Electrochemical characterization of poly(vinylidenefluoride)-zinc triflate gel polymer electrolyte and its application in solid-state zinc batteries

Gel polymer electrolyte (GPE) films comprising of poly(vinylidenefluoride), propylene carbonate, ethylene carbonate and zinc trifluoromethane sulfonate are prepared and characterized. The composition of GPE is optimized to contain minimum liquid components with a maximum specific conductivity of 3.94×10⁻³ S cm⁻¹ at (25±1) °C. A detailed investigation on the properties such as ionic conductivity, transport number, electrochemical stability window, reversibility of Zn/Zn²⁺ couple and Zn/gel electrolyte interfacial stability have been carried out. The ionic conductivity follows a VTF behaviour with an activation energy of about 0.0014 eV. Cationic transport number varies from 0.51 at 25 °C to 0.18 at 70 °C. Several cells have been assembled with GPE as the electrolyte, zinc as the anode, γ-MnO₂ as the cathode and their charge–discharge behaviour followed. Capacity values of 105, 82, 64 and 37 mAh/g of MnO₂ have been achieved at 10, 50, 100 and 200 μA/cm² discharge current densities, respectively. The discharge capacity values are almost constant for about 55 cycles for all values of current densities. Cyclic voltammetric study of MnO₂ electrode in Zn/GPE/MnO₂ cell clearly shows intercalation/deintercalation of Zn²⁺.     

Synthesis and Langmuir studies of bivalent and monovalent alpha-D-mannopyranosides with lectin Con A

Highly avid interaction between carbohydrate ligands and lectin receptors nominally requires the ligand presentation in a clustered form. We present herein an approach involving Langmuir monolayer formation of the sugar ligands and the assessment of their lectin binding at the air-water interface. Bivalent alpha-D-mannopyranoside containing the glycolipid ligand was used to study its binding profiles with lectin Con A, in comparison to the corresponding monovalent glycolipid. In addition to the bivalent and monovalent nature of the glycolipid ligands at the molecular level, the ligand densities at the monolayer level were varied with the aid of a nonsugar lipid molecule so as to obtain mixed monolayers with various sugar-nonsugar ratios. Lectin binding of bivalent and monovalent ligands at different ratios was monitored by differential changes in the surface area per molecule of the mixed monolayer, with and without the lectin. The present study shows that maximal binding of the lectin to the bivalent ligand occurs at lower sugar densities at the interface ( approximately 10% sugar in the mixed monolayer) than for that of the monovalent ligand ( approximately 20% sugar in the mixed monolayer). It is observed that complete coverage of the monolayer with only the sugar ligands does not allow all of the sugars to be functionally active.     

The Incorporation of Titania into Modified Silicates for Solar Photodegradation of Aqueous Species

A new class of sol-gel-derived photocatalytic materials has been synthesized and used in solar-assisted photodegradation studies. The materials are comprised of a homogeneous dispersion of commercial TiO₂ powder into silica and organically modified silicate (Ormosil) hosts. The efficiency of the photocatalytic properties of these TiO₂-containing materials was determined by their relative performance in the solar photodecomposition of aqueous rhodamine B. The improved adsorption properties of the modified materials compared to commercial TiO₂ increase the photodecomposition rate and the buoyancy properties, although excess hydrophobicity decreases the wetted section of the catalyst and its photocatalytic performance. These materials can be used as floatable catalysts for solar-assisted water purification.     

Silver-palladium nanodispersions in silicate matrices: highly uniform, stable, bimetallic structures

Ag-Pd nanobimetallic colloidal particles are prepared in a single step by a chemical reduction method. Organically modified aminosilicate is used as a supporting matrix as well as a stabilizing agent, to obtain very uniform, well-distributed bimetallic particles. These nanoparticles are found to be stable for several months in both the solid and the liquid phases. The structure of the bimetallic particles has been followed by X-ray photoelectron spectroscopy and ultraviolet-visible spectroscopy. The distribution and the particle size are determined by transmission electron microscope and X-ray diffraction studies. Polymerization and condensation of the support silicate material have been confirmed by Fourier transform infrared spectroscopy.     

Thermal study of accumulation of conformational disorders in the self-assembled monolayers of C8 and C18 alkanethiols on the Au111 surface

The thermal stability of short alkanethiol CH(3)(CH(2))(7)SH (C(8)) and long C(18) self-assembled monolayers (SAMs) is investigated using grazing angle reflection-absorption infrared spectroscopy, cyclic voltammetry, and molecular dynamics simulation. We track the disordering of SAM by untilting and gauche defect accumulation with increasing temperature in the 300-440 K range, a range of interest to tribology. Molecular dynamics simulation with both fully covered and partially covered C(6), C(8), and C(18) monolayers brings out the morphological changes in the SAM, which may be associated with the observed thermal stability characteristics. The molecular dynamics simulations reveal that short-chain C(6) and C(8) alkanethiols are more defective at lower temperature than the long-chain C(18) alkanethiol. With increasing temperature disorder in the SAM, as reflected in both untilting and gauche defect accumulation, tends to saturate at temperatures below 360 K for short-chain SAMs such that any further increase in temperature, until desorption, does not lead to any significant change in conformational order. In contrast the disorder in the long-chain C(18) SAM increases monotonically with temperature beyond 360 K. Thus, in a practical range of temperature, the ability of a SAM to retain order with increasing thermal perturbations is governed by the state of disorder prior to heat treatment. This deduction derived from molecular dynamics simulation helps to rationalize the significant difference we have observed experimentally between the thermal response of short- and long-chain thiol molecules.     

Correlation analysis of reactivity in the reduction of Co(en)2Br2+ by Fe(CN)64– in water–methanol/1,4-dioxane media

The reduction of [Co(en)₂Br₂]⁺ by [Fe(CN)₆]^4– in H₂O–MeOH and H₂O–1,4-dioxane mixtures has been studied over a range of solvent compositions [5–30% (v/v)]. The reduction of [Co(en)₂Br₂]⁺ was monitored under second order conditions and was found to be rapid in the various solvent compositions investigated. The favoured mechanism is an outer-sphere electron-transfer process consisting of elementary steps, ion-pair formation (K _IP), electron-transfer (k _et) and successor dissociation. Therefore, the overall rate constant, k ₂ = K _IP k _et[Co(en)₂- Br₂ ⁺][Fe(CN)₆ ^4–]. The rates increase as the proportion of organic cosolvent increases. The rates correlate with solvent properties, such as relative permittivity (_r) and the Grunwald–Winstein parameter, Y _GW, which are used to explain the non-specific interaction upon solvation of mixture of solvents on the incipient reactants and on the ion-pair. In addition, they are also subjected to multiparametric analysis employing Swain's solvent vectors A and B also with Kamlet–Taft's solvatochromic parameters , and *. The reduction rates show an excellent correlation with multiparametric equations and are susceptible to both specific and non-specific solvation effects. A quantitative estimation of the latter components has been attempted.     

X-ray and thermal studies on uranyl acetates of zinc,magnesium and nickel

Thermal decomposition of metal uranyl acetates is one of the best ways of preparation of uranates in crystalline form at low temperatures. Acetates of the type M(UO₂)₂(OAc)₆·7H₂O (M=Zn(II), Mg(II) and Ni(II) were prepared and characterised. Their X-ray powder diffraction analysis showed that they all belong to the orthorhombic crystal class.The thermal decomposition of acetates in air goes through the reduction of uranium(VI) to uranium(IV) during acetate decomposition followed by reoxidation by oxygen. Zinc uranylacetate gave on thermal decomposition ZnU₃O₁₀, the nickel salt gave NiU₃O₁₀ and the magnesium salt gave a mixture of MgUO₄ and MgU₃O₁₀. The thermal decomposition of acetates in helium led to reduction of uranium(VI) to uranium(IV) with the formation of UO₂. No lower valent uranates could be identified.

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Zusammenfassung Thermische Zersetzung von Metalluranylazetaten ist eine der geeignetsten Methoden zur Darstellung kristalliner Uranate bei niedrigen Temperaturen. Azetate des Types M(UO₂)₂(OAc)₆·7H₂O mitM=Zn(II), Mg(II) und Ni(II) wurden hergestellt und beschrieben. Eine Pulverdiffraktionsanalyse zeigte, daß alle der orthorhombischen Kristallklasse angehören. Der thermische Zerfall der Azetate in Luft vollzieht sich während des Azetatzerfalls über die Reduktion von Uran(VI) zu Uran(IV) bis zu einer anschließenden Reoxydation durch Sauerstoff. Bei der thermischen Zersetzung liefert Zinkuranylazetat ZnU₃O₁₀, das Nickelsalz liefert NiU₃O₁₀ und das Magnesiumsalz ein Gemisch aus MgUO₄ und MgU₃O₁₀. Der thermische Zerfall der Azetate in Helium führt zur Reduktion von Uran(VI) zu Uran(IV) unter Bildung von UO₃. Uranate mit niedrigerer Wertigkeit konnten nicht identifiziert werden.

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. M(UO₂)₂(OAc)₆ · 7H₂O, M = , . , . , . ZnU₃O₁₀, — NiU₃O₁₀, MgUO₄ MgU₃O₁₀. . .

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The authors thank Dr. D. D. Sood, Head, Fuel Chemistry Division, for his encouragement during the course of this work.     

An Efficient Procedure for the Preparation of 3′-Acetyl-2′,3′-dihydrobenzothiazoles by Ring Contraction of 2′,3′-Dihydro-1,5-Benzothiazepines Under Acetylating Conditions

Reaction of 2-benzoyl-6-hydroxy-3-methyl-5-(2′-substituted-2′,3′-dihydro-1,5-benzothiazein-4′-yl) benzofurans (4a-f) with a mixture of acetic anhydride and pyridine afforded 6-acetoxy-2-benzoyl-3-methyl-5-(3′-acetyl-2′-substitutedstyryl-2′,3′-dihydrobenzothiazole-2′-yl) benzofurans (5a-f) as sole products in good yields. A reaction mechanism for the ring contraction is proposed. All the compounds (5a-f) were screened for their antifeedant activity by the “Non-Choice test method” using 6 h prestarved fourth instar larvae of Spodoptera litura F. Compounds 5a, 5c and 5d exhibited highest antifeedant activity.     

A Facile Synthesis of 2-Benzoyl-6-Hydroxy-3-Methyl-5-(2-Substituted-2,3-Dihydro-1H-1,5-Benzodiazepin-4-YL) Benzo[b]Furans

The synthesis and characterisation of some new 1,5-benzodiazepines prepared from 4,6-diacetylresorcinol is reported.