Solid-phase synthesis of carbon-encapsulated magnetic nanoparticles

Carbon-encapsulated magnetic nanoparticles (CEMNPs) have wide applications. However, synthesis of such particles with superparamagnetic properties is still a great challenge. The present study reports a new method for the production of CEMNPs in the solid state. An Fe/C solid solution was first prepared by pyrolysis of Fe(CO)(5) and C2H2. Heat treatment of this material at low temperatures (<= 600 degrees C) generated fine nanoparticles (similar to 7 nm) with superparamagnetic properties, but treatment at high temperatures (> 600 degrees C) produced larger nanoparticles (>= 30 nm) exhibiting permanent magnetic behavior. The advantages of the present solid-phase approach over previous gas-phase methods include good controllability of particle size and thus magnetic properties and suitability for large-scale production.