Question

Nanotechnology is a field of research and innovation concerned with building 'things' - generally, materials and devices - on the scale of atoms and molecules. A nanometre is one-billionth of a metre: ten times the diameter of a hydrogen atom. The diameter of a human hair is, on average, 80,000 nanometres. At such scales, the ordinary rules of physics and chemistry no longer apply. For instance, materials' characteristics, such as their colour, strength, conductivity and reactivity, can differ substantially between the nanoscale and the macro. Carbon 'nanotubes' are 100 times stronger than steel but six times lighter.

make a case study should consider either :

1. Methods of nano-particle manufacturing
2. Application of nano-particle in chemical engineering field.

Answer 1

Methods of nano-particle manufacturing

The manufacturing of nanoparticle can be described in two ways bottom up approach and top down approach. Bottom up approach refers to the build-up of a material from the bottom, atom by atom or molecule by molecule.Whereas,Top down approach refers to slicing or successive cutting of bulk material to get Nano sized particle. In top down techniques, the starting material is solid state.

Top-Down Approach

Top down refers to the traditional workshop or micro fabrication method where tools are used to cut, mill and shape materials into the desired shape and order. Bottom up refers to methods where devices „create themselves‟ by self-assembly. Chemical synthesis is a good example. Bottom-up should broadly speaking be able to produce devices much cheaper than top down method, but getting control over the method is difficult when things become larger and more bulky than what is normally made by chemical synthesis.

One of the example of Top Down Approach is Mechanial Milling :

Nanoparticles from mechanical attrition are produced by a top down process. Nanoparticles formed in mechanical device, generally referred to as a mill in which energy is imparted to a course-grained material to effect a reduction in particle size. The fundamental principle of size reduction in mechanical devices lies in the energy imparted to the sample during impacts between the milling media. This model represents the moment of collision, during which particles are trapped between two colliding balls within a space occupied by mass of powder particles.

Bottom-Up Approach

This invloves the spontaneous organization of molecules into stable, structurally well-defined aggregates in nanometer length scale.Here, molecules can be transported tosurfaces through liquids to form self-assembled monolayers. Fabrication is much less expensive than the Top down approach. Also it minimizes the wastage of material, maximazing the output product.

One of the example of Bottom Up Approach is Chemical Synthesis :

Spherical shaped silver nanoparticles were synthesized through chemical reduction method using tri Sodium citrate as reducing agent and PVA as surfactant. It was found that size of the nanoparticles can be tuned by simply varying pH of the reaction system. A new method to synthesize well dispersed Cobalt (Co) needle shaped (acicular) nanoparticles in water by a room temperature chemical reduction route.

For synthesis of nanoparticle by chemical method we need three important components metal salt, reducing agent and capping agent. The reducing agent will reduce metal salt into metal nanoparticle. But these metal nanoparticles are highly unstable so it will try to join together and form the agglomeration and aggregation. So, to make the nanoparticle stable we have to add a capping agent or stabilizing agent that will prevent the agglomeration and aggregation.