[en] In this contribution, we present the results of PDF analyses coupled with other complementary experimental and theoretical approaches. From these results we have been able to show the influence of structural and textural organisation on the catalytic properties in Fe(at)SiO₂ nanocomposites. We will also discuss the effect of processing conditions on the interesting structural and physical properties of functionalized magnetite nanoparticles

[en] Highlights: • Starch-functionalized magnetic nanoparticles (MNPs) are prepared by one pot method. • Morphology and structural properties of MNPs can be tuned by varying starch amount. • Gradual evolution from bulk-like to the superparamagnetic behaviour was evidenced by Mössbauer spectroscopy. -- Abstract: In this study we report the preparation of starch-functionalized magnetic nanoparticles (Starch@MNPs) by the oxidation-precipitation method of iron (II). Special attention was devoted to the characterization of the modification of structural and magnetic properties depending on the starch to iron mass ratio R. Transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), Raman, Mössbauer, Fourier transform infrared (FTIR), X-ray photoelectron spectroscopies (XPS) and thermogravimetric analysis (TGA) were used to carefully characterize and compare the as-synthesized products. TEM and PXRD revealed the reduction of the crystallite size as R increases. The size varies from 67 ± 5 to 12 ± 4 nm by changing R from 0 to 10. The formation of a cubic inverse spinel iron oxide phase was demonstrated by PXRD and the discrimination between magnetite Fe₃O₄ and maghemite Fe₂O₃ was realized by Raman and Mössbauer spectroscopy. Mössbauer spectroscopy allowed to monitor the evolution of the magnetic properties with respect to R. The superparamagnetic behaviour was evidenced by the appearance of a doublet in the Mössbauer spectra that strongly increased in intensity with R ratio. The relative abundance (RA) of the doublet at room temperature was observed to increase from 10 to 36% for R equal 1 to 10. Lastly, the iron environment was highly perturbed by the presence of starch.

[en] Birnessite was synthetized through redox reaction by mixing MnO₄^-, Mn²⁺ and OH^- solutions. The Mn(VII): Mn(II) ratio of 0.33 was chosen and three methods were used consisting in a quick mixing under vigorous stirring of two of the three reagents and then on the dropwise addition of the third one. The obtained solids were characterized by XRD, FTIR and XPS spectroscopies. Their average oxidation states were determined from ICP and CEC measurements while their surface properties were investigated by XPS. This study provides an increased understanding of the importance of dissolved oxygen in the formation of birnessite and hausmannite and shows the ways to obtain pure birnessite. The role of counter-ion ie. Na⁺ or K⁺ was also examined. - Graphical abstract: Pathways of birnessite formation. - Highlights: • Pure birnessite is prepared through a redox reaction. • Hausmannite formation is prevented by controlling dissolved O2. • The employed counterion influences the purity of birnessite. • Initial Mn(OH)₂ is oxidized by both MnO₄^- and dissolved O₂.

[en] Highlights: • Birnessite is not a simple cationic exchanger toward ammonium ions. • Presence of two adsorption sites of NH₄⁺ on birnessite. • After reaction of birnessite with NH₄⁺, the CEC of the solid decreases. • The Mn average oxidation state increases without any Mn²⁺ release. • The symmetry of the solid changes from triclinic to hexagonal. - Abstract: The ammonium cation interaction with Na-birnessite in aqueous alkaline medium was studied. Solution and solid analysis give evidence that birnessite is not only acting as a cationic exchanger toward NH₄⁺. The surface analysis performed by XPS showed that N1s spectra are characterized by the existence of two different environments: one assignable to an interlayer NH₄⁺ and the second to a chemisorbed N-species. Structural and chemical transformations were observed on birnessite with nitrogen mass balance deficit. The monitoring of NH₄⁺, Na⁺, Mn²⁺, NO₃^- and NO₂^- and solid changes (average oxidation state of Mn, cation exchange capacity, solid nitrogen content and symmetry evolution identified by XRD and FTIR) indicate unambiguously that NH₄⁺ reacts chemically with the birnessite.

[en] This paper reports on the first study of the chemical, optical, and structural properties of lanthanum ferrite oxynitride thin films deposited by reactive magnetron sputtering. The thin films were deposited in an Ar/O₂/N₂ mixture as reactive plasma, from two elemental La and Fe targets, at a room and high temperature (25 and 800 °C). The films deposited at room temperature are amorphous and have been flash annealed to crystallize the perovskite. The oxynitride properties were investigated and compared to the oxide films deposited in Ar/O₂ gas mixture. All the oxide and oxynitride films present an orthorhombic structure. However, the nitrogen doping is limited to 1–1.5% and leads to the lattice expansion (4%), the bandgap narrowing, a lower electrical resistivity in range [25–350 °C], and a modification of Infrared and Raman spectra. Electron Energy Loss Spectroscopy measurements clearly show the presence of two nitrogen sites with an “active” intra-granular nitrogen associated to a variation of the physical properties. - Highlights: • Study of LaFeO_xN_y oxynitride thin film. • Presence of two forms of nitrogen. • Large modification of LaFeO₃ properties with slight nitrogen doping.