Synthesis of iron oxide nanoparticles using a freshly-made or recycled imidazolium-based ionic liquid

This paper reports the synthesis of iron oxide nanoparticles using a freshly-made or recycled 1-butyl-3-methylimidazolium bis(triflylmethylsulfonyl)imide ([BMIM][Tf₂N]) ionic liquid (IL). Iron pentacarbonyl (Fe(CO)₅), which dissolves in [BMIM][Tf₂N], thermally decomposed and subsequently oxidized to form iron oxide nanoparticles. These nanoparticles separated out automatically from the imidazolium-based ionic liquid mixtures. Multiple additional runs were tested in making iron oxide nanoparticles using recycled ionic liquid. The iron oxide nanoparticles made were characterized with transmission electron microscopy (TEM), high resolution TEM (HR-TEM) and powder X-ray diffraction (PXRD). The structure and thermal stability of the IL was examined using Fourier transform infrared (FT-IR) spectroscopy and thermal gravimetric analysis (TGA). We found that iron oxide nanoparticles with a narrow size distribution could be obtained. The [BMIM][Tf₂N] ionic liquid showed no degradation based on the TGA and FT-IR study. The solvent-recyclable process of making size-controlled nanoparticles should have a broad impact on the application of imidazolium-based ionic liquids in the synthesis of nanomaterials.