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Controlling the Pore Size and Morphology of Mesoporous Silica
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials . Linköping University, The Institute of Technology.
2010 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Mesoporous silica with a hexagonally ordered pore structure (SBA-15) has been synthesized. Through variations in the synthesis conditions several morphologies, such as fibers, sheets and separate rods, have been realized. Furthermore, additions of heptane and NH4F make it possible to synthesize SBA-15 with pores as large as 18 nm in the sheet morphology. Mechanisms for the formation of different morphologies have been suggested. In the case of fibers and sheets, the amount of heptane present during the synthesis determines the final morphology. For low concentrations, the heptane enters the micelles and increases the pore size while the particles (crystallites) attaches to each other end to end. When the heptane concentration increases, the heptane droplets increase in size, and above a critical droplet size the crystallites attach with one short end towards the droplet, forming the sheet morphology. The crystallites can also be separated. This is the case of the rod morphology. The separation is performed by shortening the stirring time and increasing the HCl concentration. The increased amount of HCl increases the hydration rate of the silica precursor, which can be used to control the thickness and length of the rods. Furthermore, the reaction time has been decreased from 20 h for all morphologies to less than 4 hours. The materials have been characterized with nitrogen sorption, electron microscopy and x-ray diffraction. Also, thermogravimetric analysis and fourier transformed infrared spectroscopy have been used for studying the removal of surfactants.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press , 2010. , 67 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1451
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-70405Local ID: LIU-TEK-LIC-2010:22ISBN: 978-91-7393-305-6 (print)OAI: oai:DiVA.org:liu-70405DiVA: diva2:439011
Presentation
2011-11-03, Planck, Fysikuset, Campus Valla, Linköpings universitet, Linköping, 10:15 (Swedish)
Opponent
Supervisors
Available from: 2011-09-06 Created: 2011-09-06 Last updated: 2013-10-02Bibliographically approved
List of papers
1. Synthesis and characterization of large mesoporous silica SBA-15 sheets with ordered accessible 18 nm pores
Open this publication in new window or tab >>Synthesis and characterization of large mesoporous silica SBA-15 sheets with ordered accessible 18 nm pores
2009 (English)In: Materials Letters, ISSN 0167-577X, Vol. 63, no 24-25, 2129-2131 p.Article in journal (Refereed) Published
Abstract [en]

Mesoporous silica SBA-15 in the form of 10-30 μm sized sheets with unusually large ordered pores has been synthesized using heptane as a cosolvent in the presence of NH4F. The resulting morphology of 400 nm thick sheets that contain easily accessed, hexagonally arranged, 18 nm sized pores running parallel to sheet normal has not been previously reported. The material has a BET surface area of 541 m2/g, large pore volume of 1.69 cm3/g and ordered mesopore structure with a narrow pore size distribution around 18 nm. A mechanism for sheet formation based on heptane droplets acting as sites for self assembling of silica crystallites is suggested.

Keyword
Large pore; Mesoporous silica; SBA-15; Sheet
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-21193 (URN)10.1016/j.matlet.2009.07.013 (DOI)
Note
Original Publication: Emma Johansson, Jose Manuel Cordoba and Magnus Odén, Synthesis and characterization of large mesoporous silica SBA-15 sheets with ordered accessible 18 nm pores, 2009, Materials Letters, (63), 24-25, 2129-2131. http://dx.doi.org/10.1016/j.matlet.2009.07.013 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/ Available from: 2009-09-30 Created: 2009-09-30 Last updated: 2013-10-22
2. The effects on pore size and particle morphology of heptane additions to the synthesis of mesoporous silica SBA-15
Open this publication in new window or tab >>The effects on pore size and particle morphology of heptane additions to the synthesis of mesoporous silica SBA-15
2010 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, Vol. 133, no 01-Mar, 66-74 p.Article in journal (Refereed) Published
Abstract [en]

The effect of heptane on the particle morphology and pore size in the synthesis of SBA-15 is presented. Heptane in the presence of NH4F works as a pore swelling agent, resulting in 13-18 nm sized pores in 400 nm long and 200-1000 nm wide crystallites. The pores are hexagonally arranged and run through the crystallites. Increasing the heptane to P123 molar ratio changes the morphology of SBA-15 from fibers to sheets when the crystallites rearrange during the synthesis. The pore order in the sheets is controlled by changing the molar ratio of water to P123. The surface areas of these materials are 500-800 m(2)/g with pore volumes of 1.2-1.7 cm(3)/g. The sheets have accessible pores with a size of 18 nm running parallel to the sheet normal, which makes them suitable for membranes.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2010
Keyword
SBA-15; Morphology; Heptane; H2O2; Sheet
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-58290 (URN)10.1016/j.micromeso.2010.04.016 (DOI)000279061000009 ()
Available from: 2010-08-10 Created: 2010-08-09 Last updated: 2015-05-28
3. Rapid Synthesis of SBA-15 Rods with Variable Lengths, Widths, and Tunable Large Pores
Open this publication in new window or tab >>Rapid Synthesis of SBA-15 Rods with Variable Lengths, Widths, and Tunable Large Pores
2011 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 27, no 8, 4994-4999 p.Article in journal (Refereed) Published
Abstract [en]

Dispersed SBA-15 rods have been synthesized with varying lengths, widths, and pore sizes in a low-temperature synthesis in the presence of heptane and NH4F. The pore size of the material can systematically be varied between 11 and 17 nm using different hydrothermal treatment times And/or temperatures. The particle length (400-600 nm) and width (100-400 nm) were tuned by varying the HCl concentration. All the synthesized materials possess a large surface area of 400-600 m(2)/g And a pore volume of 1.05-1.30 cm(3). A, mechanism for the effect of the HCl concentration on the particle morphology is suggested. Furthermore, it is shown that the reaction time an be decreased to 1 h, with well-retained pore size and morphology. This work has resulted in SBA-15 rods with the largest pore size reported for this morphology.

Place, publisher, year, edition, pages
ACS American Chemical Society, 2011
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-67831 (URN)10.1021/la104864d (DOI)000289321000091 ()
Available from: 2011-04-29 Created: 2011-04-29 Last updated: 2013-10-22Bibliographically approved

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