Publications by authors named "Stefan Schymura"

5 Publications

  • Page 1 of 1

Molecular-Level Speciation of Eu(III) Adsorbed on a Migmatized Gneiss As Determined Using μTRLFS.

Environ Sci Technol 2021 04 11;55(8):4871-4879. Epub 2021 Mar 11.

Helmholtz-Zentrum Dresden-Rossendorf, Institute of Resource Ecology, Bautzner Landstrasse 400, 01328 Dresden, Germany.

The interaction of Eu(III) with thin sections of migmatized gneiss from the Bukov Underground Research Facility (URF), Czech Republic, was characterized by microfocus time-resolved laser-induced luminescence spectroscopy (μTRLFS) with a spatial resolution of ∼20 μm, well below typical grain sizes of the material. By this approach, sorption processes can be characterized on the molecular level while maintaining the relationship of the speciation with mineralogy and topography. The sample mineralogy was characterized by powder X-ray diffraction and Raman microscopy, and the sorption was independently quantified by autoradiography using Eu. Representative μTRLFS studies over large areas of multiple mm reveal that sorption on the heterogeneous material is not dominated by any of the typical major constituent minerals (quartz, feldspar, and mica). Instead, minor phases such as chlorite and prehnite control the Eu(III) distribution, despite their low contribution to the overall composition of the material, as well as common but less studied phases like Mg-hornblende. In particular, prehnite shows high a sorption uptake as well as strong binding of Eu to the mineral surface. Sorption on prehnite and hornblende happens at the expense of feldspar, which showed the highest sorption uptake in a previous spatially resolved study on granitic rock. Similarly, sorption on quartz is reduced, even though only low quantities of strongly bound Eu(III) were found here previously. Our results illustrate how competition of mineral surfaces for adsorbing cations drives the metal distribution in heterogeneous systems.
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http://dx.doi.org/10.1021/acs.est.0c07998DOI Listing
April 2021

Elucidating the Role of Dissolution in CeO Nanoparticle Plant Uptake by Smart Radiolabeling.

Angew Chem Int Ed Engl 2017 06 19;56(26):7411-7414. Epub 2017 May 19.

Institute of Resource Ecology, Helmholtz-Zentrum Dresden-Rossendorf, Permoser Strasse 15, 04318, Leipzig, Germany.

The identification of major uptake pathways in plants is an important factor when evaluating the fate of manufactured nanoparticles in the environment and the associated risks. Using different radiolabeling techniques we were able to show a predominantly particulate uptake for CeO nanoparticles in contrast to a possible uptake in the form of ionic cerium.
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http://dx.doi.org/10.1002/anie.201702421DOI Listing
June 2017

On the effect of carbon nanotubes on properties of liquid crystals.

Philos Trans A Math Phys Eng Sci 2013 Apr 4;371(1988):20120261. Epub 2013 Mar 4.

Institute of Chemistry-Physical Chemistry, Martin Luther University, Halle-Wittenberg, Halle, Germany.

Liquid crystals (LCs), with their fluidity and self-organization, are attractive hosts for the dispersion and manipulation of macro- and nanoparticles, allowing the realization of their ordered assemblies. In addition, new functional materials can be created owing to the particle properties. Among the nanoparticles, carbon nanotubes (CNTs) stand out for their exceptional electrical, thermal and mechanical properties. While LCs can be used for manipulating CNTs, the nanotube properties are attractive also for influencing and tuning LC properties. In this paper, we discuss different aspects of the CNT-LC combination, briefly introducing their dispersion and interaction and then, more extensively, evaluating the CNT effect on selected properties of LCs relevant to display-related applications. We show that some previously reported improvements cannot be considered an intrinsic feature of CNT-doped LCs. In addition, we are also able to follow locally the Frederiks transition of CNT-doped LCs by Raman spectroscopy, revealing the direct effect of bundles of CNTs on LC reorientation.
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http://dx.doi.org/10.1098/rsta.2012.0261DOI Listing
April 2013

Utilizing the Krafft phenomenon to generate ideal micelle-free surfactant-stabilized nanoparticle suspensions.

Angew Chem Int Ed Engl 2012 Mar 17;51(13):3254-7. Epub 2012 Feb 17.

Martin-Luther-University Halle-Wittenberg, Institute of Chemistry, von-Danckelmann-Platz 4, 06120 Halle, Germany.

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http://dx.doi.org/10.1002/anie.201106793DOI Listing
March 2012

Nematic-smectic transition under confinement in liquid crystalline colloidal shells.

Phys Rev Lett 2011 Jun 15;106(24):247801. Epub 2011 Jun 15.

Martin-Luther University Halle-Wittenberg, Institute of Chemistry-Physical Chemistry, Halle, Germany.

We carry out the first study of smectic liquid crystalline colloidal shells and investigate how their complex internal structure depends on the director configuration in the nematic phase, preceding the smectic phase on cooling. Differences in the free energy cost of director bend and splay give an initial skewed distribution of topological defects in the nematic phase. In the smectic phase, the topological and geometrical constraints of the spherical shell imposed on the developing 1D quasi-long-range order create a conflict that triggers a series of buckling instabilities. Two different characteristic defect patterns arise, one driven by the curvature of the shell, the other by the strong nonuniformities in the director field in the vicinity of the topological defects.
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http://dx.doi.org/10.1103/PhysRevLett.106.247801DOI Listing
June 2011