NANOMATERIALS

● Nanomaterials are usually considered to be materials with at

least one external dimension that measures 100 nanometres or
less or with internal structures measuring 100 nm or less. They
may be in the form of particles, tubes, rods or fibres.
● Nanomaterials describe, in principle, materials of which a
single unit is sized between 1 and 100 nm.
 CLASSIFICATION OF NANOMATERIALS
● Nanomaterials can be classified based on the dimensions or the
nature of the materials into different types
● The classification of nanomaterials based on the number of
dimensions are Zero-dimensional (OD), one-dimensional (ID)
two-dimensional (2D) and three-dimensional (3D) nanomaterials.
 CLASSIFICATION OF NANOMATERIALS
● 1. Zero-dimensional nanomaterials: Here, all dimensions
(x,y,z) are at nanoscale i.e., no dimensions are greater than
100 nm. It includes nanospheres and nanoclusters.
● 2.One-dimensional nanomaterials: Here, two dimensions (x,y.)
are at nanoscale and the other is outside the nanoscale. This
leads to needle shaped nanomaterials. It includes nanofibers,
nanotubes, nanorods, and nanowires.
 CLASSIFICATION OF NANOMATERIALS
● 3. Two-dimensional nanomaterials: Here, one dimension (x) is
at nanoscale and the other two are outside the nanoscale.
The 2D nanomaterials exhibit plate-like shapes. It includes
nanofilms, nanolayers, and nanocoating with nanometric
thickness.
 CLASSIFICATION OF NANOMATERIALS
● 4. Three-dimensional nanomaterials: These are nanomaterials
that are not confined to the nanoscale in any dimensions.
● These materials have three arbitrary dimensions above 100 nm.
● The bulk (3D) nanomaterials are composed of a multiple
arrangement of nanosize crystals in different orientations.
● It includes dispersions of nanoparticles, bundles of nanowires
and nanotubes as well as multi nanolayers in which OD, ID and
2D structural elements are in close contact with each other and
form interfaces.
 CLASSIFICATION OF NANOMATERIALS
● Based on the nature of materials, nanomaterials are broadly
classified in to four as
● 1. Carbon based materials
● 2 Nanocomposites
● 3. Metal based materials
● 4. Nano polymers
 CLASSIFICATION OF NANOMATERIALS
● 1. Carbon based nanomaterials: These are composed of
carbon, taking the form of hollow spheres, ellipsoids or tubes.
● The spherical and ellipsoidal forms are referred to as
fullerenes, while cylindrical forms are called carbon
nanotubes.
● Spherical fullerenes are called Bucky balls. They consist of
clusters of C60, C70 etc.
● A carbon nanotube is a structure which seems to be formed
by rolling a sheet of graphite in to the shape of a cylindrical
tube.
 CLASSIFICATION OF NANOMATERIALS
● 2. Metal based nanomaterials: Metal nanoparticles such as silver,
gold, copper, and iron are widely used in catalysis, electronics,
various sensors, photonics, imaging and environmental cleanup.
Scientists have found that metal nanoparticles contain many
unexpected benefits in both medical and technology fields.
 CLASSIFICATION OF NANOMATERIALS
● 3. Nanopolymers / Dendrimers: Dendrimers are repetitively branched
molecules.The name comes from the Greek word 'Dendron' (tree).
These are nanosized polymers built from branched units. The
surface of a dendrimer has numerous chain ends, which can
perform specific chemical functions.
● Dendrimers are used in molecular recognition, nanosensing, light
harvesting and opto-electrochemical devices.
● Polymeric nanoparticles prepared from polymers are considered as
potential drug delivery devices due to recent applications in drug
targeting to particular organs and tissues.
 CLASSIFICATION OF NANOMATERIALS
● These nanoparticles are also used as DNA in gene therapy and
delivery of proteins, peptides and genes through oral route
administration.
● Dendrimers are one kind of polymeric nanoparticles constructed by
the successive addition of layers of branching groups. The
properties of dendrimers are dominated by the functional groups on
the molecular surface.
● These are used in various applications such as a) detecting agents
(dyes) b) pharmaceutically active compounds (drug delivery) c)
targeting components and d) as imaging agents. Example:
Poly(amidoamine) or (PAMAM) dendrimer.
 CLASSIFICATION OF NANOMATERIALS
● 4. Nanocomposites: The definition of nanocomposite material has
broadened significantly to encompass a large variety of systems
such as one-dimensional, two-dimensional, three-dimensional and
amorphous materials, made of distinctly dissimilar components and
mixed at the nanometer scale.
● The general class of nanocomposite organic/inorganic materials is a
fast growing area of research. The properties of nanocomposite
materials depend not only on the properties of their individual
parents but also on their morphology and interfacial characteristics:
● Therefore, nanocomposites promise new applications in many fields
such as mechanically reinforced lightweight components, non-linear
optics, battery cathodes and ionics, nano-wires, sensors and other
systems.
 PREPARATION OF NANOMATERIALS
● Synthesis of nanomaterials with strict control over size, shape, and
crystalline structure has become very important for the applications
of nanotechnology in numerous fields including catalysis, medicine,
and electronics.
● Synthesis methods for nanoparticles are typically grouped into two
categories: "top-down" and "bottom-up" approach.
● The first involves the division of a massive solid into smaller and
smaller portions, successively reaching to nanometer size. This
approach may involve milling or attrition.
● The second, "bottom-up", method of nanoparticle fabrication
involves the condensation of atoms or molecular entities in a gas
phase or in solution to form the material in the nanometer range.
 Top-down approach
● The term top-down refers to reducing size of material by
crushing/milling/cutting/ scaling- down by means of an
external agency. This is similar to making of a small statue
from a big rock or a big stone.
● In top down approach nanomaterials are synthesized by
breaking down of bulk solids in to nanosizes. It is the
predominant process in semiconductor manufacturing.
 Top-down approach
● Different kinds of techniques are used for scaling down bulk
materials.
● 1. Ball milling 2. Plasma arcing 3. Laser sputtering 4. Vapor
deposition 5. Nanolithography
● Among all top-down approaches, ball milling has been widely used
for the preparation of various nanomaterials.
● In this technique, bulk materials are broken in to nano-size particles.
The precursors or source materials (such as metal oxides) are
crushed using high energy ball mills.
 Top-down approach
Advantages
1. High production rate

2. Wide range of techniques for crushing down the size.

3. Formation of nanoparticles can be externally controlled.

4. It is slow process.
 Top-down approach
Disadvantages
1. Formation of variable nano-size particles.

2. Surface dislocations.

3. Formation of aggregates or clusters.

4. Non-homogeneity of chemical compositions.

5. Difficulty in controlling the morphology of nanomaterials.

 BOTTOM UP
● In bottom up approach, nanomaterials are synthesized by
assembling the atoms/ molecules together.
● The techniques used are by chemical processes. It is to be noted
that nature utilizes the bottom up approach to build complex
systems.
● For example, formation of DNA by cells using enzymes by taking
constituent molecules and binding them together.
 BOTTOM UP
● The bottom up approach has the following distinct advantages over
the top down approach.

1. No material is wasted as destructive processes are not involved.

2. Carbon nanotubes and silicon nanowires can be obtained using

the bottom-up approach.

3. Very small geometries can be realized.

 BOTTOM UP
● Following are common bottom-up methods for the synthesis of
nanomaterials.

1. Sol-gel method

2. Chemical precipitation method

3. Hydrothermal method/ solvochemical method

4. Colloidal method
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