Local Structure Control of Manganese Oxide Nanoparticles Encapsulated by Amorphous SiO₂

Abstract

Spinel-structured manganese oxide (M Mn2O4: M = Fe, Ni, Co, Zn) nanoparticles encapsulated in amorphous SiO2 were produced using our original wet chemical method. From the X-ray diffraction patterns, the diameters were estimated to range from 4 nm to 23 nm, depending on the annealing temperature. Bulk manganese oxide crystals are known to have the spinel structure, and a tetragonal structure with Jahn-Teller distortion is a stable and normal phase. This Jahn-Teller distortion is induced by Mn 3+ ions at the octahedral B sites. However, we have successfully produced cubic structures consisting of FeMn2O4, CoMn2O4, and NiMn2O4 nanoparticles in which the local distortion is suppressed. In order to clarify the local structure, X-ray absorption fine structure (XAFS) and magnetization measurements were performed. The cubic and tetragonal structures were selectively obtained, and their magnetic properties were investigated.

Interface-Promoted Direct Oxidation of p-Arsanilic Acid and Removal of Total Arsenic by the Coupling of Peroxymonosulfate and Mn-Fe-Mixed Oxide

“…This was further confirmed by the Fourier transform magnitudes of a k 3 -weighted extended X-ray absorption fine structure (EXAFS) spectrum (Figure f), in which the second shell peak of Mn­(A)–Mn­(A) bonds in the high R region ( R > 3 Å) was not recognizable for the MnFeO sample. On the contrary, the pre-edge peak clearly appeared in the spectrum of the Fe K-edge (Figure g), and the distance between the Fe atoms and their first oxygen neighbors (Fe1–O1) was lower than that of the Fe 3 O 4 standard sample as evidenced by the position shift of the first oxygen shell peak in Figure h. , These results indicate that the tetrahedral A sites of the MnFeO nanocubes were mainly occupied by the Fe atoms.…”

“…On the contrary, the pre-edge peak clearly appeared in the spectrum of the Fe K-edge (Figure 1g), and the distance between the Fe atoms and their first oxygen neighbors (Fe1− O1) was lower than that of the Fe 3 O 4 standard sample as evidenced by the position shift of the first oxygen shell peak in Figure 1h. 40,42 These results indicate that the tetrahedral A sites of the MnFeO nanocubes were mainly occupied by the Fe atoms.…”

“…We identified the located sites of Mn and Fe atoms in the spinel structure with the XAFS analyses. As shown in Figure 1e, the pre-edge peak, which results from the hybrid orbitals of transition metal atoms in the tetrahedral A sites, 40 was not observed in the normalized Mn K-edge spectrum of the MnFeO sample, indicating that the Mn atoms were mainly located in the octahedral B sites. This was further confirmed by the Fourier transform magnitudes of a k 3 -weighted extended Xray absorption fine structure (EXAFS) spectrum (Figure 1f), in which the second shell peak of Mn(A)−Mn(A) bonds in the high R region (R > 3 Å) 41 was not recognizable for the MnFeO sample.…”

Characterization of local structure and heat dissipation of iron oxide nanoparticles for magnetic hyperthermia treatment

“…MHT is expected to be a new cancer therapy treatment without side effects. We have reported the magnetic properties of MNPs and their characterization including their local structure [5,6]. Moreover, we have suggested the possibility of MHT [7,8].…”