No abstract

Anatase TiO2 nanosheets (ATNs) are successfully prepared by a biomimetic layer-by-layer titania mineralization approach, and the electrochemical performance of the ATNs as negative electrode for lithium-ion batteries is investigated by the galvanostatic chronopotentiometry and cyclic voltammetry. A high initial discharge capacity (311 mA h g(-1)) and initial Coulombic efficiency (81.7%) were obtained for ATNs, and capacities of 252, 202, 186, 158, 136, and 119 mA h g(-1) were obtained at 0.2, 1, 5, 10, 20, and 30 C, respectively. Particularly, the ATNs can still maintains a capacity of 108 mA h g(-1) after 4000 cycles at 30 C (only a capacity loss of 10%), which indicated a superior rate capabilities and cyclability. The CVs analysis revealed that the ANTs have both diffusive lithium storage in the bulk and pseudocapacitive lithium storage at the surface (also called interfacial lithium storage), and the pseudocapacitive lithium storage dominates the total capacity when the scan rates are above 1 mV s(-1). The fast and stable lithium storage of ATNs might be attributed to the high pseudocapacitive lithium storage contribution in the material, and it was suggested the pseudocapacitive lithium storage could occurred at grain-grain interfaces as well as nanosheet surfaces.

A new class of poly-N-vinylpyrrolidinones containing an asymmetric center at C5 of the pyrrolidinone ring were synthesized from l-amino acids. The polymers, particularly 17, were used to stabilize nanoclusters such as Pd/Au for the catalytic asymmetric oxidations of 1,3- and 1,2-cycloalkanediols and alkenes, and Cu/Au was used for C-H oxidation of cycloalkanes. It was found that the bulkier the C5 substituent in the pyrrolidinone ring, the greater the optical yields produced. Both oxidative kinetic resolution of (±)-1,3- and 1,2-trans-cycloalkanediols and desymmetrization of meso cis-diols took place with 0.15 mol % Pd/Au (3:1)-17 under oxygen atmosphere in water to give excellent chemical and optical yields of (S)-hydroxy ketones. Various alkenes were oxidized with 0.5 mol % Pd/Au (3:1)-17 under 30 psi of oxygen in water to give the dihydroxylated products in >93% ee. Oxidation of (R)-limonene at 25 °C occurred at the C-1,2-cyclic alkene function yielding (1S,2R,4R)-dihydroxylimonene 49 in 92% yield. Importantly, cycloalkanes were oxidized with 1 mol % Cu/Au (3:1)-17 and 30% HO in acetonitrile to afford chiral ketones in very good to excellent chemical and optical yields. Alkene function was not oxidized under the reaction conditions. Mechanisms were proposed for the oxidation reactions, and observed stereo- and regio-chemistry were summarized.

Through an aqueous, protein-mediated layer-by-layer titania deposition process, we have fabricated a protamine/titania composite layer on nickel foam. The coating was composed of amorphous carbon and TiO2(B)/anatase nanoparticles and formed upon organic pyrolysis under a reducing atmosphere (5% H2-Ar mixture). X-ray diffraction analyses, Auger electron spectroscopy, and high-resolution transmission electron microscopy revealed that the obtained coatings contained fine monoclinic TiO2(B) and anatase nanocrystals, along with amorphous carbon. Moreover, the coating can be used as a binder-free negative electrode material for lithium-ion batteries and exhibits high reversible capacity and fast charge-discharge properties; a reversible capacity of 245 mAh g(-1) was obtained at a current density of 50 mA g(-1), and capacities of 167 and 143 mAh g(-1) were obtained at current densities of 1 and 2 A g(-1), respectively.

The purpose of this work was to fabricate highperformance dielectric materials for electrorheological (ER) application and electromagnetic (EM) wave attenuation. Commercial MoS 2 bulks were exfoliated into nanosheets via combination of ball-milling and bath sonication procedures, which were used as the template for in situ grafting of PANI nanoneedles (PANI-NDs) to afford MoS 2 /PANI-NDs. The length−diameter (L/D) ratio of PANI-NDs on MoS 2 nanosheets was feasibly tuned via modulating the polymerization time. Therefore, the tunable electrical conductivity and dielectric properties of the obtained MoS 2 /PANI-NDs were achieved. Compared with bare MoS 2 nanosheets, MoS 2 /PANI-NDbased ER fluids constructed more robust fibril-like structure governed by the external electric energy and exhibited higher dynamic yield stress (186.8 Pa at 3 kV/mm) with wider applied electric field strength (0−3.0 kV/mm). Furthermore, as a novel EM wave absorbing material, the maximum reflection loss (RL) values of MoS 2 nanosheets reached −44.4 dB at 11.48 GHz with the thickness of 3.0 mm, while the similar RL values of MoS 2 /PANI-NDs (−44.8 dB) reached 14.5 GHz with the thickness of only 1.6 mm. The broad effective EM absorption bandwidth (RL values less than −10 dB) for MoS 2 /PANI-NDs was observed owing to the synergistic effect of PANI-NDs and MoS 2 nanosheets.