|Host:Professor Ajayan VinuPresenter:
Department of Chemistry, Graduate School of Science, Kyoto University, Japan
International Center for Materials Nanoarchitectonics (WPI-MANA)
National Institute for Materials Science (NIMS)
Novel Synthetic Challenges at Boundaries
Functional Porous Silsesquioxane Monolithic Materials from Organotrialkoxysilane-derived Sol-Gel Systems
Tuesday 18 February 2014
Level 4 Seminar Room,
Corner College and Cooper Road,
|Abstract: Novel Synthetic Challenges at BoundariesIn the field of inorganic chemistry, one of the synthetic challenges can be the construction of multinuclear heterometallic complexes by design, which requires the perfect control of the orientation of different metal centers in a single molecule. To address this issue, we have developed a new methodology, where the successive coupling of metal complex monomers by using the Merrifield solid-phase peptide synthesis technique plays the key role.
As a proof-of-concept, a series of metal complex monomers bearing an amino acid moiety were subjected to the protocols of solid-phase peptide synthesis to make linear arrays of metal centers with a controlled sequence [1–3]. Updates of this approach recently allow us to access not only linear but also branched arrays up to octanuclear heterometallic complexes, whose molecular weights reach to the range comparable to that of a small protein . In the later part of my presentation, I will also show another trial on the construction of a 2D crystalline monolayer of a metal complex, which serves a useful surface for the manipulation of fullerenes in a single molecular level [5, 6].
Abstract: Functional Porous Silsesquioxane Monolithic Materials from Organotrialkoxysilane-derived Sol-Gel Systems Silsesquioxanes (RSiO1.5) derived from organotrialkoxysilanes (RSi(OR’)3) through sol-gel offer attractive features especially in surface characters and mechanical properties. The monolithic form of silsesquioxanes from organotrialkoxysilanes, however, is not popular because of the high tendency to form polyhedral oligomeric silsesquioxanes (POSS) and/or uncontrolled hydrophobic precipitates. We have been studying on porous monoliths based on three-dimensional random networks derived from organotrialkoxysilanes through careful controls over fundamental synthetic parameters in sol-gel chemistry. The length scale of the porous structures is designed from several tens nanometers (typical aerogels) to microns (macroporous gels) by controlling phase separation tendency in the systems. From the basics of our concept and technique to recent topics including the followings will be presented.
Hydrogen silsesquioxane (HSQ, HSiO1.5) monoliths with hierarchical porosity can be prepared from trimethoxysilane (HTMS, HSi(OCH3)3) by an acid-catalyzed one-step process under the presence of poly(ethylene oxide). On the surface of the resultant monoliths are there abundant Si-H groups, which can be used for simultaneous reduction and immobilization of metal (alloy) nanoparticles.[2,3] For instance, the HSQ monoliths embedded with Pd nanoparticles were prepared and used as a supported catalyst for the Mizoroki-Heck reaction. The HSQ surface can also be modified with various alcohols under the presence of a Lewis acid by dehydrogenative addition, which would lead to a new surface modification technique.
Transparent aerogels with methylsilsesquioxane (MSQ, CH3SiO1.5) composition can be obtained from methyltrimethoxysilane (MTMS, CH3Si(OCH3)3) by an acid-base two-step process under the presence of surfactant.[6,7] Since these aerogels are mechanically strong and flexible against compression, MSQ xerogel monoliths with aerogel-like properties can be prepared by ambient pressure drying. Through further reinforcement of the MSQ xerogels, practical applications to low-cost thermal insulators are presently being explored. Hierarchically porous MSQ monoliths with macro- and mesopores can also be obtained using a similar system under a careful control of phase separation, and applications to separation media are currently underway. These systems are recently extended to ethylsilsesquioxane (ESQ, CH3CH2SiO1.5) and vinysilsesquioxane (VSQ, CH2=CHSiO1.5).
Co-condensation of MTMS with dimethyldimethoxysilane (DMDMS, (CH3)2Si(OCH3)2) leads to a unique marshmallow-like macroporous material with bendable and extremely soft features. The marshmallow-like gels can selectively absorb oil from oil-water mixtures because of the high hydrophobicity and oleophilicity. In addition, the flexibility is maintained even at liquid nitrogen temperature, due to low glass transition temperature of the less-crosslinked polysiloxane (silicone) networks. The marshmallow-like gels were also imparted with oleophobicity by surface modification of vinyl-modified marshmallow-like gels with the perfluoroalkyl thiol through the thiol-ene reaction. These examples are expected to open novel unique applications such as to monolithic antifouling materials.
Biography: Kentaro Tashiro
Dr. Kentaro Tashiro was born in 1972 and obtained Ph.D. in organic chemistry in 2000 under the direction of Professor Takuzo Aida at the University of Tokyo. He then began an academic career at the University of Tokyo as an assistant professor. From 2008, he is the deputy head of reticular materials group at National Institute for Materials Science (NIMS).
Examples of his research interests are supramolecular chemistry of fullerenes, materials engineering of conjugated molecules, and rational networking of metal complexes.
Biography: Kazuyoshi Kanamori
Kazuyoshi Kanamori received his Bachelor (2000), Master (2002), and Doctor of Engineering (2005) from Kyoto University, Japan. He worked as a postdoctoral fellow of JSPS from 2005 to 2007. He is currently an Assistant Professor at Department of Chemistry, Graduate School of Science, Kyoto University. His research interest is based on synthesis, characterization, and application of porous materials prepared via liquid-phase processes such as sol-gel and living polymerization in polymer chemistry. Porous materials composed of inorganic oxides, organic–inorganic hybrids, organic cross-linked polymers, and carbons are his particular concerns.