SOLGEL method for the synthesis of nanopaticles

1. Sol gel method for
synthesis of nanoparticles
Course title: Nanotechnology
Presented by: Sehrish Inam
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2. Sol gel
• A sol is a stable dispersion of particles or polymers
in a solvent. The particles may be amorphous or
crystalline.
• A gel consists of a three dimensional continuous
network, which encloses a liquid phase.
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3. Idea behind sol-gel method
• To “dissolve” the compound in a liquid in order to
bring it back as a solid in a controlled manner.
• Enables mixing at an atomic level.
• Results in small particles, which are easily sinterable.
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4. Sol gel
method
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5. History
• Developed in the 1960s
• A method was needed where dust was reduced
(compared to the ceramic method) and which needed
a lower sintering temperature.
• Needed synthesis by remote control.
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6. SOL GEL PROCESS
• A sol-gel process occur in several steps:
▫ Hydrolysis and condensation of molecules.
▫ Formation of a sol.
▫ Gelation
▫ Ageing.
▫ Drying.
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7. Example; SILICA
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8. HYDROLYSIS
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9. CONDENSATION
• Parameters which influences the condensation
process:
▫ Type of precursor
▫ The ratio between alkoxide and water (RW)
▫ Type of catalyst used
▫ Type of solvent
▫ Temperature
▫ pH
▫ Relative and absolute concentrations of the reactants.
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10. Network Formation
• As the sol aggregates the viscosity will increase until
a gel is formed.
• The sol-gel transition (gel-point) is reached when a
continuous network is formed.
• The gel-time is determined as the time when it is
possible to turn the container upside-down.
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11. Gel Point
• When the gel is formed, a large number of sol
particles and clusters will still not have reacted.
• Ageing of the gel is very important stage in the
process.
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12. Ageing
• As the viscosity increase, the solvent is “trapped” inside
the gel.
• The liquid phase still contains sol particles and
agglomerates, which will continue to react, and will
condense as the gel dries.
• Hydrolysis and condensation are reversible processes.
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13. Drying
• Normal drying of the gel leads to reducing the pore size.
• OH groups on opposite sides may react and form new
bonds by condensation.
• Gas will enter the pores with a thin film of liquid on the
walls. This will evaporate and only isolated spaces with
liquid are left.
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14. Advantages of Sol gel method
• Sol-gel synthesis may be used to prepare materials
with a variety of shapes, such as porous structures,
thin fibers, dense powders and thin films.
• Obtain pure , size controlled stable and
monodispersed nanoparticles ranges 20-200 nm.
• Precise control over the doping level is also easier in
this process
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15. Disadvantages of Sol gel method
• This technique is quite substrate dependent.
• Metal alkoxides are the most preferred precursor.
But they are expensive.
• We have little control over porosity of the gel which
inturn affects the rate of solvent removal from the gel
in order to form the final powder.
• Formation of gel is a slow process, which makes sol
gel a time consuming fabrication technique as
compared to other methods (combustion synthesis).
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