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Core-shell structural magnetic nanocatalysts, involving carbon-coated magnetic Fe3O4 nanoparticles supported on graphene oxide sheets (mildly reduced graphene oxide (MRGO)/Fe3O4@C) and carbonaceous coatings on magnetic Fe3O4 nanoparticles (Fe3O4@C), for immobilizing metal (CuII, CoII, FeIII or VOIV)-salen complexes were prepared by a facile, green, and efficient chemical approach and first applied in the aerobic epoxidation of styrene with air as the oxidizing agent. The prepared catalysts were characterized by different techniques, such as XRD, TEM, FTIR spectroscopy, inductively coupled plasma atomic emission spectroscopy, TEM, thermogravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. The magnetic nanocatalysts MRGO/Fe3O4@C-salen-M (M=Cu, Co, Fe, or V) exhibited higher catalytic reactivity than that of the corresponding Fe3O4@C-salen-M (M=Cu, Co, Fe, or V) species possibly owing to site isolation, good dispersion of magnetic Fe3O4 nanoparticles, and an efficiently synergistic effect between the metal complexes and the supports. Furthermore, MRGO/Fe3O4@C-salen-Co exhibited up to 92.3 % conversion of styrene and 59.2 % selectivity to the styrene oxide upon using air as the oxidizing agent and showed good recoverability with negligible loss in activity and selectivity within successive runs owing to superparamagnetism. Most importantly, these materials can be easily recovered by simple magnetic separation. [ABSTRACT FROM AUTHOR]

Abstract: In this work we report on a study of the morphological changes of LDL induced in vitro by metallic ions (Cu2+ and Fe3+). These modifications were characterized by transmission electron microscopy, nuclear magnetic resonance and the Z-scan technique. The degree of oxidative modification of LDL was determined by the TBARS and lipid hydroperoxides assays. It is shown that distinct pathways for modifying lipoproteins lead to different morphological transformations of the particles characterized by changes in size and/or shape of the resulting particles, and by the tendency to induce aggregation of the particles. There were no evidence of melting of particles promoted by oxidative processes with Cu and Fe. [Copyright &y& Elsevier]

The investigation performed by means of Mössbauer spectroscopy, X-ray diffraction and transmission electron microscopy demonstrated that the interaction in the system iron-amorphous carbon proceeds via the formation of nano-sized iron particles (10–40 nm) and the carbide nano- phases distributed over amorphous carbon matrix. The annealing of these samples causes a crystallization of the amorphous carbon, decomposition of nano-sized carbide phases and formation of iron nanoparticles (50–100 nm) encapsulated by graphite. [ABSTRACT FROM AUTHOR]

Magnetite crystals precipitated as a consequence of Fe(III) reduction by Shewanella algae BrY after 265 h incubation and 5-year anaerobic storage were investigated with transmission electron microscopy, Mössbauer spectroscopy and X-ray diffraction. The magnetite crystals were typically superparamagnetic with an approximate size of 13 nm. The lattice constants of the 265 h and 5-year crystals are 8.4164Å and 8.3774Å, respectively. The Mössbauer spectra indicated that the 265 h magnetite had excess Fe(II) in its crystal-chemistry (Fe3+1.990Fe2+1.015O4) but the 5-year magnetite was Fe(II)-deficient in stoichiometry (Fe3+2.388Fe2+0.419O4). Such crystal-chemical changes may be indicative of the degeneration of superparamagnetic magnetite through the aqueous oxidization of Fe(II) anaerobically, and the concomitant oxidation of the organic phases (fatty acid methyl esters) that were present during the initial formation of the magnetite. The observation of a corona structure on the aged magnetite corroborates the anaerobic oxidation of Fe(II) on the outer layers of magnetite crystals. These results suggest that there may be a possible link between the enzymatic activity of the bacteria and the stability of Fe(II)-excess magnetite, which may help explain why stable nano-magnetite grains are seldom preserved in natural environments. [ABSTRACT FROM AUTHOR]

Control of multi-martensite phase transformations and physical properties constitute greatly unresolved challenges in Fe7Pd3-based ferromagnetic shape memory alloys. Single crystalline Fe7Pd3 thin films reveal an austenite to martensite phase transformation, continuously ranging from the face-centered cubic (fcc) to the face-centered tetragonal (fct) and body-centered cubic (bcc) phases upon irradiation with 1.8 MeV Kr+ ions. Within the present contribution, we explore this scenario within a comprehensive experimental study: employing atomic force microscopy (AFM) and high resolution transmission electron microscopy (HR-TEM), we first clarify the crystallography of the ion-irradiation-induced austenite martensite and inter-martensite transitions, explore the multi-variant martensite structures with c-a twinning and unravel a very gradual transition between variants at twin boundaries. Accompanying magnetic properties, addressed locally and globally, are characterized by an increasing saturation magnetization from fcc to bcc, while coercivity and remanence are demonstrated to be governed by magnetocrystalline anisotropy and ion-irradiation-induced defect density, respectively. Based on reversibility of ion-irradiation-induced materials changes due to annealing treatment and a conversion electron Mößbauer spectroscopy (CEMS) study to address changes in order, a quantitative defect-based physical picture of ion-irradiation-induced austenite ⇔ martensite transformation in Fe7Pd3 is developed. The presented concepts thus pave the way for ion-irradiation-assisted optimization strategies for tailored functional alloys. [ABSTRACT FROM AUTHOR]