Ordered Mesoporous Fe₂O₃ with Crystalline Walls

Abstract

Alpha-Fe(2)O(3) has been synthesized with an ordered mesoporous structure and crystalline walls that exhibit a near-single crystal-like order. The unique magnetic behavior of the material, distinct from bulk nanoparticles of alpha-Fe(2)O(3) or mesoporous Fe(2)O(3) with disordered walls, has been established. Magnetic susceptibility, Mössbauer, and neutron diffraction data show that the material possesses the same long-range magnetic order as bulk alpha-Fe(2)O(3), despite the wall thickness being less than the 8 nm limit below which magnetic ordering breaks down in nanoparticulate alpha-Fe(2)O(3), yet the Morin transition of bulk alpha-Fe(2)O(3) is absent. It is also shown by TEM, PXRD, and EXAFS that alpha-Fe(2)O(3) with the same ordered mesoporous structure but disordered walls contains small crystalline domains. Mössbauer and magnetic susceptibility data demonstrate that this material exhibits no long-range magnetic order but superparamagnetic behavior.

Synthesised magnetic nanoparticles coated zeolite (MNCZ) for the removal of arsenic (As) from aqueous solution

“…Figure 2 presents wide-angle XRD patterns of the synthesised -Fe 3 O 4 and -Fe 2 O 3 . Welldefined peaks corresponding to the crystal structure of -Fe 3 O 4 and -Fe 2 O 3 are clearly seen in agreement with the previous studies [26,27], suggesting that the walls of both -Fe 3 O 4 and -Fe 2 O 3 are crystalline. It should be noted that because of Fe 3 O 4 gradually converted to -Fe 2 O 3 phase after exposure to air, no attempts were made to characterise Fe 3 O 4 -zeolite in this study.…”

Magnetic properties of nano-scale hematite, α-Fe2O3, studied by time-of-flight inelastic neutron spectroscopy

“…1. Crystallographic and magnetic studies (superconducting quantum interference device (SQUID) magnetometry, neutron, and x-ray powder diffraction) 19,20,29 show that the material adopts the same rhombohedral space group and magnetic structure as the weakly ferromagnetic "bulk" hematite (263 K <T < 955 K), and confirm that the sample is of high quality. However, upon cooling down to at least 2 K, the material does not undergo the Morin transition.…”

“…5,6 In the mesoporous particles, no broadening of the magnetic signal is seen within the resolution of IN10, confirming the absence of superparamagnetic behavior in this sample, as observed previously with Mössbauer measurements. 19 To model the excitations, a simplified zero-field spin wave dispersion relationship for hematite has previously been described and shall be used here, Eq. (5): 7…”

“…19 The sample has a surface area of 139 m 2 g −1 and a pore diameter centered at 38.5 Å. Microscopy images show clear repetition of the mesoporous mosaic, Fig. 1.…”

Lithium Insertion Behavior of Nanoscopic Co3O4Prepared with Avian Egg Membrane as a Template

“…It is also possible to realize an improvement in cyclability if mesoporous structures can be generated by reaction with lithium through insertion or conversion processes. [10][11][12][13] For example, β-MnO 2 in its bulk state is electrochemically inactive while in mesoporous form it can react reversibly react with 0.92 lithium.…”