21. Towards a novel method for iron species determination in Antarctic sea iceHanna Budasheva, Arne Bratkič, Dorota Korte, Mladen Franko, 2021, published scientific conference contribution abstract Abstract: Sea-ice borne iron has been found to be an important factor controlling Southern Ocean phytoplankton growth [1]. Knowing the amount and chemical speciation of its labile fraction in sea ice would advance our understanding of the involved processes. Unfortunately, it is rather difficult to perform their measurement because of limited access to the Antarctic. Thus there is a strong need for the development of a quick, simple and reliable technique for determination of iron and its speciation in sea-ice that ensures also low enough limits of detection. Recently, diffusive gradients in thin films (DGT) have been widely used as passive samplers for collecting time-averaged data on the concentrations of transition metals in different media [2]. DGTs are further coupled to an analytical technique that in case of detecting metals in passive sampler films primarily requires their extraction [3], which may potentially lead to changes of the metal specification. In the present study, the beam deflection spectrometry (BDS) is coupled to DGT and used to determine the average concentration of iron in the sea ice samples collected at the Davis Station in the Antarctic. Such a combined technique has been already successfully applied for detecting labile iron species in freshwater sediments [4]. The obtained BDS data were validated by thermal lens spectrometry (TLS) and UV-Vis spectrophotometry (SPEC). The distribution of iron species over a given ice surface area using the DGT-BDS technique revealed total iron concentrations in the range of 0.6 – 5.3 μgL-1, whereas the Fe2+ content was found to be in the range of 0.1 – 1.5 μgL-1. The range taking into account all of the measurement points (5×4), the precision of a single measured point is 0.2 μgL-1. The calculated 24 h-average concentration of total Fe labile species in the ice by using BDS is 2.3 ± 0.5 μgL-1, which coincides with data obtained by SPEC (2.5 ± 0.4 μgL-1) and TLS (2.39 ± 0.02 μgL-1). Our results indicate that it is possible to develop a robust, contamination-resilient detection method for measuring the labile iron species concentration in the sea ice. In opposite to TLS and SPEC, BDS-DGT provides reliable information not only about the speciation of iron but also about their distribution on the ice surface.
Keywords: beam deflection spectrometry, diffusive gradients, thin films, iron species, photothermal techniques, Antarctic sea ice
Published in RUNG: 30.11.2021; Views: 2248; Downloads: 0
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22. Solvothermal synthesis of iron phosphides and their application for efficient electrocatalytic hydrogen evolutionTakwa Chouki, Manel Machreki, Saim Emin, 2020, published scientific conference contribution abstract Abstract: We report the solvothermal synthesis of iron phosphide electrocatalysts using a low-cost phosphorus precursor [1]. The synthetic protocol allows for the preparation of a Fe2P phase at 300°C and FeP phase at 350°C. To enhance the catalytic activities of obtained iron phosphide particles, heat-treatments were carried out at elevated temperatures. Annealing at 500°C induced structural changes in the samples: (i) Fe2P provided a pure Fe3P phase (Fe3P−500°C) and (ii) FeP transformed into a mixture of iron phosphide phases (Fe2P/FeP−500°C). The electrocatalytic activities of heat-treated Fe2P−450°C, Fe3P−500°C, and Fe2P/FeP−500°C catalysts were studied for hydrogen evolution reaction (HER) in 0.5 M sulfuric acid (H2SO4). The HER activities of the iron phosphide catalyst were found to be phase dependent. The lowest recorded overpotential of 110 mV at 10 mA cm−2 vs. a reversible hydrogen electrode was achieved with Fe2P/FeP−500°C catalyst. The present approach allows the preparation of immobilized iron phsphide catalyst onto carbon support which is essential for application purpose. The procedure developed by us is an elegant approach to tune the composition of iron phosphide catalyst and control the morphology of particles.
Keywords: solvothermal synthesis, iron phosphide, electrocatalyst, hydrogen evolution, overpotential
Published in RUNG: 13.05.2021; Views: 2134; Downloads: 0
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25. Solvothermal synthesis of iron phosphides and their application for efficient electrocatalytic hydrogen evolutionTakwa Chouki, Manel Machreki, Saim Emin, 2020, original scientific article Abstract: Abstract
In this paper, we present a solvothermal synthesis of iron phosphide electrocatalysts using a triphenylphosphine (TPP) precursor. The synthetic protocol generates Fe2P phase at 300 °C and FeP phase at 350 °C. To enhance the catalytic activities of obtained iron phosphide particles heat-treatments were carried out at elevated temperatures. Annealing at 500 °C under reductive atmosphere induced structural changes in the samples: (i) Fe2P provided a pure Fe3P phase (Fe3P−500 °C) and (ii) FeP transformed into a mixture of iron phosphide phases (Fe2P/FeP−500 °C). Pure Fe2P films was prepared under argon atmosphere at 450 °C (Fe2P−450 °C). The electrocatalytic activities of heat-treated Fe2P−450 °C, Fe3P−500 °C, and Fe2P/FeP−500 °C catalysts were studied for hydrogen evolution reaction (HER) in 0.5 M H2SO4. The HER activities of the iron phosphide catalyst were found to be phase dependent. The lowest electrode potential of 110 mV vs. a reversible hydrogen electrode (RHE) at 10 mA cm−2 was achieved with Fe2P/FeP−500 °C catalyst.
Keywords: Solvothermal synthesis, Iron phosphide, Electrocatalyst, Hydrogen evolution, Overpotential
Published in RUNG: 20.07.2020; Views: 2679; Downloads: 0
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26. Mineral element composition in grain of awned and awnletted wheat (Triticum aestivum L.) cultivars tissue-specific iron speciation and phytate and non-phytate ligand ratioPaula Pongrac, Iztok Arčon, Hiram Castillo Michel, Katarina Vogel-Mikuš, 2020, original scientific article Abstract: In wheat (Triticum aestivum L.), the awns—the bristle-like structures extending from
lemmas—are photosynthetically active. Compared to awned cultivars, awnletted cultivars produce
more grains per unit area and per spike, resulting in significant reduction in grain size, but their
mineral element composition remains unstudied. Nine awned and 11 awnletted cultivars were
grown simultaneously in the field. With no difference in 1000-grain weight, a larger calcium and
manganese—but smaller iron (Fe) concentrations—were found in whole grain of awned than in
awnletted cultivars. Micro X-ray absorption near edge structure analysis of different tissues of
frozen-hydrated grain cross-sections revealed that differences in total Fe concentration were not
accompanied by differences in Fe speciation (64% of Fe existed as ferric and 36% as ferrous species) or
Fe ligands (53% were phytate and 47% were non-phytate ligands). In contrast, there was a distinct
tissue-specificity with pericarp containing the largest proportion (86%) of ferric species and nucellar
projection (49%) the smallest. Phytate ligand was predominant in aleurone, scutellum and embryo
(72%, 70%, and 56%, respectively), while nucellar projection and pericarp contained only non-phytate
ligands. Assuming Fe bioavailability depends on Fe ligands, we conclude that Fe bioavailability from
wheat grain is tissue specific.
Keywords: biofortification, phytate, iron, awn, X-ray fluorescence, X-ray absorption spectrometry, phosphorus, sulphur, nicotianamine
Published in RUNG: 16.01.2020; Views: 2866; Downloads: 0
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27. Determination of Iron in Environmental Water Samples by FIA-TLSMiha Tomšič, Leja Goljat, Hanna Budasheva, Dorota Korte, Arne Bratkič, Mladen Franko, 2019, original scientific article Abstract: The determination of low concentration of iron in natural waters can be difficult due to the complexity of natural water, but primarily because it requires preconcentration of the sample with solvent extraction. In this work we report on results of thermal lens spectrometry (TLS) coupled to flow injection analysis (FIA) as a highly sensitive FIA-TLS method of iron detection. The concentration of iron redox species was determined using 1,10-phenanthroline (PHN), that forms stable complexes with Fe(II) ions which are characterized by an absorption maximum at 508 nm. The TLS system using a 633 nm probe laser and 530 nm pump laser beam was exploited for on-line detection in flow injection analysis, where a PHN solution was used as the carrier solution for FIA. The concentration of the complexing agent affects the quality of the TLS signal, and the optimal concentration was found at 1 mM PHN. The achieved limits of detection (LODs) for Fe(II) and total iron were 33 nM for Fe(II) and 21 nM for total iron concentration. The method was further validated by determining the linear concentration range, specificity in terms of analytical yield and by determining concentration of iron in a water sample from a local water stream.
Keywords: Flow injection analysis, iron concentration, thermal lens spectroscopy
Published in RUNG: 18.12.2019; Views: 3247; Downloads: 105
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28. Substrate- to Laterally-Driven Self-Assembly Steered by Cu Nanoclusters: The Case of FePcs on an Ultrathin Alumina FilmManuel Corva, Fatema Mohamed, Erika Tomsič, Zhijing Feng, Tomas Skala, Giovanni Comelli, Nicola Seriani, Maria Peressi, Erik Vesselli, 2018, original scientific article Keywords: copper, nanoclusters, alumina, iron phthalocyanine, Ni3Al
Published in RUNG: 03.12.2019; Views: 2983; Downloads: 0
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30. Developing DGT technique for determination of iron redox species by photothermal beam deflection spectrometryHanna Budasheva, Arne Bratkič, Chang Zhou, Dorota Korte, Yue Gao, Mladen Franko, Bruno Delille, 2019, published scientific conference contribution abstract Keywords: Diffusive Gradients in Thin Films, Beam Deflection Spectrometry, iron redox species
Published in RUNG: 25.09.2019; Views: 3400; Downloads: 0
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