Zentrum für Umweltforschung und nachhaltige Technologien (UFT)
Lade...
Country
DE
City
Bremen
32 Ergebnisse
Filter
Einstellungen
Gerade angezeigt 1 - 10 von 32
- Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Assessing the Impacts of Cu(OH)2 Nanopesticide and Ionic Copper on the Soil Enzyme Activity and Bacterial Community(American Chemical Society, 2020-02-28)16 23 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, A comparative experimental study on the deviation of the ideal selectivity in HDTMS-functionalized and untreated ceramic structures with pores in the upper mesoporous range(Elsevier, 2015-07-15); ; ; ; Mesoporous ceramic capillary membranes with mean pore sizes of about 20 nm are prepared as model structures to investigate the influence of an altered surface chemistry on the flow behavior of gases. To modify the membrane surface, a wet chemical silanization process with hexadecyltrimethoxysilane (HDTMS) is used to gain an alkyl-functionalized surface. Structural and surface characterizations show that the surface chemistry is altered without affecting the mean pore diameter. For the non-functionalized membrane, single gas permeation measurements at 20 °C reveal ideal permselectivities which are in good agreement with the Knudsen theory. In contrast, the HDTMS-functionalized membrane shows permselectivities regarding carbon dioxide (CO2) which deviate about 20% from Knudsen theory. The gas permeation measurements further indicate a relative flow enhancement for CO2 in comparison to nitrogen (N2), argon (Ar) and methane (CH4). Adsorption and desorption isotherms of CO2 and N2 at 20 °C show a decreased specific adsorption capacity for both gases, while the adsorption selectivity for CO2/N2 is increased. This indicates a weaker interaction of gas molecules and membrane surface due to HDTMS functionalization. This weaker gas–solid interaction along with the increased adsorption selectivity is proposed as reason for the experimentally observed deviation of the permselectivities from Knudsen theory.Wissenschaftlicher ArtikelBand:217124 123 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Diffusion weighted magnetic resonance imaging for temperature measurements in catalyst supports with an axial gas flow(Royal Society of Chemistry, 2019-07-24); ; ; In situ thermometry of catalytic gas phase reactions allows the determination of temperature profiles in catalyst beds. In NMR imaging systems used for measuring the chemical composition of species in model reactors, temperature measurements by NMR spectroscopy are technically challenging and confined to a rather low temperature range. In this study, an optimized NMR in situ technique is proposed, which will allow the determination of the temperature distribution in highly exothermic reactions on structured catalysts. Diffusion weighted magnetic resonance imaging (DW-MRI) was successfully applied as an alternative method for temperature measurements commonly performed by chemical shift measurements using ethylene glycol. DW-MRI applied with different diffusion sensitizing gradients allows high-resolution imaging of the temperature dependent diffusion coefficient, without the need for high spatial homogeneity of the magnetic field. Using 3D DW-MRI on ethylene glycol, glycerol, and the temperature stable ionic liquid Pyr13 [TFSI] (decomposition temperature of 400 °C) as NMR thermometers, measurements were performed in a temperature range from 20 to 160 °C. The proposed method can be used in reaction engineering approaches performed in NMR systems.Wissenschaftlicher ArtikelBand:4109 138 - 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, 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, Multicomponent gas diffusion in nonuniform tubesIn many technical processes gas, multicomponent diffusion takes place in confinements that are rarely uniform in direction of their long axis (e.g., catalysts pores). Here, we show that in conical tubes multicomponent diffusion is hindered. This effect increases with ratio of inlet to outlet cone radius Λ, indifferent of the orientation of the tube. Based on the Maxwell–Stefan equations, predictive analytical solution for ideal multicomponent diffusion in slightly tapered ducts is developed. In two-bulb diffusion experiments on a uniform tube, the results of Duncan and Toor (1962) were reproduced. Comparison of model and experiment shows that the solution presented here provides a reliable quantitative prediction of the temporal change of H2, N2, and CO2-concentration for both tube geometries, uniform and slightly conical. In the demonstrated case (Λ = 3.16), mass diffusion is 68% delayed. Thus, for gaseous diffusion in “real,” typically tapered pores the transport limitation is more serious than considered so far. © 2014 American Institute of Chemical Engineers AIChE J, 61: 1404–1412, 2015Wissenschaftlicher ArtikelBand:61Heft:481 145 - 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, Chitosan supraparticles with fluorescent silica nanoparticle shells and nanodiamond-loaded cores(2017-02-06); ; ; ; Spherical colloidal structures with a sparsely or densely packed shell of nanoparticles have been the subject of intense research efforts for more than a decade. Research has focused on the utilization of aqueous, soft, or solid cores mainly on the micron-scale. A synthesis route that combines a stabilizing biopolymer core in combination with small (15 nm) or ultrasmall (5 nm) nanoparticles templated on the surface is still missing and pivotal to push these structures further into bionanotechnological applications. Here, we present core-shell supraparticles with a nanodiamond-loaded chitosan core and a shell assembled from fluorescent silica nanoparticles with controlled packing density which feature final sizes significantly below one micrometer. The synthesis route is highly versatile and represents a general approach for the synthesis of sophisticated supraparticles with shells formed from distinct nanoparticle shells and biopolymer cores loaded with selective nanoparticles.Wissenschaftlicher ArtikelBand:5Heft:8119 108 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, A physical explanation of the gas flow diode effectGas flow properties in channels with slightly varying cross section have a dependency on the direction of channel perfusion when the gas is in the slip and transitional flow regimes. In the past, it was observed that the flow rate in converging direction is higher compared to the case where the channel diverges alongside. This gas flow diode effect does neither exist in the continuum regime nor in the free molecular regime, and it has its maximum at the same level of gaseous rarefaction as the well-known Knudsen minimum. However, no comprehensive study on the physics of this diode effect is carried out yet. In order to overcome this knowledge gap, the current paper proceeds our previous works by an appropriate experimental study. Here we can show that the diode effect crucially depends on the proportion of inclined walls to the overall channel inner surface. Also the inclination of the wall itself determines the strength of the diode effect meaning that the diodicity increases with the opening angle. Furthermore, we found indication that the diodicity also depends on the molar mass and the internal structure of the impinging gas molecules. Finally, we propose an explanation of the diode effect that is mainly based on the tangential reflection process of gas molecules colliding with the inclined walls of a tapered channel.Wissenschaftlicher Artikel112 146 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Transient Au–CO Complexes Promote the Activity of an Inverse Ceria/Gold Catalyst: An Insight from Ab Initio Molecular DynamicsTo probe particle–support interactions and their mechanistic role for catalytic CO oxidation on nanoporous gold (np-Au) coated with ceria nanoparticles, we carried out ab initio molecular dynamics (AIMD) simulations and standard density functional theory (static DFT) computations. To this end, we studied ceria clusters (Ce10O20/19) supported on a Au(321) surface exhibiting a high density of steps and kinks. Our theoretical model represents the structurally inverse situation compared to more commonly studied ceria-supported Au nanoparticle systems. In agreement with previous results for Au(111), we find that reduced (Ce10O19) as well as stoichiometric (Ce10O20) ceria nanoparticles transfer electrons to the Au(321) support. This charge transfer (particularly strong in the case of Ce10O19) reflecting a strong chemical interaction between ceria and Au is probably responsible for the stabilization of np-Au against thermal coarsening experimentally observed upon deposition of oxide nanoparticles. The adsorption energies of the ceria cluster on Au(321) are more negative than on the Au(111) surface by around ∼0.5 eV. AIMD simulations were employed to study the mechanism of catalytic CO oxidation with O2 for the ceria/Au(321) system. We found that a CO molecule adsorbed near the ceria/gold perimeter interface can extract a Au atom from the surface in the form of a mobile linear Au–CO complex, which results in a very low activation energy when this species reacts with lattice O to CO2. The released bare Au adatom subsequently attaches to a step edge of the gold surface, leading to a dynamic restructuring of the Au support. Next, an activated O2 molecule adsorbed at a perimeter site between ceria and Au reacts with a second CO molecule to CO2 and an adsorbed O atom, which eventually fills the vacancy site created in the first half of the cycle. As compared to ceria particles supported on Au(111), the reactivity is enhanced as a new low-energy mechanism is enabled, revealing the positive impact of the stepped structure of Au(321).Wissenschaftlicher ArtikelBand:125Heft:4848 48