Cation Molar Research Articles

Composition-controllable synthesis and optical properties of non-integral stoichiometry compound Zn xCd 1− xS nanorods

Homogeneous non-integral stoichiometry semiconductor compound Zn x Cd 1− x S nanorods have been successfully synthesized at 180 °C by the reaction of a mixture ZnCl 2 and CdCl 2 with thiosemicarbazide (NH 2SNHNH 2) in the ethylenediamine. The compositions over the whole range according to JCPDS cards have been controlled only by changing the cation molar ratio of Zn:Cd in the reactants. The composition dependence of UV–vis spectra and the photoluminescence (PL) spectra of the series Zn x Cd 1− x S nanocrystals has been revealed. The lattice parameters ( a, c) calculated from XRD patterns increase linearly with the increasing of Cd content, which is consistent with Vegard's law. Two well-defined relationships have been established among the lattice parameters, the band gap energy ( E g), and the composition value ( x) of the Zn x Cd 1− x S. The mechanism of reaction and the selection of the reagents have also been investigated.

Al2O3 ‐ Ta2O5 ‐ ZrO2 Thin Films Having High Corrosion Resistance to Strong Acid and Alkali Solutions

In order to develop an insulator film for an electrolyte-insulator-semiconductor capacitor pH sensor which can be used in a wide pH range, the corrosion resistance of films formed by metallorganic chemical vapor deposition has been investigated. Dissolution rates of the films deposited on a Pt substrate were measured by ellipsometry in HCl and NaOH solutions. The films with the cationic mole fraction of Al, , smaller than 0.4, the cationic mole fraction of Ta, , larger than 0.3, and the cationic mole fraction of Zr, , larger than 0.3 showed high corrosion resistance against both solutions.

Formation of Intra- and Interparticle Polyelectrolyte Complexes between Cationic Nanogel and Strong Polyanion

Polyelectrolyte complex formation of a strong polyanion, potassium poly(vinyl alcohol) sulfate (KPVS), with positively charged nanogels was studied at 25 degrees C in aqueous solutions with different KCl concentrations (C(s)) as a function of the polyion-nanogel mixing ratio based on moles of anions versus cations. Used as the gel sample was a polyampholytic nanogel consisting of lightly cross-linked terpolymer chains of N-isopropylacrylamide, acrylic acid, and 1-vinylimidazole; thus, the complexation was performed at pH 3 at which the imidazole groups are fully protonated to generate positive charges. Turbidimetric titration was employed to vary the mixing ratio. Also employed for studies of the resulting complexes at different stages of the titration were dynamic light scattering (DLS) and static light scattering (SLS) techniques. It was found from the titration as well as DLS and SLS that there is a critical mixing ratio (cmr) at which both the size and molar mass of the complexed gel particles abruptly increase. The value of the cmr at C(s) = 0 or 0.01 M (mol/L) was observed at approximately 1:1 mixing ratio of anions versus cations but at lower mixing ratios than the 1:1 ratio under conditions of C(s) = 0.05 and 0.1 M. At the mixing ratios less than the cmr, the molar mass of the complex agrees with that of one gel particle with the calculated amount of the bound KPVS ions, indicating the formation of an "intraparticle" KPVS-nanogel complex, by the aggregation of which an "interparticle" complex is formed at the cmr. During the process of the intraparticle complex formation, both the hydrodynamic radius by DLS and the radius gyration by SLS decreased with increasing mixing ratio, demonstrating the gel collapse due to the complexation. At C(s) = 0 or 0.01 M and under conditions where the amount of KPVS bindings was less than half of the nanogel cations, however, the decrease of the hydrodynamic radius was very small, while the radius gyration fell monotonically. These results were discussed in connection with a collapse of dangling chains attached to the nanogel surface by the binding of KPVS.

Inner-sphere complexes of divalent cations with single-stranded poly(rA) and poly(rU).

A combination of ultrasound velocimetry, density, and UV spectroscopy has been employed to study the hydration effects of binding of Mn(2+) and alkaline-earth cations to poly(rA) and poly(rU) single strands. The hydration effects, obtained from volume and compressibility measurements, are positive due to overlapping the hydration shells of interacting molecules and consequently releasing the water molecules to bulk state. The volume effects of the binding to poly(rA), calculated per mole of cations, range from 30.6 to 40.6 cm(3) mol(-1) and the compressibility effects range from 59.2 x 10(-4) to 73.6 x 10(-4) cm(3) mol(-1) bar(-1). The volume and compressibility effects for poly(rU) are approximately 17 cm(3) mol(-1) and approximately 50 x 10(-4) cm(3) mol(-1) bar(-1), respectively. The comparative analysis of the dehydration effects suggests that the divalent cations bind to the polynucleotides in inner-sphere manner. In the case of poly(rU) the dehydration effects correspond to two direct coordination, probably between adjacent phosphate groups. The optical study did not reveal any effects of cation on the secondary structure or aggregation of poly(rU). In the case of single-helical poly(rA) binding is more specific: dehydration effects correspond to three to five direct contacts and must involve atomic groups of adenines, and the divalent cations stabilize and aggregate the polynucleotide.

Synthesis of ZrO 2–15 mol% CeO 2 nanopowders by a pH-controlled nitrate–glycine process

The synthesis of nanocrystalline ZrO 2–15 mol% CeO 2 powders by a pH-controlled nitrate–glycine gel-combustion process was investigated. It was found that the metastable tetragonal phase could be fully retained probably due to the small crystallite size of the powders (5–8 nm). The effect of the glycine content and calcination temperature on powder morphology was studied. The highest specific surface area was obtained for 5 mol of glycine per mole of metal cations and a calcination temperature of 350 °C, which was of (93±2) m 2/g. Lower values of the specific surface area were found for smaller glycine/metal ratios or higher calcination temperatures.

Study of Ca−ATMP Precipitation in the Presence of Magnesium Ion

ATMP (aminotri(methylenephosphonic acid)), a phosphonate scale inhibitor used in the petroleum industry, was used as a model scale inhibitor in this study. One of the goals of this work was to determine the range of conditions under which Mg ions, which are formed in reservoir formations containing dolomite, modulate the formation of Ca-ATMP precipitate as a scale inhibitor. The results revealed that the amount of ATMP precipitated decreased with addition of Mg ions in solution at all values of the solution pH. Furthermore, an increase in both the solution pH and the concentration of the divalent cations in solution resulted in a change of the molar ratio of (Ca + Mg) to ATMP in the precipitates. At a low solution pH (pH 1.5), Mg ions had little effect on the composition of the Ca-ATMP precipitate. However, at higher values of the solution pH (pH 4 and 7), the Ca to ATMP molar ratio in the precipitates decreased with increasing concentration of the Mg. Here it was found that Mg ions replaced Ca ions on available reactive sites of ATMP molecules. These results determined the limits of the Mg ion concentration, which affects the precipitation of Ca-ATMP, Mg-ATMP, and (Ca + Mg)-ATMP. The dissolution of the scale inhibitors was studied using a rotating disk reactor. These experiments showed that the total divalent cation molar ratio (Ca + Mg) to ATMP in the precipitates is the primary factor that controls the rate of dissolution (release) of the phosphonate precipitates. The phosphonate precipitate dissolution rates decreased as the molar ratio of divalent cations to ATMP in the precipitates increased.

Preparation of simple and mixed nickel and cobalt molybdates using hybrid precursors made from an ordered polymer matrix and inorganic salts

The amphiphilic poly(ampholyte) poly(N,N-diallyl-N-hexylamine-alt-maleic acid), bearing simultaneously carboxylic acids, amines and hydrocarbon side chains, was used as a matrix to stabilize inorganic ion species (anionic as well as cationic) generated in aqueous solution from Ni(NO3)(2).6H(2)O, Co(NO3)(2).6H(2)O and (NH4)2MoO(4). Drying produces hybrid organic-inorganic blends which, due to the amphiphilicity of the copolymer, exhibit supramolecular organization in the bulk. Solid state studies show that up to two moles of metal cations (alone or together with metal anions) per repeat unit of the copolymer can be blended without loss of homogeneity in the hybrid material. A systematic screening permitted the determination of the optimal conditions for the preparation of homogeneous blends. Thermal treatment of the hybrid materials produces simple and mixed nickel and/or cobalt molybdates. The alpha- as well as the P-phase were obtained, and the mixed structures are solid solutions of simple NiMoO4 and CoMoO4.

Temperature and pH Effect on the Sorption of Divalent Metal Ions by Silica Gel

The sorption of Zn2+, Ni2+ and Cd2+ ions by silica gel was studied as a function of ion concentration, pH and temperature. An increase in all three parameters led to an increase in the extent of sorption for all the metal cations studied. The selectivity of the solid was observed to be in the order Zn2+ > Ni2+ > Cd2+. Sorption of the metal cations was accompanied by the release of H+ ions into the bulk phase. On average two moles of H+ ions were released per mole of metal cation sorbed. The sorption data fitted the linear forms of both the Kurbatov and Langmuir adsorption equations. The values of the binding constants were used to estimate the apparent thermodynamic parameters, ΔH and ΔS, for the adsorption process. FT-IR spectroscopic studies also showed that the uptake of metal cations by the silica gel occurred via a cation-exchange process.

CO 2 solubility and speciation in intermediate (andesitic) melts: the role of H 2O and composition

We determined total CO 2 solubilities in andesite melts with a range of compositions. Melts were equilibrated with excess C-O(-H) fluid at 1 GPa and 1300°C then quenched to glasses. Samples were analyzed using an electron microprobe for major elements, ion microprobe for C-O-H volatiles, and Fourier transform infrared spectroscopy for molecular H 2O, OH −, molecular CO 2, and CO 3 2−. CO 2 solubility was determined in hydrous andesite glasses and we found that H 2O content has a strong influence on C-O speciation and total CO 2 solubility. In anhydrous andesite melts with ∼60 wt.% SiO 2, total CO 2 solubility is ∼0.3 wt.% at 1300°C and 1 GPa and total CO 2 solubility increases by about 0.06 wt.% per wt.% of total H 2O. As total H 2O increases from ∼0 to ∼3.4 wt.%, molecular CO 2 decreases (from 0.07 ± 0.01 wt.% to ∼0.01 wt.%) and CO 3 2− increases (from 0.24 ± 0.04 wt.% to 0.57 ± 0.09 wt.%). Molecular CO 2 increases as the calculated mole fraction of CO 2 in the fluid increases, showing Henrian behavior. In contrast, CO 3 2− decreases as the calculated mole fraction of CO 2 in the fluid increases, indicating that CO 3 2− solubility is strongly dependent on the availability of reactive oxygens in the melt. These findings have implications for CO 2 degassing. If substantial H 2O is present, total CO 2 solubility is higher and CO 2 will degas at relatively shallow levels compared to a drier melt. Total CO 2 solubility was also examined in andesitic glasses with additional Ca, K, or Mg and low H 2O contents (<1 wt.%). We found that total CO 2 solubility is negatively correlated with (Si + Al) cation mole fraction and positively correlated with cations with large Gibbs free energy of decarbonation or high charge-to-radius ratios (e.g., Ca). Combining our andesite data with data from the literature, we find that molecular CO 2 is more abundant in highly polymerized melts with high ionic porosities (>∼48.3%), and low nonbridging oxygen/tetrahedral oxygen (<∼0.3). Carbonate dominates most silicate melts and is most abundant in depolymerized melts with low ionic porosities, high nonbridging oxygen/tetrahedral oxygen (>∼0.3), and abundant cations with large Gibbs free energy of decarbonation or high charge-to-radius ratio. In natural silicate melt, the oxygens in the carbonate are likely associated with tetrahedral and network-modifying cations (including Ca, H, or H-bonds) or a combinations of those cations.

Electrochemical studies of single-wall carbon nanotubes in aqueous solutions

Studies on the voltammetric responses, capacitance, and charge storage capability of single-wall carbon nanotube sheets or papers are described. Broad redox responses have been observed probably due to the presence of oxygen-containing functional groups attached to the surface of the nanotubes or to the impurities produced during nanotube purification in nitric acid. Annealing the material at 900°C eliminates these responses. The voltammetry and capacitance of the nanotube paper varies little with either anion or cation molar mass, ion charge, or ion hydrophobicity. Acids as a group tend to produce higher capacitance but similarity between the electrochemical responses in various acids is also observed. The small variation of the capacitance within a wide range of scan rates suggests that in the time scale investigated the double layer charging process is controlled by the RC time constant and not by electrolyte ion diffusion into the pores of the nanotube paper.

Homogeneous precipitation of Cr3+–M2+ (M=Ni, Zn, Co, Cu) oxalate by oxidation of the polyethylene glycol–cation complex

Cr3+–M2+ (M = Ni, Zn, Co, Cu) oxalate complexes were obtained by heat treatment of a polyethylene glycol (PEG) solution of a metal nitrate hydrate at 353 K for 6 h. The relation between the cation mole fraction [M2+/(Cr3+ + M2+)] in the PEG solution and in the precipitate obtained depended on the molecular weight of the PEG. The structure and the cation arrangement in the oxalate precipitate also depended on the molecular weight of the PEG. Two different models for the process of precipitate formation were examined in which it is assumed that Cr3+ and M2+ coordinate to PEG independently of and cooperatively with each other, respectively. The calculated relation between the M2+ mole fraction of the PEG solution and that of the precipitate was compared with the relation obtained from the experimental results. The results obtained from the second model agreed quite well with the experimental results. We therefore conclude that Cr3+ and M2+ coordinate cooperatively to PEGs.

Specific behavior of β-zeolites upon the modification of the surface acidity by Cs and Li exchange

A study on the modification of the surface acidity of beta zeolite exchanged with Cs and Li was carried out by means of X-ray diffraction, nitrogen adsorption (BET), 27Al-MAS-NMR, (133Cs, 6Li)-MAS-NMR, surface paramagnetic shift (SUPAS) with adsorbed O2, FTIR of adsorbed pyridine and NH3-TPD. An inverse correlation between the amount of cations exchanged and the number of acid sites was verified, as well as a gradual decrease of the micropore surface area, i.e. a 38% negative variation for the fully exchanged solids ZβCs2 and ZβLi3. The 133Cs and 6Li (SUPAS)-MAS-NMR technique suggested that Cs cations were located in accessible sites, while Li cations were inaccessible and possibly located in cavities within the channels network. The crystallinity of the original beta zeolite was modified slightly after the ion exchange and no trace of amorphous material was detected by XRD and 27Al-MAS-NMR techniques. By means of NH3-TPD it was found that at similar cation molar concentrations the number of acid sites was about 4 times higher for Li-exchanged zeolites, therefore Cs showed a stronger neutralization power of the acid sites.

Composition dependence of the photoinduced refractive-index change in lead silicate glasses

A large photoinduced refractive-index change (as great as Dn=0.21+/-0.04) is obtained in lead silicate glasses by irradiation with the frequency-quadrupled output of a Q -switched YAG laser (266 nm). An approximately exponential relationship is found between the photoinduced refractive-index change and the lead cation mole fraction over the composition range from 18.7% to 57%. The induced refractive-index change is permanent and shows no decay after heating to 360 degrees C during 1 h. Dispersion of the refractive-index change suggests that the photosensitivity is associated with changes in the intrinsic glass absorption edge.

Nutrient fluctuations in Sitka spruce (Picea sitchensis) plantations: the implications for future forest management practice

Summary The nutrient supply of forest soils is strongly influenced and changed by a number of forest management practices such as the choice of tree species (‘biological acidification’) and the biomass export (thinning, harvesting). This study investigates the soil chemical conditions of Sitka spruce plantations of different age classes regarding the fluctuations in nutrient supply within a rotation period on nutrient-poor soils, and discusses implications for future forest management. The study is based on composite samples of the topsoil (Ah-horizon) that were collected from 30 plots in Sitka spruce plantations of different age classes and semi-natural oak woodlands in the Grizedale Forest area, Cumbria, UK. A number of soil chemical analyses was performed. Across the age classes, the soil chemical variables were found to fluctuate rather than linearly increase or decrease, showing distinct resilient behaviour. Furthermore, both the analysis of the fluctuation of the soil chemical variables, and the sample plot ordination assessing the importance of soil chemical variables at the plots, strongly emphasize three major groups of interacting soil chemical variables: (1) soil bases (including Ca, Mg, base saturation, cation exchange capacity, cation molar ratios); (2) soil acids (including Al, H, pH); and (3) soil organics (including organic matter content, P). A key ion was found to be reactive Al, which strongly affects the soil nutrient balance and supply to the site, as well as being toxic to the fine root system of Sitka spruce. The research findings show that unfavourable environmental factors such as acid deposition, when combined with current forest management practices are responsible for the reduction in the long-term stability of the nutrient supply. This in turn causes a diminution in site productivity and potential limitation to the subsequent establishment of native deciduous tree species. In order to maintain longterm stability of the nutrient supply and to preserve the feasibility of subsequent broadleaf restocking, some changes to current forest management practices of Sitka spruce plantations are proposed.

Formation of Al2 O 3 ‐ Ta2 O 5 Double‐Oxide Thin Films by Low‐Pressure MOCVD and Evaluation of Their Corrosion Resistances in Acid and Alkali Solutions

double‐oxide thin films with different cationic mole fractions of Ta, , were formed by metallorganic chemical vapor deposition using aluminum tetraisopropoxide and tantalum pentametoxide as source gases and oxygen as a reaction gas. The corrosion resistances of the films were examined in 6 and 12 M HCl and 1 M NaOH at 298 K by the ellipsometric measurement of thinning rates of the films. The films having values between 0.0 and 1.0 showed homogeneous amorphous structures. The thinning rate of the films in HCl solutions decreased with increasing value and reached the analytical limit of ellipsometry. The films with values larger than 0.35 hardly dissolved in 6 M HCl and those with values larger than 0.45 in 12 M HCl. The corrosion resistance of the films in 1 M NaOH increased significantly with an increase in : the dissolution rate of the film with value of about 0.5 is lower than that of pure film by six orders of magnitude. © 1999 The Electrochemical Society. All rights reserved.

Oxidation of Aminopyrine by the Hydroperoxidase Activity of Lipoxygenase: A New Proposed Mechanism of N-Demethylation

The oxidation of aminopyrine, an N-alkyl aromatic amine, by the hydroperoxidase activity of lipoxygenase was studied. Aminopyrine gave rise to a purple color in the presence of H2O2 and lipoxygenase, the color being proportional to the aminopyrine radical cation. The H2O2/aminopyrine radical cation molar ratio was 0.5. The overall reaction was considered as an enzymic-chemical second order mechanism with substrate regeneration. From the equations, the apparent constant of the radical cation's decomposition (k′app) was evaluated under different experimental conditions. It was found to be inversely proportional to the proton concentration but unaffected by the concentration of aminopyrine. These results suggest a new comprehensive mechanism for N-demethylation, which takes into account the described presence of both nitrogen- and carbon-centered radicals and the marked effect of pH on the stability of the radical cation.

ChemInform Abstract: New Class of Lithium Ion Selective Crown Ethers with Bulky Decalin Subunits

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

HETEROCYCLO-SUBSTITUTED SULFA DRUGS: PART X. NOVEL 5-IMINO-δ2-PYRAZOLIN-4-DITHIOCARBAMYL-AZO DYES AS ANTIMICROBIAL AGENTS

Abstract Synthesis of a series of novel azo-sulfa drugs as 5-imino-3-methyl-1-phenyl-δ2-pyrazolin-4-dithiocarbamy-azo dyes (I-XV) are described via a reaction of 4-sulfamoyl and/or sulfonyl diazonium chloride with 5-imino-3-methyl 1-1-phenyl-δ2-pyrazolin-4-dithiocarbamic acid in acid medium. The corresponding iron, copper, mercury, cobalt, nickel, and lead chelates were obtained in 1:1 ligand-to-metal cation molar ratio at ice temperature as monochelate compounds (Iaf-XVaf). Furthermore, heating in 1:2 molar ratio gave di-chelate compounds (I′a-f-XV′a-f). All the synthesized azo-sulfa drugs (ligands) and their mono- and/or di-chelates were characterized by microanalysis, UV, IR and H-NMR spectroscopy and were screened in vitro for their antibacterial and antifungal activities.

The Petrology of the Tholeiites through Melilite Nephelinites on Gran Canaria, Canary Islands: Crystal Fractionation, Accumulation, and Depths of Melting

We report major and trace element X-ray fluorescence (XRF) data for mafic volcanics covering the 15-Ma evolution of Gran Canaria, Canary Islands. The Miocene (12-lS^Ma) and Pliocene-Quaternary (0-6 Ma) mafic volcanics on Gran Canaria include picrites, tholeiites, alkali basalts, basanites, nephelinites, and melilite nephelinites. Olivine±clinopyroxene are the major fractionating or accumulating phases in the basalts. Plagioclase, Fe-Ti oxide, and apatite fractionation or accumulation may play a minor role in the derivation of the most evolved mafic volcanics. The crystallization of clinopyroxene after olivine and the absence of phenocrystic plagioclase in the Miocene tholeiites and in the Pliocene and Quaternary alkali basalts and basanites with MgO>6 suggests that fractionation occurred at moderate pressure, probably within the upper mantle. The presence of plagioclase phenocrysts and chemical evidence for plagioclase fractionation in the Miocene basalts with MgO<6 and in the Pliocene tholeiites is consistent with cooling and fractionation at shallow depth, probably during storage in lower-crustal reservoirs. Magma generation at pressures in excess of 3-0-3-5 GPa is suggested by (a) the inferred presence of residual garnet and phlogopite and (b) comparison of FeO1 cation mole percentages and the CIPW normative compositions of the mafic volcanics with results from high-pressure melting experiments. The Gran Canaria mafic magmas were probably formed by decompression melting in an upwelling column of asthenospheric material, which encountered a mechanical boundary layer at ~ 100-km depth.

Determination of Critical Concentrations of Silica and/or Calcia for Abnormal Grain Growth in Alumina

Minimum amounts of SiO2 and CaO required for inducing abnormal grain growth in alumina were determined using ultrapure alumina (&gt;99.999%) and sintering at 1900°C for 1 h in a contamination‐free condition. The critical concentrations of silicon in cationic mole fractions in alumina were 300 ppm without calcium, 200 ppm with 10 ppm calcium, and 150 ppm with 20 ppm calcium. The critical concentration of calcium alone was 30 ppm. These concentrations seemed to match approximately the solubility limits reported in the literature, which suggested that the abnormal grain growth in commercially pure alumina was indeed related with the formation of a small amount of liquid phase during sintering.