Micro- and nanostructured materials via ultrasonic spray pyrolysis

Guo, Jinrui

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https://hdl.handle.net/2142/72976 Copy

Description

Title

Micro- and nanostructured materials via ultrasonic spray pyrolysis

Author(s)

Guo, Jinrui

Issue Date

2015-01-21

Director of Research (if dissertation) or Advisor (if thesis)

Suslick, Kenneth S.

Doctoral Committee Chair(s)

Kenneth S. Suslick

Committee Member(s)

• Gewirth, Andrew A.
• Murphy, Catherine J.
• Lu, Yi

Department of Study

Chemistry

Discipline

Chemistry

Degree Granting Institution

University of Illinois at Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Ultrasonic spray pyrolysis
• micro- and nanostructured materials
• porous materials
• carbon materials
• Iron Oxide

Abstract

Micro- and nanostructured materials have become an important area in the materials society due to their unique physical and chemical properties. Numerous materials with nano- and microstructures have been synthesized, such as porous, core- shell, and hierarchical structures. Great emphasis has been put on the use of facile and environmental benign synthetic approaches to produce structured materials in a controllable manner. As a simple and industrially scalable technique, ultrasonic spray pyrolysis (USP) is a powerful synthetic tool especially for application-based materials due to the scalability of this technique and the environmentally friendly nature of many of the common precursors and templating methods. More importantly, the structure and composition of USP product can be readily controlled through using appropriate precursors and reaction conditions. In this dissertation, two examples of USP synthesis will be discussed: the USP preparation of gold nanoparticles in porous carbon, and the USP preparation of porous metal oxide. Another example of using traditional synthetic method to produce fluorescent carbon nanoparticles will also be demonstrated. First, USP has been applied to produce gold nanoparticles encapsulated in porous carbon for catalysis application. Gold nanoparticles (NPs) have recently been found to be surprisingly active catalysts for reactions like low temperature oxidation of CO and epoxidation of alkenes. The reactivity of gold nanoparticles, however, is difficult to exploit because of sintering. Encapsulated structures with porous supports prevent agglomeration, but prior synthetic methodologies using sacrificial templates increase complexity, cost, and waste. Using a one-step and template-free USP approach, gold NPswere encapsulated in situ in a highly porous carbon support, thus preventing sintering while still permitting accessibility to the catalytic gold surface. The surface catalytic activity of these Au/C particles for a benchmark reaction (the reduction of 4-nitrophenol) is extremely high compared with other reports in literature. In addition, in contrast to previously reported gold catalysts which only work for hydrophilic nitroaromatics, the USP Au/C exhibits good catalytic activity for both hydrophilic and hydrophobic nitroaromatics due to the presence of both hydrophilic and hydrophobic functional groups on the carbon matrix, making it a versatile catalyst with broad potential applications. Hollow iron oxide microspheres with high surface area can also be produced using USP. Nano- and microstructured iron oxides are intriguing materials owing to their high surface area, unique structures, and applications in lithium-ion batteries and biomedicine. Iron oxide structures have been synthesized mainly using colloidal synthesis, hydrothermal synthesis and sol-gel approach, which are usually cumbersome with multiple steps and the use of expensive templates, therefore are difficult to be scaled up for mass production. The iron oxides produced usually have relatively low surface areas (<100 m2/g) when compared with other materials like metals, carbons and polymers. By employing a novel precursor, a mildly energetic iron complex that can decompose into large amount of gas, hollow magnetite microspheres with high surface area have been successfully prepared via the one-step USP synthesis. The combination of “steam-iron” process with USP technique leads to surprisingly high crystallinity and purity of magnetite. These hollow Fe3O4 microspheres have been shown to maintain high lithium storage capacity. Besides the USP technique, other synthetic approaches were also applied to the preparation of nanomaterials. Specifically, fluorescent carbon nanoparticles were synthesized from pyrrole monomers by combining microemulsion polymerization and surface functionalization. The as-prepared carbon dots show strong intrinsic fluorescence with the quantum yield 1.2%, which can be increased to 12% after PEGylation. These carbon dots can be easily internalized in cells as bioimaging agents and still show bright photoluminescence after laser irradiation for several hours. Other fluorescence characteristics (e.g., photoluminescence lifetime) of these carbon dots are further studied to understand the fluorescence mechanism.

Graduation Semester

2014-12

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http://hdl.handle.net/2142/72976

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Copyright 2014 Jinrui Guo

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