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Synthesis and Chemical Modification of Boron Nitride and Graphene Aerogels and Related Nanostructures

Abstract

Aerogels based on boron nitride and graphene can integrate macroscopic amounts of nanomaterial into a single, relatively open, multifunctional structure. Such aerogels possess the textural properties typical of aerogels including high surface area, high porosity, and low density. Most importantly, they are capable of retaining a number of the extraordinary properties of their nanomaterial building blocks. For example, boron nitride-based aerogels are electrically insulating while graphene aerogels are highly electrically conductive. These properties make the aerogels particularly promising for a variety of applications in supercapacitors, batteries, catalysis, gas sensing, gas storage, polymer composites, and water treatment. However, in order to optimize their performance in these applications, chemical modification is usually necessary.

This dissertation explores chemical modification of graphene and boron nitride aerogels with the goal of being able to introduce targeted chemical modifications in order to improve the performance of the aerogel for specific applications. Additionally, the synthesis of new classes of aerogels is investigated.

Examples of chemical modification of graphene aerogels are the introduction of chemical dopants like boron, or the controlled formation of defects, often called defect-engineering (Chapter 3). These types of chemical modifications are particularly advantageous for highly sensitive and selective NO2 detection. New compositions of aerogels with electronic properties predicted to be intermediate between graphene and BN are possible by synthesizing boron carbon nitride aerogels (Chapter 4). Two chemically and electronically disparate materials can also be coupled to one another by the formation of multifunctional core-shell hybrids. Chapter 5 discusses the synthesis of photocatalytic graphitic carbon nitride shells on top of graphene aerogels cores for photocatalytic applications. In addition to chemical modification, physical modification is an approach to control the macroscopic properties of graphene and boron nitride aerogels. Chapter 6 explores density-tuning of graphene and boron nitride aerogels in order to tune the thermal conductivity for polymer composite applications.

In addition to aerogels based on 2D nanomaterials, 1D nanomaterials can also serve as aerogel building blocks. Chapter 7 discusses a new approach to synthesize aerogels based on 1D nanofibers of an organic semiconductor, as well as a treatment method to convert them into carbon nanofiber aerogels. Lastly, Chapter 8 discusses the functionalization of BN nanostructures including BN aerogels, BN nanotubes, and BN nanosheets in order to improve the interfacial interactions between BN nanofillers and host polymer matrices in polymer composites for thermal interface materials.

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