The synthesis, characterization and catalytic applications of mesocellular silica foams

Despite recent progress in materials synthesis, there are few materials with narrow pore size distributions and well-defined pore structures in the size range of 100 - 500 A. Materials with pores of 100 - 500 A possess a potential combination of high surface areas and pore sizes accommodating of large molecules that could make them of great use in the catalysis and separation of complex molecules important to the fine chemicals and pharmaceuticals industries. We have synthesized mesocellular silica foams (MCF) by using triblock copolymer (PEO-PPO-PEO, Pluronic) micelles to template the formation of silica from tetraethoxysilane precursors. The combination of the polymer amphiphile with a hydrophobic swelling agent (such as trimethylbenzene) resulted in larger pore sizes and more open pore structures than had previously been obtained with surfactant templates. The MCF materials have pore sizes of up to 350A, void fractions of > 0.85 and surface areas of - 700 m2/g. The basic properties of the swollen triblock copolymer micelles were investigated to provide a better understanding of their templating behavior. Small-angle neutron scattering (SANS) in conjunction with a thermodynamic model for swollen micelle formation were used to determine the size, shape and internal structure of the Pluronic micelles. Knowledge of the micelle structure and aggregation behavior was used to investigate the effects of changing polymer and oil types on the size of the swollen micelles and therefore to select the best systems for templating large pores in silica sol-gels.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Chemical Engineering.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2002

Author dc:creator

• Lettow, John Stangland, 1973-

Advisor dc:contributor.advisor

• Jackie Y. Ying

• Chemical Engineering.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/29276

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/29276