[Show abstract][Hide abstract] ABSTRACT: Three new two-dimensional (2D) Hofmann-type coordination polymers with general formula [Fe(3-NH2py)2M(CN)4] (3-NH2py = 3-aminopyridine, M = Ni (1), Pd (2), Pt (3)) have been synthesized. Magnetic susceptibility measurements show that they exhibited cooperative spin crossover (SCO) with remarkable hysteretic behaviors. Their hysteresis widths are 25, 37, and 30 K for 1-3, respectively. The single-crystal structure of 1 suggest that the pseudo-octahedral Fe sites are equatorially bridged by [M(CN)4](2-) to form 2D grids and axially coordinated by 3-NH2py ligands. The intermolecular interactions between layers (the offset face-to-face π···π interactions, hydrogen bonds, and weak Namino···Ni(II) contacts) together with the covalent bonds bridged by [M(CN)4](2-) units are responsible to the significant cooperativity.
[Show abstract][Hide abstract] ABSTRACT: Nickel ferrite NiFe2O4 is a typical soft magnetic ferrite with high electrical resistivity used as high frequency magnetic material. Neodymium (Nd3+) doped NiFe2O4 materials were fabricated using solid state reaction. The properties of the obtained material were investigated by X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Fourier-Transform Infrared Spectroscopy (FT-IR), magnetic measurements on SQUID and Mössbauer spectroscopy. It was found that the material consists of two different phases: Nd3+ doped NiFe2O4 and NdFeO3. The Nd3+ ions occupy cation sites of the NiFe2O4 inverse spinel structure. NdFeO3 phase occurred when the level of Nd3+ atoms exceed a percolation limit. The presence of both phases was confirmed by SEM observations. The Mössbauer spectra analysis showed two sextets, which can be ascribed to iron atoms in tetrahedral and octahedral positions. From their intensities it is concluded that Nd3+ occupies octahedral sites in the spinel structure of NiFe2O4, which were originally occupied by Ni2+.
[Show abstract][Hide abstract] ABSTRACT: Classification, chemistry, and applications of fullerenes, carbon dots, nanotubes, graphene, nanodiamonds, and combined superstructures of a range of carbon nanoallotropes are investigated. The investigations also cover superstructures consisting of combinations of carbon nanoallotropes such as fullerene aggregates, CNTs or graphene thin films, fibers, membranes, and aerogels in addition to describing individual carbon nanoallotropes. The issue of chemical modification of carbon nanoallotropes with division into several sections based on the origins of the chemical reactivity in each case is also investigated.
Chemical Reviews 05/2015; 115(11). DOI:10.1021/cr500304f · 46.57 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: This study continues our investigation of high-temperature superconductors of LaFeO(1−x)Fx
As type initiated in our previous paper (J. Supercond. Nov. Magnetism 27, 1825, ), where the high-temperature Kondo effect had been observed in the sample with x = 0.15. We proceed with exploring the properties of the LaFeO 0.88F
0.12As sample, applying the X-ray diffraction (XRD) method, resistivity measurement, and the magnetic and Mössbauer measurements at the temperature range of 4.2-300 K. We observe the emergence of high-temperature Kondo effect at the temperatures between 30 and 50 K. At the same time, as opposed to the case x=0.15, we reveal the transformation of the high-temperature Kondo effect to the high-temperature superconductivity at the temperature near 25 K. The Mössbauer spectra of the sample obtained at different temperatures represent a single line, lying near zero relative velocity and do not exhibit any visible alterations. Concurrently, the application of an external magnetic field of 5 T to the sample at 5 K induces the emergence of a hyperfine magnetic splitting with the effective magnetic field on resonant nuclei H
ef = 45.5 kOe. We suppose that the appearance of a magnetic ordering in the sample occurs due to the alignment of magnetic moments of impurities that confirms our hypothesis about a strong coupling of electron’s spins with the magnetic moments of impurities in iron-containing superconductors.
Journal of Superconductivity and Novel Magnetism 05/2015; 28(9). DOI:10.1007/s10948-015-3088-4 · 0.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: To date, iron oxides have been extensively investigated for promising high applicability in various scientific and industrial fields. Generally, several forms can be distinguished with respect to their crystal structure that drives their specific physical (particularly, magnetic) properties. In this work, the pure β-Fe2O3 phase, prepared in a nanoparticle form by solid-state synthetic strategy, was investigated employing 57Fe Mössbauer spectroscopy, magnetization measurements, transmission electron microscopy, X-ray powder diffraction, heat capacity measurements, and cyclic voltammetry. It turns out that below the Néel transition temperature, β-Fe2O3 behaves as a canted antiferromagnet with a small net moment. For further possible utilization in photoelectrochemical applications, the estimation of β-Fe2O3 band gap by cyclic voltammetry was performed amounting to ~2.2 eV.
[Show abstract][Hide abstract] ABSTRACT: In this study, dielectric properties within 8–12 GHz microwave frequencies, inductively coupled plasma-atomic emission spectrometry, Fourier transform infrared spectrometry, synchronized two thermal analyses, and 57 Fe Mössbauer spec-troscopy analysis of chalcedony, agate, and zultanite samples from Turkey are presented. Agate and chalcedony show the same nine vibrational absorption peaks obtained unlike zultanite from FTIR spectra in the 350 cm −1 to 4000 cm −1 range, ε values of chalcedony, agate and zultanite derived at 10.5 GHz were 4.67, 4.41, and 7.34, respectively, ε and ε values of the studied samples at the microwave frequencies are related to the percentage weight of their constituent parts in their chemical compositions. 57 Fe Mössbauer spectroscopy results confirm the existence of iron-containing islands in the crystal structure of zultanite, agate, and chalcedony samples, equipped them with magnetic features typical for magnetic nanopar-ticles including superparamagnetism. The presence of iron-containing islands significantly affects the magnetic, dielectric, and optical properties of studied samples that are not observed for pure minerals without any foreign inclusions.
Chinese Physics B 05/2015; 24(5). DOI:10.1088/1674-1056/24/5/059101 · 1.60 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Potassium ferrite (KFeO2) was synthesized by a new simple thermal process from natural waste ferrihydrite and KNO3 precursors. The synthesized KFeO2 showed considerable instability when it was in contact with water and CO2 of the humid air.
The decomposition of KFeO2 followed first-order kinetics with rate constants as 0.93 × 10–1 h–1 and 1.86 × 10–1 h–1 at relative humidity of 30–35% and 65–70%, respectively. The products of
decomposition, crystalline KHCO3 and nanocrystalline iron(III) oxides in the molar ratio of 2:1, were characterized in detail by X-ray powder diffraction, low-temperature and in-field 57Fe Mössbauer spectroscopy, magnetization (SQUID) measurements, thermal analysis,
and scanning and transmission electron microscopy. Washing and subsequent air drying of the decomposed products of KFeO2 yielded monodisperse superparamagnetic maghemite (γ-Fe2O3) nanoparticles, which turned out to be efficient as magnetic sorbents
for removing Cu2+ in water. A direct addition of solid KFeO2 into water containing Cu2+ ions yielded rapid coagulation of iron(III) oxyhydroxides, which subsequently removed Cu2+ more efficiently compared to its sorption on the pre-formed maghemite
[Show abstract][Hide abstract] ABSTRACT: A new category of iron oxide nanoparticles (surface active maghemite nanoparticles (SAMNs, γ-Fe2O3)) allows the intimate chemical and electrical contact with DNA by direct covalent binding. On these basis, different DNA-nanoparticle architectures are developed and used as platform for studying electrical properties of DNA. The macroscopic 3D nanobioconjugate, constituted of 5% SAMNs, 70% water, and 25% DNA, shows high stability, electrochemical reversibility and, moreover, electrical conductivity (70–80 Ω cm−1). Reversible electron transfer at the interface between nanoparticles and DNA is unequivocally demonstrated by Mössbauer spectroscopy, which shows the appearance of Fe(II) atoms on nanoparticles following nanobioconjugate formation. This represents the first example of permanent electron exchange by DNA, as well as, of DNA conductivity at a macroscopic scale. Finally, the most probable configuration of the binding is tentatively modeled by density functional theory (DFT/UBP86/6-31+G*), showing the occurrence of electron transfer from the organic orbitals of DNA to surface exposed Fe(III) on nanoparticles, as well as the generation of defects (holes) on the DNA bases. The unequivocal demonstration of DNA conduction provides a new perspective in the five decades long debate about electrical properties of this biopolymer, further suggesting novel approaches for DNA exploitation in nanoelectronics.
[Show abstract][Hide abstract] ABSTRACT: Biogenic iron oxides have been collected from a water stream and subsequently magnetically modified using water-based magnetic fluid. Both natural and magnetically modified materials have been characterized in detail using wavelength dispersive X-ray fluorescence spectrometry, X-ray powder diffraction, Mössbauer spectroscopy, electron microscopy and BET surface area measurements. The natural material is composed of 2-line ferrihydrite, forming hollow microtubules—sheaths of Leptothrix ochracea, and detrital components. As a result of the ferrofluid modification, maghemite nanoparticles were identified on the surface of the treated material. The active surface area of the bulk, magnetically-modified sample was 148 m2 g−1. The magnetically modified material was tested as inexpensive magnetically responsive adsorbent for the removal of selected organic xenobiotics, namely organic dyes, from aqueous solutions. The observed maximum adsorption capacities ranged between 34.3 and 97.8 mg of dye per 1 g of adsorbent.
International journal of Environmental Science and Technology 02/2015; 12:673-682. DOI:10.1007/s13762-013-0455-1 · 2.19 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The removal efficiency of heavy metal ions (cadmium(II) - Cd(II), cobalt(II) - Co(II), nickel(II) - Ni(II), and copper(II) - Cu(II)) by potassium ferrate(VI) (K2FeO4, Fe(VI)), was studied as a function of added amount of Fe(VI) (or Fe) and varying pH. At pH = 6.6, the effective removal of Co(II), Ni(II), and Cu(II) from water was observed at a low Fe-to-heavy metal ion ratio (Fe/M(II) = 2:1) while a removal efficiency of 70% was for Cd(II) ions at a high Fe/Cd(II) weight ratio of 15:1. The role of ionic radius and metal valence state was explored by conducting similar removal experiments using Al(III) ions. The unique combination of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), in-field Mössbauer spectroscopy, and magnetization measurements enabled the delineation of several distinct mechanisms for the Fe(VI)-prompted removal of metal ions. Under Fe/M weight ratio of 5:1, Co(II), Ni(II), and Cu(II) were removed by the formation of MFe2O4 spinel phase and partially through their structural incorporation into octahedral positions of γ-Fe2O3 (maghemite) nanoparticles. In comparison, smaller sized Al(III) ions got incorporated easily into the tetrahedral positions of γ-Fe2O3 nanoparticles. In contrast, Cd(II) ions do not create either the spinel ferrite structure or incorporate into the lattice of iron(III) oxide phase due to the distinct electronic structure and ionic radius. Environmentally-friendly removal of heavy metal ions at a much smaller dosage of Fe than those of commonly applied iron-containing coagulants, and the formation of ferrimagnetic species preventing metal ions leaching back into the environment and allowing their magnetic separation are highlighted.
[Show abstract][Hide abstract] ABSTRACT: When developing new nanoparticles for bio-applications, it is important to fully characterize the nanoparticle's behavior in biological systems. The most common techniques employed for mapping nanoparticles inside cells include transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). These techniques entail passing an electron beam through a thin specimen. STEM or TEM imaging is often used for the detection of nanoparticles inside cellular organelles. However, lengthy sample preparation is required (i.e., fixation, dehydration, drying, resin embedding, and cutting). In the present work, a new matrix (FTO glass) for biological samples was used and characterized by field emission scanning electron microscopy (FE-SEM) to generate images comparable to those obtained by TEM. Using FE-SEM, nanoparticle images were acquired inside endo/lysosomes without disruption of the cellular shape. Furthermore, the initial steps of nanoparticle incorporation into the cells were captured. In addition, the conductive FTO glass endowed the sample with high stability under the required accelerating voltage. Owing to these features of the sample, further analyses could be performed (material contrast and energy-dispersive X-ray spectroscopy (EDS)), which confirmed the presence of nanoparticles inside the cells. The results showed that FE-SEM can enable detailed characterization of nanoparticles in endosomes without the need for contrast staining or metal coating of the sample. Images showing the intracellular distribution of nanoparticles together with cellular morphology can give important information on the biocompatibility and demonstrate the potential of nanoparticle utilization in medicine.
[Show abstract][Hide abstract] ABSTRACT: The in-situ synthesis of air-stable zero-valent iron nanoparticles
(NZVI) embedded in cellulose fibers leads to an assembly of
highly reactive magnetic filter papers. These engineered
materials display a wide range of applications in treatment of
wastewater and drinking water including chromium removal,
phenol degradation, environmental bioremediation, and
Chemical Communications 09/2014; 50:15673--15676. DOI:10.1039/C4CC06241H · 6.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The synthesis of tin–titanate nanotubes (Sn-titanate) by reacting hydrogen titanate (H-titanate) with a tin salt through ion adsorption–incorporation is reported. The interactions between tin(II) ions and H-titanate are thoroughly investigated. Tin ions can be easily adsorbed by H-titanate, owing to its large surface area and lattice spacing, and the negatively charged layered structures. With Sn-titanate nanotubes as precursors, Sn-doped TiO2 nanoparticles are prepared by annealing and are investigated as anode materials in lithium-ion batteries, which show much enhanced capacity and rate capability. Such improved electrochemical properties of Sn-doped TiO2 benefit from structural characteristics such as the small size of the constituent nanoparticles, high crystallinity, and uniform tin doping. This synthetic strategy towards Sn-doped TiO2 anode materials, thus offers the synergistic effect of combining the advantages of TiO2 (cycle life and rate) and SnO2 (high capacity).
[Show abstract][Hide abstract] ABSTRACT: We report the results of investigation of high-temperature superconductor (HTSC) LaFeO (1−x)F x As at x = 0.15. We applied the XRD method, the measurement of the hysteresis curve and resistivity, as well as the Mössbauer measurements at the temperature range 4.2–300 K. We show that in the given sample, owing to doping by fluorine, full suppression of antiferromagnetism is not accompanied by the rise of superconductivity. Instead, we observe a high-temperature (at T ≤ 40 K) Kondo effect, which indicates a strong coupling of electron’s spins with the magnetic moments of impurities. We also find a correlation between the revealed high-temperature Kondo effect and the appearance of a quadrupole splitting in the Mössbauer spectra below 40 K. The revealed effects can shed light on the mechanism of superconductivity in the iron-containing HTSC.
Journal of Superconductivity and Novel Magnetism 08/2014; 27(8):1825-1829. DOI:10.1007/s10948-014-2531-2 · 0.91 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Magnetic properties of anion-radical TCNQ salt [Fe(dipy)3](TCNQ)4·(CH3)2CO have been investigated (dipy is 2,2′-dipyridil). X-ray diffraction data allow presence of two types of TCNQ stacks: tetramerized (diamagnetic) and partly dimerized (paramagnetic). Due to Mössbauer spectroscopy data iron cation appears as two-valent ion in low-spin state. Magnetic susceptibility temperature dependence is described by Bonner–Fischer model with additional weak impurity paramagnetism. Susceptibility curve is in good qualitative agreement with ESR spectra.
[Show abstract][Hide abstract] ABSTRACT: Owing to the three different orbital hybridizations carbon can adopt, the existence of various carbon nanoallotropes differing also in dimensionality has been already affirmed with other structures predicted and expected to emerge in the future. Despite numerous unique features and applications of 2D graphene, 1D carbon nanotubes or 0D fullerenes, nanodiamonds and carbon quantum dots, which have been already heavily explored, any of existing carbon allotropes does not offer competitive magnetic properties. For challenging applications, carbon nanoallotropes are functionalized with magnetic species, especially of iron oxide nature, due to their interesting magnetic properties (superparamagnetism and strong magnetic response under external magnetic fields), easy availability, biocompatibility, and low cost. In addition, combination of iron oxides (magnetite, maghemite, hematite) and carbon nanostructures brings enhanced electrochemical performance and (photo)catalytic capability due to synergetic and cooperative effects. This work aims at reviewing these advanced applications of iron-oxide-supported nanocarbon composites where iron oxides play a diverse role. Various architectures of carbon/iron oxide nanocomposites, their synthetic procedures, physicochemical properties, and applications are discussed in details. A special attention is devoted to hybrids of carbon nanotubes and rare forms (mesoporous carbon, nanofoam) with magnetic iron oxide carriers for advanced environmental technologies. The review also covers the huge application potential of graphene/iron oxide nanocomposites in the field of energy storage, biomedicine, and remediation of environment. Among various discussed medical applications, magnetic composites of zero-dimensional fullerenes and carbon dots are emphasized as promising candidates for complex theranostics and dual magneto-fluorescence imaging.
[Show abstract][Hide abstract] ABSTRACT: Magnetization and low temperature in-field 57Fe Mössbauer spectroscopy measurements have been performed on a Fe[C(SiMe3)3]2/ferrihydrite hetero-mixture. The results indicate the presence of ferromagnetic coupling of magnetic moments involving Fe[C(SiMe3)3]2 with a hyperfine magnetic field of about 151 T, attributable mainly to the non-frozen atomic orbital contribution. The present findings show the sensitivity of single-ion molecular magnets to local alterations of their lattice-environment and might explain and reconcile some of the differences found in the literature for the observed bulk magnetic properties of the title Fe[C(SiMe3)3]2 compound.
Berichte der deutschen chemischen Gesellschaft 07/2014; 2014(20). DOI:10.1002/ejic.201402033 · 2.94 Impact Factor