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We report the synthesis and electrochemical properties of Co-substituted manganese oxide nanosheets (Mn1-xCoxO2). Polycrystalline samples of layered Na0.6Mn1-xCoxO2 (x = 0.2-0.5) were synthesized as starting materials. A linear decrease in the lattice constant a with increasing Co content supported the successful substitution of Co3+ ions for Mn3+ ions in the host layers. Acid-exchange treatment of the Na0.6Mn1-xCoxO2 powders resulted in the formation of H-Mn1-xCoxO2 while preserving the Mn/Co ratio and layered structure. Exfoliation of H-Mn1-xCoxO2 was achieved by reaction with tetra-n-butylammonium ions, yielding unilamellar Mn1-xCoxO2 (x = 0.2-0.5) nanosheets with a thickness of 0.8 nm. The optical absorption peak of the obtained Mn1-xCoxO2 nanosheets was continuously blueshifted as the Co content increased. The Mn1-xCoxO2 nanosheets exhibited well-defined redox peaks, which were shifted to a negative potential with increasing Co content. These results suggest that the 3d orbitals of Mn and Co are mixed owing to their statistical distribution in the nanosheets. The Mn1-xCoxO2 nanosheet electrodes showed a capacitance of 700-1000 F g-1 and improved cycle performance compared to MnO2 nanosheets. [ABSTRACT FROM AUTHOR]

We report the solid-state reaction of MoO2 nanosheets, obtained from the soft-chemical delamination of Na0.9Mo2O4, into metallic Mo2C single layers that constitute a new family of versatile carbide nanosheets. This so-called pseudotopotactic reaction, i.e., conversion from nanosheet to nanosheet, is aided by the use of cationic polymers as binders for the film growth based on electrostatic self-assembly. Compared to Mo2C in the bulk form, 2D anisotropic Mo2C sheets having a larger surface-area-to-volume ratio are of significant use in potential electrochemical applications, and it is also worth noting that the thickness of Mo2C sheets can be controlled in the nanometer range by altering the stacking number of the precursor nanosheets. [ABSTRACT FROM AUTHOR]

The homopolar network and conjugation in d-block single elements can materialize a highly anisotropic and robust structure of a noble-metal system. Here, we have prepared ruthenium (Ru) atomic monolayers of a nonmetallic hexagonal lattice, and determined their layering scheme and metallization. The two-dimensional (2D) network is retained at the first stacking of the monolayer, while maintaining the nonmetallic features. We find out that the atop (AA) related stacking structure of bilayered Ru nanosheets occurs due to the ligancy-driven covalency, and the inception of the metallic electronic states is from trilayered stacking. These results indicate that the metallic states can be separated from covalent-bonding linkage and unpaired electrons in spd hybrid orbital systems. Our approach enables the molecular structure of noble-metal atoms to be induced via controlling the ligancy of d-block atomic bonds. [ABSTRACT FROM AUTHOR]

Eu 3+-doped perovskite nanosheets, La 0.90Eu 0.05Nb 2O 7, have been prepared by the soft chemical exfoliation reaction of K 1− xH xLa 0.90Eu 0.05Nb 2O 7with a tetrabuthylammonium hydroxide aqueous solution. The resulting colloidal La 0.90Eu 0.05Nb 2O 7nanosheet suspension exhibits photoluminescence emission from the 5D 0to 7F Jmanifold transitions of Eu 3+by either direct excitation of Eu 3+or host excitation, whereas no host emission was observed at room temperature. In the case of the bulk precursors K 1− xH xLa 0.90Eu 0.05Nb 2O 7, the direct excitation yields more intense emission than the host excitation. On the contrary, the most intense emission from the La 0.90Eu 0.05Nb 2O 7nanosheets was observed by exciting at the broad excitation band maximum (353 nm). The difference in the photoluminescence properties between the La 0.90Eu 0.05Nb 2O 7nanosheets and their bulk precursors seems to be related to the dimensionality of these host structures and the confinement of the energy-transfer process between the host layer units and Eu 3+activators. [ABSTRACT FROM AUTHOR]

Structure analysis of unilamellar manganese oxide nanosheets obtained via exfoliation of layered manganese oxides was carried out utilizing synchrotron radiation (SR) X-ray in-plane diffraction and polarization-dependent total reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) analyses. A combination of SR excitation and the total reflection of incoming X-rays provides signals strong enough for both analyses even from a monolayer of the MnO2nanosheets having a concentration of 0.7 g cm-2. In addition, the mean oxidation state of constituent manganese ions in the MnO2sheets was estimated on the basis of XANES spectra, and bond valence sum calculations with the bond length obtained from the present EXAFS analyses. The obtained structural data revealed that the two-dimensional lattice of the MnO2sheets underwent a slight elongation upon delamination. These changes correspond to approximately 1% expansion of sheet area and 1−2% expansion of thickness, which can be understood by reduction of the mean oxidation number of manganese ions in the sheet through the exfoliation process. [ABSTRACT FROM AUTHOR]

Photoinduced hydrophilic conversion properties of titania nanosheets were investigated. A highly hydrophilic state was achieved on the monolayer film surface of titania nanosheets, the thickness of which is less than 1 nm. The hydrophilic conversion rate (k) for the monolayer film of titania nanosheets was proportional to the intensity (I) of irradiated light, suggesting that the hydrophilic conversion of the titania nanosheet surface proceeded under light-limited conditions even with a high concentration of photoexcited carriers. As the number of layers of titania nanosheets increased, the dependence behavior changed from k ∝ I1.0 to k ∝ I0.5, indicating that the recombination processes become dominant in the multilayer films of titania nanosheets. In-plane X-ray diffraction (XRD) analyses showed a very small but reproducible structural change of titania nanosheets upon UV irradiation. [ABSTRACT FROM AUTHOR]

LiFePO4 is a well-known electrode material that is capable of high-rate charging and discharging despite a strong phase-separation tendency of the lithium-rich and poor end-member phases. X-ray diffraction measurements (XRD) with high time-resolution are conducted under battery operation conditions to reveal the phase-transition mechanism of LiFePO4 that leads to the high rate capability. We here propose a hidden two-step phase transition of LiFePO4 via a metastable phase. The existence of the metastable phase, not just a member of a transient solid solution, is evidenced by the operando XRD measurements. Our two-step phase-transition model explains the behavior of LiFePO4 under the battery operation conditions. It also explains asymmetric behavior during the charging and discharging at high rates and low temperatures, as well as apparent single-step two-phase reaction between the end members at low rates at room temperature. This model also suggests underlying, rate-dependent electrochemical processes that result from a competing disproportion reaction of the metastable phase. [ABSTRACT FROM AUTHOR]