Question

Explain any three characteristic features of nanoparticles.

Answer 1

The following are the characteristic features of nanoparticles:

1. Colour: It is an optical property that is different at the nanoscale.
   e.g. Elemental gold has a shining yellow colour. However, if only 100 gold atoms are arranged in a cube, its colour would be much more red.
2. Surface area: High surface-to-volume ratio is a very important characteristic of nanoparticles. If a bulk material is a sub divided into a group of individual nanoparticles, the total volume remains the same, but the collective surface area is largely increased. With a large surface area for the same volume, these small particles react much faster because more surface area provides more number of reaction sites, leading to more chemical reactivity.
3. Catalytic activity:
   a. Due to an increase in surface area with the decrease in particle size, nanomaterial-based catalysts show increased catalytic activity.
   b. Usually, they are heterogeneous catalysts that means catalysts are in solid form and the reactions occur on the surface of the catalyst.
   c. Nanoparticle catalysts can be easily separated and can be recycled.
   e.g. Pd, Pt metal nanoparticles used in hydrogenation reactions.
   TiO₂ and ZnO are used in photocatalysis.
   Gold in bulk form is unreactive, but gold nanoparticles are found to be a very good catalyst for various organic reactions.
4. Thermal strength: The melting point of nanomaterial decreases and depends on size.
5. Mechanical properties: Nanoparticles have a far higher hardness than bulk material.