Production of water-dispersible reduced graphene oxide without stabilizers using liquid-phase photoreduction.

We successfully produced water-dispersible reduced graphene oxide (rGO) by pH tuning liquid-phase photoreduction. In this method, the stabilizers and chemical modification usually used for dispersing rGO are not required. The stable carboxyl groups continue to ionize throughout the photoreduction process under alkaline conditions and continue to provide water-dispersible rGO.

All-Graphene Oxide Flexible Solid-State Supercapacitors with Enhanced Electrochemical Performance.

The rapid development of flexible and wearable electronics has led to an increase in the demand for flexible supercapacitors with enhanced electrochemical performance. Graphene oxide (GO) and reduced GO (rGO) exhibit several key properties required for supercapacitor components. Although solid-state rGO/GO/rGO supercapacitors with unique structures are promising, their moderate capacitance is inadequate for practical applications.

All-graphene oxide device with tunable supercapacitor and battery behaviour by the working voltage.

We propose a new type of all-graphene oxide device. Reduced graphene oxide (rGO)/graphene oxide (GO)/rGO functions as both a supercapacitor and a battery, depending on the working voltage. The rGO/GO/rGO operates as a supercapacitor until 1.

Coal Oxide as a Thermally Robust Carbon-Based Proton Conductor.

Inexpensive solid proton conducting materials with high proton conductivity and thermal stability are necessary for practical solid state electrochemical devices. Here we report that coal oxide (CO) is a promising carbon-based proton conductor with remarkable thermal robustness. The CO produced by simple liquid-phase oxidation of coal demonstrates excellent dispersibility in water owing to the surface carboxyl groups.

Optimization of proton conductivity in graphene oxide by filling sulfate ions.

Graphene oxide (GO) walled channels filled by sulfate ions exhibit an optimized proton conductivity, which is higher than the proton conductivity of all other forms of GO. The sulphate ion increases the water absorbing capacity and hydrogen bond reformation process in GO.

Reversibly tunable upconversion luminescence by host-guest chemistry.

Tuning upconversion (UPC) luminescence using external stimuli and fields, as well as chemical reactions, is expected to lead to novel and efficient optical sensors. Herein, highly tunable UPC luminescence was achieved through a host-guest chemistry approach. Specifically, interlayer ion exchange reactions reversibly tuned the emission intensity and green-red color of Er/Yb-codoped A2La2Ti3O10 layered perovskite, where A corresponds to proton and alkali metal ions, enabling the visualization of host-guest interactions and reactions.

Metal permeation into multi-layered graphene oxide.

Understanding the chemical and physical properties of metal/graphene oxide (M/GO) interfaces is important when GO is used in electronic and electrochemical devices because the metal layer must be firmly attached to GO. Here, permeation of metal from the surface into GO paper bulk at the M/GO interface was observed at room temperature for metals such as Cu, Ag, Ni, Au, and Pt. Cu, Ag, and Ni quickly permeated GO as ions into the bulk under humid conditions.

DNA analysis based on toehold-mediated strand displacement on graphene oxide.

Fluorescent dye-labeled probe DNA was immobilized on fluorescence-quenching graphene oxide (GO) through a capture DNA. When targets were added, the probes were released from the GO through toehold-mediated strand exchange. Higher emission recovery and more signal contrast were achieved relative to conventional methods that are based on direct adsorption of probes.

Graphene oxide nanosheet with high proton conductivity.

We measured the proton conductivity of bulk graphite oxide (GO'), a graphene oxide/proton hybrid (GO-H), and a graphene oxide (GO) nanosheet for the first time. GO is a well-known electronic insulator, but for proton conduction we observed the reverse trend, as it exhibited superionic conductivity. The hydrophilic sites present in GO as -O-, -OH, and -COOH functional groups attract the protons, which propagate through hydrogen-bonding networks along the adsorbed water film.

Simple photoreduction of graphene oxide nanosheet under mild conditions.

Graphene oxide (GO) nanosheets were reduced by UV irradiation in H2 or N2 under mild conditions (at room temperature) without a photocatalyst. Photoreduction proceeded even in an aqueous suspension of nanosheets. The GO nanosheets reduced by this method were analyzed by X-ray photoelectron spectroscopy and Raman spectroscopy.

Preparation of p-type CaFe2O4 photocathodes for producing hydrogen from water.

An (hk0)-oriented p-type CaFe2O4 (E(g): 1.9 eV) photocathode was prepared, and hydrogen and oxygen gases were produced from a photocell short-circuited by connecting the CaFe2O4 and n-type TiO2 electrodes under illumination without applying an external voltage. The open-circuited voltage was 0.

Drastic changes in photoluminescence properties of multilayer films composed of europium hydroxide and titanium oxide nanosheets.

Multilayer films consisting of Eu(OH)(3-x) and titanium oxide nanosheets showed strong Eu(3+) emission under UV-light irradiation, in which the titanium oxide nanosheet works as an antenna collecting UV-light, and then the Eu(OH)(3-x) nanosheet acts as an emitting layer receiving the absorbed energy.

Synthesis of blue amorphous TiO2 and Ti(n)O(2n-1) by the impulse plasma in liquid.

Synthesis of blue amorphous TiO2 and Ti(n)O(2n-1) by the impulse plasma in dielectric liquid is presented. The impulse plasma in liquid enables us to quench from plasma state, by which we can synthesize nanomaterials, metastable materials, etc. By the impulse plasma between titanium rods submerged into water, we have synthesized blue colored amorphous TiO2 nanoparticles suspended in water and black titanium monoxide at the bottom.

N doping of oxide nanosheets.

Photo-N doping for Nb-O system oxide nanosheets such as Nb(6)O(17), TINbO(5), and Ca(2)Nb(3)O(10) was succeeded in by treatment under mild conditions, where their H-restacked forms containing tetrabuthylammonium (TBA) ion were illuminated by UV light at room temperature. A relatively strong absorption in visible light region (400 approximately 600 nm) was observed for the N-doped samples because of formation of p-band or valence band hybridization of N in the Nb-O bandgap. The N doping proceeded only under TBA presence in water without O(2), and Pt loading promoted this doping reaction.

Synthesis of hexagonal nickel hydroxide nanosheets by exfoliation of layered nickel hydroxide intercalated with dodecyl sulfate ions.

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.

Photoluminescence of perovskite nanosheets prepared by exfoliation of layered oxides, K2Ln2Ti3O10, KLnNb2O7, and RbLnTa2O7 (Ln: lanthanide ion).

Luminescent perovskite nanosheets were prepared by exfoliation of single- or double-layered perovskite oxides, K2Ln2Ti3O10, KLnNb2O7, and RbLnTa2O7 (Ln: lanthanide ion). The thickness of the individual nanosheets corresponded to those of the perovskite block in the parent layered compounds. Intense red and green emissions were observed in aqueous solutions with Gd1.

Photoluminescence spectral change in layered titanate oxide intercalated with hydrated Eu3+.

A number of interesting photoluminescence properties of titanate layered oxide intercalated with hydrated Eu3+ have been demonstrated. Photoluminescence intensity of Eu3+ decreased rapidly with time during irradiation by UV light having energy higher than the band gap energy of the host TiO (Ti(1.81)O4) layer.

Photoluminescence properties of multilayer oxide films intercalated with rare earth ions by the layer-by-layer technique.

Multilayer oxide films consisting of a TiO-Eu3+-TiO-Tb3+-NbO-Tb3+-NbO-Eu3+ unit which was prepared by the layer-by-layer technique, showed photoluminescence with a high intensity containing both red and green lights.

Synthesis and photoluminescent properties of titanate layered oxides intercalated with lanthanide cations by electrostatic self-assembly methods.

Various lanthanide cations were intercalated into the interlayer of the exfoliated H(x)Ti((2-x)/4)) square(x/4)O(4) x H(2)O (HTO) by the electrostatic self-assembly deposition (ESD) and layer-by-layer self-assembly (LBL) methods. X-ray diffraction and thermal analysis data indicated that interlayer lanthanide cations existed as an aqua ion and were coordinated with 7-10 water molecules under ambient conditions. The interlayer distances were found to be in the range 6-7 Angstrom for HTO layered oxide intercalated with a lanthanide cation.

Photoelectrochemical oxidation of methanol on oxide nanosheets.

Photoelectrochemical oxidation of alcohol on various nanosheet electrodes such as Nb6O17, Ca2Nb3O10, Ti(0.91)O2, Ti4O9, and MnO2 system host layers were measured to evaluate the photocatalysis of water photolysis with alcohol as a sacrificial agent. The nanosheet electrodes were prepared by the layer-by-layer (LBL) method, using electrostatic principles.

Surface treatment of silicon carbide using TiO2(IV) photocatalyst.

Silicon carbide (SiC) and diamond were decomposed to CO(2)(g) by the photocatalysis with TiO(2) at room temperature, although the decomposition rate of diamond was very slow. According to the XPS spectra of Si2p on the SiC surface, SiO(2) was simultaneously formed on the surface by the TiO(2) photocatalysis. The thickness of the SiO(2) formed on the SiC surface during the photocatalytic oxidation for 1 h was estimated to be about 40 A from the depth profile of the XPS spectra using Ar etching.