Fig. 1. Scheme visualizing the three main synthesis routes to magnetite (Fe3O4): (1) magnetite formation by controlled coprecipitation from both Fe3+ and Fe2+ ions, (2) magnetite formation from Fe3+ ions through a solid ferrihydrite (Fe(OH)3) precursor and Fe2+ ions by ammonia diffusion, and (3) magnetite formation from Fe2+ ions through a solid white rust (Fe(OH)2) precursor by partial oxidation with NO3–.
