nano materials
TRANSCRIPT
NANOMATERIALS Seminar: 2013
ACKNOWLEDGEMENT
I wish to express my sincere and respectful gratitude to Sri.J.MAHENDRAN NAIR,
Chairman of PKCET for providing all our needs during the course of this seminar.
I wish to express my deep sense of gratitude to Prof: S. CHIDAMBARAM, the
Principal and Head Of Department of Mechanical Engineering Department of PKCET
for his constant support and guidance.
My deepest thanks to our respected Director of academics, Dr. A.KOMALAVALLI
AMMA for her encouragement and support. It would be unfair not to mention about the
valuable assistance from our registrar Mr.G.MOHANAN NAIR.
I express my sincere gratitude to our seminar coordinator Mr. AKHIL SASI, for his
valuable suggestions without which the successful completion of this seminar would
not have been possible.
I am grateful to Mr. AKHIL SASI, Guide of my seminar, who has contributed both
directly and indirectly throughout the completion of the seminar.
I wish to thank all the teachers and friends of PKCET, who helped me for making this
seminar successful. Also I wish to express my deep sense of gratitude to my family
members for their constant encouragement and support throughout my academic
carrier.
Last, but not the least, I am grateful to the almighty for guarding and keeping me safe
from any and all misfortunes befalling on me.
Dept: Of Mechanical Eng 1 PKCET, Kandala
NANOMATERIALS Seminar: 2013
AKHIL KUMAR S
ABSTRACT
Nanotechnology and molecular manufacturing allows for manipulation of
material size and composition. This expands the promise of application of
nanomaterials in addressing environmental problems, but also has the
potential for adversely impacting the natural environment and human
health. The primary focus is to use nanomaterials for environmental
remediation and to study the impact of the release of such materials in the
environment. The first part of this talk will focus on the aggregation
behavior of carbon nanotubes (CNTs) in environmentally relevant solution
chemistries. The MWNTs were thoroughly characterized using Raman
scattering (for state of defect), total gravimetric analysis (for metal
impurities), transmission electron microscopy(for length and diameter
distribution), Fourier transformed infrared spectroscopy (for functional
groups), and electrophoretic mobility (for surface charge). The aggregation
kinetics of MWNTs was consistent with classical DLVO theory of
colloidal stability in presence of Na, Ca, and Mg salts. Humic acid
effectively stabilized the MWNTs by steric interactions. The second part
will demonstrate the use of surface-modified nano-scale zero-valent iron
(NZVI) for remediation of dense non-aqueous-phase liquid (DNAPL).
Surface modification using novel block-copolymer and surfactants
enhanced transport through porous media. Amphiphilic block copolymer
modification helped the NZVI to localize at DNAPL/water interface. The
concluding part of the talk will focus on my research interests that include
studying the effect of functionalization on CNT aggregation and deposition
Dept: Of Mechanical Eng 2 PKCET, Kandala
NANOMATERIALS Seminar: 2013
behavior, development of nano-sensors for microbial mapping of the
subsurface, and toxicity of CNTs to microbes.
CONTENTS
INTRODUCTION……………………………………………………………….5
DEFINITION ……...……………………………………………………………6
ADVANCES IN NANOMATERIALS…....……………………………………8
TYPES OF NANO MATERIALS……………………….……………………..9
NANOMATERIAL COMPOSITION………...……………………………….14
PROPERTIES OF NANOMATERIALS…………….………………………..15
APPLICATIONS OF NANO MATERIALS…………………………….…….18
SAFETY……………………………………………………………………….24
DISADVANTAGES………………………………………………………...…25
CONCLUSION………………………………………………………………...27
BIBILIOGRAPHY……………………………………………………………..29
Dept: Of Mechanical Eng 3 PKCET, Kandala
NANOMATERIALS Seminar: 2013
LIST OF FIGURES
“HOW BIG IS 1 NANOMETER”
FULLERENES
OPTICAL PROPERTIES
ELECTRICAL PROPERTIES
MICROBIAL FUEL CELL
CARBON NANOTUBE
NANOWIRES FOR JUNCTIONLESS TRANSISTORS
Dept: Of Mechanical Eng 4 PKCET, Kandala
NANOMATERIALS Seminar: 2013
INTRODUCTION
Nanomaterials are chemical substances or materials that are manufactured
and used at a very small scale (down to 10,000 times smaller than the
diameter of a human hair).
Nanomaterials are developed to exhibit novel characteristics (such as
increased strength, chemical reactivity or conductivity) compared to the
same material without nanoscale features.
Hundreds of products containing nanomaterials are already in use.
Examples are batteries, coatings, anti-bacterial clothing etc. Analysts
expect markets to grow to hundreds of billions of Euros by 2015.
Nano innovation will be seen in many sectors including public health,
employment and occupational safety and health, information society,
industry, innovation, environment, energy, transport, security and space.
Nanomaterials have the potential to improve the quality of life and to
contribute to industrial competitiveness in Europe. However, the new
materials may also pose risks to the environment and raise health and
safety concerns.
These risks, and to what extent they can be tackled by the existing risk
assessment measures in the EU, have been the subject of several opinions
of the Scientific Committee on Emerging and Newly Identified Health
Risks (SCENIHR). The overall conclusion so far is that, even though
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NANOMATERIALS Seminar: 2013
nanomaterials are not per se dangerous, there still is scientific uncertainty
about the safety of nanomaterials in many aspects and therefore the safety
assessment of the substances must be done on a case-by-case basis.
DEFINITION OF NANOMATERIAL
A natural, incidental or manufactured material containing particles, in an
unbound state or as an aggregate or as an agglomerate and where, for 50 %
or more of the particles in the number size distribution, one or more
external dimensions is in the size range 1 nm - 100 nm.
In specific cases and where warranted by concerns for the environment,
health, safety or competitiveness the number size distribution threshold of
50 % may be replaced by a threshold between 1 and 50 %.
By derogation from the above, fullerenes, graphene flakes and single wall
carbon nanotubes with one or more external dimensions below 1 nm
should be considered as nanomaterials.
The definition will be used primarily to identify materials for which
special provisions might apply (e.g. for risk assessment or ingredient
labelling). Those special provisions are not part of the definition but of
specific legislation in which the definition will be used.
Nanomaterials are not intrinsically hazardous per se but there may be a
need to take into account specific considerations in their risk assessment.
Therefore one purpose of the definition is to provide clear and
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NANOMATERIALS Seminar: 2013
unambiguous criteria to identify materials for which such considerations
apply.
It is only the results of the risk assessment that will determine whether the
nanomaterial is hazardous and whether or not further action is justified.
Today there are several pieces of EU legislation, and technical guidance
supporting implementation of legislation, with specific references to
nanomaterials. To ensure conformity across legislative areas, where often
the same materials are used in different contexts, the purpose of the
Recommendation is to enable a coherent cross-cutting reference.
Therefore another basic purpose is to ensure that a material which is a
nanomaterial in one sector will also be treated as such when it is used in
another sector.
Dept: Of Mechanical Eng 7 PKCET, Kandala
NANOMATERIALS Seminar: 2013
ADVANCES IN NANOMATERIALS
The history of nanomaterials began immediately after the big bang when Nanostructure were formed in the early meteorites. Nature later evolved many other Nanostructures like seashells, skeletons etc. Nanoscaled smoke particles were formed during the use of fire by early humans. The scientific story of nanomaterials however began much later. One of the first scientific report is the colloidal gold particles synthesised by Michael Faraday asearly as 1857. Nanostructured catalysts have also been investigated for over 70 years. By the early 1940’s, precipitated and fumed silica nanoparticles were being manufactured and sold in USA and Germany as substitutes for ultrafine carbon black for rubber reinforcements.Nanosized amorphous silica particles have found large-scale applications in many every-day consumer products, ranging from non-diary coffee creamer to automobile tires,optical fibers and catalyst supports. In the 1960s and 1970’s metallic nanopowders for magnetic recording tapes were developed. In 1976, for the first time, nanocrystals produced by the now popular inert- gas evaporation technique was published by
Dept: Of Mechanical Eng 8 PKCET, Kandala
NANOMATERIALS Seminar: 2013
Granqvist and Buhrman. Recently it has been found that the Maya blue paint is a nanostructured hybrid material. The origin of its color and its resistance to acids and biocorrosion are still not understood but studies of authentic samples from Jaina Island show that the material is made of needle-shaped palygorskite (clay) crystals that form asuperlattice with a period of 1.4 nm, with intercalates of amorphous silicate substrate containing inclusions of metal (Mg) nanoparticles. The beautiful tone of the blue color is obtained only when both these nanoparticles and the superlattice are present, as has been shown by the fabrication of synthetic samples.
TYPES OF NANOMATERIALS
For the purpose of this article, most current nanomaterials could be
organized into four types:
• Carbon Based Materials
• Metal Based Materials
• Dendrimers
• Composites
Carbon Based Materials
Dept: Of Mechanical Eng 9 PKCET, Kandala
NANOMATERIALS Seminar: 2013
These nanomaterials are composed mostly of carbon, most commonly
taking the form of a hollow spheres, ellipsoids, or tubes.
Spherical and ellipsoidal carbon nanomaterials are referred to as
fullerenes, while cylindrical ones are called nanotubes.
These particles have many potential applications, including improved
films and coatings, stronger and lighter materials, and applications in
electronics.
Metal Based Materials
These nanomaterials include quantum dots, nanogold, nanosilver and metal
oxides, such as titanium dioxide.
A quantum dot is a closely packed semiconductor crystal comprised of
hundreds or thousands of atoms, and whose size is on the order of a few
nanometers to a few hundred nanometers.
Changing the size of quantum dots changes their optical properties.
Dendrimers
These nanomaterials are nanosized polymers built from branched units.
The surface of a dendrimer has numerous chain ends, which can be tailored
to perform specific chemical functions.
This property could also be useful for catalysis. Also, because three-
dimensional dendrimers contain interior cavities into which other
molecules could be placed, they may be useful for drug delivery.
Dept: Of Mechanical Eng 10 PKCET, Kandala
NANOMATERIALS Seminar: 2013
Composites
Composites combine nanoparticles with other nanoparticles or with larger,
bulk-type materials.
Nanoparticles, such as nanosized clays, are already being added to products
ranging from auto parts to packaging materials, to enhance mechanical,
thermal, barrier, and flame-retardant properties.
Materials referred to as "nanomaterials" generally fall into two categories:
fullerenes, and inorganic nanoparticles.
Fullerenes
The fullerenes are a class of allotropes of carbon which conceptually
are graphene sheets rolled into tubes or spheres. These include the carbon
nanotubes(or silicon nanotubes) which are of interest both because of their
mechanical strength and also because of their electrical properties.
Dept: Of Mechanical Eng 11 PKCET, Kandala
NANOMATERIALS Seminar: 2013
For the past decade, the chemical and physical properties of fullerenes have
been a hot topic in the field of research and development, and are likely to
continue to be for a long time. In April 2003, fullerenes were under study
for potential medicinal use: binding specific antibiotics to the structure of
resistantbacteria and even target certain types of cancer cells such
as melanoma. The October 2005 issue of Chemistry and Biology contains
an article describing the use of fullerenes as light-
activated antimicrobial agents. In the field of nanotechnology, heat
resistance and superconductivity are among the properties attracting
intense research.
A common method used to produce fullerenes is to send a large current
between two nearby graphite electrodes in an inert atmosphere. The
resulting carbon plasma arc between the electrodes cools into sooty residue
from which many fullerenes can be isolated.
There are many calculations that have been done using ab-initio Quantum
Methods applied to fullerenes. By DFT and TDDFT methods one can
obtain IR,Raman and UV spectra. Results of such calculations can be
compared with experimental results.
Dept: Of Mechanical Eng 12 PKCET, Kandala
NANOMATERIALS Seminar: 2013
Nano particles
Nanoparticles or nanocrystals made of metals, semiconductors, or oxides
are of particular interest for their mechanical, electrical, magnetic, optical,
chemical and other properties. Nanoparticles have been used as quantum
dots and as chemical catalysts.
Nanoparticles are of great scientific interest as they are effectively a bridge
between bulk materials and atomic or molecular structures. A bulk material
should have constant physical properties regardless of its size, but at the
nano-scale this is often not the case. Size-dependent properties are
observed such as quantum confinement in semiconductor particles, surface
plasmon resonance in some metal particles
and superparamagnetism in magnetic materials.
Nanoparticles exhibit a number of special properties relative to bulk
material. For example, the bending of bulk copper (wire, ribbon, etc.)
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NANOMATERIALS Seminar: 2013
occurs with movement of copper atoms/clusters at about the 50 nm scale.
Copper nanoparticles smaller than 50 nm are considered super hard
materials that do not exhibit the same malleability and ductility as bulk
copper. The change in properties is not always desirable. Ferroelectric
materials smaller than 10 nm can switch their magnetisation direction using
room temperature thermal energy, thus making them useless for memory
storage.Suspensions of nanoparticles are possible because the interaction of
the particle surface with the solvent is strong enough to overcome
differences in density, which usually result in a material either sinking or
floating in a liquid. Nanoparticles often have unexpected visual properties
because they are small enough to confine their electrons and produce
quantum effects. For example goldnanoparticles appear deep red to black
in solution.
Nanomaterial Composition
Comprised of many different elements such as carbons and metals
Combinations of elements can make up nanomaterial grains such as
titanium carbide and zinc sulfide
Allows construction of new materials such as C60 (Bucky Balls or
fullerenes) and nanotubes
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NANOMATERIALS Seminar: 2013
Properties of C60 and its derivatives
Black crystalline solid, thermally stable up to 400 °C
Very difficult to oxidize
Doped with alkali metals: conductor and superconductor
Fluorescence
Acceptors of electrons and electronic energy
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NANOMATERIALS Seminar: 2013
PROPERTIES OF NANOMATERIALS
Mechanical properties
The large amount of grain boundaries in bulk materials made of
nanoparticles allows extended grain boundary sliding leading to high
plasticity.
Catalytic Properties
Due to their large surface, nanoparticles made of transition element oxides
exhibit interesting catalytic properties. In special cases, catalysis may be
enhanced and more specific by decorating these particles with gold or
platinum clusters.
Magnetic Properties
In magnetic nanoparticles, the energy of magnetic anisotropy may be that
small that the vector of magnetization fluctuates thermally; this is called
superparamagnetism. Such a material is free of remanence, and
coercitivity. Touching superparamagnetic particles are loosing this special
property by interaction, except the particles are kept at distance.
Combining particles with high energy of anisotropy with
superparamagnetic ones leads to a new class of permanent magnetic
materials.
Optical Properties
Distributions of non-agglomerated nanoparticles in a polymer are used to
tune the index of refraction. Additionally, such a process may produce
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NANOMATERIALS Seminar: 2013
materials with non-linear optical properties. Gold or CdSe nanoparticles in
glass lead to red or orange coloration. Semi-conducting nanoparticles and
some oxide-polymer nanocomposites exhibit fluorescence showing blue
shift with decreasing particle size.
Unique Properties
The unique properties of these various types of intentionally produced
nanomaterials give them novel electrical, catalytic, magnetic, mechanical,
thermal, or imaging features that are highly desirable for applications in
commercial, medical, military, and environmental sectors.
These materials may also find their way into more complex nanostructures
and systems. As new uses for materials with these special properties are
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NANOMATERIALS Seminar: 2013
identified, the number of products containing such nanomaterials and their
possible applications continues to grow.
Electrical properties
Electrical Properties of Nanoparticles” discuss about fundamentals of
electrical conductivity in nanotubes and nanorods, carbon nanotubes,
photoconductivity of nanorods, electrical conductivity of nanocomposites.
One interesting method which can be used to demonstrate the steps in
conductance is the mechanical thinning of a nanowire and measurement of
the electrical current at a constant applied voltage. The important point
here is that, with decreasing diameter of the wire, the number of electron
wave modes contributing to the electrical conductivity is becoming
increasingly smaller by well-defined quantized steps.
In electrically conducting carbon nanotubes, only one electron wave mode
is observed which transport the electrical current. As the lengths and
orientations of the carbon nanotubes are different, they touch the surface of
the mercury at different times, which provides two sets of information: (i)
the influence of carbon nanotube length on the resistance; and (ii) the
resistances of the different nanotubes. As the nanotubes have different
lengths, then with increasing protrusion of the fiber bundle an increasing
number of carbon nanotubes will touch the surface of the mercury droplet
and contribute to the electrical current transport.
Dept: Of Mechanical Eng 18 PKCET, Kandala
NANOMATERIALS Seminar: 2013
APPLICATIONS OF NANOMATERIALS
Nanomaterials having wide range of applications in the field of electronics,
fuel cells,batteries, agriculture, food industry, and medicines, etc... It is
evident that nanomaterials split their conventional counterparts because of
their superior chemical, physical, and mechanical properties and of their
exceptional formability.
Fuel cells
A fuel cell is an electrochemical energy conversion device that converts the
chemical energy from fuel (on the anode side) and oxidant (on the cathode
side) directly into electricity. The heart of fuel cell is the electrodes. The
performance of a fuel cell electrode can be optimized in two ways; by
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NANOMATERIALS Seminar: 2013
improving the physical structure and by using more active electro catalyst.
A good structure of electrode must provide ample surface area, provide
maximum contact of catalyst, reactant gas and electrolyte, facilitate gas
transport and provide good electronic conductance. In this fashion the
structure should be able to minimize losses.
Carbon nanotubes - Microbial fuel cell
Microbial fuel cell is a device in which bacteria consume water-soluble
waste such as sugar, starch and alcohols and produces electricity plus clean
water. This technology will make it possible to generate electricity while
treating domestic or industrial wastewater.
Microbial fuel cell can turn different carbohydrates and complex substrates
present in wastewaters into a source of electricity. The efficient electron
transfer between the microorganism and the anode of the microbial fuel
cell plays a major role in the performance of the fuel cell. The organic
Dept: Of Mechanical Eng 20 PKCET, Kandala
NANOMATERIALS Seminar: 2013
molecules present in the wastewater posses a certain amount of chemical
energy, which is released when converting them to simplermolecules like
CO2. The microbial fuel cell is thus a device that converts the chemical
energy present in water-soluble waste into electrical energy by the catalytic
reaction of microorganisms.
Carbon nanotubes (CNTs) have chemical stability, good mechanical
properties
and high surface area, making them ideal for the design of sensors and
provide very high surface area due to its structural network. Since carbon
nanotubes are also suitable supports for cell growth, electrodes of
microbial fuel cells can be built using of CNT.
Dept: Of Mechanical Eng 21 PKCET, Kandala
NANOMATERIALS Seminar: 2013
Due to three-dimensional architectures and enlarged electrode surface area
for the entry of growth medium, bacteria can grow and proliferate and get
immobilized. Multi walled CNT scaffolds could offer self-supported
structure with large surface area through which hydrogen producing
bacteria (e.g., E. coli) can eventually grow and proliferate. Also CNTs and
MWCNTs have been reported to be biocompatible for different eukaryotic
cells. The efficient proliferation of hydrogen producing bacteria throughout
an electron conducting scaffold of CNT can form the basis for the potential
application as electrodes in MFCs leading to efficient performance.
Catalysis
Higher surface area available with the nanomaterial counterparts, nano-
catalysts tend to have exceptional surface activity. For example, reaction
rate at nano-aluminum can go so high, that it is utilized as a solid-fuel in
rocket propulsion, whereas the bulk aluminum is widely used in utensils.
Nano-aluminum becomes highly reactive and supplies the required thrust
to send off pay loads in space. Similarly, catalysts assisting or retarding the
reaction rates are dependent on the surface activity, and can very well be
utilized in manipulating the rate-controlling step.
Phosphors for High-Definition TV
The resolution of a television, or a monitor, depends greatly on the size of
the pixel.
These pixels are essentially made of materials called "phosphors," which
glow when struck by a stream of electrons inside the cathode ray tube
(CRT). The resolution improves with a reduction in the size of the pixel, or
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NANOMATERIALS Seminar: 2013
the phosphors. Nanocrystalline zinc selenide, zinc sulfide, cadmium
sulfide, and lead telluride synthesized by the sol-gel techniques are
candidates for improving the resolution of monitors. The use of
nanophosphors is envisioned to reduce the cost of these displays so as to
render highdefinition televisions (HDTVs) and personal computers
affordable to be purchase.
Next-Generation Computer Chips
The microelectronics industry has been emphasizing miniaturization,
whereby the circuits, such as transistors, resistors, and capacitors, are
reduced in size. By achieving a significant reduction in their size, the
microprocessors, which contain these components,can run much faster,
thereby enabling computations at far greater speeds. However, there are
several technological impediments to these advancements, including lack
of the ultrafine precursors to manufacture these components; poor
dissipation of tremendous amount of heat generated by these
microprocessors due to faster speeds; short mean time to failures (poor
reliability), etc. Nanomaterials help the industry break these barriers down
by providing the manufacturers with nanocrystalline starting materials,
ultra-high purity materials, materials with better thermal conductivity, and
longer-lasting, durable interconnections (connections between various
components in the microprocessors).
Example: Nanowires for junctionless transistors
Transistors are made so tiny to reduce the size of sub assemblies of
electronic systems and make smaller and smaller devices, but it is difficult
to create high-quality junctions.
Dept: Of Mechanical Eng 23 PKCET, Kandala
NANOMATERIALS Seminar: 2013
In particular, it is very difficult to change the doping concentration of a
material overdistances shorter than about 10 nm. Researchers have
succeeded in making thejunctionless transistor having nearly ideal
electrical properties. It could potentiallyoperate faster and use less power
than any conventional transistor on the market today.
The device consists of a silicon nanowire in which current flow is perfectly
controlled by a silicon gate that is separated from the nanowire by a thin
insulating layer. The entire silicon nanowire is heavily n-doped, making it
an excellent conductor. However, the gate is p-doped and its presence has
the effect of depleting the number of electrons in the region of the
nanowire under the gate. The device also has near-ideal electrical
properties and behaves like the most perfect of transistors without suffering
from current leakage like conventional devices and operates faster and
using less energy.
Dept: Of Mechanical Eng 24 PKCET, Kandala
NANOMATERIALS Seminar: 2013
SAFETY
Nanomaterials behave differently than other similarly-sized particles. It is
therefore necessary to develop specialized approaches to testing and
monitoring their effects on human health and on the environment. The
OECD Chemicals Committee has established the Working Party on
Manufactured Nanomaterials to address this issue and to study the
practices of OECD member countries in regards to nanomaterial safety.
While nanomaterials and nanotechnologies are expected to yield numerous
health and health care advances, such as more targeted methods of
delivering drugs, new cancer therapies, and methods of early detection of
diseases, they also may have unwanted effects. Increased rate of absorption
is the main concern associated with manufactured nanoparticles.
When materials are made into nanoparticles, their surface area to volume
ratio increases. The greater specific surface area (surface area per unit
weight) may lead to increased rate of absorption through the skin, lungs, or
digestive tract and may cause unwanted effects to the lungs as well as other
organs. However, the particles must be absorbed in sufficient quantities in
order to pose health risks.
As the use of nanomaterials increases worldwide, concerns for worker and
user safety are mounting. To address such concerns,
the Swedish Karolinska Institute conducted a study in which various
nanoparticles were introduced to human lung epithelial cells. The results,
released in 2008, showed that iron oxide nanoparticles caused
little DNA damage and were non-toxic. Zinc oxidenanoparticles were
slightly worse. Titanium dioxide caused only DNA damage. Carbon
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NANOMATERIALS Seminar: 2013
nanotubes caused DNA damage at low levels. Copper oxide was found to
be the worst offender, and was the only nanomaterial identified by the
researchers as a clear health risk.
DISADVANTAGES OF NANOMATERIALS
(i) Instability of the particles - Retaining the active metal nanoparticles is
highly challenging, as the kinetics associated with nanomaterials is rapid.
In order to retain nanosize of particles, they are encapsulated in some other
matrix. Nanomaterials are thermodynamically metastable and lie in the
region of high-energy local-minima. Hence they are prone to attack and
undergo transformation. These include poor corrosionresistance, high
solubility, and phase change of nanomaterials. This leads to deteriorationin
properties and retaining the structure becomes challenging.
(ii) Fine metal particles act as strong explosives owing to their high surface
area coming in direct contact with oxygen. Their exothermic combustion
can easily cause explosion.
(iii) Impurity - Because nanoparticles are highly reactive, they inherently
interact with impurities as well. In addition, encapsulation of nanoparticles
becomes necessary when they are synthesized in a solution (chemical
route). The stabilization of nanoparticles occurs because of a non-reactive
species engulfing the reactive nano-entities. Thereby,these secondary
impurities become a part of the synthesized nanoparticles, and synthesis of
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NANOMATERIALS Seminar: 2013
pure nanoparticles becomes highly difficult. Formation of oxides, nitrides,
etc can also get aggravated from the impure environment/ surrounding
while synthesizing nanoparticles. Hence retaining high purity in
nanoparticles can become a challenge hard to overcome.
(iv) Biologically harmful - Nanomaterials are usually considered harmful
as they become transparent to the cell-dermis. Toxicity of nanomaterials
also appears predominant owing to their high surface area and enhanced
surface activity. Nanomaterials have shown to cause irritation, and have
indicated to be carcinogenic. If inhaled, their low mass entraps them inside
lungs, and in no way they can be expelled out of body. Their interaction
with liver/blood could also prove to be harmful (though this aspect is still
being debated on).
(v) Difficulty in synthesis, isolation and application - It is extremely hard
to retain the size of nanoparticles once they are synthesized in a solution.
Hence, the nanomaterials have to be encapsulated in a bigger and stable
molecule/material. Hence free nanoparticles are hard to be utilized in
isolation, and they have to be interacted for intended use via secondary
means of exposure. Grain growth is inherently present in
nanomateirals during their processing. The finer grains tend to merge and
become bigger and stable grains at high temperatures and times of
processing.
(vi) Recycling and disposal - There are no hard-and-fast safe disposal
policies evolved for nanomaterials. Issues of their toxicity are still under
question, and results of exposure experiments are not available. Hence the
uncertainty associated with affects of nanomaterials is yet to be assessed in
order to develop their disposal policies.
Dept: Of Mechanical Eng 27 PKCET, Kandala
NANOMATERIALS Seminar: 2013
CONCLUSION
Nanoparticles show great promise, yet much discovery and
development still remains to be done. The examples presented in
this review were selected to exemplify the ability to significantly
alter the biodistribution of nanostructures by minor structural
changes, highlighting the importance of well-defined chemistries
for their preparation, in concert with rigorous analytic tools for their
physicochemical characterization, and PET for study of their in
vivo performance. PET serves as a highly sensitive imaging tool to
assist in the development of these materials to realize the potential
of nanomedicine for early-stage detection, diagnosis, treatment, and
monitoring of disease progression, regression, and recurrence.
The primary challenges over the next 5 y will be to accomplish
truly tissue-selective targeting, without the significant MPS organ
uptake, and full clearance of the nanomaterials once they have servedtheir
purpose. Toxicity and immunogenicity are measured routinely
for nearly every new nanomaterial being investigated. The examples
presented here included materials that have not displayed adverse
biologic responses, and they are also structures that are robust—the
robust character was important in the early studies to probe the
behavior of the nanostructures while they remained as intact
nanoscale objects. However, as development moves forward, it will
be important to replace the chemically stable components with others
that are biodegradable. In this aspect, again, organic polymer
materials have advantages over inorganic substrates, because several
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NANOMATERIALS Seminar: 2013
families of organic polymers are used regularly with Food and Drug
Administration approval for biomedical applications (poly[lactic
acid] and poly[glycolic acid], among many others).
BIBILIOGRAPHY
Applied nanotechnology. Jeremy Ramsden
http://en.wikipedia.org/wiki/Nanomaterials
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NANOMATERIALS Seminar: 2013
http://en.wikipedia.org/wiki/Atomic_force_microscopy
http://en.wikipedia.org/wiki/Nanoelectronics
Zhao H and Ning Y 2000 Gold Bull 33 103
Faraday M 1857 Philosophical Transactions 147 145
Feynman R P 1961 Miniaturization (New York: Reinhold)
Moore G 1975 IEDM Technical Digest 11
Maserjian J and Petersson G P 1974 Applied Physics Letters 25 50
Dept: Of Mechanical Eng 30 PKCET, Kandala