NANOMATERIALS FOR ADVANCED APPLICATIONS

SHRIRAM INSTITUTE FOR INDUSTRIAL RESEARCH19, UNIVERSITY ROAD, DELHI-110 007

Email : sridlhi@vsnl.com Website : www.shriraminstitute.org

Presented by :Dr. R.K. KHANDAL

Outline Materials

Nanomaterials

Nanomaterials

Applications of Nanomaterials

Experiences of SRI

Properties

Domain Process Dimensions

Challenges Properties

Definition

Classification

Features

Classification of Materials (Type & Structure)

Composites

Ceramics

Polymeric

Crystalline

Polycrystalline

Amorphous

Metallic

Electronic

Biomaterials

NanomaterialsNanomaterials include all classes of materials at the nanoscale

Nanomaterials are categorized as 0-D (nanoparticles),1-D (nanowires, nanotubes, nanorods), 2-D (nanofilms, nanocoatings), 3-D (bulk)

Properties of Materials : Critical Factors (Bulk Vs Nano)

DefectsDefects

+

Mechanical

Optical

Thermal

Magnetic

At the nanoscale, interactions with heat ,light, stress, electrical field & magnetic field give rise to interesting & novel properties

A thorough understanding of the nature of interactions at the bulk & nano levels are essential for designing nanomaterials

Internal Internal StructureStructure

Bulk

(Macro & micro)Nano

SizeSize

ShapeShape

Surface area to Surface area to Volume ratioVolume ratio

+

+

Nanomaterials:

Materials consisting of particles of the size of nanometer

Volume = Surface Area * Thickness

For a given volume:

Surface area Thickness

More atoms at surface than in the interior

Extraordinary activity

SCOPE: DEFINITION

SCOPE : DOMAIN

Keywords Domain

Particle size Distribution in the continuous phase

Modification of surfaces Interfacial tension

Surfaces Interfaces

Rising volume fraction Homogeneity of phasesof dispersing phase

Domain of Nanotechnology: Multi-phase systems Liquid : Liquid

Solid : Liquid Surfaces and interfaces involving different phases

Gas : Liquid

Gas : Solid

Systems Process

Emulsion Macro Micro

Dispersion Coarse Fine

Solution Colloid

SCOPE: PROCESS

A process to create a continuous dispersed phase as fine as possible for homogeneity with the dispersing phase

(Liquid / Liquid; Gas/Liquid)

(Solid / Liquid)

(Solid / Liquid; Liquid/Liquid)Solubilization

SCOPE : DIMENSIONS

What Happens Dimensions

Particle size More from less

Surface area Enhanced coverage

Activity Novel products

Efficiency Improved performanceper unit mass

Maximum possible benefits from minimum possible inputs

Effecting changes through and at atomic scale

Nanomaterials: Features

Synergistic combinations of materials of different kinds & characteristics is possible through nanotechnology

Coatings, Films

Surface modificationSize Reduction

10 nm

1 m

1 cm

Compatibility Huge interfaces

Solid Liquid

Homogeneous solution

Inorganic nanoparticles in a liquid media

+

Process of making Nanomaterials

Process steps Inputs

Macro

Micro

Nano

Challenges: Process Technology

Challenge: To have a process that can convert macro materials into nanomaterials spontaneously & with minimum efforts

Energy

Bulk

Sugar cube

Nano

Dissolved sugar/salt

Bulk

Output

Salt

Multi-phase systems: Approach

Ability to design materials with tunable properties In-situ way of production of nanomaterials leads to more

homogeneous matrix with higher loading of nanoparticles

Physical Ball milling Gas condensation E-beam evaporationVapour depositionSputtering

Chemical Microemulsion Sol-gel Chemical reduction

Ex-situ

In-situ

•Bulk production

•Reproducibility

•Stability

•Cost

• Single step• Non-agglomeration• Better Stability• Interfacial interaction

Hydration HydrolysisSolubilization Chemical conversionPrecipitation

Concerns

Benefits

Synthesis of Nanomaterials: Ex-situ

TiO2 TiO2

-

-

-

-

-

-

TiO2

TiO2

-

-

-

-

-

-

MonomerPolymer

Surfactant

-

-Radical

Polymerization

10 nm

100 µm

Grinding

Latex Fe2O3-Particles

Fe2O3-ParticlesLatex bead

Pre-treatment

Polymerization

Copolymer layer

Encapsulated particle

Amphiphilic molecule

Monomer

Ex-situ synthesis of nanomaterials involves number of steps

Polymer encapsulated nanomaterials used for targeted delivery of drugs-good example of ex-situ synthesis

Synthesis of Nanomaterials : In-situ

Metal salt + Monomer

Adopting in-situ approach of synthesizing nanomaterials reduces

number of steps involved and hence simple process !

Nanocomposite

1. Hydrolysis

2. Polymerization

Designing Nanomaterials : Approaches

Metal

Ceramic

Polymer

Matrix Reinforcing phase

Inorganic

Metals & inorganic

Metals

Examples

Carbides, borides, nitrides, oxides, etc.

SiC, Zr, Fe, W, Mb, Ni, Cu, Co, etc.

C nanotubes, alumina, silica, etc.

Nanocomposites have tremendous scope in all areas of science & technology.

0 - D

1 - D

2 - D

Dimension

Thermal conductivity is more prominent in 1-D & 2-D nanomaterials Thermal conductivity of C nanotubes (2-D nanomaterial) = 3000 Wm-1K-1;

Copper (bulk) = 400 Wm-1K-1

Structure of Nanomaterials: Size and Shape

3 - DBulk

x , y , z

Nanocomposite thick film

Rods

TubesWires

d=100 nm

d 100 nm

Example

Nanoparticles

NanofilmsNanocoatings

Application

Bottle-neck

Waveguides

Components for PC, Mobile phones

x , y

x

Nil

Direction of confinement

Unique Properties of Nanomaterials

Nano-sizeBulk Properties

Thermal • S / V• Heat

transport

Small

Electrons

Large

Phonons

Unique properties at the nanoscale have led to the use of nanomaterials in fields where conventional materials have limitations

Magnetic

Optical

• Super-paramagnetism

Absent Prominent

• Absorption

• Emission

• Reflection

Bulk effects

Material dependent

Surface Plasmon effects

Size dependent

Thermal Properties

Transportation of Heat: Nanomaterials

Mechanism of heat travel : Electrons (metals) &

Phonons (non-metals)

Phonons L nanostructure; Phonons < L macrostructure

When size of the material is reduced to nanoscale,

quantum confinement occurs

Confinement at nanoscale occurs in 0-D (x, y, z directions), 1-D (x,y directions), 2-D (x direction) and 3-D (bulk)

Quantum confinement effects ~ electron transport mechanism of bulk materials

Pt bulk

Pt 28 nm

Pt 15 nm 0 (

W/m

K)

T0 (K)

Properties of Nanomaterials : Thermal Conductivity

Separate 2 crystals of same materials with different orientations (grain boundary)

Separate 2 crystals of different materials (multilayer structure; different densities & sound velocities)

Phonon scattering at the interface

Interface

In nanosystems, there is presence of huge interfaces

Interfaces Thermal resistance

Phonon scattering Thermal conductivity

Films

Magnetic Properties

Magnetism in Nanomaterials

Strong coupling

Critical particle size : below which material will be in

single domain; hence magnetism

If particle size is << critical diameter, loss of

magnetization occurs; super-paramagnetism

Interaction energy is effective at sizes less than critical

diameter but above super-paramagnetism

Critical diameter of Co = 70 nm & Fe = 15 nm

Small size of particles

Features Consequence

Dominance of exchange forces

Alignment of spins

Hc

D sp D crit

Single Domain Multi- Domain

Magnetic Properties

Coercive field of Ferromagnetic materials with particle sizeParticle size < Dcrit Single domain Magnetization

Particle size <<< Dcrit Super-paramagnetism

Optical Properties

Optical effects:Metamaterials

=µrr

Most promising area of application : Metamaterials Size, shape & composition of embedded nanoparticles influence

the interactions with light, heat ,sound & waves etc

1

2

1

2

+ve R.I.

-ve R.I.

Refractive Index

=µrr

µr: Permeability to magnetic fieldr: Permeability to electric field

• µr, r= -ve

• Induced phenomena

µr, r= +veNatural phenomena

Photocatalytic Properties

SOLAR SPECTRUM

Visible light (43%)

X-rays Micro wave

Radio wave

Infra red radiation (54%)

UV (3%)

Long Wavelength

1012 nm106 nm700 nm

Chemical changes : Bond Dissociation Bond Formation Rearrangement Electron transfer

The energy of electron 1.23 eV 1000nm; thus, energies corresponding to < 1000nm can bring about chemical changes.

The region from 200nm to 1000nm is most useful for photochemical conversion.

Lu

x

400 nm 109 nm 1014 nmWavelength,Short Wavelength

200 nm

SOLAR SELECTIVITY : MATERIALS RESPONSE

Frequency (Hz)

Visib

le

Infrared

Ultraviolet

X-rays

Cosm

ic rays

1081010101210141016101810201022

Rad

iofrequ

ency

Gam

ma rays

Microw

ave

High Potential for harnessing the solar energy

Processes involved Inner

electronic transition

Outer electronic transition

Molecular Vibrations

Molecular rotations vibrations

Electron spin resonance

Nuclear magnetic resonance

Change at atomic & molecular levels can become the via media for harnessing solar energy.

Solar sensitive materials undergo region specific transition Solar energy conversion

PHOTOCHEMICAL CONVERSION : MECHANISM

The Energy E of single photon is given by the Planck equation:- E=h= hc/ Sun light

.

…….. ...………………………………electron

Excitation photon

excited state

Non-radiative relaxation

Conduction band

Valence band

h+

e-

Band gap

E=h

Every photochemical conversion process requires as an initial steps the absorption of photon energy and conversion into the internal energy of the first excited state of the molecule of the material

=Number of events

Number of photons absorbed

………………………………

Applications of Nanomaterials

The play of light on a butterfly’s wings has inspired designing of novel photonic materials for solar cells, photovoltaics, camouflaging, optical fibers and military applications

Invisibility cloak

Color play

Tailor-making of refractive index and dielectric constant

Nanomaterials : Camouflaging

Nanomaterials: Photochemical Conversion

Advantages

Utilization of unabsorbed part of solar spectrum

Reduced heat dissipation

Quantum Dots

100 nm50 nm

Re

act

ivit

y

10 nmSize (nm)

Nanotubes & nanowires

Mesoporous

MATERIALS FOR ENERGY CONVERSION : SEMICONDUCTORS

Challenge is maneuver the band gap:make it sensitive to visible light.

6.3 eV 3.15 eV 1.58 eV

U.V

200 nm 400 nm 800 nm

Visible

TiO2

ZnOCdS

WO3

Band gap Energy

EMS()

TiO2 = 3.20 eV

ZnO = 3.35 eV

WO3 = 2.80 eV

CdS = 2.42 eV

Semiconductors are the most ideal and preferred materials.

Nanomaterials: Self-Cleaning

Hydrophobic Photocatalytic

Designing of materials with novel effects like hydrophobic, hydrophilic, photocatalytic, etc. has made possible new applications like self cleaning, coatings, etc.

CoatingDirt run-off

LightCoating

Roll-off effect

Nano materials

101

Ti alloysBrassMild steelAl alloysCopper

Lead

PE, PAPP, ABSPS, PETPVC

AluminaZirconia

Glass

ConcreteBricks

Metals Polymers Ceramics

Ideal StrengthHigh Strength Building Materials

Yie

ld S

tren

gth

(y)

/ Y

oung

’s M

odul

us (

E)

10-4

10-3

10-2

10-1

Bulk materials fall short of the ideal values in every aspect; mechanical, optical, electronic, magnetic, thermal, etc.

Nanostructure, nanolayers & amorphous materials are strongest

Density (Mg/m3)

Foams

Natural materials

Polymer nano- composites

Polymers

Metals

Metallic nanocomposites

Nanocrystalline metals

Ceramics

Standard composites

Nanotubes & fibers

You

ng’

s M

odu

lus

(GP

a)

Elastomers

Ceramic nanocomposites

0. 1 1.0 10

10-4

1

10

100

10-3

1000

High Strength Materials: Smart Materials

Foams

Natural materials

Polymer CNT composites

Polymers & Elastomers

Metals

Metallic nanocom-posites

Nanocrys-talline metals

Ceramics

Standard composites

Nanowires (Cu, Ag, Au)

Ten

sile

Str

engt

h (

MP

a)

Density (Mg/m3)0. 1 1.0 10 100

0.1

10

100

104

1

105

Polymer-Ceramic nanocomposites

3-D ceramic nanoco-mposite

1-D metallic nanostructures

1-D C-nanostructures

103

Engineering Nanomaterials

Nanomaterials

Green Materials : Nanoengineered Concrete

Nanosilica

Precipitated Silica

Silica fume

MetakaolinFinely ground

mineral additivesPortland cement

Fly ash

Aggregate fines

Natural sand

Coarse aggregates

Nano engineered concreteHigh strength/ high

performance concrete

Conventional concrete

100 101 102 103 104 105 106 108107

10-1

10-2

100

101

102

103

104

105

106

Particle size(nm)

Sp

ecif

ic S

urf

ace

Are

a(K

g/m

2)

Nanoparticles allow better void filling & positive filler effects & improved bond between pastes aggregates; nanosized additives increase strength beyond what is attained with conventional materials

SRI’S EXPERIENCE

SRI has developed nanomaterials for :

Optical applications

Effluent treatment

39393939393939

High Refractive Index Materials

The refractive index of low refractive index materials increases from 1.49 to 1.66.

1 . 4 1

1 . 4 7

1 . 5 3

1 . 5 9

1 . 6 5

1 . 7 1

0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0

% o f a d d i t i v e

Ref

ract

ive

ind

ex

40404040

Refractive index increases with increase in percentage of metal salt.

1.41

1.42

1.43

1.44

1.45

1.46

1.47

1.48

0 5 10 15 20 25 30Metal salt (% by wt)

Ref

ract

ive

Ind

ex

Barium Hydroxide Lead Monoxide Lanthanum Oxide

High Refractive Index Acrylates

414141414141

High Refractive Index Titanium Nanocomposites

In-situ formation of nanoparticles of TiThe refractive index of the polymer increases from 1.45 to

1.53

1.44

1.46

1.48

1.5

1.52

1.54

0 2 4 6

% Ti

Re

fra

cti

ve

Ind

ex

Photocatalytic Material : Doped TiO2

XRD analysis confirms the doping of TiO2

Change in lattice parameter ‘a’ & ‘c’ of TiO2, confirms the

incorporation of Cd2+ in Ti4+

Influence TiO2 Doped TiO2 Doped TiO2 factor (In-situ) (External)

a/nm 3.0301 3.3184 3.3558 c/nm 9.5726 10.0136 11.2138

Inte

nsi

ty(a

.u.)

Position (2 Theta)20 30 40 50 60 70 80

External

In-Situ method

TiO2 market procured

TiO2 (Reference)

0 . 0 0

0 . 5 0

1 . 0 0

1 . 5 0

2 . 0 0

2 . 5 0

3 . 0 0

3 . 5 0

4 . 0 0

2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0

W a v e l e n g t h

Ab

so

rba

nc

e

M G A

B C

Semiconductors are used to prepare nanocomposites with enhanced photocatalytic activity

Dye

Nanocomposites & dye degradation

Nanocomposites lead to complete degradation of dyeUseful for the treatment of dye effluents

91.29 92.30 94.49

37.29

86.61 87.19

0

20

40

60

80

100

A B C

Deg

rad

ati

on

rate

(%)

Nano

Normal

Nanocomposites for dye degradation

Dye solution

Nanocomposite

Dye removal

Swelled nanocomposite after uptake of dye

Dye removal from effluent

Nanocomposites for Effluent Treatment

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