Core-Shell Nanomagnets for Magnetic Chemistry and Precious Metal Recovery: Long-Term Stability In Acids and Organic Solvents

Core-shell nanomagnets for magnetic chemistry and precious metal recovery: Long-term stability in acids and organic solvents

Christoph M. Schumacher, Robert. N. Grass, Alexander Schätz,

Wendelin J. Stark*

*Institute for Chemical- and Bioengineering,

Department of Chemistry and applied Biosciences,

ETH Zurich, HCI E 107, Wolfgang-Pauli-Strasse 10,

8093 Zurich, Switzerland, email: wstark@ethz.ch

The use of magnetic nanoparticles has gained increasing attention in a multitude of application areas over the past years. Comparably high and readily available specific surfaces in combination with the ease of separation make these kinds of materials promising candidates as precious metal extraction agents (Rossier, 2009) and in magnetic chemistry where a reagent is linked to a nanomagnet, enabling fast separation (Grass, 2007). The chemical stability in conjunction with a high saturation magnetization is decisive parameter for a broad range of practicability.

In the following work we examine the long-term stability of core - shell cobalt - carbon and ironcarbide - carbon nanoparticles under distinct conditions such as strong acidity and alkalinity compared to other well established magnetic nanomaterials, such as iron oxide nanoparticles and silica coated iron oxides. Therefore we treat the corresponding materials under the mentioned conditions for several weeks with constant monitoring of the stable fractions. In addition, the extraction of several precious metal species under relatively harsh conditions is investigated concerning kinetics, selectivity and the influence of the carbon shell properties.

This contribution will further show how ultra-stable nanomagnets allow an extension of magnetic separation from its present broad use in biochemistry to catalysis (Schaetz, 2010).

Figure 1. The use of chemically stable nanomagnets enables to tag classical molecules and enables their separation after use within seconds. This is of particular interest for recycling of precious reagents, noble metal extraction and in fine chemical synthesis.

References

M. Rossier, F.M. Koehler, E.K. Athanassiou, R.N. Grass, B. Aeschlimann, D. Günther, W.J. Stark, Gold adsorption on the carbon surface of C/Co nanoparticles allows magnetic extraction from extremely diluted aqueous solutions, J. Mater. Chem., 19, 8239-43 (2009).

R.N. Grass, E.K. Athanassiou, W.J. Stark, Covalently functionalized cobalt nanoparticles as a platform for magnetic separations in organic synthesis, Angew. Chem. Int. Ed., 46, 4909-12 (2007).

A. Schaetz, O. Reiser, W. J. Stark, Nanoparticles as Semi-Heterogeneous Catalyst Supports, Chem. Eur. J., 16(30), 8950-67 (2010).

A. Schaetz, R.N. Grass, W.J. Stark, Magnetische Chemie: Winzig und mit metallischem Kern, Nachrichten aus der Chemie, 58, 857 (2010).