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Mesoporous Building Blocks: Synthesis and Characterization of Mesoporous Silica Particles and Films
Linköping University, Department of Physics, Chemistry and Biology, Nanostructured Materials. Linköping University, The Institute of Technology.
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Catalyst supports, drug delivery systems, hosts for nanoparticles, and solar cells are just some examples of the wide range of exciting applications for mesoporous silica. In order to optimize the performance of a specific application, controlling the material’s morphology and pore size is crucial. For example, short and separated particles are beneficial for drug delivery systems, while for molecular sieves, the pore size is the key parameter.

In this thesis, mesoporous silica building blocks, crystallites, with hexagonally ordered cylindrical pores were synthesized, with the aim to understand how the synthesis parameters affect the particle morphology and pore size. The synthesis of the particles is performed using a sol-gel process, and in order to increase the pore size, a combination of low temperature, and additions of heptane and NH4F was used. By variations in the amounts of reagents, as well as other synthesis conditions, the particle morphology and pore size could be altered. Separated particles were also grown on or attached to substrates to form films. Also, a material with spherical pore structure was synthesized, for the first time using this method.

It was found that a variation in the heptane concentration, in combination with a long stirring time, yields a transition between fiber and sheet morphologies. Both morphologies consist of crystallites, which for the fibers are joined end to end, while for the sheets they are attached side by side such that the pores are accessible from the sheet surface. The crystallites can be separated to a rod morphology by decreasing the stirring time and tuning the HCl concentration, and it was seen that these rods are formed within 5 min of static time, even though the pore size and unit cell parameters were evolving for another 30 min. Further studies of the effects of heptane showed that the shape and mesoscopic parameters of the rods are affected by the heptane concentration, up to a value where the micelles are fully saturated with heptane. It was also observed that the particle width increases with decreasing NH4F concentration, independent of heptane amount, and a platelet morphology can be formed. The formation time of the particles decrease with decreasing NH4F, and the growth mechanism for platelets was further studied. The pore sizes for various morphologies were altered by e.g. variations in the hydrothermal treatment conditions, or the method for removing the surfactants.

The separated particles can be attached to substrates, either during the particle synthesis or by post grafting prior to calcination. The film formation during the one-pot-synthesis was studied and a formation mechanism including nucleation of elongated micelles on the substrate was suggested. During the post grafting film synthesis, the medium in which the particles are dispersed, as well as functionalization of both particle and substrate are crucial for the post grafting process. The pores are easily accessible independent of the method, even though they are aligned parallel to the substrate when the one-pot-method is used, while post grafting gives a perpendicular pore orientation.

In summary, this work aims to give an understanding for the formation of the synthesized material, and how to tune the material properties by alterations in parameter space. Successful syntheses of four different particle morphologies and two new types of films were performed, and the pore size could easily be tuned by various methods.

Place, publisher, year, edition, pages
Linköping: Linköping University Electronic Press, 2013. , 82 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 1542
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:liu:diva-99858DOI: 10.3384/diss.diva-99858ISBN: 978-91-7519-516-2 (print)OAI: oai:DiVA.org:liu-99858DiVA: diva2:658453
Public defence
2013-11-15, Visionen, Hus B, Campus Valla, Linköpings universitet, Linköping, 13:15 (English)
Opponent
Supervisors
Available from: 2013-10-22 Created: 2013-10-22 Last updated: 2013-10-22Bibliographically 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. Synthesis of hollow silica spheres SBA-16 with large-pore diameter
Open this publication in new window or tab >>Synthesis of hollow silica spheres SBA-16 with large-pore diameter
2011 (English)In: Materials letters (General ed.), ISSN 0167-577X, E-ISSN 1873-4979, Vol. 65, no 7, 1066-1068 p.Article in journal (Refereed) Published
Abstract [en]

Hollow silica SBA-16 spheres with cubic ordered mesoporous shells were synthesized by an emulsion-templating method, using Pluronic F127 as a structure-directing agent. tetraethyl orthosilicateas as a silica source and heptane as a cosolvent in the presence of NH4F. The size of these spheres is in the range of 10 to 30 mu m. The shell is about 700 nm thick and consists of large pores, similar to 9 nm in diameter, arranged in a cubic order. After calcination, the spheres maintain their mesoporosity and show a high surface area of 822 m(2)/g. The formation mechanism of the silica hollow spheres is discussed.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2011
Keyword
Mesoporous silica, SBA-16, Hollow spheres, Large pore, F127
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-67554 (URN)10.1016/j.matlet.2011.01.035 (DOI)000289021700002 ()
Available from: 2011-04-18 Created: 2011-04-18 Last updated: 2017-12-11Bibliographically approved
3. 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, E-ISSN 1873-3093, 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: 2017-12-12
4. 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: 2017-12-11Bibliographically approved
5. Tuning the shape of mesoporous silica particles by alterations in parameter space: from rods to platelets
Open this publication in new window or tab >>Tuning the shape of mesoporous silica particles by alterations in parameter space: from rods to platelets
2013 (English)In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 29, no 44, 13551-13561 p.Article in journal (Refereed) Published
Abstract [en]

The knowledge of how to control the pore size and morphology of separated mesoporous silica particles is crucial for optimizing their performance in applications, such as molecular sieves and drug delivery systems. In this work, we have systematically studied the effects of various synthesis parameters to gain a deeper understanding of how particle morphologies can be altered. It was found that the morphology for isolated particles of SBA-15 type, with unusually short and wide pores, could be altered from rods to platelets by variations in the NH4F concentration. The pore length is nearly constant (similar to 300 nm) for the different morphologies, but the particle width is increasing from 200 nm to >3 mu m when decreasing the amount of NH4F, and the pore size can be tuned between 10 and 13 nm. Furthermore, other synthesis parameters such as heptane concentration, pH, silica precursor, and additions of ions have also been studied. The trend regarding particle width is independent of heptane concentration, at the same time as heptane increases the particle length up to a plateau value of similar to 500 nm. In all, parameters controlling particle width, length, and pore size have been separated in order to evaluate their function in the particle formation. Additionally, it was found that the formation time of the particles is strongly affected by the fluoride ion concentration, and a mechanism for particle formation for this system, where micelles transform from a foam, to multilamellar vesicles, and finally to cylindrical micelles, is suggested.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2013
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-99859 (URN)10.1021/la403201v (DOI)000326711200029 ()
Available from: 2013-10-22 Created: 2013-10-22 Last updated: 2017-12-06Bibliographically approved
6. Single-pot synthesis of ordered mesoporous silica films with unique controllable morphology
Open this publication in new window or tab >>Single-pot synthesis of ordered mesoporous silica films with unique controllable morphology
2014 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 413, 1-7 p.Article in journal (Refereed) Published
Abstract [en]

Mesoporous silica films consisting of a monolayer of separated SBA-15 particles with unusually wide and short pores grown on silicon wafers have been fabricated in a simple single-pot-synthesis, and the formation of the films has been studied. A recipe for synthesizing mesoporous silica rods with the addition of heptane and NH4F at low temperature was used and substrates were added to the synthesis solution during the reaction. The films are ∼90 nm thick, have a pore size of 10.7–13.9 nm depending on the hydrothermal treatment time and temperature, and a pore length of 200–400 nm. All pores are parallel to the substrate, open, and easy to access, making them suitable for applications such as catalyst hosts and gas separation. The growth of the films is closely correlated to the evolution of the mesoporous silica particles. Here, we have studied the time for adding substrates to the synthesis solution, the evolution of the films with time during formation, and the effect of hydrothermal treatment. It was found that the substrates should be added within 30–60 s after turning off the stirring and the films are formed within 10 min after addition to the synthesis solution. The study has yielded a new route for synthesizing mesoporous silica films with a unique morphology.

Place, publisher, year, edition, pages
Elsevier, 2014
Keyword
SBA-15; Mesoporous silica; Large pore; Films; Rods; Film growth; Particle formation
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-99856 (URN)10.1016/j.jcis.2013.09.023 (DOI)000327168800001 ()
Available from: 2013-10-22 Created: 2013-10-22 Last updated: 2017-12-06Bibliographically approved
7. Grafting mesoporous silica particles to substrates: a method for synthesizing mesoporous films with cylindrical pores perpendicular to the substrate
Open this publication in new window or tab >>Grafting mesoporous silica particles to substrates: a method for synthesizing mesoporous films with cylindrical pores perpendicular to the substrate
2013 (English)Manuscript (preprint) (Other academic)
Abstract [en]

A method for synthesizing mesoporous silica films with cylindrical pores perpendicular to the substrate has been developed. The films consist of SBA-15 platelets that are grafted on glass substrates. The grafting is studied in terms of parameters such as pH, substrate functionalization, salt additions, time for TEOS prehydrolysis, and calcination. The best coverage of particles on the substrate was achieved for a low pH in combination with OTS-treated glass substrate. Furthermore, the prehydrolysis time of the TEOS was found to be a key parameter in order to bind the particles to the substrate. These porous films have potential in applications such as catalysis, drug delivery, and as a template for nanoparticle or nanorod, growth.

Keyword
Mesoporous silica films, platelets, particle functionalization, substrate functionalization, pH, salt
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-99857 (URN)
Available from: 2013-10-22 Created: 2013-10-22 Last updated: 2013-10-22Bibliographically approved

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