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127 Publikationen filtern

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Hervorgehobene Autoren sind Mitglieder der Forschungsgruppe.

  1. Optimization of electrochemical nitrate detection on a commercial copper electrode using D-optimal response surface methodology

    Autoren
    M. Jahan, P. Braeutigam, Q. Roode, M. Stelter, M. Franke
    Erscheinungsjahr
    Erschienen in:
    Sensors and actuators: international journal devoted to research and development of physical and chemical transducers
    Accurate and reliable nitrate detection is essential for water quality monitoring, especially in the face of rising contaminant loads from human activities. Electrochemical sensors with copper electrodes present a promising alternative to conventional nitrate detection methods. However, their broader application is limited by electrode passivation, interference from coexisting species and the requirement for solution deaeration. This study presents a simple in-situ activation strategy that prevents passivation, removes the deaeration requirement and ensures stable sensor performance. A commercial copper electrode was used for nitrate detection via linear sweep voltammetry. A multi-factor interaction approach was employed to optimize four experimental factors based on a D -optimal response surface methodology (RSM) model, providing a deeper understanding of the synergistic effects among variables. Under optimized conditions, the sensor achieved a sensitivity of 2.86 µA/µM and a limit of detection (LOD) of 22.84 µM within a linear range of 100–800 µM. In addition, the sensor showed excellent reproducibility (RSD = 1.26 ± 0.33 %) and maintained signal stability for 15 consecutive measurements at two different concentrations. Interference studies confirmed negligible effects from most ions, with nitrite enhancing the response via oxidation. Calculations showed a matrix effect (M.E.) of 10.61 % and 6.82 %, respectively for tap and river water with recoveries of 96–109 %. Furthermore, Chow tests revealed no significant matrix effects. The sensor measurements were consistent with the spectrophotometric method, with an error of 3.35 %. Collectively, these findings demonstrate the robustness, reliability, and practicality of this copper-based sensor for routine nitrate monitoring in environmental and drinking water systems.
    Universitätsbibliographie Jena:
    fsu_mods_00029654Externer Link

  2. Unraveling processes in an alkaline water electrolysis cell with reference electrodes and electrochemical impedance spectroscopy

    Autoren
    J. Scholl, C. Plank, J. Odrobina, M. Danzer, K. Skadell, M. Stelter
    Erscheinungsjahr
    Erschienen in:
    International journal of hydrogen energy : official journal of the International Association for Hydrogen Energy
    A zero-gap full cell for alkaline water electrolysis is equipped with two reference electrodes. The anode (NiO mesh), the cathode (Ni mesh), and the diaphragm are investigated simultaneously by analyzing the polarization curves and utilizing electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analysis. The shares of cell voltage are 44 % of the cathode, 23 % of the anode and 33 % of the diaphragm at 0.4 A/cm². EIS and DRT analysis focus particularly on the diaphragm, revealing a complex behavior that cannot be described merely as an ohmic resistor as it is traditionally done. EIS shows that the total resistance of the diaphragm comprises an ohmic contribution and a polarization behavior. This behavior is attributed to a funnel effect of OH− ions through the diaphragm. The effect results in a change in the concentration profile near the diaphragm, leading to concentration polarization. To gain deeper insights, two equivalent circuit models with a focus on the diaphragm are developed to describe the behavior of the full cell. Both models showed that the diaphragm cannot be described by a simple ohmic resistance, and the resistance estimated by analyzing the polarization curve is a sum of multiple resistances.
    Universitätsbibliographie Jena:
    fsu_mods_00029585Externer Link

  3. Performance Enhancement of Ca3Co4O9-based Transverse Multilayer Thermoelectric Generators for Low-Power Applications

    Autoren
    A. Ibrahim, A. Bochmann, R. Löhnert, B. Mieller, L. Wilde, B. Capraro, M. Stelter, J. Töpfer
    Erscheinungsjahr
    Erschienen in:
    Journal of the American Ceramic Society: incorporating Advanced ceramic materials and communications
    Transverse thermoelectric generators (TTEG) enable conversion of thermal into electrical energy with perpendicular directions of the applied temperature gradient and the induced thermoelectric voltage. We report on the fabrication of transverse multilayer thermoelectric generators (TMLTEG) based on p-type Ca ₃ Co ₄ O ₉ (CCO) ceramic tapes and printed silver which were conventionally sintered (CS) in air at 920°C or using pressure-assisted sintering (PAS) at 920°C and 1.5 MPa. The thermoelectric performance of TMLTEGs was evaluated using analytical calculations and simulations. The transverse thermoelectric power factor PF tr and thermoelectric figure-of-merit ZT tr of an artificial layered structure composed of CCO and silver were calculated and simulated as functions of layers tilt angle φ and metal-to-ceramic thickness ratio ν t . TMLTEG devices with various CCO layer thicknesses of 150 µm, 100 µm, or 33 µm were fabricated and cofired at 920°C in air, which exhibit power outputs of 2.3 mW, 3.2 mW, and 4.1 mW at ΔT = 160 K, respectively. TMLTEGs which were cofired using PAS show a higher power density of 16.4 mW/cm ³ at ΔT = 225 K. This enhancement in power (≈ 80%) is crucial for thermoelectric modules comprising multiple TMLTEG devices. The device measurements were compared with 3D simulations.
    Universitätsbibliographie Jena:
    fsu_mods_00035159Externer Link

  4. Toward Artificial Thylakoids: Charge Transfer in Polydopamine Nanosheets for Photocatalytic Hydrogen Production

    Autoren
    T. Herberger, M. Kaplan, M. Boecker, J. Kund, S. Harvey, L. Veith, M. Micheel, C. Neumann, A. Turchanin, C. Kranz, T. Weil, C. Synatschke, V. Ball, M. Wächtler
    Erscheinungsjahr
    Erschienen in:
    Advanced Energy and Sustainability Research
    Artificial leaves emulate biological leaves by converting photonic energy into chemical energy, yet replicating photosynthetic functionalities at the molecular level remains a challenge. Key limitations of current artificial leaves include (1) recombination in photosensitizers and (2) photooxidation of the photosensitizers, (3) inefficient electron and proton transfer to reaction centers, and (4) limited scalability of the illuminated surface area. Herein, we address these challenges by mimicking the thylakoid membrane, nature's photosynthetic machinery, in a simplified system using an electropolymerized ultrathin polydopamine (PDA) nanosheet embedded with CdSe@CdS nanorods (NRs) as photosensitizers and cobaloximes as hydrogen evolution catalysts. The PDA nanosheet provides essential functions of the thylakoid membrane: it suppresses recombination through rapid electron acceptance, facilitates efficient electron transport, and mitigates photooxidation of photosensitizers within an ultrathin layer, as demonstrated by photoelectrochemical analysis, transient absorption spectroscopy, and scanning electrochemical microscopy. These findings lay the groundwork for designing artificial thylakoid membranes, advancing the development of next-generation materials for efficient energy conversion, and addressing some of the fundamental limitations of current artificial leaf systems.
    Universitätsbibliographie Jena:
    fsu_mods_00035394Externer Link

  5. Nanomaterials and nanocomposites in the rhizosphere: Biotransformation and nanosafety assessments

    Autoren
    L. Azeez, R. Opatokun-Saliu, S. Basiru, B. Agbaogun, R. Oladeji, N. Abara
    Erscheinungsjahr
    Erschienen in:
    Nanomaterials–Microbial Interactions for Soil Health, Plant Growth, and Performance
    Universitätsbibliographie Jena:
    fsu_mods_00030782Externer Link

  6. The Harmful Footprint of Aged Biomicroplastics on Algal Development: A Comparative Study of Polylactic Acid, Polyhydroxybutyrate, and Cellulose Acetate

    Autoren
    P. Walz, S. Redlich, M. Hermesdorf, L. Calderón-Rodríguez, M. Franke, D. Leistenschneider, Q. Roode-Gutzmer, F. Schacher, M. Stelter, T. Wichard, P. Braeutigam
    Erscheinungsjahr
    Erschienen in:
    ACS Omega
    Biopolymers are increasingly produced as sustainable alternatives to plastics, but their degradation in aquatic ecosystems raises ecological concerns. This study demonstrates that the photodegradation of polylactic acid (PLA), polyhydroxybutyrate (PHB), and cellulose acetate (CA) in artificial seawater substantially increased toxicity under the elevated laboratory conditions used, compared with virgin counterparts, adversely affecting the development and growth of seaweeds. Those aged biopolymers and their leached substances impaired the growth and development of the green macroalgae Ulva (Chlorophyta) under standardized conditions, but the ecological relevance at natural seawater concentrations is likely lower. Chlorophyll a fluorescence, median lethal concentration (LC50-values), and HR-MS analysis corroborated these findings, emphasizing detrimental impacts on the fitness and development of Ulva mutabilis. Toxic effects were linked to substances released during photodegradation and hydrolysis, especially for PLA and PHB. PLA exhibited a 6.7-fold increase in toxicity following UV exposure; LC50-values indicate increased toxicity from direct polymer exposure and from leached compounds at the applied concentration. PHB exhibited the strongest degradation-related toxicity, with over a 10-fold increase. CA was the most toxic overall, with an LC50-value of <0.5 mg/mL in aged samples under laboratory conditions. Even nonaged CA showed effects at these elevated concentrations, but environmental relevance remains uncertain. Although this is an explorative model study in lab scale using elevated concentrations, the observed persistence and (post-)degradation effects of biomicroplastics highlight potential polymer-specific toxicity and emphasize the need for further research on the degradation of biopolymers in the marine environment.
    Universitätsbibliographie Jena:
    fsu_mods_00028707Externer Link

  7. Alternative Gas Diffusion Electrode Designs: Influence of Porosity Gradients on the Electrochemical Activity

    Autoren
    A. Bekisch, K. Skadell, J. Ast, M. Schulz, R. Weidl, S. Christiansen, M. Stelter
    Erscheinungsjahr
    Erschienen in:
    Advanced Energy and Sustainability Research
    In this study, it is revealed that carbon-free gas diffusion electrodes (CF-GDEs) with macropore sizes outperform the a carbon-based GDE (GDErₑf). These CF-GDEs exhibit notably reduced overpotentials and increased electrochemical stability. By combining three distinct macropore-sized substrates, coated with MnOₓ and hydrophobized with polytetrafluorethylen, a range of CF-GDEs with distinct porosity gradients is designed. In the results, the pivotal role of substrate layers and their hydrophilic/hydrophobic attributes in steering the formation of the electrolyte thin film are unveiled. Specifically, one CF-GDE shows a reduction by one-third of the ηOER (0.24 V) compared to GDErₑf at 10 mA cm−². Noteworthy, this CF-GDE also displays excellent long-term stability without degradation, which is a common issue with carbon-based GDEs due to carbon corrosion. Impressively, the stability measurement conditions the active catalyst sites of the CF-GDE and leads to the formation of NiOₓ, Ni₆MnO₈, and NiMn layered double hydroxides. This results in a doubling of the current densities.
    Universitätsbibliographie Jena:
    fsu_mods_00023527Externer Link

  8. Transverse thermoelectric devices based on thermoelectric oxide ceramics

    Autor
    A. Ibrahim
    Erscheinungsjahr
    Universitätsbibliographie Jena:
    fsu_mods_00028286Externer Link

  9. Elimination von Mikroschadstoffen im Wasser mittels hydrodynamischer Kavitation und nichtthermischem Plasma

    Autor
    M. Dommke
    Erscheinungsjahr
    Ziel dieser Arbeit war die Entwicklung eines kombinierten Kavitation/Nichtthermisches-Plasma-Verfahrens (HC/NTP) zur Eliminierung von Mikroschadstoffen im Wasser. Nichtthermisches Plasma (NTP) ist vielseitig einsetzbar, wird jedoch durch begrenzten Massentransport reaktiver Sauerstoffspezies eingeschränkt. Durch die Kopplung mit hydrodynamischer Kavitation konnte diese Limitation überwunden werden. Der Abbau des Modellschadstoffs Benzotriazol diente der Prozessbewertung. Zu Beginn wurde ein System mit atmosphärischem Plasma untersucht, das mit einem minimalen Energieeintrag von etwa 33 kWh/m³ eingesetzt werden konnte. Mit Luft als Ionisationsmedium erwies sich die Methode wegen hoher Nitratbildung als ungeeignet. Im kombinierten HC/NTP-System bestimmten abstromseitiger Absolutdruck, Leitfähigkeit, Temperatur und Düsengeometrie die Effizienz. Eine Mindestleitfähigkeit über 100 µS/cm wurde identifiziert, während ein Temperaturmaximum bei 30 °C die effizientesten Abbaubedingungen darstellte. Die Abbaueffizienz stieg mit der Schadstoffkonzentration, während die Geschwindigkeit abnahm. Das kombinierte Verfahren erreichte eine höhere Geschwindigkeitskonstante (0,63 min⁻¹ gegenüber 0,11 min⁻¹ bei atmosphärischem Plasma), gesteigerten Durchsatz (0,210 m³/h) und einen reduzierten Energieverbrauch (14,1 kWh/m³). Zudem wurde der unerwünschte Stickstoffeintrag durch das geschlossene System vermieden. Das HC/NTP-Konzept stellt damit eine energieeffiziente und skalierbare Alternative zu Einzelverfahren dar. Weitere Forschung sollte sich auf den Einfluss von Matrixkomponenten, die Optimierung des Energieeintrags im Ultraspurenbereich und die Anwendung in Realwassersystemen konzentrieren.
    Universitätsbibliographie Jena:
    fsu_mods_00028997Externer Link

  10. Integrated characterization of hydrodynamic cavitation: optical, chemical, and simulation correlations

    Autoren
    J. Xiao, M. Dommke, M. Franke, M. Stelter, P. Braeutigam
    Erscheinungsjahr
    Erschienen in:
    Chemical engineering science
    Hydrodynamic cavitation (HC) is an advanced oxidation process for degrading micropollutants, primarily driven by hydroxyl radicals (OH⋅). This study addresses the research gap by characterizing HC under high upstream pressures (up to 60 bar) and integrating chemical, optical, and simulation approaches for a comprehensive characterization of HC processes. OH radical production was quantified with salicylic acid, and bisphenol A (BPA) degradation experiments validated their role in oxidation reactions. Optical methods captured cavitation jet and luminol chemiluminescent images, while simulations estimated vapor bubble formation and cavitation gas fractions. This research focuses on the high-pressure range of 10 to 60 bar in HC systems, demonstrating a proportional relationship between pressure and both the production rate of OH radical and the rate constants of BPA degradation. At 60 bar, the highest concentration of OH radicals and BPA degradation rate were observed. This research enhances the understanding of HC and its potential for optimized pollution control.
    Universitätsbibliographie Jena:
    fsu_mods_00019628Externer Link

  11. Engineered [FeFe]-hydrogenase mimics featuring heteroaryl linkers: molecular design and photocatalytic hydrogen evolution under visible light

    Autoren
    I. Basma, K. Rediger, C. Kasahara, H. Abul-Futouh, M. Micheel, M. Farh, P. Köhler, G. Mlostoń, M. Wächtler, W. Weigand
    Erscheinungsjahr
    Erschienen in:
    Inorganic Chemistry Frontiers: an international journal of inorganic chemistry
    Inspired by the active site of [FeFe]-hydrogenase, we have developed synthetic mimics engineered from the reaction of heteroaryl thioketone derivatives ferrocenyl(5-(4-(diphenylamino)phenyl)thiophen-2-yl)methanethione (PS-Fc-1), ferrocenyl(5′-(4-(diphenylamino)phenyl)-[2,2′-bithiophen]-5-yl)methanethione (PS-Fc-2) and phenyl(5′-(4-(diphenylamino)phenyl)-[2,2′-bithiophen]-5-yl)methanethione (PS-Ph) as pro-ligands with Fe3(CO)12. The resulting complexes contain thiolato ligands, which enable a close linkage between heteroaryl chromophores and the catalytic center, thereby promoting efficient photocatalytic hydrogen evolution under visible light irradiation. These mimics incorporate a push–pull organic chromophore, consisting of triphenylamine and (bi)thiophene groups, designed to facilitate direct photoexcitation into a charge-separated state. Electrochemical properties were examined using cyclic voltammetry, and photophysical characteristics were determined by steady-state spectroscopy and nanosecond transient absorption supported by (TD-)DFT simulations. Whilst both catalytically active species revealed the formation of charge-separated states directly upon excitation, fast deactivation due to relaxation into low-lying ferrocene-located states prevents the formation of long-lived excited states in the ferrocene-linked dyad. This explains the reduced activity for hydrogen generation of the dyad containing the ferrocene moiety compared to the phenyl one.
    Universitätsbibliographie Jena:
    fsu_mods_00028319Externer Link

  12. [FeFe]-hydrogenase mimic with organic photosensitizers for long-lived excited states and efficient photocatalytic H₂ production

    Autoren
    C. Kasahara, M. Farh, K. Rediger, P. Buday, S. Gräfe, M. Micheel, S. Kupfer, M. Wächtler, W. Weigand
    Erscheinungsjahr
    Erschienen in:
    Cell Reports Physical Science
    We report a [FeFe]-hydrogenase mimic complex bearing two organic photosensitizers ( PS-CAT , C₇₀H₄₄Fe₂N₂O₆S₆) aimed at achieving superior light-absorbing properties. PS-CAT is a dyad with two light-harvesting moieties ( PS ) and one catalytic center ( CAT ). The present study investigates the electro- and photo-reduction properties of PS-CAT , combining experimental and theoretical approaches to achieve a comprehensive understanding of the (photo)reduction mechanism of the dyad. To this aim, PS-CAT was studied by means of cyclic voltammetry, IR-spectroelectrochemistry, nanosecond-transient absorption, and scalar relativistic-time-dependent-density functional theory. The results reveal that the dyad can access the photo-excited state with a large absorption coefficient due to multiple PSs. Moreover, the PS-CAT produced long-lived excited species with a ligand-centered or charge-separated character by photon absorption. The subsequent quenching can produce the catalytically active reduced species. Furthermore, the photocatalytic activities of PS-CAT under visible light irradiation were examined, and the PS-CAT exhibited high efficiency (turnover frequency 33 h−¹) of H₂ generation as a PS -bearing [FeFe]-H₂ase mimic.
    Universitätsbibliographie Jena:
    fsu_mods_00029538Externer Link
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