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theses

The development of facile synthetic methods to synthesize porous functional materials has attracted significant attention because of the various advantages these materials possess (in terms of properties and potential applications) compared with their nonporous counterparts. In this dissertation, several synthetic strategies that were developed to make some novel carbon- and silica-based porous nanomaterials, along with their properties and potential applications in electrocatalysis and drug delivery have been compiled. In Chapter 1, the various synthetic methods used to synthesize novel nanoporous silica materials, and their properties and potential applications, specifically in biomedical areas, are summarized. In addition, synthetic approaches developed to make porous carbon nanomaterials, with an emphasis on biomass-derived carbon nanomaterials, are discussed. Carbon nanomaterials are excellent candidate materials for electrochemical energy conversions, electrocatalysis, and drug adsorption / release. These topics have also been discussed in this and the subsequent chapters. In Chapter 2, the synthesis of N-doped monodispersed mesoporous carbon nanoparticles by using the self-assembled polyaniline (PANI) and colloidal silica aggregates as precursors is described. The resulting nitrogen-doped carbon materials are shown to serve as active electrocatalysts for hydrogen peroxide reduction and oxygen reduction reaction reactions, reactions that are pertinent to renewable energy and fuel cells. The advantageous features of the nanoporous structures of the materials on their electrocatalytic properties are further discussed. In addition, the method developed for PANI is shown to be versatile enough to be extended to other polymers, such as polypyrrole. Carbon nanomaterials can be prepared not only from synthetic materials, but also from sustainable precursors such as biomass. In Chapter 3, a novel synthetic method that allows morphology-controllable synthesis of carbon materials by coating shaped natural precursors with silica shells, followed by their pyrolysis and removal of the silica shells, is discussed. By applying this method to yeast cells and yeast cell walls, yeast cells-derived hollow core/shell carbon microparticles and yeast cell wall-derived carbon particles are synthesized. The former shows better electrocatalytic properties than the latter, indicating that the proteins, phospholipids, DNAs and RNAs within yeast cells are indirectly responsible for its higher electrocatalytic activity, by providing the carbon materials with more heteroatom dopants. This method can be extended to a number of microorganisms and plant materials (e.g., pollen) for the synthesis of other shape-controlled carbon nanomaterials and catalysts. Besides their potential applications for electrocatalysis, these porous carbon materials can play important roles in biomedical applications. In Chapter 4, carbon microparticles with high surface area prepared from yeast cell that are presented in Chapter 3 are further successfully used as support materials to improve the dissolution of a poorly soluble drug fenofibrate. Compared with the bulk fenofibrate, the fenofibrate-loaded carbon microparticles are found to release the drug much faster. In Chapter 5, comparative studies of the adsorption of DNA by two different kinds of mesoporous silica materials, namely KCC-1 and MCM-41, is discussed. Due to their beneficial dendritic and fibrous-like pores, KCC-1 nanoparticles can load more DNA molecules, whereas MCM-41, which has smaller cylindrical pores, has limited adsorption capacity for DNA. KCC-1 is also found to be reasonably biocompatible and is proven to be capable of carrying DNA molecules into the cells and has the potential for DNA delivery. In Chapter 6, glutathione-triggered release of model drug molecules from the pores of MCM-41-type mesoporous silica nanoparticles is described. Such nanomaterials with stimuli-triggered drug release properties are quite valuable to minimize or completely overcome the potential side effects of many types of drugs. Apart from carbon- and silica-based nanomaterials, TiO2 (P25) nanomaterials, which have inherent photocatalytic properties, are studied for photo conversion of bioactive molecules. Specifically the photocatalyzed conversion of caffeine and isocaffeine with the help of P25 nanomaterials is investigated, and the results are described in Chapter 7. The cytotoxicity, genotoxicity of caffeine and isocaffeine, as well as their converted products are also evaluated. In summary, in this dissertation a range of novel porous nanomaterials along with their properties and potential applications for electrocatalysis and nanomedicine are presented. The research in this field is likely to expand more in the near future.

ETD_7448

Ph.D.

Includes bibliographical references

by Xiaoxi Huang

doi:10.7282/T3KD216C

ETD doctoral

The author owns the copyright to this work.