HMTA-assisted One-pot Synthesis of Greigite Nano-platelet and Its Magnetic Properties

A facile one-pot hydrothermal procedure for the synthesis of magnetic greigite was investigated in this work, by using FeSO₄, thioacetamide, and a tiny amount of hexamethylenetetramine (HMTA) as starting materials. The HMTA molecule, which acted as a chelating agent and an oxidant, could not only tune the valence fluctuation of iron ions, but also direct the hydrothermal reaction towards the exclusive formation of greigite platelets with hundreds of nanometers in lateral size. In the presence of a static magnetic field during this synthesis, the greigite nano-platelets were apt to congregate to form 3D flower-like microspheres. A set of experiments suggested that the ferrous ions were at first partly oxidized by HMTA to form ferric intermediates, i.e., Fe(OH)₃ and Fe₂O₃. Then excessive ferrous ions, along with the solid intermediates, reacted with sulfide ions, and finally evolved into greigite. Taken into consideration that a similar process occurred in magnetotactic bacteria, our results may give a hint at the design of biomimetic synthesis strategies to produce nanomaterials, especially the magnetosome-like greigite.