Highlighted authors are members of the University of Jena.
Alternative Gas Diffusion Electrode Designs: Influence of Porosity Gradients on the Electrochemical Activity
Year of publicationPublished in:Advanced Energy and Sustainability Research
A. Bekisch, K. Skadell, J. Ast, M. Schulz, R. Weidl, S. Christiansen, M. Stelter
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.
Integrated characterization of hydrodynamic cavitation: optical, chemical, and simulation correlations
Year of publicationPublished in:Chemical engineering science
J. Xiao, M. Dommke, M. Franke, M. Stelter, P. Braeutigam
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.
Variability in microplastic abundance, bisphenol A contamination, antioxidant properties, and health risks associated with vegetable consumption
Year of publicationPublished in:Beni-Suef University Journal of Basic and Applied Sciences
L. Azeez, R. Adetoro, B. Agbaogun, A. Oyedeji, H. Busari, A. Oladejo, O. Oyelami, O. Deborah, R. Oladeji, S. Basiru, S. Muhammad-Lawal, A. Hammed, A. Makanjuola
Background: Plastic pollution, particularly microplastics (MPs) and toxic additives such as bisphenol A (BPA), endangers human health. Therefore, their routes in the environment need to be investigated. This study investigated microplastic (MPs) abundance, bisphenol A (BPA) levels, and antioxidant activity (AA) in three commonly consumed vegetables—green amaranth, jute mallow, and spinach sourced from two markets in Osogbo, southwestern Nigeria. Microscopic technique was used to determine MP abundance, shapes, and colours. High-performance Liquid Chromatography (HPLC) was used to analyse BPA contents while 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay was used to measure AA. A hazard index (HI) and estimated dietary intakes (EDIs) were used to estimate the associated risks and food safety concerns with MP and BPA in vegetables. Results: In this study, MP abundance in shoots ranged from 4.00 ± 0.50 to 7.67 ± 1.04 particles/g and in roots from 5.33 ± 1.53 to 18.00 ± 6.93 particles/g in spinach and green amaranth, respectively, indicating subsoil contamination. Three shapes (fragment, fibre, and irregular) and five colours (transparent, white, yellow, black, and brown) were detected, with fragment shape and transparent colour dominating. Fourier Transform Infrared spectroscopic (FTIR) analysis revealed a predominance of polyethylene, polypropylene, polyethylene terephthalate, polyvinyl chloride, and polyamide microplastics. The BPA ranged from 5.55 ± 0.56 to 6.65 ± 0.00 μg/g while AA ranged from 40.67 ± 6.79 to 72.55 ± 4.03%. A regression analysis and principal component analysis (PCA) were used to identify the relationship among the factors (MPs, BPA, and AA). It is suggested that high levels of MPs and BPA negatively impacted vegetable quality as they are associated with environmental contamination. Contrastingly, AA had a significant positive correlation with vegetable quality. Both EDIs and HI of MPs and BPA were < 1, indicating no significant risk associated with BPA exposure from their consumption. Conclusion: This study highlights the potential health risks of MPs and associated BPA contamination in vegetables. The estimated dietary intake and hazard index suggest no immediate health risks, but long-term exposure remains a concern. MPs and BPA in commonly consumed vegetables warrant stricter monitoring of agricultural soil and irrigation water sources. Microplastic exposure in food crops can be reduced with policies that regulate plastic waste disposal and promote sustainable farming practices.
Activity measurements and calculations for gamma-emitting radionuclides in concrete drill cores of unit 2 of the Greifswald NPP
Year of publicationPublished in:ISRD 17 - International Symposium on Reactor Dosimetry (Part II)
E. Poenitz, Q. Roode-Gutzmer, A. Barkleit, J. Konheiser
Due to Germany's nuclear phase-out, decommissioning and final disposal of construction materials of Nuclear Power Plants (NPP) become increasingly important. The reliable determination of radionuclides produced by neutron activation, the activity as a function of time since shutdown and investigation of subsequent radionuclide mobility are subject of a research project. Drill cores of the concrete shielding of unit 2 of the Greifswald NPP were retrieved. Specific activities of gamma emitters and the elemental composition were measured. The radiation transport code MCNP 6 was used for the calculation of spectral neutron fluences. A neutron radiation field calculation reveals that the maximum neutron fluence at the concrete component is located in the floor just below the RPV. The concrete structures closest to the reactor core are shielded efficiently against neutron radiation by the annular water tank. Measured and calculated specific activities of ¹⁵²Eu, ¹⁵⁴Eu and ⁶⁰Co for the cement screed at the position of the maximum neutron fluence are surprisingly low. A specific exemption (i.e. release from radiation protection surveillance but mandatory for final disposal) of the screed sample according to Germany's Radiation Protection Ordnance is expected to be possible approximately 4 decades after the shutdown of the NPP.
Development and investigation of a multilayer PDMS/zeolite composite membrane for CO₂ separation applications
Year of publicationPublished in:Separation and Purification Technology
A. Taherizadeh, A. Simon, H. Richter, M. Stelter, I. Voigt
This work aims to investigate and develop a concept for CO₂ separation based on PDMS/SSZ–13 (high-Si CHA) composite membranes. Firstly, an Al₂O₃ support was coated with SSZ-13 zeolite layer, then to increase the performance of the membrane, a Polydimethylsiloxane layer was effectively deposited homogeneously to cover the cracks and defects of the zeolite layer. The results of single gas permeation measurements displayed a notable increase in ideal CO₂/CH₄ selectivity up to 428 at the lowest PDMS concentration of 0.5 vol%. Moreover, a coating time of 10 min preserved CO₂ permeance while increasing CO₂/CH₄ selectivity from 5 to 120. A twentyfold increase in CO₂/CH₄ selectivity was noted with mixed gas permeation without a reduction in CO₂ permeance. Quantitative and qualitative microscopic analyses were also carried out on the coated membrane to better understand its morphology and microstructure. The outcomes indicated that PDMS layer decreased the permeation of N₂ and CH₄ and enhanced surface affinity toward CO₂, resulting in reduced defects in the zeolite membranes and enhanced selectivity for CO₂/N₂ and CO₂/CH₄.
Characterization and synthesis of high permeance SSZ-13 membranes to separate CO₂ from CH₄ for biogas upgrading
Year of publicationPublished in:Journal of Membrane Science
A. Taherizadeh, A. Simon, H. Richter, M. Stelter, I. Voigt
Small-pore zeolites, such as CHA (0.38 nm), have pores that are comparable to the size of CH₄ but larger than the size of CO₂. As a result of the combination of diffusion and adsorption, these membranes are projected to have strong CO₂/CH₄ selectivity and CO₂ permeance. During this work, SSZ-13 CHA membranes were synthesized, evaluated, and characterized by X-ray Diffraction, Field-Emission Scanning Electron Microscopy, Energy-Dispersive X-ray Spectroscopy, Fourier Transform Infrared Spectroscopy, Solid-State Nuclear Magnetic Resonance, and Thermogravimetric Analysis. Synthesized membranes on the inner surface of single channel alumina supports with a pore size of 200 nm and a length of 105 mm and an active membrane area of ∼17 cm² showed an ideal permselectivity for CO₂/CH₄ of 122 (in the single gas permeation measurement) and a CO₂ permeance of 36.1 × 10−⁷ [mol/(m² s Pa)] and CO₂/CH₄ selectivity of 173 and a CO₂ permeance of 6.5 × 10−⁷ [mol/(m² s Pa)] for equimolar CO₂ − CH₄ mixture. According to the results, the membranes are capable of separating CO₂ from natural gas and upgrading biogas for industrial purposes.
Synthesis and characterization of Chabazite membranes for gas seperation applications
Year of publication
A. Taherizadeh
Separating mixtures is crucial in industry but consumes significant energy. Membrane technology offers an energy-efficient alternative. It uses selective membranes to separate specific components from a mixture. Pressure is the most common driving force for this process. Microporous materials like zeolites are particularly useful for molecular separation due to their well-defined pore sizes. These pores act like sieves, allowing only molecules of a certain size to pass through. Chabazite (CHA) zeolites, with pores similar in size to methane (CH4) but larger than carbon dioxide (CO2), are promising for separating these gases. This research focused on developing CHA membranes for CO2/CH4 separation. The researchers synthesized, characterized, and evaluated these membranes. They also investigated factors affecting their performance, like pore size and synthesis conditions. Finally, they tested the membranes' effectiveness in separating CO2 from CH4 mixtures, demonstrating their potential for biogas upgrading. The final membranes achieved a CO2/CH4 selectivity of 122 (single gas) and 173 (mixed gas), with good CO2 permeance. These results suggest their promise for large-scale applications.
A Study of the Influence of Synthesis Parameters on the Preparation of High Performance SSZ-13 Membranes
Year of publicationPublished in:Applied Sciences
A. Taherizadeh, A. Simon, H. Richter, M. Stelter, I. Voigt
This study investigated the effect of different synthesis parameters including pre- and post-hydrothermal treatment on the formation of a high-quality SSZ-13 membrane layer. The membranes were identified initially by the gas tightness test, then were characterized by single gas permeation measurements applying H₂, He, CO₂, N₂, CH₄, and SF₆ at room temperature. The results showed how each parameter affects the performance of the membrane, including structural defects in the formed selective layer, CO₂ permeance, and the ideal CO₂/CH₄ permselectivity. This work focused on optimizing these parameters. An ideal CO₂/CH₄ permselectivity of up to 122 with CO₂ permeance of ~3.72 × 10−⁶ [mol/(m²sPa)] and CO₂/CH₄ selectivity of 111 with CO₂ permeance of 8.5 × 10−⁷ [mol/(m²sPa)] in an equimolar mixture at room temperature and pressure drop of 0.15 MPa was achieved. This is one of the highest performances compared to other publications for SSZ-13 or all-Si membranes.
Exploring the separation properties of high-Si CHA membranes for the CO₂ capturing technology: Impact of the selective layer thickness and growth mechanism
Year of publicationPublished in:Journal of Membrane Science
A. Taherizadeh, A. Simon, H. Richter, M. Stelter, I. Voigt
This study investigates the influence of the CHA selective layer's thickness, coated on a mono-channel alumina support using the secondary growth method, on the performance of CO₂ separation from CH₄. The membrane layer's thickness was explored by adjusting the concentration and duration of the seeding process, as well as the distribution of crystal size in the suspension. Single gas analysis results revealed that utilizing smaller crystal seeds, with an average crystallite size of approximately 600 nm, exhibited the highest performance. Furthermore, a membrane thickness of 2.1 μm demonstrated an ideal CO₂/CH₄ permselectivity of 205 with a CO₂ permeance of 2.39 x 10⁻⁶ [mol/(m²sPa)]. For the equimolar CO₂ - CH₄ gas mixture, the high-Si membrane displayed a CO₂/CH₄ selectivity of 210 with a CO₂ permeance of 8.06 x 10⁻⁷ [mol/(m²sPa)]. In both gas permeation measurement, CO₂ permeance exhibited a slight linear decrease with increasing thickness, while CH₄ permeance initially decreased and then increased non-linearly.
Medium-temperature solid-state batteries based on sodium-beta alumina
Year of publication
M. Fertig
The demand for more powerful and cost-effective electrochemical energy storage systems is increasing. One focus is research into so-called "post-Li-ion" batteries, which are not based on lithium but on other alkali or alkaline earth metals, such as potassium or calcium. Another prominent approach is using sodium, e.g., as a negative electrode (hereafter: anode), in combination with a solid electrolyte, resulting in solid-state sodium cells. The ceramic, polycrystalline sodium-beta alumina solid electrolyte (BASE) might be a viable candidate due to its outstanding electrochemical properties, low cost, and abundant raw materials. As positive electrodes, intercalation-type positive electrodes might be viable. These are already used successfully in Li-ion systems. Notwithstanding, there is barely any research about combining these material combinations to a cell systems operating below 100 °C yet (δm, Na = 97.7 °C). This thesis gives attention to this fact. The project focuses on clarifying the requirements for and the construction of cells consisting of metallic sodium anodes, sodium-beta alumina, and Na-ion cathodes, which are operated at temperatures below 100 °C. The work highlights the challenges for this specific material combination, suggests possible compositions and instructions for action. It provides initial characteristic values for the system. In doing so all three core components of the cell, i.e., the anode, the cathode, and the solid electrolyte, and their interaction are considered. As the solid electrolyte is the core component of the cell system, three publications (Publication 1, Publication 2, Publication 3) are dedicated to this essential cell component. The interaction of anode and solid electrolyte is examined in Publications 2 and 4. Publications 4 and 5 show the combination of Na-ion cathodes with the solid electrolyte and investigate the resulting cell system.