High temperature stability of surfactant capped CoFe2O4 nanoparticles

We investigate the effect of adsorbed surfactant on the structural stability of CoFe2O4 nanoparticles during vacuum thermal annealing. In-situ high temperature X-ray diffraction studies show a reduction of oleic acid coated CoFe2O4 nanoparticles into α-Fe and CoO under annealing at 800 °C. On the contrary, the uncoated CoFe2O4 nanoparticles remains stable, with its cubic phase intact, even at 1000 °C. Thermo-gravimetric analysis coupled mass spectra reveals that the evolved carbon from the surfactant aids the removal of oxygen atom from CoFe2O4 lattice thereby reducing it to α-Fe and CoO phases. These results are important in tailoring stable CoFe2O4 nanostructures for various applications.

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► Self-assembled molecular layers of surfactant on nanoparticles are often used to modify surface properties.
► We demonstrate that a surfactant nanolayer on CoFe2O4nanoparticles can act as a strong reducing agent under high temperature vacuum annealing.
► We propose a possible reduction mechanism of CoFe2O4 nanoparticles under air and vacuum annealing.
► Our results are important in the understanding of the stability of nanoparticles at high temperatures.