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Formation mechanism of anionic-surfactant-templated mesoporous silica (AMS)
Stockholm University, Faculty of Science, Department of Physical, Inorganic and Structural Chemistry. (Osamu Terasaki)
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This dissertation is focused on synthesis, characterization and formation mechanism of anionic-surfactant-templated mesoporous silica (AMS).

Structural control mechanisms of AMS are investigated. First, different ionization degree of anionic surfactant affected by the acidity or alkalinity of the synthesis system gives rise to different charging density of micelles and therefore determines the organic/inorganic interface curvature, producing mesophases from cage-type to cylindrical, bicontinuous and lamellar. Second, mesocage/mesocage electrostatic repulsive interaction affects the formation of cage-type mesostructure, which is derived from a full-scaled synthesis-field diagram of AMS. The mesocage/mesocage interaction changes with charge density of mesocages and gives rise to their different packing manners. Third, the structural properties of AMS materials could be tuned by molecular features of surfactant and co-structure-directing agent (CSDA).

The pore size of AMS is found to be controlled by alkyl chain length, ionization degree of surfactant and the CSDA/surfactant ratio. Alkyl chain length of surfactant determines size of micelles and thus mesopores. Larger ionization degrees of anionic surfactant give rise to smaller pore sizes due to thermodynamic coiling of alkyl chains of surfactant. The hydrophobic interactions between the pendant organic groups of CSDA on the silica wall and the hydrophobic core of the micelles drive a contraction of the mesopores.

A mesoporous silica with novel bicontinuous cubic Pn-3m structure has been prepared using a diprotic anionic surfactant. 3d-reconstruction of the structure shows that it is bicontinuous composed of an enantiomeric pair of 3d mesoporous networks that are interwoven with each other, divided by a D surface. Inverse replication suggests the possible presence of ordered complimentary micropores in the material.

Place, publisher, year, edition, pages
Stockholm: Department of Physical, Inorganic and Structural Chemistry, Stockholm University , 2009. , 75 p.
Keyword [en]
mesoporous silica, anionic surfactant, formation mechanism, structural control
National Category
Other Basic Medicine
Research subject
Structural Chemistry
Identifiers
URN: urn:nbn:se:su:diva-29628ISBN: 978-91-7155-932-6 (print)OAI: oai:DiVA.org:su-29628DiVA: diva2:234501
Public defence
2009-10-06, Magnélisalen, Kemiska övningslaboratoriet, Svante Arrhenius vägen 16 B, Stockholm, 13:30 (English)
Opponent
Supervisors
Available from: 2009-09-15 Created: 2009-09-08 Last updated: 2009-09-15Bibliographically approved
List of papers
1. Synthesis and characterization of mesoporous silica AMS-10 with bicontinuous cubic Pn-3m symmetry
Open this publication in new window or tab >>Synthesis and characterization of mesoporous silica AMS-10 with bicontinuous cubic Pn-3m symmetry
2006 (English)In: Angewandte Chemie International Edition, ISSN 1433-7851, E-ISSN 1521-3773, Vol. 45, 4295-4298 p.Article in journal (Refereed) Published
Abstract [en]

A mesoporous silica AMS-10 with novel bicontunuous cubic Pn-3m symmetry was synthesized and chracterized by electron crystallography.

Place, publisher, year, edition, pages
Weinheim: Wiley-VCH, 2006
Keyword
electron diffraction; electron microscopy; mesoporous materials; surfactant; template synthesis
Identifiers
urn:nbn:se:su:diva-29606 (URN)10.1002/anie.200504114 (DOI)
Available from: 2009-09-09 Created: 2009-09-08 Last updated: 2017-12-13Bibliographically approved
2. Formation Mechanism of Anionic Surfactant-Templated Mesoporous Silica
Open this publication in new window or tab >>Formation Mechanism of Anionic Surfactant-Templated Mesoporous Silica
2006 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 18, 3904-3914 p.Article in journal (Refereed) Published
Abstract [en]

The synthesis mechanism of anionic surfactant-templated mesoporous silica (AMS) is described. A family of highly ordered mesoporous silica structures have been synthesized via an approach based on the self-assembly of anionic surfactants and inorganic precursors by using aminopropylsiloxane or quaternized aminopropylsiloxane as the co-structure-directing agent (CSDA), which is a different route from previous pathways. Mesophases with differing surface curvatures, varying from cage type (tetragonal P42/mnm; cubic Pm-3n with modulations; cubic Fd-3m) to cylindrical (two-dimensional hexagonal p6mm), bicontinuous (cubic Ia-3d and Pn-3m), and lamellar have been obtained by controlling the charge density of the micelle surfaces by varying the degree of ionization of the carboxylate surfactants. Changing the degree of ionization of the surfactant results in changes of the surfactant packing parameter g, which leads to different mesostructures. Furthermore, variation of the charge density of positively charged amino groups of the CSDA also gives rise to different values of g. Mesoporous silicas, functionalized with amino and quaternary ammonium groups and with the various structures given above, have been obtained by extraction of the surfactant. This report leads to a deeper understanding of the interactions between the surfactant anions and the CSDA and provides a feasible and facile approach to the mesophase design of AMS materials.

Place, publisher, year, edition, pages
ACS, 2006
Keyword
mesoporous silica, anionic surfactant, formation mechanism
Research subject
Materials Science
Identifiers
urn:nbn:se:su:diva-29613 (URN)10.1021/cm061107+ (DOI)
Available from: 2009-09-09 Created: 2009-09-08 Last updated: 2017-12-13Bibliographically approved
3. Molecular design of the surfactant and the co-structure-directing agent (CSDA) toward rational synthesis of targeted anionic surfactant templatedmesoporous silica
Open this publication in new window or tab >>Molecular design of the surfactant and the co-structure-directing agent (CSDA) toward rational synthesis of targeted anionic surfactant templatedmesoporous silica
2007 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 17, 3591-3602 p.Article in journal (Refereed) Published
Abstract [en]

The formation of anionic surfactant templated mesoporous silica (AMS) is investigated from the perspective of the geometrical molecular design of the surfactant and the co-structure-directing agent (CSDA) toward the rational synthesis of the targeted mesostructure. Increasing the geometrical size of two types of head group of the anionic surfactant in the order (i) sulfonate, sulfate and phosphate, and (ii) carboxylate, N-acylalanate/N-acylglycinate and N-acylglutamate, resulted in the mesophase changing from a disordered or lamellar phase to two-dimensional (2D) hexagonal (p6mm) and three-dimensional (3D) cage-type (hexagonal and a modulated cubic phase) with increasing order of the organic/inorganic interface curvature. A change in the chain length of the surfactant also led to different surfactant packing and mesophase interfacial curvatures, and resulted in a change in mesophase from a modulated cage-type mesophase to cubic Fd-3m, cubic Pm-3n and a disordered cage-type mesophase. The geometrical change in the CSDA resulted in an increasing micellar curvature in the order: aminopropyl , N-methylaminopropyl, N,N-dimethylaminopropyl trimethoxysilane, which led to a change of mesophase from bicontinuous cubic Pn-3m to 2D-hexagonal p6mm. An increase in the CSDA/surfactant ratio in the synthesis gave rise to the mesophase change from a disordered cage-type mesophase to cubic Fm-3m or from lamellar to 2D-hexagonal p6mm, and elemental analysis results showed that the mesoporous silicas have an increased loading of organic moieties using the CSDA method.

Place, publisher, year, edition, pages
United Kingdom: The Royal Society of Chemistry, 2007
Keyword
mesoporous silica, anionic surfactant, co-structure directing agent, mesophase control
Research subject
Materials Science
Identifiers
urn:nbn:se:su:diva-29614 (URN)10.1039/b704398h (DOI)000248917400016 ()
Available from: 2009-09-09 Created: 2009-09-08 Last updated: 2017-12-13Bibliographically approved
4. Formation of Diverse Mesophases Templated by a Diprotic Anionic Surfactant
Open this publication in new window or tab >>Formation of Diverse Mesophases Templated by a Diprotic Anionic Surfactant
2008 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 14, no 36, 11423-11428 p.Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Weinheim: Wiley-VCH Verlag GmbH&Co. KGaA, 2008
Keyword
formation mechanism, mesophases, mesoporous materials, surfactants, synthesis-field diagram
National Category
Chemical Sciences
Research subject
Materials Science
Identifiers
urn:nbn:se:su:diva-29615 (URN)10.1002/chem.200800766 (DOI)000262002900021 ()
Available from: 2009-09-09 Created: 2009-09-08 Last updated: 2017-12-13Bibliographically approved
5. Molecular design of AEC tri-block anionic surfactant towards rational synthesis of targeted thick-walled mesoporous silica
Open this publication in new window or tab >>Molecular design of AEC tri-block anionic surfactant towards rational synthesis of targeted thick-walled mesoporous silica
2009 (English)In: Journal of Materials Chemistry, ISSN 0959-9428, E-ISSN 1364-5501, Vol. 19, 3404-3411 p.Article in journal (Refereed) Published
Abstract [en]

Here we report a new synthesis strategy to synthesize thick-walled two dimensional hexagonal mesoporous silicas, using tri-block surfactant fatty alcohol ether carboxylate [AEC: CnH2n+1O(CH2CH2O)mCH2COONa] with two different hydrophilic head groups of (EO)x-block and anionic carboxylate. The unique formation of double-layer silica wall arose from two types of hydrophilic head groups via the silica source condensation led to an obvious increase in the wall thickness. The successful carbon replication proved the existence of micropores formed by imbedded (EO)x-block and electrostatic bonding of carboxylate head group and organic group of co-structuredirecting agent. The template-free mesoporous silica showed a high hydrothermal stability due to the thick wall.

Place, publisher, year, edition, pages
United Kingdom: The Royal Society of Chemistry, 2009
Keyword
mesoporous, wall thickness, molecular design, AEC surfactant
Research subject
Materials Science
Identifiers
urn:nbn:se:su:diva-29616 (URN)10.1039/b822742j (DOI)
Available from: 2009-09-09 Created: 2009-09-08 Last updated: 2017-12-13Bibliographically approved
6. Formation of mesoporous Co3O4 replicas of different mesostructureswith different pore sizes
Open this publication in new window or tab >>Formation of mesoporous Co3O4 replicas of different mesostructureswith different pore sizes
2009 (English)In: Microporous and Mesoporous Materials, ISSN 1387-1811, E-ISSN 1873-3093, Vol. 123, 314-323 p.Article in journal (Refereed) Published
Abstract [en]

Mesoporous metal oxides Co3O4 are prepared via hard templating synthesis method by using various mesoporous silicas with different pore size as templates. The pore size of the mesoporous silicas with the symmetry of two-dimensional (2d)-hexagonal p6mm, bicontinuous cubic Ia-3d and Pn-3m have been controlled in the range of 6.6–10.7, 4.2–7.5 and 5.1–6.7 nm, respectively, by choosing different surfactants and co-surfactants and by adjusting either the aging temperature or the ionization degree of the surfactant. The pore size of the silica template has been considered to be an important factor that determines the mesostructure of the resulting metal oxides. It has been found that for p6mm, it is easier to replicate the mesoporous symmetry at large size of mesopores. For Ia-3d, at large-pore size two sets of bicontinuous meso-channels are replicated into mesoporous Co3O4, while small-pore Ia-3d leads to replication of both one set and two sets of meso-channels. Co3O4 can replicate both one set and two sets of bicontinuous Pn-3m meso-channels at all pore sizes that can be obtained (5.1–6.7 nm), indicating the existence of ordered complementary micropores within the silica walls.

Place, publisher, year, edition, pages
Elsevier, 2009
Keyword
mesoporous cobalt oxide, hard templating, replica, mesostructure, pore size
Research subject
Materials Science
Identifiers
urn:nbn:se:su:diva-29617 (URN)10.1016/j.micromeso.2009.04.017 (DOI)000267099000039 ()
Available from: 2009-09-09 Created: 2009-09-08 Last updated: 2017-12-13Bibliographically approved

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Output format
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