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ABSTRACT: Discrete electron tomography is a new approach for three-dimensional reconstruction of nanoscale objects. The technique exploits prior knowledge of the object to be reconstructed, which results in an improvement of the quality of the reconstructions. Through the combination of conventional transmission electron microscopy and discrete electron tomography with a model-based approach, quantitative structure determination becomes possible. In the present work, this approach is used to unravel the building scheme of Zeotile-4, a silica material with two levels of structural order. The layer sequence of slab-shaped building units could be identified. Successive layers were found to be related by a rotation of 120 degrees, resulting in a hexagonal space group. The Zeotile-4 material is a demonstration of the concept of successive structuring of silica at two levels. At the first level, the colloid chemical properties of Silicalite-1 precursors are exploited to create building units with a slablike geometry. At the second level, the slablike units are tiled using a triblock copolymer to serve as a mesoscale structuring agent.
Journal of the American Chemical Society 05/2009; 131(13):4769-73. · 9.91 Impact Factor
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ABSTRACT: A simple and low-cost method to create metal-metal hybrid nanostructures possessing fairly regularly spaced "hot-spots" of surface plasmon resonances is proposed. The nanohybrid structure was prepared via self-assembly during a simple drop-casting procedure, using chemically synthesized silver nanowires and silver nanoparticles prepared in a single batch of a polyol process. Wide field illumination of these nanohybrids produced hot-spots with spacings of around 500 nm to 1 microm. The intensity of the emission/scattering from the hot-spots fluctuates over time. The proposed structure can be useful for the development of molecular-sensors or as a substrate for surface enhanced Raman/fluorescence spectroscopy.
Journal of the American Chemical Society 01/2009; 130(51):17240-1. · 9.91 Impact Factor
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Benoit Ruelle,
Alexandre Felten,
Jacques Ghijsen,
Wolfgang Drube,
Robert L Johnson, Duoduo Liang,
Rolf Erni,
Gustaaf Van Tendeloo,
Peeterbroeck Sophie,
Philippe Dubois,
Thomas Godfroid,
Michel Hecq,
Carla Bittencourt
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ABSTRACT: In this study of the changes induced by exposing MWCNTs to a nitrogen plasma, it was found by HRTEM that the atomic nitrogen exposure does not significantly etch the surface of the carbon nanotube (CNT). Nevertheless, the atomic nitrogen generated by a microwave plasma effectively grafts amine, nitrile, amide, and oxime groups onto the CNT surface, as observed by XPS, altering the density of valence electronic states, as seen in UPS.
Micron 02/2008; 40(1):85-8. · 1.53 Impact Factor
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ABSTRACT: In this contribution, the formation and immobilisation of chromium(iii) hydroxyoxide colloids is investigated. Nano-sized Cr(iii) colloids are generated in situ upon reduction of Cr(vi), dosed to a stirred reactor. The growth of the elementary colloids by the consumption of solved Cr is kinetically unfavorable compared to their aggregation to larger secondary particles, the size of which depends on the concentration of the building block colloids. This aggregation process can be steered by simple process parameters such as dosing rate and concentration of the Cr(vi). The Cr(iii) colloids are immobilised in situ on a support material via precipitation chromatography. Upon drying, the initially amorphose hydroxyoxides are gradually transformed into crystalline Cr(2)O(3) nanoparticles, mainly located at the external surface of the support. This approach opens new opportunities for the synthesis of supported metal oxide catalysts.
Physical Chemistry Chemical Physics 11/2007; 9(39):5382-6. · 3.57 Impact Factor
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Kazuaki Hayasaka, Duoduo Liang,
Ward Huybrechts,
Bart R De Waele,
Kristof J Houthoofd,
Pierre Eloy,
Eric M Gaigneaux,
Gustaaf van Tendeloo,
Joris W Thybaut,
Guy B Marin,
Joeri F M Denayer,
Gino V Baron,
Pierre A Jacobs,
Christine E A Kirschhock,
Johan A Martens
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ABSTRACT: An ZSM-22 aluminosilicate zeolite was synthesized using the hydrothermal gel method at 150 degrees C. Products obtained after different synthesis times were characterized using various techniques and catalytic testing. Massive formation of ZSM-22 nanocrystals occurs after only a short synthesis time, appearing as isolated rods with a cross section of 12+/-4 nm. Nanorods have aluminum enriched at their external surface. Later in the crystallization process nanorods align and fuse sideways, whereby the external surface is systematically converted into an internal micropore surface. The formation of aluminum bearing micropores by the joining of nanorod surfaces is responsible for the enhanced catalytic activity. For this, the zeolite synthesis of nanoscale crystallites is ineffective for enhancing catalytic activity.
Chemistry 02/2007; 13(36):10070-7. · 5.93 Impact Factor
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Angewandte Chemie International Edition 06/2006; 45(19):3106-9. · 13.45 Impact Factor
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ABSTRACT: Platinum metal was dispersed on microporous, mesoporous, and nonporous support materials including the zeolites Na-Y, Ba-Y, Ferrierite, ZSM-22, ETS-10, and AIPO-11, alumina, and titania. The oxidation of carbon black loosely mixed with catalyst powder was monitored gravimetrically in a gas stream containing nitric oxide, oxygen, and water. The carbon oxidation activity of the catalysts was found to be uniquely related to the Pt dispersion and little influenced by support type. The optimum dispersion is around 3-4% corresponding to relatively large Pt particle sizes of 20-40 nm. The carbon oxidation activity reflects the NO oxidation activity of the platinum catalyst, which reaches an optimum in the 20-40 nm Pt particle size range. The lowest carbon oxidation temperatures were achieved with platinum loaded ZSM-22 and AIPO-11 zeolite crystallites bearing platinum of optimum dispersion on their external surfaces.
Environmental Science and Technology 05/2006; 40(8):2727-33. · 5.23 Impact Factor
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Angewandte Chemie International Edition 03/2006; 45(19):3106 - 3109. · 13.45 Impact Factor
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ABSTRACT: Aggregates of nanosized crystalline units of Silicalite-1 zeolite were detected in a detailed TEM analysis of a clear solution aged for 40 months at room temperature. Inspection of the TEM images reveals the aggregation of these building units into larger crystalline zeolite particles even without heating. The smaller individual units resemble the earlier proposed nanoslab and preferentially stack along a or b crystallographic directions.
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ABSTRACT: Ti-MCM-41 nanoparticles 80–160 nm in diameter (Ti-MCM-41 NP) were successfully prepared by a dilute solution route in sodium hydroxide medium at ambient temperature. Ti-MCM-41 NP were characterized by X-ray diffraction, nitrogen adsorption/desorption isotherms, SEM, TEM, FT-IR, and UV–vis spectroscopy. The characterization results showed the existence of highly ordered hexagonal mesoporous structure and tetrahedral Ti species in Ti-MCM-41 NP. In the epoxidation of cyclohexene with aqueous H2O2, Ti-MCM-41 NP displayed higher conversion and initial reaction rate than a Ti-MCM-41 sample with normal particle size (Ti-MCM-41 LP). Diffusion of the reactants was accelerated and the accessibility to the catalytic Ti species was enhanced in the shorter channels in Ti-MCM-41 NP samples. Ti-MCM-41 NP showed much higher selectivity for cyclohexene oxide compared with Ti-MCM-41 LP, suggesting reduced hydrolysis of cyclohexene oxide with water in the former case. The increased selectivity for cyclohexene oxide can be attributed to the lower concentration of residual surface silanols in Ti-MCM-41 NP and the shorter residence time of epoxide in the shorter mesoporous channels. Ti-MCM-41 NP also appears to be a suitable catalyst in the epoxidation of a bulky substrate, like cholesterol, with tert-butyl hydroperoxide.
Journal of Catalysis. 254(1):64-70.
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Journal of Catalysis. 263(1):75-82.
