2+)) or square-pyramidal (Cu(2+)) geometries were observed for the other metal species, according to glycine behaves as bi- or monodentate ligand. Despite the fact that the zwitterionic structure is in the ground conformation in solution, its complexes in water are less stable than those obtained from the canonical form. Binding energy values decrease in the order Cu(2+) > Ni(2+) > Zn(2+) approximately Co(2+) > Fe(2+) > Mn(2+) and Cu(2+) > Ni(2+) > Mn(2+) approximately Zn(2+) > Fe(2+) > Co(2+) for M(2+)-Gly and Gly-M(2+) (H(2)O)(n) complexes, respectively. The nature of the metal ion-ligand bonds was examined by using natural bond order and charge decomposition analyses.     

Behavior and mechanism of Ni(II) uptake on MnO2 by a combination of macroscopic and EXAFS investigation

The effects of pH, ionic strength, competing ions and initial metal concentrations on the uptake behavior and mechanism of radioactive Ni(II) onto MnO₂ was investigated using a combination of classical macroscopic methods and the extended X-ray absorption fine structure (EXAFS) spectroscopy technique. The results indicated that the uptake of Ni(II) on MnO₂ is obviously dependent on pH but independent of ionic strength, which suggested that the uptake of Ni(II) onto MnO₂ is attributed to an inner-sphere surface complex rather than an outer-sphere surface complex. EXAFS analysis shows that the hydrated Ni(II) is adsorbed through six-fold coordination with an average Ni–O interatomic distance of 2.04 ± 0.01 ?. It can be inferred from the EXAFS analysis that the inner-sphere surface complex of Ni(II) onto MnO₂ is involved in both edge-sharing and corner-sharing linkages. Both the macroscopic uptake data and the molecular level evidence of Ni(II) surface speciation at the MnO₂-water interfaces should be factored into better prediction of the bioavailability and mobility of Ni(II) in soil and water environment.     

Structural characterization of zinc(II) chloride in aqueous solution and in the protic ionic liquid ethyl ammonium nitrate by x-ray absorption spectroscopy

Extended x-ray absorption fine structure (EXAFS) spectroscopy has been used to investigate the species and structures existing in a series of ZnCl(2)-H(2)O-NaCl solutions with different chloride/zinc ratios and in a solution of ZnCl(2) in the protic ionic liquid ethyl ammonium nitrate (EAN). The average coordination numbers and distances of zinc species were determined from the analysis of the EXAFS data. In aqueous solution the number of chloride ions tightly bounded to Zn(2+) is significantly related to the chloride/zinc ratio, and no inner complex formation between Zn(2+) and Cl(-) ions has been detected for low ZnCl(2) concentration (0.1 and 0.2 M). Conversely, in the same concentration range (0.13 M) the ZnCl(2) species do not dissociate in EAN and the Zn(2+) first coordination shell has two chloride ions and is completed by two oxygen atoms of the nitrate anion. The results of this investigation show that notwithstanding the existence of similar characteristics between EAN and water, the solvation properties of the two solvents are markedly different.     

Electronic absorption spectroscopy of cobalt ions in diluted magnetic semiconductor quantum dots: demonstration of an isocrystalline core/shell synthetic method.

This paper reports the application of ligand-field electronic absorption spectroscopy to probe Co(2+) dopant ions in diluted magnetic semiconductor quantum dots. It is found that standard inverted micelle coprecipitation methods for preparing Co(2+)-doped CdS (Co(2+):CdS) quantum dots yield dopant ions predominantly bound to the nanocrystal surfaces. These Co(2+):CdS nanocrystals are unstable with respect to solvation of surface-bound Co(2+), and time-dependent absorption measurements allow identification of two transient surface-bound intermediates involving solvent-cobalt coordination. Comparison with Co(2+):ZnS quantum dots prepared by the same methods, which show nearly isotropic dopant distribution, indicates that the large mismatch between the ionic radii of Co(2+) (0.74 A) and Cd(2+) (0.97 A) is responsible for exclusion of Co(2+) ions during CdS nanocrystal growth. An isocrystalline core/shell preparative method is developed that allows synthesis of internally doped Co(2+):CdS quantum dots through encapsulation of surface-bound ions beneath additional layers of CdS.     

Preparation and characterization of imprinted monolith with metal ion as pivot

This report provided the first example of using pivot concept to prepare monolithic molecularly imprinted polymers (MIPs) with ketoprofen (KET) imprints, in which metal ions were employed as mediator between the functional monomer and the template to achieve higher fidelity of imprint. To solve metal ions in pre-polymerization system, a new ternary porogen of dimethyl sulfoxide-toluene-isooctane was developed for preparation of MIP monoliths with high porosity and good permeability. The effect of polymerization parameters such as the nature of metal ions, the ratio of template to metal ion and the degree of crosslinking, on the permeability, morphology and affinity of the metal ion mediated MIP monolith were studied. The experiments demonstrated that Ni(2+), Co(2+) and Zn(2+) can be applied as pivot to prepare KET-imprinted monolith. Relative to monolithic MIP without metal ions, all the ion-mediated macropore MIP monoliths showed enhanced permeability, capacity factor and selectivity factor. High permeability (1.06×10(-7)mm(2)) was obtained on the Co(2+)-mediated MIP monolith and great selectivity factor (3.84) was achieved on the Ni(2+)-mediated one. The stoichiometric displacement model was constructed to investigate the recognition mechanism of metal-ion mediated MIP. The results indicate that metal ion as pivot not only improves the affinity but also allows the fine-tuning on the macroporous structure of MIP monolith.     

Coordination numbers of hydrated divalent transition metal ions investigated with IRPD spectroscopy

Hydration of the divalent transition metal ions, Mn, Fe, Co, Ni, Cu, and Zn, with 5-8 water molecules attached was investigated using infrared photodissociation spectroscopy and photodissociation kinetics. At 215 K, spectral intensities in both the bonded-OH and free-OH stretch regions indicate that the average coordination number (CN) of Mn(2+), Fe(2+), Co(2+), and Ni(2+) is ~6, and these CN values are greater than those of Cu(2+) and Zn(2+). Ni has the highest CN, with no evidence for any population of structures with a water molecule in a second solvation shell for the hexa-hydrate at temperatures up to 331 K. Mn(2+), Fe(2+), and Co(2+) have similar CN at low temperature, but spectra of Mn(2+)(H(2)O)(6) indicate a second population of structures with a water molecule in a second solvent shell, i.e., a CN < 6, that increases in abundance at higher temperature (305 K). The propensity for these ions to undergo charge separation reactions at small cluster size roughly correlates with the ordering of the hydrolysis constants of these ions in aqueous solution and is consistent with the ordering of average CN values established from the infrared spectra of these ions.