03 Fakultät Chemie

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Institute: search.filters.UBSInstitut.Max-Planck-Institut für FestkörperforschungStart date: 2023Publication Type: search.filters.UBSTyp.Zeitschriftenartikel

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Now showing 1 - 10 of 24
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    Asymmetric Rh diene catalysis under confinement : isoxazole ring‐contraction in mesoporous solids
    (2024) Marshall, Max; Dilruba, Zarfishan; Beurer, Ann‐Katrin; Bieck, Kira; Emmerling, Sebastian; Markus, Felix; Vogler, Charlotte; Ziegler, Felix; Fuhrer, Marina; Liu, Sherri S. Y.; Kousik, Shravan R.; Frey, Wolfgang; Traa, Yvonne; Bruckner, Johanna R.; Plietker, Bernd; Buchmeiser, Michael R.; Ludwigs, Sabine; Naumann, Stefan; Atanasova, Petia; Lotsch, Bettina V.; Zens, Anna; Laschat, Sabine
    Covalent immobilization of chiral dienes in mesoporous solids for asymmetric heterogeneous catalysis is highly attractive. In order to study confinement effects in bimolecular vs monomolecular reactions, a series of pseudo‐C2‐symmetrical tetrahydropentalenes was synthesized and immobilized via click reaction on different mesoporous solids (silica, carbon, covalent organic frameworks) and compared with homogeneous conditions. Two types of Rh‐catalyzed reactions were studied: (a) bimolecular nucleophilic 1,2‐additions of phenylboroxine to N‐tosylimine and (b) monomolecular isomerization of isoxazole to 2H‐azirne. Polar support materials performed better than non‐polar ones. Under confinement, bimolecular reactions showed decreased yields, whereas yields in monomolecular reactions were only little affected. Regarding enantioselectivity the opposite trend was observed, i. e. effective enantiocontrol for bimolecular reactions but only little control for monomolecular reactions was found.
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    On the thermal dimorphy of the strontium perrhenate Sr[ReO4]2
    (2024) Conrad, Maurice; Bette, Sebastian; Dinnebier, Robert E.; Schleid, Thomas
    Hygroscopic single crystals of a new hexagonal high‐temperature modification of Sr[ReO4]2 were prepared from a melt of Sr[ReO4]2 ⋅ H2O and SrCl2 ⋅ 6 H2O. The structure analysis of the obtained crystals by X‐ray diffraction revealed that the title compound crystallizes in the ThCd[MoO4]3‐type structure with the hexagonal space group P63/m and the lattice parameters a=1023.81(7) pm and c=646.92(4) pm (c/a=0.632) for Z=2 in its quenchable high‐temperature form. Two crystallographically independent Sr2+ cations are coordinated by oxygen atoms forming either octahedra or tricapped trigonal prisms, whereas the Re7+ cations are found in the centers of discrete tetrahedral meta‐perrhenate units [ReO4]-. Temperature‐dependent in‐situ PXRD studies of dry powder samples of Sr[ReO4]2 exhibited its thermal dimorphy with a phase‐transition temperature at 500-550 °C from literature‐known m‐Sr[ReO4]2 into the newly discovered h‐Sr[ReO4]2 (hexagonal).
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    Insights into the first multi-transition-metal containing Ruddlesden-Popper-type cathode for all-solid-state fluoride ion batteries
    (2024) Vanita, Vanita; Waidha, Aamir Iqbal; Vasala, Sami; Puphal, Pascal; Schoch, Roland; Glatzel, Pieter; Bauer, Matthias; Clemens, Oliver
    Promising cathode materials for fluoride-ion batteries (FIBs) are 3d transition metal containing oxides with Ruddlesden-Popper-type structure. So far, the multi-elemental compositions have not been investigated, but it could alternate the electrochemical performance similar to what has been found for cathode materials for lithium-ion batteries. In this study, we investigate RP type La2Ni0.75Co0.25O4.08 as an intercalation-based active cathode material for all-solid-state FIBs. We determine the structural changes of La2Ni0.75Co0.25O4.08 during fluoride intercalation/de-intercalation by ex situ X-ray diffraction, which showed that F- insertion leads to transformation of the parent phase to three different phases. Changes in the Ni and Co oxidation states and coordination environment were examined by X-ray absorption spectroscopy and magnetic measurements in order to understand the complex reaction behaviour of the phases in detail, showing that the two transition metals behave differently in the charging and discharging process. Under optimized operating conditions, a cycle life of 120 cycles at a critical cut-off capacity of 40 mA h g-1 against Pb/PbF2 was obtained, which is one of the highest observed for intercalation electrode materials in FIBs so far. The average coulombic efficiencies ranged from 85% to 90%. Thus, La2Ni0.75Co0.25O4.08 could be a promising candidate for cycling-stable high-energy cathode materials for all-solid-state FIBs.
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    Celebrating ten years of covalent organic frameworks for solar energy conversion : past, present and future
    (2024) Rodríguez‐Camargo, Andrés; Endo, Kenichi; Lotsch, Bettina V.
    Accelerated anthropogenic emission of greenhouse gases due to increasing energy demands has created a negative impact on our planet. Therefore, the replacement of fossil by renewable energy resources has become of paramount interest, both societally and scientifically. It is within this setting that organic photocatalysts have emerged as a new generation of earth‐abundant catalysts for the conversion of solar radiation into chemical energy. In 2014, the first example of a covalent organic framework (COF) photocatalyst for the hydrogen evolution reaction was reported by our group, which has not only marked the beginning of COF photocatalysis for solar fuel production but also helped to accelerate research into “soft photocatalysis” based on porous polymers in general. In the last decade, significant progress has been made toward developing COFs as robust, molecularly precise platforms emulating artificial photosynthesis. This mini‐review commemorates the 10th anniversary of COF photocatalysis and gives a brief historical overview of the milestones in the field since its inception in 2014. We review milestones in the development of COFs for solar fuel production and related photocatalytic transformations, including hydrogen evolution, oxygen evolution, overall water splitting, CO2 reduction, N2 fixation, oxygen reduction, and alcohol oxidation. We discuss lessons learned for the design of structure‐property‐function relationships in COF photocatalysts, and future perspectives and challenges for the field of “soft photocatalysis” are given.
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    Toward carbon‐free cathodes for fluoride ion batteries : deconvoluting effects of active material and conductive additive on charging and cyclic stability
    (2025) Aalto, Tommi Hendrik; Talei, Roham; Küster, Kathrin; Schmitz, Guido; Clemens, Oliver
    In this study, conductive, fluorine and antimony codoped tin oxide nanoparticles (FATO‐NPs) are highlighted as a possible alternative for conductive carbon additives in fluoride ion batteries, successfully circumventing oxidative side reactions. Since good cyclability with high and stable discharge capacities is achieved with both types of conductive additive at a high stack pressure of 180 MPa, it is concluded that conductive carbon is well‐suited for high‐voltage fluoride ion batteries, contrary to prior assumptions. However, FATO‐NP‐based cathodes outperform those based on conductive carbon at lower stack pressures of 50 MPa, emphasizing the importance of avoiding carbon fluorination at low stack pressures.
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    A reflection on ‘A hydrazone-based covalent organic framework for photocatalytic hydrogen production’ : teaching sponges new tricks
    (2026) Rodríguez-Camargo, Andrés; Lotsch, Bettina V.
    Covalent organic frameworks (COFs) are a unique class of porous materials built entirely from organic building blocks. As such, COFs unite the tunability of molecules with the robustness and optoelectronic functionality of extended solids-key requisites for (photo)catalysis. This LEGO®-like design of crystalline “molecular sponges” has captivated the imagination of chemists and inspired the first COF photocatalyst: a hydrazone-linked COF capable of harnessing visible light to drive the evolution of hydrogen from water. This commentary revisits that seminal contribution, published 11 years ago in Chemical Science (L. Stegbauer, K. Schwinghammer, B. V. Lotsch, Chem. Sci. , 2014, 5 , 2789-2793, https://doi.org/10.1039/C4SC00016A ), and reflects on its lasting impact. We survey the major advances that have shaped COF photocatalysis over the past decade and outline emerging opportunities and challenges, offering a forward-looking perspective on the role of COFs in solar energy conversion.
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    Shedding light on the active species in a cobalt‐based covalent organic framework for the electrochemical oxygen evolution reaction
    (2024) Hosseini, Pouya; Rodríguez‐Camargo, Andrés; Jiang, Yiqun; Zhang, Siyuan; Scheu, Christina; Yao, Liang; Lotsch, Bettina V.; Tschulik, Kristina
    While considerable efforts have been devoted to developing functionalized covalent organic frameworks (COFs) as oxygen evolution electrocatalysts in recent years, studies related to the investigation of the true catalytically active species for the oxygen evolution reaction (OER) remain lacking in the field. In this work, the active species of a cobalt‐functionalized COF (TpBpy‐Co) is studied as electrochemical OER catalyst through a series of electrochemical measurements and post‐electrolysis characterizations. These results suggest that cobalt oxide‐based nanoparticles are formed in TpBpy‐Co from Co(II) ions coordinated to the COF backbone when exposing TpBpy‐Co to alkaline media, and these newly formed nanoparticles serve as the primary active species for oxygen evolution. The study thus emphasizes that caution is warranted when assessing the catalytic activity of COF electrocatalysts, as the pristine COF may act as the pre‐catalyst, with the active species forming only under catalyst operating conditions. Specifically, strong coordination between COFs and metal centers under electrochemical operation conditions is crucial to avoid unintended transformation of COF electrocatalysts. This work thus contributes to the rational development of earth‐abundant COF OER catalysts for the production of green hydrogen from renewable resources.
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    Investigating the long-term kinetics of Pd nanoparticles prepared from microemulsions and the Lindlar catalyst for selective hydrogenation of 3-hexyn-1-ol
    (2024) Tari, Faeze; Hertle, Sebastian; Wang, Hongguang; Fischer, Julian; Aken, Peter A. van; Sottmann, Thomas; Klemm, Elias; Traa, Yvonne
    The effect of non-saturated corner and edge sites of Pd particles on the long-term selectivity of cis-3-hexen-1-ol in the hydrogenation of 3-hexyn-1-ol was studied in this work. Non-supported Pd agglomerates were synthesized through the microemulsion synthesis route and used at  nalkynol/APdratios between 0.08 and 21 mol/m2for the catalytic conversion of 3-hexyn-1-ol for 20 h. The selectivity of the cis-hexenol product increased by reducing the quantity of Pd catalytic sites (increasing the nalkynol/APdratio) without introducing any modifier or doping agent to poison the nonselective sites. Then, Pd aggregates with fused primary particles and, thus, fewer corner and edge sites were produced through thermal sintering of the agglomerates at 473-723 K. By comparing the catalytic performance of the agglomerates and aggregates, it was observed that at a rather similar kinetic behavior (99.99% conversion and 85-89% selectivity to cis-hexenol), the sintered aggregates could stay selective despite a catalytic surface area about seven times larger. This emphasizes the role of low-coordinated edge and corner sites on the final selectivity of the cis product and demonstrates that thermal sintering allows the number of non-selective sites to be reduced without any need for toxic or organic doping agents or modifiers.
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    Upconversion nanoparticle‐covalent organic framework core-shell particles as therapeutic microrobots trackable with optoacoustic imaging
    (2025) Kim, Dong Wook; Wrede, Paul; Rodríguez‐Camargo, Andrés; Chen, Yi; Dogan, Nihal Olcay; Glück, Chaim; Lotsch, Bettina V.; Razansky, Daniel; Sitti, Metin
    Despite the development of various medical imaging contrast agents, integrating contrast signal generation with therapeutic and microrobotic functions remains challenging without complicated fabrication processes. In this study, upconversion nanoparticle‐covalent organic framework (UCNP‐COF) core-shell sub‐micron particles are developed that function as therapeutic microrobots trackable with multi‐spectral optoacoustic tomography (MSOT) imaging and can be loaded with desired therapeutic molecular agents in a customizable manner. The mechanism of optoacoustic signal generation in UCNP‐COF particles is attributed to the quenching of upconversion luminescence emitted by the UCNPs, which is absorbed by the encapsulating COF and subsequently converted into acoustic waves. Unlike other microparticulate agents previously imaged with MSOT, UCNP‐COF particles do not pose concerns about their stability and biocompatibility. Simultaneously, the mesoporous texture of the COF provides a large surface area, allowing for the efficient loading of various drug molecules, which can be released at target sites. Furthermore, the magnetic UCNP‐COF Janus particles can be magnetically navigated through in vivo vasculature while being visualized in real‐time with volumetric MSOT. This study proposes an approach to design photonic materials with multifunctionality, enabling high‐performance medical imaging, drug delivery, and microrobotic manipulation toward their future potential clinical use.
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    Solvothermal template‐induced hierarchical porosity in covalent organic frameworks : a pathway to enhanced diffusivity
    (2025) Heck, Fabian; Grunenberg, Lars; Schnabel, Nadine; Heilmaier, Amelie; Sottmann, Thomas; Yao, Liang; Lotsch, Bettina V.
    The rapid advancement of covalent organic frameworks (COFs) in recent years has firmly established them as a new class of molecularly precise and highly tuneable porous materials. However, compared to other porous materials, such as zeolites and metal‐organic frameworks, the successful integration of hierarchical porosity into COFs remains largely unexplored. The challenge lies in identifying appropriate synthetic methods to introduce secondary pores without compromising the intrinsic structural porosity of COFs. In this study, a template‐induced synthetic methodology is realized to facilitate the construction of hierarchically porous COFs (hCOFs). This novel approach utilizes commercially available zinc oxide nanoparticles as a hard template, enabling to increase the total pore volume of a series of β ‐ketoenamine‐linked COFs as well as an imine‐based COF while preserving their surface areas. In addition to transmission electron microscopy and gas adsorption analyses, small‐angle X‐ray scattering and pulsed field gradient nuclear magnetic resonance techniques are employed to investigate the hierarchical porosity and diffusivity of guest molecules within hCOFs. This study demonstrates that the hierarchically porous nature of hCOFs significantly reduces diffusion limitations, thus leading to simultaneous enhancements in adsorption capacity, diffusivity, and catalytic performance.