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Eingeladener Vortrag
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Formation Mechanism of a Nano-Ring of Bismuth Cations and Mono-Lacunary Keggin-Type Phosphomolybdate
(2022)
A new hetero-bimetallic polyoxometalate (POM) nano-ring was synthesized in a one-pot procedure. The structure consists of tetrameric units containing four bismuth-substituted monolacunary Keggin anions including distorted [BiO8] cubes. The nano-ring is formed via self-assembly from metal precursors in aqueous acidic medium. The compound (NH4)16[(BiPMo11O39)4] ⋅ 22 H2O; (P4Bi4Mo44) was characterized by single-crystal X-ray diffraction, extended X-ray absorption fine structure spectroscopy (EXAFS), Raman spectroscopy, matrix-assisted laser desorption/ionisation-time of flight mass spectrometry (MALDI-TOF), and thermogravimetry/differential scanning calorimetry mass spectrometry (TG-DSC-MS). The formation of the nano-ring in solution was studied by time-resolved in situ small- and wide-angle X-ray scattering (SAXS/WAXS) and in situ EXAFS measurements at the Mo−K and the Bi−L3 edge indicating a two-step process consisting of condensation of Mo-anions and formation of Bi−Mo-units followed by a rapid self-assembly to yield the final tetrameric ring structure.
The increasing pollution of terrestrial and aquatic ecosystems with plastic debris, which leads to the accumulation of microscopic plastic particles of still unknown fate, is an upcoming problem of our time. In order to monitor the degree of contamination and to understand the underlying processes of degradation and internalization of plastic debris, analytical methods are urgently needed, which help to identify and quantify microplastics. Currently, expensive collected and purified materials enriched on filters are investigated by (micro) infrared spectroscopy (FTIR). Few studies using micro-Raman spectroscopy have been published as well. In contrast to FTIR, Raman spectroscopy can handle wet samples, but it suffers from interference of fluorescent materials. Both micro-FTIR- and micro-Raman, always include time consuming scanning and mapping procedures followed by the manual inspection and measurement of selected particles.
Ramanmikroskopie kombiniert den chemischen Informationsgehalt von Ramanspektren mit einer Ortsauflösung im Mikrometer- bis Sub-Mikrometerbereich und eignet sich daher hervorragend zur Analyse mikrostrukturell und chemisch komplexer Materialien.
Zemente des 19. Jahrhunderts sind chemisch wie mikrostrukturell wesentlich komplexer als die heute aus definierten Rohmaterialien unter optimalen Bedingungen erbrannten Mörtelbinder. Der erstmalige Einsatz bildgebender Ramanmikroskopie im Bereich zementbasierter Materialien zeigte das Potential dieser Analytik auf. Gezieltes, flächendeckendes Abrastern von Klinkerrelikten in der hydratisierten Zementmatrix ermöglicht die Bestimmung von Silikaten, Aluminaten, Ferriten und anderer Phasen inklusive polymorpher Formen und Änderungen der Zusammen-setzung innerhalb von Mischkristallreihen und aufgrund des Einbaus von Fremdionen, wobei auch mikropartikuläre Bestandteile erfasst werden, deren Konzentrationen unter der Nachweisgrenze makroskopischer Analyseverfahren liegen. So lassen sich Rückschlüsse auf die verwendeten Rohmaterialien und die Herstellungsbedingungen ziehen, was die Bestimmung des verwendeten Zementtyps zulässt und damit Auswirkungen auf die Auswahl von Restaurierungsmaterialien hat. Möglichkeiten zur quantitativen Verteilungsanalyse von Kristallorientierungen und mechanischer Spannungen zeigten sich bei der Untersuchung von Dünnschicht-Solarzellen-Absorbern wie Cu(In,Ga)Se2 und daraus abgeleiteter Materialien. Die direkte Kompatibilität mit Lichtmikroskopie-Proben und die hohe chemisch-strukturelle Spezifizität von Ramanspektren kamen der Untersuchung naturhistorischer Mikroskopiepräparate aus Museumssammlungen zugute. Sowohl das Eindeckmedium und seine aktuelle Zusammensetzung (z.B. bezüglich leichtflüchtiger Bestandteile) als auch durch Alterung entstandene Schäden lassen sich mit der Technik zerstörungsfrei erfassen. Damit können in Zukunft Beiträge zum Erhalt der weltweit mehrere Millionen Proben umfassenden naturhistorischen Sammlungen geleistet werden.
Die in der Forschung gesammelte Erfahrung fließt in der BAM direkt in die Sonder-probenanalytik für Industriekunden ein, wo Ramanbildgebung, eingebettet in ein Arsenal komplementärer Methoden, ebenfalls häufig eine zentrale Rolle spielt.
Troubleshooting Samples Analytics:
Impurities in products: unexpected & unwanted occurrence, unknown identity, analytical method unclear, often various analytical methods, necessary, short response time important (< 1 d), benefits: allocation of its source within hours safes cost
• Investigations planned, coordinated and documented by TSA team
• Variety of analytical methods available
The quantification of the elemental content in soils with laser-induced breakdown spectroscopy (LIBS) is challenging because of matrix effects strongly influencing the plasma formation and LIBS signal. Furthermore, soil heterogeneity at the micrometre scale can affect the accuracy of analytical results. In this paper, the impact of univariate and multivariate data evaluation approaches on the quantification of nutrients in soil is discussed. Exemplarily, results for calcium are shown, which reflect trends also observed for other elements like magnesium, silicon and iron. For the calibration models, 16 certified reference soils were used. With univariate and multivariate approaches, the calcium mass fractions in 60 soils from different testing grounds in Germany were calculated. The latter approach consisted of a principal component analysis (PCA) of adequately pre-treated data for classification and identification of outliers, followed by partial least squares regression (PLSR) for quantification. For validation, the soils were also characterised with inductively coupled plasma optical emission spectroscopy (ICP OES) and X-ray fluorescence (XRF) analysis. Deviations between the LIBS quantification results and the reference analytical results are discussed.
Raman microspectroscopy provides the means to obtain local orientations on polycrystalline materials at the submicrometer level. The present work demonstrates how orientation-distribution maps composed of Raman intensity distributions can be acquired on large areas of several hundreds of square micrometers. A polycrystalline CuInSe2 thin film was used as a model system. The orientation distributions are evidenced by corresponding measurements using electron backscatter diffraction (EBSD) on the same identical specimen positions. The quantitative, local orientation information obtained by means of EBSD was used to calculate the theoretical Raman intensities for specific grain orientations, which agree well with the experimental values. The presented approach establishes new horizons for Raman microspectroscopy as a tool for quantitative, microstructural analysis at submicrometer resolution.
Shedding light onto the spectra of lime: Raman and luminescence bands of CaO, Ca(OH)2 and CaCO3
(2015)
In microscopy studies of 19th-century cement stone, we found free lime in the form of darkened spherical structures, as they were described in the literature already. When trying to determine their phase composition by Raman spectroscopy, we encountered contradictive assignments in literature spectra of the lime phases CaO, Ca(OH)2 and CaCO3 and observed strong spectral features that have been ignored or erroneously assigned so far. In this study we present Raman spectra of pure lime phases and of a naturally grown calcite crystal, burnt limestone (quick lime, mainly CaO), aged slaked lime putty (mainly Ca(OH)2), and carbonated lime putty (mainly CaCO3). Based on the results, we shed light mainly onto these two questions: (1) Does CaO have a Raman spectrum? (2) Which features in the spectra are luminescence bands that could be (and already have been) misinterpreted as Raman bands? We proof our assignment of luminescence bands in lime phases by using three different laser wavelengths for excitation, and give hypotheses on the origin of the luminescence as well as practical advices on how to identify these misleading features in Raman spectra. This article is mainly addressed to users of Raman spectroscopy in different fields of material analysis who might not be aware of the presence of interfering bands in their spectra.