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Synthesis Methods (synthesis + methods)
Selected AbstractsMechanisms Controlling Crystal Habits of Gold and Silver ColloidsADVANCED FUNCTIONAL MATERIALS, Issue 7 2005C. Lofton Abstract Examples of gold and silver anisotropic colloids, such as prisms and rods, have appeared in the literature for many years. In most cases, the morphologies of these thermodynamically unfavorable particles have been explained by the particular reaction environment in which they were synthesized. The mechanisms used to explain the growth generally fall into two categories, one in which chemically adsorbed molecules regulate the growth of specific crystal faces kinetically, and the other where micelle-forming surfactants physically direct the shape of the particle. This paper raises questions about the growth of anisotropic metal colloids that the current mechanisms cannot adequately address, specifically, the formation of multiple shapes in a single homogeneous reaction and the appearance of similar structures in very different synthesis schemes. These observations suggest that any growth mechanism should primarily take into consideration nucleation and kinetics, and not only thermodynamics or physical constrictions. The authors suggest an alternative mechanism where the presence and orientation of twin planes in these face-centered cubic (fcc) metals direct the shape of the growing particles. This explanation follows that used for silver halide crystals, and has the advantage of explaining particle growth in many synthesis methods. In this mechanism, twin planes generate reentrant grooves, favorable sites for the attachment of adatoms. Shape and structural data are presented for gold and silver particles synthesized using several different techniques to support this new model. Triangular prisms are suggested to contain a single twin plane which directs that growth of the initial seed in two dimensions, but limits the final size of the prism. Hexagonal platelets are suggested to contain two parallel twin planes that allow the fast growing edges to regenerate one another, allowing large sizes and aspect ratios to form. Rods and wires were found to have a fivefold symmetry, which may only allow growth in one dimension. It is expected that a superior mechanistic understanding will permit shape-selective synthesis schemes to be developed. [source] Research and Prospects of Iron-Based SuperconductorsADVANCED MATERIALS, Issue 45 2009Zhi-An Ren Abstract The discovery of a new superconductor, LaFeAsO1,xFx with a superconducting critical temperatureT,c, of 26,K in 2008, has quickly renewed interest in the exploration of iron-based superconductors. More than 70 new superconductors have been discovered within several months, with the highest Tc of up to 55,K being observed in the SmFeAsO1,x compound. High Tcs have previously only been observed in cuprates; these new iron-based superconductors have been added as second members of the high- Tc family. The crystal structure of these compounds contains an almost 2D Fe,As layer formed by FeAs4 tetrahedrons, which can be separated by an oxide or metal layer that provides extra electrons to the Fe,As layer, and the itinerant iron 3d electrons form an antiferromagnetic (AFM) order state in the undoped parent compounds at around 100,200,K. Superconductivity can be induced by carrier doping, which destroys the AFM ground state. In this Review, the most recent findings on and basic experimental facts about this class of high- Tc materials will be presented, including the various superconducting structures, the synthesis methods, the physical properties of the parent compounds, the doping methods that could produce superconductivity, pressure effects, and the prospects for this new iron-based high- Tc family. [source] Effectiveness and limitation of circle criterion for LTI robust control systems with control input nonlinearities of sector typeINTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Issue 17 2005Tsuyoshi Kiyama Abstract This paper considers linear time invariant systems with sector type nonlinearities and proposes regional ,2 performance analysis and synthesis methods based on the circle criterion. In particular, we consider the effect of non-zero initial states and/or an ,2 disturbance inputs on the ,2 norm of a selected performance output. We show that both analysis and synthesis problems can be recast as linear matrix inequality (LMI) optimization problems, where, for synthesis, the outputs of the nonlinear elements are assumed available for control. Moreover, it is shown when the circle criterion does or does not help to improve the performance bound in robust control synthesis when compared with the existing linear analysis method. Copyright © 2005 John Wiley & Sons, Ltd. [source] The imaging continuum: bench to biomarkers to diagnostics,JOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 9-10 2007Richard A. Frank Abstract Innovation in basic and applied science has brought radiotracers to fruition as diagnostics. Non-invasive, longitudinal, and quantifiable molecular imaging is the key to diagnosing and monitoring numerous illnesses, with more to come from characterization of the clinical relevance of findings from genomics research. Radiotracers enable real-time in vivo studies of the effects of drug candidates on receptors, pathways, pharmacodynamics, and clinically relevant endpoints, thereby providing both early detection of pathophysiology to enable early intervention, and then monitoring of treatment responses to enable individualization of treatment regimens. We review developments which have translated imaging from ,bench to bedside', or ,biomarkers to diagnostics'. Notable developments include (1) synthesis methods for rapid 11C labeling of biomolecules to high specific radioactivity; (2) ligand-binding assays for screening molecular imaging agents rather than drugs; (3) in vivo imaging of radiotracers in animals; (4) discovering the imaging advantages of 99mTc, 11C, and 18F; (5) co-registration and automated quantitative assessment of high spatial resolution CT and MR images with molecular images from PET for longitudinal studies of treatment effect. Copyright © 2007 John Wiley & Sons, Ltd. [source] Improved synthesis of [18F]fluoromethyl tosylate, a convenient reagent for radiofluoromethylationsJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 8 2005Timothy R. Neal Abstract The utility of [18F]fluoromethyl tosylate as an [18F]fluoromethylation reagent has been reexamined. The preparation of this potentially useful compound from the reaction of bis(tosyloxy) methane with 18F- was reported several years ago, but it had not found use as a labeling reagent. When the reported reaction of bis(tosyloxy) methane with 18F- was carried out, [18F]fluoromethyl tosylate was formed along with [18F]tosyl fluoride. The product ratio depended upon reaction conditions, with the yield of [18F]fluoromethyl tosylate usually in the range of 25,40%. Addition of a small amount of water to the reaction mixture resulted in a significant increase in the yield of [18F]fluoromethyl tosylate. Reaction conditions were defined that produced a yield of 71±6% of [18F]fluoromethyl tosylate (decay corrected). The product was conveniently purified by alumina chromatography. Reaction of [18F]fluoromethyl tosylate with the (des-fluoromethyl) fluticasone propionate thioacid precursor produced [18F]fluticasone propionate in improved yield (16%, from fluoride in production-scale runs) over other synthesis methods. Similarly, formation of [18F]choline, [18F]fluoromethionine and N- ([18F]fluoromethyl)spiperone from the reaction of [18F]fluoromethyl tosylate with corresponding precursors was examined. Copyright © 2005 John Wiley & Sons, Ltd. [source] Architecture and performance of mesoporous silica-lipase hybrids via non-covalent interfacial adsorptionAICHE JOURNAL, Issue 2 2010Shan Lu Abstract To investigate the effects of surface property of mesoporous supports on the lipase immobilization and the performance of immobilized lipase, the mesoporous molecular sieve SBA-15 is functionalized with three organic moieties, dimethyl (DM), diisopropyl (DIP), and diisobutyl (DIB), respectively, by post-synthesis grafting and one-pot synthesis methods. Porcine pancreas lipase (PPL) is immobilized on SBA-15 supports through hydrogen bonding and hydrophobic interaction. The hydrophobic adsorption involves no active sites of PPL, and neither hyper-activation nor total inactivation occurs. The study on the intrinsic stability of PPL, including thermal stability, pH stability, and storage stability, indicates that the entrapment in mesoporous supports, and especially in organic-functionalized supports, makes PPL more resistant to temperature increment but more sensitive to pH change. The reusability investigation shows that the organic modification of mesoporous surface inhibits the enzyme leaching to some extent, resulting in a better operational stability. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Tandem mass spectrometry of synthetic polymersJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 9 2009Anna C. Crecelius Abstract The detailed characterization of macromolecules plays an important role for synthetic chemists to define and specify the structure and properties of the successfully synthesized polymers. The search for new characterization techniques for polymers is essential for the continuation of the development of improved synthesis methods. The application of tandem mass spectrometry for the detailed characterization of synthetic polymers using the soft ionization techniques matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and electrospray ionization mass spectrometry (ESI-MS), which became the basic tools in proteomics, has greatly been increased in recent years and is summarized in this perspective. Examples of a variety of homopolymers, such as poly(methyl methacrylate), poly(ethylene glycol), as well as copolymers, e.g. copolyesters, are given. The advanced mass spectrometric techniques described in this review will presumably become one of the basic tools in polymer chemistry in the near future. Copyright © 2009 John Wiley & Sons, Ltd. [source] Addressing chemical diversity by employing the energy landscape conceptACTA CRYSTALLOGRAPHICA SECTION A, Issue 5 2010Martin Jansen Exploring the structural diversity of a chemical system rests on three pillars. First, there is the global exploration of its energy landscape that allows one to predict which crystalline modifications can exist in a chemical system at a given temperature and pressure. Next, there is the development of new synthesis methods in solid-state chemistry, which require only very low activation energies such that even metastable modifications corresponding, for example, to minima on the landscape surrounded by low barriers can be realized. Finally, there is the theoretical design of optimal synthesis routes, again based on the study of the system's energy landscape. In this paper the energy landscape approach to the prediction of stable and metastable compounds as a function of temperature and pressure is presented, with a particular focus on possible phase transitions. Furthermore, several examples are presented, where such predicted compounds were subsequently successfully synthesized, often employing a newly developed synthesis method, low-temperature atom-beam deposition. [source] In situ time-resolved measurements of carbon nanotube and nanohorn growthPHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 11 2007D. B. Geohegan Abstract Growth mechanisms of carbon nanotubes are investigated and compared for both high- and low-temperature synthesis methods through experiments utilizing time-resolved, in situ imaging and spectroscopy. High-speed videography and pyrometry measured the timeframes for growth for single-wall carbon nanotubes (SWNTs) and nanohorns (SWNHs) by laser vaporization (LV) at 1150 °C, revealing that C can self-assemble at high temperatures preferentially into SWNH structures without catalyst assistance at rates comparable to catalyst-assisted SWNT growth by either laser vaporization or chemical vapor deposition (CVD). Laser interferometry and videography reveal the coordinated growth of vertically-aligned nanotube arrays (VANTAs) by CVD at 550,900 °C. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Effects of synthesis conditions on crystal morphological structures and thermal degradation behavior of hydrotalcites and flame retardant and mechanical properties of EVA/hydrotalcite blendsPOLYMER COMPOSITES, Issue 2 2007Longchao Du The effects of synthesis methods and reaction conditions on the crystal morphological structures and thermal degradation behavior of hydrotalcites have been studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), particle size analysis (PSA), and differential thermal analysis (DTA). The flame retardant and mechanical properties of ethylene,vinyl acetate (EVA) blends with the corresponding hydrotalcites have been estimated by limiting oxygen index (LOI), UL-94, and mechanical measurements. The results from the XRD, TEM, and PSA demonstrate that the hydrotalcites synthesized by ultrasound method have larger crystal sizes and particle size distribution than those by mechanical stirring method. Higher reaction temperature, longer dripping time, and lower solution concentration can increase the crystal and particle sizes of ultrasound-synthesized hydrotalcites, whereas the longer ultrasound aging time can increase the crystal sizes and decrease the particle sizes of hydrotalcites because of the smashing conglomeration. The DTA data give a positive evidence that the hydrotalcite samples prepared by mechanical stirring method with longer alkaline dripping time have higher thermal degradation temperature than those by ultrasound method, since the ultrasound-synthesized hydrotalcites have more lattice defects than stirring-prepared hydrotalcites. The data from LOI, UL-94, and mechanical tests show that the ultrasonic-synthesized hydrotalcites have better flame retardant properties, whereas the stirring-synthesized hydrotalcites have better tensile strength in the EVA/hydrotalcite blends. POLYM. COMPOS., 28:131,138, 2007. © 2007 Society of Plastics Engineers [source] Large-scale extrusion processing and characterization of hybrid nylon-6/SiO2 nanocompositesPOLYMERS FOR ADVANCED TECHNOLOGIES, Issue 4 2004Monserrat García Abstract Solution impregnations, pulltrusion and film stacking are widely used methods to prepare thermoplastic composite materials. Extruders are used to melt the polymer and to incorporate fibers into the polymer in order to modify physical properties. In this article, the compounding of colloidal silica nanoparticles filled polyamide-6 (PA-6) is achieved using a twin-screw extruder, which has a significant market share due to its low cost and easy maintenance. The experiments were performed at 250 rpm and the bulk throughput was 6,kg,h,1 with a pump pressure of 30 bars. The composites were characterized with nuclear magnetic resonance (NMR), wide angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). As determined by WAXD, the PA-6 showed higher amounts of , -phase when compared to other synthesis methods such as in situ polymerization. TEM pictures showed that the silica particles aggregated nevertheless, upon addition of 14% (w/w) silica the E-modulus increased from 2.7 to 3.9,GPa indicating that an effective mechanical coupling with the polymer was achieved. The behavior, illustrated with dynamic mechanical analysis (DMA) curves, indicated that in general when a filled system is compared to unfilled material, the values of the moduli (E, and E,) increased and tan , decreased. Determination of molecular mass distribution of the samples by means of size exclusion chromatography (SEC) coupled to a refractive index (RI), viscosity (DV) and light scattering (LS) detector revealed that the addition of silica did not decrease the average molecular weight of the polymer matrix, which is of importance for composite applications. Copyright © 2004 John Wiley & Sons, Ltd. [source] Combustion synthesis of ceramic nanoparticles for solid oxide fuel cellsASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 4 2010Dehua Dong Abstract Two combustion synthesis methods involving the use of polyacrylamide hydrogel and humic acids (HAs) as fuels were developed to synthesize ceramic nanoparticles for fabrication of solid oxide fuel cells (SOFCs). Using polyacrylamide hydrogel as fuel, highly crystalline NiO/Ce0.8Sm0.2O1.9 (SDC) and SDC nanoparticles were synthesized to make a modified layer and subsequent dense electrolyte film on the anode support. HA was used as complexible fuel to synthesize Sm0.5Sr0.5CoO3 nanoparticles for preparing the SOFC porous cathode. The single SOFCs made from these nanoparticles exhibited a maximum power density of 740 mW cm,2 at 650 °C operated with H2/air as fuel/oxidant, suggesting the synthesized nanoparticles are of high quality as SOFC materials. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Water Splitting on Semiconductor Catalysts under Visible-Light IrradiationCHEMSUSCHEM CHEMISTRY AND SUSTAINABILITY, ENERGY & MATERIALS, Issue 6 2009Rufino Abstract Splitting image: Sustainable hydrogen production is a key target for the development of alternative, future energy systems that will provide a clean and affordable energy supply. This Minireview focuses on the development of semiconductor catalysts that enable hydrogen production via water splitting upon visible-light irradiation. Sustainable hydrogen production is a key target for the development of alternative, future energy systems that will provide a clean and affordable energy supply. The Sun is a source of silent and precious energy that is distributed fairly all over the Earth daily. However, its tremendous potential as a clean, safe, and economical energy source cannot be exploited unless the energy is accumulated or converted into more useful forms. The conversion of solar energy into hydrogen via the water-splitting process, assisted by photo-semiconductor catalysts, is one of the most promising technologies for the future because large quantities of hydrogen can potentially be generated in a clean and sustainable manner. This Minireview provides an overview of the principles, approaches, and research progress on solar hydrogen production via the water-splitting reaction on photo-semiconductor catalysts. It presents a survey of the advances made over the last decades in the development of catalysts for photochemical water splitting under visible-light irradiation. The Minireview also analyzes the energy requirements and main factors that determine the activity of photocatalysts in the conversion of water into hydrogen and oxygen using sunlight. Remarkable progress has been made since the pioneering work by Fujishima and Honda in 1972, but he development of photocatalysts with improved efficiencies for hydrogen production from water using solar energy still faces major challenges. Research strategies and approaches adopted in the search for active and efficient photocatalysts, for example through new materials and synthesis methods, are presented and analyzed. [source] | |||||||||||||