Author
Shunsuke Asahina
Other affiliations: Tohoku University, Stockholm University
Bio: Shunsuke Asahina is an academic researcher from JEOL Ltd.. The author has contributed to research in topics: Scanning electron microscope & Nanoparticle. The author has an hindex of 23, co-authored 61 publications receiving 3581 citations. Previous affiliations of Shunsuke Asahina include Tohoku University & Stockholm University.
Papers
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TL;DR: A strategy to expand the pore aperture of metal-organic frameworks (MOFs) into a previously unattained size regime (>32 angstroms) is reported, as evidenced by their permanent porosity and high thermal stability (up to 300°C).
Abstract: We report a strategy to expand the pore aperture of metal-organic frameworks (MOFs) into a previously unattained size regime (>32 angstroms). Specifically, the systematic expansion of a well-known MOF structure, MOF-74, from its original link of one phenylene ring (I) to two, three, four, five, six, seven, nine, and eleven (II to XI, respectively), afforded an isoreticular series of MOF-74 structures (termed IRMOF-74-I to XI) with pore apertures ranging from 14 to 98 angstroms. All members of this series have noninterpenetrating structures and exhibit robust architectures, as evidenced by their permanent porosity and high thermal stability (up to 300°C). The pore apertures of an oligoethylene glycol–functionalized IRMOF-74-VII and IRMOF-74-IX are large enough for natural proteins to enter the pores.
1,637 citations
TL;DR: Zhang et al. (p. 1684) show that a hierarchical zeolite can be made through a simple process using a single structure-directing agent that causes repetitive branching, which leads to a material with improved transport and catalytic properties.
Abstract: Hierarchical zeolites are a class of microporous catalysts and adsorbents that also contain mesopores, which allow for fast transport of bulky molecules and thereby enable improved performance in petrochemical and biomass processing. We used repetitive branching during one-step hydrothermal crystal growth to synthesize a new hierarchical zeolite made of orthogonally connected microporous nanosheets. The nanosheets are 2 nanometers thick and contain a network of 0.5-nanometer micropores. The house-of-cards arrangement of the nanosheets creates a permanent network of 2- to 7-nanometer mesopores, which, along with the high external surface area and reduced micropore diffusion length, account for higher reaction rates for bulky molecules relative to those of other mesoporous and conventional MFI zeolites.
615 citations
TL;DR: An efficient and stable photoanode is reported that couples an active barium-doped tantalum nitride nanostructure with a stable cobalt phosphate co-catalyst and yields a maximum solar energy conversion efficiency more than three times higher than that of state-of-the-art single-photon photoanodes.
Abstract: Spurred by the decreased availability of fossil fuels and global warming, the idea of converting solar energy into clean fuels has been widely recognized. Hydrogen produced by photoelectrochemical ...
298 citations
TL;DR: In this paper, in situ CO IR spectroscopy and density functional theory (DFT) was used to establish that Pd/CeO2-rods are active due to a Langmuir-Hinshelwood mechanism involving isolated Pd atoms in the form of Pd 1O and Pd1O 2 species.
Abstract: Pd/CeO2 is an active component in emission control catalysts for CO oxidation. Nanostructured CeO2 powders can be prepared in the form of rods exposing predominantly (111) surfaces and cubes exposing (100) surfaces. While differences in the reactivity of Pd supported on these facets of ceria have been reported, the origins of the reactivity differences are not well understood. Pd supported on (111) surfaces of ceria rods exhibits room-temperature CO oxidation activity, while Pd on (100) surface of ceria cubes shows comparable activity at a temperature that is 60 °C higher. Earlier, we established that Pd/CeO2-rods are active due to a Langmuir-Hinshelwood mechanism involving isolated Pd atoms in the form of Pd1O and Pd1O2 species. Here, we establish using in situ CO IR spectroscopy and density functional theory (DFT) that, in addition to TEM-visible Pd nanoparticles, Pd/CeO2-cubes also contain isolated Pd species, predominantly in the form of Pd1O. DFT calculations show that CO oxidation proceeds via a Mars-van Krevelen pathway, which is possible for the (100) surface because of the lower Ce-O binding energy compared to the (111) surface. Overall, the catalytic cycle for CO oxidation on Pd/CeO2(100) involves a higher free energy barrier than on Pd/CeO2(111) in keeping with the experimentally observed activity difference. EXAFS measurements show that the active Pd phase in both Pd/CeO2-rods and Pd/CeO2-cubes responds dynamically with respect to reducing and oxidizing conditions. The redispersion of Pd in oxidative conditions is more pronounced for Pd/CeO2-rods and the catalyst is more active after an oxidative treatment.
217 citations
TL;DR: The synthesis of chiral TiO2 fibres via transcription of the helical structure of amino acid-derived amphiphile fibres through coordination bonding interactions between the organics and theTiO2 source is reported.
Abstract: The optical chirality induced at the absorption bands due to electronic exciton coupling of the transition dipole moments between chromophores in close proximity is ubiquitous in helical organic materials. However, inorganic materials with optical activity resulting from electronic transitions have not been explored. Here we report the synthesis of chiral TiO2 fibres via transcription of the helical structure of amino acid-derived amphiphile fibres through coordination bonding interactions between the organics and the TiO2 source. Upon calcination, the as-prepared amorphous TiO2 double-helical fibres with a pitch length of ~100 nm were converted to double-helical crystalline fibres with stacks of anatase nanocrystals in an epitaxial helical relationship. Both the amorphous and anatase crystalline helical TiO2 fibres exhibited optical response to circularly polarized light at the absorption edge around ~350 nm. This was attributed to the semiconductor TiO2-based electronic transitions from the valence band to the conduction band under an asymmetric electric field. Optical activity resulting from electronic transitions in chiral inorganic materials is rare. Liu et al. report the synthesis of amino acid-derived amphiphile templated chiral TiO2fibres, which exhibit an optical response to polarized light resulting from valence to conduction band electronic transitions.
136 citations
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TL;DR: Metal-organic frameworks are porous materials that have potential for applications such as gas storage and separation, as well as catalysis, and methods are being developed for making nanocrystals and supercrystals of MOFs for their incorporation into devices.
Abstract: Crystalline metal-organic frameworks (MOFs) are formed by reticular synthesis, which creates strong bonds between inorganic and organic units. Careful selection of MOF constituents can yield crystals of ultrahigh porosity and high thermal and chemical stability. These characteristics allow the interior of MOFs to be chemically altered for use in gas separation, gas storage, and catalysis, among other applications. The precision commonly exercised in their chemical modification and the ability to expand their metrics without changing the underlying topology have not been achieved with other solids. MOFs whose chemical composition and shape of building units can be multiply varied within a particular structure already exist and may lead to materials that offer a synergistic combination of properties.
10,934 citations
01 Dec 1991
TL;DR: In this article, self-assembly is defined as the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds.
Abstract: Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.
2,591 citations
2,430 citations
1,800 citations
Donostia International Physics Center1, Rovira i Virgili University2, Victoria University of Wellington3, MacDiarmid Institute for Advanced Materials and Nanotechnology4, University of Cambridge5, University of California, Santa Barbara6, Queen's University Belfast7, Technical University of Denmark8, University of Victoria9, Chung-Ang University10, Leibniz Institute of Photonic Technology11, University of Jena12, Rutgers University13, University of Strathclyde14, University of Liverpool15, University of Iowa16, University of Minnesota17, Heidelberg University18, National Institute of Advanced Industrial Science and Technology19, Chalmers University of Technology20, Humboldt University of Berlin21, University of Michigan22, Jiangnan University23, Stanford University24, Xiamen University25, Ludwig Maximilian University of Munich26, Hokkaido University27, Seoul National University28, University of Illinois at Urbana–Champaign29, Kwansei Gakuin University30, University of Vigo31, Free University of Berlin32, Northwestern University33, University of Duisburg-Essen34, National Research Council35, Indian Institute of Science Education and Research, Thiruvananthapuram36, Duke University37, Northeastern University (China)38, Temple University39, Wuhan University40, Japan Advanced Institute of Science and Technology41, Jilin University42, Ikerbasque43
TL;DR: Prominent authors from all over the world joined efforts to summarize the current state-of-the-art in understanding and using SERS, as well as to propose what can be expected in the near future, in terms of research, applications, and technological development.
Abstract: The discovery of the enhancement of Raman scattering by molecules adsorbed on nanostructured metal surfaces is a landmark in the history of spectroscopic and analytical techniques. Significant experimental and theoretical effort has been directed toward understanding the surface-enhanced Raman scattering (SERS) effect and demonstrating its potential in various types of ultrasensitive sensing applications in a wide variety of fields. In the 45 years since its discovery, SERS has blossomed into a rich area of research and technology, but additional efforts are still needed before it can be routinely used analytically and in commercial products. In this Review, prominent authors from around the world joined together to summarize the state of the art in understanding and using SERS and to predict what can be expected in the near future in terms of research, applications, and technological development. This Review is dedicated to SERS pioneer and our coauthor, the late Prof. Richard Van Duyne, whom we lost during the preparation of this article.
1,768 citations