Adsorption studies of organosubstituted laminar silicates. 1. Adsorption deformation of organosubstituted laminar silicates

A dilatometric method was used to determine the deformations of organosubstituted Pyzhevsk montmorillonite and synthetic fluorohectorite upon the adsorption of water, hexane, and benzene vapor. These results were compared with the adsorption calorimetry data. The dilatometric method was shown to be highly sensitive to structural changes of the laminar silicates.Institute of Physical Chemistry, Russian Academy of Sciences, 117915 Moscow. Institute of Colloid Chemistry and Water Chemistry, Academy of Sciences of the Ukraine, 252180 Kiev. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 9, pp. 1979–1986, September, 1992.     

Proteins in mesoporous silicates

Mesoporous silicates (MPS) have an ordered pore structure with dimensions comparable to many biological molecules. They have been extensively explored as supports for proteins and enzymes in biocatalytic applications. Since their initial discovery, novel syntheses methods have led to precise control over pore size and structure, particle size, chemical composition, and stability, thus allowing the adsorption of a wide variety of biological macromolecules, such as heme proteins, lipases, antibody fragments, and proteases, into their structures. This Review discusses the application of ordered, large-pore, functionalized mesoporous silicates to immobilize proteins for biocatalysis.     

Dispersion and filler network structure of fibrillar silicates in elastomers

The dispersion and filler network of fibrillar silicate (FS) in elastomers were studied. The results showed that a good dispersion of FS in matrix during mechanical blending in unvulcanized composites contributed to a strong FS filler network, different from that of traditional reinforcing fillers. Meanwhile, the filler re-aggregation during vulcanization caused by the overlapping and intertwining of FS further strengthened the filler network. The factors including Mooney viscosity and molecular polarity of elastomer, type and amount of silane coupling agents used for filler modification, that may influence the filler network, were studied. Our study helps us to understand the mechanism for the formation of filler network of FS in elastomers and provides guidance for the preparation of high performance FS/elastomer composites.     

Surface energy of oxides and silicates

Published data and the author’s own data on the surface energy of hydrophilic oxides, silicates, and hydrophobic adsorbents based on them are reviewed. The prospects of using the combined Gibbs-Helmholtz-Young equation to obtain data on the surface pressure, heat of wetting, and wetting contact angle of hydrophilic and hydrophobic adsorbents are demonstrated. These data are used to estimate the thermodynamic characteristics of the surface and interfacial regions at the boundary between the materials and water. It is shown that the boundary layers of water close to the hydrophobic surfaces are more ordered while those close to the hydrophobic surfaces are less ordered than with liquid water. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 42, No. 3, pp. 133–149, May–June, 2006.     

Preparation and reactivity of polyfunctional six- and eight-membered cyclic silicates

Six- and eight-membered cyclic silicates with reactive SiH or Si-vinyl functional groups have been prepared: hexakis(dimethylsiloxy)cyclotrisiloxane (I), hexakis(vinyldimethylsiloxy)cyclotrisiloxane (II), octakis(dimethylsiloxy)cyclotetrasiloxane (III) and octakis(vinyldimethylsiloxy)cyclotetrasiloxane (IV). Reaction of pseudo wollastonite (Ca₃Si₃O₉) with dimethylchlorosilane or vinyldimethylchlorosilane gives I and II, respectively. IV has been prepared similarly by reaction of octakis[chloro calcium oxy]cyclotetrasilicate [Ca₈Si₄O₁₂Cl₈] with vinyldimethylchlorosilane. On the other hand, acid catalyzed siloxane exchange between tetramethyldisiloxane and octakis(trimethylsiloxy)cyclotetrasiloxane (V) gave III. Cyclic silicates (I-VI) are surprisingly resistant to acid catalyzed ring opening polymerization. In addition, II, IV, V and hexakis(trimethylsiloxy)cyclotrisiloxanes (VI) are resistant to phosphazene P₄-t-Bu superbase catalyzed ring opening polymerization.     

Preparation and characterization of manganese-containing silicates with ZSM-48 structure

报道了新型杂原子分子筛Ｍｎ－ＺＳＭ－４８的合成与表征。红外光谱和紫外漫反射光谱测试表明Ｍｎ（Ⅱ）离子进入了分子筛骨架。Ｍｎ（Ⅱ）同晶取代Ｓｉ（Ⅳ）导致产物晶粒的形貌和热性质有所不同。反应混合物中１,６－己二胺的含量,水含量和ＳｉＭｎ比对产物的晶化有很大影响。Ｍｎ－ＺＳＭ－４８作为ＣＯ加氢合成低碳烯烃的催化剂载体较Ｓｉ－ＺＳＭ－４８显示出很高的催化活性和明显的选择性     

Adsorption of surfactants on low-charged layer silicates Part II: Adsorption of non-ionic surfactants

Nonionic surfactants were adsorbed on low-charged layer silicates in the interlayers. After drying, the surfactants were arranged in densely packed double layers. However, in suspension considerably higher basal spacings are measured by x-ray diffraction which indicate that large quantities of non-ionic surfactants are adsorbed. With the aid of calorimetry, enthalpies of displacement were recorded which suggest strong interactions of the non-ionic surfactants with smectites. In analogy to tests on hydrophilic SiO₂, the adsorption of smectites is found to depend on the degree of ethoxylation of the non-ionic surfactant. The adsorption declines with increasing EO content.List of symbols n ^s adsorbed amount of surfactants (mmol/g) - n _max ^s maximal adsorbed amount of surfactants - d _L basal spacing (nm) - d _L interlayer separation because of adsorption - V _M molar volume of surfactant - V _max ^s volume of adsorbed surfactants (cm³/g) - V _int volume between the silicate layers (interlayer volume) (cm³/g) - H enthalpy of displacement (J/g) - h _max max. molar enthalpy of displacement (kJ/mol) Part I: Prog. Colloid Polymer Sci. 84, 206This paper is part of W. Röhl's doctorial dissertation at the Heinrich-Heine University, Düsseldorf     

X-ray photoelectron spectroscopy of some silicates

The binding energies of Si(2S) and O(1S) electrons in a number of silicate compounds are reported and correlated with their respective calculated charges by applying an iterative Pauling method. The use of ESCA to establish the molecular structure of the metasilicates is also discussed.     

Spectral, thermal and X-ray studies on some new bis-hydrazine metal glyoxylates and bis-hydrazine mixed metal glyoxylates

Bis-hydrazine complexes of metal glyoxylates and mixed metal glyoxylates of 3d-metal ions of the formula M(OOCCHO)₂(N₂H₄)₂, where M = Mg, Mn, Co, Ni, Cu, Zn or Cd and M_1/3Co_2/3(OOCCHO)₂(N₂H₄)₂, where M = Mg, Mn, Ni, Zn or Cd, respectively, have been prepared and studied. The compositions of the complexes have been determined by chemical analyses. The magnetic moments and electronic spectra suggest a high-spin octahedral geometry for the metal complexes. Infrared spectral data indicate the bidentate bridging by hydrazine molecules and monodentate coordination by glyoxylate ions in both the metal and mixed metal compounds. Thermogravimetry and differential thermal analyses in air have been used to study the thermal behaviour of the complexes. The simultaneous TG-DTA traces of all the complexes show multi-step degradation and the final products are found to be the respective metal oxides in the case of metal complexes and metal cobaltites in the case of mixed metal complexes. The final residues were identified by their X-ray powder diffraction patterns. X-ray powder diffraction patterns of the complexes including mixed metal complexes are almost superimposable with in each of the series indicating isomorphism. The metal cobaltites MCo₂O₄, where M = Mg, Mn, Ni, Zn or Cd were also prepared by decomposing the respective mixed metal complex in a pre-heated silica crucible at about 300 °C, and their identities were confirmed by chemical analyses, infrared spectra and X-ray powder diffraction.     

Factors and processes influencing the reinforcing effect of layered silicates in polymer nanocomposites

The analysis of the tensile yield stress of a large number polymer/layered silicate composites showed widely differing mechanical properties. The composition dependence of yield stress can be described and evaluated quantitatively by a simple model developed earlier for particulate filled polymers. The comparison of data produced in our laboratory or taken from the literature indicated that several processes may take place during the preparation of the composites and a considerable number of factors influence composite properties. Quite a few of these are often neglected and percentage increase in modulus, strength or other properties is reported in published papers instead. The most important of such effects are changing matrix properties when a functionalized polymer is used to promote adhesion (PE, PP), modification of crystalline structure due to nucleation (PA, PP), plasticization or lubrication (PVC), decreased interaction (PA, PVC, PET, rubbers) or chemical reactions (PVC, PP, PET). Using a few simple assumptions, most of which are supported by previous experience, the extent of exfoliation can be estimated quantitatively in nanocomposites. The analysis of the tensile yield stress of more than 80 composites with various matrices indicated that the extent of exfoliation is very low in most composites; it reaches maximum 10% in the best case, which corresponds to about 10 silicate layers per stack. Although the approach has limitations and several factors were neglected during analysis, this result is in agreement with observations indicating that complete exfoliation rarely can be reached in thermoplastic/clay composites. In order to achieve larger reinforcement, silicates must be exfoliated more perfectly in the future.     

Crystal structure and hydrogenation properties of pseudo-binary Mg6Pd0.5Ni0.5 complex metallic alloy

The crystal structure of the Ni-substituted Mg_6.10(2)Pd_0.52(2)Ni_0.41(2) complex metallic alloy has been determined by X-ray and neutron powder diffraction. The reaction of this compound at 573 K towards deuterium absorption for pressures up to 23 bar has also been studied. The crystal structure of Mg_6.10(2)Pd_0.52(2)Ni_0.41(2) compound was determined in the light of Samson's [Acta Crystallogr. B 28 (1972) 936) and Makongo's (Philos. Mag. 86 (2006) 427] models for the binary Mg₆Pd compound. It crystallizes in space group with lattice parameter 20.13331(7) Å. The refined unit-cell composition is Mg₃₄₂₍₁₎Pd₂₉₍₁₎Ni₂₃₍₁₎ with Z=56. Nickel by palladium substitution is not fully random. Nickel atoms preferentially locate on Pd sites with low coordination number due to steric effects. Deuterium uptake is 9.6 D/f.u. under the given conditions of pressure and temperature. Upon absorption, the intermetallic compound disproportionates into MgD₂, Mg₅Pd₂ and Mg₂NiD₄ phases. The Mg₂NiD₄ phase is observed to crystallize in the orthorhombic LT2 modification for which an averaged crystal structure in the Pcc2 space group is proposed.     

Analytical applications of organically modified silicates

Inorganic-organic hybrid materials prepared by the sol-gel process have become an attractive field of study due to the immense versatility associated with this method of composite material preparation. The blending of inorganic precursors with organosilicon reagents enables unique materials to be fabricated with the desired chemical and physical characteristics. The ability to control the interfacial polarity, the degree of porosity, and the chemical functionality in the matrix has been shown to be a powerful tool in the design of materials for sensor, optical, chromatographic, and catalytic applications. In this review, the preparation of the organically modified silicates (ORMOSILs) where the individual precursors are covalently bound to each other is discussed and selected examples of their potential usefulness in analytical applications is presented.     

Agricultural biomasses as sorbents of some trace metals

The studies of sorption of six metal ions (Cd²⁺, Cu²⁺, Pb²⁺, Zn²⁺, Ni²⁺, Cr³⁺ and Cr(VI)) from by-products of agriculture are taken into account. The Langmuir q_max values obtained with the use of different biomasses are evaluated and, in order to acquire comparable results, the necessity of using molar concentrations is stressed. The main effects of pH on sorption are estimated by considering both the behaviour of metal ions (hydrolysis and hydroxide precipitation) and the effect of pH on coordination, using a simulated example. Some considerations are made on the information that can be obtained using the most common isotherms and on the need to use chemical dimensions rather than weight in order to make comparison among various metal ions (since atomic weight differences deeply alter the significance of parameters in non-chemical units) and to predict the effects of competition between two (or more) of these for the same sorbent sites on the biomass surface.     

Structural, microstructural and vibrational characterization of apatite-type lanthanum silicates prepared by mechanical milling

Apatite-type lanthanum silicates have been successfully prepared at room temperature by dry milling hexagonal A-La₂O₃ and either amorphous or low cristobalite SiO₂. Milling a stochiometric mixture of these chemicals in a planetary ball mill with a moderate rotating disc speed (350 rpm), allows the formation of the target phase after only 3 h although longer milling times are needed to eliminate all SiO₂ and La₂O₃ traces. Thus, the mechanically activated chemical reaction proceeds faster when using amorphous silica instead of low cristobalite as silicon source and pure phases are obtained after only 9 and 18 h, respectively. As obtained powder phases are not amorphous and show an XRD pattern as well as IR and Raman bands characteristic of the lanthanum silicate. The domain size of the as-prepared phases varies gradually with the temperature of post-milling thermal treatment with activation energies of about 26(8) and 52(10) kJ mol⁻¹ K⁻¹ for the apatites obtained from amorphous silica and low-cristobalite, respectively. These values suggest crystallite growth to be favored when using amorphous silica as reactant.     

Construction of 2D niobium carbide-embedded silver/silver phosphate as sensitive disposable electrode material for epinephrine detection in biological real samples

Our daily activities are in control and functioned by the neurotransmitter that helps in balancing the signals send to the brain. Epinephrine (EPN) is a commonly known neurotransmitter and the imbalance in EPN leads to several dysfunctions and diseases. Moreover, the uptake of EPN and the importance of EPN have provoked the need for the detection of EPN. Such detection will be helpful in the diagnostics and clinical monitoring of the diseases. The electrode material with intriguing properties for the detection is important and was designed. The niobium carbide (NbC) with silver/silver phosphate (Ag/AgPO) with interesting physical and chemical properties was synthesized. The physical and structural analysis of Ag/AgPO/NbC was characterized by different analytical techniques. The electrochemical detection of EPN was executed after the physicochemical presence of the material. The specific surface area, and high electrical conductivity, with improved active sites enhances the electrochemical performance of EPN. With these properties, the fabricated electrode records a lower limit of detection of about 0.004 μM with a linear range of 0.09–422.45 μM and the sensitivity was about 9.25 μAμM^?1cm^?2. The other parameter analysis such as repeatability, reproducibility, and stability showed excellent performances at Ag/AgPO/NbC/screen-printed carbon electrode. The real sample analysis with human serum and urine samples also had good recovery results. Thus, the Ag/AgPO/NbC nanocomposite is highly efficient with all these unique features which can be employed in several applications in near future.     

Triazoles as complexing agents: Synthesis and structural studies of some bivalent metal ion complexes with Bi- and tridentate ligands

Summary Co(II), Ni(II), Cu(II), Zn(II) and Cd(II) complexes of 4-amino-5-mercapto-3-trifluoromethyl-s-triazole (AMTT) and 5-mercapto-4-salicylideneamino-3-trifluoromethyl-s-triazole (MSTT) have been synthesized and characterized on the basis of elemental analyses, magnetic measurements, infrared and electronic spectral data. The ligandsAMTT andMSTT were characterized by elemental analyses, infrared and¹H NMR spectral studies.AMTT, involving N and S as donor atoms, andMSTT, involving N, O and S as donor atoms, act as bi- and tridentate ligands, respectively. The geometry of the complexes has been assigned on the basis of magnetic and electronic spectral data. EPR parameters for copper (II) complexes have been calculated. Thermal stabilities of the complexes are also reported. Due to insolubility in water and common organic solvents and infusibility at higher temperatures, all the complexes are thought to be polymeric in nature.

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Triazole als Komplexierungs-Agentien: Synthese und Strukturuntersuchungen an einigen bivalenten Metallionenkomplexen mit zwei- und dreizähnigen Liganden

Zusammenfassung Es wurden Co(II)-, Ni(II)-, Cu(II)-, Zn(II)- und Cd(II)-Komplexe von 4-Amino-5-mercapto-3-trifluormethyl-s-triazol (AMTT) und 5-Mercapto-4-salizylidenamino-3-trifluormethyl-s-triazol (MSTT) hergestellt und mittels Elementaranalyse, magnetischen Messungen, Infrarot- und Elektronenspektroskopie charakterisiert. Die LigandenAMTT undMSTT wurden elementaranalytisch und spektroskopisch (IR und¹H-NMR) charakterisiert.AMT wirkt über die N-und S-Donoratome als zweizähniger Ligand,MSTT über N, O und S als dreizähniger Ligand. Die Geometrie der Komplexe wurde auf der Basis von magnetischen und elektronenspektroskopischen Daten zugeordnet. Für die Cu(II)-Komplexe wurden die EPR-Parameter berechnet. Die thermischen Stabilitäten der Komplexe wurde ebenfalls untersucht. Wegen ihrer Unlöslichkeit in Wasser und gängigen organischen Lösungsmitteln und der Unschmelzbarkeit bei höheren Temperaturen wird eine polymere Natur der Komplexe angenommen.

     

Application of the sol-gel method for the preparation of some inorganic ion-exchangers in spherical form

Starting from the principles of sol-gel method, developed originally for the preparation of nuclear fuels in spherical form, their application to the preparation of microspheres of various non-nuclear elements is presented. In addition to the preparative conditions of the primarily hydroxidic spheres, their conversion into other insoluble compounds such as phosphates, ferrocyanides, sulphides, etc. is described. These sol-gel products work very well as ion-exchangers; their sorption properties are quite comparable to those of the common powder sorbents, the sphere from being their main beauty. Applicability of these sorbents as well as their limitations are also discussed.