Synthesis of Magnetic Nanocrystals by Thermal Decomposition in Glycol Media: Effect of Process Variables and Mechanistic Study

The nucleation and growth of water dispersible iron-oxide nanoparticles synthesized by high temperature decomposition of iron(III) acetylacetonate in the presence of different solvents has been studied. A battery of techniques was used to characterize the products obtained under different conditions and to elucidate the synthesis mechanism. Results show that the synthesis of iron-oxide nanoparticles in triethylene glycol (TEG) proceeds through a multistep process whose first stage is likely to be the formation of an intermediate TEG-iron-complex that evolves into a low-crystallinity iron-oxide-organic precursor during aging at 180 degrees C. Raising the temperature above 240 degrees C caused the thermal decomposition of the precursor and the sudden nucleation of small iron-oxide nanocrystals. Keeping the reactant mixture at 280 degrees C led to the growth of iron-oxide nanocrystals, as did increasing the time at reflux temperature, the amount of initial iron precursor or the use high boiling point solvents. The particle size could be reproducibly controlled between 1.5 and 13 nm, with a relatively narrow size distribution. Larger particles could also be obtained using a solvothermal method in an autoclave reactor.