The word 'nano' is getting popular by the day in all fields. Strictly speaking, the word 'nano' refers to particle size less than 50 nano meters, though a size range of 100 nm is seldom considered. Even slight variation in the particle size may result in entirely different properties of the particles (See photograph of different coloured Cadmium selenide nanoparticles).

Synthesising uniform nano sized particles is still a challenge to scientists. Prof Dr Helmut Bönnemann of the world renowned Max-Planck Institute (Germany) for Carbon Research (Kohlenforschung) is a pioneer in this field. The institute is known for many firsts.

Our own Bangalorean young scientist Dr K S Nagabhushana, who worked as one of the senior members of Prof Bonnemann's group, spent five years with him. Nagabhushana, who is an expert in Synthesising 1-5 nm sized metal nanoparticles, was directly involved with the synthesis of various metal nanoparticles, which proved to be of tremendous implication in the nano industry (eg. catalysis).

The impact of the ‘Bönnemann Method’ has provided nanochemists with an answer to the greatest challenge that existed then and even today - the monodispersity of the nanoparticles.

Metal nanoparticles with diminished sizes (1-10 nm) are prone to agglomeration (combining together) and oxidation. A stabiliser is therefore needed to prevent this. Also, any particular special property of nanoparticles is attributed to their unique uniformity in size and therefore obtaining such particles becomes essential.

In the present method, nanoparticle synthesis was achieved when the reducing agent was used in combination with the stabiliser. Since only gaseous by-products are generated during synthesis, evaporation of solvent should result in a colloid that can be isolated in the form of a solid and can be re-dispersed in various solvents in high concentration of the metal.

The method is applicable for generating most of the transition metal nanoparticles and their combinations having different structures, not possible by any wet chemical methods known so far. According to Nagabhushana, success does not come without expertise to make this work. The conditions that is necessary to carry out these reactions makes it “not in any lab” work practice.

“Any student who enters Bonnemann's group will receive training for one month, just to get to know how to make these reactions with utmost cleanness and the accuracy and precision to which Germans are known in the world,” explains Nagabhushana.

While generating metal colloids formed one part of the problem, applying them to various technologies formed another issue. The prestigious Apollon Project (funded by the European Union) was to use them for low temperature PEMFC (proton exchange membrane Fuel Cell) applications.

The prime objective of his group in the project was to prepare catalysts with optimised catalytic performances and their arsenal was colloidal precursor synthetic route. The colloidal metal nanoparticles were used as precursors of the catalyst. By suitable deposition of these colloidal precursors on the support material, a uniform carpet of the colloidal metal nanoparticle on the support is generated.

In the subsequent step, the stabiliser is removed, leaving behind naked metal nanoparticles on the support that can be readily used as a catalyst.

Use of natural product (cashewnut shell liquid), which was Nagabhushana's doctoral thesis material, as a metal nanoparticle stabiliser was also revealed and many commercially available products are now seen due to this unique property. He explains that in future cashewnut oil business may grow into a million dollar trade!

Dr Nagabhushana can be contacted at nagbhushana@yahoo.com