Nanocrystalline Al-doped nickel ferrite powders have been synthesized by sol-gel auto-ignition method and the effect of non-magnetic aluminum content on the structural and magnetic properties has ...been studied. The X-ray diffraction (XRD) revealed that the powders obtained are single phase with inverse spinel structure. The calculated grain sizes from XRD data have been verified using transmission electron microscopy (TEM). TEM photographs show that the powders consist of nanometer-sized grains. It was observed that the characteristic grain size decreases from 29 to 6nm as the non-magnetic Al content increases, which was attributed to the influence of non-magnetic Al concentration on the grain size. Magnetic hysteresis loops were measured at room temperature with a maximum applied magnetic field of {approximately equal to}1T. As aluminum content increases, the measured magnetic hysteresis curves become more and more narrow and the saturation magnetization and remanent magnetization both decreased. The reduction of magnetization compared to bulk is a consequence of spin non-collinearity. Further reduction of magnetization with increase of aluminum content is caused by non-magnetic Al3+ ions and weakened interaction between sublattices. This, as well as the decrease in hysteresis was understood in terms of the decrease in particle size.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The heterodimetallic compounds {CaCr2(L)2(C2O4)4·xH2O}n L = 2,2′‐bipyridine (bpy), x = 0.83 (1); L = 1,10‐phenanthroline (phen), x = 0.33 (2) were synthesized and characterized by IR spectroscopy, ...X‐ray diffraction and magnetic measurements. The crystal structure of 2 is reported: the chelation of a Cr(phen)(C2O4)2– units towards Ca cations results in 1D double zigzag chains. The ability of 1 and 2 to act as single‐source precursors for the formation of Ca–Cr oxides is explored by thermal analysis, powder X‐ray diffraction and IR spectroscopy. The thermal processing of 1 and 2 at 1100 °C in air led to the appearance of the β‐CaCr2O4 phase as the major crystalline oxide. By heating the samples up to 1100 °C in nitrogen, only the β‐CaCr2O4 phase formed, whereas heating at 1400 °C caused the crystallization of two polymorphs, α‐ and β‐CaCr2O4. The magnetic behaviour of β‐CaCr2O4 pointed to the freezing of magnetic moments in coexistence with a weak ferromagnetic order.
The heat treatment of {CaCr2(L)2(C2O4)4·xH2O}n L = 2,2′‐bipyridine, x = 0.83 (1) and 1,10‐phenanthroline, x = 0.33 (2) at 1100 °C in a nitrogen flow resulted in the isolation of the β‐CaCr2O4 phase, whereas heating at 1400 °C caused the crystallization of two polymorphs, α‐CaCr2O4 and β‐CaCr2O4. The spectroscopic, structural and magnetic properties of the single‐source precursors and the β phase are investigated.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In this work, magnetic nanoparticles based on magnetite were successfully prepared via rapid microwave-assisted synthesis. In order to obtain the ternary core–shell Fe3O4/SiO2/TiO2 nanocomposite, ...first magnetite (Fe3O4) nanoparticles were coated with a protective layer of silica (SiO2) and finally with titania (TiO2). The composite configuration comprising porous and photoactive shells should facilitate the removal of organic micropollutants (OMPs) from water. Furthermore, the magnetic core is critical for processing the management of the photocatalytic powder suspension. The magnetization of the prepared magnetic nanoparticles was confirmed by vibrating-sample magnetometry (VSM), while the structure and morphology of the core–shell nanocomposite were investigated by means of XRD, FTIR, and SEM. Adsorption and photocatalysis were evaluated by investigating the removal efficiency of ciprofloxacin (CIP) as a model OMP using the prepared magnetic core–shell nanocomposite under UV-A light irradiation. It was found that the Fe3O4/SiO2/TiO2 nanocomposite showed good synergistic adsorption and photocatalytic properties. The measurement of iron in eluate confirmed that no leaching occurred during the photocatalytic examination. The recovery of magnetic nanocomposite by an external magnetic field confirmed that the magnetically separated catalyst is highly suitable for recycling and reuse.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
A series of seven tetranuclear Ni( ii ) cubane-like complexes of general formulae Ni 4 L 4 (ROH) 4 ( 1–3 ) and Ni 4 L 4 (R 1 OH) x (R 2 OH) y ( x = y = 2 for complex 6 , x = 1, y = 3 for complexes ...4 , 5 and 7 ; R = –C 3 H 7 , –C 4 H 9 , –C 5 H 11 ; R 1 and R 2 = –CH 3 , –C 2 H 5 , –C 3 H 7 , –C 4 H 9 , –C 5 H 11 ; L = N -(2-hydroxy-5-methylphenyl)salicylideneimine) were synthesized and their structural and magnetic properties were correlated in order to find out if the type of coordinated alcohol has any influence on magnetic properties. Their molecular structures reveal an octahedral coordination around nickel via five oxygen donor atoms and an imino nitrogen atom. Three out of the five oxygen atoms are derived from imine and one from the phenolate part of the Schiff base ligand, while the fifth one is derived from the neutral ROH ligand. Distortion of the cubane topology has been determined by Ni–O–Ni angle values and by O⋯Ni⋯O dihedral angle values. Intramolecular hydrogen bonds are various and rich, some are of the O–H⋯O type, spanning the cubane core and probably being one of the dominant causes of the distortion. Other weak intramolecular hydrogen bonds of the C–H⋯N type are present in complexes 1 , 2 , 3 , 5 and 7 . Very weak C–H⋯O intramolecular hydrogen bonds are responsible for the supramolecular architecture of complexes 2 , 5 and 6 . Intermolecular hydrogen bonds are present only in the crystal structures of complexes 2 , 5 and 6 . An unexpectedly high maximum of the χT ( T ) curve, above 20 emu K mol −1 Oe −1 , is observed in some of the complexes. Significantly high χT maxima come from the quadratic spin–spin interactions depicted in the ZFS term as a consequence of the influence of the structural distortions and intermolecular interactions on the magnetic environment of Ni( ii ) ions. The influence of this contribution to the magnetic behaviour is revised in the known magneto-structural correlations between the values of the parameter of magnetic interaction J and the average Ni–O–Ni angle. The influence of the other structural characteristics, the average angle between O⋯Ni⋯O planes and the average angle between one O⋯Ni⋯O plane and the Ni⋯Ni vector, on the values of the parameter of magnetic interaction J is also analysed.
The study of the transition from high-entropy alloys (HEAs) to conventional alloys (CAs) composed of the same alloying components is apparently important, both for understanding the formation of HEAs ...and for proper evaluation of their potential with respect to that of the corresponding CAs. However, this transition has thus far been studied in only two types of alloy systems: crystalline alloys of iron group metals (such as the Cantor alloy and its derivatives) and both amorphous (a-) and crystalline alloys, TE-TL, of early (TE = Ti, Zr, Nb, Hf) and late (TL = Co, Ni, Cu) transition metals. Here, we briefly overview the main results for the transition from HEAs to CAs in these alloy systems and then present new results for the electronic structure (ES), studied with photoemission spectroscopy and specific heat, atomic structure, thermal, magnetic and mechanical properties of a-TE-TL and Cantor-type alloys. A change in the properties of the alloys studied on crossing from the HEA to the CA concentration range mirrors that in the ES. The compositions of the alloys having the best properties depend on the alloy system and the property selected. This emphasizes the importance of knowing the ES for the design of new compositional complex alloys with the desired properties.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
► Ir-doped hematites were prepared by heating Ir-doped goethites. ► Ir-doping in hematite led to an increase in unit cell and a decrease in crystallite size. ► Ir-doping significantly affected ...magnetic, infrared and UV–Vis properties of hematite. ► The Morin transition temperature increased with an increase in Ir-doping. ► Ir ions brought about changes in the size and shape of the formed hematite particles.
The effect of the incorporation of Ir3+ ions on the properties of α-Fe2O3 formed by dehydroxylation of α-FeOOH was investigated using X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), 57Fe Mössbauer, UV–Vis–NIR and FT-IR spectroscopies, SQUID magnetometer, field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray spectroscopy (EDS). Pure and Ir-doped hematite samples were obtained by heating of pure and Ir-doped goethites (α-FeOOH) formed by precipitation from mixed Fe(III)–Ir(III) chloride solutions in a highly alkaline medium. The incorporation of Ir3+ ions into the α-Fe2O3 structure led to changes in unit-cell dimensions, crystallinity, particle size and shape, as well as changes in the magnetic, infrared and UV–Vis properties. An increase in the temperature of the Morin transition with an increase in Ir-doping was observed by Mössbauer spectroscopy and magnetic measurements.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Iron(III) chloride deaerated alkaline aqueous colloidal solutions in the presence of 2-propanol and DEAE-dextran (diethylaminoethyl-dextran hydrochloride) were γ-irradiated with doses of 36 and ...130 kGy. The dose rates were ~7 and ~31 kGy h−1. The extremely stable aqueous suspension of substoichiometric Fe2.83O4 magnetite nanoparticles ~4.7 nm in size were formed at a dose rate of ~7 kGy h−1 and at a dose of 36 kGy. At a dose of 130 kGy the anisotropic δ-FeOOH magnetic discs with a diameter of ~256 nm and thickness of ~40 nm were formed. Each disc has a substructure consisting of approximately eighteen laterally stacked thin nanodiscs of about 2.2 nm in thickness. At a higher dose rate of ~31 kGy h−1and at a dose of 36 kGy, XRD revealed the presence of highly substoichiometric Fe2.75O4 magnetite, whereas TEM analysis revealed the presence of ~4.3 nm magnetite nanoparticles along with rod-shaped γ-Fe2O3 nanoparticles. The values of isomer shift in Mössbauer spectra of about 0.33 mm s−1 showed that all Fe(II) in substoichiometric magnetites oxidized to Fe(III) one month after synthesis. At high dose and dose rate, the rolled rod-like δ-FeOOH magnetic nanoparticles were formed having the diffraction patterns with streaks, which are characteristic of tubular structures. The magnetic measurements showed exceptional intrinsic room-temperature magnetic properties of both δ-FeOOH nanostructures with the Curie temperature above 300 K. In order to ascertain the formation of Fe(II) intermediate products prior to their oxidation, γ-irradiated samples were isolated by admixing glycerol. The amounts of Fe(II) in glycerol-isolated solid samples were determined using Mössbauer spectroscopy. Carbonate Green Rust I GR(CO32−) and Fe(OH)2 intermediate phases were confirmed by XRD and Mössbauer spectroscopy. The amounts of Fe2+ in the acidified solutions containing dissolved γ-irradiation ferrous products were determined using the potassium permanganate titration. The amounts of Fe2+ were 68.9% and 96.1% at doses of 36 and 130 kGy, respectively. Thus, at a dose of 130 kGy the radiolytically generated Fe(OH)2, after coming in contact with oxygen and CO2 from the air, topotactically oxidized to GR(CO32−) and further to δ-FeOOH without any structural changes. The lower dose rate (~7 kGy h−1) favored the δ-FeOOH nanodisc morphology, whereas the higher dose rate (~31 kGy h−1) favored the formation of tubular rod-like δ-FeOOH nanoparticles.
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•γ-Irradiation can reduce Fe(III) up to Fe(OH)2 in the presence of DEAE-dextran.•The intermediate phases Fe(OH)2 and GR(CO32−) were captured by admixing glycerol.•Magnetite NPs 4.7 nm in size formed at dose rate of 7 kGy h−1 and at a dose of 36 kGy.•At a dose of 130 kGy the δ-FeOOH nanodiscs or δ-FeOOH tubular rod-like NPs formed.•Synthesized δ-FeOOH has unique magnetic properties with Curie temperature above 300 K.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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