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theses

Nanocatalysts have attracted considerable research attention due to their tunable physical and chemical properties. In this dissertation, several synthetic strategies have been developed to prepare novel porous nanocatalysts for various applications, including photocatalytic carbon dioxide reduction, photocatalytic degradation of pollutants, and electrocatalytic hydrazine oxidation reaction.

In chapter 1, a brief introduction is first given regarding the current status and latest developments of novel nanoporous catalysts, including titania, silica, and carbon-based nanomaterials. The applications of these nanocatalysts including photocatalysis, electrocatalysis, and energy storage and conversion are summarized. Future challenges and prospects are also discussed.

In chapter 2, a simple template-free synthetic route is employed to prepare highly crystalline mesoporous titanium dioxides. The resulting materials are shown to serve as highly active photocatalysts for the conversion of carbon dioxide reduction with water into hydrocarbon fuels. The formation of nanoporous structure and the maintaining of anatase phase during hydrolysis-calcination synthetic route are found to be critical for the desired catalytic activity and their roles are discussed in detail.

In chapter 3, a series of metallic copper-decorated nanoporous titanium dioxide materials with different loadings of Cu are synthesized by in situ hydrolysis of Sn2+-grafted titanium glycolate microspheres in the presence of Cu2+ ions. With the optimal amount of deposited Cu species, the material exhibits the highest photocatalytic activity toward carbon dioxide reduction thanks to the optimized structural features, the increased visible-light absorption and the enhanced separation of photogenerated electron-hole pairs.

In chapter 4, small vacancy-rich anatase nanoparticles is prepared by mesoporous carbon-assisted synthesis, by taking advantage of the pores of a polymer-derived nanoporous carbon as a hard template to hydrolyze and condense a titania precursor. The titania/carbon composite material exhibits unprecedented “blinking” property under an electron beam without decaying for an extended period of time. After being extracted from the carbon template, the vacancy-rich anatase nanoparticles show an exceptional electron trapping ability with long lived electron-hole pairs. As an example, the material is demonstrated to be an efficient photocatalyst for reduction of carbon dioxide with water into hydrocarbons.

In chapter 5, besides being used as template, the above-mentioned polyaniline-derived mesoporous carbon is employed as supporting material for copper nanoparticles. The inclusion of copper nanoparticles into nanoporous carbon are found to reduce the overpotential and increase the current density of the electrocatalytic hydrazine oxidation reaction. The synthetic method can be extended for the development of other non-noble metal-based electrocatalysts.

Chapter 4 and chapter 5 have successfully demonstrated that colloidal silica nanoparticles with different sizes can serve as hard templates to prepare carbon materials with controlled porosity and large surface area. By employing the same idea, this synthetic strategy is extended to synthesize mesoporous graphitic carbon nitride materials in chapter 6. Besides the size of the colloidal silica nanoparticles, the initial melamine-to-silica template ratios are also found to be crucial for the formation of graphitic carbon nitride with desirable surface are and porosity. After decoration with copper nanoparticles, the composite material shows excellent photocatalytic activity for degradation of tartrazine yellow dye.
Lastly, protonated polyaniline is functionalized onto the surface of mesoporous silica nanomaterial SBA-15. The resulting composite material possesses high surface area and ideal surface properties for the adsorption of anionic dyes Orange G from wastewater and has a significantly higher adsorption capacity compared with the conventional emeraldine salt of polyaniline. Modeling studies are also carried out to further analyze the adsorption properties of the material. This work could encourage further research on porous inorganic/polymer hybrid nanomaterials for various applications.

In summary, this dissertation presents a few novel synthetic strategies for fabrication of nanostructured titania, carbon and silica materials and demonstrates their potential applications in the fields of photocatalytic carbon dioxide reduction, electrocatalytic hydrazine oxidation reaction, photocatalytic degradation of tartrazine yellow dye and removal of organic dye Orange G from wastewater.

ETD_10806

Ph.D.

Includes bibliographical references

doi:10.7282/t3-zm8j-ej19

ETD doctoral

The author owns the copyright to this work.