Structure and applications of chemically modified graphene

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Abstract

Owing to its extraordinary electrical, optical, and mechanical properties, graphene
has emerged as a promising material for a variety of applications in the future. However,
not all these applications will be able to employ or require pristine graphene; hence
several alternative methods have developed for the mass production of graphene and
related materials. Graphene oxide (GO), a material closely related to graphene, allows
engineering of its chemical composition by means of chemical, thermal, and
electrochemical methods. This provides an opportunity to tune physical and chemical
properties of graphene. This work reports on investigations of the structure of chemically
modified graphenes (CMGs) derived from GO, interactions of metals and organic thin films
with CMG, and application of metal-CMG as a hydrogen gas sensor.
GO was fabricated by a modified Hummers method. GO, being insulating, was
reduced by hydrazine and thermal annealing to produce reduced graphene oxide (rGO).
The CMG sheets were deposited on TEM grids and on Si/SiO2 substrates for
characterization by atomic force microscopy, transmission electron microscopy (TEM), xray
photoelectron spectroscopy, and Raman spectroscopy. The structural analysis of GO
performed by TEM revealed that in GO, on average, the underlying carbon lattice
maintains the symmetry and lattice-spacings of graphene. Compositional analysis disclosed
that the as-produced GO is actually made of oxidized graphene like sheets strongly
attached with oxidative debris that make the as produced GO hydrophilic and insulating.
In the TEM, both GO and reduced GO (rGO) were nearly transparent and stable
under the electron beam and hence they made excellent supports to study the growth of
thin organic and metal films deposited by physical vapour deposition. The study revealed
the interactions of organic molecules, fluorinated copper phthalocyanine, with CMG and
packing of the molecules in the crystal structure. Film-thicknesses from sub-monolayer to
tens of monolayers were analysed. In the study of metal thin film growth, the factors
determining the growth and morphology of different metals-on-CMG were studied. Fine
control over the size and coverage of nanoparticles were achieved. This control was used
to combine Pd nanoparticles and rGO to design selective, highly sensitive, and practical
hydrogen gas sensor.

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