Denis Karpov

CoxCu1-xFe2O4 nanoparticles (NPs) with x = 0, 0.4, 0.7, and 1.0 were synthesized by anion-exchange resin technique applying the same controlled conditions including the calcinations temperature (800 ºC) and cooling (0.1 °C/s) regimes. Additionally, CuFe2O4 NPs were synthesized in the rapid (23.3 °C/s) cooling mode (quenching) and CoFe2O4 NPs– at a calcination temperature of 600 ºC. The impact of a Co2+ doping content and the synthesis conditions on the NPs crystal phase, size, and magnetic properties were studied using XRD, thermal analysis, FTIR, Mossbauer spectroscopy, VSM and magnetic circular dichroism spectroscopy. It was found that cubic nanocrystals of the Fd3m space group form in all cases except CuFe2O4 NPs cooled at a rate 0.1 °C/s. The cubic phase for these NPs was obtained by quenching. Strong changes in the Co2+, Cu2+, and Fe3+ ions distribution between octahedral and tetrahedral crystal sites was revealed with Mossbauer spectroscopy in dependence on Co concentration. When cooling samples containing larger nanoparticles, wasp-waist hysteresis loops were observed, the formation of which was attributed to spinodal decomposition and chemical segregation. For the first time, MCD spectra of Cu- and mixed CuCo-ferrite NPs were obtained, and their features, which change radically with NPs composition change, were analyzed in comparison with the distribution of cations between crystal sites, as determined by Mössbauer spectroscopy.

Two-dimensional (2D) materials and phenomena attract huge attention in modern science. Herein, we introduce a family of layered materials inspired by the minerals valleriite and tochilinite, which are composed of alternating “incompatible”, and often incommensurate, quasi-atomic sheets of transition metal chalcogenide (sulfides and selenides of Fe, Fe-Cu and other metals) and hydroxide of Mg, Al, Fe, Li, etc., stacked via electrostatic interaction rather than van der Waals forces. We survey the data available on the composition and structure of the layered minerals, laboratory syntheses of such materials and the effect of reaction conditions on the phase purity, morphology and composition of the products. The spectroscopic results (Mössbauer, X-ray photoelectron, X-ray absorption, Raman, UV-vis, etc.), physical (electron, magnetic, optical and some others) characteristics, a specificity of thermal behavior of the materials are discussed. The family of superconductors (FeSe)·(Li,Fe)(OH) having a similar layered structure is briefly considered too. Finally, promising research directions and applications of the valleriite-type substances as a new class of prospective multifunctional 2D materials are outlined.

Copper ferrite is of great interest to researchers as a material with unique magnetic, optical, catalytic, and structural properties. In particular, the magnetic properties of this material are structurally sensitive and can be tuned by changing the distribution of Cu and Fe cations in octahedral and tetrahedral positions by controlling the synthesis parameters. In this study, we propose a new, simple, and convenient method for the synthesis of copper ferrite nanoparticles using a strongly basic anion-exchange resin in the OH form. The effect and possible mechanism of polysaccharide addition on the elemental composition, yield, and particle size of CuFe₂O₄ are investigated and discussed. It is shown that anion-exchange resin precipitation leads to a mixture of unstable cubic (c-CuFe₂O₄) phases at standard temperature and stable tetragonal (t-CuFe₂O₄) phases. The effect of reaction conditions on the stability of c-CuFe₂O₄ is studied by temperature-dependent XRD measurements and discussed in terms of cation distribution, cooperative Jahn–Teller distortion, and Cu²⁺ and oxygen vacancies in the copper ferrite lattice. The observed differences in the values of the saturation magnetization and coercivity of the prepared samples are explained in terms of variations in the particle size and structural properties of copper ferrite.

Copper ferrite attracts a lot of interest from researchers as a material with unique magnetic, optical, catalytic and structural properties. In particular, the magnetic properties of this material are structurally sensitive and can be tuned by changing the distribution of Cu and Fe cations in octahedral and tetrahedral positions by controlling synthesis parameters. In this study, we propose a new simple and convenient method for the synthesis of copper ferrite nanoparticles using a strongly basic anion exchange resin in OH form. The effect and possible mechanism of polysaccharides addition on the elemental composition, yield and particle size of CuFe2O4 is investigated and discussed. It is shown that anion exchange resin precipitation leads to a mixture of unstable at standard temperature cubic (c-CuFe2O4) and stable tetragonal (t-CuFe2O4) phases. The effect of the reaction conditions on the c-CuFe2O4 stability is studied by temperature-dependent XRD measurements and discussed in terms of the cations distribution, Jahn−Teller distortion and Cu2+ and oxygen vacancies in the copper ferrite lattice. The obtained differences in the values of saturation magnetization and the coercive force of prepared samples are explained with a reference to variations in the particle sizes and the structural characteristics of copper ferrite.

We report here a simple hydrothermal synthesis of 100-200 nm flakes of tochilinite m(Fe1 xS)n(Mg,Fe)(OH)2 constructed by interchanging atomic sheets of iron sulfide and magnesium hydroxide as a representative of a new platform of multifunctional two-dimensional materials. The formation and characteristics of the material was studied using X-ray and electron diffraction, TEM, EDS, X-ray photoelectron and 57Fe Mössbauer and UV-vis-NIR spectroscopies, measurements of magnetization, dielectric permittivity, and zeta potential of aqueous dispersions. The reliable formation of tochilinite was ensured by a large excess of sodium sulfide, which induced negative zeta potential (about -30 mV) of tochilinite dispersions, whereas the potential approached zero for nearly-stoichiometric S/Fe precursor ratios. The assembly of the metal sulfide and hydroxide sheets driven by their opposite electric charges starts immediately after mixing the reagents at room temperature. The hydroxide layers contain Fe3+, not Fe2+, cations, the quantity of which was reduced and increased in the range 10 to 40% of Mg2+ by addition of Al and Li, respectively. The Fe-deficient sulfide sheets contain comparable amounts of high-spin Fe3+ and Fe2+ centers, and minor S-S bonding. The room-temperature Mössbauer spectra were fitted with several doublets with the chemical shift of 0.35-0.4 mm/s and varying quadrupole splitting. Magnetic ordering at 4.2 K manifested by three six-line patterns with the hyperfine fields of ~290, 350 and 480 kOe attributed to overlapped Fe2+-S and Fe3+-OH signals, Fe3+-S centers and some Fe3+-O centers, respectively; a paramagnetic behavior was observed in SQUID experiments. The temperature and frequency dependences of permittivity revealed the activation energy of ~0.3 eV, probably, due to electron transitions involving Fe 3d states. A series of UV-vis absorption maxima were explained in terms of the high-index all-dielectric Mie resonance and the ligand-to-metal charge transfer alike Fe-S clusters in proteins. Prospective properties and applications of the materials are discussed.

During the past few decades, hybrid nanoparticles (HNPs) based on a magnetic material and gold have attracted interest for applications in catalysis, diagnostics and nanomedicine. In this paper, magnetic CoFe₂O₄/Au HNPs with an average particle size of 20 nm, decorated with 2 nm gold clusters, were prepared using methionine as a reducer and an anchor between CoFe₂O₄ and gold. The methionine was used to grow the Au clusters to a solid gold shell (up to 10 gold deposition cycles). The obtained nanoparticles (NPs) were studied by X-Ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared (FT-IR) spectroscopy, X-Ray photoelectron spectroscopy (XPS) and UV-vis spectroscopy techniques. The TEM images of the obtained HNPs showed that the surface of cobalt ferrite was covered with gold nanoclusters, the size of which slightly increased with an increase in the number of gold deposition cycles (from 2.12 ± 0.15 nm after 1 cycle to 2.46 ± 0.13 nm after 10 cycles). The density of the Au clusters on the cobalt ferrite surface insignificantly decreased during repeated stages of gold deposition: 21.4 ± 2.7 Au NPs/CoFe₂O₄ NP after 1 cycle, 19.0 ± 1.2 after 6 cycles and 18.0 ± 1.4 after 10 cycles. The magnetic measurements showed that the obtained HNPs possessed typical ferrimagnetic behavior, which corresponds to that of CoFe₂O₄ nanoparticles. The toxicity evaluation of the synthesized HNPs on Chlorella vulgaris indicated that they can be applied to biomedical applications such as magnetic hyperthermia, photothermal therapy, drug delivery, bioimaging and biosensing.