TOP-DOWN & BOTTOM-UP
APPROACH FOR
NENOPARTICALS SYNTHESIS
Presented by:
Almas Rana
PH-04/2018
Nanotechnology
PH-524
Nanoparticle Fabrications
• Design and fabricate nanoparticles that have suitable properties for
application.
• Methods of obtaining nanomaterial vary and mostly depend on the
material, its morphology and also the targeted applications
Key Issues For Nanoparticles Synthesis
• Uniformity of particle size
• Size control
• Shape control
• Crystal structure uniformity
• Purity
Synthesis of nanomaterial
Two general approaches based on the phase of
starting material:
TOP-DOWN APPROACH
Slicing or successive cutting of bulk materials to
get neno sized particles
BOTTOM-UP APPROACH
Built up of the material from the bottom, atom to
atom or molecule to molecule to get to neno
scale
Processing Method
Top-Down
Physical processing methods:
methods:
Bottom-Up
Chemical processing
Mechanical methods :
- Sol gel method
- cutting , etching, grinding
- Two phase method
- ball milling
- Co precipitation method
Lithographic techniques:
- Polyols method
- Photo Lithography
- Electron Beam Lithography
- Hydrothermal reaction
- Sonolysis
Advantages
Top-Down
• Large scale production
Bottom-Up
• Ultra-fine nanoparticles, nanoshells,
nanotubes can be prepare
• Quick to manufacture
• Cheaper technique
• Chemical purification is not
• Narrow size distribution (1-20 nm)
required
Disadvantages
Top-Down
Bottom-Up
• Broad size distribution (10-1000 nm)
• Large scale production is difficult
• Varied particle shapes or geometry
• Presence of impurities
• Chemical purification of nanoparticles
is required.
• Expensive technique
Sol-Gel Method
Steps involved
• Hydrolysis and condensation of molecule
• Gelation
• Ageing
• Drying
• calcination
Steps
• Metal alkoxides or inorganic salts as precursors is used.
• Precursors undergoes a series of hydrolysis and condensation reaction to
form a colloidal suspension or a sol.
• Transition of system from liquid “sol” (mostly colloidal) into a solid “gel”
phase.
• Drying of the gel followed by calcination at different temperatures to obtain
the metal oxide nanopowder
Advantage
•
In sol-gel method it is possible to control the shape, morphology and textual
properties of the final materials
•
Superior purity and compositional homogeneity can be achieved
•
This technique offers ability to control porosity to obtain high surface area materials
•
Iron oxide-silica gel composites are 2-3 times more reactive than conventional iron
oxide.
•
Ceramic and glass materials can be obtained in a wide variety of forms: ultra-fine
or spherical shaped powders, thin film coatings, ceramic fibres, microporous
inorganic membranes.
Disadvantage
• Weak bonding
• High permeability
• Difficulty in controlling porosity
• Substrate dependency
• Contamination from by-products needs to be post treated
Thank you