To date aerosol flame synthesis is the most important manufacturing process for ceramic nanoparticles including silica, titania, ceria and zinc oxide with a total production volume of several million metric tons per year. The process advantages include low cost, scalability and purity of the formed product. It has been however limited to a very narrow range of oxidic product compounds. This contribution presents investigated strategies to overcome these limitations. I was able to successfully show, that a modified flame process (patented by ETH) can not only be used to synthesize salt nanoparticles (Grass et al. Chem. Commun. 2005) but also non-noble metal nanoparticles such as bismuth (Grass et al. J. Nanoparticle Res. 2006) and cobalt (Grass et al. J. Mater. Chem. 2006).

This new synthesis tool allowed the fast and low-cost preparation of a large range of highly interesting materials with novel electronic, optical and mechanical properties. This very market oriented research led to the development of improved sensors (Athanassiou et al. Nanotechnology 2006; Luechinger et al. Langmuir 2007), more stable bulk nanocrystalline metals (Grass et al. Nanotechnology 2007), metal matrix nanocomposites with beneficial mechanical properties (Grass et al. J. Mater. Chem. 2007) and magnetic nanobeads which can be used for magnetic separation applications.

The separation of compounds from mixtures is one of the major problems in chemical engineering. The complexity and cost of separation largely increases if the compounds which are to be separated have a similar chemical structure, are sensitive to increased temperatures and are initially present at low concentrations. To overcome these difficulties for the separation of proteins and antibodies, biochemists are currently using magnetic microbeads. The technology utilizes magnetic polymer beads which carry a surface functionality. The beads react with the target compound which can then be retrieved from the mixture together with the bead by magnetic forces. The high cost of the beads and the rather poor quality in respect of magnetic properties and low binding capacities very much limited the application of such materials to specialized research laboratories and ultra high-value biotechnological applications.

Besides low cost an ideal material for the use in magnetic separation has to fulfill a range of constraints including: small size (nm scale), good magnetic properties (ideally metallic Co, Fe, Ni), stability over a wide temperature and pH range and enabling the covalent and stable bonding of ligands. All these demands can be met by applying covalently functionalized carbon coated cobalt nanoparticles (Grass et al. Angew. Chem. Int. Ed. In press) which were prepared by flame synthesis and functionalized by the use of diazonium chemistry yielding chloro-, nitro-, and amino terminated nanobeads.

References:

[1] R. N. Grass, T. F. Albrecht, F. Krumeich, W. J. Stark, J. Mater. Chem. 2007, 17, 1485.

[2] R. N. Grass, E. K. Athanassiou, W. J. Stark, Angewandte Chemie 2007, accepted.

[3] R. N. Grass, M. Dietiker, R. Spolenak, W. J. Stark, Nanotechnology 2007, 18, 035703.

[4] R. N. Grass, W. J. Stark, Chem. Commun. 2005, 1767.

[5] R.N. Grass, W. J. Stark, J. Nanopart. Res. 2006, 8, 729.

[6] R. N. Grass, W. J. Stark, J. Mater. Chem. 2006, 16, 1825.

[7] N. A. Luechinger, S. Loher, E. K. Athanassiou, R. N. Grass, W. J. Stark, Langmuir 2007, 23, 3473.

[8] E. K. Athanassiou, R. N. Grass, W. J. Stark, Nanotechnology 2006, 17, 1668.