Direct evidence for chemically distinct regions within nation films on electrodes

Electrochemical and spectroelectrochemical experiments on the complexes [(bpy)₂(py)Ru^II(OH₂)]²⁺ and [(trpy)(bpy)Ru^II(OH₂)]²⁺ (py is pyridine; bpy is 2,2'-bipyridine; trpy is 2,2',2“-terpyridine) with Nation films coated on electrodes demonstrate that the complexes partition amongst three chemically distinct regions or phases. As Ru(II) the complexes reside both in an electroinactive phase and, based on the pH dependence of the Ru(III)/(II) couples, e.g., [(bpy)₂(py)Ru^III(OH)]²⁺/[(bpy)₂(py)Ru^II(OH₂)]²⁺, in two electroactive phases. Partitioning amongst the three phases depends on the pH of the external solution and on the oxidation state and proton content of the complex. Addition of alcohols releases the complex from the electroinactive phase but at the expense of loss of the bound water molecule and binding to the sulfonate sites by anation and, therefore, to a fourth distinct chemical or physical state in which the complex can exist within Nation films.     

Binding cadmium and copper ions with chemically modified cellulosic materials

Equilibrium sorption of cadmium and copper ions by modified and unmodified maize stalk was studied using a range of metal-ion concentrations and temperatures at various metal ion-substrate contact periods. The amount of metal ion removed from solution depended on the metal ion concentration, the metal ion-substrate contact period and the metal ion type. The level of metal ion uptake reached 15 mg/g of the substrate for cadmium ions at 0 degree C and was of the order Cd(II) greater than Cu(II). Modification improved the metal ion binding capacity of the substrate and increased the rate of metal ion uptake. The influence of temperature on the level and rate of metal ion uptake by the substrate was investigated.     

Separation of noble metal ions on silica with chemically bonded ligands

The separation of noble metal ions was investigated by chemically bonded ligands based on the concept of hard and soft acids and bases according to Pearson; influences of ion pairing and chelating effects are discussed. Complexing groups containing oxygen, nitrogen and sulphur were immobilized on silica gel. Ag, Au, Ir, Os, Pd, Pt and Rh were adsorbed in the acidic range (pH 0 to pH 5) and eluted from the gel in the range from pH 0 to pH 7.5 avoiding formation of hydroxides and coprecipitation of the noble metals. The separation is dependent on the immobilized ligand, the pH-value of sorption and desorption and the eluent.     

Extraction of copper ions using silica gel with chemically modified surface

The applicability of silica gels for the application in solid-phase extraction was tested. Silica was modified with ketoimine groups. Surface characteristics of the modified silica were determined by elemental analysis, NMR spectra of solid phases (²⁹Si CP MAS NMR), analysis of pore size distribution of the silica support, and nitrogen adsorption-desorption. Newly proposed sorbents with ketoimine groups were applied in the preconcentration of trace amounts of the Cu (II) ions from lake water, post-industrial water, and demineralized water unburdened back to the lake. Presented at the 34th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 21–25 May 2007.     

Transport of ions of pyrophosphoric acid through chemically different anion-exchange membranes

Characteristics of mass transport of the anions of pyrophosphoric acid are investigated during electrodialysis through MA-40 and MA-41 anion-exchange membranes. It is established that the rate of mass transport for counterions is greater through the MA-41 membrane than the MA-40 membrane, and thus the former can be used for demineralizing solutions with salts of pyrophosphoric acid. Higher selectivity to pyrophosphate ions is found for the MA-40 membrane compared to the MA-41 membrane in the electrodialysis of mixtures of pyrophosphate and hydropyrophosphate ions, and thus the MA-40 membrane can be regarded as promising for the separation of such mixtures.     

Guest excitation energy in dilute organic mixed crystals with chemically distinct guests

Philpott's theory of vibronic transitions of substitutional impurities in molecular crystals has been examined. The lowest energy guest transition in a number of mixed crystals has been calculated and compared with experiment. Satisfactory agreement is achieved. In some cases consideration of charge overlap of the guest and nearest host gives better agreement.     

Sorption of noble-metal ions on silica with chemically bonded nitrogen-containing ligands

A study has been made of the sorption of Ir(IV), Rh(III), Pt(IV), Ru(IV), Os(VIII), Pd(II) and Au(III) from aqueous solutions by silica chemically modified with nitrogen-containing organic ligands, as a function of hydrochloric acid concentration, time of contact, concentration of the element and the ionic strength. Sorption of noble-metal ions at pH > 1 on a sorbent containing monoamine groups seems to be due to a complexation mechanism, and to an anion-exchange mechanism at pH < 1. With aminopropyl-silica 1000-fold concentration of Ir(IV) and Rh(III) from their 10(-8)-10(-7)M solutions was achieved and these metals were subsequently determined on the sorbent surface by X-ray fluorescence. Detection limits were 10-20 ng/ml. There was no interference from 1000-fold quantities of non-ferrous metal ions and Fe(III). With the sorbent containing bonded diethylenetriamine groups, 1000-fold concentration of Au(III) was achieved, and it was then determined on the sorbent surface by an atomic-emission method. Conditions for desorption of Au(III) with pyridine and potassium thiocyanate were developed.     

Adsorption of bismuth ions on graphite chemically modified with gallic acid

Graphite modified with gallic acid to form 'gallic acid-carbon' is demonstrated to be efficient for the removal of bismuth(III) ions from aqueous solutions. The uptake is demonstrated to be rapid but not to follow standard adsorption isotherm models. Instead, the uptake was found to be further promoted by the presence of the adsorbed metal. Additionally, the bismuth uptake showed linear dependence on the square of its concentration suggesting the possible formation of polymeric bismuth species. The gallic acid-carbon shows great promise as a relatively inexpensive material for solid-phase extraction and water purification with extraction efficiency close to 98%.     

Kinetic-energy-sensitive mass spectrometry for separation of different ions with the same m/z value

A double-focusing mass spectrometer (MS) equipped with a superconducting-tunnel-junction (STJ) detector has been applied to measure relative ionization cross-sections for the production of ions that are accompanied by different ion species with the same mass-to-charge (m/z) value. The STJ detector fabricated for this study enables kinetic energy (E) measurement of incoming individual ions at a counting rate of up to approximately 100 k ions/s and an energy resolution (DeltaE/E) of 15%. Both high counting rate and high-energy resolution are necessary to independently determine both m and z and not the m/z value only in ion-counting MS experiments. Ions such as (14)N(2) (2+) and (14)N(+) with the same m/z value can be clearly discriminated using a kinetic-energy-sensitive MS. This fine discrimination capability allows direct determination of relative ionization cross-sections of the homonuclear diatomic ions (14)N(2) (2+)/(14)N(2) (+) and (16)O(2) (2+)/(16)O(2) (+), which are difficult to measure due to the strong interference by the signals of their dissociated atomic ions with noticeably large ionization cross-sections. The new instrument requires no low-abundance heteronuclear diatomic molecules of the forms (14)N(15)N or (16)O(17)O to carry out ionization studies and thus, is expected to be useful in fields such as atmospheric science, interstellar science, or plasma physics.     

Extraction of metal ions using chemically modified silica gel: a PIXE analysis

Organic ligand with carboxyhydrazide functional group was immobilised on the surface of silica gel and the metal binding capacity of the ligand-embedded silica was investigated. The functional group was covalently bonded to the silica matrix through a spacer of methylene groups by sequential reactions of silica gel with dibromobutane, malonic ester and hydrazine in different media. Surface area value of the modified silica was determined. The changes in surface area were correlated with the structural change of the silica surface due to chemical modifications. A mixture solution of metal ions [K(I),Cr(III),Co(II),Ni(II),Cu(II),Zn(II),Hg(II) and U(VI)] was treated with the ligand-embedded silica in 10(-3) M aqueous solution. The measurement of metal extraction capacity of the silica based ligand was done by multielemental analysis of the metal complexes thus formed by using Proton Induced X-ray Emission (PIXE) technique.     

Valence orbital ionization potentials of 1s 22s m2p n atoms and ions

The 2s and 2p valence orbital ionization potentials (VOIP) are determined systematically for atoms and ions with configurations 1s ²2s ^m2p ⁿ , using the Anno-Teruya values of the average energies of the configurations. All the cases with possible values of m and n, in conformity with the Pauli principle, are treated. The 2s or 2p VOIP of a particular ion with the configuration of this type is almost independent of the electron configuration. The VOIP's of an isoelectronic series are fitted to a quadratic equation in terms of atomic number Z: VOIP=A ₀+A ₁ Z+A ₂ Z ², by a least-squares method. There are remarkable regularities among A ₀'s, A ₁'s or A ₂'s, for different isoelectronic series, which may be explained by Slater's simple expression for the total energy of an atom (or ion) with the idea of screening effect due to inner electrons. Various screening constants have been determined from the analysis of such regularities.

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Zusammenfassung Unter Benutzung der Anno-Teruya-Werte für die durchschnittliche Energie der Konfigurationen werden systematisch für Atome und Ionen der Konfiguration 1^{s 2}2s ^m 2p ⁿ die 2s- und 2p-VOIP's bestimmt. Alle FÄlle mit den nach dem Pauli-Prinzip möglichen Werten für m und n werden behandelt. Das 2s- oder 2p-VOIP eines besonderen Ions ist beinahe unabhÄngig von der Elektronenkonfiguration. Nach der Methode der kleinsten quadratischen Abweichung werden die VOIP's einer isoelektronischen Serie mit Hilfe einer in Z (Z=Kernladungszahl) quadratischen Gleichung bestimmt: VOIP=A ₀ +A ₁ Z+A ₂ Z ². Die Koeffizienten A ₀,A₁ und A ₂ zeigen untereinander für verschiedene isoelektronische Serien bemerkenswerte RegelmÄ\igkeiten, die mit der einfachen Slaterformel für die Gesamtenergie eines Atoms oder Ions als Abschirmeffekte der inneren Elektronen erklÄrt werden können. Durch die Untersuchung dieser RegelmÄ\igkeiten konnten verschiedene Abschirmkonstanten bestimmt werden.

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Résumé Les potentiels d'ionisation des orbitales de valence (VOIP) 2s et 2p sont systématiquement déterminés pour les atomes et les ions de configuration 1s ²2s ^m2p ⁿ, en utilisant les valeurs de Anno-Teruya pour les énergies moyennes des configurations. Tous les cas possibles d'après le principe de Pauli sont traités. Le VOIP 2s ou 2p d'un ion donné avec une configuration de ce type est presque indépendant de la configuration électronique. Une relation quadratique en fonction du numéro atomique Z est ajustée pour les VOIP d'une série isoélectronique par la méthode des moindres carrés: VOIP=A ₀+A ₁ Z +A ₂ Z ². Des régularités remarquables se manifestent pour A ₀, A ₁, A ₂ dans différentes séries isoélectroniques; ceci peut Être expliqué à l'aide des expressions simples de Slater pour l'énergie totale d'un atome (ou d'un ion) avec l'idée d'un effet d'écran d aux électrons internes. Différentes constantes d'écran ont été déterminées par l'analyse de ces régularités.

     

H2/CO2 separations in multicomponent metal-adeninate MOFs with multiple chemically distinct pore environments

Metal–organic frameworks constructed from multiple (≥3) components often exhibit dramatically increased structural complexity compared to their 2 component (1 metal, 1 linker) counterparts, such as multiple chemically unique pore environments and a plurality of diverse molecular diffusion pathways. This inherent complexity can be advantageous for gas separation applications. Here, we report two isoreticular multicomponent MOFs, bMOF-200 (4 components; Cu, Zn, adeninate, pyrazolate) and bMOF-201 (3 components; Zn, adeninate, pyrazolate). We describe their structures, which contain 3 unique interconnected pore environments, and we use Kohn–Sham density functional theory (DFT) along with the climbing image nudged elastic band (CI-NEB) method to predict potential H₂/CO₂ separation ability of bMOF-200. We examine the H₂/CO₂ separation performance using both column breakthrough and membrane permeation studies. bMOF-200 membranes exhibit a H₂/CO₂ separation factor of 7.9. The pore space of bMOF-201 is significantly different than bMOF-200, and one molecular diffusion pathway is occluded by coordinating charge-balancing formate and acetate anions. A consequence of this structural difference is reduced permeability to both H₂ and CO₂ and a significantly improved H₂/CO₂ separation factor of 22.2 compared to bMOF-200, which makes bMOF-201 membranes competitive with some of the best performing MOF membranes in terms of H₂/CO₂ separations.

Tailorable multicomponent MOFs and MOF membranes for efficient H₂/CO₂ separation.     

Potentiometric study using chemically modified silica gel with pyridinium as membrane for ClO 4 − ions

A potentiometric sensor for the perchlorate anion was developed by mixing chemically modified silicagel with pyridinium perchlorate, with an epoxy polymer and graphite. The electrode showed Nernstian response between 1.0 × 10^–2 and 1.0 × 10^–3 M perchlorate concentrations. The electrode showed high selectivity to this ion at solutions pH between 5.5 and 8.0. The presence of IO ₄ ^– , NO ₃ ^– ,Br^–, IO ₃ ^– , Cl^– and SO ₄ ^2– ions in the solutions, had only small interference in the electrode response in the range mentioned.     

Valence stabilization of polyvalent ions during gamma irradiation of their aqueous solutions by sacrificial protection. III-Valence stabilization of Fe(II) ions by organic additives

Valence stabilization of polyvalent ions in gamma irradiated aqueous solutions is sometimes necessary in some chemical operations. In previous publications, valence stabilization of some polyvalent ions in solution upon gamma irradiation was achieved by using inorganic additives capable of interacting with the oxidizing or reducing species formed during water radiolysis. The results showed that the nature and duration of valence stabilization of Fe(II) depend on the concentration of the inorganic additives used. In the present work, a series of some organic additives has been used to investigate their capability in inducing valence stabilization of polyvalent iron ions, taken as an indicator, in aqueous acidic solutions when subjected to extended gamma irradiation. The results showed that the efficiency of valence stabilization depends on the amount and chemical structure of the organic additive used.     

Tandem mass spectrometric analysis of distinct fragmentation patterns to [M+Na]/z and [M+H]/z of dendritic Al(III) and Zn(II) quinolates

The synthesis of two novel dendritic aluminum and zinc quinolates, which are soluble in common solvents, was monitored effectively by positive ion electrospray ionization mass spectrometry (ESI-MS). Through tandem mass spectrometric analysis of the complexes, distinct fragmentation pathways for sodium adduct molecular ion [M+Na]+ and protonated molecular ion [M+H]+ were observed.     

Sorption and preconcentration of metal ions in ethanol solution with a silica gel surface chemically modified with benzimidazole

The adsorption isotherms of MCl(2) (M Mn, Ni, Cu, Zn and Cd) and FeCl(3) by silica gel chemically modified with benzimidazole molecules ( Si(CH(2))(3)NC(7)H(5)N) were studied in ethanol solution at 298 K. A column made of modified silica was used to adsorb and preconcentrate the above metal ions from ethanol solution. Elution was done with 0.1 M hydrochloric acid in an ethanol/water mixture having a mole fraction of water of 0.8. The material was applied in the preconcentration of metal ions from commercial ethanol normally used as engine fuel.