Recently, predictive pathways have been developed to materials with high surface areas and well-defined nanoscale pores, either arranged in periodic arrays or existing in individual nanoparticles. These novel materials are attractive in catalysis, separations, environmental cleanup, controlled drug delivery, electronics and development of sensors. Some of the most powerful synthetic approaches involve surfactant aggregates known as micelles, which are usually spherical or cylindrical in shape, as templates for nanoscale pores in periodic materials or in hollow nanospheres or nanotubes. However, the pathways to different kinds of micelle-templated nano-porous materials evolved separately with little synergy. The project is intended to bridge the divide between the micelle-templated periodic nanostructures and the nanoparticles, so that the knowledge about each of these structures can readily be used to understand other known structures and design new ones. The design features considered include the pore shape, pore diameter and size of the entrances to pores. The project is primarily focused on pores of size from 10 to 40 nanometers, which are important in immobilization of biomolecules (for instance in enzymatic catalysis), adsorption of large and small molecules, and heterogeneous catalysis. Convenient methods for the synthesis of materials with pores at this length scale are developed to facilitate their applications and gain fundamental insight into nanoscale materials design.
TECHNICAL DETAILS: The project is focused on two families of closely related micelle-templated materials: ordered (periodic) mesoporous materials and single-micelle-templated nanoparticles (nanospheres or nanotubes). A predictive pathway to single-micelle-templated nanoparticles was recently proposed which involves the lowering of the ratio of the framework precursor to surfactant under conditions known to afford ordered mesoporous materials. This new approach is the beginning of a unified conceptual framework for understanding of the formation of these two kinds of nanomaterials governed by the structure of micellar objects occurring at early stages of the synthesis and their ability to cross-link. The current project is intended to bridge the divide between the ordered mesoporous materials and single-micelle-templated nanoparticles. The objective is being achieved through an in-depth study of the formation and structural tailoring of large-pore ordered mesoporous materials, as well as the related nanospheres and nanotubes, templated by Pluronic block copolymer surfactants. The relatively large size of pores (14-40 nm) in these materials provides enhanced opportunities for the structure visualization (including the porosity on the shells of nanoparticles) by transmission electron microscopy, and is readily probed by gas adsorption porosimetry and small-angle X-ray scattering. Laser light scattering is being used to gain profound insight into micellar structures present at different stages of the synthesis and this knowledge is being correlated with the properties of the micelle-templated porous materials. The conditions for the formation of either periodic porous materials or individual nanoparticles are elucidated and the structural development in the synthesis of the individual particles is followed. The tailoring of the size of openings on the shells of the nanoparticles is being investigated. Convenient, room-temperature syntheses of ordered mesoporous materials and related single-micelle-templated particles are developed. The extension of the synthesis of large-pore silicas on gyroidal porous networks is pursued. The project is designed to involve a postdoctoral fellow, graduate students and undergraduate students in the project's research.
