Metastable iron(iii) oxide polymorphs derived from Fe/Mn bimetallic coordination polymer particles in confined space: SiO2 shell effect on crystal phase transition

Abstract

Metal–organic framework (MOF) or coordination polymer particle (CPP) derived metal oxide nanomaterials with precisely designed crystal phases and shapes are important for many applications. However, the control of crystal phases and the understanding about the mechanism are studied less than the morphology of tuned metal oxides derived from MOFs or CPPs. This research shows that the crystal phase transition through a thermal decomposition process of iron(III) oxide polymorphs derived from bimetallic CPPs bearing Fe and Mn ions was altered via the coated silica shell, which played a significant role. The crystalline phase and particle shape of the resulting materials were characterized, and silica-coated Mn-doped β-Fe₂O₃ metastable structures were identified. Additionally, it is experimentally discovered that the presence of the silica shell is essential to stabilize the β-Fe₂O₃ metastable phase.