Adsorption properties of crystalline silicas: (II) Adsorption of anionic surfactants and delamination

Lamellar crystalline silicas (crystalline silicic acids, chemical composition SiO₂·xH₂O; examples: H₄Si₁₄O₃₀·xH₂O, H₄Si₂₀O₄₂·xH₂O) are distinguished from the amorphous forms by their layered structure and exceptional adsorption properties. One outstanding example is the reaction with anionic surfactants. Several types of crystalline silicas (typical H₄Si₂₀O₄₂·xH₂O) can intercalate ionic pairs consisting of surfactant anion and gegen ion into the interlayer space. The saturation value of SDS adsorption is 0.475 mmol SDS/g H₄Si₂₀O₄₂·3H₂O. The acid H₄Si₁₄O₃₀·xH₂O adsorbs anionic surfactants at the external surfaces only (saturation value 0.04 mmol/g H₄Si₁₄O₃₀·0.8 H₂O). When anionic surfactants are adsorbed in the interlayer space, the layer separation increases to such an extent that the crystals disarticulate in a fan-like manner or delaminate into thinner packets of layers or smaller aggregates. Washing-out the SDS ionic pairs or drying reconstitutes the parallel layer orientation and leads to re-aggregation of the packets and fragments.     

Synthesis and magnetic properties of ZnFe2O4 obtained by mechanochemically assisted low-temperature annealing of mixtures of Zn and Fe oxalates

The mechanism of formation of zinc ferrite (ZnFe₂O₄) from ZnC₂O₄·1.8H₂O-2Fe^IIC₂O₄·2H₂O and ZnC₂O₄·1.8H₂O-Fe₂^III(C₂O₄)₃·6H₂O mixtures is investigated. By combination of TG and XRPD measurements it has been shown that microcrystalline ZnFe₂O₄ forms from physical mixtures after prolonged annealing at 1000 °C while nanocrystalline ZnFe₂O₄ powders are produced by mild annealing (1 h at 500 °C in air) of mechanically activated mixtures. The magnetic properties of ZnFe₂O₄ powders obtained from physical and from milled mixtures are compared.     

Synthesis and thermal decomposition of potassium trioxalatoaluminate hydrate

The preparation of pure K₃Al(C₂O₄)₃·mH₂O (2<m<3) is described. Dependent on the mode of preparation, the following were found to be contaminants of the desired product: K₂C₂O₄·1H₂O; KHC₂O₄; KHC₂O₄·H₂C₂O₄·2H₂O; H₂C₂O₄·2H₂O; different forms of aluminium oxide hydrate; K₄Al₂(OH)₂(C₂O₄)₄· (2+x)H₂O (0.7<x<1.7) and K₂Al₂(H₂O)₂(C₂O₄)₄· 4H₂O.     

Synthesis, structure and properties of CsHSi3O7, a layered silicate with a chiral structure

The chiral layered silicate CsHSi₃O₇ has been synthesized by hydrothermal techniques, and its structure determined by single crystal X-ray diffraction. The compound crystallizes in the space group P2₁2₁2₁. The silicate single layer consists of both four- and three-connected SiO₄ tetrahedra and may be considered as a member of a series of layer structures with the general formula (Si₄O₉)_m(Si₂O₅)_n. Strong hydrogen bonds occur between the terminal OH⁻ and O²⁻ ions of neighboring layers. The Cs⁺ cations can be ion-exchanged by protons to give a phase of composition H₂Si₃O₇·H₂O with a water molecule occupying the original Cs position, as confirmed by single crystal X-ray diffraction data. The water molecule in H₂Si₃O₇·H₂O can be readily removed without collapse of the crystal structure. Both CsHSi₃O₇ and H₂Si₃O₇·H₂O show SHG (second harmonic generation) efficiencies comparable to that of quartz, and both are not phase-matchable materials.     

A rare multi-coordinate tellurite, NH4ATe4O9·2H2O (ARb or Cs): The occurrence of TeO3, TeO4, and TeO5 Polyhedra in the same material

Two new tellurites, NH₄RbTe₄O₉·2H₂O and NH₄CsTe₄O₉·2H₂O have been synthesized and characterized. The compounds were synthesized hydrothermally, in near quantitative yields, using the alkali metal halide, TeO₂, and NH₄OH as reagents. The iso-structural materials exhibit layered, two-dimensional structural topologies consisting of TeO_x (x=3, 4, or 5) polyhedra separated by NH₄⁺, H₂O, Rb⁺ or Cs⁺ cations. Unique to these materials is the presence of TeO₃, TeO₄, and TeO₅ polyhedra. Thermogravimetric and infrared spectroscopic data are also presented. Crystal data: NH₄RbTe₄O₉·2H₂O: Monoclinic I2/a (no. 15), a=18.917(3) Å, b=6.7002(11) Å, c=21.106(5) Å, β=101.813(2)°, V=2618.5(9) Å³, Z=8; NH₄CsTe₄O₉·2H₂O: Monoclinic I2/a (no. 15), a=18.9880(12) Å, b=6.7633(4) Å, c=21.476(2) Å, β=102.3460(10)°, V=2694.2(3) Å³, Z=8.     

Conductivity and Morphology of Composite Solid Electrolytes SnO2· nH2O–Heteropolycompounds

The structure and surface characteristics of SnO₂ · 1.5H₂O and composite materials with heteropolycompounds (HPC) formulated as SnO₂ · 1.5H₂O–HPC (where HPC = (NH₄)₃PW₁₂O₄₀ · nH₂O, (NH₄)₂HPW₁₂O₄₀ · nH₂O, and H₃PW₁₂O₄₀ · nH₂O) are studied by scanning tunneling microscopy. Hydrated tin oxide is characterized by a globular structure which differs substantially from the morphology of composite materials. The conductivity is studied as a function of both the temperature and humidity of environment and the composition of composite materials. For composite materials containing ((NH₄)₂HPW₁₂O₄₀ · nH₂O, the conductivity is shown to vary monotonously with the composition and obey the mixture rule. Introduction of (NH₄)₃PW₁₂O₄₀ · nH₂O to a composite is found to cause an extremely fast conductivity decay, whereas addition of H₃PW₁₂O₄₀ · nH₂O results in the appearance of a plateau on the conductivity vs. composition curve. The explanation given to the phenomena observed is based on the mechanism of protonic transport in heteropolycompounds.     

A Fast and Direct Amperometric Determination of Hg2+ by a Bienzyme Electrode Based on the Competitive Activities of Glucose Oxidase and Laccase

A new concept of enzyme inhibition‐based biosensor involving the appearance of an amperometric signal for an inhibition by mercury was developed. The bienzyme sensor was composed of two layers of clay materials. The inner layer was constituted of layered double hydroxides entrapping laccase wired by ABTS. The outer laponite layer contained glucose oxidase (GOD). GOD catalyzed the glucose oxidation with the reduction of O₂ into H₂O₂. This induced a drastic decrease of the biosensor response to O₂ by the electrically wired laccase. HgCl₂ inhibited the O₂ consumption by GOD leading to a signal increase of the electroenzymatic reduction of O₂.     

Lanthankomplexe mit 2,2′-Bipyridin-N,N′-dioxid

Compounds of the composition La(bpyO₂ ^*)₄Cl₃·4H₂O, La(bpyO₂)₃Cl₃·5H₂O, La(bpyO₂)₂Cl₃·3H₂O, La(bpyO₂)Cl₃·3H₂O, La(bpyO₂)₄Br₃·4H₂O, La(bpyO₂)₃Br₃·8H₂O, La(bpyO₂)₂Br₃·7H₂O, La(bpyO₂)Br₃·4H₂O, La(bpyO₂)₄I₃·3H₂O, La(bpyO₂)₃(NO₃)₃·2H₂O, La(bpyO₂)₂(NO₃)₃·2H₂O, La(bpyO₂)₄(SCN)₃·3H₂O, La(bpyO₂)₃(SCN)₃·2H₂O, La(bpyO₂)₂(SCN)₃·2H₂O were isolated. They were investigated by means of thermoanalysis, I.R. spectroscopy, X-ray diffraction and molar conductivity.     

Thermal decomposition of Np(IV) and Pu(III, IV) oxalates

Thermal decomposition of Pu(C₂O₄)₂·6H₂O, Pu₂(C₂O₄)₃·10H₂O and Np(C₂O₄)₂ ·6H₂O has been studied by using combination of gas chromatography, infrared spectroscopy, spectrophotometry and complex thermal analysis. We also investigated the decomposition of Pu oxalate under its -radiation. The reduction of Pu(IV) to Pu(III) has been confirmed. We found Np(V), which is formed from Np(IV), on the basis of infrared and absorption spectra of the intermediate compounds.     

Synthesis of layered cathode material Li[CoxMn1−x]O2 from layered double hydroxides precursors

Cathode materials Li[Co_xMn_1−x]O₂ for lithium secondary batteries have been prepared by a new route—precursor method of layered double hydroxides (LDHs). In situ high-temperature X-ray diffraction (HT-XRD) and thermogravimetric analysis coupled with mass spectrometry (TG-MS) were used to monitor the structural transformation during the reaction of CoMn LDHs and LiOH·H₂O: firstly the layered structure of LDHs transformed to an intermediate phase with spinel structure; then the distortion of the structure occurred with the intercalation of Li⁺ into the lattice, resulting in the formation of layered Li[Co_xMn_1−x]O₂ with α-NaFeO₂ structure. Extended X-ray absorption fine structure (EXAFS) data showed that the Co-O bonding length and the coordination number of Co were close to those of Mn in Li[Co_xMn_1−x]O₂, which indicates that the local environments of the transitional metals are rather similar. X-ray photoelectron spectroscopy (XPS) was used to measure the oxidation state of Co and Mn. The influences of Co/Mn ratio on both the structure and electrochemical property of Li[Co_xMn_1−x]O₂ have been investigated by XRD and electrochemical tests. It has been found that the products synthesized by the precursor method demonstrated a rather stable cycling behavior, with a reversible capacity of 122.5 mAh g⁻¹ for the layered material Li[Co_0.80Mn_0.20]O₂.     

对苯二甲酸镁作为钠离子电池的有机负极材料

报道了对苯二甲酸镁作为钠离子电池负极材料的研究. 以对苯二甲酸和氢氧化镁为原料,采用酸碱中和反应制备了含结晶水的对苯二甲酸镁（MgC₈H₄O₄·2H₂O）,该材料对钠离子电池表现出了较好的电化学活性、优异的倍率性能以及良好的循环稳定性. 在0.5C（1C=300 mA·g^-1）倍率下循环50 周以后,可逆容量由114mAh·g^-1降至95 mAh·g^-1,容量保持率高达83%;在2C的倍率下有高达90 mAh·g^-1的可逆比容量. 另外,在氮气气氛中,400 ℃进行后续热处理得到了不含结晶水的对苯二甲酸镁（MgC₈H₄O₄）,探讨了结晶水对其电化学性能的影响. 结果表明,MgC₈H₄O₄·2H₂O的比容量、倍率性能以及循环稳定性都明显优于不含结晶水的对苯二甲酸镁.     

Benzylammonium,imidazolium and pyridinium polyvanadates — Synthesis and characterization

Summary From the reaction systems,B-V₂O₅-HClO₄-H₂O andB-V₂O₅-H₂O, whereB is benzylamine (Bz), imidazole (Im) or pyridine (Py), eight new compounds were synthesized: at 20°C, the metavanadate and decavanadates of composition (BzH)VO₃, (BzH)₆V₁₀O₂₈·3H₂O, (ImH)₆V₁₀O₂₈·2H₂O, (PyH)₆V₁₀O₂₈·2H₂O, (ImH)₄H₂V₁₀O₂₈·2H₂O and (PyH)₄H₂V₁₀O₂₈·3H₂O, and at 60°C, the hexavanadates of composition (ImH)₂V₆O₁₆·H₂O and (PyH)₂V₆O₁₆·H₂O. ThepH ranges of solutions the polyvanadates can be isolated from, were estimated. The compounds prepared were characterized by chemical analysis and IR spectroscopy. The synthesis of deuterated analogues allowed to assign the IR bands corresponding to vibrations of water in the spectra of deca- and dihydrogendecavanadates and to V-OH vibrations in the spectra of dihydrogendecavanadates.

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Benzylammonium-, Imidazolium- und Pyridinium-Polyvanadate. Synthese und Charakterisierung

Zusammenfassung Aus dem ReaktionssystemB-V₂O₅-HClO₄-H₂O undB-V₂O₅-H₂O [B=Benzylamin (Bz), Imidazol (Im) oder Pyridin (Py)] wurden acht neue Verbindungen synthetisiert: bei 20°C entstanden die Metavanadate und Decavanadate der Zusammensetzung (BzH)VO₃, (BzH)₆V₁₀O₂₈·3H₂O, (ImH)₆V₁₀O₂₈·2H₂O, (PyH)₆V₁₀O₂₈·2H₂O, (ImH)₄H₂V₁₀O₂₈·2H₂O und (PyH)₄H₂V₁₀O₂₈·3H₂O, bei 60°C entstanden die Hexavanadate (ImH)₂V₆O₁₆·H₂O und (PyH)₂V₆O₁₆·H₂O. DiepH-Bereiche, innerhalb derer Polyvanadate isoliert werden können, wurden abgeschätzt. Die Verbindungen wurden mittels chemischer Analyse und IR-Spektroskopie charakterisiert, wobei die Synthese deuterierter Analoga die Zuordnung von Banden unterstützte.

     

Structural and thermal interpretation of the synergy and interactions between the fire retardants magnesium hydroxide and zinc borate

The mechanism of cooperative action of commercial fire retardants is interpreted as resulting from specific chemical reaction and phase changes. This investigation focuses on the thermally initiated interactions between two forms of commercially available fire retardant compounds. The fire performance of a polyolefin with a metal hydroxide fire retardant, magnesium hydroxide, can significantly reduce the heat release rate through absorption of heat during conversion to its metal oxide. Formation of water, followed by vaporisation, decreases heat and dilutes volatiles from polymer degradation. The second form of fire retardant compounds are zinc borates (2ZnO·3B₂O₃·3H₂O and 4ZnO·B₂O₃·H₂O), that undergo dehydration with increasing temperature. Differential thermal analysis and wide-angle X-ray spectroscopy indicated that various structural changes occurred during heating. Endothermic transitions were observed for all components, while zinc borate (2ZnO·3B₂O₃·3H₂O) showed an exothermic crystallisation transition at relatively high temperature. The exotherm was modified by the development of a new crystalline phase, magnesium orthoborate (3MgO·B₂O₃) that formed on reaction with magnesium oxide (MgO) at temperatures greater than 500 °C. Formation of crystalline zinc oxide (ZnO) was also detected. From zinc borate (4ZnO·B₂O₃·H₂O), ZnO was primarily formed. No new crystalline phases were observed in the presence of MgO over the temperature range investigated.     

Synthesis and characterization of homo- and heterobimetallic niobium and tantalum peroxo-polyaminocarboxylato complexes and their use as single or multiple molecular precursors for Nb-Ta mixed oxides

New water-soluble bimetallic peroxo complexes of niobium^V and/or tantalum^V with high-denticity polyaminocarboxylate ligands have been prepared, characterized from the spectroscopic point of view, and used as molecular precursors for Nb-Ta mixed oxides. Four new homobimetallic complexes, (gu)₃[Nb₂(O₂)₄(dtpaO₃)]·3H₂O 1, (gu)₃[Ta₂(O₂)₄(dtpaO₃)]·5H₂O 2, (gu)₃[Nb₂(O₂)₄(HtthaO₄)]·2H₂O 4 and (gu)₃[Ta₂(O₂)₄(HtthaO₄)]·3H₂O 5 and the corresponding heterometallic complexes, (gu)₃[NbTa(O₂)₄(dtpaO₃)]·2.5H₂O 3 and (gu)₃[NbTa(O₂)₄(HtthaO₄₎]·2H₂O 6 have been obtained. In these compounds, the in situ oxidation of the nitrogen atoms of the PAC ligands into N-oxide groups has been evidenced by IR spectroscopy and mass spectrometry. The thermal treatment of the homonuclear complexes in air at 700 or 800 °C, depending on the Ta content, provided Nb₂O₅ or Ta₂O₅ while the heteronuclear compounds led to the solid solution TaNbO₅. BET and SEM measurements have been carried out and comparison of the morphology of the samples prepared from homo- and heterometallic precursors is discussed.     

Thermal, structural and acidic characterization of some vanadyl phosphate materials modified with trivalent metal cations

A set of new materials with general formula [M(H₂O)]_X(VO)_1–XPO₄·2H₂O (M ³⁺=Al, Cr, Ga, Mn), isomorphous with layered tetragonal VOPO₄·2H₂O and having potential catalytic properties, have been characterized by TG and DTA, X-ray diffraction and surface acid strength. During heating the compounds transform in the monohydrated and anhydrous phases, all maintaining a layered structure, with a proper interlayer spacing. Catalytic tests performed with 1-butene show that theM ³⁺-vanadyl phosphates greatly improve the conversion of the olefine with respect to pure vanadyl phosphate.This work was carried out in the framework of the Agreement for scientific cooperation between the National Research Council of Italy and the Academy of Sciences of the Czech Republic. V.Z. and L.B. wish to thank the Grant Agency of the Czech Republic for financial support (Grant no. 203/95/1321). Funds from Ministero dell'Universita e della Ricerca Scientifica (MURST) are also acknowledged by M.A.M.     

A new approach for the synthesis of layered niobium sulfide and restacking route of NbS2 nanosheet

We have developed a new process for the synthesis of a layered niobium sulfide that involves heating K₄Nb₆O₁₇·3H₂O with a H₂S/N₂ gas mixture. It was confirmed that heating the starting layered oxide at 750 °C for 10 h under the gas flow yielded a highly crystalline, single-phase K_0.34(H₂O)_0.7NbS₂. The layered sulfide slabs had a large plate-like shape. Potassium ions in the interlayer of K_0.34(H₂O)_0.7NbS₂ could be exchanged with protons by stirring in 2 M H₂SO₄. It was found that the proton in the proton-exchanged form can be easily exchanged with other cations. The proton-exchanged form was exfoliated into NbS₂ nanosheets by ultrasonication in water. According to the atomic force microscopy (AFM) images, NbS₂ nanosheets had a thickness of around 4 Å, which roughly corresponded to the thickness of a single NbS₂ host layer. NbS₂ nanosheets could be restacked with the intercalation of Eu³⁺ or tetrabutylammonium ions by an electrostatic self-assembly deposition (ESD) technique.     

Synthesis and Crystal Structure of Supramolecular Adducts of Macrocyclic Cavitand Cucurbituril with Chromium(III) and Nickel(II) Aqua Complexes

Supramolecular compounds {[Cr(H₂O)₆](C₃₆H₃₆N₂₄O₁₂)}(NO₃)₃ · 13H₂O (I) and {[Ni(H₂O)₆]₂(C₃₆H₃₆N₂₄O₁₂)}(SO₄)₂ · 16H₂O (II) were obtained from aqueous solutions of chromium nitrate or nickel sulfate and the macrocyclic cavitand cucurbituril. According to X-ray diffraction analysis data, the cucurbituril molecule is closed from both sides by metal aqua complexes due to the formation of hydrogen bonding between the cucurbituril CO groups and aqua ligands. Compound I has a chain structure, while the structure of compound II is layered. Modes of cucurbituril coordination, depending on the size and charge of the metal cation, are discussed.     

Vanadyl phosphate dihydrate,a solid acid: the role of water in VOPO4·2H2O and its sodium derivatives Na x (VIV x VV 1−x O)PO4·(2−x)H2O

Sodium-containing intercalates having as general formula Na _x VOPOP₄·(2–x)H₂O (0.25x<0.50) have been obtained and characterized. Orthorhombic phases, which essentially maintain the structure of the layered oxide hydrate VOPO₄·2H₂O result. Intercalated sodium ions act as pillars. The presence of H₃O⁺ ions in the parent VOPO₄·2H₂O and also in some reduced phases, is detected. The understanding of the structural role of the water molecules is advanced and the topotactic dehydration/rehydration processes are studied. The formation of a new metastable VOPO₄·H₂O phase is established.     

Synthesis of LiNi1/3Co1/3Mn1/3O2−zFz cathode material from oxalate precursors for lithium ion battery

The layered LiNi_1/3Co_1/3Mn_1/3O_2−zF_z (0 ≤ z ≤ 0.12) cathode materials were synthesized from oxalate precursors by a simple self-propagating solid-state metathesis method with the help of the ball milling and the following calcination. Li(Ac)·2H₂O, Ni(Ac)₂·4H₂O, Co(Ac)₂·4H₂O, Mn(Ac)₂·4H₂O(Ac = acetate), LiF and excess H₂C₂O₄·2H₂O were used as starting materials without any solvent. The structural and electrochemical properties of the prepared LiNi_1/3Co_1/3Mn_1/3O_2−zF_z were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and electrochemical measurements, respectively. The XRD patterns indicate that all samples have a typical hexagonal structure with a space group of . The FESEM images show that the primary particle size of LiNi_1/3Co_1/3Mn_1/3O_2−zF_z gradually increases with increasing fluorine content. Though the fluorine-substituted LiNi_1/3Co_1/3Mn_1/3O_2−zF_z have lower initial discharge capacities, a small amount of fluorine-substituted LiNi_1/3Co_1/3Mn_1/3O_2−zF_z (z = 0.04 and 0.08) exhibit excellent cycling stability and rate capability compared to fluorine-free LiNi_1/3Co_1/3Mn_1/3O₂.     

Hydrothermal synthesis, characterization and thermochemistry of Ca2[B2O4(OH)2]·0.5H2O

A pure calcium borate Ca₂[B₂O₄(OH)₂]·0.5H₂O has been synthesized under hydrothermal condition and characterized by XRD, FT-IR and TG as well as by chemical analysis. The molar enthalpy of solution of Ca₂[B₂O₄(OH)₂]·0.5H₂O in HC1·54.582H₂O was determined. From a combination of this result with measured enthalpies of solution of H₃BO₃ in HC1·54.561H₂O and of CaO in (HCl + H₃BO₃) solution, together with the standard molar enthalpies of formation of CaO(s), H₃BO₃(s) and H₂O(l), the standard molar enthalpy of formation of −(3172.5 ± 2.5) kJ mol⁻¹ of Ca₂[B₂O₄(OH)₂]·0.5H₂O was obtained.