Yoshihiro Nemoto

Direct Synthesis of Spatially-Controlled Pt-on-Pd Bimetallic Nanodendrites with Superior Electrocatalytic Activity

Here we report a facile synthesis of Pt-on-Pd bimetallic nanodendrites with a Pd interior and dendritic Pt exterior. The developed route rationally utilizes the spontaneous separation of the depositions of Pd and Pt, which endows direct formation of Pt-on-Pd nanodendrites. This is a truly simple and unique process that is quite different from the traditional seed-mediated growth strategy. Fine-tuning of the Pt and Pd ratios afforded Pt-on-Pd nanodendrites with superior electrocatalytic activity in comparison with commercial Pt electrocatalysts.

Synthesis of Prussian Blue Nanoparticles with a Hollow Interior by Controlled Chemical Etching

Hollow particles, an important class of materials with large internal cavities and thin shells, present a wide range of potential applications, such as energy storage, chemical catalysis, photonics, and biomedical carriers. The properties of hollow particles are strongly affected by the compositions and exquisite nanostructures of the shell regions. Many efforts have been made to control these parameters. Recently, hollow particles with nanoporous shells have attracted great interest because the large pore volumes and high surface areas provided by the nanoporous shells show large storage capacity and allow guest species to pass easily into the internal cavity. For instance, metal oxide hollow particles present a superior lithium storage capacity and good cycle performance, 8] which could improve gas sensitivity and catalytic performance 10] in other applications. Inspired by the superiority of nanoporous shells, the creation of microporous crystal shells with outstanding properties is also expected. Porous coordination polymers (PCPs) (or metal–organic frameworks, MOFs) and zeolites are representative microporous crystals. Having adjustable porosity and properties, microporous crystals show great potential in applications such as separation, catalysis, adsorption, and gas storage. 13] To date, however, there have been no reports on the successful synthesis of uniformly nanosized hollow particles with microporous crystalline shells. 15] Very few reports on microporous zeolite and PCP hollow particles have been published, and several problems have been encountered. A major problem is that the synthesized hollow particles are very large and have a broad size distribution. Considering their practical use in various catalysis reaction processes, uniformly sized hollow particles are ideal because they can densely fill reactors or columns. Another problem is that the microporous crystallinity in the shells decreases seriously during the formation process (that is, amorphous regions are formed in the shells), causing a loss of thermal stability, acidic sites, and surface area. Therefore, the development of a general method of synthesizing uniformly nanosized hollow particles with highly crystalline microporous shells is in demand. Herein, we present a facile route to the fabrication of uniform-sized Prussian blue (PB) hollow particles by utilizing a controlled self-etching reaction in the presence of PVP. PB crystals consisting of metal ions coordinated by CN bridges are very typical coordination polymers with a high surface area, showing excellent properties in many applications such as catalysis, sensors, molecular magnets, gas storage, and bioimaging. The critical point in our procedure is the selection of PB mesocrystals as a starting material. PB mesocrystals are formed by the aggregation of PB nanocrystals in an oriented way, thereby showing single-crystal-like behavior. Through small pores (or defects) in the aggregated PB nanocrystals, the etching solution can be diffused into the core of the mesocrystals. We succeeded in the formation of an interior hollow cavity with the retention of the original PB crystallinity. Although a few attempts to prepare PB hollow structures have been reported, the obtained shells were amorphous or poorly crystalline, with large organic impurities. Such hollow particles cannot show high surface areas and good magnetic responses. Two types of PB mesocrystals with different particle sizes were used as starting materials (details regarding the synthetic conditions are given in the Experimental Section). SEM images indicated that the particle-size distributions of the original PB mesocrystals were very narrow and their average diameters were around 110 nm (Figure 1a) and 190 nm (Supporting Information, Figure S1a). From highly magnified SEM images (insets of Figure 1 a; Supporting Information, Figure S1a), very rough surfaces were observed at the edges and corners of the cubes, suggesting that the cube shapes were created by the aggregation of small PB nano[*] Dr. M. Hu, Dr. Y. Nemoto, Prof. Dr. Y. Yamauchi World Premier International (WPI) Research Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) 1-1 Namiki, Tsukuba, Ibaraki 305-0044 (Japan) E-mail: yamauchi.yusuke@nims.go.jp

Electrochemical Synthesis of Mesoporous Pt–Au Binary Alloys with Tunable Compositions for Enhancement of Electrochemical Performance

Mesoporous Pt-Au binary alloys were electrochemically synthesized from lyotropic liquid crystals (LLCs) containing corresponding metal species. Two-dimensional exagonally ordered LLC templates were prepared on conductive substrates from diluted surfactant solutions including water, a nonionic surfactant, ethanol, and metal species by drop-coating. Electrochemical synthesis using such LLC templates enabled the preparation of ordered mesoporous Pt-Au binary alloys without phase segregation. The framework composition in the mesoporous Pt-Au alloy was controlled simply by changing the compositional ratios in the precursor solution. Mesoporous Pt-Au alloys with low Au content exhibited well-ordered 2D hexagonal mesostructures, reflecting those of the original templates. With increasing Au content, however, the mesostructural order gradually decreased, thereby reducing the electrochemically active surface area. Wide-angle X-ray diffraction profiles, X-ray photoelectron spectra, and elemental mapping showed that both Pt and Au were atomically distributed in the frameworks. The electrochemical stability of mesoporous Pt-Au alloys toward methanol oxidation was highly improved relative to that of nonporous Pt and mesoporous Pt films, suggesting that mesoporous Pt-Au alloy films are potentially applicable as electrocatalysts for direct methanol fuel cells. Also, mesoporous Pt-Au alloy electrodes showed a highly sensitive amperometric response for glucose molecules, which will be useful in next-generation enzyme-free glucose sensors.

Unusual antibacterial property of mesoporous titania films: drastic improvement by controlling surface area and crystallinity.

One of the most urgent requirements of human life in the 21 century is development of new antibacterial materials and sterilization technologies that can improve human health. Until now, the most commonly used antibacterial agents are based on chlorine, chlorine dioxide, and organic biocide compounds. These agents are extremely toxic for humans and their residues are also not environmentally friendly. Therefore, it is very important to develop antibacterial biocompatible materials. Titanium dioxide (titania, TiO2) materials in the anatase form have attracted great interest as a new antibacterial material. Titania can work well under ultraviolet (UV) light owing to its photo-semiconductor properties. Currently, this property has been widely utilized for various applications such as water treatment, air and environmental purification, hazardous waste remediation, and deactivation of bacteria. Commercial products with titania (e.g., self-cleaning glasses and anti-fogging coatings) are well known all over the world. To date, various titania-based nanostructures including nanorods and nanoparticles have been reported. To further enhance the photocatalytic performance, many efforts have been made for doping various metal/semiconductor elements into titania materials. In this system, the electrons accumulated on the metal and holes remained on the photocatalyst surface. Therefore, a significant reduction in the recombination rate is realized owing to better charge separation between the electrons and holes. Therefore, the titania-based composites with metal/semiconductor elements can enhance the overall photocatalytic efficiency and the damage of microorganisms of the cell. In this Communication, we focused on a further simple and low-cost synthetic method and synthesized mesoporous titania films by utilizing bottom-up nanotechnology with surfactant assembly. Mesoporous materials with extremely high surface area should be good candidates for the next generation of antibacterial materials. Compared with the traditional titania materials mentioned above, the high surface area originated from mesoporous networks can provide a higher amount of hydroxyl radicals (·OH) which can increase the photoactivity. In the past few years, special attention has been paid to the synthesis of mesoporous titania powders as effective photocatalysts including an antibacterial application. However, the mesoporous titania in the powder form has some disadvantages. The powders which are not fixed on substrates are washed out easily by external treatments and then the released particles themselves may pollute the environment. Also, nanosized powders generally cause serious problems to human health. Therefore, the mesoporous titania films reported here are more applicable [a] H. Oveisi, X. Jiang, Dr. Y. Nemoto, Prof. Dr. Y. Yamauchi World Premier International (WPI) Research Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) 1-1 Namiki, Tsukuba, Ibaraki, 305-0044 (Japan) Fax: (+81)29-860-4706 E-mail : Yamauchi.Yusuke@nims.go.jp [b] Dr. S. Rahighi, Prof. Dr. S. Wakatsuki Structural Biology Research Center High Energy Accelerator Research Organization (KEK) 1-1 Oho, Tsukuba, Ibaraki, 305-0801 (Japan) [c] H. Oveisi, Prof. Dr. A. Beitollahi Center of Excellence in Advanced Materials and Processing Department of Metallurgy and Materials Engineering Iran University of Science and Technology (IUST) Narmak, Tehran 16844 (Iran) [d] X. Jiang, Prof. Dr. Y. Yamauchi Faculty of Science and Engineering Waseda University 3-4-1 Okubo, Shinjuku, Tokyo 169-8555 (Japan) [e] Prof. Dr. Y. Yamauchi Precursory Research for Embryonic Science and Technology (PRESTO) Japan Science and Technology Agency (JST) 4-1-8 Honcho, Kawaguchi, Saitama 332-0012 (Japan). [] These authors contributed equally to this work. Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201000351.

Fullerene/cobalt porphyrin hybrid nanosheets with ambipolar charge transporting characteristics.

A novel supramolecular nanoarchitecture, comprising C(60)/Co porphyrin nanosheets, was prepared by a simple liquid-liquid interfacial precipitation method and fully characterized by means of optical microscopy, AFM, STEM, TEM, and XRD. It is established that the highly crystalline C(60)/Co porphyrin nanosheets have a simple (1:1) stoichiometry, and when incorporated in bottom-gate, bottom-contact field-effect transistors (FETs), they show ambipolar charge transport characteristics.

Preparation and Optical Properties of Fullerene/Ferrocene Hybrid Hexagonal Nanosheets and Large-Scale Production of Fullerene Hexagonal Nanosheets

The supramolecular nanoarchitectures, C(60)/ferrocene nanosheets, were prepared by a simple liquid-liquid interfacial precipitation method and fully characterized by means of SEM, STEM, HRTEM, XRD, Raman and UV-vis-NIR spectra. The highly crystallized C(60)/ferrocene hexagonal nanosheets had a size of ca. 9 microm and the formulation C(60)(ferrocene)(2). A strong charge-transfer (CT) band between ferrocene and C(60) was observed at 782 nm, indicating the presence of donor-acceptor interaction in the nanosheets. Upon heating the nanosheets to 150 degrees C, the CT band disappeared due to the sublimation of ferrocene from the C(60)/ferrocene hybrid, and C(60) nanosheets with an fcc crystal structure and the same shape and size as the C(60)/ferrocene nanosheets were obtained.

Rapid synthesis of biocompatible gold nanoflowers with tailored surface textures with the assistance of amino acid molecules

Au particles with several unique morphologies (e.g., flower-shaped and confieto-shaped) are successfully synthesized through a chemical reduction with the assistance of amino acid molecules (gum Arabic). The highly branched nanostructures of the obtained Au particles show an enhanced SERS effect. Furthermore, the Au nanoflowers exhibit excellent biocompatibility to human bladder cancer cells T-24, which shows their potential in biomedical applications.

Ferromagnetic Mesostructured Alloys: Design of Ordered Mesostructured Alloys with Multicomponent Metals from Lyotropic Liquid Crystals

Mesoporous materials have attracted worldwide interest because of their outstanding structural characteristics, such as high surface area, narrow pore size distribution, and wellordered arrangement of mesopores, which are suitable for a wide variety of applications. Significant advances in synthetic approaches have made it possible to synthesize mesoporous materials with various components, such as non-siliceous metal oxides, organosilicas, carbon meterials, and even polymers. The synthesis of mesoporous materials with magnetic properties has been subject to extensive research. In the presence of an external magnetic field, magnetic mesoporous materials are attracted to the magnet. This magnetic motor effect is indeed attractive for the development of separation technology. Traditionally, magnetic nanoparticles were loaded after the synthesis of mesoporous materials. However, blocking of the mesopores was observed, which prevented effective incorporation of guest species into the mesopores. Several strategies have been reported to overcome this problem. A simple block-copolymer-based “one-pot” selfassembly approach was developed to incorporate magnetic giron oxide nanoparticles in the mesopore walls. However, the amount of the embedded nanoparticles in the framework is limited, which is a serious problem for higher magnetizations. Microspheres consisting of a magnetic nanoparticle core and mesoporous silica shell have attracted particular attention. These characteristics endow them with significant application potential in various fields, such as bioseparation, enzyme immobilization, and diagnostic analysis. Another route is hard-templating, which involves the deposition of metal oxides within original templates, such as mesoporous silica or carbon, and the subsequent removal of the templates. This nanocasting approach is widely applicable to the preparation of metal oxides that are difficult to synthesize by conventional pathways. So far, various kinds of magnetic metal oxides, such as CoO, Co3O4, [13] Mn3O4, [14] NiO, a-Fe2O3, g-Fe2O3, Fe3O4, [16] and Gd2O3, [17] have been prepared. Although these mesoporous metal oxides have magnetic properties, the saturation magnetization has a lower value than that of pure ferromagnetic metals, such as Fe, Co, and Ni. The saturation magnetization of mesoporous materials depends on the compositions and amounts of magnetic phases. Higher magnetization and greater control are much in demand for current separation technology. Furthermore, if we can proportionally change the saturation magnetization just by changing the framework compositions, we can selectively collect particular ferromagnetic mesoporous materials by changing the external magnetic field. Fe group elements (Ni, Co, and Fe) and Gd are the only ferromagnetic metallic elements at ambient conditions. From a Slater–Pauling curve, Fe has the highest magnetic moment (fcc Ni: 0.6 mB/atom, fcc Co: 1.7 mB/atom, bcc Fe: 2.2 mB/ atom). With such multicomponent alloying, more precise control of the magnetization over a wide range and higher [*] Prof. Dr. Y. Yamauchi, Dr. Y. Nemoto, Dr. K. Sato World Premier International (WPI) Research Center for Materials Nanoarchitectonics (MANA) National Institute for Materials Science (NIMS) Namiki 1-1, Tsukuba, Ibaraki 305-0044 (Japan) Fax: (+ 81)29-860-4706 E-mail: yamauchi.yusuke@nims.go.jp Homepage: http://www.nims.go.jp/mana/members/ independent_scientist/y_yamauchi/index.html

In Situ TEM Observation of a Microcrucible Mechanism of Nanowire Growth

Nanowire Growth Observed In the hypothetical microcrucible growth mechanism for nanowires, a molten catalytic particle located in a pore on a substrate continually feeds the outward growth of the wire. To observe such a mechanism requires the ability to examine nanowire growth in situ. Boston et al. (p. 623) studied various stages of Y2BaCuO5 nanowire growth using transmission electron microscopy and were able to observe a microcrucible growth mechanism directly. Nanowire growth from a microcrucible catalyst particle at the bottom of the wire is observed in situ. The growth of metal oxide nanowires can proceed via a number of mechanisms such as screw dislocation, vapor-liquid-solid process, or seeded growth. Transmission electron microscopy (TEM) can resolve nanowires but invariably lacks the facility for direct observation of how nanowires form. We used a transmission electron microscope equipped with an in situ heating stage to follow the growth of quaternary metal oxide nanowires. Video-rate imaging revealed barium carbonate nanoparticles diffusing through a porous matrix containing copper and yttrium oxides to subsequently act as catalytic sites for the outgrowth of Y2BaCuO5 nanowires on reaching the surface. The results suggest that sites on the rough surface of the porous matrix act as microcrucibles and thus provide insights into the mechanisms that drive metal oxide nanowire growth at high temperatures.

Block-copolymer-assisted synthesis of hydroxyapatite nanoparticles with high surface area and uniform size

Abstract We report the synthesis of hydroxyapatite nanoparticles (HANPs) by the coprecipitation method using calcium D-gluconate and potassium hydrogen phosphate as the sources of calcium and phosphate ions, respectively, and the triblock copolymer F127 as a stabilizer. The HANPs were characterized using scanning electron microscopy, x-ray diffraction, and nitrogen adsorption/desorption isotherms. Removal of F127 by solvent extraction or calcination alters the structure of HANPs. The solvent-extracted HANPs were single crystals with their 〈001〉 axis oriented along the rod axis of the HANP, whereas the calcined HANPs contained two crystal phases that resulted in a spherical morphology. The calcined HANPs had much higher surface area (127 m2 g−1) than the solvent-extracted HANPs (44 m2 g−1).