Synthesis and Covalent Surface Functionalization of Nonoxidic Iron Core−Shell Nanomagnets

Abstract

The rapidly growing applications of nanomagnets require acid/base stable, oxidation-resistant shells with chemically controlled surface structure. An ideal core should be metallic and highly magnetic. We demonstrate the production of iron-based nanoparticles, ranging from iron oxide to iron and iron carbide, by systematically modifying the degree of reduction during flame spray synthesis under a controlled atmosphere. At a laboratory scale, continuous production yields iron-based particles of 20-50 nm at a production rate of >10 g h -1 . Carbon-encapsulated iron carbide (C/Fe 3 C) combines exceptionally high saturation magnetization (140 emu g -1 ), air stability (up to 200°C), and resistance against acidic dissolution (1 week in 24% HCl). The top graphene-like carbon layer could be covalently functionalized with various linkers, thus allowing us to chemically design the particle surface. Activity was demonstrated by reacting 2-phenyl ethyl amine functionalized nanomagnets with carboxylic acid chlorides as a model reaction. The present nanomagnets consist of biologically well-accepted constituents. They combine the required chemical reliability, improved magnetization if compared to magnetite with the potential for technical scale manufacturing, and therefore open stable nanomagnets to a broad range of fascinating separation problems (extraction/water treatment) and biomedical research.

Decoration of multiwalled carbon nanotubes with protected iron nanoparticles

“…Hydrochloric acid was chosen as, unlike other mineral acids (HNO 3 and H 2 SO 4 ), it is not expected to oxidise the carbon shell [37]. Resistance to an external environment is required for medical applications, such as cancer treatment [1].…”

“…The same method has also produced graphitic carbon coatings [34], other method of producing graphitic carbon coatings include evaporation of metals with a hydrocarbon flow [35] and decomposition of iron nitrate in the presence of starch [36]. However, no resistance to acidic media is shown, where acid resistance is shown [37], multiple synthesis steps are required.…”

The convenient preparation of stable aryl-coated zerovalent iron nanoparticles

“…A variety of different approaches have been employed to protect this sensitive material from oxidation, where commonly used methods include coating with carbon [19,22], silica [23], noble metals and oxides [24][25][26], or the utilization of different surfactants and stabilizers [27]. However, none of these approaches lead to covalent grafting.…”

Aerosol Process for theIn SituCoating of Nanoparticles with a Polymer Shell

“…This carbon film allows the attachment of functional groups thereby linking the coated nanoparticles covalently to a polymer matrix. However, so far they have used only core materials such as Fe x C and Co that are known to build up carbon layers on the surface (Herrmann et al 2009;Zeltner et al 2012).…”