Supramolecular Modification of Mesoscale Materials

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Title: Supramolecular Modification of Mesoscale Materials
Author: Fontenot, Sean
Abstract: The process of surface modification allows us to combine the structural advantages of materials with the chemical functionality of organic compounds. Attachment of functional organic molecules to surfaces of high surface area substrates yields materials having dense chemical functionality. Materials with meso- and nanoscale features are often used as support substrates because their small-scale features provide very high surface area. Mesoporous silica is one of the most chemically accessible mesoscale materials, and the well-established chemistries of its production and modification lead to controlled pore structure and rapid kinetics. Such materials have seen use as sorbents for environmental remediation of contaminated water. For this application, their high degree of functionality and high-affinity surface chemistries permit a relatively small amount of material to effectively treat a large volume of water. The many advantages of these highly engineered materials come at a relatively high economic cost. The high-affinity chemical functionalities that provide these materials with unprecedented efficiencies also make them correspondingly more difficult to recycle. One-time utilization of these materials makes the cost-per-use high which consequently limits their economically viable applications. The goal of this work has been to explore surface chemistries that will allow high performance, regenerable or recyclable sorbent materials. Shifting from a single-use material to a regenerable platform in which the mesoscale supports are recycled may lower the environmental and economic costs of the material while retaining the advantageous properties of the meso- and nanostructured materials. We chose to approach this goal by developing non-covalent, supramolecular surface modification techniques as alternatives to current surface modification techniques which, almost without exception, are based on covalent modification motifs. Non-covalent attachment of organic molecules to surfaces allows us to avoid the necessity of optimizing the attachment for each class of organic molecule as well as avoid protection and de-protection procedures necessary to attach delicate or reactive functional groups to surfaces. In this way, supramolecular modification processes reduce the cost of material research and development in addition to the costs of material production and use. The process of surface modification allows us to combine the structural advantages of materials with the chemical functionality of organic compounds. Attachment of functional organic molecules to surfaces of high surface area substrates yields materials having dense chemical functionality. Materials with meso- and nanoscale features are often used as support substrates because their small-scale features provide very high surface area. Mesoporous silica is one of the most chemically accessible mesoscale materials, and the well-established chemistries of its production and modification lead to controlled pore structure and rapid kinetics. Such materials have seen use as sorbents for environmental remediation of contaminated water. For this application, their high degree of functionality and high-affinity surface chemistries permit a relatively small amount of material to effectively treat a large volume of water. The many advantages of these highly engineered materials come at a relatively high economic cost. The high-affinity chemical functionalities that provide these materials with unprecedented efficiencies also make them correspondingly more difficult to recycle. One-time utilization of these materials makes the cost-per-use high which consequently limits their economically viable applications. The goal of this work has been to explore surface chemistries that will allow high performance, regenerable or recyclable sorbent materials. Shifting from a single-use material to a regenerable platform in which the mesoscale supports are recycled may lower the environmental and economic costs of the material while retaining the advantageous properties of the meso- and nanostructured materials. We chose to approach this goal by developing non-covalent, supramolecular surface modification techniques as alternatives to current surface modification techniques which, almost without exception, are based on covalent modification motifs. Non-covalent attachment of organic molecules to surfaces allows us to avoid the necessity of optimizing the attachment for each class of organic molecule as well as avoid protection and de-protection procedures necessary to attach delicate or reactive functional groups to surfaces. In this way, supramolecular modification processes reduce the cost of material research and development in addition to the costs of material production and use. This dissertation contains previously published and unpublished co-authored material.
URI: http://hdl.handle.net/1794/12356
Date: 2012


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