Geoscience Reference
In-Depth Information
nanobeads. These new solid forms of carbon have attracted intense interest owing
to their several outstanding properties such as: high specific surface area, good
mechanical stability, chemical inertness, and porous nature having large pore
volume. Amongst these, graphene, as the fundamental 2D carbon structure with
exceptionally high crystal and electronic quality, has emerged as a rapidly rising
star in the field of materials science. Its sudden discovery in 2004 led to an explo-
sion of interest in the study of graphene with respect to its unique physical, chemi-
cal, and mechanical properties, opening up a new research area for materials
science and condensed-matter physics, and aiming for wide-ranging and diversified
technological applications [65].
Nanometer-sized diamond has been found in meteorites, protoplanetary nebulae
and interstellar dusts, as well as in residues of detonation and in diamond films.
It is known that primitive chondritic meteorites contain up to approximately
1500 ppm of nanometer-sized diamonds, containing isotopically anomalous noble
gases, nitrogen, hydrogen, and other elements. These isotopic anomalies indicate
that meteoritic Nano-diamond (ND) probably formed outside our solar system prior
to the Sun's formation (they are thus presolar grains)
[65]
. Nanoscale diamond parti-
cles were first produced by detonation in the USSR in the 1960s
[66]
, but they
remained essentially unknown to the rest of the world until the end of the 1980s
[67]
. Presser et al., have reviewed that beginning in the late 1990s, a number of
important breakthroughs led to wider interest in these particles, which are now
known as nanodiamonds
[68]
. First, colloidal suspensions of individual diamond
particles with diameters of 4
5 nm (“single-digit” nanodiamonds) became avail-
able. Second, researchers started to use fluorescent nanodiamonds as a nontoxic
alternative to semiconductor QDs for biomedical imaging. Third, nanoscale mag-
netic sensors based on nanodiamonds were developed. Fourth, the chemical reactiv-
ity of the surface of nanodiamonds allowed a variety of wet and gas chemistry
techniques to be employed to tailor the properties of nanodiamonds for use in com-
posites and also for other applications, such as attaching drugs and biomolecules.
Fifth, new environmentally benign purification techniques were developed, and
these allowed high-purity nanodiamond powders with controlled surface chemistry
to be produced in large volumes at a low cost.
Finally, ND was found to be less toxic than other carbon nanoparticles and, as a
result, is currently being considered for applications in biomedical imaging, drug
delivery, and other areas of medicine. It appears that some interstellar emission
bands approximately in the 21
m spectral regions could originate from NDs
[68]
.
There is an array of carbon nanoforms synthesis available today for researchers
and industrialists with relatively fair amount of success [
69
]. Most of them need
high-energy processes like high-temperature arc discharge/laser ablation and the
chemical routes like plasma-assisted CVD, chemical vapor transport, and supercriti-
cal hydrothermal fluids. The other methods that are equally popular are detonation
technique, high-energy ball milling of HPHT diamond microcrystals, chlorination of
carbides, and ion irradiation of graphite. Some researchers are even envisaging the
moderate conditions of various forms of carbon synthesis with a relatively high yield
compared to the other high-energy methods using supercritical fluids
[70]
.
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