Studies on structural,dielectric and electrical properties of Dy<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Bi<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>FeO<Subscript>3</Subscript> solid solutions

The polycrystalline samples of Dy _x Bi_1−x FeO₃ (x = 1, 0.8, 0.6, 0.4 and 0.2) were synthesized by standard solid state reaction technique. The samples synthesized were characterized by X-ray diffraction (XRD) technique. Further the samples were characterized by infrared (IR) spectroscopic technique. The dielectric measurements were carried out as a function of frequency in the range 100 Hz to 1 MHz at room temperature. Also the dielectric measurements were carried out as a function of temperature at certain fixed frequencies. The ac and dc resistivity measurements were carried out using two probe method. Also temperature dependence of ac and dc resistivity was noted. These measurements suggest polaron conduction in the samples. Finally, the data from XRD, IR, dielectric measurements were correlated.     

Optical Properties of Spin-Deposited Nanocrystalline Ni-Zn Ferrite Thin Films Processed by Sol-Gel

Nano crystalline Zn-substituted Ni ferrite films with compositions of Ni_1?xZn_xFe₂O₄ (x = 0.25, 0.50, 0.75) were synthesized by sol–gel spin coating method. The synthesized films were characterized for their structural, morphology, optical, electric, and magnetic properties using x-ray diffraction, scanning electron microscope, UV-Vis spectrometer, two probe resistivity, and vibrating sample magnetometer techniques, respectively. The corresponding results indicate that zinc content has significant effect on physical, magnetic, and optical properties of the ferrite. X-ray diffraction studies of thin films showed that the samples have pure cubic spinel phase. The crystallite size is of the nanoparticles estimated using Debey-Scherrer’s method was found to be in the range of 10.27 to 14.97 nm. The lattice parameter was found to be increased from 8.35 to 8.40 Å with increasing Zn²⁺ contents. The morphology of the thin films depicted the formation of well-developed nano-sized clusters with homogeneous and agglomerated. The optical absorption seen to be affected due to the presence of Zn in Ni-Zn ferrite thin films. Ni-Zn ferrite thin films possess small coercivity and remnant magnetization, which indicates the soft magnetic nature of the material. Electrical resistivity of the films decreases with increasing temperature, suggesting the semiconducting nature of the samples.     

Fast microwave-assisted solvothermal synthesis of metal nanoparticles (Pd,Ni, Sn) supported on sulfonated MWCNTs: Pd-based bimetallic catalysts for ethanol oxidation in alkaline medium

The preparation of metal nanoparticles (Pd, Ni, Sn) supported on sulfonated multi-walled carbon nanotubes (SF-MWCNTs) using a very rapid microwave-assisted solvothermal strategy has been described. Electrocatalytic behaviour of the SF-MWCNT-Pd and its ‘mixed’ bimetallic electrocatalysts (i.e., SF-MWCNT-PdSn_mix and SF-MWCNT-PdNi_mix) towards ethanol oxidation in alkaline medium was investigated. The result shows that the mixed Pd-based catalysts (obtained by simple ultrasonic-mixing of the individual MWCNT-metal nanocomposites) gave better electrocatalytic activity than their alloy nanoparticles (obtained by co-reduction of metal salts) or Pd alone. The SF-MWCNT platform gave better electrocatalytic performance compared to the unsulfonated and commercial Vulcan carbons. Detailed electrochemical studies (involving cyclic voltammetry, chronoamperometry, chronopotentiometry, and impedance spectroscopy) prove that the electrocatalytic oxidation of ethanol at the SF-MWCNT-PdNi_mix platform is more stable, occurs at lower potential, gives lower Tafel slopes, with faster charge-transfer kinetics compared to its SF-MWCNT-PdSn_mix counterpart. Also, result revealed that SF-MWCNT-PdNi_mix is more tolerant to CO poisoning than the SF-MWCNT-PdSn_mix. The results provide some important insights into the electrochemical response of microwave-synthesised Pd-based bimetallic catalysts for potential application in direct ethanol alkaline fuel cell technology.     

Fabrication of core–shell MIL-101(Cr)@UiO-66(Zr) nanocrystals for hydrogen storage

The fabrication of core–shell nanocrystals by incorporating microporous UiO-66 into mesoporous MIL-101 is reported. The growth of the core–shell MIL-101@UiO-66 nanocrystals was observed and supported by TEM and PXRD. The accessible pore volumes of the individual metal-organic framework (MOF) components and the core–shell hybrid crystals were also characterized. The hydrogen storage capacity exhibited by the resulting core–shell nanocrystals was 26% and 60% higher than those of pure phase MIL-101 and UiO-66, respectively. Finally, the fabricated core–shell MIL-101@UiO-66 structure exhibited a high degree of moisture tolerance.     

Chemical modification of polysulfone: Composite anionic exchange membrane with TiO2 nano-particles

Synthesis of quaternary polysulfone/Titanium dioxide (QPSf/TiO₂) nanocomposite membranes by the recasting procedure as suitable electrolyte in alkaline fuel cells is described. The composite membranes were characterized by ionic conductivity measurements, TGA, SEM, XRD, and AFM. Thermal analysis results showed that the composite membranes have good thermal properties. The introduction of the inorganic filler supplies the composite membrane with a good thermal resistance. The physico-chemical properties studied by means of SEM and XRD techniques suggested the uniform and homogeneous distribution of TiO₂ at 2.5 wt.% loading, and negligible agglomeration at 10 wt.% loading, also indicated enhancement of crystalline character of these membranes. The energy dispersive X-ray spectra (EDS) analysis gave proportional percentages that the distribution of Titania element on the surface of the composite membrane was uniform. Observations from the results suggest that QPSf/TiO₂ nanocomposite membranes have good prospects for possible use in AFC.     

Diphtheria immunity in Flanders

A serological survey to determine the immunity to diphtheria in the Flemish population was conducted according to the recommendations of the World Health Organization. Immunity to diphtheria was determined on a randomised, stratified sample (1679 serum samples) from an existing serum bank (4058 serum samples) representative of the Flemish population. All age groups between 0 and 100 years were included. A tissue (Vero cell) culture toxin neutralisation assay was used to measure serum diph-theria antitoxin concentrations. The results showed that 43% of the Flemish population was protected against diphtheria (antitoxin titre, > or = 0.1 IU/ml), while 32% was susceptible (antitoxin titre, < 0.01 IU/ml); for 25%, protection was of limited duration (antitoxin titre, > or = 0.01 IU/ml and < 0.1 IU/ml). The proportion of susceptible subjects showed a significant age-related increase, with the highest values in the 35 to 44 and 45 to 54 age groups (57.9% and 55.5%, respectively). These results emphasise the need for booster immunization of adults.     

Double cross-linked polyetheretherketone proton exchange membrane for fuel cell

The proton exchange membrane based on polyetheretherketone was prepared via two steps of cross-linking. The properties of the double cross-linked membrane (water uptake, proton conductivity, methanol permeability and thermal stability) have been investigated for fuel cell applications. The prepared membrane exhibited relatively high proton conductivity, 3.2 × 10⁻² S cm⁻¹ at room temperature and 5.8 × 10⁻² S cm⁻¹ at 80 °C. The second cross-linking significantly decreased the water uptake of the membrane. The performance of direct methanol fuel cell was slightly improved as compared to Nafion^® 117 due to its low methanol permeability. The results indicated that the double cross-linked membrane is a promising candidate for the polymer electrolyte membrane fuel cell, especially for the direct methanol fuel cell due to its low methanol permeability and high stability in a methanol solution.     

Magnetic properties of nanocrystalline CoFe2O4 synthesized by thermal plasma in large scale

The paper reports the large scale synthesis of nanoparticles of CoFe₂O₄ using thermal plasma reactor by gas phase condensation method. The yield of formation was found to be around 15 g h⁻¹. The magnetic properties of CoFe₂O₄, synthesized at different reactor powers, were investigated in view of studying the effect of operating parameters of plasma reactor on the structural reorganization leading to the different cation distribution. The values of saturation magnetization, coercivity and remanent magnetization were found to be influenced by input power in thermal plasma. Although the increase in saturation magnetization was marginal (61 emu g⁻¹ to 70 emu g⁻¹) with increasing plasma power; a significant increase in the coercivity (552 Oe to 849 Oe) and remanent magnetization (16 emu g⁻¹ to 26 emu g⁻¹) were also noticed. The Mössbauer spectra showed mixed spinel structure and canted spin order for the as synthesized nanoparticles. The detailed analysis of cation distribution using the Mössbauer spectroscopy and X-ray photoelectron spectroscopy leads to the conclusion that the sample synthesized at an optimized power shows the different site selective states.     

Enhanced conductivity and stability of composite membranes based on poly (2,5-benzimidazole) and zirconium oxide nanoparticles for fuel cells

Poly (2,5-benzimidazole) (ABPBI) and zirconium oxide (ZrO₂) nanoparticles composite membranes were synthesized. These membranes can be fabricated into tough, dense membranes by blending Poly (2,5-benzimidazole) (ABPBI) with zirconium oxide (ZrO₂) nanoparticles, which were characterized by using FTIR, XRD, SEM, TGA, DSC and tensile test. These composite membranes showed increased conductivity compared with original ABPBI membrane. Maximum proton conductivity at 100 °C was found to be 0.069 S cm⁻¹ on 10% ZrO₂ incorporated ABPBI composite membrane, almost four times as high as the 0.018 S cm⁻¹ obtained in the case of the ABPBI membrane. The conductivity was 0.0325 S cm⁻¹ at 180 °C in dry condition for ABPBI with 10% ZrO₂ nanoparticles composite membrane, higher than the conductivity 0.011 S cm⁻¹ of the ABPBI membrane at same condition. Furthermore, the composite membranes were shown to have high thermal and mechanical stability. These results suggest that ABPBI/ZrO₂ composite membranes may be a promising polymer electrolyte for fuel cells at medium or high temperature, due to their strong physical properties.