| 1. |
- Yu, Yatao, et al.
(författare)
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Synthesis and characterization of silica nanotubes with radially oriented mesopores
- 2008
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Ingår i: Advanced Functional Materials. - : Wiley. - 1616-301X .- 1616-3028. ; 18, s. 541-550
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Tidskriftsartikel (refereegranskat)abstract
- Hierarchical silica nanotubes with radially oriented mesoporous channels perpendicular to the central axis of the tube were synthesized by using self-assembled chiral anionic surfactant, co-structure directing agent (CSDA) and silica precursor. The average inner diameter and the wall thickness were similar to 94, similar to 62, and similar to 62 nm and to similar to 27, similar to 33, and similar to 45 nm, respectively, by manipulating the synthesis gel composition, while the diameter of the wall mesopofes was kept constant at similar to 4 nm. These materials with such a unique structure were produced only with chiral surfactant and achiral or racemic surfactant did not give rise to mesoporous silica nanotubes. The existence of helicity in the lipid bilayer template was confirmed by means of circular dichroism spectroscopy. The mesoporous penetrating from outside to inside of silica nanotubes are thought to originate from the initial formation of self-assembled lipid tubes with helical bilayers, which in turn re-assemble to form the mesopores in the wall of the nanotubes upon addition of co-structure directing agent and silica source.
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| 2. |
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| 3. |
- Atluri, Rambabu, 1981-, et al.
(författare)
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Co-Structure Directing Agent Induced Phase Transformation of Mesoporous Materials
- 2009
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:5, s. 3189-3195
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis of cubic Pm (3) over barn mesocaged solid templated by cetyltrimethyl ammonium bromide (C(16)TMABr) surfactant by direct cocondensation of (3-aminopropyl)triethoxysilanes (APES) under strong alkaline conditions is reported. The novel route gives direct incorporation of amino functional groups on the porous silica wall, and the structural formation has been followed by means of in situ SAXS studies performed at a synchrotron beam line. Data shows that a molar ratio of C(16)TMABr/APES = 0.6 favors the formation of 3D cubic mesocaged solid with Pm3n symmetry which transforms to a cylindrical mesoporous phase with p6mm symmetry at higher molar ratios. Further structural evaluation has been performed by means electron crystallography (EC). Reconstructed 3D models based on EC show the presence of spherical cages (A-cages, 45 angstrom) and ellipsoidal cages (B-cages, 48 x 43 angstrom) whereby every cage in the unit cell is connected to 14 nearest cages with a window size of 18 angstrom. Finally, a mechanism is proposed, denoted S+similar to N degrees I-, in which penetration of the neutral aminopropyl moiety within the micellar corona is responsible for the formation of the Pm (3) over barn phase, accounting for the formation of the hexagonal phase at higher molar ratios and higher temperatures. In comparison to other mesocaged materials with the same symmetry this structure possesses a more open porous network which will help assess its potential in a variety of applications discussed herein.
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| 4. |
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| 5. |
- Choi, Minkee, et al.
(författare)
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Stable single-unit-cell nanosheets of zeolite MFI as active and long-lived catalysts
- 2009
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 461:7261, s. 246-249
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Tidskriftsartikel (refereegranskat)abstract
- Zeolites-microporous crystalline aluminosilicates-are widely used in petrochemistry and fine-chemical synthesis(1-3) because strong acid sites within their uniform micropores enable size- and shape-selective catalysis. But the very presence of the micropores, with aperture diameters below 1 nm, often goes hand-in-hand with diffusion limitations(3-5) that adversely affect catalytic activity. The problem can be overcome by reducing the thickness of the zeolite crystals, which reduces diffusion path lengths and thus improves molecular diffusion(4,5). This has been realized by synthesizing zeolite nanocrystals(6), by exfoliating layered zeolites(7-9), and by introducing mesopores in the microporous material through templating strategies(10-17) or demetallation processes(18-22). But except for the exfoliation, none of these strategies has produced 'ultrathin' zeolites with thicknesses below 5 nm. Here we show that appropriately designed bifunctional surfactants can direct the formation of zeolite structures on themesoporous and microporous length scales simultaneously and thus yield MFI (ZSM-5, one of the most important catalysts in the petrochemical industry) zeolite nanosheets that are only 2 nm thick, which corresponds to the b-axis dimension of a single MFI unit cell. The large number of acid sites on the external surface of these zeolites renders them highly active for the catalytic conversion of large organic molecules, and the reduced crystal thickness facilitates diffusion and thereby dramatically suppresses catalyst deactivation through coke deposition during methanol-to-gasoline conversion. We expect that our synthesis approach could be applied to other zeolites to improve their performance in a range of important catalytic applications.
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| 6. |
- Diaz, Isabel, et al.
(författare)
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Transmission electron microscopy in formation and growth of ordered mesoporous materials
- 2006
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Ingår i: Current Opinion in Colloid & Interface Science. - : Elsevier BV. - 1359-0294. ; 11:5, s. 302-307
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Forskningsöversikt (refereegranskat)abstract
- In the boundary of materials and colloidal science, TEM became a very powerful technique used to image the interfaces and early stages of mesoporous materials formation, to obtain symmetry information about the porous network at the meso-scale, furthermore to obtain images of final structures and transformations that could not be observed otherwise. The aim of the present contribution is to give insights that may contribute to a better understanding of TEM applied to the study of ordered mesoporous materials from three points of view: i) mechanism ii) formation from zeolite precursors; iii) structure of intermediate mesophases. (c) 2006 Elsevier Ltd. All rights reserved.
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| 7. |
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| 8. |
- Fujioka, Masayuki, et al.
(författare)
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ADAMTS13 gene deletion enhances plasma high-mobility group box1 elevation and neuroinflammation in brain ischemia-reperfusion injury
- 2012
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Ingår i: Neurological Sciences. - : Springer Science and Business Media LLC. - 1590-1874 .- 1590-3478. ; 33:5, s. 1107-1115
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Tidskriftsartikel (refereegranskat)abstract
- Highly adhesive glycoprotein von Willebrand factor (VWF) multimer induces platelet aggregation and leukocyte tethering or extravasation on the injured vascular wall, contributing to microvascular plugging and inflammation in brain ischemia-reperfusion. A disintegrin and metalloproteinase with thrombospondin type-1 motifs 13 (ADAMTS13) cleaves the VWF multimer strand and reduces its prothrombotic and proinflammatory functions. Although ADAMTS13 deficiency is known to amplify post-ischemic cerebral hypoperfusion, there is no report available on the effect of ADAMTS13 on inflammation after brain ischemia. We investigated if ADAMTS13 deficiency intensifies the increase of extracellular HMGB1, a hallmark of post-stroke inflammation, and exacerbates brain injury after ischemia-reperfusion. ADAMTS13 gene knockout (KO) and wild-type (WT) mice were subjected to 30-min middle cerebral artery occlusion (MCAO) and 23.5-h reperfusion under continuous monitoring of regional cerebral blood flow (rCBF). The infarct volume, plasma high-mobility group box1 (HMGB1) level, and immunoreactivity of the ischemic cerebral cortical tissue (double immunofluorescent labeling) against HMGB1/NeuN (neuron-specific nuclear protein) or HMGB1/MPO (myeloperoxidase) were estimated 24 h after MCAO. ADAMTS13KO mice had larger brain infarcts compared with WT 24 h after MCAO (p < 0.05). The rCBF during reperfusion decreased more in ADAMTS13KO mice. The plasma HMGB1 increased more in ADAMTS13KO mice than in WT after ischemia-reperfusion (p < 0.05). Brain ischemia induced more prominent activation of inflammatory cells co-expressing HMGB1 and MPO and more marked neuronal death in the cortical ischemic penumbra of ADAMTS13KO mice. ADAMTS13 deficiency may enhance systemic and brain inflammation associated with HMGB1 neurotoxicity, and aggravate brain damage in mice after brief focal ischemia. We hypothesize that ADAMTS13 protects brain from ischemia-reperfusion injury by regulating VWF-dependent inflammation as well as microvascular plugging.
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| 9. |
- Gao, Chuanbo, 1981-, et al.
(författare)
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Formation of Diverse Mesophases Templated by a Diprotic Anionic Surfactant
- 2008
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Ingår i: Chemistry - A European Journal. - Weinheim : Wiley-VCH Verlag GmbH&Co. KGaA. - 0947-6539 .- 1521-3765. ; 14:36, s. 11423-11428
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis system for mesophase formation, using the diprotic anionic surfactant N-myristoyl-l-glutamic acid (C14GluA) as the structuredirecting agent (SDA) and N-trimethoxylsilylpropyl-N,N,N-trimethylammonium chloride (TMAPS) as the co-structure-directing agent (CSDA), has been investigated and a full-scaled synthesis-field diagram is presented. In this system we have obtained mesophases including three-dimensional (3D) micellar cubic Fm-3m, Pm-3n, Fd-3m, micellar tetragonal P42/mnm, two-dimensional (2D) hexagonal p6mm and bicontinuous cubic Pn-3m, by varying the C14GluA/NaOH/TMAPS composition ratios. From the diagram it can be concluded that the mesophase formation is affected to a high degree by the organic/inorganicinterface curvature and the mesocage–mesocage electrostatic interaction. Bicontinuous cubic and 2D-hexagonalphases were found in the low organic/inorganic-interface curvature zones, whereas micellar cubic and tetragonal mesophases were found in the high organic/inorganic-interface curvature zones. Formation of cubic Fm-3m and tetragonal P42/mnm was favoured in highly alkaline zones with strong mesocage–mesocage interactions, and formation of cubic Pm-3n and Fd-3m was favoured with moderate mesocage–mesocage interactions in the less alkaline zones of the diagram.
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| 10. |
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