Part 5. Graphene, graphene oxide and fluorographene - structure, properties and
Brown's Chemistry KS4 science GCSE/IGCSE/O level/A Level Chemistry Revision Notes
NANOCHEMISTRY Nanoscience Nanotechnology Nanostructures
Why is graphene so strong? What is
the structure of graphene and fluorographene?
GCSE Chemistry Revision
Index of nanoscience revision notes
Index of smart materials pages
General survey of materials - natural & synthetic, properties, uses
mobile phone or ipad etc. in 'landscape' mode
allotropes of carbon - diamond, graphite,
Alphabetical keyword index for
the nanoscience pages : Index of nanoscience pages
: boron nitride *
Buckminsterfullerenes-bucky balls *
carbon nanotubes * fat nanoparticles
* fluorographene *
graphene * health and
* liposomes *
nanoscale * nanoscience *
* nanotechnology *
problems in nanomaterial use *
silver nanoparticles *
safety issues * sunscreens-sunblockers *
chemistry revision notes science GCSE chemistry, IGCSE chemistry, O level
& ~US grades 8, 9 and 10 school science courses or equivalent for ~14-16 year old
science students for national examinations in chemistry for topics including
nanoparticles nanoscience nanochemistry uses of nanomaterials
Part 5. Graphene and
Graphene - structure and properties
What is graphene? What is
graphene's molecular structure? What might we use graphene for?
Graphene is a smart material, but can
also be considered as a 2D nanomaterial because it is only one atom thick.
Graphene is essentially a single
layer of carbon in the form of graphite, with its layered structure of
hexagonal rings of carbon atoms (structure
It is possible to synthesise graphite
in individual layers just one atom thick and the product is known as
'honeycombed' lattice is shown below.
Each graphene molecule is a
fully planar shape.
The C-C bond length is 0.142 nm,
as in graphite, its mid-way between 0.154 nm for C-C bond and 0.134 for a
The C-C-C bond angle is 120o,
what you expect for the internal angle of a perfectly symmetrical planar
The C-C bonds are strong, giving
a strong 2D lattice of carbon atoms.
Each layer consists of hexagonal
rings of carbon atoms linked together in a planar lattice, the formula is Cn
where n is a very large number BUT a graphene layer is just a single atom in
another version of the skeletal formula representation of graphene.
This image shows how the
structure of graphene relates to polyaromatic hydrocarbons like
C14H10 consisting of 2 and 3 fused benzene
rings respectively. If you take this 'aromatic fusion' to its extreme in two
dimensions, the hydrogens go and the result is a graphene molecule of almost
100% carbon atoms.
Graphene is spatially considered
a 2D material.
In graphene each carbon atom forms three
sigma bonds with other carbon atoms (sp2 hybridisation) via three of its four valency
the 4th electron is 'delocalised' i.e. shared in common with other carbon
atoms giving extra bonding (pi electrons, pi bonding) ...
... this gives a very tightly
packed and strongly bonded network of carbon atoms within the layer, the
carbon - carbon bonds are short and strong (three per carbon atom) giving it
a very high tensile strength (300 times that of steel) and yet is very light
low density material.
... AND because these pi or
delocalised electrons are free to move through the layer,
electrical conduction readily occurs if a potential difference is applied.
This delocalised system means
that it is unsaturated and theoretically atoms can add to it, BUT it is
chemically relatively inert apart from combustion!
Graphene has a high thermal
stability (like graphite, up to 3000oC if no oxygen present),
conductivity, a high optical transparency and is chemically relatively
Graphene, this remarkable
material made of sheets of carbon just one atom thick, has been shown to
undergoes a self-repairing process to correct holes when exposed to loose
It would appear that when holes
were punched in it by a beam of atoms, if carbon atoms where near the
surface of the graphene sheets, complete hexagonal rings would reform making
the two-dimensional (2D) sheets complete.
Graphene has outstanding mechanical strength with respect to
its thinness and combined with its electronic properties, it is a promising
material for a wide range of future applications.
However, graphene's very
thinness makes it easily damaged when working with it, so any 'self-healing'
property is most welcome!
USES of graphene - potential
applications of graphene
So, what can we use
Graphene can be used to
manufacture excellent transistors for the electronics industry.
Conduction can be made to depend
on an ambient electric field, making it a very sensitive surface and metal
films cannot be made as thin, so less sensitive.
Graphene could be used in highly
sensitive gas sensors - molecules 'landing' on the surface cause measurable
electronic changes and perhaps even individual molecules can generate a
Graphene is 100x stronger than
steel in bulk so has the potential to be used for small scale BUT strong
components in devices.
Graphene is highly resistant to
attack by strong acids (e.g. nitric, hydrochloric, sulfuric, hydrofluoric
acids) or strong alkalis (e.g. sodium hydroxide, potassium hydroxide) and so
can be used to give surfaces an ultra-thin protective layer which is
It can be used as support
membrane for transmission electron microscopy used to study the molecular
detail of materials such as fragile DNA molecules and nanoparticles
New techniques have been
developed to produces highly selective filter materials based on
graphene that could lead to more efficient desalination. Scientists have
succeeded in creating subnanoscale pores in a sheet of the
one-atom-thick materials including graphene, which is one of the
strongest materials known.
Therefore sheets of graphene,
with these subnanoscale pores, can behave like a semi-permeable membranes.
So, one possible use of
is the desalination of seawater, very important in regions of the world
where fresh water is scarce e.g. desert regions of countries in Africa
and the Middle-East.
Pure water can be extracted
as the water molecules can diffuse through the graphene membrane,
leaving behind the larger hydrated ions from the salts found in seawater
e.g. the sodium ions and chloride ions from sodium chloride.
The idea is to get these
subnanoscale pores small enough to stop larger molecules or ions passing
through the graphene membrane filter, but large enough to allow water
molecules to diffuse through.
NOT on some syllabuses yet, but
Technically graphene is an
allotrope of carbon (like diamond and graphite) though it is, in reality, a
single layer of graphite.
Graphene is a two-dimensional
(2D) allotrope of carbon (diamond is 3D).
However, since carbon has a
valency of four, there are other possible linear one-dimensional (1D) forms
based on single, double or triple carbon-carbon covalent bonding systems.
So, research is going into
trying to synthesise and investigating the properties of linear structures
(also a smart material)
What is fluorographene? What
is fluorographene's molecular structure? What might we use fluorographene
In fluorographene, the fourth
valency electron of carbon is paired with one from fluorine to form a 4th
single covalent bond between carbon and fluorine.
Each carbon atoms forms four
single bonds directed to the corners of a tetrahedron.
The C-C-F and C-C-C bond angles
will al be around 109o (the symmetrical tetrahedral angle, as in
The three strong C-C
carbon-carbon bonds from each carbon atom produce a
strong giant 2D network of links, but the fourth bond (carbon-fluorine C-F,
also very strong) 'pokes' up
and down from this 'rippled' 2D array of carbon atoms.
This means, unlike in graphene,
there is no 'spare' 4th electron from carbon to form a delocalised electron
system that allows conduction of electricity, so it is an electrical
Fluorographene is a saturated
organic compound of (CF)n where n is a very large number
(empirical formula CF).
It is, in a simplified way, a 2D
version of TEFLON/PTFE which consists of long 1D poly(tetrafluoroethene) polymer
Like PTFE, fluorographene has a very high
thermal stability and excellent 'non-stick' properties.
Also like PTFE, it is chemically very stable, i.e. very
inert, so, combined with its great thermal stability, it can be used as a
very stable surfacing material over a wide temperature range.
Uses of fluorographene
It is a high quality super-thin
Its electronic applications
include use in LEDs (light emitting diodes)
Like TEFLON, it can used as an
inert protective 'non-stick' surface, but I think Teflon is lot cheaper to
Graphene oxide - use as a water
Research is on going to develop water
filters based on graphene e.g. to convert sea water or brackish fresh water
into potable drinking water.
This could aid millions of people,
especially in the developing world like Africa, to have access to clean
graphene oxide sieve has been shown to filter out salts but it
is not as efficient as desired and rather costly at the moment.
The idea is to just letter water through
and act as a barrier to salts like sodium chloride, a process called
The graphene oxide layers would act like
a semi-permeable membrane.
allotropes of carbon - diamond, graphite,
NANOSCIENCE - NANOCHEMISTRY INDEX
Introduction to nanoscience,
nanoparticles, commonly used terms explained
Part 2. Nanochemistry - introduction,
uses & potential
Uses of Nanoparticles of titanium(IV) oxide (e.g. sun
cream), fat (e.g. cosmetics), silver (e.g. medical applications)
From fullerenes & bucky balls to carbon nanotubes -
structure, properties, uses
graphene oxide and
fluorographene - structure, properties, uses
Cubic and hexagonal boron nitride BN
Problems, issues and
implications associated with
see also INDEX
Smart materials pages
A general survey of materials - natural & synthetic,
their properties & uses
|Website content © Dr
Phil Brown 2000+. All copyrights reserved on revision notes, images,
quizzes, worksheets etc. Copying of website material is NOT
permitted. Exam revision summaries & references to science course specifications