Synthesis and physical properties of mixed Co3O4/CoO nanorods by microwave hydrothermal technique

A mixture of crystalline Co₃O₄/CoO nanorods with non-uniform dense distribution has been successfully synthesized by microwave hydrothermal technique. The synthesized nanorods have been characterized by several techniques such as X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), and Fourier transforms infrared spectroscopy (FT-IR). The results showed that the as synthesized specimens contained mixed crystalline Co₃O₄/CoO nanorods with an average length of around 80 nm and an average diameter of 42 nm. UV–Vis spectrum of the nanorods exhibited a strong UV emission. The band energy gap of the product was 1.79 eV which lies between the energy gap of CoO and that for Co₃O₄. The obtained carrier concentration is of the order 4.32 × 10²⁷ m⁻³ and the dielectric constant is found to be 4.89. The electrical conductivity increases with increasing temperature and behaves as a semiconducting material with an activation energy of a bout 0.26 eV. This makes the as synthesized mixed Co₃O₄/CoO nanorods very useful for supercapacitor devices application. Magnetic hysteresis loops at room temperature of the as synthesized mixed oxides (Co₃O₄/CoO) nanorods exhibit typical soft magnetic behavior.     

Poly(urethane‐co‐benzoxazine)s via reaction of phenol terminated urethane prepolymers and benzoxazine monomer and investigation of their properties

In the present work, a new method was developed for the combination of polyurethanes (PUs) and polybenzoxazine (PBz) to obtain novel thermoset poly(urethane‐co‐benzoxazine)s with good thermal, mechanical, and electrical properties as well as low temperature curing profile. Knowing the catalytic effect of compounds possessing free phenolic groups on ring opening polymerization of benzoxazine monomers, preparation of phenol terminated urethane oligomers (PTPU) as the macroinitiator for a benzoxazine monomer (Ba) was considered. Firstly, NCO‐terminated urethane prepolymers were prepared from the reaction of poly(tetramethyleneether glycol), and 2,4‐tolylene diisocyanate, and then end functionalized with bisphenol‐A under proper condition. DSC, DMTA, and gel content measurements were applied to find optimum ring opening polymerization condition (170°C for 1 hr and 200°C for 15 min). Various kinds of thermoset polymers were prepared by the reaction of PTPU at different molecular weights with variable contents of Ba. All of monomeric and polymeric materials were characterized by conventional spectroscopic methods and their thermal, mechanical, viscoelastic, and electrical properties were measured and properties were correlated to their structure. Due to the interesting properties of these new materials, the possibility of using them as electrical insulators with higher service temperature in comparison to common PUs were examined and their potential applicability was confirmed. Copyright © 2010 John Wiley & Sons, Ltd.     

Layer-by-layer assemblies of chitosan and heparin: effect of solution ionic strength and pH

The growth of polysaccharide multilayers consisting of positively charged chitosan (CH) and negatively charged heparin (HEP) was monitored in situ by employing a quartz crystal microbalance (QCM-D) and dual-polarization interferometry (DPI). The main focus was on how the physicochemical properties of the solution affect the growth and structure of the resulting multilayer film. These results showed that when increasing the ionic strength of the polysaccharide solutions at a fixed pH, both the "dry" (optical) (DPI) mass and wet (QCM) mass of the adsorbed multilayer film increased. The same effect was found when increasing the pH while keeping the ionic strength constant. Furthermore, the growth of multilayers showed an exponential-like behavior independent of the solution conditions that were used in this study. It was also established that chitosan was the predominant species present in the chitosan-heparin multilayer film. We discuss the viscoelastic properties of the adsorbed layers and their variation during the multilayer buildup. Interestingly and contrary to common interpretation of the QCM-D results, we found that under one particular solution condition (pH 4.2 and 30 mM NaCl) the increase in the dissipation of oscillation energy from the adsorbed layer was a consequence of layer stiffening rather than indicating a more hydrated and viscous film. On the basis of the widely used Voigt viscoelastic model for an adsorbed layer, we show that it is the film viscosity and shear that define the layer viscoelasticity (structure) of the film and not the absolute value of energy dissipation, which in fact can be very misleading.     

The effect of polymers onto the size of zinc layered hydroxide salt and its calcined product

Zinc hydroxide nitrate, a brucite-like layered material was synthesized using pH control method. Poly(vinyl alcohol) and poly(ethylene glycol) were used at various percentages as size decreasing agents during the synthesis of zinc hydroxide nitrate. SEM and PXRD showed the decrease of size and thickness of the resultant zinc hydroxide nitrates. TG and surface area data confirmed the decrease of the particle sizes, too. When zinc hydroxide nitrates were heat treated at 500 °C, the physical properties of nano zinc oxides obtained depended on the parent material, zinc hydroxide nitrate.     

Production of Anti-Methicillin-Resistant <Emphasis Type="Italic">Staphylococcus</Emphasis> Activity from <Emphasis Type="Italic">Bacillus subtilis</Emphasis> sp. Strain B38 Newly Isolated from Soil

B38 bacterial strain, isolated from Tunisian soil showed a strong antimicrobial activity. Based on biochemical characterization and 16S rDNA sequence analysis, B38 strain was identified as Bacillus subtilis. Cell culture supernatant showed antibacterial activity against clinical isolates of methicillin-resistant Staphylococcus species and several Gram-positive and Gram-negative bacteria. Antifungal activity against phytopathogenic fungi was also observed. Antibacterial activity production started at early exponential growth phase, and maximum activity was reached at the stationary phase. This antibacterial activity was neither affected by proteases, lipase, and organic solvents, nor by surfactants. It was stable over a wide pH range and still active after autoclaving at 121 °C during 20 min. Thin layer chromatography followed by bioautography assay allowed the detection of four active spots with R _f values of 0.30, 0.47, 0.70, and 0.82. The single spot with R _f 0.30 showed antifungal activity, whereas the spots with R _f values of 0.47, 0.70, and 0.82 exhibited antibacterial activity.     

Thermal decomposition pathway of undoped and doped zinc layered gallate nanohybrid with Fe3+, Co2+ and Ni2+ to produce mesoporous and high pore volume carbon material

A series of brucite-like materials, undoped and doped zinc layered hydroxide nitrate with 2% (molar) Fe³⁺, Co²⁺ and Ni²⁺ were synthesized. Organic–inorganic nanohybrid material with gallate anion as a guest, and zinc hydroxide nitrate, as an inorganic layered host was prepared by the ion-exchange method. The nanohybrid materials were heat-treated at various temperatures, 400–700 °C. X-ray diffraction, thermal analysis and also Fourier transform infrared results showed that incorporation of the doping agents within the zinc layered hydroxide salt layers has enhanced the heat-resistivity of the nanohybrid materials in the thermal decomposition pathway. Porous carbon materials can be obtained from the heat-treating the nanohybrids at 600 and 700 °C. Calcination of the nanohybrids at 700 °C under nitrogen atmosphere produces mesoporous and high pore volume carbon materials.     

Cover Picture: Spectroscopic Tracking of Molecular Transport Junctions Generated by Using Click Chemistry (Angew. Chem. Int. Ed. 28/2009)

The in situ generation of molecules that bridge nanogaps generated by on‐wire lithography is achieved by using click chemistry. C. A. Mirkin, M. A. Ratner, and co‐workers show in their Communication on page 5178 ff. that these molecular junctions give high yields, and they describe how this strategy can be generalized to incorporate diverse molecular architectures within the nanogaps. Tracking of the molecular assembly process within the nanogaps is allowed by their strong electromagnetic field.

     

Gallate-Zn-Al-layered double hydroxide as an intercalated compound with new controlled release formulation of anticarcinogenic agent

A new organic-clay material, in which the organic moiety is intercalated into the inorganic interlayer, was prepared using gallate anion (GA) as a guest, and Zn-Al-layered double hydroxide, as clay host. The ion-exchange technique was found to be effective for the intercalation process in the formation of the compound. Although the basal spacings of the LDH and its intercalated product were fairly similar, FTIR, CHNS and TGA/DTG results indicated that the GA was actually intercalated into the interlayer of the host in parallel orientation. The resulting nanostructure material possessed a well ordered layered structure with 42.2% GA loading (w/w). The release of the anion from the interlayer of the intercalated compound was found to be of controlled manner, governed by the first order kinetic and it was also concentration dependent. The material has potential as a nano-storage of anticarcenogenic agent with controlled delivery capability.     

Effects on the micellar solubilization of organic compounds by surfactant micelles. I. Length of carboxylic side chains in aromatic acids

The semiequilibrium dialysis method has been used to determine solubilization equilibrium constants and activity coefficients of benzoic, phenylacetic, and hydrocinnamic acids (solubilizate) in micelles of the cationic surfactant hexadecylpyridinum chloride (cetylpyridinium chloride) in 0.1M HCl aqueous solutions. Methods described previously were employed to infer the concentrations of monomeric organic solute and surfactant on both sides of the dialysis cell. Values of the apparent solubilization constant K of the neutral acids have been correlated with mole fractions of the acid in the micelle X_A, where K=X_A/[monomeric acid]. The activity coefficients of both acid and surfactant were obtained, consistent with the Gibbs-Duhem equation. The solubilization constants of all three acids are nearly the same, indicating that there is no significant effect owing to the presence of one or more methylene groups between the carboxylate and the phenyl groups of benzoic acid. The solubilization constants also decrease appreciably, and the activity coefficients of the acids increase, as the mole fraction of the acid in the micelle increases.