Nanoporous Pt with high surface area by reaction-limited aggregation of nanoparticles

Nanoporous structures with high active surface areas are critical for a variety of applications. Here, we present a general templateless strategy to produce such porous structures by controlled aggregation of nanostructured subunits and apply the principles for synthesizing nanoporous Pt for electrocatalytic oxidation of methanol. The nature of the aggregate produced is controlled by tuning the electrostatic interaction between surfactant-free nanoparticles in the solution phase. When the repulsive force between the particles is very large, the particles are stabilized in the solution while instantaneous aggregation leading to fractal-like structures results when the repulsive force is very low. Controlling the repulsive interaction to an optimum, intermediate value results in the formation of compact structures with very large surface areas. In the case of Pt, nanoporous clusters with an extremely high specific surface area (39 m2/g) and high activity for methanol oxidation have been produced. Preliminary investigations indicate that the method is general and can be easily extended to produce nanoporous structures of many inorganic materials.

Delamination of surfactant-intercalated brucite-like hydroxy salts of cobalt and copper and solvothermal decomposition of the resultant colloidal dispersions

Surfactant anion intercalated hydroxy salts of copper and cobalt of the formula M(OH)2- x (surf)x.mH2O [M = Cu, Co; surf = dodecyl sulfate, dodecyl benzene sulfonate, and x = 0.5 for Cu and 0.67 for Co] delaminate readily in 1-butanol to give translucent colloidal dispersions that are stable for months. The extent of delamination and the colloidal dispersion observed in these solids is higher than what had been observed for layered double hydroxides. The dispersions yield the corresponding nanoparticulate oxides on solvothermal decomposition. While the copper hydroxy salt forms approximately 300 nm dendrimer-like CuO nanostructures comprising nanorods of approximately 10 nm diameter, the cobalt analogue forms approximately 20 nm superparamagnetic particles of Co3O4.

Mechanical properties of tricalcium phosphate single crystals grown by molten salt synthesis

Mechanical properties of flux-grown tricalcium phosphate (TCP) single crystals ranging in size from 50 to 75microm have been characterized by performing micro- and nanoindentation on their facets. Notwithstanding the inherent brittleness and anisotropy, these single crystals exhibit nanoscale plasticity in the form of pile-up around the edges of indents. A similar plastic response was observed in hydroxyapatite (HA) single crystals during nanoindentation in an earlier study. The hardness and elastic modulus obtained during nanoindentation are discussed in comparison with the polycrystalline forms of both TCP and HA found in the literature. The indentation fracture toughness values of TCP single crystals were found to be higher than those of HA single crystals. The higher values are attributed not only to the difference in crystal structure and corresponding differences in surface energy, but also to extensive crack bridging by ligament formation across crack faces during crack propagation.

Graphite oxide-intercalated anionic clay and its decomposition to graphene-inorganic material nanocomposites

A graphite oxide-intercalated anionic clay (nickel zinc hydroxysalt) has been prepared using the aqueous colloidal dispersions of negatively charged graphite oxide sheets and aminobenzoate-intercalated anionic clay layers as precursors. When the two colloidal dispersions are reacted, the interlayer aminobenzoate ions are displaced from the anionic clay and the negatively charged graphite oxide sheets are intercalated between the positively charged layers of the anionic clay. The thermal decomposition of the intercalated solid at different temperatures yields graphene-metal oxide/metal nanocomposites. Electron microscopic analysis of the composites indicates that the nanoparticles are intercalated between the layers of graphite in many regions of these solids although the graphite layers are largely exfoliated and not stacked well together.

Predicting the growth of two-dimensional nanostructures

The ability to predict the morphology of crystals formed by chemical reactions is of fundamental importance for the shape-controlled synthesis of nanostructures. Based on the atomistic mechanism for crystal growth under different driving forces, we have developed morphology diagrams to predict regimes for the growth of two-dimensional crystals. By using controlled reactions for crystal growth in the absence of surfactants/capping agents, we demonstrate the validity of this approach for the formation of 2D structures of Au, Ag, Pt and Pd.

Polymer assisted hydroxyapatite microspheres suitable for biomedical application

Hollow Microspheres of hydroxyapatite-polymer composite can be used as carriers in drug delivery and fillers in tissue engineering. Based on the concept of soft chemistry, a battery of technique is available in the literature to synthesize hollow microspheres, however, an economically viable synthesis route, having good control over the microarchitect and easy to be scaled up, is yet to be developed. Polymer matrix mediated synthesis of inorganic nanoparticles is known to synthesize nanoparticles with controlled morphology and dimensions. It is termed as biomimetic synthesis. Integrating the biomimetic synthesis of nano-particles and spray drying techniques, a novel process of producing hydroxyapatite-polymer composite hollow microspheres is briefly discussed here.

Suppression of the reversible thermal behavior of the layered double hydroxide (LDH) of Mg with Al: stabilization of nanoparticulate oxides

The layered double hydroxide of Mg with Al decomposes below 600 degrees C with the loss of nearly 48% mass, resulting in the formation of an oxide residue having the rock salt structure and nanoparticulate morphology. However, this product reconstructs back into the parent LDH, owing to its compositional and morphological metastability. The oxide can be kinetically stabilized within an amorphous phosphate network built up through an ex situ reaction with a suitable phosphate source such as (NH4)H2PO4. This oxide transforms into a thermodynamically more stable phase with a spinel structure on soaking in an aqueous medium. The oxide residue has a nanoparticulate morphology as revealed by the Scherrer broadening of the Bragg reflections as well as by electron microscopy. This work shows that the hydroxide reconstruction reaction and spinel formation are competing reactions. Suppression of the former catalyzes spinel formation as the excess free energy of the metastable oxide residue is unlocked to promote the diffusion of Mg2+ ions from octahedral to tetrahedral sites, which is the essential precondition to the formation of a normal spinel. This reaction taking place as it does at ambient temperature and in solution helps in the retention of a nanostructured morphology for the spinel. Another way of stabilizing the oxide is by incorporating the thermally stable borate anion into the LDH. This paves the way for an in situ reaction between the cations of the host LDH and the borate guest. The in situ reaction directly leads to the formation of an oxide with a spinel structure.

Gold Nanostructures from Cube-Shaped Crystalline Intermediates

Conventional bottom-up approaches for building nanostructures rely on the ability to synthesize nanoparticles of different shapes and sizes in a controlled manner that are then assembled to produce useful structures. Here, we present an alternate approach for producing nanostructures based on the formation of a crystalline intermediate in which the metal ion can be reduced in a controlled manner. Partial reduction of HAuCl4 by a long-chain amine results in the formation of a cube-shaped crystalline intermediate in which Au is present in a +1 oxidation state. By control of the nucleation of the metal in the intermediate, a variety of nanostructures can be synthesized. Here, we present results on the formation of superlattices, hollow cubes, nanotubes, and extended hollow structures starting from the intermediate. Direct evidence for the formation of metal within the intermediate by in situ electron-beam-induced reduction in the transmission electron microscope is presented.

Enhanced Reducibility of Ce1-xTixO2 Compared to That of CeO2 and Higher Redox Catalytic Activity of Ce1-x-yTixPtyO2-δ Compared to That of Ce1-xPtxO2-δ

Nanocrystalline Ce(1)(-)(x)Ti(x)O(2) (0 < or = x < or = 0.4) and Ce(1-)(x)(-)(y)Ti(x)Pt(y)O(2)(-)(delta) (x = 0.15, y = 0.01, 0.02) solid solutions crystallizing in fluorite structure have been prepared by a single step solution combustion method. Temperature programmed reduction and XPS study of Ce(1)(-)(x)Ti(x)O(2) (x = 0.0-04) show complete reduction of Ti(4+) to Ti(3+) and reduction of approximately 20% Ce(4+) to Ce(3+) state compared to 8% Ce(4+) to Ce(3+) in the case of pure CeO(2) below 675 degrees C. The substitution of Ti ions in CeO(2) enhances the reducibility of CeO(2). Ce(0.84)Ti(0.15)Pt(0.01)O(2)(-)(delta) crystallizes in fluorite structure and Pt is ionically substituted with 2+ and 4+ oxidation states. The H/Pt atomic ratio at 30 degrees C over Ce(0.84)Ti(0.15)Pt(0.01)O(2)(-)(delta) is 5 and that over Ce(0.99)Pt(0.01)O(2)(-)(delta) is 4 against just 0.078 for 8 nm Pt metal particles. Carbon monoxide and hydrocarbon oxidation activity are much higher over Ce(1-)(x)(-)(y)Ti(x)Pt(y)O(2) (x = 0.15, y = 0.01, 0.02) compared to Ce(1)(-)(x)Pt(x)O(2) (x = 0.01, 0.02). Synergistic involvement of Pt(2+)/Pt degrees and Ti(4+)/Ti(3+) redox couples in addition to Ce(4+)/Ce(3+) due to the overlap of Pt(5d), Ti(3d), and Ce(4f) bands near E(F) is shown to be responsible for improved redox property and higher catalytic activity.

Layered Double Hydroxide−CdSe Quantum Dot Composites through Colloidal Processing: Effect of Host Matrix−Nanoparticle Interaction on Optical Behavior

Layered double hydroxide (LDH)-monodispersed 4-nm CdSe nanoparticle composites were prepared through restacking of layers of colloidally dispersed delaminated LDH in the presence of CdSe nanoparticles in 1-butanol. The composites exhibit a blue shift for CdSe absorption, which increases with a decrease in nanoparticle content. The observed blue shift is due to the interaction of the quantum dots with the LDH layers, which leads to surface modification of the nanoparticles.

Surfactant intercalated α-hydroxides of cobalt and nickel and their delamination-restacking behavior in organic media

Dodecyl sulfate and dodecylbenzene sulfonate intercalated alpha-hydroxides of nickel and cobalt were synthesized by ammonia precipitation. These solids delaminate to give a colloidal dispersion of layers in organic solvents such as 1-butanol. The dispersed layers could be reassembled either by evaporation of the colloid or by coagulation by the addition of a polar solvent.

Ferrimagnetic Nanogranular Co3O4 through Solvothermal Decomposition of Colloidally Dispersed Monolayers of α-Cobalt Hydroxide

Co3O4 nanoparticles of 35 nm with a cauliflower-like morphology were obtained when a monolayer colloidal dispersion of dodecyl sulfate intercalated alpha-cobalt hydroxide in butanol was subjected to solvothermal hydrolytic decomposition. The nanogranular particles exhibit weakly ferromagnetic properties in contrast with both bulk and dispersed nanoparticulate Co3O4.

Measurement of intra-abdominal pressure in intensive care units in the United Kingdom: a national postal questionnaire study

BACKGROUND

To explore the attitudes of intensivists in the UK to intra-abdominal pressure (IAP) measurement and abdominal compartment syndrome (ACS) and to determine current practice.

METHODS

A postal questionnaire study addressed to the lead clinician in the intensive care unit was sent to hospitals in the UK with a general surgical service.

RESULTS

Completed questionnaires were received from 137 of the 207 hospitals surveyed (66.2% response rate). Only 1.5% of the respondents (n=2) had no prior knowledge of intra-abdominal hypertension and ACS. IAP had been measured on some occasion by 75.9% (n=104) of the respondents, always by the intravesical route. Among those intensive care units that measured IAP, in 93.2% (n=97) it was only measured when there was a suspicion of the development of ACS; 3.8% of units (n=4) measured IAP on all patients who had undergone an emergency laparotomy, and 2.9% (n=3) measured IAP only in those who had undergone emergency laparotomy associated with massive fluid resuscitation. There was major disparity in the frequency of IAP measurement and when to recommend abdominal decompression.

CONCLUSIONS

Despite widespread awareness of IAH and the ACS, many intensive care units never measure the IAP. When it is measured, the intravesical route is used exclusively. No consensus exists on optimal timing of measurement or when decompressive laparotomy should be performed.

Synthesis and structure of nanocrystalline TiO2 with lower band gap showing high photocatalytic activity

Nanocrystalline TiO2 was synthesized by the solution combustion method using titanyl nitrate and various fuels such as glycine, hexamethylenetetramine, and oxalyldihydrazide. These catalysts are active under visible light, have optical absorption wavelengths below 600 nm, and show superior photocatalytic activity for the degradation of methylene blue and phenol under UV and solar conditions compared to commercial TiO2, Degussa P-25. The higher photocatalytic activity is attributed to the structure of the catalyst. Various studies such as X-ray diffraction, Raman spectroscopy, Brunauer-Emmett-Teller surface area, thermogravimetric-differential thermal analysis, FT-IR spectroscopy, NMR, UV-vis spectroscopy, and surface acidity measurements were conducted. It was concluded that the primary factor for the enhanced activity of combustion-synthesized catalyst is a larger amount of surface hydroxyl groups and a lowered band gap. The lower band gap can be attributed to the carbon inclusion into the TiO2 giving TiO(2-2x)C(x) VO2**.

Dewetting of liquids on ceramic surfaces at high temperatures

The influence of surface structure and chemistry on high-temperature dewetting of silicate liquids on ceramic surfaces has been investigated. Model systems based on well-defined crystallography and known chemistry have been used to illustrate the effect of surface roughness and chemistry on the dewetting process. Reconstructed ceramic surfaces provide ideal substrates to study effects of surface roughness. It has been shown that the morphology of dewet droplets depend on the length scale and the crystallography of the facets on the surface. Complex pattern formation due to solute redistribution during dewetting is illustrated in the case of SiO2 dewetting on (001) rutile substrates. The role of kinetics on the dewetting process has also been clarified.

Herniation through triple defects of the diaphragm with gastric volvulus

A rare case of herniation through triple defects in the diaphragm with volvulus of the stomach is reported. Herniation with gastric volvulus was diagnosed preoperatively. Three diaphragmatic defects were detected at surgery. Repair of the defects after reduction of the abdominal contents resulted in an uneventful recovery.