Morphology‐dependent electrocatalytic activity of nanostructured Pt/C particles from hybrid aerosol–colloid process

An optimum nanostructure and pore size of catalyst supports is very important in achieving high catalytic performances. In this instance, we evaluated the effects of various carbon nanostructures on the catalytic performances of carbon‐supported platinum (Pt/C) electrocatalysts experimentally and numerically. The Pt/C catalysts were prepared using a hybrid method involving the preparation of dense, hollow, and porous nanostructured carbon particle via aerosol spray pyrolysis followed by microwave‐assisted Pt deposition. Electrochemical characterization of the catalysts showed that the porous Pt/C catalyst gave the best performance; its electrochemical surface area was much higher, more than twice than those of hollow or dense Pt/C. The effects of pore size on electrocatalysis were also studied. The results showed the importance of a balance between mesopores and macropores for effective catalysis with a high charge transfer rate. A fluid flow model showed that good oxygen transport contributed to the catalytic activity. © 2015 American Institute of Chemical Engineers AIChE J, 62: 440–450, 2016     

Studies on spinel cobaltites,MCo2O4 (M = Mn,Zn, Fe,Ni and Co) and their functional properties

Optimization of electrodes for charge storage with appropriate processing conditions places significant challenges in the developments for high performance charge storage devices. In this article, metal cobaltite spinels of formula MCo₂O₄ (where M = Mn, Zn, Fe, Ni and Co) are synthesized by oxalate decomposition method followed by calcination at three typical temperatures, viz. 350, 550, and 750 °C and examined their performance variation when used as anodes in lithium ion batteries. Phase and structure of the materials are studied by powder x-ray diffraction (XRD) technique. Single phase MnCo2O4,ZnCo2O4 and Co3O4 are obtained for all different temperatures 350 °C, 550 °C and 750 °C; whereas FeCo₂O₄ and NiCo₂O₄ contained their constituent binary phases even after repeated calcination. Morphologies of the materials are studied via scanning electron microscopy (SEM): needle-shaped particles of MnCo₂O₄ and ZnCo₂O₄, submicron sized particles of FeCo₂O₄ and agglomerated submicron particle of NiCo₂O₄ are observed. Galvanostatic cycling has been conducted in the voltage range 0.005–3.0 V vs. Li at a current density of 60 mA g^?1 up to 50 cycles to study their Li storage capabilities. Highest observed charge capacities are: MnCo₂O₄ – 365 mA h g^?1 (750 °C); ZnCo₂O₄ – 516 mA h g^?1 (550 °C); FeCo₂O₄ – 480 mA h g^?1 (550 °C); NiCo₂O₄ – 384 mA h g^?1 (750 °C); and Co₃O₄ – 675 mA h g^?1 (350 °C). The Co₃O₄ showed the highest reversible capacity of 675 mA h g^?1; the NiO present in NiCo₂O₄ acts as a buffer layer that results in improved cycling stability; the ZnCo₂O₄ with long needle-like shows good cycling stability.     

Strategies for stereocontrol at C1 or C2 in syntheses of α-glucosaminides

The C1 and C2 stereocenters of α-glucosaminides can be prepared by establishing the stereocenters in either order. For the former, a C2-azido glucosyl donor is prepared first, and the restraining effect of a 4,6-O-benzylidene ring is used to induce α-coupling. For the latter, the C1 linkage is prepared first by use of an n-pentenyl-manno-1,2-orthoester donor which ensures (a) clean α-coupling and (b) a convenient C2-ester. The C2-ester is replaced with a triflate leaving group, and nucleophilic displacement is effected by use of a hypervalent silicon azide.     

Polyphosphazenes—A Promising Candidate for Drug Delivery,Bioimaging, and Tissue Engineering: A Review

Synthetic polymer materials have been surged to the forefront of research in the fields of tissue engineering, drug delivery, and biomonitoring in recent years. Biodegradable synthetic polymers are increasingly needed as transient substrates for tissue regeneration and medicine delivery. In contrast to commonly used polymers including polyesters, polylactones, polyanhydrides, poly(propylene fumarates), polyorthoesters, and polyurethanes, biodegradable polyphosphazenes (PPZs) hold great potential for the purposes indicated above. PPZ's versatility in the synthetic process has enabled the production of a variety of polymers with various physico-chemical, and biological properties have been produced, making them appropriate for biomedical applications. Biocompatible PPZs are often used as scaffolds in the regeneration of skeleton, bones, and other tissues. PPZs have also received special attention as potential drug vehicles of high-value biopharmaceuticals such as anticancer drugs. Additionally, by incorporating fluorophores into the PPZ backbone to produce photoluminescent biodegradable PPZs, the utility of polyphosphazenes is further expanded as they are used in tracking the regeneration of the target tissue as well as the fate of PPZ based scaffolds or drug delivery vehicles. This review provides a summary of the evolution of PPZ applications in the fields of tissue engineering, drug delivery, and bioimaging in recent 5 years.     

Comparative examination of adhesive and cohesive properties of fluorinated coatings on stone/tile surfaces

A NanoScratch methodology was used to evaluate the relative adhesive and cohesive strength of fluorinated poly(methyl methacrylate-co-methacrylic acid) and fluorinated phosphate coatings on stone and tile surfaces. In general, all coatings showed ability to bind to the stone and tile surfaces, and polymer-based coatings expressed stronger adhesion compared to a small-molecule fluorinated phosphate coating. Also, anionic fluorinated polymers containing methacrylic acid (MAA) residues in the ammonium carboxylate form adhered more strongly compared to corresponding acidic polymer counterparts. In addition, anionic fluorinated polymers, shown to adhere more strongly to granite than marble, possibly due to strong Lewis acid-base interaction between carboxylate and aluminosilicates. Conversely, the fluorinated polymers, bearing the MAA side-chains in their free-acid form, bound more strongly to marble via possible Brønsted acid-base interactions between carboxylic acid and calcium carbonate. Lastly, in most cases, comparable fracture thresholds were observed for the same coating material on different substrates. This was expected since fracture threshold is a measure of the mechanical strength of the coating material, independent of the substrate difference.     

Nanometric Micelles with Photo‐Triggered Cytotoxicity

The development of a photo‐responsive micellar system capable of triggering cell death is reported. Precursors of the micelles are synthesized by connecting a lipophilic chain to a hydrophilic polyethylene glycol via a photo‐labile nitrobenzyl group. The resulting amphiphilic units are self‐assembled in water forming 12 nm micelles that are readily internalized into cells. Upon photo‐irradiation, micelles undergo cleavage and yield a cytotoxic nitrosobenzaldehyde derivative, which significantly inhibits the proliferation of MDA‐MB‐231 cells under standard in vitro conditions.     

Conformal Band Notched Circular Monopole Antenna Loaded with Split Ring Resonator

This article presents the design and analysis of conformal circular monopole antenna with split ring resonator to get frequency notch characteristics in the wideband. Split ring resonators placed on one side of the substrate and complementary split ring resonators placed on the other side of the substrate at defected ground structure, which yields the frequency notch characteristics with respect to the microstrip feeding. Dual notch band characteristics are obtained between 4–4.3 and 7.3–8.1 GHz. The analyzed conformal characteristic of the antenna supports excellent constant reflection coefficient characteristics over the band at different angles. The impedance and radiation characteristics of the antenna model is analysed in simulation along with unit cell analysis of the SRR and the measured results are providing good agreement with them.     

Anisotropic photoresponse investigation of chemical vapor transport (CVT) grown quaternary Cu2ZnSnS4 single crystals

The single crystals of quaternary transition metal chalcogenide Cu₂ZnSnS₄ (CZTS) are grown by a closed system chemical vapor transport technique. The high purity individual elemental precursors are employed in the growth of the crystals. These crystals are found to be single-phase by X-ray diffraction and Raman analysis. The near stoichiometry of the grown crystals is confirmed by spectroscopy analysis of the photoelectron generated by X-rays and analysis of the energy of the dispersive X-rays generated by electrons. The surface study by scanning electron microscopy showed the growth to happen by sheet spread mean and the electron diffraction showed fringe width match with (112) plane spacing. The study of the CZTS/Ag-paste/Cu-wire system for incident white light and three wavelengths of laser lights in two configuration modes of top-contact (II to the plane) and bottom-top-contact (⊥ to the plane) showed anisotropic behavior. The incident white light illumination intensity of 120 mW/cm² showed utmost photoresponse. The top-contact mode configuration showed maximum responsivity and detectivity of 0.72 mA/W and 0.33 × 10⁹ Jones, respectively, while bottom-top-contact showed 0.18 mA/W and 0.13 × 10⁹ Jones, respectively. The anisotropic photoresponse by the CZTS crystals insinuates the potential for future applications.

     

Molecular transport characteristics of poly (ethylene‐co‐vinyl acetate) membranes in the presence of normal alkanes

Solvent transport into poly (ethylene‐co‐vinyl acetate) membranes exposed to n‐alkanes has been studied in the temperature interval of 30–60°C. Pure and cross‐linked membranes were prepared. Membranes with different loading of cross‐linking agent were also prepared. It was found that for all liquids, the equilibrium penetrant uptake was influenced by the introduction of cross links. The mechanism of transport has been found to deviate from the regular Fickian behaviour. Transport parameters such as diffusion coefficient, sorption constant and permeability coefficient have been calculated. The influence of temperature on transport was analysed. Transport parameters and activation parameters for the process of diffusion have been calculated. The transport coefficients and the activation parameters showed a dependence on cross‐link density. The Van't Hoff's relationship was used to compute the entropy change. The values of polymer–solvent interaction parameters have been used to calculate the molar mass between cross links of the network polymer. The phantom and affine models were used to analyse the deformation of the networks during swelling. A correlation between theoretical and experimental results was also done. Copyright © 2007 John Wiley & Sons, Ltd.     

Role of Drying Techniques on the Development of Porosity in Silica Gels

Silica gel has been prepared by the hydrolysis of TEOS under three different pH conditions. These gels have been subjected to drying in an air oven, under humidity, and also by exposure to microwaves, followed by further calcination at 500°C under slow heating schedule (3°C/min). Silica samples thus obtained are characterised by B.E.T. specific surface area and pore volume data. The thermal decomposition behaviour of the precursor gels are also reported. The adsorption isotherms of these samples indicate different behaviour related to the method of synthesis. Increase in pH of hydrolysis of the TEOS from 3 to 8 results in increase in specific surface area in tune with the earlier reports. However more significant observation is the variation in pore size distribution as evidenced from adsorption isotherms related to method of drying. Silica gels prepared at pH 3 show Type I behaviour irrespective of the method of drying. However gel prepared at pH 6 shows Type II behaviour when dried under microwave with specific surface area as high as 635 m₂/g and pore volume 0.9733 cc/g. The precursor gels prepared at still higher pH exhibit Type IV behaviour when subjected to microwave drying. The pH conditions of synthesis of precursor gels along with drying techniques appear to affect not only the surface areas and porosities but also the resultant adsorption isotherms, in sol-gel silica.