Zn- A nd (Mn, Zn)-substituted versus unsubstituted magnetite nanoparticles: Structural, magnetic and hyperthermic properties

In this work, we studied structural and magnetic properties of 18 nm sized Zn-substituted magnetite, 28 nm sized unsubstituted and 17 nm sized (Mn, Zn)-substituted iron oxide nanoparticles, synthesized by thermal decomposition method. Their features were examined by analyzing the X-ray diffraction data, 57Fe Mössbauer spectra and magnetization measurements by SQUID interferometer. The microstructure was inspected comparing the different size and strain broadening models incorporated into Fullprof software. In terms of crystallinity and size dispersion, applied synthesis protocol shows superiority over decomposition of iron oleate and the co-precipitation synthesis route. The saturation magnetization at T = 5 K was found to be within the M S = 91.2-98.6 A m2kg-1 range, while at 300 K M S of pure and Zn-substituted Fe3O4 nanoparticles is 83.6 and 86.2 A m2kg-1, respectively. Effective magnetic anisotropy constant K eff, estimated under slow measurements by SQUID, is below 20 kJ m-3 in all three samples. Some preliminary measurements of the magnetic hyperthermia performance, expressed via specific absorption rate value showed that the best heating performances were displayed by 18 nm sized oleic acid-coated Zn0.13Fe2.87O4 cubo-octahedrons with SAR ≅ 425 W/gFe at H 0 = 20 kA m-1 and f = 228 kHz.Fil: Jović Orsini, Nataša. University of Belgrade; SerbiaFil: Milić, Mirjana. University of Belgrade; SerbiaFil: Torres Molina, Teobaldo Enrique. Universidad de Zaragoza. Instituto de Nanociencia de Aragón; España. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte; Argentin

Interfacial Polarization and Dielectric Properties of Epoxy/Graphite Flakes Composites

Dielectric properties of composites based on bisphenol-A-epoxy resin loaded with various content of graphite flakes (GF) have been studied. The dielectric permeability, tangent loss and ac conductivity have been examined in wide temperature (170 – 370 K) and frequency (20 Hz – 200 kHz) range. In composites loaded with GF flakes up to 10 wt.%, the dominant conduction mechanism is tunneling of electrons, while loading of 15 wt.% gives rise to electron conduction through direct contacts between fillers. Dielectric properties of composites are largely determined by the nature of the filler/matrix interface, the filler surface area and the inherent conductivity of the fillers. At low electric field frequencies, dominates socalled interfacial (or space charge) polarization due to accumulation of free charges at the interfaces between two phases (filler and matrix), which differ in electrical conductivity.Influence of the filler surface chemistry have been studied for composites loaded with 5 wt.% graphite flakes obtained: (i) under wet milling, without (GF) or with (GF-Tr100x) adding Triton-100x as a surfactant, or (ii) under dry milling in the presence of KOH (GF-KOH). The surface treatment with KOH notable increased dielectric constant of the epoxy/GF-KOH5 composite, keeping low tangent loss, comparable to the counterpart, the epoxy/GF5 composite

Agates of the Lece Volcanic Complex (Serbia): Mineralogical and Geochemical Characteristics

Agate veins and nodules occur in the Lece Volcanic Complex (Oligocene-Miocene) situated in the south of Serbia and occupying an area of 700 km2. This volcanic complex is composed predominantly of andesites, with sporadic occurrences of andesite-basalts, dacites and latites, and features agate formations that have been very little investigated. This study focuses on five selected agate occurrences within the Lece Volcanic Complex, employing optical microscopy, scanning electron microscopy (SEM), X-ray powder diffraction analysis, inductively coupled plasma mass spectrometry (ICP-MS), and Fourier transform infrared spectroscopy (FTIR). In three localities (Rasovača, Mehane, and Ždraljevići), agate mineralization is directly related to distinct fault zones with strong local brecciation. In the other two localities (Vlasovo and Sokolov Vis), the agate is found in nodular form and does not show any connection with fracture zones. The silica phases of the Lece volcanic agates consist of cristobalite and tridymite, length-fast chalcedony, quartzine (length-slow chalcedony), and macrocrystalline quartz. Vein agates show a frequent alternation between length-fast chalcedony and quartz bands. Nodular agates consist primarily of length-fast chalcedony, occasionally containing notable quantities of opal-CT, absent in vein agates. Microtextures present in vein agates include crustiform, colloform, comb, mosaic, flamboyant, and pseudo-bladed. Jigsaw puzzle quartz microtexture supports the recrystallization of previously deposited silica in the form of opal or chalcedony from hydrothermal fluids. Growth lines in euhedral quartz (Bambauer quartz) point to agate formations in varying physicochemical conditions. These features indicate epithermal conditions during the formation of hydrothermal vein agates. Due to intense hydrothermal activity, vein agate host rocks are intensively silicified. Vein agates are also enriched with typical ore metallic elements (especially Pb, Co, As, Sb, and W), indicating genetic relation with the formation of polymetallic ore deposits of the Lece Volcanic Complex. In contrast, nodular agates have a higher content of major elements of host rocks (Al2O3, MgO, CaO, Na2O, and K2O), most probably mobilized from volcanic host rocks. Organic matter, present in both vein and nodular agate with filamentous forms found only in nodular agate, suggests formation in near-surface conditions

The improvement of ferroelectric properties of BiFeO3 ceramics by doping with La3+ and Eu3+

Bismuth ferrite is a unique multiferroic material that has a ferroelectric and antiferromagnetic order at room temperature. The rhombohedrally (R3c) distorted BiFeO3 perovskite structure is a result of relative cation displacement along [111] axis of the cubic perovskite structure and relative rotation of two oxygen octahedra in opposite directions around [111] axis [1]. The partial substitution of Bi3+ with rare-earth ions can affect the magnitude of lattice distortion and thus the value of electric polarization. The presence of undesirable secondary phases (Bi2Fe4O9 and Bi25FeO39) and structural point defects (oxygen and bismuth vacancies) in pure BiFeO3 lead to a high leakage current, which deteriorates its ferroelectric properties. Doping with rare-earth elements with large ionic radii is found to reduce the number of the structural defects and thus improve ferroelectric properties [2]. The influence of partial substitution of Bi3+ with La3+ and/or Eu3+ on ferroelectric properties of BiFeO3 ceramics was investigated. The Bi1-(x+y)LaxEuyFeO3 (x = 0, 0.025 0.05, 0.10; y = 0, 0.025, 0.05, 0.10) powders were synthesized by hydro-evaporation method, uniaxially pressed at 9 t/cm2 and sintered at 835 °C for 3 h. All the ceramic samples showed a rhombohedral structure, without presence of the secondary phases. Their morphology indicated the complete sintering under the given conditions. The grain size and grain shapes differed more depending on the dopant type and amount. The introduction of La3+ and/or Eu3+ at the site of Bi3+ led to such distortions within the rhombohedral lattice that resulted in much greater remnant electric polarization (Pr) in comparison with the undoped sample. The Bi1-(x+y)LaxEuyFeO3 ceramic samples with x+y = 0.10 showed approximately quadratic polarization vs. electric field P(E) hysteresis curves as well as significantly high values of pure ferroelectric polarization Pr, in large electric fields (100 – 140) kV/cm. The leakage currents of La3+/Eu3+-doped samples are mostly reduced, especially those doped only with Eu3+

Ferroelectric properties of BiFeO3 ceramics with cation substitutions at Bi-site (La3+, Eu3+) and Fe-site (Nb5+, Zr4+)

BiFeO3 is one of the few multiferroic perovskites that exhibits magnetic and ferroelectric properties at room temperature. However, it is also distinguished by high leakage current, low remnant electric and magnetic polarization, and high electric coercive field. These features keep it away from any practical use in electronics. Therefore, many attempts have been made to improve the properties of BiFeO3 by Bi- or Fe-site doping or by both. Previous investigations suggest that doping with Nbat Fe-site can positively affect the magnetic behavior of BiFeO3 and decrease the leakage current. In this study, various cation substitutions at Bi-site (La3+, Eu3+) and Fe-site (Nb5+, Zr4+) were examined to investigate their possible synergism and benefit for the ferroelectric properties. The role of the cations with higher valence is to suppress the formation of structural defects during synthesis, such as oxygen and bismuth vacancies. These defects are responsible for high leakage currents and, consequently, low breakdown voltages characteristic of the pure BiFeO3. On the other hand, rare earth cations at the Bisite usually enable densification of the ceramics in a wider range of temperatures, preventing bismuth loss and forming defects and secondary phases during sintering. However, do pant concentrations above 10–15mol% may give rise to transition from polar, rhombohedral (R3c) to non-polar, orthorhombic (Pnma) symmetry. The carefully selected compositions of doped BiFeO3 were synthesized by a simple hydro-evaporation method. The ceramics samples were characterized using X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and polarization techniques, including leakage current measurements. Although the introduction of Nb5+or Zr4+decreased the leakage current, they surprisingly deteriorated the ferroelectric properties even at concentrations as low as 1 mol%. This effect was more pronounced for the samples containing Nb. On the contrary, both La3+ and Eu3+ (incorporated at the Bi-site) improved the ferroelectric properties as their concentrations increased. The La-doped samples exhibited higher remnant electric polarizations at observed electric fields. The highest remnant electric polarization of31.9 μC/cm2at 150 kV/cm was measured for Bi0.85La0.15Fe0.998Zr0.002O3, indicating the synergetic effect of La3+ and Zr4+, which is limited to very low Zr4+concentrations

Bioimaging of liver cancer cells incubated with partially reduced graphene oxide

Functional materials based on graphene oxide (GO) and reduced graphene oxide (rGO) have a high potential for application in the fields of biophysics, material science, and biomedical engineering [1]. It is due to their tunable physical properties, high surface area, remarkable photoluminescence, as well as their controllable chemical functionalization [2]. Beyond their applications in nanomedicine for drug/gene delivery, phototherapy and bioimaging, they have shown significant interaction and adhesive properties with proteins, mammalian cells and microorganisms, which makes them potential candidates for multifunctional biological applications. In this lecture, we will present a study of the interaction of partially reduced graphene oxide (prGO) with Huh7.5.1 liver cancer cells. The study was conducted by means of synchrotron excitation DUV fluorescence bioimaging (performed on DISCO beamline of synchrotron SOLEIL) [3]. The prGO sample was obtained by the reduction (to a certain extent) of the initially prepared GO nanosheets. The fluorescence of the GO nanosheets increases with time of the reduction due to a change in the ratio of the sp2 and sp3 carbon sites, and the prGO sample was extracted from the dispersion when the intensity of the fluorescence reached its maximum. After that, Huh7.5.1 cells were incubated with GO, prGO and rGO nanosheets and used in bioimaging studies. The presence of graphene materials influenced the fluorescence properties of the cells, and by analyzing fluorescence photobleaching dynamics, we were able to localize graphene nanosheets inside the liver cancer cells.VII International School and Conference on Photonics : PHOTONICA2019 : Abstracts of Tutorial, Keynote, Invited Lectures, Progress Reports and Contributed Papers; August 26-30; Belgrad

TUNING OF FERROELECTRIC PROPERTIES OF BiFeO3 CERAMICS BY CATION SUBSTITUTIONS AT Bi-SITE AND Fe-SITE

In this study, we tried various cation substitutions at Bi-site (La3+, Eu3+) and Fesite (Nb5+ , Zr4+ ) to explore their possible synergism and improvement of the ferroelectric properties of bismuth ferrite. The cations with higher valence ought to suppress the formation of structural defects during syntheses, such as oxygen and bismuth vacancies. These defects are responsible for high leakage currents and low breakdown voltages characteristic of pure BiFeO3. On the other hand, rare earth cations at the Bi-site usually enable densification of the ceramics at a broader range of temperatures, preventing bismuth loss and formation of defects and secondary phases during sintering. However, dopant concentrations above 10–15 mol% may give rise to a transition from polar, rhombohedral (R3c) to non-polar, orthorhombic (Pnma) symmetry. Thus, we synthesized pure and selected compositions doped BiFeO3 by a hydroevaporation method and determined the optimal calcination temperature by thermal analyses of the precursor powders. Then we characterized ceramics samples using X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM) and polarization techniques. Although only 1 mol% Nb5+ decreased the leakage current, it surprisingly deteriorated the ferroelectric properties of BiFeO3. Similar effect exhibited the samples containing Zr4+ that showed no improvement compared with undoped bismuth ferrite. On the contrary, La3+ and Eu3+ (incorporated at the Bi-site) improved the ferroelectric properties as their concentrations increased, whereby the samples doped with 15 mol% La exhibited higher remnant electric polarizations at observed electric fields. The highest remnant electric polarization of 31.9 µC/cm2 at 150 kV/cm, was measured for Bi0.85La0.15Fe0.998Zr0.002O3, indicating the synergetic effect of La3+ and Zr4+, which is limited to low Zr4+ concentrations

CA and/or EDTA functionalized magnetic iron oxide nanoparticles by oxidative precipitation from FeCl2 solution: structural and magnetic study

Four samples containing magnetic iron oxide nanoparticles (MIONs) of various sizes are prepared employing a simple low-temperature method of oxidative precipitation from FeCl2∙4H2O-NaOH-NaNO3 aqueous solution. For the preparation of two samples, the usual oxidation-precipitation synthesis protocol is modified by using ethylenediaminetetraacetic acid (EDTA) chelating agent as a stabilizer of the Fe2+ ions in a solution, which results in the partial capping of the prepared MIONs with EDTA molecules. Three out of four samples are subjected to citric acid (CA) functionalization in the post synthesis protocol. Structural and magnetic properties of the synthesized MIONs are assessed using various experimental techniques (XRD, TEM, Fourier transform infrared, dynamic light scattering, Mössbauer, and SQUID). The average size of spherical-like MIONs is tuned from 7 nm to 38 nm by changing the synthesis protocol. Their room temperature saturation magnetization, M s, is in the range of 43 to 91 emu g−1. Magnetic heating ability, expressed via specific absorption rate value, which ranges from 139 to 390 W/gFe, is discussed in relation to their structural and magnetic properties and the possible energy dissipation mechanisms involved. The best heating performance is exhibited by the sample decorated with EDTA and with a bimodal size distribution with average particle sizes of 14 and 37 nm and M s = 87 emu g−1. Though this sample contains particles prone to form aggregates, capping with EDTA provides good colloidal stability of this sample, thus preserving the magnetic heating ability. It is demonstrated that two samples, consisting of 7 nm-sized CA- or 14 nm-sized EDTA/CA-functionalized superparamagnetic MIONs, with a similar hydrodynamic radius, heat in a very similar way in the relatively fast oscillating alternating current magnetic field, f = 577 kHz

Evaluating PVP coated iron oxide particles for localized magnetic hyperthermia and MRI imaging

Ferrofluids based on magnetic iron oxide nanoparticles (IONPs) have been widely studied as multipurpose agents in various medical applications including magnetic hyperthermia, targeted drug delivery and magnetic resonance imaging (MRI). To increase their stability and compatibility with the living cells and thus improve their suitability for these purposes, the IONPs are often functionalized with different organic or inorganic molecules. In this work we report on the preparation of polyvinilpyrrolidone (PVP) functionalized IONPs through a simple co-precipitation method and investigated their suitability for magnetic hyperthermia and as a MRI contrast agent. Spherical PVP-coated IONPs, with an average particle size of ≈ 15 nm, showed superparamagnetic behavior and high saturation magnetization Ms = 80.7 emug−1, at room temperature. The specific absorption rate (SAR), a measure of the heating ability, ranged from 17 W/g to 721 W/g (evaluated for various combinations of AC magnetic field amplitudes and frequencies), while the intrinsic loss power (ILP) was in the range from 0.53 nHm2 kg−1 to 2.34 nHm2 kg−1. In addition to relatively good heating ability, high T2 relaxivity, r2 = 126 mM−1 s−1 and high r2/r1 ratio demonstrated that the preparation procedure used here can yield nanoparticles suitable for MRI guided localized magnetic hyperthermia

Dielectric properties of epoxy/graphite flakes composites: Influence of loading and surface treatment

Epoxy-rich carbon-based composites are well recognized materials in industries owing to their good mechanical properties and thermal stability. Here, dielectric properties of composites based on bisphenol-A-epoxy resin loaded with 5, 6, 10, and 15 wt% of graphite flakes (GF) have been studied. The frequency and temperature dependence of the dielectric permittivity, dielectric loss, and ac conductivity have been examined in temperature (−103 to 97°C) and frequency (20 Hz–200 kHz) range. Influence of the filler surface chemistry have been studied for composites loaded with 5 wt% GF obtained: (i) under wet milling, without or with adding Triton-100x as a surfactant, or (ii) under dry milling in the presence of KOH. The composite made of epoxy loaded with 5 wt% exfoliated expanded graphite flakes (EEG), was also prepared. The surface treatment with KOH notably increased dielectric constant of the composite, keeping low dielectric loss, while treatment with Triton-100x significantly increased tanδ. The composite loaded with exfoliated expanded graphite shows higher ac conductivity than those obtained with flaky graphite, GF. Possibility to change dielectric properties of the composites without changing the loading content can be used as an approach in tailoring one with desired dielectric properties