Showing papers by "Peter Baláž published in 2022"

The Art of Positronics in Contemporary Nanomaterials Science: A Case Study of Sub-Nanometer Scaled Glassy Arsenoselenides

Abstract: The possibilities surrounding positronics, a versatile noninvasive tool employing annihilating positrons to probe atomic-deficient sub-nanometric imperfections in a condensed matter, are analyzed in application to glassy arsenoselenides g-AsxSe100−x (0 < x < 65), subjected to dry and wet (in 0.5% PVP water solution) nanomilling. A preliminary analysis was performed within a modified two-state simple trapping model (STM), assuming slight contributions from bound positron–electron (Ps, positronium) states. Positron trapping in g-AsxSe100−x/PVP nanocomposites was modified by an enriched population of Ps-decay sites in PVP. This was proven within a three-state STM, assuming two additive inputs in an overall trapping arising from distinct positron and Ps-related states. Formalism of x3-x2-CDA (coupling decomposition algorithm), describing the conversion of Ps-decay sites into positron traps, was applied to identify volumetric nanostructurization in wet-milled g-As-Se, with respect to dry-milled ones. Under wet nanomilling, the Ps-decay sites stabilized in inter-particle triple junctions filled with PVP replaced positron traps in dry-milled substances, the latter corresponding to multi-atomic vacancies in mostly negative environments of Se atoms. With increased Se content, these traps were agglomerated due to an abundant amount of Se-Se bonds. Three-component lifetime spectra with nanostructurally- and compositionally-tuned Ps-decay inputs and average lifetimes serve as a basis to correctly understand the specific “rainbow” effects observed in the row from pelletized PVP to wet-milled, dry-milled, and unmilled samples.

Ternary and Quaternary Nanocrystalline Cu-Based Sulfides as Perspective Antibacterial Materials Mechanochemically Synthesized in a Scalable Fashion

Abstract: Twelve Cu-based ternary (Cu–Me1–S, Me1 = Fe, Sn, or Sb) and quaternary (Cu–Me2–Sn–S, Me2 = Fe, Zn, or V) nanocrystalline sulfides are shown as perspective antibacterial materials here. They were prepared from elemental precursors by a one-step solvent-free mechanochemical synthesis in a 100 g batch using scalable eccentric vibratory ball milling. Most of the products have shown strong antibacterial activity against Escherichia coli and Staphylococcus aureus bacteria. For instance, stannite Cu2FeSnS4 and mohite Cu2SnS3 were the most active against E. coli, whereas kesterite Cu2ZnSnS4 and rhodostannite Cu2FeSn3S8 exhibited the highest antibacterial activity against S. aureus. In general, stannite has shown the best antibacterial properties out of all the studied samples. Five out of twelve products have been prepared using mechanochemical synthesis for the first time in a scalable fashion here. The presented synthetic approach is a promising alternative to traditional syntheses of nanomaterials suitable for biological applications and shows ternary and quaternary sulfides as potential candidates for the next-generation antibacterial agents.

Properties of CuFeS2/TiO2 Nanocomposite Prepared by Mechanochemical Synthesis

Abstract: CuFeS2/TiO2 nanocomposite has been prepared by a simple, low-cost mechanochemical route to assess its visible-light-driven photocatalytic efficiency in Methyl Orange azo dye decolorization. The structural and microstructural characterization was studied using X-ray diffraction and high-resolution transmission electron microscopy. The presence of both components in the composite and a partial anatase-to-rutile phase transformation was proven by X-ray diffraction. Both components exhibit crystallite size below 10 nm. The crystallite size of both phases in the range of 10–20 nm was found and confirmed by TEM. Surface and morphological properties were characterized by scanning electron microscopy and nitrogen adsorption measurement. Scanning electron microscopy has shown that the nanoparticles are agglomerated into larger grains. The specific surface area of the nanocomposite was determined to be 21.2 m2·g−1. Optical properties using UV-Vis and photoluminescence spectroscopy were also investigated. CuFeS2/TiO2 nanocomposite exhibits strong absorption with the determined optical band gap 2.75 eV. Electron paramagnetic resonance analysis has found two types of paramagnetic ions in the nanocomposite. Mössbauer spectra showed the existence of antiferromagnetic and paramagnetic spin structure in the nanocomposite. The CuFeS2/TiO2 nanocomposite showed the highest discoloration activity with a MO conversion of ~ 74% after 120 min irradiation. This study has shown the possibility to prepare nanocomposite material with enhanced photocatalytic activity of decoloration of MO in the visible range by an environmentally friendly manner

Mechanochemical synthesis of non-stoichiometric copper sulfide Cu1.8S applicable as a photocatalyst and antibacterial agent and synthesis scalability verification.

Abstract: An effort to prepare different non-stoichiometric CuxSy compounds starting from elemental precursors using mechanochemistry was made in this study. However, out of the 7 stoichiometries tested, it was only possible to obtain three phases: covellite CuS, chalcocite Cu2S and digenite Cu1.8S and their mixtures. To obtain the digenite phase with the highest purity, the Cu : S stoichiometric ratio needed to be fixed at 1.6 : 1. The reaction between copper and sulfur was completed within a second range, however, milling was performed for up to 15 minutes until the equilibrium in phase composition between digenite and covellite was reached. The possibility of preparing the product in a 300 g batch by eccentric vibratory milling in 30 minutes was successfully verified at the end. The estimated crystallite sizes for the digenite Cu1.8S obtained via lab-scale and scalable experiments were around 12 and 17 nm, respectively. The obtained products were found to be efficient photocatalysts under visible light irradiation in the presence of hydrogen peroxide, being capable of the complete degradation of the Methyl Orange dye in a concentration of 10 mg L-1 in 2 hours. Finally, the antibacterial potential of both lab-scale and large-scale industrial products was proven and, regardless of the manufacturing scale, the nanoparticles retained their properties against bacterial cells.

Novel Mechanically Assisted Dissolution of Platinum Using Cerium(IV) Oxide

Abstract: Platinum group metals (PGMs) are important for a variety of applications, including catalysis; however, the amounts mined are inadequate relative to global requirements. Therefore, methods for the recovery of PGMs from spent resources are urgently required. Herein, we report that platinum (Pt) can be dissolved by hydrochloric acid (HCl) alone using cerium(IV) oxide (CeO2) as a solid oxidizing agent, which can minimize the highly corrosive chlorine. Pt-containing catalysts were subjected to high-energy ball milling in the presence of CeO2, and their dissolution behavior in HCl was subsequently investigated. Ball milling was found to promote direct Pt-oxidation, as indicated by the significantly increased solubility in HCl. Several analytical techniques, including X-ray diffractometry, surface area and pore size analysis, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, inductively coupled plasma mass spectrometry, and atomic emission spectroscopy, were used for characterization. This study demonstrates the environmentally acceptable characteristics of high-energy ball milling and its applicability in the recycling of important noble metal substances from waste materials.

Volumetric Nanostructurization in Glassy Arsenoselenides Driven by High‐Energy Mechanical Dry‐ and Wet‐Milling

Abstract: The method of positron annihilation lifetime (PAL) spectroscopy is employed to study atomic-deficient free-volume evolution in nanocomposites prepared by high-energy mechanical milling of glassy arsenoselenides g-As-Se in dry mode and water solution of polyvinylpyrrolidone (PVP). Formalism of x3-x2-CDA (coupling decomposition algorithm) describing conversion of bound positron-electron (positronium, Ps) states into positron traps is applied to identify free-volume changes in the pelletized PVP-capped g-As-Se nanocomposites in respect to dry-milled samples. Under wet milling, the inter-nanoparticle Ps-decaying sites in preferential PVP environment are shown to replace free-volume positron traps in dry-milled g-As-Se samples with defect-specific positron lifetime approaching ∼0.36-0.38 ns, corresponding to di-/tri-atomic vacancies in g-As-Se matrix.

Bioleaching Test of Polymetallic Nodule Samples from the IOM Exploration Area

Abstract: The Interoceanmetal Joint Organization’s (IOM) exploration license is granted in the area located within the Clarion–Clipperton Zone of the Eastern Central Pacific. All activities related to exploration of minerals in this area are beyond the limits of national jurisdiction and come under the provision of the United Nations Convention on the Law of the Sea and related regulations. The geological survey, which was the subject of the exploration, focused on the polymetallic nodule deposits. Other activities covered the tests of nodule processing, including alternative methods of metal extraction. This article describes the methodology of the bioleaching process and provides a summary of the initial results of the bioleaching test, applied to the samples of polymetallic nodules taken from the H22 exploration block of the IOM exploration area. The bioleaching efficiency under different pulp density conditions was studied. The enrichment of heterotrophic Mn-reducing microorganisms was prepared as the leaching medium. Bioleaching of the samples took place with different sample weights in order to determine the maximum possible extraction yield and the highest concentration of elements obtained in the leachate. During the bioleaching, the media were also exchanged to achieve maximum polymetallic nodule decomposition with regular addition of nutrients for heterotrophic Mn-reducing bacteria. The bioleaching efficiency of the polymetallic nodules increased to 100% (without Cu) when the pulp density was reduced to 0.1% (w/v). The discontinuous bioleaching and washing process recovered 55% Mn, 36% Ni, 15% Co, 27% Zn, and 38% Cu when the pulp density was increased to 10% (w/v). To achieve total Mn, Cu, Zn, Co, and Ni recovery from the polymetallic nodules, an intermittent bioleaching with about 25 changes of 60% of the medium was required when the pulp density was increased to 10% (w/v). Bioleaching has the potential to be used as an environmentally friendly alternative to other commonly used options for leaching and processing.