Topotactic Transformation in Fe₃O₄ Induces Spontaneous Growth of Compositionally Diverse Nanostructures

Topotactic transformation is an emerging strategy for synthesizing materials with exotic functional properties. In this report, instead of producing new crystals with related structures, we exploited the topotactic transformation phenomenon to spontaneously produce compositionally diverse nanostructures on the transforming substrate. The surface of magnetite nanoparticles (Fe₃O₄ NPs) is topotactically transformed into maghemite (γ-Fe₂O₃). Benefiting from such oxidation susceptibility of ultrasmall Fe₃O₄ NPs, we achieved spontaneous growth of metals (Ag, Au, Pt, and Pd), a non-metal (Se), and a metal oxide (MnO₂) based nanostructures onto the surface of Fe₃O₄. No spontaneous growth of nanostructures was observed when the oxidized Fe₃O₄ NPs were tested, likely due to the loss of the Fe²⁺-associated mobile electrons. The obtained nanostructures displayed appreciable antioxidant activities, which we utilized to effectively treat inflammation in the intestines. It is anticipated that this synthetic route, based on topotactic transformation, represents a significant advancement in synthesizing various chemically diverse hetero-nanostructures.