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SOLGEL method for the synthesis of nanopaticles

1. Sol gel method for synthesis of nanoparticles Course title: Nanotechnology Presented by: Sehrish Inam 1 3/21/2020

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 . 2 3/21/2020

3. Idea behind sol-gel method T o “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 . 3 3/21/2020

4. Sol gel method 4 3/21/2020

5. History D eveloped 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 . 5 3/21/2020

6. SOL GEL PROCESS A sol-gel process occur in several steps: Hydrolysis and condensation of molecules. Formation of a sol. Gelation Ageing. Drying . 6 3/21/2020

7. Example; SILICA 7 3/21/2020

8. HYDROLYSIS 8 3/21/2020

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. 9 3/21/2020

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 . 10 3/21/2020

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 . 11 3/21/2020

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 . 12 3/21/2020

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. 13 3/21/2020

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 14 3/21/2020

15. Disadvantages of Sol gel method T his 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. F ormation of gel is a slow process, which makes sol gel a time consuming fabrication technique as compared to other methods (combustion synthesis ). 15 3/21/2020

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