NER: Catalytic formation of nanostructured ceramics by a bio-mimetic and environmentally friendly approach

Princeton University, Princeton NJ

Investigators

Abstract

National Science Foundation - Active Nanostructure and Nanosystems (ANN) (NSF 06-595) Nanoscale Exploratory Research (NER) Proposal Number: CBET-0708054 Principal Investigator: Adamson, Douglas Affiliation: Princeton University Proposal Title: NER: Catalytic formation of nanostructured ceramics by a bio-mimetic and environmentally friendly approach NER:Catalytic formation of nanostructured ceramics by a bio-mimetic and environmentally friendly approach For millions of years nature has been able to make ceramic structures with precise detail and control at the nanoscale. The strength of the abalone shell and the intricate designs found in diatoms are two examples of organisms producing highly ordered ceramic materials under conditions of near-neutral pH at ambient temperatures. In the case of man-made materials, not only is the precise nano-structure lacking, the conditions required to form ceramics involve extremes of pH and/or high temperatures. These conditions are detrimental in terms of cost and environmental impact, and may preclude the use of many organic structure-directing agents as well as the incorporation of catalysts that could be included in a porous ceramic matrix. A synthetic system that can mimic the ability of nature to produce well ordered ceramics at the nano-scale under mild conditions would find applications ranging in structural materials, catalysis, and filtration technologies. The natural system on which we have focused our efforts is the protein Silicatein, found in the marine sponge Tethya aurantia. This sponge creates silica spicules that are composed of a silica outer casing comprising 75% of the spicule weight and a core containing a mixture of proteins. Of the protein found in the core, 70% is Silicatein. We focused on this protein for two reasons: first, the structure of the protein had been determined and second, the mechanism of its catalysis had been elucidated. These studies revealed that Silicatein has the ability to catalyze the hydrolysis of tetraethoxysilane (TEOS). The subsequent condensation of the hydrolyzed silane is rapid and results in the formation of silca. Exploiting this mechanism, the relatively stable TEOS can be quickly converted to silca at room temperature and under near neutral pH. We have recently developed a synthetic, non-peptide based polymer that mimics the catalytic function of the protein Silicatein. By incorporating analogs of the functional groups shown to be critical in the catalytic activity of the protein into a purely synthetic polymer, we have demonstrated catalytic function in a non-peptide block copolymer. This work has been described in a manuscript currently under consideration by the Journal of the American Chemical Society. We have demonstrated by numerous analytical and chemical methods the catalytic nature of our polymer with respect to TEOS condensation. Building on our successful demonstration of catalysis, we will exploit the amphiphilic nature of our block copolymer catalyst to form nano-structured ceramics under near-neutral pH and ambient temperatures. The high-risk element of this work is the use of this polymer to template ceramics with nanoscale features and the incorporation of ceramics other than silica, neither of which has been previously demonstrated. We thus will create a synthetic system that mimics the natural system in which a nanoscale templating agent is also a catalyst. The broader impacts of this grant include the creation of new materials that increase the efficiency of catalysis, produce new nanostructured ceramics, and create new structural materials, under environmentally benign conditions. It will also allow for the incorporation of temperature or pH sensitive materials into a porous ceramic matrix. Additionally, this grant will support the PI's involvement in outreach programs that include a Research Experience for Undergraduates (REU) program, Princeton University Materials Academy (PUMA) targeted at underrepresented minority high school students, and the Scientist in Residence program at the Liberty Science Center. This grant also includes research activities for an undergraduate student. Every effort will be made to attract a female or minority student and introduce them to cutting edge research. The intellectual impact of this work is two-fold. Being able to mimic a biological process is one of the best ways to truly understand it. Thus our efforts to reproduce what nature does in a completely synthetic system will lead to a deeper understanding of the natural process. Secondly, in synthesizing a ceramic ordered at the nano-scale, we will increase our understanding of self-assembled amphiphilic systems and how the structures formed can be immobilized and exploited.