03 Fakultät Chemie
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Item Open Access Chromium in minerals as tracer of the polycyclic evolution of eclogite and related metabasite from the Pohorje Mountains, Slovenian Eastern Alps(2023) Li, Botao; Massonne, Hans‐JoachimSignificantly different peak pressure-temperature (P-T) conditions (18-26 kbar and 630-760°C versus 29-37 kbar and 750-940°C) have previously been published for eclogite and related metabasites from the south‐eastern flank of the Pohorje Mountains in Slovenia. These rocks can show a bimodal distribution of chromium in the rock‐forming minerals, particularly garnet, the role of which in their metamorphic evolution is unclear. Therefore, we studied an eclogite and a related rock with clinopyroxene containing only 17 mol% jadeite + acmite (sample 18Ca35a). KαCr intensity maps of garnet particularly in sample 18Ca35a show a sharp irregular boundary between the core (Gt1) and the mantle (Gt2). Gt1 of millimetre‐sized garnet in this rock is nearly Cr‐free and unzoned, whereas Gt2 is of different composition (0.22 wt.% Cr2O3) and slightly zoned. Nearly Cr‐free amphibole, (clino)zoisite, kyanite and staurolite inclusions are present in Gt1. The matrix consists of garnet and Cr‐bearing clinopyroxene, (clino)zoisite and amphibole. Thermodynamic modelling suggests peak P-T conditions of 22.5 ± 2 kbar at 710 ± 25°C (Gt1) and 23 ± 2 kbar at 700 ± 25°C (Gt2) in both samples. We interpret these findings to suggest that olivine‐ and hornblende‐bearing gabbros with some chromite experienced early metamorphism in the eclogite facies, when Gt1 formed. The rock was subsequently exhumed and cooled leading to significant garnet corrosion. A second stage of metamorphism, recognized by mappable Cr contents in garnet, led to the growth of Gt2 and other Cr‐bearing minerals at the expense of chromite relics, which survived stage I. The peak P-T conditions of stage II are compatible with those previously derived by same authors and support the view that probably no ultrahigh‐pressure eclogite exists in the Pohorje Mountains. We relate the two metamorphic events to the Cretaceous and Palaeogene high‐pressure events recently reported from micaschists of the Pohorje Mountains.Item Open Access Designing covalent organic framework‐based light‐driven microswimmers toward therapeutic applications(2023) Sridhar, Varun; Yildiz, Erdost; Rodríguez‐Camargo, Andrés; Lyu, Xianglong; Yao, Liang; Wrede, Paul; Aghakhani, Amirreza; Akolpoglu, Birgul M.; Podjaski, Filip; Lotsch, Bettina V.; Sitti, MetinWhile micromachines with tailored functionalities enable therapeutic applications in biological environments, their controlled motion and targeted drug delivery in biological media require sophisticated designs for practical applications. Covalent organic frameworks (COFs), a new generation of crystalline and nanoporous polymers, offer new perspectives for light‐driven microswimmers in heterogeneous biological environments including intraocular fluids, thus setting the stage for biomedical applications such as retinal drug delivery. Two different types of COFs, uniformly spherical TABP‐PDA‐COF sub‐micrometer particles and texturally nanoporous, micrometer‐sized TpAzo‐COF particles are described and compared as light‐driven microrobots. They can be used as highly efficient visible‐light‐driven drug carriers in aqueous ionic and cellular media. Their absorption ranging down to red light enables phototaxis even in deeper and viscous biological media, while the organic nature of COFs ensures their biocompatibility. Their inherently porous structures with ≈2.6 and ≈3.4 nm pores, and large surface areas allow for targeted and efficient drug loading even for insoluble drugs, which can be released on demand. Additionally, indocyanine green (ICG) dye loading in the pores enables photoacoustic imaging, optical coherence tomography, and hyperthermia in operando conditions. This real‐time visualization of the drug‐loaded COF microswimmers enables unique insights into the action of photoactive porous drug carriers for therapeutic applications.Item Open Access Dynamic breathing behaviour of the titanium-based metal-organic framework NTU-9 upon adsorption of water and organic solvents(2025) Knapp, Julia E.; Ortín-Rubio, Borja; Heck, Fabian; Gjorgjevikj, Kristina; Sleptsova, Anastasia; Krause, Simon; Bette, Sebastian; Lotsch, Bettina V.Understanding the structural response of framework materials to external stimuli has been of great interest. However, little is known about the stimuli responsiveness of titanium-based metal-organic frameworks. We investigate the reproducibility of the synthesis of the two-dimensional metal–organic framework NTU-9 (NTU = Nanyang Technological University) composed of Ti 4+ cations and 2,5-dihydroxyterephtalate as the organic linker and the flexible response of the framework structure to external stimuli. Using acetic acid simultaneously as mediator and solvent leads to the reproducible formation of large NTU-9 crystallites after long reaction times. The MOF synthesis in isopropanol:acetonitrile ( i -PrOH : MeCN) mixtures without a modulator is significantly faster but yields smaller NTU-9 crystallites. Pure heat treatment under ambient conditions removes a significant amount of the incorporated host solvent molecules without alteration of the framework's structure. After applying additional external stimuli ( i.e. , vacuum), the material exhibits a pore distortion by compression in the lateral dimension, depending on the synthetic procedure. The new, distorted, metastable form NTU-9-d shows a reduction in unit cell volume, pore size, and crystal symmetry. Under humidity/air exposure or solvent resuspension, the framework reverts into its original state. The synthesis conditions significantly affect the flexibility of the MOF structure, where samples synthesized without modulator showed a lower tendency for distortion. Our results emphasise the importance of an in-depth understanding of the structure–property relationships in flexible MOFs through a detailed characterisation of the material's stimuli responsiveness process.Item Open Access Eclogite with biotite porphyroblasts : which conditions are responsible for their formation? An example from the northern Fleur‐de‐Lys Supergroup, Newfoundland, Canada(2024) Massonne, Hans‐JoachimAn eclogite from the Early Palaeozoic Fleur‐de‐Lys Supergroup in Newfoundland was studied because of its biotite porphyroblasts, which very rarely occur in this rock type. Thermodynamic modelling suggests that eclogitic biotite in common metabasite (former basalt-gabbro) is limited to (1) bulk‐rock compositions, which are relatively rich in Fe2+ and K and poor in Fe3+, and (2) the low‐pressure range of the eclogite facies. The latter reason is supported by the determination of the pressure-temperature (P-T) path of the Newfoundland eclogite. Chemical zonation of garnet, presence of phengite with Si contents of ~3.4 per formula unit, Zr contents in rutile and petrographic observations resulted in a P-T trajectory starting at medium‐pressure conditions. Nearly isothermal burial led to a peak pressure of 18-19 kbar at ~575°C, followed by exhumation and slight heating. Deformation occurred at or close to the peak pressure. Subsequent introduction of hydrous fluids caused the formation of porphyroblasts of biotite and Ca-amphibole in the pressure range of 12-17 kbar at peak temperatures of 625-640°C. Retrogression led to very fine‐grained symplectites around omphacite and phengite and marginal replacement of biotite porphyroblasts by plagioclase and titanite. Geodynamic scenarios invoking either a flat subduction of oceanic crust followed by continent-continent collision or intracontinental subduction along a transpressional fault system might best explain the formation of eclogite with biotite porphyroblasts in general. For the Newfoundland eclogite, the latter scenario is preferred.Item Open Access Elucidating the structure and the impact of synthesis methods on the flexibility of the metal‐organic framework MIL‐88 A (Fe) during water capture(2025) Manitz, Timo; Heck, Fabian; Rezeki, Sri; Gjorgjevikj, Kristina; Tokuda, Shun; Bette, Sebastian; Canossa, Stefano; Leistenschneider, Desirée; Krause, SimonFlexible metal‐organic frameworks (MOFs) have emerged as a new generation of porous materials and are considered for various applications such as sensing, water or gas capture, and water purification. MIL-88 A (Fe) is one of the earliest and most researched flexible MOFs, but to date, there is a lack in the structural aspects that govern its dynamic behaviour. Here, we report the first crystal structure of DMF‐solvated MIL-88 A and investigate the impact of real structure effects on the dynamic behaviour of MIL-88 A (Fe), particularly upon water adsorption. Four differently synthesized materials are studied with powder X‐ray diffraction (PXRD), THz Raman spectroscopy, and N2 sorption. The very high water vapor sorption capacity is probed by utilizing in situ humidity PXRD and calorimetric cycling studies. At least four different crystallographic phases are identified during the sorption measurements and a structural concept and models are developed that explain the changes in the XRD patterns. From this, it is derived that MIL-88 A (Fe) is an excellent material for a new concept of responsive water harvesting technologies.Item Open Access Identifying bottlenecks in the photocatalytic oxygen evolution reaction with covalent organic frameworks(2025) Trenker, Stefan; Vignolo-Gonzalez, Hugo A.; Rodríguez-Camargo, Andrés; Yao, Liang; Zwijnenburg, Martijn A.; Lotsch, Bettina V.Covalent organic frameworks (COFs) have emerged as promising semiconducting materials for photocatalytic applications due to their large surface area, high crystallinity, and vast synthetic tunability. This is especially noticeable in the context of photocatalytic water splitting, where many COFs have been employed for the hydrogen evolution half-reaction. There, sacrificial reagents typically replace the kinetically demanding oxygen evolution half-reaction. On the contrary, only few reports focus on (sacrificial) water oxidation with COF photocatalysts. In most of these cases, cobalt species are employed as oxygen evolution cocatalyst, often with limited insight into their structure and detailed role in the catalysis. Herein, we use heterogenization of a molecularly defined iridium half-sandwich complex onto a bipyridine-based COF (Ir@TAPB-BPY COF) and provide detailed structural insights ensuring the integrity of the targeted cocatalyst. First, we demonstrate the retained catalytic activity of the anchored Cp*Ir(III) motifs in chemical water oxidation experiments. In contrast, subsequent photocatalytic and electrocatalytic tests indicate that Ir@TAPB-BPY COF does not evolve oxygen and that careful control experiments have to be conducted in order to avoid false positive results, caused for example by the sacrificial electron acceptor. Using computational methods, we trace back the missing performance to thermodynamic and kinetic limitations of the employed systems. This work demonstrates the pitfalls associated with low-performing oxygen evolution photocatalysts as well as the indispensability of control experiments and their careful evaluation.Item Open Access Insights into decoupled solar energy conversion and charge storage in a 2D covalent organic framework for solar battery function(2025) Rath, Bibhuti Bhusan; Fuchs, Laura; Stemmler, Friedrich; Rodríguez-Camargo, Andrés; Wang, Yang; Dorfner, Maximilian F. X.; Olbrich, Johann; Slageren, Joris van; Ortmann, Frank; Lotsch, Bettina V.Decoupling solar energy conversion and storage in a single material offers a great advantage for off-grid applications. Herein, we disclose a two-dimensional naphthalenediimide (NDI)-based covalent organic framework (COF) exhibiting remarkable solar battery performance when used as a photoanode. Light-induced radicals are stabilized within the framework for several hours, offering on-demand charge extraction for electrical energy production. Our study reveals mechanistic insights into the long-term charge stabilization using optical spectroscopy and (photo)electrochemical measurements, in conjunction with density functional theory (DFT) simulations. Among several solvents, water provides the best dielectric screening and energetically favorable proton exchange to stabilize photoinduced radicals for more than 48 h without the need for additional metal cations. This study provides fundamental insights into the optoionic charge storage mechanism in NDI-COF, while introducing a highly tunable, nanoporous material platform that surpasses related materials, such as carbon nitrides, metal–organic frameworks (MOFs), or metal oxides, in terms of charge storage capacity. This study opens new perspectives for the design of optoionic charge-storing materials and the direct storage of solar energy to overcome the intermittency of solar irradiation.Item Open Access Metapelite from the high‐ to ultrahigh‐pressure terrane of the Eastern Alps (Pohorje Mountains, Slovenia) : new pressure, temperature and time constraints on a polymetamorphic rock(2021) Li, Botao; Massonne, Hans‐Joachim; Koller, Friedrich; Zhang, JunfengThe Austroalpine nappe stack of the Pohorje Mountains (Mts.) in northeastern Slovenia comprises a suite of eclogite facies metamorphic rocks that were partially assigned to Eo‐Alpine ultrahigh‐pressure metamorphism (UHPM). We selected a micaschist, which was previously related to this metamorphism, for a detailed study including the chemical zonation of garnet and potassic white mica, the identification of mineral inclusion assemblages, pseudosection modelling with PERPLE_X, and monazite in‐situ dating with the electron microprobe. Polymetamorphism was revealed by (at least) two generations of garnet and phengite and four populations of monazite yielding ages of 283.6 ± 6.1 (2σ), 94.1 ± 3.7, 47.9 ± 10.8 and 26.2 ± 2.8 Ma. The Permian monazite population is characterized by relatively high Y contents (~1.15 wt% Y) and low La/Gd mass ratios (8.7) indicating its formation before the growth of porphyroblastic garnet. The Eo‐Alpine population, however, grew synchronously with garnet based on low Y contents (~0.05 wt%) and high La/Gd ratios (21.4). The older Tertiary population (48 Ma) shows also high Y contents (1.1 wt%) and low La/Gd ratios (10.6) whereas the younger Tertiary population is characterized by low Y contents. The Permian P-T conditions of 7.5-10 kbar at 600-650°C were obtained using the inclusion assemblage of staurolite+rutile+biotite in porphyroblastic garnet. High pressure (HP) but no UHPM was reconstructed for both Eo‐Alpine coarse phengite (Si = 3.22 per formula unit = pfu) and small Tertiary garnet+fine‐grained phengite (Si = 3.27 pfu) at peak pressures ~16 kbar and 18.5-23 kbar respectively. Maximum temperatures close to 650°C were likely reached during the Eo‐Alpine HP event, whereas those of the Tertiary HP event were probably ~580°C. These HP metamorphic events suggest that the Pohorje Mts. experienced both an Eo‐Alpine and a Tertiary subduction-exhumation history, the latter of which was mainly reported for underlying Penninic nappes so far.Item Open Access Mixed-length multivariate covalent organic framework for combined near-infrared photodynamic therapy and drug delivery(2025) Rodríguez-Camargo, Andrés; Yildiz, Erdost; Juela, Diego; Fischer, Felix Richard; Graf, Daniel; Rath, Bibhuti Bhusan; Ochsenfeld, Christian; Bauer, Matthias; Sitti, Metin; Yao, Liang; Lotsch, Bettina V.Covalent organic frameworks (COFs) have been emerging as versatile reticular materials due to their tunable structures and functionalities, enabled by precise molecular engineering at the atomic level. While the integration of multiple components into COFs has substantially expanded their structural complexity, the strategic engineering of diverse functionalities within a single framework via the random distribution of linkers with varying lengths remains largely unexplored. Here, we report a series of highly crystalline mixed-length multivariate COFs synthesized using azobenzene and bipyridine as linkers, where tuning the ratio of linkers and incorporating palladium effectively modulates the balance between near-infrared (NIR) light absorption and catalytic sites for NIR-generation of hydrogen peroxide (H2O2). Capitalizing on the deep tissue penetration of NIR light and the generated H2O2 as reactive oxygen species, as a proof of concept, the optimal mixed-length multivariate COF reduces breast cancer cell viability by almost 90% after 1 h of irradiation in a combined in vitro photodynamic therapy and drug delivery.Item Open Access Monazite beats zircon regarding dating of young metamorphic events : an example from polycyclic granitic gneiss of the Pohorje Mountains, Slovenia(2024) Li, Botao; Massonne, Hans‐Joachim; Zhang, Junfeng; Yuan, Xiaoping; Luo, TaoThe result of dating U-(Th)-Pb bearing minerals in metamorphic rocks frequently suffers from the interpretative relation of their growth to a specific metamorphic event. This problem occurs in the southern Pohorje Mountains. Therefore, granitic gneiss from this area was studied. Rims of zircon in these rocks gave U-Pb ages around 90 Ma interpreted as an indicator of Late Cretaceous metamorphism. However, in situ dating of monazite with LA-ICP-MS yielded Early Miocene U-Th-Pb ages consistent with contact metamorphism by magmas forming the Pohorje pluton. This is supported by geothermobarometry using compositions of garnet and muscovite in granitic gneiss. This method led to pressure–temperature conditions of 6.5 kbar and 625°C, in line with intrusion depths estimated for the southeastern part of the Pohorje pluton. Consequently, zircon was not suitable for dating the latest metamorphic event but monazite was. Furthermore, monazite dating suggests two main intrusion pulses of magmas differing by 2-3 Ma.Item Open Access Pressure-temperature-time evolution of a polymetamorphic paragneiss with pseudomorphs after jadeite from the HP-UHP gneiss‐eclogite unit of the Variscan Erzgebirge crystalline complex, Germany(2024) Massonne, Hans‐JoachimA quartz‐rich paragneiss from the Variscan Erzgebirge Crystalline Complex (ECC) was studied in detail because of abundant millimetre‐sized and clearly oriented pseudomorphs after a sodic mineral interpreted to have been jadeite. This mineral, or pseudomorphs after it, is rarely found in extensive high‐pressure (HP)-ultrahigh‐pressure (UHP) terranes worldwide despite reported pressure-temperature (P-T) conditions suitable for the formation of jadeite in common paragneisses and orthogneisses. In the studied rock, which contains abundant large and oriented potassic white mica flakes and minor millimetre‐sized garnet grains, the pseudomorphs consist of clusters of small albite grains with thin phengitic muscovite flakes in between. X‐ray maps for Ca and Mg in garnet demonstrate that an early generation of this mineral (Gt1) was corroded and subsequently overgrown by a Ca‐richer generation (Gt2). White mica is phengite with maximum Si contents of 3.42 atoms per formula unit. P-T conditions of 0.85 GPa and 650°C and 1.7 GPa and 660°C were derived for the formation of Gt1 and Gt2 rim + Si‐rich phengite, respectively, using pseudosection modelling. The latter conditions representing the pressure peak experienced by the paragneiss are compatible with the original presence of jadeite and possibly paragonite as well. This metamorphic peak occurred at 338.4 ± 2.3 (2σ) Ma based on in situ dating of monazite grains with the electron microprobe. A single monazite age of 386.4 ± 10.5 (2σ) Ma is related to the formation of Gt1. Thus, a Late Devonian metamorphism is suggested here for the first time to have occurred in ECC gneisses before the major HP event in the Early Carboniferous. Furthermore, the study demonstrates that the eclogite‐facies gneisses of the Gneiss‐Eclogite Unit of the ECC experienced peak pressures of not more than 2 GPa in contrast to recent proposals of an extensive UHP area in this unit. In addition, it is suggested that the localized occurrence of UHP rocks surrounded by other lithologies otherwise lacking evidence for UHP conditions should be interpreted with caution with respect to their regional extent and significance.Item Open Access 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, KristinaWhile 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.