Chemical synthesis of Fe nanocrystals via hydrogenation of ferric acetylacetonate

Uniform pure iron (Fe) nanocrystals with particle size smaller than 10nm were synthesized via hydrogenation reduction of a nontoxic organometallic precursor ferric acetylacetone [Fe(acac)₃] in an autoclave at elevated temperature. Since reaction is conducted with a pressure of 6MPa, choice of solvent become more convenient because some low-boiling-point solvents could also be used. In order to better control the composition, morphology and size of iron nanocrystals, various factors including reaction temperature, solvents, stabilizers, and reducing agents were investigated by means of XRD, TEM and HRTEM. Apart from a necessary temperature range from 260 to 300°C, and a combination of hydrogen gas (H₂), protective stabilizers (oleic amine, trioctylphosphine (TOP) and 1,2-dodecanediol (DDD) ), a suitable mol ratio of DDD to Fe(acac)₃ (between 1:1 and 2:1) are found crucial to obtain uniform pure iron nanocrystals. Under suitable conditions, the average particle size of resultant iron nanocrystals is 6.9 nm and the standard derivation is 6%, which is already narrow enough. Also, magnetic characterization for the α-Fe nanocrystals shows that their saturation magnetization is 146 emu/g. Perfect superlattice of these particles with interplanar spacing of 0.204 and 0.286 nm was observed with HRTEM, suggesting that the nanocrystals are single crystals.