Small angle neutron and X-ray scattering studies of carbons prepared using inorganic templates

Small angle neutron (SANS) and X-ray (SAXS) scattering analyses of carbons derived from organic-loaded inorganic template materials, used as anodes in lithium ion cells, have been performed. Two clays were used as templates to load the organic precursors, pillared montmorrillonite (PILC), a layered silicate clay whose sheets have been permanently propped open by sets of thermally stable molecular props, and sepiolite, a natural channeled clay. Five different organic precursors were used to load the PILC: pyrene, styrene, pyrene/trioxane copolymer, ethylene and propylene, whereas only propylene and ethylene were used to load sepiolite. Pyrolysis took place at 700{degrees}C under nitrogen. Values such as hole radius, fractal dimension, cutoff length and density of the final carbons will be compared as a function of the clay and carbon precursors

Novel carbonaceous materials for lithium secondary batteries

Carbonaceous materials have been synthesized using pillared clays (PILCs) as templates. The PILC was loaded with organic materials such as pyrene in the liquid and vapor phase, styrene in the vapor phase, trioxane, ethylene and propylene. The samples were then pyrolyzed at 700 C in an inert atmosphere, followed by dissolution of the inorganic template by conventional demineralization methods. X-ray powder diffraction of the carbons showed broad d{sub 002} peaks in the diffraction pattern, indicative of a disordered or turbostratic system. N{sub 2} BET surface areas of the carbonaceous materials range from 10 to 100 m{sup 2}/g. There is some microporosity (r < 1 nm) in the highest surface area carbons. Most of the surface area, however, comes from a mixture of micro and mesopores with radii of 2--5 nm. Electrochemical studies were performed on these carbons. Button cells were fabricated with capacity- limiting carbon pellets electrodes as the cathode a/nd metallic lithium foil as the anode. Large reversible capacities (up to 850 mAh/g) were achieved for most of the samples. The irreversible capacity loss was less than 180 mAh/g after the first cycle, suggesting that these types of carbon materials are very stable to lithium insertion and de-insertion reactions

Anomalous small angle x-ray scattering study of layered silicate clays containing Ni(II) and Er(III)

These studies concern the synthesis of heterogeneous catalysts and the incorporation of heavy metals in trapping media. The Ni(II) containing clays were synthesized at 200{degree}C whereas those containing Er(III) were ion-exchanged natural clays. For the first system, ASAXS data were measured at 5 different energies near the K{alpha} edge of Ni at three different reaction times: unreacted, 4 hrs, and 15 hrs, when the crystallization is essentially complete. The data for the unreacted sample showed no correlations for a lamellar particle, while that reacted for 4 hrs indicated the evolution of lamella, and the crystallized sample (15 hrs) exhibits much larger lamellar correlations. Systematic variations are seen in the data for the 4 hr and 15 hr samples that are due to the anomalous scattering from the ordered Ni atoms in the layered silicates. The erbium study provides the first scattering measurements of heavy metal ion salvation and migration in clays, which has implications for both catalysis and environmental issues. Systematic energy-dependent variations in the signals near the L{sub III} edge of Er are observed for the hydrated sample, but not for the ``dry,`` as-prepared sample

The crystallization of new synthetic organo-clays

A novel method for the preparation of new synthetic, potentially catalytic clays has been discovered. In this method, a diverse variety of organic and-organometallic molecules can be directly incorporated during crystallization of the clay. This method has great potential for the incorporation of catalytically active species to create new heterogeneous catalysts. The catalyst precursors are organic-inorganic composites comprised of a layered silicate intercalated with such molecules as porphyrins or metalloporphyrins, organic aromatic dyes, a Cu(II) phthalocyanine dye, or bulky transition metal chelates. This procedure is readily applicable for introducing specific molecules for highly tailored applications, because successful templates include a variety of catalytically, electrochemically, and photochemically active species. Characterization studies were performed to establish the composition of the synthetic products, including x-ray absorption spectroscopy at NSLS

Xenon-129 NMR study of the microporous structure of clays and pillared clays

{sup 129}Xe NMR studies have been carried out using xenon gas adsorbed in clays and pillared clays. Data from the measurements provide information on the pore structure of clays before and after pillaring. The results indicate that the effective pore diameter of montmorillonite increases, for example, from 5.4 {Angstrom} to 8.0 {Angstrom} after pillaring cheto-montmorillonite with aluminum polyoxohydroxy Keggin cations. The data are consistent with X-ray powder diffraction results, which show a corresponding increase in the interlamellar gallery height from 5.6 {Angstrom} to 8.4 {Angstrom}

Designer carbons as potential anodes for lithium secondary batteries

Carbons are the material of choice for lithium secondary battery anodes. Our objective is to use designed synthesis to produce a carbon with a predictable structure. The approach is to pyrolyze aromatic hydrocarbons within a pillared clay. Results from laser desorption mass spectrometry, scanning tunneling microscopy, X-ray diffraction, and small angle neutron scattering suggest that we have prepared disordered, porous sheets of carbon, free of heteroatoms. One of the first demonstrations of template-directed carbon formation was reported by Tomita and co-workers, where polyacrylonitrile was carbonized at 700{degrees}C yielding thin films with relatively low surface areas. More recently, Schwarz has prepared composites using polyfurfuryl alcohol and pillared clays. In the study reported here, aromatic hydrocarbons and polymers which do not contain heteroatoms are being investigated. The alumina pillars in the clay should act as acid sites to promote condensation similar to the Scholl reaction. In addition, these precursors should readily undergo thermal polymerization, such as is observed in the carbonization of polycyclic aromatic hydrocarbons