Decomposition Of Organic Precursors Research Articles

On the gas-phase graphene nanosheet synthesis in atmospheric microwave plasma torch: Upscaling potential and graphene nanosheet‑copper nanocomposite oxidation resistance

Efficient gas-phase synthesis of few-layer graphene nanosheets (GNS) is based on the controlled formation of the high-temperature environment and the reaction pathway of gas-phase species formed by the decomposition of organic precursors. Such a process results in the formation of high-quality carbon nanomaterial and hydrogen while the concentration of other gaseous by-products is minimized. In this work, the main factors affecting the efficiency of such processes in the TIAGO microwave plasma torch were investigated using detailed material analysis and mass spectrometry of the gas-phase products during the synthesis process. The results showed a limiting effect of increasing the microwave power (MW) on both the product yield as well as material quality, as shown by Raman and x-Ray photoelectron spectroscopy. The change in the reaction pathway increased the formation of C2H4, resulting in the upper limit of the achievable nanopowder yield. The prepared material showed a decrease in its high oxidation resistance, with increasing the delivered MW power as determined by thermogravimetry analysis. This behavior was related to the formation of GNS-Cu nanoparticles composite due to the presence of copper nanoparticles originating from erosion of the electrode of the TIAGO torch during the synthesis process at high MW powers.

Effect of different carbon precursors on properties of LiFePO4/C

The anoxic decomposition and influence of carbon precursors on the properties of LiFePO4/C prepared by using Fe2O3 were investigated. X-ray powder diffractometry, Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and carbon content and charge–discharge tests were applied to the characterization of the as-synthesized cathodes. Partial carbon is lost in the anaerobic decomposition of organic precursors and a high hydrogen content leads to a high residual carbon rate. Pyromellitic anhydride and citric acid participate in reactions before and in ball-milling. All the chosen carbon precursors are capable of producing LiFePO4 with high degree of crystallinity and purity. The carbon derived from α-D-glucose, pyromellitic anhydride, soluble starch, citric acid and polyacrylamide has a loose and porous texture in LiFePO4/C which forms conduction on and between LiFePO4 particles. LiFePO4/C prepared by using α-D-glucose, pyromellitic anhydride, citric acid and sucrose exhibits appreciable electrochemical performance. Graphite alone is able to enhance the electrochemical performance of LiFePO4 to a limited extent but incapable of preparing practical cathode.

Olefin metathesis for the functionalization of superparamagnetic nanoparticles

The functionalization of iron oxide superparamagnetic nanoparticles (NP) is one of the most active research fields due to the necessity of robust and, particularly, reproducible methods for the attachment of new biomolecules on the surface. Olefin metathesis offers many of these features, thanks to the new family of catalysts, especially Hoveyda-Grubbs second generation. Iron oxide NP were synthesized by the decomposition of organic precursors obtaining hydrophobic Fe3O4 NP with oleic acid as surfactant. These NP have been functionalized by the use of olefin metathesis reaction with different ligands. The metathesis was performed between the double bond in oleic acid structure and four different molecules with a terminal olefin, methyl acrylate, 6-hexenenitrile, allyltrifluoroacetate and 3-allyloxy-1,2-propandiol, in presence of the catalyst. These new NPs were fully characterized showing the success of the functionalization, small hydrodynamic size, narrow size distribution, and stability in water. This proof of concept opens a new way for the formation of carbon–carbon bonds on the surface of NP for biomedical applications.

Effect of Nature and Particle Size on Properties of Uniform Magnetite and Maghemite Nanoparticles

Magnetite nanoparticles with two different sizes, 5 and 17 nm, have been prepared by the decomposition of organic precursors in an organic media in the presence of oleic acid. The particles were characterized by TEM, X-ray diffraction, and IR and Mossbauer spectroscopy to clarify their structural and physicochemical properties. The samples consist of noninteracting magnetite nanoparticles in both cases with a more uniform size distribution and higher crystal order degree than particles of similar sizes prepared by coprecipitation. A controlled heat treatment of the samples in air leads to the transformation of magnetite to maghemite, which can be followed by the appearance of many IR bands forbidden for a spinel structure. In addition to that, an important reduction of saturation magnetization and coercivity at low temperature takes place whenever the oleic acid is preserved. Finally, Mossbauer spectra at different temperatures clearly show the effect of the nature of the iron oxide phase, the particle si...

EXAFS and XANES Study of a Pure and Pd Doped Novel Sn/SnOx Nanomaterial

EXAFS and XANES at the Pd and/or Sn K-edge have been used to characterize pure and palladium doped spherical particles (10−63 nm diameter) of a novel Sn/SnOx nanocomposite. This nanomaterial prepared by decomposition of organic precursors has found application in a new type of high performance solid-state gas sensor. Except for the sample annealed at 600 °C that is mainly pure crystalline tetragonal cassiterite SnO2, the undoped nanoparticles consist of a Sn metallic core surrounded by a layer of tin oxide that is mostly amorphous. In this outer layer, tin atoms were found to be 4−5-fold coordinated to oxygen with bond distances slightly larger than in bulk cassiterite SnO2. The average tin oxidation state in the oxide phase was evaluated using the length of the tin−oxygen bond to be between +3.7 and +3.5. The relative ratio of Sn atoms in the metallic phase was estimated between 15 and 36% of the total number of Sn atoms using the coordination number of the first Sn shell corresponding to the tin β tetra...

Synthesis of ultrafine Fe2O3 powders by decomposition of organic precursors and structural control by doping

Synthesis of ultrafine Fe2O3 powders by decomposition of organic precursors and structural control by doping

The high pressure synthesis of the graphitic form of C3N4

Basing on “ab-initio” calculations, C3N4 was claimed to be an ultra-hard material with a bulk-modulus close to that of diamond. Five different structural varieties were announced: the graphitic form, the zinc blende structure, the α and β forms of Si3N4 and another form, isostructural with the high pressure variety of Zn2Si04. Using the same strategy as that developed for diamond or c-BN synthesis, it appears that the graphitic form could be an appropriate precursor for preparing the 3D varieties. Two main problems characterize the C3N4 synthesis: (-) the temperature should be reduced in order to prevent nitrogen loss, (-) the reactivity of the precursors should be improved. Consequently, we have developed a new process using the solvothermal decomposition of organic precursors containing carbon and nitrogen in the presence of a nitriding solvent. The resulting material, with a composition close to C3N4, has been characterized by different physico-chemical techniques.

Model of carbon nanotube growth through chemical vapor deposition

This Letter outlines a model to account for the catalyzed growth of nanotubes by chemical vapor deposition. It proposes that their formation and growth is an extension of other known processes in which graphitic structures form over metal surfaces at moderate temperatures through the decomposition of organic precursors. Importantly, the model also states that the form of carbon produced depends on the physical dimensions of the catalyzed reactions. Experimental data are presented that correlate nanotube diameters to the size of the catalyst particles. Nanotube stability as a function of nanotube type, length and diameter are also investigated through theoretical calculations.

Pd and Pd−Cu Bimetallic Particles Prepared by Decomposition of Organic Precursors on Clean MgO Microcrystals

Pd and bimetallic Pd−Cu particles are prepared by decomposition of acetylacetonate precursors on clean MgO microcubes. Large Pd particles (>8 nm) are found with an octahedral shape asymmetrically truncated at the top and at the interface, epitaxially (001) and (110) oriented on MgO. Both the dislocations in the Pd lattice and the reentrant angles at the interface indicate a low interaction with the substrate. Small particles (<5 nm) are half octahedral truncated at the top. They are (001) oriented on the MgO surface and accommodated at the interface, as in the case of the particles prepared by ultrahigh vacuum (UHV) condensation. Bimetallic Pd−Cu particles are homogeneous in composition (50% Pd−50% Cu), with perfectly ordered CsCl structure, as in the case of the particles prepared by simultaneous condensation of Pd and Cu under UHV and high-temperature annealing. They are (001) oriented on MgO.

A novel synthetic method for the preparation of oxide superconductors: Anionic oxidation-reduction

A new chemical method for the bulk synthesis of Ba 2YCu 3O 7 powder is described and is applicable to the synthesis of other superconducting oxides. Ionic salt precursors are used which are intimately mixed by spray-drying an aqueous solution of these salts. The anions in the spray-dried mixtures (which in this study are mixtures of nitrate and acetate salts) participate in a low-temperature oxidation-reduction reaction. The exothermic redox reaction and the heat evolved from the reaction completely convert the precursors into their corresponding mixed oxides at temperatures below 300°C in one reaction step. Phase segregation (normally apparent in the decomposition of organic precursors) is not observed in the decomposition of the mixed anion (nitrate/acetate) precursors. The enthalpy of this reaction is strongly dependent upon acetate content in the mixture: −ΔH (9:4, acetate:nitrate) = 4016 (70) kJ/mole, whereas −ΔH (5:8, acetate:nitrate) = 890 (70) kJ/mole. These precursors can be reacted at 910°C for 10 min to produce single-phase Ba 2YCu 3O x . Sintered disks of Ba 2YCu 3O 7, prepared from Ba 2YCu 3O x powder, show onset T c's of 94–95 K and are fully superconducting by 90.5–91 K.