Mesoporous silica materials containing functionalized organic monolayers have been synthesized. Solid-state nuclear magnetic resonance suggests that a cross-linked monolayer of mercaptopropylsilane was covalently bound to mesoporous silica and closely packed on the surface. The relative surface coverage of the monolayers can be systematically varied up to 76 percent. These materials are extremely efficient in removing mercury and other heavy metals from both aqueous and nonaqueous waste streams, with distribution coefficients up to 340,000. The stability of these materials and the potential to regenerate and reuse them have also been demonstrated. The surface modification scheme reported here enables rational design of the surface properties of tailored porous materials and may lead to the synthesis of more sophisticated functionalized composites for environmental and industrial applications.T h e synthesis of mesoporous silica has greatly expanded the possibilities for the design of open pore structures (1, 2). Because of their large surface area and welldefined pore size and pore shape, these materials have great potential in environmental and industrial processes. However, many applications (such as adsorption, ion exchange, catalysis, and sensing) require the materials to have specific attributes such as binding sites, stereochemical configuration, charge density, and acidity (3). Here, we report the formation of organic monolayers within ordered mesoporous silica and show that these functionalized layers confer specific adsorption behavior for heavy metal ions.Functional groups (thiol groups in this case) were introduced to the pore surface of mesoporous silica as the terminal groups of organic monolayers. The hydrocarbon chains aggregated and formed close-packed arrays on the substrate. The siloxane groups then underwent hydrolysis and ultimately became covalently attached to the substrate and cross-linked to one another. This material, called functionalized monolayers on mesoporous supports (FMMS), can efficiently remove mercury and other heavy metals (such as lead and silver) from contaminated aqueous and organic solutions.The distribution coefficient, Kd, has been measured to be as high as 340,000. [Kd is defined as the amount of adsorbed metal (in micrograms) on 1 g of adsorbing material divided by the metal concentration (in micrograms per milliliter) remaining in the treated waste stream.]Mesoporous silica materials were synthesized in cetyltrimethylammonium chloride/ hydroxide (CTACIOH), silicate, and mesitylene solutions (1, 4). The calcined mesoporous silica has a surface area of>00 m2 g-l and an average pore size of 55 A, as determined by the gas adsorption technique and transmission electron microscopy (TEM). To prepare the FMMS material, we mixed tris-(methoxy)mercaptopropylsilane (TMMPS) with mesoporous silica in an appropriate solvent (5). We selected TMMPS because it has been used previously to make functionallzed monolayers (6) and the thiol groups have a high affiiity for binding metals. Th...

X-ray photoelectron spectroscopy and scanning electron microscopy were used to study electrode samples obtained from 18650-type lithium-ion cells subjected to accelerated calendar-life testing at temperatures ranging from 25 to 70°C and at states-of-charge from 40 to 80%. The cells contained LiNi0.8Co0.2O2 -based positive electrodes (cathodes), graphite-based negative electrodes (anodes), and a 1 M LiPF6 ethylene carbonate:diethyl carbonate (1:1) electrolyte. The results from electrochemically treated samples showed surface film formation on both electrodes. The positive electrode laminate surfaces contained a mixture of organic species that included polycarbonates, and LiF, LixPFy -type and LixPFyOz -type compounds. The same surface compounds were observed regardless of test temperature, test duration, and state-of-charge. On the negative electrode laminates lithium alkyl carbonates false(ROCO2normalLifalse) and Li2CO3 were found in addition to the above-mentioned compounds. Decomposition of lithium alkyl carbonates to Li2CO3 occurred on negative electrodes stored at elevated temperature. Initial depth-profiling results suggest that the surface layer thickness is greater on positive electrode samples from cells stored at high temperature than on samples from cells stored at room temperature. This observation is significant because positive electrode impedance, and more specifically, charge-transfer resistance at the electrode/electrolyte interface, has been shown to be the main contributor to impedance rise in these cells. © 2002 The Electrochemical Society. All rights reserved.

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We have studied the electrochemical and thermal properties of Li 4/3 Ti 5/3 O 4 spinel as a promising anode material for lithium ion batteries. The spinel/rock-salt two-phase transition process was interpreted using a core-shell model, which provided a good explanation of the different area-specific impedance behaviors during the charge and discharge processes. The constant dE/dT during the spinel/rock-salt phase transition was calculated from the heat-flow profile by isothermal microcalorimeter results and found to be around −0.04 mV/K. This very low and constant entropy change indicates that Li 4/3 Ti 5/3 O 4 is a good anode material in terms of thermal stability. Also, we propose that there is a new phase generation when more than one lithium atom is inserted into Li 4/3 Ti 5/3 O 4 . According to the discontinuity of dE/dT results, the order/disorder transition at the low-voltage region ͑around 0.6 V vs Li͒ occurs during further lithium insertion.

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Lithium difluoro͑oxalato͒borate is reported as a salt for high-performance lithium-ion batteries with improved cycle life and power capability. The experimental results showed that lithium difluoro͑oxalato͒borate, LiC 2 O 4 BF 2 , can be reduced at about 1.7 V vs Li + /Li and forms a robust protective SEI film on the graphite surface, as lithium bis͑oxalato͒borate does. The lithium-ion cells using lithium difluoro͑oxalato͒borate-based electrolyte had very good capacity retention at 55°C. The lithium-ion cells using the lithium difluoro͑oxalato͒borate-based electrolyte had very low interfacial impedance. Therefore, lithium difluoro͑oxalato͒borate is a promising salt for advanced lithium-ion batteries with improved capacity retention and power capability.