(346a) 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).