Date of Completion
Graphene, Exfolation, Graphite, Surface Chemistry
Field of Study
Doctor of Philosophy
Graphene, a two-dimensional sheet of atomically thin carbon, has recently gained
attention due to its excellent electronic, mechanical, and optical properties. It has the
potential for use in a variety of applications such as circuits, solar cells, and
transparent conducting electrodes. In order to feasibly produce graphene, practical
methods for its preparation need to be developed. Current methods, such as
micromechanical exfoliation (Scotch tape™), solvent exfoliation and chemical vapor
deposition (CVD) are far from ideal. Micromechanical exfoliation produces minute
amounts of very small graphene flakes, and CVD is expensive and lacks scalability.
This work presented in this thesis focuses on producing graphene sheets from
natural flake graphite. Graphite, composed of stacked graphene sheets, is naturally
available at low costs. Our use of graphite as a source for graphene will allow for the
large-scale production of inexpensive graphene. This thesis presents two
approaches for the preparation of graphene from graphite: chemical modification
and direct exfoliation.
Chemically modifying graphite with oxygen functional groups to form graphite oxide
(GO) increases the interlayer spacing and reduces the van der Waals attractive
forces holding the stacked sheets together. Oxidation increases the water
dispersibility of the graphene and subsequent reduction restores some of the
electrical and mechanical properties of the sheets. We study the oxidation process in
order to optimize the resulting GO material and study the diazonium functionalization
of the dispersed GO. Diazonium salt addition allows for the addition of nitro groups,
increasing the water solubility of the graphene sheets and increasing the processing
options of the sheets.
Direct exfoliation of graphite to graphene sheets is studied using both experimental
and computational techniques. First, we demonstrate the use of an equimolar
mixture of benzene and hexafluorobenzene (B/HFB). This solvent mixture self
assembles into alternating B/HFB stacks due to strong quadrupolar interactions. We
find this stacked morphology can be templated by graphene sheets during
sonication, resulting in order 30 Å from the basal plane of the graphene. This
ordering suspends graphene in solution by preventing re-aggregation and the result
is a suspension of exfoliated, pristine graphene in a highly volatile, easily removable
solvent. A second system, using a water/heptane solvent mixture, is shown stabilize
the graphene sheets at the interface of the phase-separated solvents in order to
minimize interfacial energy. This stabilization is then used to form thin, transparent
and conductive films of graphene as the sheets spread at the interface and climb the
walls of the sample vials.
Oyer, Andrew Jason, "Exfoliation and Chemical Modifications of Natural Flake Graphite" (2013). Doctoral Dissertations. 137.