Aerogel Graphine (Research Paper Sample)

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Aerogel Graphine
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Introduction
Over the past two decades, discoveries of several new forms of all tropic carbon structures have filled scientific world in several fields from the look of innovative material design from the perspective of innovative material design and development. Carbon nanotubes (CNTs) and graphite (as well as graphene) are given attention because of their functional properties i.e. thermal and electrical conductivity, mechanical stiffness and strength. CNT and graphene are considered as 1D and 2D structures which result in their anisotropic material properties. Graphite possesses excellent tensile modulus and strength in the planar directions due to strong covalent bonds, but weak shear properties because of the weak van der Waals interactions between the graphene sheets (Nanocyl.com, 2009).
Science can never seize to amaze many. Each day passes and a new thing is invented. As it advances what is known to be solid becomes hard to define. Very light aerogels have been the target of research for decades, getting less dense as new variants are developed. Owing it to their friend Graphene, a team of researchers from China's Zhejiang University in the Department of Polymer Science and Engineering sat down, thought, and came up making a record for the lowest density solid to date with a new type of aerogel (Singh, 2013).
The team, headed by Professor Gao Chao, discovered that aerogel has surprising flexibility and oil-absorbing abilities. Apart from making aerogel graphine, the team has long been developing macroscopic graphene materials, such as one-dimensional graphene fibers and two-dimensional graphene films, however this time they decided to make three-dimensional porous material out of graphene in order to break the record. Graphene, a single layer of graphite, is the strongest material ever measured and the breaking strength for grapheme represents the calculated intrinsic strength of a defect-free sheet (Singh, 2013). Prof. Gao quoted, "With no need for templates, its size only depends on that of the container," He continued and said "Bigger container can help produce the aerogel in bigger size, even to thousands of cubic centimeters or larger.”
Structure of graphite
Graphene sheets comprise a 2D layer of sp2 hybridized carbon atoms, arranged in a hexagonal lattice. In graphite, adjacent graphene layers are arranged with overlapping pz orbitals, whose vast number of interactions inhibit the complete delamination of bulk graphite into individual graphene sheets under typical mechanical actions. Attempts to mechanically exfoliate graphite typically only result in stacks of sheets, or a few isolated sheets in low yield. (Nanocyl.com, 2009).
Methods of producing graphene and HRG can be put in 5 classes:
* Mechanical exfoliation of a single sheet of graphene from bulk graphite using scotch.
* Growth of graphene films.
* Chemical vapor deposition of graphene monolayers.
* Unzipping of CNT's
* Reduction of graphene derivatives e.g. graphene oxide and graphene fluoride.
Graphene consists of a single layer of sp2 hybridized carbon atoms forming a two-dimensional (2D) hexagonal lattice. It could be considered as a fundamental building block for all sp2-hybridized carbon allotropes e.g. graphite, nanotubes and fullerenes. Aerogel is usually composed of silica or carbon compounds and is highly-prized for its durability and thermal insulation properties. This family of substances is sometimes called "frozen smoke" due to its hazy appearance. In 2012 a type of aerogel composed of graphite (dubbed Aerographite) took the crown as the least dense solid at 0.18 mg/cm3 (Singh, 2013). The Zhejiang University graphene aerogel edges that out with a density of just 0.16 mg/cm3.
A "multiwalled carbon nanotube (MCNT) aerogel" dubbed "frozen smoke" with a density of 4 mg/cm3 lost its world's lightest material title in 2011 to a micro-lattice material with a density of 0.9 mg/cm3. Less than a year later, aerographite claimed the crown with its density of 0.18 mg/cm3 (Singh, 2013). To put those numbers in perspective, the new aerogel has a lower density than helium and only twice as much as hydrogen. Regular air, like you're breathing right now, has a density of about 1.2 mg/cm3 (Singh, 2013; Whitwam, 2013). That's 7.5 times heavier than graphene aerogel (Anthony, 2013). Yes, it's less dense than air, but this near-magical substance is still a solid.
A sample of graphene aerogel a few centimeters across is so light that it can be supported by delicate plants as seen above. The new carbon sponge has a density lower than helium, and while this is enough to break the Guinness World Record, the Chinese team believe that the material's true value lies in its performance (Singh, 2013). The new material is not only extremely elastic, but it can absorb up to 900 times their own weight in oil and water. It can also absorb organics at a high speed: one gram of such aerogel can absorb 68.8 grams of organics per second, which is useful in the event of an oil spill.
 We report the synthesis of ultra-low-density three-dimensional macroassemblies of graphene sheets that exhibit high electrical conductivities and large internal surface areas. These materials are prepared as monolithic solids from suspensions of single-layer graphene oxide in which organic sol−gel chemistry is used to cross-link the individual sheets. The resulting gels are supercritically dried and then thermally reduced to yield graphene aerogels with densities approaching 10 mg/cm3. In contrast to methods that utilize physical cross-links between GO, this approach provides covalent carbon bonding between the graphene sheets (Chen et al., 2013; Worsley et al., 2010).
These graphene aerogels exhibit an improvement in bulk electrical conductivity of more than 2 orders of magnitude ( 1 × 102 S/m) compared to graphene assemblies with physical cross-links alone ( 5 × 10−1 S/m). The graphene aerogels also possess large surface areas (584 m2/g) and pore volumes (2.96 cm3/g), making these materials viable candidates for use in energy storage, catalysis, and sensing applications (Whitwam, 2013).
 Carbon nanotubes
Carbon nanotubes (CNTs) being an allotrope of carbon was discovered by Kroto, Curl and Smalley in 1985. Taking the form of cylindrical carbon molecules and having novel properties make them potentially useful in a wide variety of applications in nanotechnology, electronics, and other fields of material science. They have great strength and unique electrical properties and are good conductors of heat. They belong to the family of the fullerene family.
The name nanotube was derived from their size since their diameter is on the order of a few nanometers (approximately 50,000 times smaller than the width of a human hair) while they can be up to several millimeters in length (Science Daily, 2014).
In nanotubes, the graphite layer appears somewhat like a rolled-up chicken wire with a continuous unbroken hexagonal mesh and carbon molecules at the apexes of the hexagons. Although they are formed from the same graphite sheet, their electrical characteristics differ depending on these variations, acting either as metals or as semiconductors. Carbon nanotubes typically have diameters ranging from <1 nm up to 50 nm. Their lengths are typically several microns, but recent advancements have made the nanotubes much longer, and measured in centimeters (Science Daily, 2014).
Carbon nanotubes are categorized by their structures i.e. single-wall, multi-wall and double-wall nanotubes. The properties of being stiff, strong and tenacious compared to other fiber materials exhibited in carbon nanotubes made it to be used in the making of aerogel graphine. The intrinsic mechanical and transport properties of carbon nanotube makes them the best carbon fibers (Science Daily, 2014). The table below shows the mechanical properties and transport properties of conductive materials of carbon nanotube compared to other engineering materials.
Mechanical properties (Source: Nanocyl.com, 2009).
Fiber Material

Specific Density

E (TPa)

Strength (GPa)

Strain at Break (%)

Carbon Nanotube

1.3 - 2

1

10 - 60

10

HS Steel

7.8

0.2

4.1

< 10

Carbon Fiber - PAN

1.7 - 2

0.2 - 0.6

1.7 - 5

0.3 - 2.4

Carbon Fiber - Pitch

2 - 2.2

0.4 - 0.96

2.2 - 3.3

0.27 - 0.6

E/S - glass

2.5

0.07 / 0.08

2.4 / 4.5

4.8

Kevlar* 49

1.4

0.13

3.6 - 4.1

2.8

Kevlar is a registered trademark of DuPont. 
Transport Properties of Conductive Materials (Source: Nanocyl.com, 2009).
Material

Thermal Conductivity (W/m.k)

Electrical Conductivity

Carbon Nanotubes

> 3000

106 - 107

Copper

400

6 x 107

Carbon Fiber - Pitch

1000

2 - 8.5 x 106

Carbon Fiber - PAN

8 - 105

6.5 - 14 x 106

Solutions of carbon nanotubes are used in the drying process, eliminating the need for a template, as with most aerogels. The size of the gel is dependent on the size of the container it is made in, according to Gao. He believes the technique could be used to make aerogels thousands of cubic centimeters in size. The nanotubes act as a stabilizing structure holding the layers of graphene together allowing for easier production (Science Daily, 2014).
3D gel
3D high-efficient GO base...