Question

What do you mean by sol and gel? Describe the sol-gel method of preparation for nanoparticles.

Answer 1

(1) Sol : Sols are dispersions of colloidal particles in a liquid. Colloids are solid particles with diameter of 1-100 nm.

(2) Gel : A gel is interconnected rigid network with pores of submicrometer dimensions and polymeric chains whose average length is greater than a micrometer.

(3) Sol-gel Process : A sol-gel process is an inorganic polymerisation reaction. It is generally carried out at room temperature, it includes four steps : Hydrolysis, polycondensation, drying and thermal decomposition. This method is widely used to prepare oxide materials.

The reactions involved in the sol-gel process are as follows :

MOR + H₂O → MOH + ROH (hydrolysis) metal alkoxide

MOH + ROM → M-O-M + ROH (condensation)

• Formation of different stable solution of the alkoxide or solvated metal precursor.
• Gelation involves the formation of an oxide or alcohol-bridged network (gel) by a polycondensation reaction.
• Aging of the gel means during that period gel transforms into a solid mass.
• Drying of the gel involves removal of water and other volatile liquids from the gel network.
• Dehydration is achieved when the material is heated at temperatures up to 800°C.