Ionic studies of sodium alginate isolated from Sargassum terrarium (brown algea) karachi coast with 2,1-electrolyte

Physical and chemical analysis of the polysaccharide isolated from Sargassum Terarrium (brown algae) of Karachi coast showed characteristics of the sodium alginate. Optical rotations and sulphated ash content were found and FTIR spectra showed a sharp and strong absorption band at 1600 cm^?1 representing carboxylate ion which conforms high uronic acid content of the product. The viscosities of aqueous 0.1% sodium alginate solution were measured in the presence of copper II chloride (CuCl₂). The viscosities were found to be increased with the increase in the concentration of electrolyte. Viscosities were also found affected with temperature. ‘A’ and ‘B’ coefficients of Jones–Dole equation were evaluated. The increase in positive values of ‘B’ coefficient with the rise of temperature led to conclusion that given electrolyte in 0.1% aqueous sodium alginate solution behaves as structure maker. Thermodynamic parameters regarding to activated state like energy of activation E_η, change in free energy of activation ΔG_η and change of entropy of activation ΔS_η were also evaluated. Straight-line plots of log η versus 1/T observed with positive slopes show the effect of temperature on the viscosities of solutions. Energy of activation (E_η) was found to be decreased with the rise of temperature. Change in free energy of activation (ΔG_η) was also found to be increased with increase in concentrations of electrolyte and also with rise of temperature. The values of change in entropy of activation (ΔS_η) were also calculated. Negative values of ΔS_η were found to be increased with increase in concentration of electrolyte and also with rise of temperature.     

Morphology, crystallization behavior and properties of impact-modified polypropylene copolymer with or without sodium benzoate as a nucleating agent

 The morphology, crystallization behavior, and properties of an impact-modified polypropylene (PP) copolymer with or without sodium benzoate were investigated. The contents of ethylene–propylene rubber (EPR) in the reactor-made PP copolymer is about 15 wt%. For comparison, blends of PP and EPR containing the same EPR composition were prepared by melt-mixing. Morphological studies by scanning probe microscopy indicated that the impact-modified copolymer consists of three different phases, i.e., polyethylene, PP, and EPR phases, which is considerably different from the morphology of the conventional PP/EPR blend of the corresponding composition. The impact-modified PP copolymer exhibited a higher crystallization rate in terms of the lower crystallization half-time and thus higher thermal and mechanical properties, such as impact strength and hardness, than the PP/EPR blend did. The addition of sodium benzoate as a nucleating agent to the copolymer increased the crystallization rate and the mechanical properties. Received: 4 June 2001 Accepted: 31 October 2001     

Silver(I) Complexes with Nitrogen-Containing Noncyclic, Macrocyclic, and Macrobicyclic Ligands in Propylene Carbonate

Stability constants and thermodynamic data for complex formation of silver(I) with noncyclic, macrocyclic, and macrobicyclic ligands have been measured in propylene carbonate using potentiometric and calorimetric methods. All ligands containing two nitrogen donor atoms form extremely stable complexes. Only if substituents reduce the basicity of the nitrogen donor atoms, the stability of the complexes decreases drastically. However, the cryptand (221) forms the most stable complex of all ligands examined. In this case, the dimensions of the ligand cavity and of the cation are nearly identical.     

Electrosorption of sodium cellulose sulfates with different substitution patterns

Various types of sodium cellulose sulfate (SCS), dissolved in a 1M LiCl solution, were investigated by alternating current (AC)polarography. The SCS samples differed in the degree of substitution (DS), thedistribution of substituents within the anhydroglucose unit (AGU), and alongthechain, due to the method of synthesis. The goal was to study theelectrosorptionbehavior, characterized by the shape of the desorption wave in the polarogram,as a function of the chemical structure of the SCS samples. The shape of thedesorption wave reflects domains of different substitution. A superimpositionofparameters like DS and pattern of substitution on the electrosorption behaviorwas observed. The AC polarography method described can be used as a tool todistinguish between an even or uneven distribution of substituents along thecellulose chain.     

Modification of poly(propylene carbonate) with chain extender ADR-4368 to improve its thermal,barrier, and mechanical properties

Melt blending with the application of epoxy compound ADR-4368 as a chain extender was used to chemically modify polypropylene carbonate (PPC). ¹H nuclear magnetic resonance spectroscopy (¹H NMR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and tests using a universal material testing machine, a gas permeability tester, a water vapor permeability tester and other instruments were used to assess changes in the chemical structure, thermal and mechanical properties, and barrier efficacy of PPC before and after modification.The epoxy group in ADR-4368 reacted with the terminal hydroxyl group in PPC, considerably enhancing its mechanical properties, thermal stability and barrier efficacy to O₂ and CO₂. With the addition of 1% ADR-4368, the glass transition temperature of PPC was increased from 17 °C to 26.9 °C, while the thermal decomposition temperature (T_−5%) of PPC was increased from 177.3 °C to 240.6 °C. Moreover, the tensile strength of the modified PPC was improved from 3.3 MPa to 20.7 MPa.     

A new nonlinear optical silicate carbonate K2Ca[Si2O5](CO3) with a hybrid structure of kalsilite and soda-like layered fragments

Single crystals of a new silicate carbonate, K₂Ca[Si₂O₅](CO₃), have been synthesized in a multi-components hydrothermal solution with a pH value close to neutral and a high concentration of a carbonate mineralizer. The new compound has an axial structure (s.g. P6₃22) with unit cell parameters a = 5.04789 (15), c = 17.8668 (6) Å. Pseudosymmetry of the structure corresponds to s.g. P6₃/mmc which is broken only by one oxygen position. The structure consists of two layered fragments: one of the type of the mineral kalsilite (KAlSiO₄) and the other of the high-temperature soda-like α-Na₂CO₃, Ca substituting for Na. The electro-neutral layer K₂[Si₂O₅] (denoted K) as well as the layer Ca(CO₃) (denoted S) may separately correspond to individual structures. In K₂Ca[Si₂O₅](CO₃) the S-K layers are connected together via Ca-O interactions between Ca atoms from the carbonate layer and apical O atoms from the silicate one, and also via K-O interlayer interactions. A hypothetical acentric structure, sp.gr. P-62c, is predicted on the basis of the order-disorder theory. It presents another symmetrical option for the arrangement of K-layers relative to S-layers. The K,Ca-silicate-carbonate powder produces a moderate SHG signal that is two times larger that of the α-quartz powder standard and close to other silicates with acentric structures and low electronic polarizability.     

Activation of Carbon Dioxide and Synthesis of Propylene Carbonate

Cycloaddition of carbon dioxdie and propylene oxide to propylene carbonate catalyzed by tetra-tert-butyl metal phthalocyanine in the presence of tributylamine(TBA) shows higher yield than catalyzed by unsubstituted metal phthalocyanine.Comparing different catalysts of diverse metals,(t-Bu)4PcMg is more active than (t-Bu)PcFe ,But(t-Bu)4PcCo and (t-Bu)4PcNi only have low catalytic activities towards the reaction.Moreover,the yield will increase as the temperature increases.     

Synthesis and application of silica and calcium carbonate nanoparticles in the reduction of organics from refinery wastewater

Oil refinery is one of the fast growing industries across the globe and it is expected to progress in the near future. The worldwide increase in the generation of refinery wastewater along with strict environmental regulations in the discharge of industrial effluent, persistent efforts have been devoted to recycle and reuse the treated water. The wastewater from the refining operation leads to serious environmental threat to the ecosystem. Therefore, this study aimed to synthesize silica (SiO₂) and calcium carbonate nanoparticles (CaCO₃) in the reduction of organics from refinery wastewater. The synthesized nanoparticles were employed in the reduction of chemical oxygen demand (COD) from refinery wastewater by studying the influence of solution pH, contact time, dosage of nanoparticles and stirring speed on adsorption performance. From the batch experimental studies, the optimized processing conditions for the reduction of COD using SiO₂ nanoparticles are pH 4.0, dosage 0.5 g, stirring speed 125 rpm and 90 min stirring time, and the corresponding values for CaCO₃ nanoparticles are pH 8.0, dosage 0.4 g, stirring speed 100 rpm and 90 min stirring time. The study demonstrates that SiO₂ and CaCO₃ nanoparticles have a promising future in the reduction organics from refinery wastewater in different pH regimes.     

Effect of agar hydrogel and magnesium ions on the biomimetic mineralization of calcium carbonate

Here, agar hydrogel was selected as diffusion medium and template to control the biomimetic mineralization of calcium carbonate (CaCO₃). Due to three dimensional network structures and abundant functional groups (such as, hydroxyl groups), Ca²⁺ ions were uniformly distributed in the network and electrostatically attracted. The diffusion speed and range of CO₃^2? ions were mediated by the concentration of hydrogel medium. Under the synergistic effect of Mg²⁺ ions, the crystal CaCO₃ was induced by gas phase diffusion method in the hydrogel system. The results showed that the concentrations of Mg²⁺ ions and agar hydrogel had no obvious effect on the calcite phase of CaCO₃, but the morphologies and sizes changed with concentrations of medium and Mg²⁺ ions. Attribute to template effect, the crystallization behavior and growth rate of CaCO₃ crystals were regulated. Since Mg²⁺ ions were easily adsorbed on the surfaces of unit cell, the unique structure of CaCO₃ was precisely controlled. This study provides a useful reference and inspiration for the understandings of the contributions of ion supply rate in bio-mineralization and hydrogel medium in biomimetic mineralization.     

Zwei neue Metatitanate mit fünffach koordiniertem Titan: CsNaTiO3 und RbNaTiO3

Two New Metatitanates with Five-coordinated Titanium: CsNaTiO₃ and RbNaTiO₃ [1] The new oxides CsNaTiO₃ (I) and RbNaTiO₃ (II) are obtained by heating well grounded mixtures of the binary oxides in Ni-tubes as colourless platelike crystals. I: CsO_0.56, NaO_0.48 and TiO₂, Cs:Na:Ti = 1.1:1.1:1.0; 600°C, 61 d as well as CsO_0.97, NaO_0.48 and Ti₂O₃, Cs:Na:Ti = 1.5:3.0:1.0; 760°C, 27 d. II: RbO_0.52, NaO_0.48 and TiO₂, Rb:Na:Ti = 1.1:1.1:1.0; 750°C, 14 d as well as RbO_0.98, NaO_0.48 and Ti₂O₃, Rb:Na:Ti = 1.5:3.1:1.0; 760°C, 27 d. CsNaTiO₃ (orthorhombic, Cmcm) is nearly isostructural with KNaTiO₃ [2]; a = 601.4(1) pm, b = 1 120.3(1) pm, c = 563.4(1) pm (Guinier-Simon-Data, Z = 4). RbNaTiO₃ (monoclinic, C2/c) is isostructural with KNaTiO₃; a = 590.3(1) pm, b = 1 098.4(1) pm, c = 555.1(0) pm, β = 92.15° (Guinier-Simon-Data, Z = 4). Both structures are determined by using four-circle diffractometer data (CsNaTiO₃: Siemens AED2, 2 896I_o(hkl), MoKα , R = 2.4%, R_w = 2.3%; RbNaTiO₃: Philips PW 1 100, 2 743I_o(hkl), AgKα , R = 9.9%, R_w = 8.9%; additional data see text). The Madelung Part of Lattice Energy (MAPLE), Effective Coordination Numbers (ECoN), Mean Fictive Ionic Radii (MEFIR) and the Charge Distribution in Solids are calculated and discussed.