Zentrum für Umweltforschung und nachhaltige Technologien (UFT)
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Item-typ:Veröffentlichung, Recovery of submicron particles using high-throughput dielectrophoretically switchable filtration(Elsevier, 2014-06-25); ; ; ; Conventional methods for separation of submicron particles, e.g., filtration or centrifugation, suffer from severe problems, such as loss of particles during resuspension and high energy demands due to fouling of separating membranes. Here we present the novel concept of dielectrophoretically switchable filtration using pore sizes that are two to three orders of magnitude larger than the particles. We used layer-by-layer (LbL) assembled nanocapsules of 340 nm diameter that were to be separated and recovered from polyelectrolyte solution. The filter being an insulating porous structure is placed in between two electrodes generating an electric field which is bend at the solid–liquid interface and is thus highly inhomogeneous. Dielectrophoresis (DEP) is used as a driving force to trap particles in the filter. The filtration is based on electric effects and could thus be easily turned off by switching off the electric field allowing safe and easy resuspension of the trapped nanocapsules. A parametric study has been conducted to investigate the influence of voltage, pore size, flux and membrane thickness on the separation efficiency. Maximum separation and recovery efficiencies in a semi-continuous run reached almost 65% when working with a specific flow rate of 4.12 mL s−1 m−2, a voltage of 200 V, frequency of 210 kHz and a filter with thickness of 1.5 mm and pore sizes in the range of 20–60 μm. The results demonstrate that electrically switchable retardation of nanoparticles is possible even in large flow systems. This finding paves the way for preparative DEP chromatography of nanoparticles. Its ease makes this switchable filtration attractive for nanoparticle separation and purification in general.Wissenschaftlicher ArtikelBand:132103 131 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The gas flow diode effect: theoretical and experimental analysis of moderately rarefied gas flows through a microchannel with varying cross sectionModerately rarefied gas flows are clearly distinguished from viscous flow in the continuum regime and from free molecular flow at high rarefaction. Being of relevance for various technical applications, the understanding of such flow processes is crucial for considerable enhancement in micro electromechanical systems (MEMS) and vacuum techniques. In this work, we focus on the isothermal rarefied gas flow through long channels with longitudinally varying cross section. We apply two approaches, an analytical one and a numerical one that is based on the solution of the linearized S-model, both allowing us to predict the mass flow rate in diverging and converging flow directions for arbitrary pressure gradients. Both approaches are validated by CO2, N2 and Ar permeation experiments on tapered microchannels manufactured by means of micromilling. The local Knudsen numbers ranged from 0.0471 to 0.2263. All the numerical and analytical results are in good agreement to the experimental data and show that the mass flow rate is significantly higher when the duct is perfused in converging direction. The understanding of the physical phenomenon of this gas flow diode effect might pave the way for novel components in MEMS such as static one-way valves.Wissenschaftlicher ArtikelBand:18109 139 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Cu(OH)2 nanorods undergo sulfidation in water: in situ formation of CuO nanorods as intermediates and enhanced toxicity to Escherichia coli(Springer, 2020-06-20)8 45 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Soil properties can evoke toxicity of copper oxide nanoparticles towards springtails at low concentrationsCopper oxide nanoparticles (CuO-NP) are used as an efficient alternative to conventional Cu in agriculture and might end up in soils. They show a high toxicity towards cells and microorganisms, but only low toxicity towards soil invertebrates. However, most existing soil ecotoxicological studies were conducted in a sandy reference soil and at test concentrations ≥100 mg Cu/kg soil. Therefore, there is a knowledge gap concerning the effect of soil texture on the toxicity of CuO-NP at lower, more realistic test concentrations. In our study, a sandy reference soil and three loamy soils were spiked with CuO-NP at up to four concentrations, ranging from 5 to 158 mg Cu/kg. We investigated 28-day reproduction as well as weight and Cu content after 14-day bioaccumulation and subsequent 14-day elimination for the springtail Folsomia candida. For the first time we analysed the size distribution of CuO-NP in aqueous test soil extracts by single particle-ICP-MS which revealed that the diameter of CuO-NP significantly increased with increasing concentration, but did not vary between test soils. Negative effects on reproduction were only observed in loamy soils, most pronounced in a loamy-acidic soil (−61%), and they were always strongest at the lowest test concentration. The observed effects were much stronger than reported by other studies performed with sandy soils and higher CuO-NP concentrations. In the same soil and concentration, a moderate impact on growth (−28%) was observed, while Cu elimination from springtails was inhibited. Rather than Cu body concentration, the diameter of the CuO-NP taken up, as well as NP-clay interactions might play a crucial role regarding their toxicity. Our study reports for the first time toxic effects of CuO-NP towards a soil invertebrate at a low, realistic concentration range. The results strongly suggest including lower test concentrations and a range of soil types in nanotoxicity testing.Wissenschaftlicher ArtikelBand:27016 23 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Electrodeless dielectrophoresis: Impact of geometry and material on obstacle polarizationInsulator-based (electrodeless) dielectrophoresis (iDEP) is a promising particle manipulation technique, based on movement of matter in inhomogeneous fields. The inhomogeneity of the field arises because the excitatory field distorts at obstacles (posts). This effect is caused by accumulation of polarization charges at material interfaces. In this study, we utilize a multipole expansion method to investigate the influence of geometry and material on field distortion of posts with arbitrary cross-sections in homogeneous electric fields applied perpendicular to the longitudinal axis of the post. The post then develops a multipole parallel or anti parallel to the excitatory field. The multipoles intensity is defined by the post's structure and material properties and directly influences the DEP particle trapping potential. We analyzed posts with circular and rhombus-shaped cross-sections with different cross-sectional width-to-height ratios and permittivities for their polarization intensity, multipole position, and their particle trapping behavior. A trade-off between high maximum field gradient and high coverage range of the gradient is presented, which is determined by the sharpness of the post's edges. We contribute to the overall understanding of the post polarization mechanism and expect that the results presented will help optimizing the structure of microchannels with arrays of posts for electrodeless DEP application.Wissenschaftlicher ArtikelBand:37Heft:2100 124 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Microparticle trajectories in a high-throughput channel for contact-free fractionation by dielectrophoresisContinuous, contact-free fractionation of sensitive microparticles at high throughput is a challenge. For this purpose, we developed a sheath flow assisted dielectrophoretic (DEP) field-flow separator with a tailored arrangement of cylindrical interdigitated electrodes (cIDE) and observed size-dependent trajectories of dispersed particles. Using a voltage input of 200 Veff at a frequency of 200 kHz, polystyrene particles (45, 25, and 11 µm in diameter) levitated to different heights along the channel length due to a negative DEP force. Experimental observations agree well with simulated particle trajectories that were obtained by a modified Lagrangian particle tracking model in combination with Laplace's and Navier–Stokes equations. By exploiting the size-dependent levitation height difference the desired particle size fraction can be collected at a specific channel length. The required channel length of the proposed cIDE separator increases with decreasing particle size to be separated. The quality of theoretical fractionation, which we quantify by resolution, improves strongly with reduced collector width, reduced volume flow rate and increased voltage input. The sensitivity of these dependencies increases with decreasing particle size. We calculated a theoretical throughput of up to 47 mL min−1 when trading-off design and operation parameters, allowing for contact-free fractionation of sensitive microparticles with negligible shear stress.Wissenschaftlicher ArtikelBand:153148 111 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Effects of pyrolytic biochar on soil properties, Collembola, mites and seed performance(2025-01-16); ; Abstract: Worldwide soils are degrading, reducing the suitable habitat for soil organisms. The loss of soil biodiversity in response adversely affects soil ecosystem functions and services which humans depend on. Pyrolytic biochar is produced by pyrolysis under oxygen-limited conditions, thereby converting biomass into a more degradation-resistant carbon. Its application to soils is intended to support environmental and soil management, while mitigating climate change through carbon sequestration. The present dissertation investigated the effects of a bio-activated, wood-based, pyrolytic biochar (BCa) on soil properties, soil mesofauna and early seed performance of plants. Therefore, I conducted one field experiment and three in the laboratory using soil and mesofauna from the fiele experiment test area (a temperate grassland in Germany). Key aspects and findings of this thesis – that mesofauna are an abundant and essential part of soil ecosystems, that they can affect soil properties and seed performance (e.g., increase the seed germination rate), that they can be affected by BCa, but themselves can also influence the effects of BCa (although their influence may depend on other factors such as soil moisture, plant species or the soil additive) - suggest a high relevance of the effects observed in this thesis for grassland ecosystems where BCa is applied, with consequences from the species level up to the community level. This thesis has also shown that the characteristics of the observed effects (presence, magnitude, direction) may depend on several other factors, that there is a potential for beneficial effects, but also for detrimental effects, and that effects of BCa on Collembola can change from positive to negative over time. Zusammenfassung: Weltweit verschlechtert sich Bodenzustand, wodurch der für Bodenorganismen geeignete Lebensraum abnimmt. Der damit einhergehende Verlust der biologischen Vielfalt im Boden beeinträchtigt die Ökosystemfunktionen und -leistungen des Bodens, auf welche der Mensch angewiesen ist. Pyrolytische Pflanzenkohle wird unter Sauerstoff-limitierten Bedingungen durch Pyrolyse hergestellt, wobei Biomasse in einen abbauresistenteren Kohlenstoff umgewandelt wird. Ihre Anwendung im Boden soll das Umwelt- und Bodenmanagement unterstützen und zugleich den Klimawandel durch die Bindung von Kohlenstoff im Boden abschwächen. Die vorliegende Dissertation untersuchte die Effekte einer bio-aktivierten, holz-basierten, pyrolytischen Pflanzenkohle (BCa) auf Bodeneigenschaften, Bodenmesofauna und die Keimlingsentwicklung von Pflanzen. Hierzu führte ich ein Experiment im Feld und drei im Labor durch, mit dem Boden und der Mesofauna von dem Standort des Feldversuches (ein gemäßigtes Grünland in Deutschland). Wichtige Aspekte und Erkenntnisse dieser Dissertation - dass die Mesofauna ein häufiger und wesentlicher Bestandteil von Bodenökosystemen ist, dass sie die Bodeneigenschaften und die Keimlingsentwicklung beeinflussen kann (z.B. Anstieg der Keimungsrate), dass sie zwar von BCa beeinflusst wird, aber auch selbst die Auswirkungen von BCa beeinflussen kann (wobei ihr Einfluss von anderen Faktoren wie Bodenfeuchtigkeit, Pflanzenart oder dem Bodenhilfsstoff abhängen kann) - deuten auf eine hohe Relevanz der in dieser Arbeit beobachteten Effekte für Grünlandökosysteme hin, in denen BCa eingesetzt wird; mit Konsequenzen von der Art- bis hin zur Gemeinschaftsebene. Diese Arbeit hat außerdem gezeigt, dass die Charakteristika der beobachteten Effekte (deren Vorhandensein, Größenordnung, Richtung) von mehreren anderen Faktoren abhängen können, dass es ein Potenzial für positive, aber auch für schädliche Wirkungen gibt und dass sich die Effekte von BCa auf Collembolen mit der Zeit von positiv zu negativ verändern können.Dissertation31 45 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Analysis of the diodic effect of flows of rarefied gases in tapered rectangular channelsPressure driven flows of rarefied single gases through long tapered rectangular channels are studied computationally. A part of the results is compared to the available experimental data. The flow is modeled by the linearized Bhatnagar-Gross-Krook kinetic equation. The mass flow rate and the distributions of the pressure and the rarefaction parameter are deduced. Calculations are performed in the whole range of the gaseous rarefaction. The diodicity has a maximum at intermediate values of the Knudsen number and increases with large to small cross section ratio. The diodic effect is explained phenomenologically. The pressure profile depends on the flow direction and varies strongly near the small height. The mass flow rates of CO2, N2 and Ar gases in a mini/microchannel at moderate rarefactions are compared to the numerical results. An end-correction to the numerical calculation is applied. A relatively good agreement is found between the computational and experimental flow rates. The agreement is improved if the end-correction is used. The experimental diodicity is reproduced well with the numerical simulation. The results presented in the paper might be useful for the development and optimal design of pumping systems based on the diode effect.Wissenschaftlicher Artikel102 115 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Implementation of parcel method for surface reactions in DSMC(Elsevier, 2019-05-06); ; ; ; The parcel concept in Direct Simulation Monte Carlo method has been added to the reaction algorithm to the DSMC solver in OpenFOAM to reduce computational demand. Parcel per cell is checked for different cell sizes and different parcel sizes to obtain the right cell size for a given system. At this cell size, diffusion of CO in O2 is simulated in a porous structure to ascertain the feasibility of this concept. After adding adsorption and reaction models, concentration profiles are obtained for different temperatures and different time steps. These profiles are compared with the single molecule algorithm written by Pesch et al. [14]. The local surface coverages and reaction rates are evaluated at a parcel size ranging from 10 to 100 to further validate the new approach. Computational time demand reduces by half at maximum parcel size to reach similar steady state results as that of the single molecule approach.Wissenschaftlicher ArtikelBand:187135 107 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, The influence of the functional group density on gas flow and selectivity: Nanoscale interactions in alkyl-functionalized mesoporous membranesMesoporous inorganic structures with mean pore diameters of 26 nm are prepared by extrusion based on a yttria stabilized zirconia nanopowder. The sintered capillary membranes serve as model structures to investigate the influence of an alkyl-chain (C16) surface functionalization on the gas diffusion kinetics of argon (Ar), nitrogen (N2) and carbon dioxide (CO2) in mesopores. The density of the C16 alkyl-chains immobilized on the membrane surface has an effect on both, gas flow as well as gas selectivity. For low functional group densities (<4 groups nm−2), the gas flow is reduced without having an effect on the selectivity. In contrast, for high alkyl-chain densities (>4 groups nm−2) the mean distance between the C16-chains is reduced to the order of magnitude of the gas molecules leading to a reduction in gas flow and a significant change of the gas selectivity. The selectivity is found to be influenced depending on the molecular diameter of the gas species, being more evident for CO2 compared to Ar and N2, suggesting a separation mechanism more comparable to molecular sieving than to surface diffusion.Wissenschaftlicher ArtikelBand:237145 129