Guido Kickelbick

Vanadium oxides and alkali metal vanadates are promising electrode materials for electrochemical energy storage owing to their ability to access multiple oxidation states. In this study, mechanochemical reduction of V₂O₅ with alkali metal hydrides is explored as a facile route to obtain reduced vanadium oxide phases. Sodium hydride enables the rapid formation of mixed sodium vanadium oxide phases at room temperature, proceeding in a self-propagating manner after only a short milling period. To assess the generality of this approach, lithium hydride was evaluated as an alternative reducing agent and exhibited comparable reaction behavior and product distributions. Complementary theoretical calculations indicate that the corresponding reductions with elemental sodium and lithium are thermodynamically more favorable, displaying lower reaction enthalpies. This prediction is experimentally corroborated by the instantaneous ignition observed when elemental metals are used. Rietveld refinement reveals that all investigated reducing agents follow similar reaction pathways, yielding comparable mixtures of alkali metal vanadium oxides with consistent main phases. However, the use of highly ductile sodium metal results in significant mixing limitations, which can be mitigated only through cryogenic milling. These findings highlight mechanochemical reduction with alkali metal hydrides as a robust and practical strategy, particularly for systems in which metal ductility limits process efficiency, despite the associated risk of hydrogen evolution.

Synthesis of europium aluminates is usually conducted from the binary oxides (EuO/Eu2O3 + Al2O3) at high temperatures alongside a reductive gas for the stabilization of Eu2+. We are reporting on an alternative pathway starting from EuAl2 (cubic Laves phase, MgCu2 type, Fd3̅m), which was oxidized under different conditions. By heating the intermetallic precursor to different temperatures, first amorphous and at higher temperatures highly crystalline products were observed. However, the question of the Eu valence state in the product will immediately arise. Depending on the reaction procedure used both, the di- and trivalent state could be achieved in the reaction with elemental oxygen. EuIIIAlO3 (GdFeO3 type, Pnma) was observed as the sole crystalline product with excess O2 in the powder X-ray diffraction experiments. The differing chemical composition could be explained by the formation of amorphous γ-Al2O3 proven by 27Al solid-state NMR spectroscopy. Oxidizing EuAl2 under controlled conditions yields X-ray pure EuIIAl2O4 (SrAl2O4 type, P21). Surprisingly, annealing of the EuIIIAlO3/amorphous γ-Al2O3 mixture under vacuum led to the formation of EuIIAl2O4, which was investigated in detail. The different oxidation states of the Eu atoms were proven by magnetic measurements, 151Eu Mössbauer spectroscopic investigations, and photoluminescence studies.

Oligo‐ and polysilsesquioxanes are typically synthesized via wet‐chemical routes employing acids or bases as catalyst. In this study we report a catalyst‐ and solvent‐free thermal condensation approach for the preparation of oligosilsesquioxanes from arylsilanetriols and their corresponding disiloxanetetraols. Three substituents, namely phenyl (Ph), 1‐napthyl (1Np), and 2‐naphthyl (2Np) were investigated along with their condensed products. Structural analysis revealed that the Ph and 1Np systems form ladder‐like oligosilsesquioxane architectures, whereas the 2Np system exhibits a markedly different structure, suggesting a layered arrangement of planar rings, as supported by FT‐IR and PXRD. Comparison of the silanetriols and disiloxantetraols as precursors indicated only minor differences, with crystal structures largely preserved after solid‐state condensation reactions. The thermal process achieved a higher degree of condensation than conventional wet‐chemical methods and enabled access to structurally distinct products without the need for solvents or catalysts, highlighting its potential for sustainable synthesis of novel polysilsesquioxane materials.

Mechanochemical activation of Na _1.2 V ₃ O ₈ induces crystallite size reduction, surface area enhancement, and local structural changes, accelerating Na de/intercalation kinetics.

The influence of sulfur-containing aromatic substituents on silsesquioxane melting gels: condensation degree, local network organization, reversible softening, thermal decomposition pathways, optical properties, and chemical accessibility.

Mechanochemical activated NaTi ₂ (PO ₄ ) ₃ , a NASICON-type sodium titanium phosphate (NTP), exhibits enhanced sodium intercalation activity. Thus this activation offers great potential for sodium-ion energy storage.

As a versatile platform technology, polymer nanoparticles enable the effective delivery of hydrophobic drug substances. To achieve therapeutic efficacy, adequate drug loading is required, which requires a quantitative understanding of formulation component affinities. In this study, we investigate how the choice of organic solvent affects drug loading in poly(lactic‐ co ‐glycolic) acid (PLGA) nanoparticles prepared by nanoprecipitation. For the encapsulation of various 1,4‐naphthoquinone derivatives used as model substances, we observe a correlation between drug loading and the Hansen solubility parameter distance ( R _a ) between the drug and the organic solvents. To elucidate the interactions at the nanoscale level thin polymer films are analyzed using atomic force microscopy (AFM), quantifying surface pore formation as an indicator of interaction. Additionally, scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) were utilized to investigate drug–polymer miscibility. A concentration‐dependent phase separation in drug‐polymer matrices was observed, which correlates with the drug loading in the nanoparticles. This work emphasizes the need to move beyond trial‐and‐error approaches by the incorporation of predictive parameters like Hansen solubility parameter‐derived affinities and solid‐state solubility metrics into formulation strategies.

Magnesium spinels such as MgAl₂O₄ and MgFe₂O₄ have been widely explored for energy storage and sensing applications, but MgV₂O₄ remains relatively unexplored despite its promising potential, e.g., as a battery electrode material. In this study, we report the first mechanochemical synthesis of MgV₂O₄ at room temperature using either MgO or Mg with various vanadium oxides as reactants. Directed by thermodynamic calculations on a DFT level, only the self-sustaining reaction between V₂O₅ and Mg led to MgV₂O₄ within 20 min of milling, along with MgO as a side product. With increasing rotational speed, an earlier reaction ignition after a few minutes of milling, smaller crystallite sizes in the nanometer range, and increased strain in MgV₂O₄ were observed. In addition, harsh milling conditions induce increasing nonstoichiometry in both phases, leading to a magnesium-rich spinel and a vanadium-containing rock salt phase, as supported by X-ray diffraction and electron paramagnetic resonance measurements. Acid washing after synthesis removed MgO, and electrochemical impedance spectroscopy showed that milder grinding conditions increased the conductivity of MgV₂O₄ due to the smaller number of defects.

A novel melt-emulsion strategy is presented for synthesizing fluorescent polyphenylsilsesquioxane microspheres from a thermoplastic polymer containing hydrophobic perylene-based dyes.

Hybrid siloxane/silsesquioxane materials containing sterically demanding aromatic groups synthesized by hydrolysis and condensation suffer from incomplete cross-linking after thermal consolidation, limiting their thermal and mechanical performance. In this study, we systematically investigated a post-cross-linking strategy using various additives to enhance structural integrity and thermal stability. These include dimethyldimethoxysilane (DMDMS), diphenyldimethoxysilane (DPDMS) and phenyltrimethoxysilane (PTMS), as well as the organotin condensation catalyst di-n-butyltin diacetate (DBTA). Notably, we achieved thermal stability up to 453 °C and long-term transparency (up to 99%) at 200 °C with only little yellowing. Dynamic mechanical analysis demonstrated that post-cross-linking of precondensed siloxanes with PTMS, DPDMS, and DBTA enabled the formation of elastic materials exhibiting a rubbery plateau up to 200 °C. This behavior reflects enhanced structural rigidity and elasticity, which are essential for high-temperature applications. Our results show that high-temperature stability in siloxane/silsesquioxane materials is strongly influenced by factors such as the number of phenyl groups, cross-linking density, structural regularity, and degree of condensation. Most notably, the complete incorporation of a sterically demanding naphthyl-functionalized monomer during consolidation proved to be critical. Post-cross-linking significantly enhances all these parameters, which is essential for achieving robust thermal performance.