Synthesis of nanomaterials Lecture note.pdf

Lecture note

1. Synthesis Of Nano Materials
Subject: Methods and Techniques of Experimental Physics
By
Dr. Hafiz Naeem-ur-Rahman

2. Introduction
Nanomaterialsdescribe,inprinciple,materialsofwhicha
singleunitissized(inatleastonedimension)between1
and1000nanometres.
Biological systems often feature natural, functional
nanomaterials. The structure of foraminiferaand viruses
(capsid), the wax crystals covering a lotus or nasturtium
leaf, spider and spider-mite silk are few examples of natural
nanomaterials.

3. Natural inorganic nanomaterials occur through crystal
growth in the diverse chemical conditions of theearth's
crust. For example clays display complex nanostructures
due to anisotropy of their underlying crystal structure, and
volcanic activity can give rise to opals, which are an
instance of a naturally occurring photonic crystals due to
their nanoscalestructure.
Introduction

5. PhotonicCrystals
A photonic crystal is a periodic opticalnanostructure that
affects the motion of photons. They are used to
manipulate light flow. Used to form colour changing
paints andinks.

6. Synthesis
Includes twomethods
Bottom UpApproach
Top DownApproach

7. TopDown
Start with bulk material and “cut away material “to
make what youwant.
Examples:
ATTRITION: In attrition, macro-or micro-scale
particles are ground in a ball mill, a planetary ball mill,
or other size-reducing mechanism. Theresulting
particles are air classified to recovernanoparticles.

8. TopDown
Lithography : It is a wafer scale process to prepare
homogenous 1D,2D or 3Dnanomaterials.
The method combines the advantages of both top down
and bottom up approaches and is a two step process:
The preparation of colloidal crystal mask (CCM) made ofnano
spheres.
The decomposition of desired material through themask.
The mask is then removed and the layer keeps the orderedpattern
of the maskinterstices.

9. BottomUp
Building what you want by assembling it from building
blocks (Such as atoms andmolecules).
Controlled
Controlled Processes involve thecontrolled delivery of
the constituent atoms or molecules to the site(s) of
nanoparticle formation such that the nanoparticle can
grow to a prescribed sizes in a controlled manner.

10. BottomUp
Bottom up approach are further classifiedinto 1.)
Gas (Vapor) Phase Fabrication:Pyrolysis
2.) Liquid Phase Fabrication: Solvothermal Reaction,Sol-
gel.

11. Bottom Up ApproachTypes

12. Simplest method of making nanoparticle in the form
ofpowder
Various types ofmills
•Planetary
•Vibratory
•Rod
•Tumbler
HIGH ENERGY BALL
MILLING

14. Consists of a container filled with hardened steel or
tungsten carbideballs
Material of interest is fed asflakes
2:1 mass ratio of balls tomaterials
Container may be filled with air or inertgas
Containers are rotated at high speed around a central
axis
Material is forced to the walls and pressed against the
walls

15. Controlthespeedofrotationanddurationofmilling-
grindmaterialtofinepowder(fewnmtofewtensof
nm)
SomematerialslikeCo,Cr,W,Al-Fe,Ag-Feetcare
madenanocrystallineusingballmill.

17. To form or arrest nanoparticles in glass
Glass –amorphous solid, lackingsymmetric
arrangement ofatoms/molecules
Metals , when cooled at very high cooling rates (10⁵-
10⁶ K/s) can form amorphous solids-metallicglasses
Mixing molten streams of metals at high velocity with
turbulence-formnanoparticles
Ex: a molten stream of Cu-B and molten stream ofTi
form nanoparticles ofTiB₂
MELTMIXING

18. Pyrolysis
Inpyrolysis,isaprocessinwhichathinfilmisdepositedbysprayinga
solutiononaheatedsurface,wheretheconstituentsreacttoforma
chemicalcompound.Thechemicalreactantsareselectedsuchthatthe
productsotherthanthedesiredcompoundarevolatileatthe
temperatureofdeposition
Theadvantagesofvaporphasepyrolysisincludeitbeingasimple
process,costeffective,acontinuousoperationwithhighyield.

19. Solvothermal Process
Precursors are dissolved in hot solvents (e.g., n-butyl
alcohol) and solvent other than water can provide milder
and friendlier reaction conditions. If the solventis water
then the process is referredtoas hydrothermal
method.
Itissynthesismethodforgrowingforcrystalsfromanon
aqueoussolutioninaautoenclave(athickwalledsteel
vessel)athightemperature(400deg.C)andpressure.

20. Sol-Gel
The sol-gel process is a wet-chemical technique (also
known as chemical solution deposition) widely used
recently in the fields of materials science andceramic
engineering.

21. StepsInclude
Formation of stablesol.
Gelation
Gel aging into a solid mass. This causes contractionof the
gel network, also phase transformations and Ostwald
ripening.
Drying of the gel to remove liquid phases. This canlead
to fundamental changes in the structure of thegel.

22. Nanoparticles synthesized by chemical methods form “colloids”
Two or more phases (solid, liquid or gas) of same or different materials co-exist
with the dimensions of at least one of the phases less than amicrometre
May be particles, plates orfibres
Nanomaterials are a subclass of colloids, in which the dimensions of colloids is in
the nanometrerange
COLLOIDS AND COLLOIDS IN
SOLUTION

24. Reduction of some metal salt oracid
Highly stable gold particles can be obtained by
reducing chloroauric acid (HAuCl₄)with tri sodium
citrate(Na₃C₆H₅O₇)
HAuCl₄+Na₃C₆H₅O₇ Au ⁺+ C₆H₅O₇⁻+ HCl+3NaCl
Metal gold nanoparticles exhibitintense
red, magenta etc., colours depending upon the
particle size
SYNTHESIS OF METAL NANOPARTICLES BY
COLLOIDALROUTE

26. Gold nanoparticles can be stabilised by repulsive
Coloumbicinteractions
Also stabilised by thiol or some othercapping
molecules
In a similar manner, silver, palladium, copper and few
other metal nanoparticles can besynthesized.

27. Wet chemical route using appropriatesalts
Sulphide semiconductors like CdS and ZnS can be
synthesized bycoprecipitation
To obtain Zns nanoparticles, any Zn salt is dissolved in
aqueous( or non aqueous) medium and H₂S isadded
ZnCl₂+ H₂S ZnS + 2HCl
SYNTHESIS OF SEMI-CONDUCTOR
NANOPARTICLES BY COLLOIDALROUTE

28. Steric hindrance created by “chemicalcapping”
Chemical capping-high or low temperature
depending on thereactants
High temp reactions-cold organometallicreactants
are injected in solvent like
trioctylphosphineoxide(TOPO) held at >300ºC
Although it Is a very good method of synthesis, most
organometallic compounds areexpensive.

29. 2types of materials or components-“sol” and“gel”
M. Ebelman synthesized them in1845
Low temperature process-less energy consumption
and lesspollution
Generates highly pure, well controlled ceramics
Economical route, provided precursors are not
expensive
Possible tosynthesize
nanoparticles, nanorods, nanotubesetc.,
SOL GELMETHOD

30. Sols are solid particles in a liquid-subclass of colloids
Gels –polymers containingliquid
The process involves formation of ‘sols’ in a liquidand
then connecting the sol particles to form a network
Liquid is dried-powders, thin films or even monolithic
solid
Particularly useful to synthesize ceramics or metal
oxides

32. Hydrolysis of
precursors
condensation
polycondensation
Precursors-tendency to formgels
Alkoxidesor metalsalts
Oxide ceramics are best synthesized by sol gelroute

33. For ex: in SiO₄, Si is at the centre
and 4 oxygen atoms at theapexes
oftetrahedron
Very ideal for formingsols
By polycondensationprocess
sols are nucleated and sol-gel isformed

35. Simple techniques
Inexpensiveinstrumentation
Low temperature (<350ºC)synthesis
Doping of foreign atoms (ions) is possibleduring
synthesis
Large quantities of material can be obtained
Variety of sizes and shapes arepossible
Self assembly or patterning ispossible
ADVANTAGES

36. BIOLOGICAL
METHODS

37. Greensynthesis
3types:
1.Use of microorganisms like fungi, yeats(eukaryotes)
or bacteria,actinomycetes(prokaryotes)
2.Use of plant extracts orenzymes
3.Use of templates like DNA, membranes, virusesand
diatoms

38. Microorganisms are capable of interacting with
metals coming in contact with hem through their cells
and formnanoparticles.
The cell-metal interactions are quitecomplex
Certain microorganisms are capable of separating
metalions.
SYNTHESIS USING MICROORGANISMS

39. Pseudomonas stuzeri Ag259 bacteria are commonly found
in silvermines.
Capable of accumulating silver inside or outside their cell
walls
Numerous types of silver nanoparticles of differentshapes
can be produced having size <200nmintracellularly
Low concentrations of metal ions (Au⁺,Ag⁺ etc) can be
converted to metal nanoparticles by Lactobacillus strain
present in buttermilk.

40. Fungi –Fusarium oxysporum challenged with gold or
silver salt for app. 3 days produces gold or silver
nanoparticlesextracellularly.
Extremophilic actinomycete Thermomonospora sp.
Produces gold nanoparticlesextracellularly.
Semiconductor nanoparticles like CdS, ZnS, PbS
etc., can be produced using different microbial
routes.

41. Sulphate reducing bateria of thefamily
Desulfobacteriaceae can form 2-5nm ZnSnanoparticle.
Klebsiellapneumoniaecan be used to synthesizeCdS
nanoparticles.
when [Cd(NO₃)₂] salt is mixed in a solution containing
bacteria and solution is shaken for about1 dayat
~38ºC ,CdS nanoparticle in the size range ~5 to 200 nm
can beformed.

42. Leaves of geranium plant ( Pelargonium graveolens)
have been used to synthesize goldnanoparticles
Plant associated fungus-produce compounds such as
taxol andgibberellins
Exchangeofintergenicgeneticsbetween
fungus andplant.
Nanoparticles produced by fungus and
leaves have different shapes andsizes.
SYNTHESIS USING PLANTEXTRACTS

43. Nanoparticles obtained using Colletotrichum sp.,
fungus is mostly spherical while thoe obtained
from geranium leaves are rod and diskshaped.

44. finely crushedleaves
(Erlenmeyerflask)
boiled in water ( 1min)
cooled anddecanted
added to HAuCl₄ aq.Solution
gold nanoparticles within aminute

45. CdS or other sulfide nanoparticles can be synthesized
usingDNA.
DNAcan bind to the surface ofgrowing
nanoparticles.
ds Salmon sperm DNA can be sheared to anaverage
size of500bp.
Cadmium acetate is added to a
desired medium like water, ethanol,
propanol etc.
SYNTHESIS USINGDNA

46. Reaction is carried out in a glass flask-facility topurge
the solution and flow with an inert gas likeN₂.
Addition of DNA should be made and then Na₂S can
be added dropwise.
Depending on the concentrations of cadmium
acetate, sodium chloride and DNA ,nanoparticles of
CdS with sizes less than ~10 nm can beobtained.
DNA bonds through its negatively charged PO₄ group
to positively charged (Cd⁺) nanoparticlesurface.

47. Various inorganic materials such as carbonates,
phosphates, silicates etc are found in parts of bones,
teeth, shellsetc.
Biological systems are capable of integrating with
inorganicmaterials
Widely used to synthesizenanoparticles
USE OF PROTEINS, TEMPLATES LIKE
DNA , S-LAYERSETC

48. Ferritin is a colloidal protein ofnanosize.
Stored iron in metabolic process and is abundant in
animals.
Capable of forming 3 dimensional hierarchical
structure.
24 peptide subunits –arranged in such a way that
they create a central cavity of ~6nm.
Diameter of polypeptide shell is 12 nm.
Ferritin can accommodate 4500 Featoms.
FERRITI
N

50. Ferritin without inorganic matter in its cavity is called
apoferritin and can be used to entrap desired
nanomaterial inside the proteincage.
Remove iron from ferritin to formapoferritin
Introduce metal ions to form metalnanoparticles
inside thecavity

52. Horse spleenferritin
diluted with sodium
acetate buffer (placedin
dialysisbag)
sodium+thioglycolic
acetateacid
dialysis bag keptunder
N₂ gas flow for 2-3hrs
PROCEDURE TO CONVERT FERRITIN TO
APOFERRITIN

53. solution needs to be
replaced from time totime
for 4-5hrs.
saline for 1hr
refreshedsaline
for 15-20hrs
APOFERRITIN

54. APOFERRITIN
mixed with NaCl and N-tris
methyl-2-aminoethanosulphonic
acid (TES)
aq. Cadmium acetate added and
stirred with constant N₂spurging
aq. Solution of Na₂S is addedtwice
with 1 hr interval.

55. Applications
Drug deliverysystems
Anti-corrosion barriercoatings
UV protectiongels
Lubricants and scratch freepaints
New fire retardantmaterials
New scratch/abrasion resistantmaterials
Superior strength fibres andfilms