Stefano Diodati

Green and low temperature synthesis of nanocrystalline transition metal ferrites by simple wet chemistry routes

Crystalline and nanostructured cobalt (CoFe2O4), nickel (NiFe2O4), zinc (ZnFe2O4) and manganese (MnFe2O4) spinel ferrites are synthesized with high yields, crystallinity and purity through an easy, quick, reproducible and low-temperature hydrothermal assisted route starting from an aqueous suspension of coprecipitated metal oxalates. The use of water as a reaction medium is a further advantage of the chosen protocol. Additionally, the zinc spinel is also prepared through an alternative route combining coprecipitation of oxalates from an aqueous solution with thermal decomposition under reflux conditions. The nanocrystalline powders are obtained as a pure crystalline phase already at the extremely low temperature of 75 °C and no further thermal treatment is needed. The structure and microstructure of the prepared materials is investigated by means of X-ray powder diffraction (XRPD), while X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) analyses are used to gain information about the surface and bulk composition of the samples, respectively, confirming the expected stoichiometry. To investigate the effect of the synthesis protocol on the morphology of the obtained ferrites, transmission electron microscopy (TEM) observations are performed on selected samples. The magnetic properties of the cobalt and manganese spinels are also investigated using a superconducting quantum device magnetometer (SQUID) revealing hard and soft ferrimagnetic behavior, respectively.

Simple, common but functional: biocompatible and luminescent rare-earth doped magnesium and calcium hydroxides from miniemulsion†

Nanostructured (d∼ 20-35 nm) and highly luminescent Ca(OH)2:Ln and Mg(OH)2:Ln (Ln = EuIII, SmIII, TbIII, Mg(Ca)/Ln = 20 : 1 atomic) nanostructures were obtained in inverse (water in oil - w/o) miniemulsion (ME), by exploiting the nanosized compartments of the droplets to spatially confine the hydroxide precipitation in basic environment (NaOH). The functional nanostructures were prepared using different surfactants (Span80 (span) and a mixture of Igepal co-630 and Brij 52 (mix)) to optimise ME stability and hydroxide biocompatibility as well as tune the droplet sizes. X-Ray diffraction (XRD) analyses testify the achievement of a pure brucite-Mg(OH)2-phase and pure portlandite-Ca(OH)2-phase with a high degree of crystallinity. Besides structural characterisations, the products were thoroughly characterised by means of several and complementary techniques (dynamic light scattering (DLS), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), micro-Raman spectroscopy, inductively coupled plasma mass spectrometry (ICP-MS) and Fourier transform infrared spectroscopy (FT-IR)) to assess their chemico-physical properties as well as their morphological and microstructural features. The stoichiometry of the doped systems was confirmed using ICP-MS measurements. Finally, the cytotoxicity of the nanoparticles was assessed by in vitro tests using ES2 cells in order to provide preliminary data on the biocompatibility of this kind of nanoparticles. The luminescence of the Eu-doped and Tb-doped materials is clearly visible to the naked eye in the red and green regions, respectively, corroborating their employment as materials for imaging in the optical window of interest.

Coprecipitated Transition Metal Ferrites Investigated by XPS

In the present contribution, four transition metal ferrites, namely the manganese perovskite MnFeO3 and the nickel, cobalt and zinc spinels NiFe2O4, CoFe2O4, and ZnFe2O4, were investigated through XPS (X-ray Photoelectron Spectroscopy). The synthesis route for the analyzed materials involved the precipitation of metal oxalates from an aqueous solution of metallic salts and oxalic acid. The precipitate was then isolated and calcined at 900 °C in order to obtain the crystalline ferrite powders. Along with survey scans of the analyzed samples, detailed spectra of the O 1s, C 1s, Fe 2p and M 2p (where M = Mn, Ni, Co, Zn depending on the compound in question) regions were collected. The data resulting from these analyses is discussed.

Pursuing the stabilisation of crystalline nanostructured magnetic manganites through a green low temperature hydrothermal synthesis

A quick, easy and green water-based synthesis protocol involving coprecipitation of oxalates combined with hydrothermal treatment resulted in the crystallisation of nanostructured manganites at a relatively low temperature (180 °C). The subcritical hydrothermal approach was shown to play a key role in stabilising phases which are generally achieved at much higher temperatures and under harsher conditions, thus disclosing an exciting alternative for their synthesis. Through this mild wet chemistry approach, the compounds CuMnO2, ZnMn2O4 and ZnMnO3 were synthesised as nanocrystalline powders. Noticeably, the optimised route proved to be effective in stabilising the exotic polymorph cubic spinel ZnMnO3 in pure form. This is particularly notable, as very few records concerning this compound are available in the literature. The compounds were fully characterised from compositional, structural, morphological and magnetic points of view.

Transition Metal Manganites Prepared by a Green and Low-Temperature Wet Chemistry Route, Investigated by XPS

In the present contribution, three transition metal manganites, namely the copper manganite CuMnO2 and the zinc manganites ZnMnO3 and ZnMn2O4, were investigated through X-ray photoelectron spectroscopy (XPS). The chosen synthesis route involved the combination of coprecipitation of oxalates from an aqueous solution and hydrothermal processing at a mild temperature (180 °C). The precipitates were then separated and dried for 4 h at 80 °C, yielding crystalline nanostructured powders without the need for calcination. Along with survey scans of the analyzed samples, detailed spectra of the C 1s, O1s, Mn 2p, Mn 3p, Mn LMM as well as Cu 2p, Cu 3p, Cu LMM, Zn 2p and Zn LMM (depending on the sample in question) were collected. The data obtained from these analyses is discussed.