The sol gel method is a process for synthesizing nanoparticles that involves dissolving a compound in a liquid to bring it back as a solid in a controlled manner. It allows mixing at an atomic level and results in small, easily sinterable particles. The key steps are hydrolysis and condensation of precursor molecules to form a sol, which then undergoes gelation and aging before drying to form the final product. The method offers advantages like precise size control and doping but is also substrate dependent and time consuming.

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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