Publications at the Department of Mathematics and Natural Sciences

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Gizatullin, Bulat; Mattea, Carlos; Stapf, Siegfried;
Molecular dynamics in ionic liquid/radical systems. - In: The journal of physical chemistry. - Washington, DC : Soc., ISSN 1520-5207, Bd. 125 (2021), 18, S. 4850-4862

Molecular dynamics of the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide (Emim-Tf2N) with either of the four organic stable radicals, TEMPO, 4-benzoyloxy-TEMPO, BDPA, and DPPH, is studied by using Nuclear Magnetic Resonance (NMR) and Dynamic Nuclear Polarization (DNP). In complex fluids at ambient temperature, NMR signal enhancement by DNP is frequently obtained by a combination of several mechanisms, where the Overhauser effect and solid effect are the most common. Understanding the interactions of free radicals with ionic liquid molecules is of particular significance due to their complex dynamics in these systems, influencing the properties of the ion-radical interaction. A combined analysis of EPR, DNP, and NMR relaxation dispersion is carried out for cations and anions containing, respectively, the NMR active nuclei 1H or 19F. Depending on the size and the chemical properties of the radical, different interaction processes are distinguished, namely, the Overhauser effect and solid effect, driven by dominating dipolar or scalar interactions. The resulting NMR relaxation dispersion is decomposed into rotational and translational contributions, allowing the identification of the corresponding correlation times of motion and interactions. The influence of electron relaxation time and electron-nuclear spin hyperfine coupling is discussed.
Knauer, Andrea; Kuhfuss, Danja; Köhler, Michael;
Electrostatic control of Au nanorod formation in automated microsegmented flow synthesis. - In: ACS applied nano materials. - Washington, DC : ACS Publications, ISSN 2574-0970, Bd. 4 (2021), 2, S. 1411-1419

An automated flow rate program was applied for the synthesis of gold nanorods of different aspect ratios dependent on a two-dimensional concentration space of reducing agent and additional silver ions. It was found a regular redshift of the spectral position of the electromagnetic in-axis resonance of metal nanorods with decreasing concentration of reducing agent and increasing concentration of silver ions. The increase of resonance wavelength is strongly correlated with the aspect ratio of the formed nanorods. The experimental results agree with an electrostatic model of self-polarization due to positive excess charge of the nanorods in the presence of CTAB and confirm the crucial role of electrostatic control in the formation of nonspherical and composed nanoparticles in general.
Wu, Yuhan; Zhang, Chenglin; Zhao, Huaping; Lei, Yong;
Recent advances in ferromagnetic metal sulfides and selenides as anodes for sodium- and potassium-ion batteries. - In: Journal of materials chemistry. - London [u.a.] : RSC, ISSN 2050-7496, Bd. 9 (2021), 15, S. 9506-9534

In next-generation rechargeable batteries, sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) have been considered as attractive alternatives to lithium-ion batteries due to their cost competitiveness. Anodes with complicated electrochemical mechanisms determine the performance and safety of battery systems to a large degree. Among a wide range of anode materials for SIBs and PIBs, ferromagnetic metal (Fe, Co, and Ni) sulfides and selenides have captured prominent attention by virtue of their high theoretical capacities, suitable potentials, and relatively low price. Although some breakthrough results have been achieved, a few intrinsic issues stemming from the materials themselves need to be further explored and studied, especially in the field of PIBs, an emerging research interest. Herein, in this review, we highlight the pioneering investigation of typical ferromagnetic metal sulfides and selenides for application as anodes in SIBs and PIBs and overview their recent research progress. Meanwhile, the preparation methods, structural characteristics, charge storage mechanisms, and electrochemical properties are outlined. Finally, the present challenges and research perspectives are discussed.
Reiß, Stephanie; Hopfeld, Marcus; Romanus, Henry; Pfeifer, Kerstin; Krischok, Stefan; Rädlein, Edda;
Chemical changes of float glass surfaces induced by different sand particles and mineralogical phases. - In: Journal of non-crystalline solids : a journal on the chemical, electronic, optical and mechanical properties of glasses, amorphous semiconductors and metals, sol-gel materials, the liquid state of these solids and the processes by which they are formed.. - Amsterdam [u.a.] : Elsevier Science, ISSN 0022-3093, Bd. 566 (2021), 120868

Particles play an important role in the storage, transportation and natural weathering of glasses, but their influence on glass degradation is little studied. In this work, the influence of main sand components is investigated. Feldspar exhibits the strongest leaching rate for the network former Na, while quartz has the lowest. The leaching rate of natural sands is in between. Based on these findings, a model describing the leaching mechanism was developed: Hereby, hydroxyl groups adhering on sand grains adsorb network modifiers by substituting their hydrogen by network formers from the glass surface. The amount of available hydroxyl groups determines the leaching rate. This model is supported by loss on ignition performed for the sands, which might be a suitable method to roughly estimate their leaching rates. The adsorption of network modifiers suppresses carbonate formation, dendritic growth and Mg diffusion in the glass surface region. Pimple-like crystal growth is observed.
Gizatullin, Bulat; Papmahl, Eric; Mattea, Carlos; Stapf, Siegfried;
Quantifying crude oil contamination in sand and soil by EPR spectroscopy. - In: Applied magnetic resonance : AMR.. - Wien [u.a.] : Springer, ISSN 1613-7507, Bd. 52 (2021), 5, S. 633-648

Crude oil frequently contains stable radicals that allow detection by means of EPR spectroscopy. On the other hand, most sands and soils possess significant amounts of iron, manganese or other metallic species that often provide excessively broad EPR signatures combined with well-defined sharp features by quartz defects. In this study, we demonstrate the feasibility to identify oil contamination in natural environments that are subject to oil spillage during production on land, as well as beachside accumulation of marine oil spillage. Straightforward identification of oil is enabled by the radical contributions of asphaltenes, in particular by vanadyl multiplets that are absent from natural soils. This potentially allows for high-throughput soil analysis or the application of mobile EPR scanners.
Zhang, Da; Xie, Zhipeng; Zhang, Kaiwen; Wang, Haoyu; Qu, Tao; Ma, Wenhui; Yang, Bin; Dai, Yongnian; Liang, Feng; Lei, Yong; Watanabe, Takayuki;
Controlled regulation of the transformation of carbon nanomaterials under H2 mixture atmosphere by arc plasma. - In: Chemical engineering science. - Amsterdam [u.a.] : Elsevier Science, Bd. 241 (2021), 116695
- Im Titel ist "2" tiefgestellt

Hydrogen plays a pivotal role in carbon nanomaterials synthesis by arc plasma. However, the effect of hydrogen on morphological regulation of carbon nanomaterials has received little attention. In this paper, carbon nanomaterials synthesized under mixed H2/Ar, H2/N2, and Ar/N2 atmospheres with different ratios were investigated in detail to tackle the issue. Graphene, carbon nanocages, polyhedral graphite particles, amorphous carbon nanoballs, and carbon nanohorns underwent structural transformation as hydrogen content reduced. As a result of varying hydrogen concentration, the number of C-H bond sites at the edge of graphene islands differed, leading to the structural transformation of carbon nanomaterials originating from the formation of various types of precursors. Meanwhile, X-ray photoelectron spectroscopy results revealed that hydrogen impeded nitrogen doping because it tended to bond with electronegative nitrogen. Moreover, morphology control capability followed the order of H2 > N2 > Ar during the preparation of carbon nanomaterials through arc plasma under a mixed atmosphere.
Eichfelder, Gabriele; Kirst, Peter; Meng, Laura; Stein, Oliver;
A general branch-and-bound framework for continuous global multiobjective optimization. - In: Journal of global optimization. - Dordrecht [u.a.] : Springer Science + Business Media B.V, ISSN 1573-2916, (2021), insges. 33 S.
- Published: 19 January 2021

Current generalizations of the central ideas of single-objective branch-and-bound to the multiobjective setting do not seem to follow their train of thought all the way. The present paper complements the various suggestions for generalizations of partial lower bounds and of overall upper bounds by general constructions for overall lower bounds from partial lower bounds, and by the corresponding termination criteria and node selection steps. In particular, our branch-and-bound concept employs a new enclosure of the set of nondominated points by a union of boxes. On this occasion we also suggest a new discarding test based on a linearization technique. We provide a convergence proof for our general branch-and-bound framework and illustrate the results with numerical examples.
Wu, Yuhan; Zhang, Qingcheng; Xu, Yang; Xu, Rui; Li, Lei; Li, Yueliang; Zhang, Chenglin; Zhao, Huaping; Wang, Shun; Kaiser, Ute; Lei, Yong;
Enhanced potassium storage capability of two-dimensional transition-metal chalcogenides enabled by a collective strategy. - In: ACS applied materials & interfaces. - Washington, DC : Soc., ISSN 1944-8252, Bd. 13 (2021), 16, S. 18838-18848

Potassium-ion batteries (PIBs) have been considered as a promising alternative to lithium-ion batteries due to their merits of high safety and low cost. Two-dimensional transition-metal chalcogenides (2D TMCs) with high theoretical specific capacities and unique layered structures have been proven to be amenable materials for PIB anodes. However, some intrinsic properties including severe stacking and unsatisfactory conductivity restrict their electrochemical performance, especially rate capability. Herein, we prepared a heterostructure of high-crystallized ultrathin MoSe2 nanosheet-coated multiwall carbon nanotubes and investigated its electrochemical properties with a view to demonstrating the enhancement of a collective strategy for K storage of 2D TMCs. In such a heterostructure, the constructive contribution of CNTs not only suppresses the restacking of MoSe2 nanosheets but also accelerates electron transport. Meanwhile, the MoSe2 nanosheets loaded on CNTs exhibit an ultrathin feature, which can expose abundant active sites for the electrochemical reaction and shorten K+ diffusion length. Therefore, the synergistic effect between ultrathin MoSe2 and CNTs endows the resulting nanocomposite with superior structural and electrochemical properties. Additionally, the high crystallinity of the MoSe2 nanosheets further leads to the improvement of electrochemical performance. The composite electrode delivers high-rate capacities of 209.7 and 186.1 mAh g-1 at high current densities of 5.0 and 10.0 A g-1, respectively.
Schumann, Peter; Kalensee, Franziska; Cao, Jialan; Criscuolo, Alexis; Clermont, Dominique; Köhler, Michael; Meier-Kolthoff, Jan Philipp; Neumann-Schaal, Meina; Tindall, Brian J.; Pukall, Rüdiger;
Reclassification of Haloactinobacterium glacieicola as Occultella glacieicola gen. nov., comb. nov., of Haloactinobacterium album as Ruania alba comb. nov, with an emended description of the genus Ruania, recognition that the genus names Haloactinobacterium and Ruania are heterotypic synonyms and description of Occultella aeris sp. nov., a halotolerant isolate from surface soil sampled at an ancient copper smelter. - In: International journal of systematic and evolutionary microbiology : IJSEM ; official publication of the International Committee on Systematic Bacteriology and the Bacteriology and Applied Microbiology Division of the International Union of Microbiological Societies.. - Reading : SGM, ISSN 1466-5034, Bd. 71 (2021), 4, S. 004769

In the course of screening the surface soils of ancient copper mines and smelters (East Harz, Germany) an aerobic, non-motile and halotolerant actinobacterium forming small rods or cocci was isolated. The strain designated F300T developed creamy to yellow colonies on tryptone soy agar and grew optimally at 28 ˚C, pH 7-8 and with 0.5-2% (m/v) NaCl. Its peptidoglycan was of type A4α l-Lys-l-Glu (A11.54). The menaquinone profile was dominated by MK-8(II, III-H4) and contained minor amounts of MK-8(H2), MK-8(H6) and MK-9(H4). The polar lipids comprised diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, mono and diacylated phosphatidylinositol dimannosides, and components that were not fully characterized, including two phospholipids, two glycolipids and an uncharacterized lipid. Major whole-cell sugars were rhamnose and ribose. The fatty acid profile contained mainly iso and anteiso branched fatty acids (anteiso-C15:0, iso-C14:0) and aldehydes/dimethylacetals (i.e. not fatty acids). Sequence analysis of its genomic DNA and subsequent analysis of the data placed the isolate in the group currently defined by members of the genera Ruania and Haloactinobacterium (family Ruaniaceae , order Micrococcales ) as a sister taxon to the previously described species Haloactinobacterium glacieicola , sharing an average nucleotide identity and average amino acid identity values of 85.3 and 85.7%, respectively. Genotypic and chemotaxonomic analyses support the view that strain F300T (=DSM 108350T=CIP 111667T) is the type strain of a new genus and new species for which the name Occultella aeris gen. nov., sp. nov. is proposed. Based on revised chemotaxonomic and additional genome based data, it is necessary to discuss and evaluate the results in the light of the classification and nomenclature of members of the family Ruaniaceae , i.e. the genera Haloactinobacterium and Ruania . Consequently, the reclassification of Haloactinobacterium glacieicola as Occultella glacieicola comb. nov. and Haloactinobacterium album as Ruania alba comb. nov., with an emended description of the genus Ruania are proposed.,
Allen, Peter; Koch, Christoph; Parczyk, Olaf; Person, Yury;
Finding tight Hamilton cycles in random hypergraphs faster. - In: Combinatorics, probability & computing : CPC.. - Cambridge : Cambridge Univ. Press, ISSN 1469-2163, Bd. 30 (2021), 2, S. 239-257