title: Magnetic studies of mesoporous nanostructured iron oxide materials synthesized by one-step soft-templating.
abstract: A combined magnetization and (57)Fe spin-echo nuclear magnetic resonance (NMR) study has been carried out on mesoporous nanostructured materials consisting of the magnetite (Fe3O4) and maghemite (γ-Fe2O3) phases. Two series of samples were synthesized using a recently developed one-step soft-templating approach with systematic variations in calcination temperature and reaction atmosphere. Nuclear magnetic resonance has been shown to be a valuable tool for distinguishing between the two magnetic iron oxide spinel phases, Fe3O4 and γ-Fe2O3, on the nanoscale as well as monitoring phase transformation resulting from oxidation. For the Fe3O4 and γ-Fe2O3 phases, peaks in the NMR spectra are attributed to Fe in the tetrahedral (A) sites and octahedral (B) sites. The magnetic field dependence of the peaks was observed and confirmed the site assignments. Fe3O4 on a nanoscale readily oxidizes to form γ-Fe2O3 and this was clearly evident in the NMR spectra. As evidenced by transmission electron microscope (TEM) images, the porous mesostructure for the iron oxide materials is formed by a random close-packed aggregation of nanoparticles; correspondingly, superparamagnetic behavior was observed in the magnetic measurements. Although X-ray diffraction (XRD) shows the spinel structure for the Fe3O4 and γ-Fe2O3 phases, unlike NMR, it is difficult to distinguish between the two phases with XRD. Nitrogen sorption isotherms characterize the mesoporous structures of the materials, and yield BET surface area values and limited BJH pore size distribution curves.
authors.affiliation: Institute of Materials Science, University of Connecticut, Storrs, CT 06269-3136, USA. steven.suib@uconn.edu.
authors.forename: Jing
authors.initials: J
authors.lastname: Jin
authors.forename: William A
authors.initials: WA
authors.lastname: Hines
authors.forename: Chung-Hao
authors.initials: CH
authors.lastname: Kuo
authors.forename: David M
authors.initials: DM
authors.lastname: Perry
authors.forename: Altug S
authors.initials: AS
authors.lastname: Poyraz
authors.forename: Yan
authors.initials: Y
authors.lastname: Xia
authors.forename: Taha
authors.initials: T
authors.lastname: Zaidi
authors.forename: Mu-Ping
authors.initials: MP
authors.lastname: Nieh
authors.forename: Steven L
authors.initials: SL
authors.lastname: Suib
mesh_terms: D005290:Ferric Compounds / Q000737:chemistry*; D052203:Ferrosoferric Oxide / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D059346:Magnets / Q000737:chemistry*; D049329:Nanostructures / Q000737:chemistry* / Q000648:ultrastructure; D016062:Porosity; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds; C000499:ferric oxide; D052203:Ferrosoferric Oxide