Polyethylene glycol-assisted hydro-solvothermal growth of anisotropic magnetic iron oxides: The role of mixed environment conditions

In this study, an alternative mixed hydro-solvothermal route has been investigated for the synthesis of magnetic iron oxide nanoparticles with anisotropic shape. The synthesis was performed at mild conditions (150 °C) in a water/2-propanol environment, using poly(ethylene glycol) (PEG400) as structure directing agent, sodium thiosulfate as reducing agent, and NaOH as precipitating agent. The resulting systems were characterized by combining morphological, structural, and magnetic techniques. Experimental results clearly demonstrate that magnetite/maghemite nanorods are preferentially obtained in water/PEG400 environment, whereas 2-propanol/PEG400 environment promotes the growth of magnetite/maghemite polyhedral systems. Interestingly, synthesis performed in a mixed hydro-solvothermal (i.e., water/2-propanol) environment favors the preferential growth of hematite phase.