One-nanometer-thick nickel hydroxide nanosheets were prepared by exfoliation of layered nickel hydroxides intercalated with dodecyl sulfate (DS) ions. The shape of the nanosheets was hexagonal, as was that of the layered nickel hydroxides intercalated with DS ions. The nickel hydroxide nanosheets exhibited charge-discharge properties in strong alkaline electrolyte. The morphology of the nanosheet changed during the electrochemical reaction.

Semiconductor oxide nanosheets synthesized by exfoliation of layered oxides are two-dimensional crystals with a thickness of about 1 nm. [1][2][3][4] New layered materials and their films can be reassembled by electrostatic self-assembly deposition (ESD) [5] and by layer-by-layer (LBL) [6][7][8] techniques, respectively. Since the nanosheets have a negative charge in aqueous solution they can be used with various cationic species as the starting materials. Layered materials prepared from nanosheets and lanthanide (Ln) ions are promising as new functional materials because Ln ions have unique properties, such as luminescence and magnetic properties, that are attributable to the 4f electron orbital. For example, the titanate layered oxide intercalated with Eu 3+ ions prepared from titanate nanosheets and Eu 3+ ions has unique luminescence properties. [9][10][11] The layered oxide gives a red emission from the Eu 3+ ions which is induced by energy transfer through excitation of the bandgap of the titanate nanosheet, [9,10] and the emission from the Eu 3+ ions is promoted by intercalated water molecules.[10] Furthermore, spectral hole burning caused by the intercalated water molecules was observed in the excitation spectra at room temperature. [11] Nanosheets of TiO x , NbO x , and TaO x give a high photocurrent during the photoelectrochemical reaction under UV illumination with an energy higher than that of the bandgap. [12] This finding indicates that a large charge separation is produced between the holes in the valence band and the electrons in the conduction band during excitation of the bandgap. Consequently, layered oxide materials intercalated with Ln ions simultaneously exhibit both photoluminescence and a photoelectrochemical reaction during excitation of the bandgap on illumination with UV light. The study reported herein demonstrates a new form of dynamic control over the photoluminescence of Ln ions intercalated in self-assembled nanosheet films of TiO x and NbO x . The photoluminescence properties of Ln ions are changed by factors such as a change in the pH value and the addition of anionic species. [13][14][15][16][17] However, it is difficult to dynamically control the photoluminescence properties of Ln 3+ ions. In the present system, the emission intensities of the intercalated Eu 3+ and Tb 3+ ions can be readily controlled by varying the applied potential.The Figure S-1 in the Supporting Information). Figure 1 shows a schematic illustration of the system used for the measurement of the photoluminescence. The photoelectrochemical cell with three electrodes, with the nanosheet/Ln 3+ film acted as a working electrode, was placed in the sample chamber of a fluorescence spectrophotometer. A 0.1m K 2 SO 4 solution (pH 6.5) was used as the electrolyte solution. Figure 2 shows the emission intensities of the TiO/Eu and NbO/Tb films under illumination by UV light (wavelength: 260 nm) as a function of potential (sweep rate: 20 mV s À1 ). The red emission of the Eu 3+ ions (614 nm, 5 D 0 -7 F 2 ) appeared in...

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