(458b) Synthesis and Covalent Surface Functionalization of Non-Oxidic Iron Core-Shell Nanomagnets for Large Scale Magnetic Separations

Successful use of magnetic nanoparticles for target isolation strongly relies on rapid response of the nanomagnets to magnetic field gradients (high saturation magnetization) and additionally requires stability under a wide range of different conditions. Nanomagnets with optimal magnetic properties for above applications can be obtained by the use of metals (Ms, bulk ≤ 220 emu/g). Unfortunately, naked metal nanoparticles are chemically highly active (typically pyrophoric) and readily oxidize upon contact with air or water, generally resulting in a complete loss of magnetism. Up to now, this has promoted the widespread use of moderately magnetic oxide nanoparticles, such as magnetite (Ms, bulk ≤ 92 emu/g). In this work, we show the production of iron-based nanomagnets by a flame spray synthesis process under reducing atmosphere [1-3]. The reducing flame spray synthesis setup allows the continuous production of carbon coated iron carbide particles with a mean diameter of 30 nm at a production rate of > 10 g/h [3]. The carbon-encapsulated iron carbide nanoparticles have an exceptionally high saturation magnetization of 140 emu/g and are highly air stable (up to 200°C). Additionally, the carbon surface of these iron carbide nanomagnets could be covalently functionalized with various linkers by following the procedures initially described by Grass et al.[1]. The high saturation magnetization, thermal and chemical stability, low raw material costs, and the efficient synthesis process make the herein described carbon encapsulated iron carbide nanoparticles an attractive low cost alternative for currently applied nanomagnets. Figure: Reducing Flame Spray Synthesis setup (left) allows a continuous production of highly magnetic core/shell nanomagnets (center). The nanomagnets can be completely recovered from suspension within a few minutes (right). [1] Grass R. N., Athanassiou E.K., Stark W.J., (2007), Angew. Chem. Int. Ed., 46, 4909-12. [2] Athanassiou E.K., Grass R.N., Osterwalder N., Stark W.J., (2007) , Chem. Mater., 19 (20), 4847-53. [3] Herrmann I. K., Grass R.N., Mazunin D., Stark W.J., under review.

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