Iron Nitride and Carbide: from Crystalline Nanoparticles to Stable Aqueous Dispersions

Iron nitride and carbide nanoparticles were synthesized using iron oxide particles as template. They were furthermore dispersed in aqueous solution via stabilization with a poly­(ionic liquid). They provide a great potential combining a high saturation magnetization with low toxicity compared to the iron based compounds that are currently used in several applications such as cell-sorting and hyperthermia or as contrast enhancers for magnetic resonance imaging. We here present a sustainable and green procedure to synthesize iron nitride and carbide by resorting to the variety of iron oxide template nanoparticles. In this way the shape and the size can be precisely controlled and tuned within the nanometer range. During calcination, urea enables to control the composition of the product material, whereas a biopolymer agar protects the particles from agglomeration. We dispersed the particles in water by using poly­(1-ethyl-3-vinylimidazolium bromide) as stabilizing agent. Magnetic measurements of the converted particles show that particles with a diameter of 18 nm are located at the border of superparamagnetic and ferromagnetic behavior. As expected after conversion the saturation magnetization of the particles was notably increased. The herein presented synthetic approach can be applied to other metals and has thus the potential to be important for the synthesis of nitrides and carbides in general.