| 1. |
- Hedlund, Jonas, et al.
(författare)
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Ultrathin oriented zeolite LTA films
- 1997
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Ingår i: Chemical Communications. - 1359-7345 .- 1364-548X. ; :13, s. 1193-1194
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Tidskriftsartikel (refereegranskat)abstract
- Ultrathin oriented films of zeolite LTA are prepared on single-crystal alumina supports by a method including adsorption of LTA seeds on the support followed by hydrothermal film crystallization.
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| 2. |
- Mintova, Svetlana, et al.
(författare)
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Continuous films of zeolite ZSM-5 on modified gold surfaces
- 1997
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Ingår i: Chemical Communications. - 1359-7345 .- 1364-548X. ; :1, s. 15-16
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Tidskriftsartikel (refereegranskat)abstract
- Thin continuous films of zeolite ZSM-5 on gold surfaces are prepared by a novel method including silanization, charge modification and seeding of the surface prior to the hydrothermal crystallization of the zeolite.
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| 3. |
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| 4. |
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| 5. |
- Mintova, Svetlana, et al.
(författare)
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Preparation of zeolite Y-vegetal fiber composite materials
- 1996
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Ingår i: Journal of porous materials. - 1380-2224 .- 1573-4854. ; 3:3, s. 143-150
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Tidskriftsartikel (refereegranskat)abstract
- Zeolite Y crystallization on chemi thermo mechanical pulp (CTMP) fluff, linen and cotton substrates using two different approaches for the deposition was studied. In the first approach a seed-film method was applied. This method involves surface charge modification of the substrates, adsorption of a monolayer of colloidal zeolite Y crystals onto the surfaces and subsequent growth of these colloidal zeolite crystals into a continuous zeolite film. Application of this method resulted in continuous films of zeolite Y on all substrates investigated. The second approach involved direct synthesis on substrates subjected to chemical or mechanical pretreatment in order to modify their surface properties. Chemical treatment was found to improve the crystallization on cotton and linen fibers but not so for the CTMP. Mechanical pretreatment enhanced the zeolite crystallization on the linen fibers but not on the other substrates. The zeolite Y-vegetal fiber composites were characterized by SEM, XRD, and thermal analysis.
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| 6. |
- Mintova, Svetlana, et al.
(författare)
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Preparation of ZSM-5 films from template free precursors
- 1997
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Ingår i: Journal of Materials Chemistry. - 0959-9428 .- 1364-5501. ; 7:12, s. 2341-2342
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of zeolite ZSM-5 on quartz substrates have been prepared in the absence of organic templates by growth of adsorbed seed crystals attached to a polymer-modified substrate surface.
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| 7. |
- Mintova, Svetlana, et al.
(författare)
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ZSM-5 films prepared from template free precursors
- 1998
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Ingår i: Journal of Materials Chemistry. - 0959-9428 .- 1364-5501. ; 8:10, s. 2217-2221
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Tidskriftsartikel (refereegranskat)abstract
- Thin continuous films of zeolite ZSM-5 were synthesized on quartz substrates. The substrates were first surface modified and covered by a monolayer of colloidal silicalite-1 seed crystals. These crystals were grown into continuous films with thicknesses in the range 230-3500 nm by hydrothermal treatment in a synthesis gel free from organic templates. The preferential orientation of the crystals constituting the film was initially one with thec-axis close to parallel to the substrate surface. During the course of crystallization this orientation changed to one with most of the crystals having the c-axes directed approximately 35° from perpendicular to the substrate surface. A mechanism explaining this behavior is proposed. The final thickness of the film was controlled by the synthesis time but also by the addition of seed crystals to the synthesis gel. Films prepared according to this method may be of great value for the development of zeolite based membranes.
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| 8. |
- Ravishankar, Raman, et al.
(författare)
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Characterization of Nanosized Material Extracted from Clear Suspensions for MFI Zeolite Synthesis
- 1999
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 103:24, s. 4960-4964
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Tidskriftsartikel (refereegranskat)abstract
- The silica species contained in an aged clear suspension, which upon heating gives rise to the crystallization of Silicalite-1, were extracted with 80% efficiency using a sequence of acidification, salting out, phase transfer into organic solvent, and freeze-drying methods. This silica powder was characterized by X-ray scattering, transmission electron microscopy, atomic force microscopy, and 29Si magic angle spinning nuclear magnetic resonance. These techniques gave evidence for the presence of a very specific morphology, corresponding to slab shaped particles, with dimensions of 1.3 × 4.0 × 4.0 nm. The nanoslabs have the MFI structure with nine channel intersections per particle, each containing a TPA cation. The identity of the extracted nanoslabs with the species in suspension is evidenced with in situ and ex situ X-ray scattering.
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| 9. |
- Ravishankar, Raman, et al.
(författare)
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Physicochemical characterization of silicalite-1 nanophase material
- 1998
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 102:15, s. 2633-2639
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Tidskriftsartikel (refereegranskat)abstract
- A silicalite-1 nanophase material with an elementary particle size of 18-100 nm is synthesized from clear solution and isolated and purified using supercentrifugation. The nanopowder is characterized in detail using scanning electron microscopy, high-resolution transmission electron microscopy, attenuated force microscopy, 29Si magic angle spinning NMR, 13C cross polarization magic angle spinning NMR, X-ray diffraction, dinitrogen physisorption, and thermogravimetric analysis and compared with micrometer-sized silicalite-1. The nanosized and micrometer-sized materials have many common properties including the refined structure and the nature and concentrations of tetrapropylammonium species incorporated during the synthesis. Unique properties of the nanophase are a splitting of the characteristic framework vibration at 550 cm-1 into a doublet at 555 and 570 cm-1, a high concentration of defect sites, and a strain in the crystallites along the "a" crystallographic direction. The nanophase exhibits a two-stage dinitrogen physisorption in the low-pressure region, ascribed to adsorptions in micropores created by the stacking of the nanoparticles in addition to adsorptions in the intracrystalline micropores.
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| 10. |
- Schoeman, Brian J.
(författare)
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A high temperature in situ laser light-scattering study of the initial stage in the crystallization of TPA-silicalite-1
- 1997
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Ingår i: Zeolites. - 0144-2449. ; 18:2-3, s. 97-105
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Tidskriftsartikel (refereegranskat)abstract
- The events occurring in a clear TPA-silicalite-1 precursor solution, hydrothermally treated at 70°C, were monitored in situ by dynamic light scattering using a high-effect laser light source. Subcolloidal silicate particles with an average diameter of 3.3 nm are detected in the greater part of the crystallization. An initial decrease in the scattered light intensity upon hydrothermal treatment indicates a reduction in the particle number concentration at the expense of an increase in the particle size. This is interpreted as being due to an Ostwald ripening mechanism. A second discrete particle population (which coexists with the subcolloidal particles) is detected after ca. 9.5 h of hydrothermal treatment, at which time the average particle size is ca. 12 nm. The two particle populations (subcolloidal particles and the growing crystals) present in suspension before sampling at 9.5 h cannot be distinguished due to the resolution limitations inherent in the light-scattering technique. Deconvolution of intensity data collected during the time interval, corresponding to particle sizes of ca. 3 to 10 nm, indicates that the large-sized particles (crystalline silicalite-1) have as their origin subcolloidal particles initially present in solution before hydrothermal treatment. There are indications therefore that certain subcolloidal particles may possess a short-range structure such that they increase in size upon hydrothermal treatment and may thus be termed zeolitic nuclei. The initial growth of the growing crystals may be described as being a non-linear function of time until an average particle size of ca. 20 nm is attained, after which linear growth at a rate of 0.72 nm/h was recorded.
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