Magnetite
Magnetite has many uses, incl. as a catalyst in the Fischer_Tropsch process that converts syngas to liquid fuels.
Preparation
Simple recipe for the production of magnetite nanoparticles. (This is from Wikipedia - please feel free to replace with more extensive recipe).
Magnetite can be prepared in the laboratory as a ferrofluid in the Massart method by mixing iron(II) chloride and iron(III) chloride in the presence of sodium hydroxide.[10]
Magnetite also can be prepared by chemical co-precipitation, which consist in a mixture of a solution 0.1 M of FeCl3·6H2O and FeCl2·4H2O with mechanic agitation of about 2000 rpm. The molar ratio of FeCl3:FeCl2 can be 2:1; heating this solution at 70 °C, and immediately the speed is elevated to 7500 rpm and adding quickly a solution of NH4OH (10 volume %), immediately a dark precipitate will be formed, which consists of nanoparticles of magnetite.