Exploring the high-temperature thermoelectric performance of la-substituted Ca3Co4O9 bulk ceramics

It is well-known that the electrical properties of the Ca3Co4O9 thermoelectric (TE) compound are strongly influenced by the valence of the substituting cation, while its solubility and “functional” impact depend largely on the preparation and/or processing methods used. Furthermore, this material’s hybrid crystal structure allows for different cation substitutions in/from different sublattices. This research work presents the relevant effects of different La substitutions for the Ca ions from the insulating rock salt type [Ca2CoO3] crystal component (considered as a “charge reservoir” for the conductive [CoO2] layers) for a series of bulk samples prepared and processed via a solid-state method, chosen for simplicity. The results show that the actual level of La substitutions does not exceed 0.03 (x < 0.03), in Ca3-xLaxCo4O9 samples with x = 0.01, 0.03, 0.05 and 0.07, and that beyond this limit, simultaneous Ca3Co4O9 phase decomposition and secondary Ca3Co2O6 and (La,Ca)CoO3 phase formation take place. The morpho-structural features were found to be quite moderate, with a negligible effect on the charge carries transport. The electrical measurements and average oxidation state of cobalt (~3.11) suggest that the substitutions with La have only a minor effect on the charge carrier concentration. The electrical resistivity of the samples with x = 0.01, 0.03 and 0.05 is found to be ~1.3 times lower than of pristine Ca3Co4O9, while the changes in the Seebeck coefficient values are only moderate in the whole measured temperature range. The highest power factor, representing the electrical counterpart of the TE performance, was found for the Ca2.99La0.01Co4O9 samples (~0.28 mW/K2m, at 800 C), being among the best found in the literature for similar materials. Our results suggest that low substitutions with rare-earth cations in the “charge reservoir” layers of the Ca3Co4O9 compound can be promising in designing and improving these p-type oxides, provided by the strongly correlated nature of their conduction mechanism.publishe

Determination by UHPLC – UV – MS of polyphenol content of Amaranthus retroflexus

Having a very large area globally, the genus Amaranthus has been known since ancient times and used as a medicinal plant used in the treatment of various ailments. For the treatment of gastrointestinal disorders, the main constituents considered active are compounds from the polyphenol class. In order to identify and quantify some of these compounds, this paper briefly presents a UHPLC–UV–MS analysis study of polyphenolic compounds from Amaranthus retroflexus. Through our study we identified a high concentration of rutin. Thus, if rutin is intended to be used in medical practice, only the leaves will be used, the rest of the plant would produce an unwanted dilution. In addition, C₁₆H₁₈O₉, C₉H₈O₄, C7H6O4, C9H8O3 and C10H10O4 were identified. It has been observed that the leaves contain flavonoids in a higher amount than other parts of the plant. Through our study, we contributed to establishing the working parameters necessary to perform the analyses. For the first time, we have indicated the organs with the highest content of flavonoids, from the composition of the plants in the Oltenia area, Romania. For medical practice, the results obtained by us can represent important milestones in the production of pharmaceutical preparations

Exploring the high-temperature electrical performance of Ca3-xLaxCo4O9 thermoelectric ceramics for moderate and low substitution levels

Aliovalent substitutions in Ca3Co4O9 often result in complex effects on the electrical prop-erties and the solubility, and impact of the substituting cation also depends largely on the prepara-tion and processing method. It is also well-known that the monoclinic symmetry of this material’s composite crystal structure allows for a significant hole transfer from the rock salt-type Ca2CoO3 buffer layers to the hexagonal CoO2 ones, increasing the concentration of holes and breaking the electron–hole symmetry from the latter layers. This work explored the relevant effects of relatively low La-for-Ca substitutions, for samples prepared and processed through a conventional ceramic route, chosen for its simplicity. The obtained results show that the actual substitution level does not exceed 0.03 (x < 0.03) in Ca3-xLaxCo4O9 samples with x = 0.01, 0.03, 0.05 and 0.07 and that further introduction of lanthanum results in simultaneous Ca3Co4O9 phase decomposition and secondary Ca3Co2O6 and (La,Ca)CoO3 phase formation. The microstructural effects promoted by this phase evolution have a moderate influence on the electronic transport. The electrical measurements and determined average oxidation state of cobalt at room temperature suggest that the present La sub-stitutions might only have a minor effect on the concentration of charge carriers and/or their mobil-ity. The electrical resistivity values of the Ca3-xLaxCo4O9 samples with x = 0.01, 0.03 and 0.05 were found to be ~1.3 times (or 24%) lower (considering mean values) than those measured for the pris-tine Ca3Co4O9 samples, while the changes in Seebeck coefficient values were only moderate. The highest power factor value calculated for Ca2.99La0.01Co4O9 (~0.28 mW/K2m at 800 °C) is among the best found in the literature for similar materials. The obtained results suggest that low rare-earth substitutions in the rock salt-type layers can be a promising pathway in designing and improving these p-type thermoelectric oxides, provided by the strong interplay between the mobility of charge carriers and their concentration, capable of breaking the electron–hole symmetry from the conduc-tive layers.publishe

A framework for research into continental ancestry groups of the UK Biobank

BACKGROUND: The UK Biobank is a large prospective cohort, based in the UK, that has deep phenotypic and genomic data on roughly a half a million individuals. Included in this resource are data on approximately 78,000 individuals with “non-white British ancestry.” While most epidemiology studies have focused predominantly on populations of European ancestry, there is an opportunity to contribute to the study of health and disease for a broader segment of the population by making use of the UK Biobank’s “non-white British ancestry” samples. Here, we present an empirical description of the continental ancestry and population structure among the individuals in this UK Biobank subset. RESULTS: Reference populations from the 1000 Genomes Project for Africa, Europe, East Asia, and South Asia were used to estimate ancestry for each individual. Those with at least 80% ancestry in one of these four continental ancestry groups were taken forward (N = 62,484). Principal component and K-means clustering analyses were used to identify and characterize population structure within each ancestry group. Of the approximately 78,000 individuals in the UK Biobank that are of “non-white British” ancestry, 50,685, 6653, 2782, and 2364 individuals were associated to the European, African, South Asian, and East Asian continental ancestry groups, respectively. Each continental ancestry group exhibits prominent population structure that is consistent with self-reported country of birth data and geography. CONCLUSIONS: Methods outlined here provide an avenue to leverage UK Biobank’s deeply phenotyped data allowing researchers to maximize its potential in the study of health and disease in individuals of non-white British ancestry. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s40246-022-00380-5

Alkaline electrochemical reduction of a magnesium ferrospinel into metallic iron for the valorisation of magnetite-based metallurgical waste

The electrochemical reduction of iron oxides in alkaline media arises as a novel approach for ironmaking and iron-rich waste valorisation. Strong advantages and attractive aspects of alkaline electroreduction include lower electric energy consumption, absence of CO2 emissions, and non-polluting valuable by-products such as H2 and O2. Another potential advantage originates from the compatibility of this concept with intermittent renewable energies. However, to bring this technology to a competitive level, especially compared to the traditional steelmaking, innovative approaches and developments in materials processing and their appropriate integration into the electrolysis process are required. This research work explores the prospects for electrochemical reduction of a magnesium-containing ferrospinel, as a potential component in iron-containing wastes. The experimental approach considers bulk cathode- and suspension-based electrolysis concepts, which allow reaching 55% and 20% Faradaic efficiencies of the reduction to metallic iron, respectively. The effects imposed by the magnesium presence on the electroreduction kinetics, phase composition and morphology of the electroreduction products are evaluated and discussed. The obtained results open new perspectives for the recovery of metallurgical residues with low magnesium impurities content.publishe

Prospects for electrical performance tuning in Ca3Co4O9 materials by metallic Fe and Ni particles additions

This work further explores the possibilities for designing the high-temperature electrical performance of the thermoelectric Ca3Co4O9 phase, by a composite approach involving separate metallic iron and nickel particles additions, and by employing two different sintering schemes, capable to promote the controlled interactions between the components, encouraged by our recent promising results obtained for similar cobalt additions. Iron and nickel were chosen because of their similarities with cobalt. The maximum power factor value of around 200 µWm−1K−2 at 925 K was achieved for the composite with the nominal nickel content of 3% vol., processed via the twostep sintering cycle, which provides the highest densification from this work. The effectiveness of the proposed approach was shown to be strongly dependent on the processing conditions and added amounts of metallic particles. Although the conventional one-step approach results in Feand Ni-containing composites with the major content of the thermoelectric Ca3Co4O9 phase, their electrical performance was found to be significantly lower than for the Co-containing analogue, due to the presence of less-conducting phases and excessive porosity. In contrast, the relatively high performance of the composite with a nominal nickel content of 3% vol. processed via a two-step approach is related to the specific microstructural features from this sample, including minimal porosity and the presence of the Ca2Co2O5 phase, which partially compensate the complete decomposition of the Ca3Co4O9 matrix. The obtained results demonstrate different pathways to tailor the phase composition of Ca3Co4O9 -based materials, with a corresponding impact on the thermoelectric performance, and highlight the necessity of more controllable approaches for the phase composition tuning, including lower amounts and different morphologies of the dispersed metallic phases.publishe

Photocatalytic removal of benzene over Ti3C2Tx MXene and TiO2–MXene composite materials under solar and NIR irradiation

MXenes, a family of two-dimensional (2D) transition metal carbides, nitrides and carbonitrides based on earth-abundant constituents, are prospective candidates for energy conversion applications, including photocatalysis. While the activity of individual MXenes towards various photocatalytic processes is still debatable, these materials were proved to be excellent co-catalysts, accelerating the charge separation and suppressing the exciton recombination. Titanium-containing MXenes are well compatible with the classical TiO2 photocatalyst. The TiO2 component can be directly grown on MXene sheets by in situ oxidation, representing a mainstream processing approach for such composites. In this study, an essentially different approach has been implemented: a series of TiO2-MXene composite materials with controlled composition and both reference end members were prepared, involving two different strategies for mixing sol-gel-derived TiO2 nanopowder with the Ti3C2Tx component, which was obtained by HF etching of self-propagating high-temperature synthesis products containing modified MAX phase Ti3C2Alz (z > 1) with nominal aluminium excess. The prospects of such composites for the degradation of organic pollutants under simulated solar light, using benzene as a model system, were demonstrated and analysed in combination with their structural, microstructural and optical properties. A notable photocatalytic activity of bare MXene under near infrared light was discovered, suggesting further prospects for light-to-energy harvesting spanning from UV-A to NIR and applications in biomedical imaging and sensors.publishe

MXene-containing composite electrodes for hydrogen evolution: material design aspects and approaches for electrode fabrication

This work explores the possibilities for the processing of Ni- and Ti3C2Tx (T = OH, O) MXene-containing composite electrodes, by co-pressing and plastic deformation or by etching of the electrodes prepared directly by self-propagation high-temperature synthesis (SHS). Various material design approaches were also explored. In order to tune the Ti3C2 interlayer distance in Ti3C2Al MAX phase, an introduction of additional Al to form Ti3C2Alz materials with z > 1 was attempted. Self-propagation high-temperature synthesis of powder mixtures with extra Ni and Al content (e.g. Ni:Ti:Al:C = 1:2:3:1) resulted in SHS products containing Ti3C2Alz z > 1 material and Ni–Al alloys. Further etching of these products in 10M NaOH allowed the direct formation of electrodes with active surface containing Ti3C2Tx (T = OH, O) MXene- and Raney nickel-containing composites. The electrochemical studies were focused on hydrogen evolution and showed the potential for boosting the electrochemical reaction in Ni and MXene-containing composite electrodes, especially at high current densities. The guidelines for the processing of such electrodes under fluorine-free conditions are proposed and discussed.publishe

Strontium titanate and zinc-oxide-based materials for high-temperature thermoelectric harvesting

Broad societal needs have focused increased attention to providing a sustainable energy supply to the population, based on technologies with minimal environmental impact and reduced fossil fuels usage. One solution is to improve energy conversion efficiency in key consuming sectors. Since most of the energy (60-70%) used worldwide is discharged as waste heat, ”green” thermoelectric (TE) conversion has received considerable attention due to its intrinsic simplicity, employing no moving parts, silent operation, excellent scalability and reliability, and self-sufficiency to enable mobile or remote applications. In some energy-conversion scenarios, the cost and thermal stability requirements may dominate over efficiency issues, making abundant, high-temperature-stable and low-toxic oxides an interesting alternative TE material. This talk will feature some oxide-specific approaches towards tuning the thermoelectric performance in strontium titanate and zincoxide-based materials, including defects engineering and in-situ induced nanostructuring.publishe

Measurement of the cross-section and charge asymmetry of WW bosons produced in proton-proton collisions at s=8\sqrt{s}=8 TeV with the ATLAS detector

This paper presents measurements of the $W^+ \rightarrow \mu^+\nu$ and $W^- \rightarrow \mu^-\nu$ cross-sections and the associated charge asymmetry as a function of the absolute pseudorapidity of the decay muon. The data were collected in proton--proton collisions at a centre-of-mass energy of 8 TeV with the ATLAS experiment at the LHC and correspond to a total integrated luminosity of 20.2~\mbox{fb^{-1}}. The precision of the cross-section measurements varies between 0.8% to 1.5% as a function of the pseudorapidity, excluding the 1.9% uncertainty on the integrated luminosity. The charge asymmetry is measured with an uncertainty between 0.002 and 0.003. The results are compared with predictions based on next-to-next-to-leading-order calculations with various parton distribution functions and have the sensitivity to discriminate between them.Comment: 38 pages in total, author list starting page 22, 5 figures, 4 tables, submitted to EPJC. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2017-13