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Pakdel A.,Japan International Center for Materials Nanoarchitectonics | Bando Y.,Japan International Center for Materials Nanoarchitectonics | Golberg D.,Japan International Center for Materials Nanoarchitectonics
Chemical Society Reviews | Year: 2014

Recent years have witnessed many breakthroughs in research on two-dimensional (2D) nanomaterials, among which is hexagonal boron nitride (h-BN), a layered material with a regular network of BN hexagons. This review provides an insight into the marvellous nano BN flatland, beginning with a concise introduction to BN and its low-dimensional nanostructures, followed by an overview of the past and current state of research on 2D BN nanostructures. A comprehensive review of the structural characteristics and synthetic routes of BN monolayers, multilayers, nanomeshes, nanowaves, nanoflakes, nanosheets and nanoribbons is presented. In addition, electronic, optical, thermal, mechanical, magnetic, piezoelectric, catalytic, ecological, biological and wetting properties, applications and research perspectives for these novel 2D nanomaterials are discussed. © The Royal Society of Chemistry.

Takada K.,Japan International Center for Materials Nanoarchitectonics
Langmuir | Year: 2013

Strong demand for solid-state lithium batteries has prompted intensive research for achieving fast ionic conduction in solids. Although the highest conductivity found among sulfides is higher than that of liquid electrolytes, it improves the battery performance only in combination with electrodes via a low-resistance interface. This Article reviews some interfacial structures that lower the interfacial resistance to enable high-power interfaces by controlling the carrier density. © 2013 American Chemical Society.

Winnik F.M.,University of Montréal | Winnik F.M.,Japan International Center for Materials Nanoarchitectonics | Maysinger D.,McGill University
Accounts of Chemical Research | Year: 2013

The dramatic increase in the use of nanoparticles (NP) in industry and research has raised questions about the potential toxicity of such materials. Unfortunately, not enough is known about how the novel, technologically- attractive properties of NPs correlate with the interactions that may take place at the nano/bio interface. The academic, industrial, and regulatory communities are actively seeking answers to the growing concerns on the impact of nanotechnology on humans. In this Account we adopt quantum dots (QDs) as an illustrative example of the difficulties associated with the development of a rational science-based approach to nanotoxicology.The optical properties of QDs are far superior to those of organic dyes in terms of emission and absorption bandwidths, quantum yield, and resistance to photobleaching. Moreover, QDs may be decorated with targeting moieties or drugs and, therefore, are candidates for site-specific medical imaging and for drug delivery, for example in cancer treatment. Earlier this year researchers demonstrated that QD-based imaging using monkeys caused no adverse effects although QDs accumulated in lymph nodes, bone marrow, liver, and spleen for up to 3 months after injection. Such persistence of QDs in live animals does, however, raise concerns about the safety of using QDs both in the laboratory and in the clinic.Researchers anticipate that QDs will be increasingly used not only in clinical applications but also in various manufactured products. For example, QD-solar cells have emerged as viable contenders to complement or replace dye-sensitized solar cells; CdTe/CdS thin film cells have already captured approximately 10 percent of the global market, and in addition, QDs can serve as components of sensors and as emitting materials in LEDs. Given the clear indications that QDs will inevitably become components of a wide range of manufactured and consumer products, researchers and policy makers need to understand the possible health risks associated with exposure to QDs.In this Account, we initially review the known mechanisms by which QDs can damage cells, including oxidative stress elicited by reactive oxygen species (ROS). We discuss lesser-known impairments induced in cells by nanomolar to picomolar concentrations of QDs, which imply that cadmium-containing QDs can exert genotoxic, epigenetic, and metalloestrogenic effects. These observations strongly suggest that minute concentrations of QDs could be sufficient to cause long lasting, even transgenerational, effects. We also consider various modes by which humans could be exposed to QDs in their work or through the environment. Although considerable advances have been made in enhancing the stability and overall quality of QDs, over time they can partially degrade in the environment or in biological systems, and eventually cause small, but cumulative undesirable effects.A combination of toxicological, genetic, epigenetic and imaging approaches is required to create comprehensive guidelines for evaluating the nanotoxicity of nanomaterials, including QDs. Prior to biological investigations with these materials, an indispensible step must be the full characterization of NPs by complementary techniques. Specifically, the concentration, size, charge, and ligand stability of NPs in biological media must be known if we are to understand fully how the properties of nanoparticles and of their biological environment contribute to cytotoxicity. © 2012 American Chemical Society.

Tominaka S.,Japan International Center for Materials Nanoarchitectonics
Chemical Communications | Year: 2012

A facile, low-temperature reduction method using sodium borohydride to yield corundum-type Ti 2O 3 nanorods from rutile-type TiO 2 nanorods with morphology retention is proposed. The electrochemical analyses confirmed their promising performance as electrodes and excellent stability to the environment of interest for fuel cell operation. © 2012 The Royal Society of Chemistry.

Ma R.,Japan International Center for Materials Nanoarchitectonics | Sasaki T.,Japan International Center for Materials Nanoarchitectonics
Accounts of Chemical Research | Year: 2015

CONSPECTUS: Two-dimensional (2D) materials, represented by graphene, have attracted tremendous interest due to their ultimate structural anisotropy and fascinating resultant properties. The search for 2D material alternatives to graphene, molecularly thin with diverse composition, structure, and functionality, has become a hot research topic. A wide variety of layered metal oxides and hydroxides have been exfoliated into the form of individual host layers, that is, 2D nanosheets. This Account presents an overview of 2D oxide and hydroxide nanosheets on the following subtopics: (1) controllable preparation of high-quality nanosheets and (2) molecular assembly and the exploration of functionality of the nanosheets. High-quality exfoliation is generally achieved via a multistep soft chemical process, comprised of ion-exchange, osmotic swelling, and exfoliation. A high degree of hydration-induced swelling, typically triggered by intercalation of organo-ammonium ions, is a critical stage leading to the high-yield production of molecularly thin nanosheets. Recent studies reveal that massive swelling, an astounding ∼100 times the original size, can be induced by a range of amine solutions. The degree of swelling is controlled by the balance of osmotic pressure between the inner gallery and the outer electrolyte solution, which is strongly influenced by amine molarity. Conversely, the stability of the resultant swollen structure is dependent on the chemical nature of the amine/ ammonium ions. Particular species of lower polarity and bulky size, for example, quaternary ammonium ions, are beneficial in promoting exfoliation. Rational design and tuning of the lateral dimension, chemical composition, and structure of nanosheets are vital in exploring diverse functionalities. The lateral dimension of the nanosheets can be tuned by controlling the crystal size of the parent layered compounds, as well as the kinetics of the exfoliating reaction, for example, the type of amine/ammonium ions, their concentration, and the mode of exfoliation (manual versus mechanical shaking, etc.). Employing optimum conditions enables the production of high-quality nanosheets with a lateral size as large as several tens of micrometers. A couple of examples tailoring the nanosheets have been demonstrated with a highlight on a novel class of 2D perovskite-type oxide nanosheets with a finely tuned composition and a progressively increasing thickness at a step of 0.4-0.5 nm (corresponding to the height of the MO6 octahedron). The charge-bearing nanosheets can be organized through solution-based molecular assembly techniques (e.g., electrostatic layer-by-layer deposition, Langmuir?Blodgett method) to produce highly organized nanofilms, superlattices, etc., the exploration of which holds great potential for the development of various electronic and optical applications, among others. (Figure Presented). © 2014 American Chemical Society.

Belik A.A.,Japan International Center for Materials Nanoarchitectonics
Inorganic Chemistry | Year: 2013

Magnetic properties of BiFe0.7Mn0.3O3 (with a Néel temperature (TN) of 425 K) and BiFe 0.6Mn0.4O3 (with TN = 350 K) were investigated by magnetic measurements between 5 and 400 K. They crystallize in space group Pnma with the √2ap × 4ap × 2√2ap superstructure (ap is the parameter of the cubic perovskite subcell) with a = 5.57800(9) Å, b = 15.7038(3) Å, and c = 11.22113(16) Å for BiFe0.6Mn0.4O 3. Both compounds show magnetization reversal or negative magnetization phenomena. However, it was found that the magnetization reversal is dependent on magnetic prehistory of a sample and measurement protocols. No magnetization reversal was observed when virgin samples were measured below TN. Magnetization reversal effects appeared only when the samples were cooled in small magnetic fields from temperatures above TN or after the samples were magnetized. The exchange bias effect or a shift of isothermal magnetization curves, depending on the measurement conditions, was also observed. The exchange bias changes its sign as a function of temperature and cooling conditions. Our findings allowed us to propose the extrinsic origin (related to sample inhomogeneities) of the magnetization reversal effect in these two compounds. © 2013 American Chemical Society.

Hamada I.,Japan International Center for Materials Nanoarchitectonics
Physical Review B - Condensed Matter and Materials Physics | Year: 2014

I propose a van der Waals density functional (vdW-DF) that improves upon the description of energetics and geometries of molecules, solids, and adsorption systems over the original vdW-DF. The functional is based on the nonlocal correlation for the second version of the vdW-DF [10Lee, Phys. Rev. B 82, 081101(R) (2010)PRBMDO1098-012110.1103/PhysRevB.82.081101] and an exchange functional that recovers the second-order gradient expansion approximation in the slowly varying limit, while reproducing the large density gradient behavior proposed by Becke [16J. Chem. Phys. 85, 7184 (1986)JCPSA60021-960610.1063/1. 451353]. A systematic assessment of the proposed functional is presented, which demonstrates the applicability of the proposed vdW-DF to a wide range of systems. © 2014 American Physical Society.

Zhai T.,Japan International Center for Materials Nanoarchitectonics
Nanoscale | Year: 2010

One-dimensional (1D) semiconductor nanostructures are of prime interest due to their potential in investigating the size and dimensionality dependence of the materials' physical properties and constructing nanoscale electronic and optoelectronic devices. Cadmium sulfide (CdS) is an important semiconductor compound of the II-VI group, and its synthesis and properties have been of growing interest owing to prominent applications in several fields. This article provides a comprehensive review of the state-of-the-art research activities that focus on the rational synthesis, novel properties and unique applications of 1D CdS nanostructures in nanotechnology. It begins with the rational design and synthesis of 1D CdS nanostructures, and then highlights a range of unique properties and applications (e.g. photoluminescence, cathodoluminescence, electrochemiluminescence, photocatalysis, lasers, waveguides, modulators, solar cells, field-effect transistors, photodetectors, field-emitters, and nanogenerators) associated with them. Finally, the review is concluded with the author outlook of the perspectives with respect to future research on 1D CdS nanostructures.

Ouyang S.,Japan International Center for Materials Nanoarchitectonics | Ye J.,Japan International Center for Materials Nanoarchitectonics
Journal of the American Chemical Society | Year: 2011

A series of β-AgAl1-xGaxO2 solid-solution materials were explored as novel visible-light-sensitive photocatalysts. These Ag-based solid solutions crystallize in a homogeneous crystal structure with orthorhombic symmetry but possess continuously modulated band gaps from 2.19 to 2.83 eV by decreasing the ratios of Ga/Al. Their photoactivities for iso-propanol degradation were found to be dependent on the variation of chemical compositions. Among them, the β-AgAl 0.6Ga0.4O2 sample showed the highest photocatalytic performance, which simultaneously exhibited 35 and 63 times higher activities than two terminus materials, β-AgAlO2 and β-AgGaO2, respectively. The apparent quantum efficiency of this sample for iso-propanol photodegradation achieved up to 37.3% at the wavelength of 425 ± 12 nm. The theoretical calculation based on density functional theory demonstrated that the levels of valence band maximum of β-AgAl 1-xGaxO2 are similar, but the levels of conduction band minimum are gradually negatively shifted with the increase of the ratio of Ga/Al, thereby continuously narrowing the band gap. Nevertheless, the highest activity observed on β-AgAl0.6Ga0.4O 2 may be attributed to its optimized band structure, which adapts the balance between effective visible-light absorption and adequate redox potentials. © 2011 American Chemical Society.

Ma R.,Japan International Center for Materials Nanoarchitectonics | Sasaki T.,Japan International Center for Materials Nanoarchitectonics
Advanced Materials | Year: 2010

A wide variety of cation-exchangeable layered transition metal oxides and their relatively rare counterparts, anion-exchangeable layered hydroxides, have been exfoliated into individual host layers, i.e., nanosheets. Exfoliation is generally achieved via a high degree of swelling, typically driven either by intercalation of bulky organic ions (quaternary ammonium cations, propylammonium cations, etc.) for the layered oxides or by solvation with organic solvents (formamide, butanol, etc.) for the hydroxides. Ultimate two-dimensional (2D) anisotropy for the nanosheets, with thickness of around one nanometer versus lateral size ranging from submicrometer to several tens of micrometers, allows them to serve either as an ideal quantum system for fundamental study or as a basic building block for functional assembly. The charge-bearing inorganic macromolecule-like nanosheets can be assembled or organized through various solution-based processing techniques (e.g., flocculation, electrostatic sequential deposition, or the Langmuir-Blodgett method) to produce a range of nanocomposites, multilayer nanofilms, and core-shell nanoarchitectures, which have great potential for electronic, magnetic, optical, photochemical, and catalytic applications. A huge number of cation-exchangeble layered metal oxides, as well as anion-exchangeable layered double hydroxides and layered rare-earth hydroxides, have been successfully exfoliated into nanosheets, the ultimate 2D charge-bearing functional crystallites. The current status of research on oxide and hydroxide nanosheets is reviewed, with emphasis on synthesis, characterization, novel physiochemical properties, and prospects for application. Copyright © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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