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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 ErscheinungsjahrErschienen 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. The Influence of Samarium Doping on the Photoelectrochemical (PEC) Activity of SrTiO ₃ for Solar Water Splitting

    Autoren T. Islam, M. Arnold, A. Görne, M. Stelter ErscheinungsjahrErschienen in:Journal of the American Ceramic Society: incorporating Advanced ceramic materials and communications
    The effect of Sm ³⁺ doping (0–5 mol%) on the photoelectrochemical properties of SrTiO ₃ was systematically investigated as a photoanode candidate for solar water splitting. Dense bulk ceramics synthesized via solid-state route retained the cubic perovskite structure. Rietveld refinement of the 5 mol% Sm-doped SrTiO ₃ (Sm:STO) sample confirmed successful A-site substitution with Sm. Photoluminescence emission spectra revealed enhanced emission intensities upon doping, with concentration quenching observed at 5 mol% Sm. UV–Vis diffuse reflectance spectroscopy indicated only a marginal bandgap narrowing (3.18 for pure STO to 3.14 eV for 5% Sm:STO), suggesting that band structure modification alone does not account for the enhancement in the PEC performance. The 1.5% Sm:STO photoanode exhibited the highest photocurrent density of 64 µA cm − ² at 1.23 V RHE , nearly two orders of magnitude higher than the undoped SrTiO ₃ reference. This improvement is attributed to Sm induced grain refinement, increased electrochemically active surface area, and partially to oxygen-vacancy formation. Mott–Schottky analysis confirmed n-type conductivity, while chronoamperometry tests verified the material's chemical stability over 3 h under continuous illumination. These findings show that Sm doping could be used to activate bulk SrTiO ₃ ceramics, demonstrating the potential of customized perovskites as scalable photoelectrodes for solar water splitting.
    Universitätsbibliographie Jena:
    fsu_mods_00039350Externer Link

  3. 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 ErscheinungsjahrErschienen 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

  4. 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 ErscheinungsjahrErschienen 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

  5. Ionic functionalization of ultra-microporous carbon materials for atmospheric water harvesting

    Autor S. Rezeki Erscheinungsjahr
    In dieser Arbeit zeigen ultramikroporöse Materialien auf Kohlenstoffbasis – Poly(heptazinimide) (PHIs) und Cyclodextrine (CDs) –, die sich durch einen stickstoff- und sauerstoffreichen atomaren Aufbau auszeichnen, hydrophile Eigenschaften, die denen von metallorganischen Gerüstverbindungen (MOFs) und Zeolithen ähneln. PHI, K-PHI sowie Fe-PHI-Varianten mit drei unterschiedlichen Fe-Konzentrationen wurden hinsichtlich ihrer Wasseradsorptionskapazität bei niedriger und hoher relativer Luftfeuchtigkeit (RH) charakterisiert. Unter den untersuchten Materialien (K-PHI, Fe-0.1-PHI, Fe-1-PHI und Fe-10-PHI) zeigte Fe-10-PHI die vielversprechendste Leistung: Die Wasseradsorptionskapazitäten lagen bei p/p0-Werten von 0,05 bzw. 0,9 bei ca. 7,2 mmol g⁻¹ (ca. 0,13 g g⁻¹) und ca. 13,6 mmol g⁻¹ (ca. 0,24 g g⁻¹). Basierend auf der dynamischen Wasseradsorption lässt sich abschätzen, dass Fe-10-PHI bei 20 % RH eine Wasserausbeute von ca. 0,013 L kg⁻¹ Tag⁻¹ in einem passiven AWH-System und ca. 1,17 L kg⁻¹ Tag⁻¹ in einem aktiven AWH-System (bei einer Rückgewinnungsrate von 41 %) liefert, wobei die Adsorptions- und Desorptionszeiten mit jeweils ca. 8 Minuten vergleichsweise kurz sind. Die hier vorgestellten Ergebnisse belegen die potenziellen Vorteile von Fe-10-PHI als Material zur Wassergewinnung, insbesondere in ariden Regionen, sowie von γCD-300-Li2000 für AWH-Systeme über den gesamten Bereich der relativen Luftfeuchtigkeit. Wie in dieser Arbeit gezeigt wird, können beide Materialien hinsichtlich Wasserausbeute, Herstellungskosten, Syntheseverfahren und Stabilität mit bekannten porösen Materialien wie DUT-67, Al-Fumarat, MOF-801, UiO-66, MCM-41, CAU-10-H und LTA konkurrieren. Diese Erkenntnisse unterstreichen das vielversprechende Potenzial von insbesondere Fe-10-PHI für die AWH-Technologie und bilden eine solide Grundlage für weiterführende Untersuchungen auf diesem Gebiet.
    Universitätsbibliographie Jena:
    fsu_mods_00044000Externer Link

  6. Photochemical Aging Triggers Zn(II) Mobilization and Toxicity in Metallopolymer Microplastics to the Green Macroalga Ulva

    Autoren P. Walz, M. Jäger, S. Jeß, M. Hermesdorf, Y. Carstensen, D. Leistenschneider, S. Zechel, M. Hager, M. Franke, F. Schacher, U. Schubert, M. Stelter, T. Wichard, P. Braeutigam ErscheinungsjahrErschienen in:ACS ES&T water
    UV-induced aging alters the chemical composition and leaching of metal-containing polymer microparticles, influencing the environmental fate of microplastics in marine systems. Two stimuli-responsive metallopolymers (based on histidine methacrylate, butyl methacrylate, zinc triflate) were artificially aged, and three sample types were tested on germinating gametes of the macroalga Ulva (Chlorophyta): (i) the untreated polymers, (ii) substances released during UV exposure (Leaching Extract1), and (iii) substances released after UV exposure (Leaching Extract2). Aged polymers and their leachates exhibited higher toxicity than virgin samples. UV irradiation enhanced the release of Zn-containing species; however, the LC ₅₀ of Zn(II) alone (1.24 mg L –¹ ) exceeded that of the variously treated polymer samples (0.05–0.99 mg L –¹ ), indicating that Zn(II) alone cannot account for the toxicity and that additional leached substances contribute to the toxic response. In some cases, Leaching Extract2 exhibited higher toxicity than Leaching Extract1, suggesting that bioactive compounds continued to be released after aging. These findings demonstrate that UV-induced aging alters the chemical composition and release behavior of metallopolymers, thereby enhancing their toxicity to marine organisms and resulting in continuous zinc mobilization that can impair algal growth. This highlights the importance of considering aging-driven leaching when assessing the environmental risks of metal-containing microplastics.
    Universitätsbibliographie Jena:
    fsu_mods_00039234Externer Link

  7. 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 ErscheinungsjahrErschienen in:Advanced energy & 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

  8. Surface-modification of γ-Al2O3 pellets with organic phosphonic acids-quaternary ammonium compounds for adsorptive nitrate removal from water

    Autoren J. Gützlaff, T. Kutschin, P. Bräutigam, F. Schacher ErscheinungsjahrErschienen in:PLOS Water
    The increased discharge of nitrate into natural waters, particularly in agriculturally impacted areas, has become a major challenge in water treatment because elevated nitrate concentrations are harmful to both human health and environmental equilibria. Therefore, the objective of this study is to present a novel method for the efficient adsorptive removal of nitrate from water. Regenerable γ-Al ₂ O ₃ -based adsorbers were prepared by surface functionalization with phosphonate-based quaternary ammonium modifiers synthesized in a two-step reaction. At an initial nitrate concentration of 50 mg L ⁻¹ , nitrate uptake increased rapidly to about 3.3 mg g ⁻¹ within 60 min and reached a plateau of about 3.45 mg g ⁻¹ after 120 min. Langmuir capacities ranged from 9.7 to 13.2 mg g ⁻¹ , with the highest value obtained for C2TMABr-modified Al ₂ O ₃ . Competing anions reduced nitrate uptake, with sulfate showing a substantially stronger inhibitory effect than chloride. Regeneration with 16.13 mmol L ⁻¹ NaCl restored about 95% of the initial adsorption performance after 30 min, and the C2TMABr-modified adsorber retained 93 ± 2% of its initial capacity over the last seven of ten adsorption–desorption cycles. These results show that phosphonate-functionalized γ-Al₂O₃ pellets provide moderate nitrate uptake combined with practical separability, modifier-dependent selectivity, and good regeneration stability.
    Universitätsbibliographie Jena:
    fsu_mods_00039150Externer Link

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

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

  10. 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 ErscheinungsjahrErschienen 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

  11. 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 ErscheinungsjahrErschienen in:Advanced energy & 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

  12. Transverse thermoelectric devices based on thermoelectric oxide ceramics

    Autor A. Ibrahim Erscheinungsjahr
    Universitätsbibliographie Jena:
    fsu_mods_00028286Externer Link
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