Showing papers by "Galen D. Stucky published in 2006"
TL;DR: By using the synthetic route described, large-scale syntheses of both mono- and alloyed metallic nanoparticles with a narrow size distribution can be easily achieved.
Abstract: A variety of metallic nanoparticles with a narrow size distribution have been synthesized in a facile one-phase method in which amine−borane complexes are applied as reducing agents. It is particularly striking that large colloidal crystals with sizes up to tens of micrometers can directly form from the reaction mixtures without any further treatment. By using the synthetic route described, large-scale syntheses of both mono- and alloyed metallic nanoparticles with a narrow size distribution can be easily achieved.
525 citations
TL;DR: This work describes a synthetic methodology that takes advantage of recent advances in the synthesis of metal and oxide nanomaterials and helps to bring together these two classes of materials for catalysis applications and develops efficient gold catalysts for green chemistry processes.
Abstract: Despite recent exciting progress in catalysis by supported gold nanoparticles, there remains the formidable challenge of preparing supported gold catalysts that collectively incorporate precise control over factors such as size and size-distribution of the gold nanoparticles, homogeneous dispersion of the particles on the support, and the ability to utilize a wide range of supports that profoundly affect catalytic performance. Here, we describe a synthetic methodology that achieves these goals. In this strategy, weak interface interactions evenly deposit presynthesized organic-capped metal nanoparticles on oxide supports. The homogeneous dispersion of nanoparticles on oxides is then locked in place, without aggregation, through careful calcination. The approach takes advantage of recent advances in the synthesis of metal and oxide nanomaterials and helps to bring together these two classes of materials for catalysis applications. An important feature is that the strategy allows metal nanoparticles to be well dispersed on a variety of oxides with few restrictions on their physical and chemical properties. Following this synthetic procedure, we have successfully developed efficient gold catalysts for green chemistry processes, such as the production of ethyl acetate from the selective oxidation of ethanol by oxygen at 100 degrees C.
452 citations
TL;DR: In this article, the Czochralski method was used to grow a 46mm-long crystal of the Ba8Ga16Ge30 clathrate, which was cut into disks that were evaluated for thermoelectric performance.
Abstract: The Czochralski method was used to grow a 46-mm-long crystal of the Ba8Ga16Ge30 clathrate, which was cut into disks that were evaluated for thermoelectric performance. The Seebeck coefficient and electrical and thermal conductivities all showed evidence of a transition from extrinsic to intrinsic behavior in the range of 600–900K. The corresponding figure of merit (ZT) was found to be a record high of 1.35 at 900K and with an extrapolated maximum of 1.63 at 1100K. This makes the Ba8Ga16Ge30 clathrate an exceptionally strong candidate for medium and high-temperature thermoelectric applications.
401 citations
TL;DR: An approach for the continuous and selective shortening of Au NRs synthesized by the silver ion-assisted seed-mediated method through oxidation with environmentally benign oxygen at slightly elevated temperatures is described.
Abstract: Gold nanorods (NRs) have received much attention due to their size-dependent surface plasmon-related optical properties. A seed-mediated approach has recently been developed for the synthesis of Au NRs with varying length-to-diameter aspect ratios. With the introduction of silver ions in the growth solution, Au NRs of narrow size distributions can be produced in high yields. Herein we describe an approach for the continuous and selective shortening of Au NRs synthesized by the silver ion-assisted seed-mediated method through oxidation with environmentally benign oxygen at slightly elevated temperatures. UV−visible extinction measurements indicate that the longitudinal surface plasmon band of Au NRs decreases in intensity and blue-shifts as a function of the oxidation time. Transmission electron microscopy (TEM) imaging shows that the length of Au NRs decreases with oxidation and their diameter stays almost constant, which suggests that oxidation starts at the ends of Au NRs. The size distributions of shor...
295 citations
TL;DR: In this paper, a simple and widely applicable methodology for the synthesis of multicomponent mesostructured metal oxides (MMMOs) from the combination of inexpensive and commercially available polymers with metal alkoxides solubilized in a sol−gel solution consisting of acetic acid, hydrochloric acid, and ethanol (AcHE).
Abstract: Multicomponent metal oxides have attracted attention for their potential use in electronic, (photo)catalytic, photovoltaic, and energy storage applications. The ability to simultaneously control the nanoscale structure and composition of such materials using simple and inexpensive routes is important for that potential to be realized. Here we introduce a simple and widely applicable methodology for the synthesis of multicomponent mesostructured metal oxides (MMMOs) from the combination of inexpensive and commercially available polymers with metal alkoxides solubilized in a sol−gel solution consisting of acetic acid, hydrochloric acid, and ethanol (AcHE). MMMOs obtained utilizing the AcHE system have tunable pore structures, a high degree homogeneity, and in certain cases thermal stability above 1000 °C. The ability to easily process these diverse MMMOs in the form of thin films, free-standing membranes, and monoliths provides distinct advantages over previously reported MMO synthesis proceduresespecially ...
229 citations
215 citations
TL;DR: Transmission electron microscopy characterizations reveal that the gold nanorods grown from both types of gold nanoparticle seeds are single-crystalline and that thegold bipyramids are penta-twinned.
Abstract: Gold nanorods and bipyramids have been synthesized using the seed-mediated approach in aqueous cetyltriethylammonium bromide (CTEAB) solutions in the presence of silver nitrate. Gold nanoparticle seeds that are stabilized with either CTEAB or sodium citrate have been used. The use of the CTEAB-stabilized seeds gives gold nanorods in high yield in one step with the longitudinal plasmon wavelength ranging from 750 to 1030 nm, depending on the amount of the seeds. The longitudinal plasmon wavelength can be extended to 1100 nm by the use of a two-step growth method. The growth of gold nanorods in CTEAB solutions takes 5−10 h, more than 5 times slower than that in cetyltrimethylammonium bromide solutions at the same concentration of surfactants. The use of the citrate-stabilized seeds gives both gold bipyramids and a small percentage of gold nanorods. The longitudinal plasmon wavelength of the bipyramids is tunable from 700 to 1100 nm by varying the amount of the citrate-stabilized seeds. The growth of gold bi...
131 citations
126 citations
TL;DR: The use of zeolite hemostat can control hemorrhage and dramatically reduce mortality from a lethal groin wound in a swine model of battlefield injury.
Abstract: Background:We have previously identified a granular zeolite hemostat (ZH) as an effective agent for control of severe bleeding, and it is currently being used by the US troops in the battlefield. ZH causes an exothermic reaction on application, which theoretically can be decreased by altering its ch
102 citations
TL;DR: In this article, molecular beam epitaxy growth of Al0.3Ga0.7As∕GaAs multijunction solar cells with epitaxial, semimetallic ErAs nanoparticles at the interface of the tunnel junction was reported.
Abstract: We report the molecular beam epitaxy growth of Al0.3Ga0.7As∕GaAs multijunction solar cells with epitaxial, semimetallic ErAs nanoparticles at the interface of the tunnel junction. The states provided by these nanoparticles reduce the bias required to pass current through the tunnel junction by three orders of magnitude, and therefore drastically reduce the voltage losses in the tunnel junction. We have measured open-circuit voltages which are 97% of the sum of the constituent cells, which result in nearly double the efficiency of our multijunction cell with a conventional tunnel junction.
87 citations
TL;DR: In this paper, mesoporous silica nanofibers with longitudinal pore channels are synthesized in high yields using cetyltrimethylammonium bromide as the structure-directing agent in hydrobromic acid solutions.
Abstract: Mesoporous silica nanofibers with longitudinal pore channels are synthesized in high yields using cetyltrimethylammonium bromide as the structure-directing agent in hydrobromic acid solutions. These nanofibers are used as templates to prepare gold nanoparticles along the fiber axis. For the gold-precursor-loaded nanofibers that are not completely dried, nearly spherical gold nanoparticles are produced by hydrogen reduction. As the reduction temperature is lowered, the size of the gold nanoparticles decreases and the number density greatly increases, resulting in surface plasmon coupling between neighboring gold nanoparticles. For the gold-precursor-loaded nanofibers that undergo an additional drying process, ellipsoidal gold nanoparticles are obtained, with their major axes oriented along the direction of the pore channels. The major axes of ellipsoidal gold nanoparticles can be controlled to be oriented either parallel or perpendicular to the fiber axis by use of nanofibers with either longitudinal or circular pore channels, respectively. These gold-nanoparticle-embedded nanofibers can be expected to find interesting applications in the area of photonics and optoelectronics.
TL;DR: It is shown that Br and I are unlikely to play a purely mechanical role, but that the local Zn and Cl concentrations and jaw microstructure are the prime determinants of local jaw hardness.
Abstract: Mineralized tissues are produced by most living organisms for load and impact functions. In contrast, the jaws of the clam worm, Nereis, are hard without mineralization. However, they are peculiarly rich in halogens, which are associated with a variety of post-translationally modified amino acids, many of which are multiply halogenated by chlorine, bromine, and/or iodine. Several of these modified amino acids, namely dibromohistidine, bromoiodohistidine, chloroiodotyrosine, bromoiodotyrosine, chlorodityrosine, chlorotrityrosine, chlorobromotrityrosine, and bromoiodotrityrosine, have not been previously reported. We have found that the distributions of Cl, Br, and I differ: Cl is widespread whereas Br and I, although not colocalized, are concentrated in proximity to the external jaw surfaces. By using nanoindentation, we show that Br and I are unlikely to play a purely mechanical role, but that the local Zn and Cl concentrations and jaw microstructure are the prime determinants of local jaw hardness. Several of the post-translationally modified amino acids are akin to those found in various sclerotized structures of invertebrates, and we propose that they are part of a cross-linked protein casing.
TL;DR: The tunable in vitro blood clotting activity of high-surface-area hemostatic bioactive glass is evaluated by Thromboelastograph, a clinical instrument for quantifying changes in blood during coagulation.
Abstract: The tunable in vitro blood clotting activity of high-surface-area hemostatic bioactive glass is evaluated by Thromboelastograph, a clinical instrument for quantifying changes in blood during coagulation. The hemostatic trends associated with hemostatic bioactive glass and a new preparation of spherical hemostatic bioactive glass, along with similar Si- and Ca-containing oxides, are described and related to Si:Ca ratios, Ca2+ availability and coordination environment, porosity, DeltaHHydration, and surface area. Hemostatic bioactive glass is a new material with an excellent efficacy for inducing hemostasis and is chemically distinct from the traditional bioglass employed for bone growth.
TL;DR: Glycera jaws represent the first known integument to exploit melanin as a cohesive load- and shape-bearing material and chemical inertness withstanding boiling concentrated hydrochloric acid as well as boiling concentrated sodium hydroxide.
TL;DR: The internalization of a series of water-soluble CdSe/CdS quantum dots stabilized by citrate, isocitrate, succinate, and malate by Escherichia coli is established by epifluorescence and confocal fluorescence scanning microscopy, fluorimetry, and UV–vis spectroscopy on whole and lysed bacterial cells.
Abstract: The internalization of a series of water-soluble CdSe/CdS quantum dots (QDs) stabilized by citrate, isocitrate, succinate, and malate by Escherichia coli is established by epifluorescence and confocal fluorescence scanning microscopy, fluorimetry, and UV–vis spectroscopy on whole and lysed bacterial cells. The organic-acid-stabilized QDs span a range in size from 3.8±1.1 to 6.0±2.4 nm with emission wavelengths from 540 to 630 nm. QDs of different sizes (i.e., 3.8–6 nm) can enter the bacterium and be detected on different fluorescence channels with little interference from other QDs as a result of the distinct emission profiles (i.e., 540–630 nm, respectively). Costaining QD-labeled E. coli with 4′,6-diamidino-2-phenylindole dihydrochloride (DAPI) demonstrates that the QDs and DAPI are colocalized within E. coli, whereas costaining QD-labeled E. coli with membrane dye FM4-64 shows that the FM4-64 is localized in the outer bacterial membrane and that the QDs are inside.
Patent•
04 Apr 2006TL;DR: In this article, the authors provide compositions, methods and devices relating to a silaceous oxide that generates a reduced heat of hydration upon contact with blood, which attenuates a tissue burning side effect of conventional hemostatic agents without adversely affecting the wound healing properties.
Abstract: The invention provides compositions, methods and devices relating to a silaceous oxide that generates a reduced heat of hydration upon contact with blood. By reducing the heat of hydration, the compositions provide a hemostatic agent that attenuates a tissue burning side effect of conventional hemostatic agents without adversely affecting the wound healing properties of the composition.
TL;DR: It is shown that the reaction of methane and bromine (CH4:Br2 > or = 1) may yield either a kinetically or a thermodynamically determined bromomethane product distribution and proceeds in two main phases under ambient pressure on the laboratory time scale.
Abstract: The reaction of methane and bromine is a mildly exothermic and exergonic example of free radical alkane activation. We show here that the reaction of methane and bromine (CH4:Br2 ≥ 1) may yield either a kinetically or a thermodynamically determined bromomethane product distribution and proceeds in two main phases between 450 and 550 °C under ambient pressure on the laboratory time scale. This is in contrast to the highly exothermic methane fluorination or chlorination reactions, which give kinetic product distributions, and to the endergonic iodination of methane, which yields an equilibrium distribution of iodomethanes. The first phase of reaction between methane and bromine is a relatively rapid consumption of bromine to yield a kinetic methane bromination product distribution characterized by low methane conversion, low methyl bromide selectivity, and higher polybromomethane selectivity. In the second slower phase CHxBr4-x reproportionation leads to significantly higher methane conversion and higher me...
Patent•
15 Aug 2006TL;DR: In this article, a homogeneous composition comprising a hemostatically effective amount of a charged oxide, wherein the composition has an isoelectric point, as measured in calcium chloride, below 7.3 or above 7.4.
Abstract: The invention provides a homogeneous composition comprising a hemostatically effective amount of a charged oxide, wherein the composition has an isoelectric point, as measured in calcium chloride, below 7.3 or above 7.4. Typically, the charged oxide is selected from the group consisting of silaceous oxides, titanium oxides, aluminum oxides, calcium oxides, zinc oxides, nickel oxides and iron oxides. In some embodiments, the composition further comprises a second oxide selected from the group consisting of calcium oxide, sodium oxide, magnesium oxide, zinc oxide, phosphorus oxide and alumina. In a typical embodiment of the invention, the charged oxide is silaceous oxide, the second oxide comprises calcium oxide and the ratio, by molar ratio, of silaceous oxide to calcium oxide is 0.25 to 15. Optionally, the composition further comprises phosphorous oxide. Also described are methods of making and using such compositions.
TL;DR: In this paper, a self-assembling amphiphile is used to control the precipitation of CaCO 3 microspheres by acting as a template to form giant CaCO3 rhombohedra.
TL;DR: It is discovered that Zn, I, and Br in the jaws have single chemical environments whereas chlorine is present in two distinct modes (Cl-Zn and Cl-C), and it is unlikely that the halogens contribute directly to mechanical properties such as wear and hardness.
Abstract: The outstanding mechanical properties of impact-bearing tissues, such as Nereis jaws, make their morphology and chemical composition a subject of particular interest. The complex structure of the jaw was recently reported to exhibit molecular gradients that were closely correlated with stiffness and hardness.(18) Accordingly, we have explored the spatial distribution and bonding chemistries of Zn and the halogens in the surface structure of the jaws. Using secondary ion mass spectrometry (SIMS) and scanning electron microscopy (SEM), we found that Cl, Br, and I distributions are enhanced in surface layers of the basal protected portion of the jaw but are shifted to greater depths toward the exposed jaw tip. There are thus two complementary halogen gradients in the jaw: one on the surface that decreases from the base to the tip, coupled to an increasing one in the subsurface layers. The outer surface coating appeared to have granular morphology, in contrast to the anisotropic, fibrous core that dominates the subarchitecture. Using X-ray photoelectron spectroscopy (XPS), we discovered that Zn, I, and Br in the jaws have single chemical environments whereas chlorine is present in two distinct modes (Cl-Zn and Cl-C). Given the inverse relationship between surface exposure and halogen abundance in the jaws, it is unlikely that the halogens contribute directly to mechanical properties such as wear and hardness.
TL;DR: In this article, an ordered array of silver-tipped silica nanorods was used as a substrate for surface enhanced Raman spectroscopy (SERS) signal intensities from test molecules in regions of aggregated pillars.
Abstract: The image shows an ordered array of silver-tipped silica nanorods, which serve as a substrate for surface enhanced Raman spectroscopy (SERS). Signal intensities from test molecules in regions of aggregated pillars (indicated by the green laser beam) were enhanced by factors of 10 to 20 compared to arrays of separated pillars, as reported by Moskovits and co-workers on p. 2829. This hybrid structure maximizes SERS signal intensities from analytes while minimizing the quantities needed for detection due to the precise formation of “hot regions” at the intersection of the silver tips.
Patent•
16 May 2006TL;DR: A membrane/film casting method for fabricating composite membranes/films from a host polymer and a fullerene, often with the mixing of the poly(ethylene oxide) associated with a poly(methylene oxide)-associated fullerenes mixing agent, is described in this paper.
Abstract: A membrane/film casting method for fabricating composite membranes/films, and the produced composite membranes/films thereby fabricated, from a host polymer and a fullerene, often with the mixing of the host polymer and fullerene further promoted by a poly(ethylene oxide) attached fullerene mixing agent.
TL;DR: In this paper, the authors demonstrate the assembly of magnetic nanoparticles and polycations into hybrid microspheres in a single-step synthesis via complex coacervation and demonstrate the potential use of these assemblies in drug release by controlling their porosity.
Abstract: The synthesis of organic and inorganic nano- and microspheres has attracted much interest for a variety of applications ranging from drug delivery to chemical storage and catalysis. We recently demonstrated the assembly of magnetic nanoparticles and polycations into hybrid microspheres in a single-step synthesis via complex coacervation. These microspheres showed viability for bio-applications as indicated by toxicity tests, and are therefore potential targeted drug delivery devices, as they can be directed magnetically. This work reports the recent progress on the potential use of these assemblies in drug release by controlling their porosity. Fluorescein tagged dextran molecules with different MW have been infiltrated into these entities to determine critical pore size by confocal fluorescence microscopy. Different physicochemical characterization results are also presented.
TL;DR: In this paper, the authors describe three strategies: using molecular linkers to self-assemble silver clusters possessing the correct geometry, fabricating nanowire rafts in which the gaps between nanowires are "hot", and structuring the interior of nanopores so as to produce finely-architectured nanostructured arrays.
Abstract: Surface-enhanced Raman spectroscopy (SERS), an effect discovered in the 1970s and studied systematically in the 1980s, received a significant "second wind" with the report (primarily by Nie and by Kneipp) of enhancements large enough to allow the Raman spectrum of single molecules to be obtained. It is now understood that this occurs as a result of the extremely high electromagnetic fields that can exist at appropriately configured gaps and interstices between nanoparticles and other nanostructures composed of suitable materials (such as silver). With this insight one is now in a position to fabricate structures that will dependably and repeatably produce single-molecule SERS. We describe three such strategies: using molecular linkers to self-assemble silver clusters possessing the correct geometry; fabricating nanowire rafts in which the gaps between nanowires are "hot"; and structuring the interior of nanopores so as to produce finely-architectured nanostructured arrays.