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Mechanochemical Preparation and Magnetic Properties of Fe₃O₄/ZnS Nanocomposite

100%
Bujňáková Z., Zorkovská A., Kováč J.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1120-1122
EN
Powder nanocomposite of Fe₃O₄/ZnS was prepared by mechanochemical synthesis in a planetary ball mill. In this reaction natural magnetite mineral Fe₃O₄ was used, together with zinc acetate (CH₃COO)₂Zn·2H₂O and sodium sulfide Na₂S·9H₂O, as precursors for the zinc sulfide ZnS. X-ray diffraction revealed that the sample is composed of small nanocrystalline particles, containing Fe₃O₄ and ZnS. The non-milled magnetite showed distinctive Verwey transition at around 120 K, this becomes suppressed after milling, as a consequence of structural disorder and presence of defects. Moreover, the reduction of saturation magnetization from 91 A m²/kg to 69.2 A m²/kg was observed, as a consequence of the milling process. The magnetization of the Fe₃O₄/ZnS nanocomposite was the lowest (34.5 A m²/kg), due to the milling and to the decreased weight fraction of the ferrimagnetic component. Nevertheless, the Fe₃O₄/ZnS sample demonstrates ferrimagnetic behavior as well, and its structure is less perturbed by milling, the Verwey transition, although less impressive, but is preserved.
2
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Mechanochemistry of Solids: New Prospects for Extractive Metallurgy, Materials Science and Medicine

88%
Baláž P., Baláž M., Achimovičová M., Bujňáková Z., Dutková E.
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vol. 126
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issue 4
879-883
EN
In this review paper recent advances in chalcogene mechanochemistry are described. Three selected areas are being covered, i.e. metallurgy, materials science, and medicine. In extractive metallurgy, the processing of copper arsenic mineral enargite (Cu_3AsS_4) with the aim of its dearsenification and subsequent preparation of a new anticancer drug (Na_3AsS_4) and of copper in nanocrystalline state ( ≈ 20 nm) illustrate the non-traditional prospect of ore treatment. In material science, the new nanocrystalline semiconductors were synthesized mechanochemically, e.g. selenides of zinc and lead (ZnSe, PbSe) and bismuth sulphide (Bi_2S_3). Metal and chalcogene were applied as reaction precursors. In some cases, the amino acids (cystine, cysteine) were applied as sulphur precursor, in order to provide reactive sites on synthesized solid (PbS) for bioconjugation and to prevent agglomeration. The concept of nanomilling is described as a way to prepare effective substances for cancer treatment in medicine. In vitro activity of realgar (As_4S_4) as an example is described. In all three areas the focus is aimed also on industrial applications where suitable large-scale mills are described. The described examples represent the contemporary aim of mechanochemists - to prepare substances with the desired properties in a reproducible way under easy-operating, environmentally friendly and essentially waste-free conditions.
3
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Kinetics of Solid-State Synthesis of Quaternary Cu₂FeSnS₄ (Stannite) Nanocrystals for Solar Energy Applications

76%
Baláž P., Baláž M., Zorkovská A., Škorvánek I., Bujňáková Z., Trajić J.
Acta Physica Polonica A
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2017
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vol. 131
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issue 4
1153-1155
EN
In this study we demonstrate the use of elemental precursors (Cu, Fe, Sn, S) to obtain stannite forms by a solid-state one-pot mechanochemical synthesis. In the processing route, we report the kinetics of the synthesis. For the characterization of the unique nanostructures, X-ray diffraction, specific surface area measurements and SQUID magnetometry methods were applied. CFTS polymorphs with the tetragonal body-centered structure with the average crystallite size 18-19 nm were obtained. The weak ferromagnetic properties of the quaternary nanocrystals after maximum milling time were also documented.
4
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Physico-Chemical and Biological Properties of Arsenic Sulfide (As_{55}S_{45}) Nanosuspension Prepared by Milling

76%
Bujňáková Z., Shpotyuk O., Sedlák J., Pastorek M., Turianicová E., Baláž P., Ingram A.
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vol. 126
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issue 4
902-906
EN
Nanosuspension based on melt-quenched arsenic sulfide of nominal As_{55}S_{45} composition was prepared by nanomilling and tested as potential anticancer drug. Polyvinylpyrrolidone was used as steric stabilizer and inhibitor of agglomeration. Individual nanoparticles had average size of 192 nm (determined by photon cross-correlation spectroscopy) and had several times better dissolution ability in comparison with bulk As_{55}S_{45}. Effect of nanomilling is shown to be associated with formation of arsenic sulfide crystalline nanoparticles and free-volume entities located at the interface between nanoparticles and surrounding matrix as it follows from positron annihilation measurements. Cytotoxicity tests were performed using human melanoma cell line Bowes and confirmed high toxicity of the studied nanosuspension.
5
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Mechanochemical Dechlorination of PVC by Utilizing Eggshell Waste

76%
Baláž M., Baláž P., Bujňáková Z., Pap Z., Kupka D., Zorkovská A.
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vol. 126
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issue 4
884-887
EN
Within this work, the dechlorination of polyvinylchloride (PVC) chemical as a model by co-milling with eggshell was performed in a planetary ball mill in order to show that mechanochemistry can be utilized for the simultaneous treatment of two wastes, while the products of the treatment can be used in further applications. The products of the reaction are water-soluble calcium chloride (CaCl_2), which can be used e.g. for de-icing of roads in winter and organic residue on the basis of ethylene, which can be recovered as energy source. The highest dechlorination yield (almost 97%) was achieved under following milling conditions: molar ratio between Ca and Cl: 2.34, ball-to-powder ratio: 65, rotation speed of the planet carrier: 550 rpm, milling time: 4 h and material of milling media: tungsten carbide. The optimum conditions were then applied for the removal of chlorine from industrial waste - the abandoned PVC window parapet. In this case, 95% dechlorination was evidenced.
6
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Magnetic Properties and Sorption Activity of Mechanically Activated Magnetite Fe_3O_4

76%
Baláž P., Timko M., Kováč J., Bujňáková Z., Ďurišin J., Myndyk M., Šepelák V.
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issue 5
1005-1007
EN
It is known that the action of mechanical forces on solids (mechanical activation and/or mechanochemistry) leads to changes of their properties and reactivity. We have studied the physico-chemical and sorption properties of magnetite Fe_3O_4 (Kiruna, Sweden) mechanically activated in a planetary mill. Several methods such as X-ray diffractometry, Mössbauer spectroscopy, magnetometry, specific surface area measurement as well as arsenic sorption tests have been applied. By X-ray diffractometry strong amorphisation of magnetite has been evidenced. In parallel, specific surface area increased from 0.1 m^2/g for the reference (non-milled) sample to the values 0.5-6.1 m^2/g for milled samples. The Mössbauer spectrum of the reference sample is well fitted with two subspectra corresponding to tetrahedrally (A) and octahedrally (B) coordinated iron cations in the spinel structure of Fe_3O_4. In mechanically activated samples (B)-site subspectrum becomes asymmetric, while (A)-site spectrum remains more or less unchanged. The more covalent character of the Fe(A)-O bond compared to the Fe(B)-O bond can explain qualitatively why the spin-density transfer from (A) to (B) in the spinel structure is more effective than vice versa. The value of the saturation magnetization at room temperature was 67.4 ≈ 43.6 emu/g which is significantly lower than that of the bulk particles 92 emu/g. This reduction may be attributed to the surface disorder or spin canting at the particle surface. During the milling process the coercivity value increases from 150 Oe up to 460 Oe with milling time. This increase can be related to the fact that magnetic anisotropy may increase when particle size decreases. The sorption activity of Fe_3O_4 was enhanced as a consequence of its disordering: 88% of As^{3+} was captured for the mechanically activated sample in comparison with 0% for the non-milled one.
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