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JLUpub ist das institutionelle Repositorium der Justus-Liebig-Universität.
JLUpub bietet Mitgliedern und Angehörigen der Universität die Möglichkeit neben wissenschaftlichen Dokumenten auch Forschungsdaten elektronisch zu veröffentlichen und dauerhaft zugänglich zu machen. Alle Veröffentlichungen erhalten einen Digital Object Identifier (DOI) und werden über nationale und internationale Bibliothekskataloge sowie Suchmaschinen nachgewiesen und auffindbar.
Neue Veröffentlichungen:
Combinatorial Separation of Cd and Te from CdTe via Chemical Vapor Transport with Sulfur and Air/Methane Treatment for the Recovery of Critical Resources from Thin Film Solar Cells
(2024) Bemfert, Lucas H.; Burkhart, Julian; Sedykh, Alexander; Richter, Sophie; Mitura, Eliane; Maxeiner, Moritz; Sextl, Gerhard; Müller-Buschbaum, Klaus
Elemental Te and Cd are successfully recovered from CdTe via a combinatorial process involving chemical vapor transport (CVT) using sulfur as transport agent giving elemental Te being deposited. Separation is successfully enabled by the first process for CVT of Te starting with CdTe. Cd is subsequently recovered by an oxidation of the formed CdS to CdO followed by reduction to Cd metal with natural gas, in which Cd can also be separated via the gas phase. Hereby, the process addresses the main critical elements of the active material in thin film CdTe solar cells regarding both, scarcity and toxicity. Both, closed and open systems were investigated displaying more or less thermodynamic control of the system. Transport rates were determined for the closed system as well as for an open system working with sulfur vapour at moderate temperatures below and close to the boiling point of sulfur. Excellent purity of tellurium was achieved already by the initial transport, leading to low Cd2+ concentrations in the obtained Te being below the quantification limit of microwave plasma-atomic emission spectroscopy (MP-AES) (≪0.05 wt %).
In-situ Oxidation and Coupling of Anilines towards Unsymmetric Azobenzenes Using Flow Chemistry
(2024) Griwatz, Jan H.; Campi, Chiara E.; Kunz, Anne; Wegner, Hermann A.
Molecular switches, especially azobenzenes, are used in numerous applications, such as molecular solar thermal storage (MOST) systems and photopharmacology. The Baeyer-Mills reaction of anilines and nitrosobenzenes has been established as an efficient synthetic method for non-symmetric azobenzenes. However, nitrosobenzenes are not stable, depending on their substitution pattern and pose a health risk. An in-situ oxidation of anilines with Oxone® was optimized under continuous flow conditions avoiding isolation and contact. The in-situ generated nitrosobenzene derivatives were subjected to a telescoped Baeyer-Mills reaction in flow. That way azobenzenes with a broad substituent spectrum were made accessible.
The impact of Activation on the Performance of Optical Oxygen Sensing with the Luminescent Metal–Organic Framework MOF-76(Eu)
(2024) Kasper, Thomas; Burkhart, Julian; Müller-Buschbaum, Klaus
The influence of activation as key parameter for oxygen sensing by luminescent metal–organic frameworks has been investigated and quantified for the archetype MOF-76(Eu). Activation at different conditions (regarding temperature and solvent-exchange for distinct vacuum pressure and heating time), shows an influence on the overall quenching, response time and cyclability due to different pore accessibility and surface area and therefore on the overall performance of the sensor. The optical sensing process is based on luminescence quenching, analyzed from high vacuum (10−7 bar) to ambient pressure by dosing oxygen from 0.01 bar to 1 bar. Strong influence of the different activation parameters is observed, as MOF-76(Eu) activated at 50 °C shows limited quenching of the luminescence intensity within 30 min, while methanol-exchange and subsequent activation at 250 °C leads to a quenching rate of 98.6 %. In addition, the sensor response occurs more than 1000 times faster within 0.2 s. These results correlate well with physisorption data, which reveal a significant change in porosity and surface area according to the degree of activation. For a better understanding of the involved processes, adsorption isotherms were recorded, surface areas determined and correlated to the photophysical parameters, including Stern-Volmer kinetics and cycling experiments for the differently activated MOF sensors.
Functional Groups Accessibility and the Origin of Photoluminescence in N/O-containing Bottom-up Carbon Nanodots
(2024) Debes, Paul P.; Langer, Michal; Pagel, Melanie; Menna, Enzo; Smarsly, Bernd; Osella, Silvio; Gallego, Jaime; Gatti, Teresa
Chemical surface functionalization of carbon nanodots (CNDs) offers a valuable opportunity to tailor multifunctionality in these nanocarbons, by engineering the composition of their molecular surface. Therefore, it is important to elucidate the type and amount of CNDs surface functionalization to be able to design their properties accurately. CNDs are often functionalized through amide coupling without validating the degree of surface functionalization. As a measure of surface functionalization, the amounts of primary amines via Kaiser test (KT) or imine reactions of the bare CNDs is often considered. However, this may lead to overestimating the degree of surface functionalization obtained by the pure amide coupling due to different reaction mechanisms and involved intermediates. Herein, four different CNDs prepared by microwave-assisted synthesis from arginine or citric acid with varying amounts of ethylenediamine are presented. We resorted to combining physicochemical methods to provide elemental, structural, and optical information. By that, we developed a method to quantify the degree of surface functionalization by amide coupling and show that the surface functionalization is lower than anticipated. Comparing experimental optical features of the CNDs with different computed model systems enables us to provide a more advanced vision of structure-property relationships in these still elusive nanocarbons.
Unusual Stability of an End-on Superoxido Copper(II) Complex under Ambient Conditions
(2024) Campi, Chiara Eleonora; Parkatzidis, Kostas; Anastasaki, Athina; Schindler, Siegfried
Superoxido copper complexes play an important role as usually short-lived intermediates in biology and chemistry. The unusual stability of an end-on superoxido copper complex observed in an oxygen-enhanced atom transfer radical polymerization (ATRP) led to a detailed mechanistic investigation of the formation of [CuII(Me6tren)(O2⋅−)]+ (Me6tren=tris(2-dimethyl-aminoethyl)amine) under ambient conditions. The persistence of the superoxido copper complex could be explained by a reaction cycle including the peroxido complex [(Me6tren)2CuII2(O2)]2+ together with [CuI(Me6tren)(DMSO)]+ and [CuII(Me6tren)(OH)]+ in the overall reaction.