Fabrication and Characterization of Manganese-based Self-assembled Cubic Structures

Self-assembled cubic structures of manganese-based nanomaterials were achieved successfully, in case of manganese fluoride, for the very first time. The indirect synthesis of manganese oxide (Mn₂O₃) and manganese fluoride (MnF₂/MnF₃) self-assembly involved an individual two step synthesis protocol. In first step of the protocol, NH₄MnF₃ self-assembled cubic structures were fabricated by a simple liquid phase reaction using polystyrene (PS) as structure directing agent (SDA), while manganese nitrate tetrahydrate (Mn(NO₃)₂.4H₂O) and ammonium fluoride (NH₄F) as manganese and fluorine sources, respectively. In second step, the NH₄MnF₃ was transformed by calcination to manganese oxide (Mn₂O₃) at 450 °C for 5 hours under open atmosphere (air/O₂), and individually, to manganese fluoride (MnF₂/MnF₃) at 350 °C for 5 hours under pure molecular fluorine (F₂) environment. The temperature regimes for the transformation reactions were deduced from thermogravimetric analysis (TGA). The crystal structures and the compositions of all the samples were established by powder X-rays diffraction (PXRD). Further, structural characterizations were carried out by spectroscopic analyses. The key objective, preservation of self-assembled cubic structures in the resulting manganese oxide and fluoride, were confirmed by electron microscopic analyses. The self-assembly structures formation mechanism was illustrated based on the transmission electron microscopy (TEM) and scanning electron microscopy (SEM) results.