Sathyabama University
CHAPTER- I
INTRODUCTION TO NANOMATERIALS
Introduction: Nanomaterials: Definition - Classification based on dimensions - Size dependent
properties. Types of nanomaterials: Nanoparticles: Synthesis by chemical reduction method.
Nanoporous materials: Synthesis by sol-gel method. Nanowires: Synthesis by VLS mechanism.
Carbon Nanotubes (CNTs): Single walled and multi walled nanotubes - Mechanical and electrical
properties of CNTs - Applications of CNTs - Synthesis of CNTs by electric arc discharge method
and laser ablation method.
1.1 INTRODUCTION
Nano science and technology is a broad and interdisciplinary area growing explosively worldwide
in the past few years. Nanomaterials are cornerstones of nanoscience and nanotechnology. Now
a days in research & development the major sectors are energy, environment, water technology,
pharmaceuticals etc. The usage of nanomaterials are enormous as energy storage devices such
as fuel cells, detection of threats in defense, navy, drug delivery and water purification. Industrial
revolution has made life easy and pleasant. Today’s high speed personal computers and mobile
communications would not have certainly been possible without the use of nano science and nano
technology.
1.2 MAIN TERMINOLOGY
a) Nano science and nanotechnology - The science and technology which deals with the
particles in size between 1 to 100nm is known as nano science and nano technology.
b) Classification of nanomaterials on the basis of dimensions
On the basis of reduction in size of materials in different dimensions, nanomaterials are classified
into three groups.
Reduction in size in
S. No. Size Examples
different coordinates
1. 3-dimensions < 100 nm Nanoparticles, quantum dots
2. 2-dimensions < 100 nm Nanotubes, nanowires, nanofibers
3. 1-dimension < 100 nm Thin films, coatings
c) Classification based on pore dimensions
A useful way to classify nanoporous materials is by the diameter size of their pores, since most
of the properties, which are interesting for the applications of adsorption and diffusion are
dependent on this parameter. The prefix nano- means a typical dimension between 1 and 100
nm. In this range material properties change drastically, when materials interact with other
molecules. In fact, pore diameter establishes the size of molecules that could diffuse inside and
, Sathyabama University
comparison between the pore size and the dimension of guest molecule gives an idea about
diffusion and interaction properties. If the two dimensions are same, we can expect that the
molecule-wall interaction will be prevalent along with the molecule-molecule interaction. By the
other way, if guest molecules are smaller than the pore size, there will be less molecule wall
interaction than the molecule-molecule interaction during the diffusion process.
According to IUPAC definition, nanoporous materials are classified in three main groups
depending on their pore dimension:
Microporous materials (d<2 nm): These materials have very narrow pores. They can host only
small molecules, such as gases or linear molecules, and generally show slow diffusion kinetics
and high interaction properties. They are generally used in gas purification systems, membrane
filters or gas-storage materials.
Example: Na-Y and naturally occurring clay materials.
Mesoporous materials (2<d<50 nm): These materials have pores with diameter size enough to
host some big molecules, for example aromatic systems or large polymeric monomers. Diffusion
kinetics of the adsorbed molecules is often due to capillarity, with an initial interaction with the
pore wall followed by pore filling. These systems can be used as nano-reactors for the
polymerization or adsorbing systems for liquids or vapours.
Example: MCM-41, MCM48, SBA15 and carbon mesoporous materials etc.
Macroporous systems (d>50 nm): Pores of these materials could host very large molecules,
such as poly-aromatic systems or small biological molecules, and interactions with pore walls are
often secondary respect to the interactions with other molecules, overall in the case of very small
guest molecules. These materials are principally used as matrices to store functional molecules,
as scaffolds to graft functional groups, such as catalytic centres, and as sensing materials, thanks
to the quick diffusion of chemical species in the pore system.
Example: Carbon micro tubes, Porous gels and porous glasses
d) Synthetic approaches for nanomaterials
(i) Bottom-up approach: The building of nanostructures starting with small components
such as atoms or molecules is called bottom-up approach.
Ex: Chemical vapour deposition, Sol-Gel Process, Chemical Reduction methods, etc.
(ii) Top-down approach: The process of making nanostructures starting with larger
structures and breaking away to nano size is called top-down approach.
Ex: Lithography, Ball milling, Epitaxy, etc.
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e) Porosity – It is the ratio of pore volume to its total volume. Here, pore volume is the difference
between the total volume and solid volume.
f) Pore diameter - The average or effective diameter of the openings in a membrane, screen,
or other porous material is known as pore diameter. Based on the pore diameter range, porous
materials are classified into three types.
(i) Microporous materials: They are materials having the average pore diameter less than
2nm Ex: Zeolites, organic frame works and surgical tape.
(ii) Mesoporous materials: They are materials having the average pore diameter in the
range of 2nm to 50 nm Ex: Mobile Crystalline Materials (MCM-41), Mesoporous
Molecular Sieves, Xerogels, Silica, Alumina, titanium Oxide and Niobium oxide
materials.
(iii) Macroporous materials: They are materials having the average pore diameter greater
than 50nm. Ex: Porous glasses and Aerogels.
g) Wafer - A wafer is a thin slice of semiconductor or substrate material.
h) Sol - It is a colloidal suspension of very small solid particles in liquid medium. Ex: Ink and
Blood.
i) Gel - It is a colloidal suspension of very small liquid particles in solid medium Ex: agar, gelatin,
jelly and tooth paste.
j) Aerogel - It is a synthetic porous ultra light material derived from a gel, in which the liquid
component of the gel has been replaced with a gas. Ex: Silica aerogel, Alumina aerogel and
carbon aerogel. Silica aerogel is a best insulator as well as lowest density solid. It porosity is
99%, surface area is 1000 m2/gm, Its average pore size is 2-50nm.
k) Xerogel - A solid formed from a gel by drying with unhindered shrinkage is called a xerogel.
l) Surface area - The accessible or detectable area of solid surface per unit mass of material is
called the surface area.
m) Characterization techniques of nanomaterials
S. No. Techniques Information acquired
Scanning Electron Microscopy
Surface topography (up to 10nm) and
1. (SEM) with Energy-dispersive X-ray
composition
spectroscopy
Transmission Electron Microscopy
2. Surface morphology (up to 0.2nm)
(TEM)
3. Atomic Force Microscopy Identification of individual surface atoms
, Sathyabama University
4. Particle Size Analyzer Particle Size distribution
Distinguish single walled carbon
5. FT-Raman Spectra nanotubes and multi walled carbon
nanotubes
CNT chirality or Asymmetry
6. Photoluminescence Spectra
determination
7. X-ray photoelectron spectroscopy Electronic state of the element
n) Chiral - A chiral molecule is a type of molecule that has non-superimposable mirror images
(i.e. enantiomers).
Example: A carbon having four different substituents.
o) Helicity - It is a form of axial chirality or with respect to axis non-superimposable mirror
images. Example: Protein folding.
1.3 SIZE DEPENDENT PROPERTIES OF NANOMATERIALS
The various properties, which get tremendously altered due to the size reduction in at least one
dimension are:
a) Chemical properties: Reactivity; Catalysis.
b) Thermal property: Melting point temperature.
c) Electronic properties: Electrical conduction.
d) Optical properties: Absorption and scattering of light.
e) Magnetic properties: Magnetization.
1.3.1 Chemical Properties
• Based on the surface area to volume effect, nanoscale materials have:
a) Increased total surface area.
b) Increased number of atoms accessible on the surface.
c) Increased catalytic activity of those large number surface atoms.
d) Different/tunable surface catalytic properties by the change in shape, size and
composition.
• Hence, nanoscale catalysts can increase the rate, selectivity and efficiency of various
chemical reactions.
CHAPTER- I
INTRODUCTION TO NANOMATERIALS
Introduction: Nanomaterials: Definition - Classification based on dimensions - Size dependent
properties. Types of nanomaterials: Nanoparticles: Synthesis by chemical reduction method.
Nanoporous materials: Synthesis by sol-gel method. Nanowires: Synthesis by VLS mechanism.
Carbon Nanotubes (CNTs): Single walled and multi walled nanotubes - Mechanical and electrical
properties of CNTs - Applications of CNTs - Synthesis of CNTs by electric arc discharge method
and laser ablation method.
1.1 INTRODUCTION
Nano science and technology is a broad and interdisciplinary area growing explosively worldwide
in the past few years. Nanomaterials are cornerstones of nanoscience and nanotechnology. Now
a days in research & development the major sectors are energy, environment, water technology,
pharmaceuticals etc. The usage of nanomaterials are enormous as energy storage devices such
as fuel cells, detection of threats in defense, navy, drug delivery and water purification. Industrial
revolution has made life easy and pleasant. Today’s high speed personal computers and mobile
communications would not have certainly been possible without the use of nano science and nano
technology.
1.2 MAIN TERMINOLOGY
a) Nano science and nanotechnology - The science and technology which deals with the
particles in size between 1 to 100nm is known as nano science and nano technology.
b) Classification of nanomaterials on the basis of dimensions
On the basis of reduction in size of materials in different dimensions, nanomaterials are classified
into three groups.
Reduction in size in
S. No. Size Examples
different coordinates
1. 3-dimensions < 100 nm Nanoparticles, quantum dots
2. 2-dimensions < 100 nm Nanotubes, nanowires, nanofibers
3. 1-dimension < 100 nm Thin films, coatings
c) Classification based on pore dimensions
A useful way to classify nanoporous materials is by the diameter size of their pores, since most
of the properties, which are interesting for the applications of adsorption and diffusion are
dependent on this parameter. The prefix nano- means a typical dimension between 1 and 100
nm. In this range material properties change drastically, when materials interact with other
molecules. In fact, pore diameter establishes the size of molecules that could diffuse inside and
, Sathyabama University
comparison between the pore size and the dimension of guest molecule gives an idea about
diffusion and interaction properties. If the two dimensions are same, we can expect that the
molecule-wall interaction will be prevalent along with the molecule-molecule interaction. By the
other way, if guest molecules are smaller than the pore size, there will be less molecule wall
interaction than the molecule-molecule interaction during the diffusion process.
According to IUPAC definition, nanoporous materials are classified in three main groups
depending on their pore dimension:
Microporous materials (d<2 nm): These materials have very narrow pores. They can host only
small molecules, such as gases or linear molecules, and generally show slow diffusion kinetics
and high interaction properties. They are generally used in gas purification systems, membrane
filters or gas-storage materials.
Example: Na-Y and naturally occurring clay materials.
Mesoporous materials (2<d<50 nm): These materials have pores with diameter size enough to
host some big molecules, for example aromatic systems or large polymeric monomers. Diffusion
kinetics of the adsorbed molecules is often due to capillarity, with an initial interaction with the
pore wall followed by pore filling. These systems can be used as nano-reactors for the
polymerization or adsorbing systems for liquids or vapours.
Example: MCM-41, MCM48, SBA15 and carbon mesoporous materials etc.
Macroporous systems (d>50 nm): Pores of these materials could host very large molecules,
such as poly-aromatic systems or small biological molecules, and interactions with pore walls are
often secondary respect to the interactions with other molecules, overall in the case of very small
guest molecules. These materials are principally used as matrices to store functional molecules,
as scaffolds to graft functional groups, such as catalytic centres, and as sensing materials, thanks
to the quick diffusion of chemical species in the pore system.
Example: Carbon micro tubes, Porous gels and porous glasses
d) Synthetic approaches for nanomaterials
(i) Bottom-up approach: The building of nanostructures starting with small components
such as atoms or molecules is called bottom-up approach.
Ex: Chemical vapour deposition, Sol-Gel Process, Chemical Reduction methods, etc.
(ii) Top-down approach: The process of making nanostructures starting with larger
structures and breaking away to nano size is called top-down approach.
Ex: Lithography, Ball milling, Epitaxy, etc.
, Sathyabama University
e) Porosity – It is the ratio of pore volume to its total volume. Here, pore volume is the difference
between the total volume and solid volume.
f) Pore diameter - The average or effective diameter of the openings in a membrane, screen,
or other porous material is known as pore diameter. Based on the pore diameter range, porous
materials are classified into three types.
(i) Microporous materials: They are materials having the average pore diameter less than
2nm Ex: Zeolites, organic frame works and surgical tape.
(ii) Mesoporous materials: They are materials having the average pore diameter in the
range of 2nm to 50 nm Ex: Mobile Crystalline Materials (MCM-41), Mesoporous
Molecular Sieves, Xerogels, Silica, Alumina, titanium Oxide and Niobium oxide
materials.
(iii) Macroporous materials: They are materials having the average pore diameter greater
than 50nm. Ex: Porous glasses and Aerogels.
g) Wafer - A wafer is a thin slice of semiconductor or substrate material.
h) Sol - It is a colloidal suspension of very small solid particles in liquid medium. Ex: Ink and
Blood.
i) Gel - It is a colloidal suspension of very small liquid particles in solid medium Ex: agar, gelatin,
jelly and tooth paste.
j) Aerogel - It is a synthetic porous ultra light material derived from a gel, in which the liquid
component of the gel has been replaced with a gas. Ex: Silica aerogel, Alumina aerogel and
carbon aerogel. Silica aerogel is a best insulator as well as lowest density solid. It porosity is
99%, surface area is 1000 m2/gm, Its average pore size is 2-50nm.
k) Xerogel - A solid formed from a gel by drying with unhindered shrinkage is called a xerogel.
l) Surface area - The accessible or detectable area of solid surface per unit mass of material is
called the surface area.
m) Characterization techniques of nanomaterials
S. No. Techniques Information acquired
Scanning Electron Microscopy
Surface topography (up to 10nm) and
1. (SEM) with Energy-dispersive X-ray
composition
spectroscopy
Transmission Electron Microscopy
2. Surface morphology (up to 0.2nm)
(TEM)
3. Atomic Force Microscopy Identification of individual surface atoms
, Sathyabama University
4. Particle Size Analyzer Particle Size distribution
Distinguish single walled carbon
5. FT-Raman Spectra nanotubes and multi walled carbon
nanotubes
CNT chirality or Asymmetry
6. Photoluminescence Spectra
determination
7. X-ray photoelectron spectroscopy Electronic state of the element
n) Chiral - A chiral molecule is a type of molecule that has non-superimposable mirror images
(i.e. enantiomers).
Example: A carbon having four different substituents.
o) Helicity - It is a form of axial chirality or with respect to axis non-superimposable mirror
images. Example: Protein folding.
1.3 SIZE DEPENDENT PROPERTIES OF NANOMATERIALS
The various properties, which get tremendously altered due to the size reduction in at least one
dimension are:
a) Chemical properties: Reactivity; Catalysis.
b) Thermal property: Melting point temperature.
c) Electronic properties: Electrical conduction.
d) Optical properties: Absorption and scattering of light.
e) Magnetic properties: Magnetization.
1.3.1 Chemical Properties
• Based on the surface area to volume effect, nanoscale materials have:
a) Increased total surface area.
b) Increased number of atoms accessible on the surface.
c) Increased catalytic activity of those large number surface atoms.
d) Different/tunable surface catalytic properties by the change in shape, size and
composition.
• Hence, nanoscale catalysts can increase the rate, selectivity and efficiency of various
chemical reactions.
