Synthesis of Core-Shell CoFe2O4 Nanoparticles

Three samples of CoFe₂O₄ NPs of different sizes, labelled as CoA, CoB, and CoC, were prepared by the solvothermal hydrolysis of mixed cobalt-iron oleates in a mixture of organic solvents with different polarities and water contents. The samples were used as seeds to produce core–shell nanostructures using a second solvothermal treatment (seed-mediated growth), with a shell of spinel iron oxide (maghemite/magnetite) and manganese ferrite, indicated as Cox@Fe and Cox@Mn (where x = A, B, C), respectively.^{43 (link)} The samples CoA, CoA@Fe, CoA@Mn, CoC, CoC@Fe, and CoC@Mn correspond to the samples Co1, Co1@Fe, Co1@Mn, Co2, Co2@Fe, and Co2@Mn, respectively, described in previous work.^{43 (link)} The experimental synthesis conditions for the samples CoB, CoB@Fe, and CoB@Mn are reported in the section “Experimental conditions” of the ESI (Tables 8S–10S†).