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The rare earth-free Mn5Ge3 compound shows magnetocaloric properties similar to those of pure Gd; therefore, it is a good candidate for magnetic refrigeration technology. In this work, we investigate the influence of chemical substitution on the crystal structure and the magnetic, thermodynamic, and magnetocaloric properties of a polycrystalline Mn5Ge3 compound prepared by induction melting. For this purpose, we replaced 5% of the Mn with Cr or Co and 5% of the Ge with B or Al. The additional chemical elements were shown not to change the crystal structure of the parent compound (space group P63/mcm, No. 193). In the case of the magnetic properties, all samples remained ferromagnetic with the ordering temperature (TC) lower than for the original compound (TC = 295(1) K). The exception was the sample with B, where we observed an increase in TC by 3 K. The maximum value of the magnetic entropy change, |∆Sm|MAX (for a magnetic field change of 5 T), decreased from 7.1(1) for Mn5Ge3 to 6.2(1), 6.8(1), 4.8(1), and 5.8(1) J kg−1 K−1 for the alloys with B, Al, Cr, and Co, respectively. The adiabatic temperature change (∆Tad) (for a magnetic field change of 1 T) was determined from the specific heat measurements and was equal to 1.1(1), 1.2(1), 1.2(1), 0.8(1), and 0.8(1) K for Mn5Ge3, Mn5Ge2.85B0.15, Mn5Ge2.85Al0.15, Mn4.75Cr0.25Ge3, and Mn4.75Co0.25Ge3, respectively. The obtained data were compared with those from the literature. It was found that the substitution allowed for tuning of the ordering temperature in a wide temperature range. At the same time, the reduction in the magnetocaloric parameters’ values was relatively small. Therefore, the produced Mn5Ge3-based alloys allow for the expansion of the operation temperature range of the parent compound as a magnetocaloric material.

Introduction We present a multimodal nanoplatforms for the treatment of hepatocellular carcinoma (HCC) in vitro. The nanoplatforms are based on polydopamine (PDA)-coated magnetite nanoparticles (NPs) and spheres (sMAG) with PAMAM dendrimers and functionalized with NHS-PEG-Mal (N-hydroxysuccinimide-polyethylene glycol-maleimide) linker, which allows their functionalization with a folic acid derivative. The nanomaterials bearing a folic acid-targeting moiety show high efficiency in killing cancer cells in the dual chemo- and photothermal therapy (CT-PTT) of the liver cancer cells in comparison to modalities performed separately. Materials and methods All materials are characterized in detail with transmission electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, zeta potential and magnetic measurements. Also, photothermal properties were determined under irradiation of nanoparticles with laser beam of 2 W/cm2. The nontoxicity of nanoparticles with doxorubicin and without was checked by WST and LIVE/DEAD assay. Those tests were also used to evaluate materials bearing folic acid and anticancer drug in combined chemo- and photothermal therapy of HCC. Further, the generation of reactive oxygen species profile was also evaluated using flow cytometry test. Results Both NPs and sMAG showed high photothermal properties. Nevertheless, the higher photothermal response was found for magnetic spheres. Materials of concentration above 10 µg/mL reveal that their activity was comparable to free doxorubicin. It is worth highlighting that a functionalized magnetic sphere with DOXO more strongly affected the HepG2 cells than smaller functionalized nanoparticles with DOXO in the performed chemotherapy. This can be attributed to the larger size of particles and a different method of drug distribution. In the further stage, both materials were assessed in combined chemo- and photothermal therapy (CT-PTT) which revealed that magnetic spheres were also more effective in this modality than smaller nanoparticles. Conclusion Here, we present two types of nanomaterials (nanoparticles and spheres) based on polydopamine and PAMAM dendrimers g.5.0 functionalized with NHS-PEG-Mal linker terminated with folic acid for in vitro hepatocellular carcinoma treatment. The obtained materials can serve as efficient agents for dual chemo- and photothermal therapy of HCC. We also proved that PDA-coated magnetic spheres were more efficient in therapies based on near-infrared irradiation because determined cell viabilities for those materials are lower than for the same concentrations of nanomaterials based on small magnetic nanoparticles.

Polydopamine (PDA) has a wide range of applications in biomedicine due to its high biocompatibility and surface chemistry and because of the presence of many functional groups in it, enabling further modification. As a catechol-like material, it has chelation properties for various types of metal ions, including iron. Here, we developed a procedure that uses PDA as a template to grow iron structures β-FeOOH directly on its surface. The innovative approach of this work relies on that these structures can be obtained in neutral conditions and selective iron-ion source. The influence of iron-ion source, environment, and solution concentration on the structure and amount of resulting material is presented. The growth has been characterized over time, taking into account their photothermal, magnetic, and colloidal stability properties. Moreover, we shed new light on understanding the interaction of PDA with iron ions for the growth of iron-based nanostructure on polydopamine particles. Finally, we predict that PDA@β-FeOOH nanoparticles could be a promising material in dual therapy merging photothermal therapy (PTT) treatment and magnetic resonance imaging (MRI) contrast agents.

We present the magnetic, specific heat, electrical resistivity, and thermoelectric power measurements for the intermetallic compound CeSi1.2Ga0.8. This composition belongs to the series CeSi2-xGax, which exhibits diverse magnetic orderings and different crystallographic structures depending on the substitution level x. It has been previously suggested that for 0.0 < x < 1.3 the compounds crystallize in the alpha-ThSi2 type structure and for 0.7 < x < 1.3 they order ferromagnetically below 14 K. Our complementary studies for x = 0.8 reveal that it is a complex system due to the Kondo scattering competing with the RKKY interactions. The transition from the paramagnetic to the ferromagnetic state takes place at T-C = 12.5(1) K. Moreover, the Seebeck coefficient and electrical resistivity show not only an anomaly related to the magnetic transition, but also a broad maximum at-90 K related to the crystal field effect. The case of x = 0.8 is of special interest as it is at the crossing of the characteristic temperatures, i.e. T-ord (magnetic ordering temperature)similar to & nbsp; T-K (Kondo temperature) similar to 10 K. Additionally, ab initio electronic structure calculations were performed allowing us to determine phase stability, (revealing two stable phases -alpha-GdSi2-type and alpha-ThSi2-type structures) as well as spin and orbital moment decomposition on Ce-states for both considered structures. Web of Science 547 art. no. 168833

The research on magnetocaloric materials for applications concentrates, among other, on two parameters: the ordering temperature and the value of the magnetocaloric effect (MCE). The optimization consists in tuning the former without significant drop in the latter. These studies report on the magnetic susceptibility, magnetization curves, heat capacity and magnetocaloric effect measurements for compositionally and structurally modified Gd5Si4 compound. The modifications are based on the doping of the parent compound with an excess Gd atoms and substitution of Si with B as well as on the dimensional effect studied by mechanical milling. Moreover, composite samples of the type Gd:Gd5Si2Ge2 were investigated revealing the influence of the intergranular interactions on the magnetocaloric properties. It appears that these interventions enable a controllable steering of the ordering temperature shifting it towards the room temperature with, in some cases, minor reduction of the parameters characterizing MCE.

The low-temperature magnetic, thermal, electrical transport and magnetocaloric properties of the TmNiSn compound were investigated. A polycrystalline sample was prepared by arc-melting. Powder X-ray diffraction confirmed the formation of TmNiSn with orthorhombic TiNiSi-type crystal structure (space group Pnma, no. 62). It was found that TmNiSn undergoes paramagnetic to antiferromagnetic state transition at the Neel temperature TN = 2.4 K. A week inflection of isothermal magnetization curve taken at 1.8 K, can indicate a spin-flop transition. Magnetocaloric properties obtained from isothermal magnetization curves demonstrate positive and negative magnetocaloric effect. In the magnetic field change of 3 T the maximum magnetic entropy change of −10.5 J/(kg K) was obtained at 3.5 K along with the corresponding relative cooling power (RCP) value of 81 J/K. The electrical resistivity result shows metallic behavior from 2 K up to 400 K with clear anomaly at TN.

A transformation between the magnetically ordered CeCoGe3 and heavy fermion CeFeGe3 is isostructural but not isoelectronic, therefore the characterization of the electronic structure of the CeCo1−xFexGe3 series is of special importance. We report both the experimental investigation by the X-ray photoelectron spectroscopy (XPS) measurements and the first-principles calculations within the full-potential local-orbital (FPLO) scheme based on the density functional theory. Experimentally, we investigate mainly the valence band and the Ce 3 d spectra, both giving the possibility to conclude about the level of the f states localization. Computationally, we investigate the most characteristic CeCoGe3, CeCo0.5Fe0.5Ge3, and CeFeGe3 compositions. Based on the electronic band structure results we calculate the X-ray photoelectron spectra of the valence band. We consider the effects of the spin-orbit coupling and intra-atomic Hubbard U repulsion. Furthermore, we discuss the charge distribution and occupation of valence-band orbitals. The experimentally observed evolution of the 3d band with the Fe concentration is related to the decrease of the number of electrons and reduction of the 3d photoionization cross-sections. Calculations indicate that charge is transferred mainly from the Ce to Ge sites and the bondings are formed mainly by the Ce 5d, Fe/Co 3d, and Ge 4p and Ge 4s orbitals.

In an effort to find new thermoelectric materials, a series of half-Heusler alloys Sc1-xTmxNiSb (x = 0.0, 0.25, 0.5, 0.75, 1.0) was synthesized by arc melting and subsequent high-pressure high-temperature sintering. The products were examined by means of X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectrometry. The crystal structure of each sample was established to be of the MgAgAs-type, and the cubic lattice parameter was found to behave in accordance to the Vegard's law. The electrical transport properties of the Sc1-xTmxNiSb alloys were determined via resistivity and thermoelectric power measurements performed at temperatures 2–950 K. For each sample a semiconducting-like behavior was found with rather small values of the room-temperature resistivity (ρ = 10–50 μΩm), and fairly large positive Seebeck coefficient (Smax = 80–136 μV/K). For the alloy Sc0.75Tm0.25NiSb, combination of relatively small ρ (similar to that of TmNiSb) with rather high S (comparable to that of ScNiSb) yielded the thermoelectric power factor PF = 1.2 × 10 mW/(m K2) at 650 K, which is about twice larger than that found for ScNiSb. Increasing the amount of Tm in Sc1-xTmxNiSb brings about significant reduction in the thermal conductivity at 350 K from about 6 W/(m K) to ca. 3 W/(m K), and consequently leads to sizable enhancement of the thermoelectric figure of merit.

Polycrystalline samples of Er1-xHoxNiSb (x = 0, 0.2, 0.3, 0.5, 0.7, 0.8, 1) were characterized by means of x-ray powder diffraction (XRD), scanning electron microscopy (SEM), and optical metallography. The results proved the formation of half-Heusler alloys in the entire composition range. Their electrical transport properties (resistivity, thermoelectric power) were studied in the temperature interval 350-1000 K. The measured electrical resistivity spanned between 5 and 25 μΩm. The maximum thermopower of 50-65 μV/K was observed at temperatures 500-650 K. Replacing Ho for Er resulted in a non-monotonous variation of the thermoelectric power factor (PF = S2/ρ). The largest PF of 4.6 μWcmK-2 was found at 660 K for Er0.5Ho0.5NiSb. This value is distinctly larger than PF determined for the terminal phases ErNiSb and HoNiSb

Analysis of bipolar thermal conductivity might be very useful in preliminary stages of thermoelectric materials discovery. Using its product---mobility ratio between electrons and holes---it is possible to choose the most promising compound from the series and pave the correct direction of doping. Current work presents positive verification of this approach for $\mathrm{Sc}\mathrm{Ni}\mathrm{Sb}$, which is anticipated to show superior mobility when tuned towards n-type behavior. In agreement with expectation, the mobility increases by an order of magnitude due to rising tellurium content in the ${\mathrm{Sc}\mathrm{Ni}\mathrm{Sb}}_{1\ensuremath{-}x}{\mathrm{Te}}_{x}$ series. The effect is most likely driven by change of the dominant charge carriers' scattering mechanism from ionized impurity influence to point defect and acoustic phonon interaction. Simultaneously, due to a highly anisotropic conduction band, the effective mass of the carriers rises towards the n-type regime. These two effects lead to an improved thermoelectric power factor of electron-doped samples, up to $40\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}{\mathrm{WK}}^{\ensuremath{-}2}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ at 740 K for ${\mathrm{Sc}\mathrm{Ni}\mathrm{Sb}}_{0.85}{\mathrm{Te}}_{0.15}$. Based on this result, we suggest n-type doping for other rare-earth-based half-Heusler compounds. Representatives of this group exhibit the smallest lattice thermal conductivity in the pristine form among any half-Heusler thermoelectrics, and are anticipated to show comparably good electrical properties to ScNiSb due to their high mobility ratio in favor of electrons.

We present the results of our investigations of physical properties for the novel ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}\mathrm{Co}{\mathrm{Ge}}_{3}$ system performed with a number of experimental methods: magnetic susceptibility, specific heat, electrical resistivity, magnetoresistance, and thermoelectric power. Moreover, the electronic structure was studied by means of photoelectron spectroscopy measurements and first-principles calculations. All investigated compositions of the ${\mathrm{Ce}}_{1\ensuremath{-}x}{\mathrm{Pr}}_{x}\mathrm{Co}{\mathrm{Ge}}_{3}$ series crystallize in the tetragonal $\mathrm{Ba}\mathrm{Ni}{\mathrm{Sn}}_{3}$-type structure. The lattice parameters and unit cell volumes decrease with increasing Pr concentration. On the basis of the measurements taken, a preliminary magnetic phase diagram was created. Continuous suppression of the long-range magnetic ordering was observed with an increase of Pr concentration. The critical Pr concentration for magnetic moment ordering was determined from linear extrapolation of the ordering temperature versus $x$ to the lowest temperatures ($T=0$ K) and is equal to about 0.66. Based on the first-principles calculations, we show how the substitution of Pr for Ce affects the electronic structure and magnetic properties of the considered alloys. Within a single model, we take into account the magnetic ordering, fully relativistic effects, and Hubbard $U$ repulsion on Ce and Pr. The impact of Hubbard $U$ on the results of calculations is also discussed. We present the valence band analysis, Mulliken electronic population analysis, and calculated electronic specific heat coefficients. For $\mathrm{Ce}\mathrm{Co}{\mathrm{Ge}}_{3}$, it is found that the $++\ensuremath{-}\ensuremath{-}$ configuration of magnetic moments on Ce is slightly more stable than the $+\ensuremath{-}+\ensuremath{-}$ one, and also that the calculated value of total magnetic moment on Ce (including spin and orbital parts) is in good agreement with the measurements.

Deeper understanding of electrical and thermal transport is critical for further development of thermoelectric materials. Here we describe the thermoelectric performance of a group of rare-earth-bearing half-Heusler phases determined in a wide temperature range. Polycrystalline samples of $\mathrm{Sc}\mathrm{Ni}\mathrm{Sb}$, $\mathrm{Dy}\mathrm{Ni}\mathrm{Sb}$, $\mathrm{Er}\mathrm{Ni}\mathrm{Sb}$, $\mathrm{Tm}\mathrm{Ni}\mathrm{Sb}$, and $\mathrm{Lu}\mathrm{Ni}\mathrm{Sb}$ are synthesized by arc melting and densified by spark plasma sintering. They are characterized by powder x-ray diffraction and scanning electron microscopy. The physical properties are studied by means of heat-capacity and Hall-effect measurements performed in the temperature range from 2 to 300 K, as well as electrical-resistivity, Seebeck-coefficient, and thermal-conductivity measurements performed in the temperature range from 2 to 950 K. All the materials except $\mathrm{Tm}\mathrm{Ni}\mathrm{Sb}$ are found to be narrow-gap intrinsic $p$-type semiconductors with rather light charge carriers. In $\mathrm{Tm}\mathrm{Ni}\mathrm{Sb}$, the presence of heavy holes with large weighted mobility is evidenced by the highest power factor among the series ($17\phantom{\rule{0.2em}{0ex}}\ensuremath{\mu}\mathrm{W}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{\ensuremath{-}2}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ at 700 K). The experimental electronic relaxation time calculated with the parabolic band formalism is found to range from $0.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ to $2.8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}14}$ s. In all the materials studied, the thermal conductivity is between 3 and $6\phantom{\rule{0.2em}{0ex}}{\mathrm{W m}}^{\ensuremath{-}1}\phantom{\rule{0.2em}{0ex}}{\mathrm{K}}^{\ensuremath{-}1}$ near room temperature (i.e., smaller than in other pristine $d$-electron half-Heusler phases reported in the literature). The experimental observation of the reduced thermal conductivity appears fully consistent with the estimated low sound velocity as well as strong point-defect scattering revealed by Debye-Callaway modeling. Furthermore, analysis of the bipolar contribution to the measured thermal conductivity yields abnormally large differences between the mobilities of $n$-type and $p$-type carriers. The latter feature makes the compounds examined excellent candidates for further optimization of their thermoelectric performance via electron doping.

The TiO2-Fe3O4 composite materials were fabricated via the hydrothermal-assisted technique. It was determined how the molar ratio of TiO2 to Fe3O4 influences the crystalline structure and morphology of the synthesized composite materials. The effect of the molar ratio of components on the antibacterial activity was also analyzed. On the basis of XRD patterns for the obtained titanium(IV) oxide-iron(II, III) oxide composites, the two separate crystalline forms&mdash, anatase and magnetite &mdash, were observed. Transmission electron microscopy revealed particles of cubic and tetragonal shape for TiO2 and spherical for Fe3O4. The results of low-temperature nitrogen sorption analysis indicated that an increase in the iron(II, III) oxide content leads to a decrease in the BET surface area. Moreover, the superparamagnetic properties of titanium(IV) oxide-iron(II, III) oxide composites should be noted. An important aim of the work was to determine the antibacterial activity of selected TiO2-Fe3O4 materials. For this purpose, two representative strains of bacteria, the Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, were used. The titanium(IV) oxide-iron(II, III) oxide composites demonstrated a large zone of growth inhibition for both Gram-positive and Gram-negative bacteria. Moreover, it was found that the analyzed materials can be reused as antibacterial agents in three consecutive cycles with good results.

In this paper, a synthesis and physicochemical characterization of a novel magnetite/lignin (Fe3O4/Lig) and magnetite/lignin/polydopamine (Fe3O4/Lig/PDA) materials are presented as a novel and effective platforms for an enzyme immobilization or biosensing application. The hybrid has interesting features like improved thermal and mechanical stability, excellent adhesion for inorganic and organic materials, transferability of electrons and photothermal properties. In order to characterize features of the materials, carried out Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), thermogravimetry analysis (TGA), electrokinetic potential (zeta), and magnetic measurements (SQUID). From the TEM analysis, magnetite/lignin hybrid is proved to be covered by a 2–3 nm uniform layer of polydopamine. In a further study, the resultant functional biomaterial Fe3O4/Lig and Fe3O4/Lig/PDA were used to immobilize glucose oxidase (GOx). The immobilization capacity of 26.92 and 29.24 mg/g were achieved for Fe3O4/Lig and Fe3O4/Lig/PDA, respectively. After mixing of the materials with graphite and ferrocene, the modified carbon paste electrodes CPE/Fe3O4/Lig/GOx/Fc and CPE/Fe3O4/Lig/PDA/GOx/Fc were obtained and they were tested for application as bioelectrochemical glucose sensing system. The linear ranges of CPE/Fe3O4/Lig/GOx/Fc and CPE/Fe3O4/Lig/PDA/GOx/Fc were from 0.5 to 4.5 and 0.5–9.0 mM glucose, respectively. The hysteresis loops of the prepared materials show no coercivity and remanent magnetizations at room temperature, exhibiting typical superparamagnetic behavior.

High temperature thermoelectric properties of bulk and ball-milled cold-pressed (DyNiSn)1−x(DyNiSb)x composite materials have been studied. For bulk pure DyNiSn and DyNiSb samples the Seebeck coefficient reaches − 5.5 μV/K at 480 K and 120 μV/K at 540 K, respectively. Composite materials show metallic-like electrical resistivity and positive sign of Seebeck coefficient with values up to 50 times higher than in pure DyNiSn compound at 1000 K. Only for the sample with x = 0.47, the ball-milling drives to increase of Seebeck coefficient of about 37% at 650 K.

Presented research deals with novel approach for synthesis of zirconia/magnetite hybrid with core-shell like structure, for effective enzyme immobilization. The material was obtained via two stage sol-gel method, including firstly preparation of magnetite followed by its merging with zirconia particles during in situ synthesis of ZrO2. As prepared zirconia/magnetite hybrid was thoroughly characterized in order to examine its usability as support for laccase immobilization. The effectiveness of enzyme immobilization as well as characterization of obtained biocatalytic system were presented. The activity tests of ZrO2-Fe3O4-enzyme showed high catalytic activity over wide pH and temperature range. The utilitarian aspect of the research was related to evaluation of application potential of as prepared biocatalytic system towards degradation of tetracycline from model wastewaters. It was shown that over pH range 4–7 and temperature from 25 to 45 °C, over 80% of tetracycline was removed from 1 mg/L solution. Additionally, the reusability study of the biocatalyst showed that even after ten repeated degradation trials, still over 80% of antibiotic was removed. The products of tetracycline conversion were also identified. Based on collected experimental data, the mechanism of tetracycline degradation was proposed and discussed.

Using the by-product biopolymer lignin and nanoparticles of magnetite, well-known for its nontoxicity and magnetic properties, novel nanomagnetite–lignin hybrid materials were synthesized. In the first step, magnetite was produced via a co-precipitation method with hydrothermal treatment, and was found to have a particle size of around 20 nm. Nano–Fe 3 O 4 was then combined with pre-activated lignin to obtain hybrids with various magnetite–lignin ratios, whose physicochemical and magnetic properties were thoroughly analyzed. Thermal analysis showed the hybrids to have higher thermal stability than pure lignin. Based on Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy it was demonstrated that the Fe 3 O 4 and lignin are connected via Fe O C bonds. Further measurements showed the nanomagnetite–lignin hybrid materials to have good magnetic properties. The results of this study suggest that the synthesized hybrids may find practical applications in many fields of science and industry.

We report on the high-temperature (350 K, Comment: 5 pages, 3 figures. Subbmited to Materials Today: Proceedings, 15th European Conference on Thermoelectrics (ECT2017)

We report on the CeNi4Mn (ferromagnet FM) - CeCu4Mn (spin-glass SG) transformation leading to a complex magnetic phase diagram (MPD). It is verified that all the Ce(Cu1-xNix)4Mn alloys are isostructural and the transformation is governed only by the Cu-Ni substitution. MPD is built based on the magnetic dc/ac susceptibility measurements and reveals SG formation as well as the region of the coexistence of the FM and SG state in the middle range of the Ni concentration. The complex MPD is explained by clusters formation and a competition of interactions between various crystallographic sites of the hexagonal CaCu5-type structure, mainly the 3g-3g and 3g-2c interactions. The predominance of the SG state is confirmed by the analysis of the frequency dependence of the ac magnetic susceptibility components and the relaxation of the remanent magnetization. Additionally, the presence of two multicritical points is observed.

TiO2-MoO3 composite systems were successfully prepared using a template-assisted microwave method at molar ratios TiO2:MoO3 = 8:2, 5:5 and 2:8. The synthesized material systems were comprehensively characterized, in terms of their crystalline structure (XRD and Raman spectroscopy), morphology (SEM, TEM and HRTEM analysis) and parameters of the porous structure (low-temperature N2 sorption). The materials exhibited highly crystalline phases: anatase and hexagonal molybdenum trioxide. Moreover, TEM analysis revealed hexagonal prism particles of MoO3 and nanocrystalline particles of TiO2. The proposed template-assisted microwave synthesis enabled the incorporation of TiO2 particles on the surface of hexagonal particles of MoO3, which resulted in a stable junction between titania and molybdenum trioxide. The values of BET surface area were 57, 29 and 11 m2/g for samples obtained at molar ratios TiO2:MoO3 = 8:2, 5:5 and 2:8 respectively. In electrochemical applications, titanium dioxide plays a crucial role as an intercalation intensifier, in which MoO3 is responsible for current conduction. Taking account of the potential electrochemical applications, the best system was obtained at the molar ratio TiO2:MoO3 = 5:5. The anode could maintain a capacity of 400 mAh/g at current densities in the range 100&ndash, 1000 mA/g at potential values ranging from 1.00 to 3.30 V vs. Li/Li+. X-ray photoelectron spectroscopy (XPS) confirmed the effective intercalation of lithium ions into the TiO2-MoO3 composite materials.

Study on half-Heusler compounds RENiSb, RE = Sc, Dy, Ho, Er, Tm, Lu, was performed in perspective of high-temperature thermoelectric application. Relatively small electrical resistivity (4–60 μ Ω m in 300–1000 K) combined with fairly high positive Seebeck coefficient (40–160 μV/K) yielded for the RENiSb ternaries rather large thermoelectric power factors at 750 K, namely 14 μW K−2cm−1 for ScNiSb and 11 μW K−2cm−1 for TmNiSb. At room temperature the thermal conductivity measured for the two materials was 8.1 W K−1m−1 and 4.4 W K−1m−1, respectively. The value obtained for the latter compound is smaller than those reported for unoptimized half-Heusler phases based on d-electron elements. This finding may be explained by strong point defect scattering occurring due to intrinsic disorder in crystal structure of TmNiSb, or to smaller extent by enhanced scattering on incoherent grain boundaries with the impurity phases. Nevertheless, achieving good thermoelectric performance of the RENiSb phases at high temperatures requires proper tuning of carrier concentration, as well as further reduction in their thermal conductance by means of alloying and/or nanostructurization.

Enzymatic cofactor-dependent conversion of monosaccharides can be used in the bioproduction of value-added compounds. In this study, we demonstrate co-immobilization of xylose dehydrogenase (XDH, EC 1.1.1.175) and alcohol dehydrogenase (ADH, EC 1.1.1.1) using magnetite-silica core-shell particles for simultaneous conversion of xylose into xylonic acid (XA) and in situ cofactor regeneration. The reaction conditions were optimized by factorial design, and were found to be: XDH:ADH ratio 2:1, temperature 25 °C, pH 7, and process duration 60 min. Under these conditions enzymatic production of xylonic acid exceeded 4.1 mM and was more than 25% higher than in the case of a free enzymes system. Moreover, the pH and temperature tolerance as well as the thermo- and storage stability of the co-immobilized enzymes were significantly enhanced. Co-immobilized XDH and ADH make it possible to obtain higher xylonic acid concentration over broad ranges of pH (6–8) and temperature (15–35 °C) as compared to free enzymes, and retained over 60% of their initial activity after 20 days of storage. In addition, the half-life of the co-immobilized system was 4.5 times longer, and the inactivation constant (kD = 0.0141 1/min) four times smaller, than those of the free biocatalysts (kD = 0.0046 1/min). Furthermore, after five reaction cycles, immobilized XDH and ADH retained over 65% of their initial properties, with a final biocatalytic productivity of 1.65 mM of xylonic acid per 1 U of co-immobilized XDH. The results demonstrate the advantages of the use of co-immobilized enzymes over a free enzyme system in terms of enhanced activity and stability.

In the presented study synthesized magnetic nanoparticles were used as an inorganic precursor for the preparation of novel magnetite-lignin and magnetite-chitin hybrid supports for enzyme immobilization. Effective synthesis of the hybrids was confirmed by Fourier transform infrared spectroscopy and powder X-ray diffraction analysis. The materials exhibited good thermal stability and surface areas of 4.3 and 5.6 m2/g respectively. The magnetite-lignin + trypsin and magnetite-chitin + trypsin systems were found to have good storage stability and reusability. After 20 days they retained over 75% and 90% respectively of their initial activity, and after 10 consecutive biocatalytic cycles retained over 60% and 80% respectively of their initial activity. The kinetic parameters of the free and immobilized enzyme were also comprehensively examined and compared. The results of peptide digestion tests confirmed the high proteolytic activity of the produced trypsin-based magnetic biocatalytic systems.

The influence of the modification of the 3d electronic states in the heavy fermion compound CeCu4Ga by substitution of Cu by Ni is reported. It has been verified that the crystallographic structure is hexagonal of the CaCu5 type and is preserved for all the x values in the alloys Ce(Cu1−xNix)4Ga. The measurements of the specific heat Cp(T) have revealed that the huge electronic specific coefficient γ = 3.3 J mol−1 K−2 for CeCu4Ga is reduced with the progressive Ni addition and follows the behavior of the hybridization parameter of the Ce f states with the conduction electrons. The analysis of the specific heat of the non-magnetic reference compound LaCu4Ga has shown that including the mass correction corresponding to the change of Ce by La and Cu by Ni does not provide a correct estimation of the phonon term in the Ce(Cu1−xNix)4Ga alloys.

We report our studies of the intermediate compositions between CeNi2Si2 and CeNi2Ge2, i.e., the alloys CeNi2(Si1-yGey)2 by means of the thermopower, electrical resistivity, specific heat, magnetic susceptibility, and X-ray photoemission measurements. CeNi2Si2 is a fluctuating valence system and CeNi2Ge2 is known to show the heavy fermion behaviour. The change of the temperature dependence of the resistivity towards the typical metallic behaviour occurs below y ~ 0.25. The transition between CeNi2Si2 and CeNi2Ge2 is discussed in the frames of competition between the crystal electric field and Kondo interactions. It is found that valence stabilisation occurs for Ge content y > 0.25. The hybridization energy Δ determined from the XPS Ce 3d spectrum reflects well the behaviour of the parameter E ex obtained from the analysis of the magnetic susceptibility by the interconfiguration fluctuation model. It has been also shown that thermopower data can be successfully described employing the single ion model for 0.6

A Co zigzag nanocolumn sample was grown by glancing angle deposition using molecular beam epitaxy. A structural study was carried out using scanning electron microscopy and the magnetic properties and the magnetoresistance were investigated at room temperature. Each zigzag consisted of six arms tilted with respect to each other by approx. 60°, had a club-like shape, diameter in the range of 20–100 nm, a single arm length of about 150 nm and a total height of approx. 370 nm. The magnetization hard axis was observed for the magnetic field oriented parallel to the zigzag long axis and the easy axis for the field oriented perpendicular to the long axis. The system exhibited very high maximum coercivity values, which could find potential applications. The angular dependences of the coercive field and the remanent to saturation magnetization ratio, as well as magnetoresistance curves, indicated the presence of curling magnetization reversal mode.

We report the X-ray photoemission spectra (XPS) and the electrical resistivity measurements for the transition Kondo lattice – spin-glass (SG) in the series CeCu 4 Mn y Al 1− y . The study includes additionally the low temperature (down to T = 400 mK) heat capacity results. The XPS measurements revealed that the Ce 4f states are well localized. Electrical resistivity studies illustrate a smooth evolution from the ∼ −ln T relation to the metallic behaviour with the increase of the Mn content. Moreover, the specific heat has been analysed considering the electronic, phonon, Schottky (Crystal Electric Field – CEF), Kondo, and SG contributions. The assumption that the CEF splitting of the energy levels is similar for all the compositions allowed us to estimate the SG and Kondo contribution to the heat capacity. Additionally, the neutron diffraction experiment on the parent CeCu 4 Mn compound has confirmed that it does not show a long-range magnetic order.

The specific heat C p ( T ) of the Mn 5 Ge 3 ferromagnet has been studied in a wide temperature range of 2–400 K. The ferromagnetic ordering has been confirmed at T C = 297.4 K, however the behaviour of C p ( T , H ) in small magnetic fields suggests a presence of a weak antiparallel component in the magnetic structure. The combination of the C p ( T , H ) and magnetization M ( T , H ) measurements enabled the determination of not only the isothermal magnetic entropy change Δ S M but the adiabatic temperature change Δ T ad as well. It has been also found that the mechanical milling process leads only to a moderate drop of the magnetocaloric effect. The reduction of the grain size by 50% decreases the relative cooling power by 28%.

We report extensive studies of a series of alloys CeCo1−xFexGe3 in which suppression of the antiferromagnetic order in CeCoGe3 with temperature decreasing to 0 K was observed as a result of substitution of Co with Fe. Unusual temperature dependences were observed of a number of parameters characterizing these compounds: magnetic susceptibility, specific heat, electrical resistivity, magnetoresistance and thermoelectric power, which may be indication towards non-Fermi liquid behaviour connected with quantum critical point (QCP) or can result from a quantum Griffiths phase (QGP) formation. The three AFM transitions found previously for a single crystal CeCoGe3 compound were also detected in our high quality polycrystalline samples, including the case of x > 0 . All measurements, especially those of magnetocaloric effect (MCE), suggest that for samples with x ≥ 0.1 the contribution of ferromagnetic component, known already for x = 0 from the neutron diffraction experiments, increases significantly, with the AFM contribution still present at low temperatures. Finally, the use of different complementary methods enabled construction of a comprehensive magnetic phase diagram of CeCo1−xFexGe3 system.

A transition from a heavy fermion Kondo lattice CeCu2Si2 to the fluctuating valence CeNi2Si2 compound has been studied for the series Ce(Ni1−xCux)2Si2 employing the magnetic susceptibility, electrical resistivity, thermal conductivity, thermopower, and specific heat measurements methods. Apart from the confirmation of the fluctuating valence and heavy fermion state for the Ni-rich and Cu-rich samples, respectively, a crossing of the energy scales for x of about 0.5–0.6 has been observed and ascribed to the proximity of the Kondo temperature and the crystal electric field (CEF) excitations for these compositions. All the experimental methods used provide compatible values of the characteristic energy scales, like those related to the Kondo temperature and the CEF excitations. Especially, agreement between the low and high temperatures regimes is also possible if the changes of the degeneracy of the Ce 4f states are correctly considered.

Inelastic and quasielastic excitations in the neutron scattering on the compounds CeCo 1 − x Cu x Al 4 ( x =0, 0.05, 0.1) have been studied above and below the antiferromagnetic ordering temperature. The quasielastic contribution disappears below the Neel temperature, T N = 13.5 K , and its linewidth Γ / 2 is below T N , therefore these results suggest that Kondo screening is not relevant in these Ce compounds. Based on the example of CeCoAl 4 we show that the inelastic excitations provide crystal electric field energy levels scheme, which in consistent way describes both the magnetic susceptibility and the specific heat. The inelastic neutron scattering spectrum below T N is interpreted as the splitting of the crystal electric field levels by the internal molecular field.

Magnetic and transport properties of near-stoichiometric metastable FexMnyGaz alloys (46

Magnetocaloric (MCE) effect has been studied in the ferromagnetic (FM) GdNi 4 Al, GdNi 4 Si, and the antiferromagnetic (AFM) NdNiAl 4 compounds. All the compounds order magnetically between 9 and 30 K. The maximum magnetic entropy change −Δ S M is in the range of 10–16 J kg −1 K −1 for the studied R Ni 4 M compounds. Arrott plots suggest that the phase transition in GdNi 4 Al and GdNi 4 Si may be of a first order-type. It is ascribed to a field-induced AFM–FM transition. Neutron diffraction experiments on NdNiAl 4 show that its magnetic structure is not of a simple AFM-type. Additionally, the specific heat measurements for NdNiAl 4 reveal a change of the sign of MCE and very small values of −Δ S M and the adiabatic temperature change Δ T ad .

A large magnetocaloric (MCE) effect has been observed for the ternary compound DyCo 3 B 2 . This material shows the magnetic ordering below T C = 22 K for H = 0 T. MCE has been determined based on the isothermal magnetization curves measurements and the isomagnetic heat capacity dependence on temperature. The maximum magnetic entropy change −Δ S M = 17.5 J kg −1 K −1 and the adiabatic temperature change Δ T ad = 14 K have been observed in the neighborhood of the magnetic phase transition at the magnetic field change of 9 T. The analysis of the magnetic contribution to the specific heat indicates on the important role of the crystal electric field and the anisotropy for the properties of the DyCo 3 B 2 compound.

The ferromagnetic CeNi4Mn compound has been recently studied due to its promising properties resembling half-metallic behavior. It has structure (cubic or hexagonal), which is sensitive to small changes of the stoichiometry. On the other hand, the hexagonal CeCu4Mn compound shows features typical of spin-glasses. We report on investigations of the evolution of the magnetic properties in the series CeCuxNi4−xMn. We present the measurements of the dc and ac magnetic susceptibility, the later as a function of the frequency. Besides, the magnetization relaxation has been studied. The decay of the remanent magnetization as a function of time is observed already for a small substitution of Ni with Cu or Ce with Nd. The frustration within these compounds is explained by disorder due to the statistical occupation of the 3g site in the CaCu5-type structure.