Time filter

Source Type

Akishima Tokyo, Japan

Liu Z.,Japan National Institute of Advanced Industrial Science and Technology | Fujita N.,Tohoku University | Miyasaka K.,Korea Advanced Institute of Science and Technology | Han L.,Shanghai JiaoTong University | And 9 more authors.
Journal of Electron Microscopy | Year: 2013

This paper reviews diverse capabilities offered by modern electron microscopy techniques in studying fine structures of nanoporous crystals such as zeolites, silica mesoporous crystals, metal organic frameworks and yolk-shell materials. For the case of silica mesoporous crystals, new approaches that have been developed recently to determine the three-dimensionally periodic average structure, e.g., through self-consistent analysis of electron microscope images or through consideration of accidental extinctions, are presented. Various structural deviations in nanoporous materials from their average structures including intergrowth, surface termination, incommensurate modulation, quasicrystal and defects are demonstrated. Ibidem observations of the scanning electron microscope and atomic force microscope give information about the zeolite-crystal-growth mechanism, and an energy for unstitching a building-unit from a crystal surface is directly observed by an anatomic force microscope. It is argued how these observations lead to a deeper understanding of the materials. © The Author 2013. Published by Oxford University Press [on behalf of The Japanese Society of Microscopy]. All rights reserved.

Xi D.,Jilin University | Sun Q.,Jilin University | Xu J.,CAS Wuhan Center for Magnetic Resonance | Cho M.,KAIST | And 6 more authors.
Journal of Materials Chemistry A | Year: 2014

Silicoaluminophosphate zeolite SAPO-34 with CHA topology is known as one of the best catalysts for methanol-to-olefin (MTO) conversion. In this work, we demonstrate a facile one-step hydrothermal synthesis of hierarchically macroporous SAPO-34 through the etching effect of hydrofluoric acid. The highly crystalline hierarchically macroporous SAPO-34 is prepared as central-holed rhombohedral crystals with particle size of ca. 5-10 μm that comprise intracrystalline parallel macrochannels of ca. 100 nm. The formation of macroporous structures via in situ growth-etching can be directly imaged by SEM. Strikingly, a particular crystal configuration consisting of eight pyramidal parts has been first observed during the zeolite crystal growth process, which eventually grows to form a perfect rhombohedral shape. The HF etching effect is further elucidated by the analysis of changes of pH values as well as of solid and liquid compositions following the evolution of crystallization. The texture properties, chemical environments of framework atoms, and acidity of the synthesized SAPO-34 are characterized by N2 adsorption/desorption, MAS NMR and NH3-TPD measurements. The hierarchically macroporous SAPO-34 shows larger micropore volume, slightly stronger acid strength, and lower external surface acidity than its conventional counterpart synthesized without using HF. Consequently, the hierarchically macroporous SAPO-34 exhibits excellent MTO catalytic performance, showing much higher selectivity to ethylene and propylene as well as longer lifetime than the conventional counterpart. In comparison with previously reported methods for the generation of hierarchical porosity, this one-step HF-assisted in situ growth-etching synthetic route is simple, straightforward and cost-effective, which offers a new approach to prepare hierarchically porous zeolites with improved catalytic activity. This journal is © the Partner Organisations 2014.

Ma L.,Shanghai JiaoTong University | Duan Y.,Shanghai JiaoTong University | Cao Y.,Shanghai JiaoTong University | Asahina S.,SMBU | And 2 more authors.
Chemical Communications | Year: 2013

Chiral metal oxide complexes with tunable optical response to circularly polarised light over the full range of the UV-Vis absorption band were synthesised. This optical activity was attributed to electronic transitions from the ground state to the excited state or from the valence band to the conduction band under an asymmetric electric field. © 2013 The Royal Society of Chemistry.

Duan Y.,Shanghai JiaoTong University | Liu X.,Shanghai JiaoTong University | Han L.,Shanghai JiaoTong University | Asahina S.,SMBU | And 4 more authors.
Journal of the American Chemical Society | Year: 2014

Helical symmetry can be found in most flowers with a rotation of contort petal aestivation. For micro- and nanoscale analogies, flower mimicking structures have been reproduced; however, the conceptual chirality of "nanoflowers" has not yet been defined. Here, the chirality of the "flower" was defined by its nanosized chiral structure and consequent optical activity (OA), opening new horizons for the physical theory and chiral materials. We report the surfactant-mediated hydrothermal synthesis of chiral CuO nanoflowers using sodium dodecyl sulfate (SDS) as a structure-directing agent, an amino alcohol as a symmetry-breaking agent, and cupric salt as the inorganic source. Two levels of hierarchical chirality exist for a CuO nanoflower including primary helically arranged "nanoflakes" and secondary helical "subnanopetals" that form "nanopetals". The nanoflowers exhibited a prominent optical response to circularly polarized light (CPL) at the absorption bands characteristic of CuO. © 2014 American Chemical Society.

Duan Y.,Shanghai JiaoTong University | Han L.,Shanghai JiaoTong University | Zhang J.,Shanghai JiaoTong University | Asahina S.,SMBU | And 15 more authors.
Angewandte Chemie - International Edition | Year: 2015

Inorganic nanomaterials endowed with hierarchical chirality could open new horizons in physical theory and applications because of their fascinating properties. Here, we report chiral ZnO films coated on quartz substrates with a hierarchical nanostructure ranging from atomic to micrometer scale. Three levels of hierarchical chirality exist in the ZnO films: helical ZnO crystalline structures that form primary helically coiled nanoplates, secondary helical stacking of these nanoplates, and tertiary nanoscale circinate aggregates formed by several stacked nanoplates. These films exhibited optical activity (OA) at 380 nm and in the range of 200-800 nm and created circularly polarized luminescence centered at 510 nm and Raman OA at 50-1400 cm-1, which was attributed to electronic transitions, scattering, photoluminescent emission, and Raman scattering in a dissymmetric electric field. The unprecedented strong OA could be attributed to multiple light scattering and absorption-enhanced light harvesting in the hierarchical structures. © 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Discover hidden collaborations