Nanotechnology/Nanometals

Quick Review of nanometals

Nanometal (also called metal nanoparticles) is very attractive and that is because of their size and shape dependent properties. The optical properties (linear and nonlinear) depend on that and they on dominated by something called the collective oscillation of conduction electrons. There are so many ways that you can prepare metal nanoparticles but the most used methods are based on wet chemistry. You can find nanometal being used in medical applications to the weaponry the military use. Nanometals also have a thing called Surface Plasmon Resonance (SPR) this is what cause the change in colors that we see. For example in the 4th century when the Lycurgus cup was created. The cup changes red when the light is shone inside of the cup and green when reflective light is shone on the outside of it. There are so many methods that you can prepare nanometals and the most popular way is by reducing HAuCl₄ (chlorauric acid) in a sodium citrate solution that is boiling and then the formation of gold nanoparticles are revealed by a deep red color that looks like wine in about 10 min.

Types of nanometal synthesis

The most common types of nanometal synthesis deal with 'wet' methods in which metal nanoparticles are produced in a colloid with an organic material of some sort.

Gold nanoparticles can be produced by either:

1) Reduction of HAuCl₄ in a solution of sodium citrate, then boiling it, causing gold nanoparticles to form in a wine-red solution.

2) Mixing HAuCl₄ in water, which produces a solution that is subsequently transferred into toluene using tetraoctylammonium bromide (TOAB), a phase transfer catalyst. Phase transfer catalysts help reactants dissolve in organic (carbon-containing) material where the reactant otherwise couldn't w/o the PTC. Afterwards, the solution is stirred with sodium borohydride, in the presence of certain alkanes, which bind to the gold in the solution, allowing for the formation of gold nanoparticles.

Synthesis of other metal nanoparticles can possibly be achieved by reducing metal salts in organic solvents such as ethanol, or by variations of the above methods which synthesize gold nanoparticles.