TY - JOUR A1 - Razzaq, M. Y. A1 - Behl, M. A1 - Frank, U. A1 - Koetz, J. A1 - Szczerba, Wojciech A1 - Lendlein, A. T1 - Oligo(omega-pentadecalactone) decorated magnetic nanoparticles N2 - Hybrid magnetic nanoparticles (mgNP) with a magnetite core diameter of 10 ± 1 nm surface functionalized with oligo(ω-pentadecalactone) (OPDL) oligomers with Mn between 1300 and 3300 g mol-1 could be successfully prepared having OPDL grafted from 200 mg g-1 to 2170 mg g-1. The particles are dispersible in chloroform resulting in stable suspensions. Magnetic response against an external magnetic field proved the superparamagnetic nature of the particles with a low coercivity (Bc) value of 297 µT. The combination of the advantageous superparamagnetism of the mgNP with the exceptional stability of OPDL makes these novel hybrid mgNP promising candidates as multifunctional building blocks for magnetic nanocomposites with tunable physical properties. KW - PPDL KW - OPDL KW - Magnetic core-shell nanoparticles PY - 2012 DO - https://doi.org/10.1039/c2jm16146j SN - 0959-9428 SN - 1364-5501 VL - 22 IS - 18 SP - 9237 EP - 9243 PB - Royal Society of Chemistry CY - Cambridge AN - OPUS4-25741 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mandel, K. A1 - Szczerba, Wojciech A1 - Thünemann, Andreas A1 - Riesemeier, Heinrich A1 - Girod, Matthias A1 - Sextl, G. T1 - Nitric acid-stabilized superparamagnetic iron oxide nanoparticles studied with X-rays N2 - Agglomerated superparamagnetic iron oxide nanoparticles can easily and in large scale be precipitated from iron salt solutions. Although the process is well known, it is ambiguously either assumed that magnetite or maghemite is obtained. The first part of our study clarifies this question using X-ray absorption spectroscopy. For further processing of the nanoparticles, i.e., for giving them a surface functionality or incorporating them into composites, it is important to break the agglomerates and individualize the particles at first. This can effectively be done with nitric acid treatment. The influence of this process on the particles chemistry and structure was analyzed in great detail using X-ray diffraction, X-ray absorption, and smallangle X-ray scattering. In contrast to our expectation, no oxidation from magnetite (Fe3O4) to maghemite (γ- Fe2O3) was found; the formal valence of the particles in any case is magnetite (Fe3O4). Instead, an increase in the particles' surface disorder was discovered from X-ray absorption analyses and high-resolution transmission electron microscopy. The acid treatment roughens and distorts the surface of the nanoparticles which is connected with an increased spin disorder. KW - XANES KW - EXAFS KW - SAXS KW - Coprecipitation KW - Iron oxide spectra KW - Ferrofluid PY - 2012 DO - https://doi.org/10.1007/s11051-012-1066-3 SN - 1388-0764 SN - 1572-896X VL - 14 IS - 8 SP - 1 EP - 9 PB - Kluwer CY - Dordrecht AN - OPUS4-26357 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Szczerba, Wojciech A1 - Schott, M. A1 - Riesemeier, Heinrich A1 - Thünemann, Andreas A1 - Kurth, D.G. T1 - Thermally induced structural rearrangement of the Fe(II) coordination geometry in metallo-supramolecular polyelectrolytes N2 - Rigid rod-type metallo-supramolecular coordination polyelectrolytes with Fe(II) centres (Fe-MEPEs) are produced via the self-assembly of the ditopic ligand 1,4-bis(2,2':6',2''-terpyridine-4'-yl)benzene (tpy-ph-tpy) and Fe(II) acetate. Fe-MEPEs exhibit remarkable electrochromic properties; they change colour from blue to transparent when an electric potential is applied. This electrochemical process is generally reversible. The blue colour in the ground state is a result of a metal-to-ligand charge transfer at the Fe(II) centre ion in a quasi-octahedral geometry. When annealed at temperatures above 100 °C, the blue colour turns into green and the formerly reversible electrochromic properties are lost, even after cooling down to room temperature. The thermally induced changes in the Fe(II) coordination sphere are investigated in situ during annealing of a solid Fe-MEPE using X-ray absorption fine structure (XAFS) spectroscopy. The study reveals that the thermally induced transition is not accompanied by a redox process at the Fe(II) centre. From the detailed analysis of the XAFS spectra, the changes are attributed to structural changes in the coordination sphere of the Fe(II) site. In the low temperature state, the Fe(II) ion rests in a quasi-octahedral coordination environment surrounded by six nitrogen atoms of the pyridine rings. The axial Fe–N bond length is 1.94 Å, while the equatorial bond length amounts to 1.98 Å. In the high temperature state, the FeN6-site exhibits a distortion with the axial Fe–N bonds being shortened to 1.88 Å and the equatorial Fe–N bonds being elongated to 2.01 Å. KW - Metallo-supramolecular polyelectrolytes KW - Electrochromism KW - XANES KW - EXAFS KW - Local structure KW - Thermal stability PY - 2014 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-317331 DO - https://doi.org/10.1039/c4cp01187b SN - 1463-9076 SN - 1463-9084 VL - 16 IS - 36 SP - 19694 EP - 19701 PB - The Royal Soc. of Chemistry CY - Cambridge AN - OPUS4-31733 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Szczerba, Wojciech A1 - Riesemeier, Heinrich A1 - Thünemann, Andreas T1 - Bond length cntraction in gold nanoparticles N2 - The structure of nanoparticles typically differs from its bulk counterpart. Predominantly, the structures of gold nanoparticles have been under exceedingly intense discussion since the discovery of their high catalytic activity. We found an increasing bond length contraction with decreasing particle size for citrate-stabilized gold nanoparticles in aqueous solution as determined by in situ extended X-ray absorption fine structure (EXAFS) spectroscopy. Particle sizes and size distributions were determined by small-angle X-ray scattering. The analysis of the obtained EXAFS spectra employing ab initio calculations reveals that the Au–Au bond length undergoes a contraction of 2 pm for nanoparticles with a radius of 2.9 nm. NIST reference material RM 8011 gold nanoparticles with a radius of 4.4 nm exhibit a smaller contraction of approximately 1 pm. Finally, gold atoms in RM 8013 particles with a radius of 25.7 nm show distances of 288 pm— identical to the distance in gold foil—and exhibits bulk-like properties. The observed bond length contraction of gold nanoparticles in solution is significantly smaller than previously reported for gold nanoparticle deposited on surfaces, which is up to 15 pm. This indicates that the bond length contraction effect of 'free' and 'surfaceimmobilized' nanoparticles differ fundamentally. Such difference could be essential for the understanding of nanoparticle-supported catalysis. KW - Small-angle X-ray scattering KW - SAXS KW - EXAFS KW - XAFS KW - Nanoparticle KW - Gold PY - 2010 DO - https://doi.org/10.1007/s00216-010-4200-z SN - 1618-2642 SN - 1618-2650 VL - 398 IS - 5 SP - 1967 EP - 1972 PB - Springer CY - Berlin AN - OPUS4-22173 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Girod, Matthias A1 - Vogel, Stefanie A1 - Szczerba, Wojciech A1 - Thünemann, Andreas T1 - How temperature determines formation of maghemite nanoparticles N2 - We report on the formation of polymer-stabilized superparamagnetic single-core and multi-core maghemite nanoparticles. The particle formation was carried out by coprecipitation of Fe(II) and Fe(III) sulfate in a continuous aqueous process using a micromixer system. Aggregates containing 50 primary particles with sizes of 2 nm were formed at a reaction temperature of 30 °C. These particles aggregated further with time and were not stable. In contrast, stable single-core particles with a diameter of 7 nm were formed at 80 °C as revealed by small-angle X-ray scattering (SAXS) coupled in-line with the micromixer for particle characterization. X-ray diffraction and TEM confirmed the SAXS results. X-ray absorption near-edge structure spectroscopy (XANES) identified the iron oxide phase as maghemite. KW - Iron Oxide Nanoparticles KW - Micromixer KW - SAXS KW - XANES KW - Carboxydextran KW - Nanotechnology PY - 2015 DO - https://doi.org/10.1016/j.jmmm.2014.09.057 SN - 0304-8853 VL - 380 SP - 163 EP - 167 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-32564 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Batzdorf, Lisa A1 - Wilke, Manuel A1 - Szczerba, Wojciech A1 - Reinholz, Uwe A1 - Emmerling, Franziska T1 - Mechanochemical synthesis and characterisation of two new bismuth metal organic frameworks N2 - Two metal organic structures composed of the ligands benzene-1,4-dicarboxylate and pyridine-2,5-dicarboxylate and bismuth cations are presented: (H2Im)[Bi(1,4-bdc)2] (1) and [Bi(pydc)(NO3)2(H2O)2]*H2O (2) (bdc = benzenedicarboxylate, H2Im = imidazole cation, pydc = pyridinedicarboxylate). Both compounds were synthesised via grinding and the crystal structure of compound (2) was solved based on its powder diffraction pattern. Compound 1 crystallises isostructurally to the dimethyl ammonium containing compound (dma)[(Bi(1,4-bdc)2]. Raman spectroscopy and Extended X-ray absorption fine structure (EXAFS) measurements provided additional information about the two mechanochemically synthesised metal organic compounds. KW - Crystal structure KW - Mechanochemically synthesis KW - Powder diffraction measurements PY - 2014 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-306296 DO - https://doi.org/10.1039/C3CE42633E SN - 1466-8033 N1 - Geburtsname von Batzdorf, Lisa: Tröbs, L. - Birth name of Batzdorf, Lisa: Tröbs, L. VL - 16 IS - 25 SP - 5560 EP - 5565 CY - London, UK AN - OPUS4-30629 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -