Synthesis and evaluation as CO_2 chemisorbent of the Li_5(Al_(1-x)Fe_x)O_4 solid solution materials: Effect of oxygen addition

Pentalithium aluminate(β-Li_5AlO_4) and the corresponding iron-containing solid solution(Li_5(Al_(1-x)Fe_x)O_4)were synthetized by solid-state reaction. All the samples were characterized structural and microstructurally by X-ray diffraction, solid-state nuclear magnetic resonance, scanning electron microscopy, N_2 adsorption-desorption and temperature-programmed desorption of CO_2. Results showed that 30 mol% of iron can be incorporated into the β-Li_5AlO_4 crystalline structure at aluminum positions. Moreover, iron addition induced morphological and superficial reactivity variations. Li_5(Al_(1-x)Fe_x)O_4 samples chemisorbed CO_2 between 200 and 700 °C, where the superficial chemisorption presented the highest enhancement,in comparison to β-Li_5AlO _4. Additionally, Li_5(Al_(1-x)Fe_x)O_4 samples sintered at higher temperatures thanβ-Li_5AlO_4. Isothermal CO_2 chemisorption experiments of β-Li_5AlO_4 and Li_5(Al_(1-x)Fe_x)O_4 were fitted to a first order reaction model, corroborating that iron enhances the CO_2 chemisorption, kinetically. When oxygen was added to the gas flow, CO_2 chemisorption process was mainly enhanced between 400 and 600 °C for the Li_5(Al_(0.8)Fe_(0.2))O_4 sample in comparison to β-Li_5AlO_4. Hence, Li_5(Al_(1-x)Fe_x)O_4 solid solution presented an enhanced CO_2 chemisorption process, in the presence and absence of oxygen, in comparison to β-Li_5AlO_4.     

The effects of Li2SO4 addition,moisture, and LiOH on the ionic conductivity of Li5AIO4

The ionic conductivity and thermal properties of 80Li₅AlO₄ + 20Li₂SO₄, 75Li₂SO₄ + 25LiOH, and 50Li₂SO₄ + 50LiOH composite polycrystalline samples have been determined in both wet and dry environments. A large increase in the ionic conductivity of 80Li₅AlO₄ + 20Li₂SO₄ in a wet environment above ～350°C is due to the presence of LiOH. This same increase in conductivity is found for the two LiOH + Li₂SO₄ mixtures and is related to a eutectic reaction in the Li₂SO₄LiOH system. The phase diagram for the Li₂SO₄LiOH system was determined and supports this conclusion. The conductivity of 80Li₅AlO₄ + 20Li₂SO₄ in a dry environment is thermally activated [$\text{σ = σ}{}_0\text{exp}\text{(}\text{?E}\text{kT}\text{)}$] with E = 0.66 eV and $\text{σ}{}_0\text{= 450 (Ω-}\text{cm}\text{)}{}^{\mathrm{?1}}$. The addition of Li₂SO₄ to Li₅AlO₄ increases the total conductivity but decreases the electronic conductivity. Pressed pellets of Li₅AlO₄ and 80Li₅AlO₄ + 20Li₂SO₄ are stable in lithium up to at least 550 and 450°C, respectively.     

Phase and chemical transformations in the SiO2-Fe2O3(Fe3O4) system at various oxygen partial pressures

The SiO₂-Fe₂O₃(F₃O₄) system has been studied in air, oxygen, and an inert atmosphere. The dissociation temperatures for iron oxides, the onset and full melting temperatures for coexisting phases, and the melt demixing temperatures have been determined as a function of the oxygen partial pressure. A scenario of the phase and chemical transformations in the title systems has been developed.     

A gravimetric method for the determination of oxygen in uranium oxides and ternary uranium oxides by addition of alkaline earth compounds

A simple gravimetric determination of oxygen in uranium oxides and ternary uranium oxides is described. In alkaline earth uranates which are formed by heating in air at 800–1100°C, uranium is in the hexavalent state over certain continuous ranges of alkaline earth-to-uranium ratios. Thus, if an alkaline earth uranate or a compound containing an alkaline earth element, e.g. MgO, is mixed with the oxide sample and heated in air under suitable conditions, oxygen can be determined from the weight change before and after the reaction. The standard deviation of the O:U ratio for a UO_2+x test sample is ±0.0008–0.001, if a correction is applied for atmospheric moisture absorbed during mixing.     

Chemistry of trans-resveratrol with singlet oxygen: [2+2] addition, [4+2] addition, and formation of the phytoalexin moracin M

Resveratrol (1) reacts with singlet oxygen by two major pathways: A [2+2] cycloaddition forming a transient dioxetane that cleaves into the corresponding aldehydes and a [4+2] cycloaddition forming an endoperoxide that, upon heating, undergoes a rearrangement to moracin M. The rate constant by which singlet oxygen is removed by 1 (k(T)) was determined by time-resolved infrared luminescence spectroscopy to be 1.5 × 10(6) M(-1) sec(-1) in CD(3)OD, smaller than previously reported values. Chemical reaction accounts for ca. 25% of k(T).     

The effect of the physical form of the oxide on the conductivity changes produced by CH4, CO and H2O on ZnO

A study has been made of the effects of carbon monoxide, methane and water vapour on the electrical conductivity of zinc oxide at atmospheric pressure. Three physical forms of zinc oxide were investigated; polycrystalline masses, single crystals and compressed discs. Results are presented which show major differences in behaviour between the different physical forms. Methane and water vapour have much greater effects on the conductances of polycrystalline oxide than on those of single crystals. Single crystals of zinc oxide are shown to be potentially useful as sensors for low concentrations (ppm) of carbon monoxide in the presence of high concentrations (per cent) of methane.     

Effects of low hydrogen partial pressures on propylene polymerization by Cp*TiMe2(μ-Me)B(C6F5)3

Polymerization of propylene by Cp*TiMe₂(μ-Me)B(C₆F₅)₃ in the presence of increasing partial pressures of H₂ results in ever decreasing polymer molecular weights, which is consistent with the hydrogenolytic chain transfer processes involving metal–polymer bonds in many heterogeneous and homogeneous systems. However, catalytic activities are not significantly increased as the extent of hydrogenolysis increases, unlike metallocene catalyst systems in which the H₂ reacts primarily with dormant catalytic sites containing propylene 2,1-insertion products. It was shown previously that monocyclopentadienyl systems do not become seriously deactivated following 2,1 insertions, and thus hydrogenolysis does not result in enhanced activities. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4386–4389, 1999     

Composition of the condensed medium and the partial pressures of the gas-phase components forming on heating the As2O5 and As2O3 oxides: Computer experiment

Thermodynamic modeling of the compositions of the condensed medium and the partial pressures of the gas-phase components forming on heating arsenic oxides in an inert atmosphere under isobaric conditions (p = 9.8066 MPa) in the range from 300 K to the evaporation temperatures of these oxides has been performed.     

Effect of rich R-TiO_2 on the rate and cycle properties of Li_4Ti_5O_(12) as anode for lithium ion batteries

Li_4Ti_5O_(12)(LTO) with rich R-TiO_2(17.06, 23.69, and 34.42 wt%), namely, R-TiO_2@Li_4Ti_5O_(12) composites, were synthesized using the hydrothermal method and tetrabutyl titanate(TBT) as the precursor. Rietveld refinement of X-ray diffraction(XRD) results show that the proportion of Li occupying 16 d sites is extraordinary low and the lattice constants of LTO and R-TiO_2 change with the titanium dioxide content. EIS measurements showed that with increasing R-TiO_2 content, both its charge transfer impedance(Rct) and lithium ion diffusion coefficient(DLi) decreased. The changes of Rctand DLicaused by the increase of titanium dioxide content have synergic-antagonistic effects on the rate and cycle properties of Li_4Ti_5O_(12). The rate performance is positively related to DLi, while the cycle property is negatively correlated with Rct,indicating that the rate performance is mainly related to DLi, while Rctmore significantly affects the cycle performance. LTO-RT-17.06% exhibited excellent rate properties, especially under a high current density(5.0 C, 132.5 mAh/g) and LTO-RT-34.42% showed superior long-term cycle performance(0.012% capacity loss per cycle) compared to that of LTO-RT-17.06% and LTO-RT-23.69%.     

Effects of hydroxyl radicals and oxygen species on the 4-chlorophenol degradation by photoelectrocatalytic reactions with TiO2-film electrodes

The supported nano-TiO₂ electrode was prepared by sol–gel and hydrothermal method, and the photoelectrocatalytic degradation of 4-chlorophenol (4-CP) under UV irradiation has been investigated to reveal the roles of hydroxyl radicals and dissolved oxygen species for TiO₂-assisted photocatalytic reactions. The degradation kinetics, the formation and decay of intermediates, the isotopic tracer experiments with H₂O¹⁸, the removal yield of total organic carbon and the formation of active radical species in the presence of oxygen or not were examined by HPLC, GC–MS, TOC and spin-trap ESR spectrometry. It was found that most of OH radicals in the primary hydroxylated intermediates derived from the oxidation of adsorbed H₂O or HO⁻ by photo-holes in the electrochemically assisted TiO₂ photocatalytic system. It also indicates that the enhancement in the separation efficiency of photogenerated charges by applying a positive bias (+0.5 V vs SCE) has little role in the following decomposition and mineralization of these hydroxylated intermediates in the absence of oxygen. According to above experimental results, the pathway of 4-CP photocatalytic degradation was deduced initially. Due to the combined effect of OH radicals and dissolved oxygen species, the hydroxylated 4-chlorphenol, via cis, cis-3-chloromuconic acid, was decomposed into low molecular weight acid and CO₂.     

The regioselectivity of the addition of benzeneselenyl chloride to 7-azanorborn-5-ene-2-yl derivatives is controlled by the 2-substituent: new entry into 3- and 4-hydroxy-5-substituted prolines

The electrophilic addition of benzeneselenyl chloride to the alkene moiety of 7-azabicyclo[2.2.1]hept-5-en-2-yl derivatives has been studied. With camphanates 8 and 9N-Boc-5-endo-chloro-6-exo-phenylseleno-7-azanorborn-2-yl camphanates 10 and 11 are obtained with high regioselectivity due to a steric control. With N-Boc-7-azanorbor-5-en-2-one (2) the corresponding 6-endo-chloro-5-exo-phenylseleno derivative 15 is obtained in high yield due to a kinetic control attributed to the electron-releasing ability of the homoconjugated carbonyl group. Bicyclic adducts 10 and 11 and 15 are readily converted into 4-hydroxy-(14) and 3-hydroxy-5-substituted proline derivatives 19, respectively.     

Rearrangement of 3-ethoxycarbonyl-5-hydroxyimino-2-methyl-4-oxonaphtho[1,2-b]furan and 3-ethoxycarbonyl-5-hydroxyimino-2-methyl-4-oxo-1-phenylbenzo[g]indole by the action of benzenesulfonyl chloride in an alkaline medium

The treatment of 3-ethoxycarbonyl-2-methyl-4,5-dioxonaphtho[1,2-b]furan 5-monoximes and also the similarly substituted benzo[g]indole with benzenesulfonyl chloride in an alkaline medium give 5-(2-cyanophenyl)-3-ethoxycarbonyl-2-methylfuran-4-carboxylic and pyrrole-4-carboxylic acids with high yields as a result of a second-order Beckmann rearrangement. The structures of the initial and final compounds were confirmed by analysis of their mass spectra.Institute of Cardiology, Kaunas Medical Academy, Kaunas 233007, Lithuania M. V. Lomonosov Moscow State University, Moscow 119899, Russia Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1462-1465, November, 1999.     

Synthesis of the bis-potassium salts of 5-hydroxy-3-oxopent-4-enoic acids and their use for the efficient preparation of 4-hydroxy-2H-pyran-2-ones and other heterocycles

5-Hydroxy-3-oxopent-4-enoic acid esters can be efficiently transformed into the stable bis-potassium salts of the corresponding 5-hydroxy-3-oxopent-4-enoic acids, from which the sensitive acids are released in situ, the latter being converted into substituted 4-hydroxy-2H-pyran-2-ones, pyrazoles and isoxazoles under mild conditions; the efficiency of this method is demonstrated by the first synthesis of two naturally occurring pyrones.     

Lone electron pair (E) role on the crystal structures and the mechanism of high ionic conductivity of PbSnF4E2. Stereochemical and ab initio investigations

The F^– anion mobility of archetype fast ionic conductor PbSnF₄ formerly investigated by neutron diffraction with temperature is revisited based on a joint stereochemical and DFT investigation. It is mainly shown that a rapid exchange between F anions at the different tetragonal lattice sites is enhanced within the polyhedra enclosing the lone pair E in a dynamic change of coordination from octahedral to square pyramidal as for Sn(II). E stereoactivity in the interspaces along c direction is illustrated by the electron localization function ELF isosurface representations and followed by the non linear change of the c lattice constant with temperature.     

Effect of oxygen content on the 29Si NMR, Raman spectra and oxide ion conductivity of the apatite series, La8+xSr2-x(SiO4)6O2+x/2

29Si NMR data have been recorded for the apatite series La8+xSr2-x(SiO4)6O2+x/2 (0 < or = x < or = 1.0). For x = 0, a single NMR peak is observed at a chemical shift of approximately -77 ppm, while as the La : Sr ratio and hence interstitial oxygen content is increased, a second peak at a chemical shift of approximately -80 ppm is observed, which has been attributed to silicate groups neighbouring interstitial oxide ions. An increase in the intensity of this second peak is observed with increasing x, consistent with an increase in interstitial oxide ion content, and the data are used to estimate the level of interstitial oxide ions, and hence Frenkel-type disorder in these materials. The increase in second 29Si NMR peak intensity/interstitial oxide ion content is also shown to correlate with an increase in conductivity. The effect of interstitial oxygen content can also be studied by means of Raman spectroscopy, with a new mode at 360 cm(-1) appearing for samples with x > 0 in the symmetric bending mode energy region of the SiO4 group. The intensity of this mode increases with increasing oxygen content, yielding results comparable to those from the NMR studies, showing the complementarities of the two techniques.     

Ammonium tetraphenylborate-naphthalene adsorbent for the preconcentration and trace determination of uranium in standard alloys and synthetic samples using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol by fourth-derivative spectrophotometry

A solid ion-pair material produced from ammonium tetraphenylborate (ATPB) and naphthalene has been used for the preconcentration of uranium from the large volume of its aqueous complex samples. Uranium reacts with 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP) to form a water insoluble, coloured complex. This complex is quantitatively retained on the ATPB-naphthalene adsorbent filled in a column in the pH range 7.0–9.5 and at a flow rate of 2 ml/min. The solid mass from the column is dissolved with 5 ml of dimethylformamide (DMF) and uranium is determined by fourth-derivative spectrophotometry. The calibration curve is linear over the concentration range of 0.13–15.0 g of uranium in 5 ml of the final DMF solution. Seven replicate determinations of 6 g of uranium gave a mean peak height (peak-to-peak signal between 592 nm and 582 nm) of 1.02 with a relative standard deviation of 0.95%. The sensitivity is 0.8419 (d⁴A/d⁴)/(g ml^–1) found from the slope of the calibration curve. The interference of a large number of anions and cations on the estimation of uranium has been studied and the method applied for the determination of uranium in coal fly ash, Zr-base alloy and some synthetic samples corresponding to standard alloys.     

Ammonium tetraphenylborate-naphthalene adsorbent for the preconcentration and trace determination of iron in alloys and biological samples using 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol by third derivative spectrophotometry

A solid ion-pair material produced from ammonium tetraphenylborate on naphthalene (ATPB-naphthalene) provides a simple, rapid, economical and selective technique for preconcentrating iron from approximately 500 ml of aqueous solution of standard alloys and biological samples. Iron reacts with 2-(5-bromo-2-pryidlazo)-5-diethylaminophenol (5-Br-PADAP) to form a water-soluble cationic complex. When the aqueous solution of this cationic species in the pH range 3.2-8.5 is passed over the adsorbent ATPB-naphthalene at a flow rate of 1 ml min(-1), it is quantitatively retained on naphthalene as an uncharged ion-associated complex. The solid mass from the column was dissolved out with 5 ml of dimethylformamide (DMF) and iron is determined by third derivative spectrophotometry by measuring the signal d(3)A/ dlambda(3) between lambda(2)(773 nm) and lambda(3)(737 nm). The calibration curve is linear over the concentration range 0.10-25.0 mug of iron in 5 ml of DMF solution. Eight replicate determinations of 5 mug of iron gave a mean intensity (peak-to-peak signal between lambda(2) and lambda(3)) of 1.534 with a relative standard deviation of 0.90%. The sensitivity of the method is 0.307 (d(3)A/dnm(3) )/mug found from the slope of the calibration curve. The interference of a large number of anions and cations has been studied and the optimized conditions developed were utilized for the trace determination of iron in various standard alloys and biological samples.     

Products of the addition of water molecules to Al3O3- clusters: structure, bonding, and electron binding energies in Al3O4H2-, Al3O5H4-, Al3O4H2, and Al3O5H4

Two stable products of reactions of water molecules with the Al3O3- cluster, Al3O4H2- and Al3O5H4-, are studied with electronic structure calculations. There are several minima with similar energies for both anions and the corresponding molecules. Dissociative absorption of a water molecule to produce an anionic cluster with hydroxide ions is thermodynamically favored over the formation of Al3O3-(H2O)n complexes. Vertical electron detachment energies of Al3O4H2- and Al3O5H4- calculated with ab initio electron propagator methods provide a quantitative interpretation of recent anion photoelectron spectra. Contrasts and similarities in these spectra may be explained in terms of the Dyson orbitals associated with each transition energy.     

Elimination of spectral interferences in the reaction of 2-thiobarbituric acid with malonaldehyde, 2-furfuraldehyde and 5-hydroxymethyl-2-furfuraldehyde by partial least squares multivariate calibration (PLS)

Summary The spectral resolution of ternary mixtures of malonaldehyde (MLD), 2-furfuraldehyde (FUR) and 5-hydroxymethyl-2-furfuraldehyde (HMF) in the presence of glyoxal and biliverdine is achieved by partial least squares multivariate calibration (PLS). The spectrophotometric method is based on the reaction of these substances with 2-thiobarbituric acid (TBA). A calibration set of standard samples has been statistically designed in the presence of adequate amounts of both interferent compounds in several degrees of concentration. The possibility of a spectrophotometric determination of mixtures of MLD, FUR and HMF in the presence of glyoxal and biliverdine is demonstrated. A comparative study of the results found by application of PLS-1 and PLS-2 methods is presented.