Functional and Functionalized Silicate Materials
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Functional and Functionalized Silicate Materials Brandy J. Johnson, Brian J. Melde, Baochuan Lin, Paul T. Charles, Anthony P. Malanoski, and Mansoor Nasir Naval Research Laboratory, Washington, DC 20375 ABSTRACT Mesoporous organosilicate materials combine tunable binding characteristics, high surface area, and low materials density with an ordered pore network. Surface modifications provide the potential for incorporation of a variety of functional groups. We have taken advantage of these characteristics for the development of a range of materials to be utilized in various applications. In one approach, porphyrins are incorporated into the materials to provide unique catalytic properties. In these materials, the organosilicate scaffold stabilizes the porphyrin catalyst and facilitates interaction of the catalyst and target. Catalysis can be stimulated through exposure to light or application of an electrical current. The selectivity of the materials can be influenced through choice of organic bridging groups in the organosilicate structure and through selection of the porphyrin component. In addition, a type of molecular imprinting can be applied to provide sites on the pore walls that enhance adsorption selectivity for the target. These materials are directed at the development of self-decontaminating surfaces and coatings. Similar materials characteristics have been utilized in the development of solidphase extraction materials for use in the pre-concentration of nitroenergetic targets from ground and surface water samples. These materials are being incorporated into systems for in situ water quality monitoring. Mesoporous organosilicates can also be applied to the encapsulation of proteins and nucleic acids, stabilizing them for wider application of technologies utilizing these reagents. Modifications to the pore surfaces, in this case, are used to incorporate stabilizing agents such as sugars and proteins which should extend shelf-life and reduce storage restrictions. INTRODUCTION The overarching focus of this research group is on protective capabilities for support of the warfighter. Specific efforts seek to provide advances in protective fabrics, filters, and surfaces and enhanced detection capabilities. Each of these areas is supported by the development of novel materials. Appropriate materials have been developed through the utilization of a single approach to synthesis of porous scaffolds. The well known periodic mesoporous organosilica (PMO) materials are organic-inorganic hybrids with highly ordered pore networks and large internal surface areas (often >500 m2/g). The materials are synthesized using a surfactant template approach and acid catalyzed condensation of precursors [1, 2]. They offer narrow pore size distributions with few blocked pores or obstructions facilitating molecular diffusion throughout the pore networks. The alternating siloxane and organic moieties give PMOs properties associated with both organic and inorganic materials. The siloxane groups provide the rigidity required for surfacta
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