Małgorzata A. Małecka

Facile non-hydrolytic synthesis of highly water dispersible, surfactant free nanoparticles of synthetic MFe2O4 (M–Mn2+, Fe2+, Co2+, Ni2+) ferrite spinel by a modified Bradley reaction

A series of the highly crystalline MFe2O4 ferrite spinel nanoparticles were synthesized via a modified Bradley reaction using microwave stimulation. Particle size was estimated using theoretical calculations from the X-ray data (Scherrer and Rietveld methods) as well as by direct experimental techniques such as TEM, DLS and NTA. The calculated average grain size for dry powders is in the range 10 to 23 nm. Hydrodynamic size was measured using DLS on non-modified, surfactant free particles of the whole MFe2O4 series. Raman spectra used for additional verification of the structure features of the produced spinel phases showed strong asymmetric behavior of the A1g mode, which was deconvoluted revealing additional components. Among all the products the lowest site inversion was found for the manganese ferrite (MnFe2O4). The oxidation of Fe3O4 leading to the formation of the Fe2O3 hematite phase induced by laser irradiation was observed. Magnetic characterization of the MFe2O4 family was carried out, showing that superparamagnetic blocking temperatures and calculated anisotropy constants K are in good agreement with the data for similar fine-particle systems.

Lanthanum molybdate nanoparticles from the Bradley reaction: factors influencing their composition, structure, and functional characteristics as potential matrixes for luminescent phosphors.

Interaction of lanthanum isopropoxide with molybdenum(VI) alkoxides in La/Mo ratios varying from 3:1 to 1:1 in acetophenon or allyl alcohol as solvents offers nanosized poorly crystalline products of complex composition, where the precipitation of Mo-rich ones is followed by the formation of La-rich ones with conservation of the reaction stoichiometry in total. Thermal treatment of the precipitates at temperatures over 700 °C leads to the formation of stoichiometric phases of the α- and β-La2Mo2O9 compositions. Introduction of smaller Re3+ cations such as Sm3+ by doping favors stabilization of the La2–xRExMo2O9 phase with improved crystallinity even after lower-temperature thermal treatment. The doping is successful only when the Re3+ (Sm3+, Eu3+, and Tb3+) is introduced as an alkoxide: application of Re3+(acac)3 as Re3+ sources leads to materials free from Re3+. The produced samples were characterized by XPD, TGA, SEM, and TEM studies as well as the luminescent properties for the Sm3+-doped phases.

New, intermediate polymorph of CeAlO3 with hexagonal structure – formation and thermal stability

This work presents the results of studies on solid state reaction in a highly dispersed CeO2–Al2O3 system under a reducing atmosphere. The formation of a new metastable hexagonal form of CeAlO3, isomorphous to hexagonal YAlO3, at 850 °C has been confirmed for the first time by TEM, XRD, FT-IR and measurement of magnetic susceptibility. Above 900 °C, the hexagonal phase transformed into a common tetragonal polymorph. Magnetic susceptibility data indicates that both CeAlO3 polymorphs contain Ce3+ ions, but the unit cell volume per formula unit is noticeably bigger (26%) for the hexagonal polymorph. This may suggest that the hexagonal CeAlO3 polymorph is stabilized by the interaction with the Al2O3 support.

Ce0.4IIICe0.6IVAlO3.3 – an unexpected product of a solid state reaction in the CeO2–Al2O3 system

Phase transformations in the highly dispersed CeO2–Al2O3 system subjected to heating under reducing and oxidizing atmospheres were studied by HRTEM, EDX, XRD, ICP, TPR and magnetic susceptibility measurements. It has been found that the nanocrystalline CeIIIAlO3 phase with a hexagonal structure appearing in the system during reduction in H2 at 850 °C transforms upon oxidation at 175–200 °C into a similar hexagonal phase with structural formula Ce0.4IIICe0.6IVAlO3.3. The Ce0.4IIICe0.6IVAlO3.3 phase is unstable in air above 600 °C and decomposes to nanocrystalline CeO2 and alumina. Reduction in hydrogen at 700 °C transforms the Ce0.4IIICe0.6IVAlO3.3 back to hexagonal CeIIIAlO3, which at 1000 °C (in hydrogen flow) recrystallizes into the well-known, tetragonal CeAlO3. The red–ox behaviour of the hexagonal CeAlO3 is compared with that of CeO2 and the possible implications for catalysis are discussed.

Non-contact Mn1−xNixFe2O4 ferrite nano-heaters for biological applications – heat energy generated by NIR irradiation

Mn1−xNixFe2O4 nanoparticles with primary particle size of 6 nm ± 4 nm were synthesized using fast and effective microwave stimulated technique without addition of surfactants or other specific agents to open more flexible post-surface modification potential. Structural, chemical and morphological characterization were performed using XRD, SEM-EDS and TEM techniques. DLS and absorption measurements were performed in order to evaluate hydrodynamic size of particles/objects and nanoparticles dispersion stability upon addition of stabilizing agents in water. The J774.E murine macrophage and U2OS human osteosarcoma cells exposed to particle dispersions revealed high loading of macrophages and moderate loading of osteosarcoma cells. Difference was ascribed to phagocytic activity of macrophages and their explicit role in elimination of particulate matter under in vivo conditions. It was shown that the effective heat generation can be achieved with Mn1−xNixFe2O4 magnetic ferrites by using NIR light irradiation instead of AC magnetic field reaching temperatures suitable for application in hyperthermia-based therapies.

Up-conversion emission and in vitro cytotoxicity characterization of blue emitting, biocompatible SrTiO3 nanoparticles activated with Tm3+ and Yb3+ ions

Functional SrTiO3 nanoparticles activated with a broad concentration range of Tm3+ and Yb3+ ions were obtained utilizing the citric route. The effect of the sintering temperature and optically active co-dopant concentration on the structural and up-conversion emission properties was studied by using XRD (X-ray powder diffraction) and spectroscopic techniques (emission, power dependence, emission kinetics). The particle size was verified by the TEM technique being in the range of 20–90 nm depending on the annealing temperature. It was shown that cross-relaxations contribute to depopulation of both 1G4 and 3H4 levels, whereas some of them populate the 3H4 level. These processes are strongly dependent on the concentration of Tm3+ and are responsible for the specific interplay between blue and NIR emissions. Extraordinary short decays were recorded due to the relatively high concentrations of rare earths, structural features of the host matrix, extended surface area and contribution of the non-radiative processes. The cytotoxic activity of the nanoparticles to J774.E murine macrophages and U2OS human osteosarcoma cells was assessed showing that SrTiO3:Tm3+/Yb3+ nanoparticles are biocompatible and can be potentially used in further bio-related applications such as active implant layers or injectable medical cement ingredients.

The effect of Eu doping on the growth, structure and red-ox activity of ceria nanocubes

Ce1–xEuxO2 nanocubes, with maximum Eu content x = 0.4, were synthesized by a simple hydrothermal method. Application of various experimental techniques (SEM-EDS, STEM-EDS, XPS, ICP-AES) revealed a uniform distribution of Eu and Ce in the nanocubes, but some oxygen depletion near the surface was detected. A model explaining the effect of the Eu doping on the growth of ceria nanocubes by the oriented attachment mechanism is proposed. The oxygen vacancy ordering in high-doped (x ≥ 0.1) ceria nanoparticles was found, and its effect on the reduction of ceria nanocubes is discussed.

Characterization and thermal stability of Yb-doped ceria prepared by methods enabling control of the crystal morphology

This study presents the results of investigations on the shape stability of crystalline ceria-based Ce1−xYbxO2−(x/2) mixed oxides with increasing Yb content (x = 0 to 0.15). Cube-like and octahedral nanocrystals of the oxides were synthesized by a hydrothermal method. Additionally, nano-sized (∼5 nm) mixed oxides were prepared by precipitation with a water-in-oil (W/O) microemulsion method. Clearly visible differences in the aggregations and shapes of the formed particles were detected as a function of the Yb-content and morphology of the oxide crystals. As has been presented in this paper, individual crystallites of pure ceria and mixed Ce–Yb oxides with cube-like shapes were observed in TEM images. On the other hand, in the case of the octahedral crystals of oxides with the same nominal compositions, individual crystallites were observed only for pure CeO2, in contrast to the Ce–Yb mixed oxides, where large agglomerates with octahedral shapes (built from smaller octahedral crystals of the mixed oxides) were observed. One of the most interesting observations connected with the formation of octahedral agglomerates of the mixed Ce–Yb oxides is the very similar orientations of the crystals which make up the large agglomerates.