Alexander Gutsche

Oriented attachment of ultra-small Mn(1−x)ZnxFe2O4 nanoparticles during the non-aqueous sol–gel synthesis

The advantages of ultra-small manganese–zinc ferrite nanoparticles are manifold and can be exploited in a wide range of applications. Here we show that ultra-small, highly crystalline Mn–Zn ferrite nanoparticles with variable compositions can be obtained by non-aqueous sol–gel synthesis in a facile, scalable process. The growth of Mn0.6Zn0.4Fe2O4 nanoparticles has been investigated exemplarily for a series of Mn–Zn ferrites. It is thereby shown that the initially formed ultra-small 2 nm sized particles grow via oriented attachment into shamrock-like shaped particles, and clusters with an ordered structure are formed during synthesis. Throughout the synthesis, the crystallinity of the particles improves until after 24 h of synthesis highly crystalline, monodisperse nanostructures with a size of around 6 nm are obtained. Furthermore, the influence of the chemical as well as physical properties of the ultra-small Mn(1−x)ZnxFe2O4 nanoparticles with 0 ≤ x ≤ 1 on their Curie temperature was evaluated. It is shown that by variation of the Mn/Zn ratio the Curie temperature of the particles can be tailored in a broad range from 200 to 400 °C.

Probing the absolute scattering intensity by means of a laboratory-based small-angle X-ray scattering camera using an imaging plate detector

This paper deals with the application of an imaging plate (IP) detector for probing absolute intensities in small-angle X-ray scattering experiments. The IP detector is used with an in-house modified Kratky camera. It is shown that the normalization of scattering data to the transmitted primary beam intensity properly compensates for various unwanted features typically associated with the IP detector, e.g. the fading effect and poorly reproducible scanning times, promoting precise absolute intensity calibration. The absolute intensity calibration was performed by measuring a large number of different silica sols serving as secondary standards. The calibration factor, which converts the measured data into absolute units, was determined by the average over the data obtained for different silica sols, providing a precise calibration of the IP detector. In particular, it is shown that silica sols do not require application of synchrotron radiation or a long exposure time as typically needed if pure liquids or standard proteins are used as secondary standards. To check the applicability of the IP detector in a real synthesis, Stober silica particles were synthesized under various reaction conditions and the scattering intensity was probed and converted into absolute units. The volume fractions and the number densities of silica particles provided by the absolute intensities showed a good agreement with theoretical values predicted for the different reaction conditions. Therefore, the IP detector can be used for accurate probing of absolute intensities.

Targeted design of water-based humic substances-silsesquioxane soft materials for nature-inspired remedial applications

Water-based humic substances-silsesquioxane (HS-SQ) soft materials are synthesized by hydrolysis of (3-aminopropyl-triethoxy)-silane in the HS solution. The aggregation dynamics of this system was studied using in situ small-angle X-ray scattering (SAXS) technique, which revealed three consecutive stages in the evolution of the HS-SQ system based on its fractal dimension (D): HS-SQ oligomeric polyelectrolyte complexes with D 3 (surface fractals). It was suggested that the reaction time needed for the HS-SQ system to transit from mass to surface fractal stage can be used to control its self-assembly onto a solid support. The corresponding studies have confirmed that the HS-SQ networks could be successfully immobilized onto sand columns only at the aggregation stage with fractal dimensions of 2.5 < Dm < 3. This enabled the targeted design of HS-SQ systems capable of guided self-assembly onto the solid support. The corresponding lab column studies have demonstrated successful passive installation of a humic permeable reactive barrier on sand which was capable of intercepting azo dyes from contaminated water. The prospects of using HS-SQ soft materials in nature-inspired remedial technologies and soil restoration are discussed.

SAXS-Charakterisierung von SiO2-Nanopartikeln zur Erforschung der stattfindenden Partikelwachstumsvorgänge im Stöber-Prozess

bringen konnten. Einige dieser Verfahren werden vorgestellt und es wird gezeigt, wie diese durch die kombinierte Entwicklung neuer Verfahren und Gerate eingesetzt werden konnen. Basierend auf einem neuen Kristallisationsverfahren und Probentrager wurde ein Gerat entwickelt, das uber optische Messungen potenzielle Kristallisationsbedingungen fur die jeweiligen Proteine erkennen lasst. Durch die Moglichkeit, die Wechselwirkungen zwischen gelosten Proteinmolekulen in einem Kristallisationsexperiment messen zu konnen, lassen sich aus einer Serie solcher Messungen Trends analysieren und Vorhersagen fur eine verbesserte Zusammensetzung der Kristallisationslosung treffen. Ein iterativer Prozess aus Probenpraparation, Messung und Vorhersage neuer Losungsparameter kann damit schneller und vor allem zielgerichteter zu hochwertigen Proteinkristallen fuhren.