Bartels, Julia
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Item-typ:Veröffentlichung, Effect of divalent versus monovalent cations on the MS2 retention capacity of amino-functionalized ceramic filters(Royal Society of Chemistry, 2018-04-10); ; ; ; Ceramic capillary membranes conditioned for virus filtration via functionalization with n-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA) are analyzed with respect to their virus retention capacity when using feed solutions based on monovalent and divalent salts (NaCl, MgCl2). The log reduction value (LRV) by operating in dead-end mode using the model bacteriophage MS2 with a diameter of 25 nm and an IEP of 3.9 is as high as 9.6 when using feeds containing MgCl2. In contrast, a lesser LRV of 6.4 is observed for feed solutions based on NaCl. The TPDA functionalized surface is simulated at the atomistic scale using explicit-solvent molecular dynamics in the presence of either Na+ or Mg2+ ions. Computational prediction of the binding free energy reveals that the Mg2+ ions remain preferentially adsorbed at the surface, whereas Na+ ions form a weakly bound dissolved ionic layer. The charge shielding between surface and amino groups by the adsorbed Mg2+ ions leads to an upright orientation of the TPDA molecules as opposed to a more tilted orientation in the presence of Na+ ions. The resulting better accessibility of the TPDA molecules is very likely responsible for the enhanced virus retention capacity using a feed solution with Mg2+ ions.Wissenschaftlicher ArtikelBand:20Heft:16121 100 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Hydrophobic ceramic capillary membranes for versatile virus filtration(Elsevier, 2018-10-23); ; ; ; In this study, we present hydrophobic yttria-stabilized zirconia capillary membranes conditioned for virus filtration. These macroporous ceramic filters (d50 = 150 nm) efficiently extract viruses regardJess of their surface charge with high throughput rates. For hydrophobic functionalization of the ceramic membranes we used two different silanes, n-hexyltriethoxysilane (HTS, C6-chain) and n-octyltriethoxysilane (OTS, C8-chain), in three different molarities. The virus retention of the membranes is tested in dead-end mode by intracapillary virus feeding using two small bacteriophages as model species: MS2 and PhiX174. Virus retention increases most strongly for hydrophobic capillaries functionalized with 0.05 M OTS, showing a virtually complete retention with log-reduction values (LRVs) of - 9 for both bacteriophages compared to the non-functionalized membrane with LRVs of 0.3 ± 0.1 for MS2 and 3.4 ± 0.2 for PhiXl 74. The functionalized membranes allow a high membrane flux of - 150 L/(m2hbar), with throughput rates up to - 400 L/(m2 h) while maintaining high filtration efficiency. Even under varying feed conditions using only mono- or divalent salt ions or pH values ranging from 3 to 9, retention capacities of the capillary membranes are high. Accordingly, such hydrophobic ceramic membranes offer a versatile alternative to conventional polymeric membranes for virus removal with greatly improved membrane flux.Wissenschaftlicher ArtikelBand:570-571120 166 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Vibrational Spectroscopy as a Promising Toolbox for Analyzing Functionalized Ceramic MembranesCeramic materials find use in many fields including the life sciences and environmental engineering. For example, ceramic membranes have shown to be promising filters for water treatment and virus retention. The analysis of such materials, however, remains challenging. In the present study, the potential of three vibrational spectroscopic methods for characterizing functionalized ceramic membranes for water treatment is evaluated. For this purpose, Raman scattering, infrared (IR) absorption, and solvent infrared spectroscopy (SIRS) were employed. The data were analyzed with respect to spectral changes as well as using principal component analysis (PCA). The Raman spectra allow an unambiguous discrimination of the sample types. The IR spectra do not change systematically with functionalization state of the material. Solvent infrared spectroscopy allows a systematic distinction and enables studying the molecular interactions between the membrane surface and the solvent.Wissenschaftlicher ArtikelBand:72Heft:6110 112 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Porous ceramics with tailored pore size and morphology as substrates for coral larval settlement(Elsevier, 2018-08-07); ; ; ; The growing demand for stony corals as ornamental aquarium animals requires defined aquacultural breeding strategies. For the sexual propagation of corals, material substrates are needed, that attract larvae and support their settlement and development. In this study, five types of highly porous ceramic materials were developed following the example of coral skeleton. The applicability of these settlement substrates was tested using larvae of the stony coral Pocillopora damicornis. Partial sintering of pressed clay pellets, freeze casting of clay and alumina-mullite based slurries and direct foaming of high alkane phase emulsified suspensions (HAPES) using alumina were employed. By the addition of mm-sized spherical polystyrene beads as sacrificial templates during freeze casting (alumina-mullite), superficial pores in the size of the larvae were created. The inorganic substrates featured open porosities between 35% (pressed clay) and 83% (foamed alumina), pore sizes ranging from nm to mm-scale and pore morphologies dominated by interparticle porosity (pressed), lamellar pores (freeze casting) and cellular pore types (direct foaming). The ceramic substrates were incubated in artificial sea water for 3 months to induce necessary biofilm formation and algae growth. Afterwards, individual substrates were exposed to 5 coral larvae, and their settlement behavior was monitored over 14 days. At the end of this period, all ceramic materials were successfully accepted as settlement substrates, with a mean settlement rate of 46.2%, and no significant differences between the substrate types. On samples with large surface superficial pores, a significantly reduced survival of settled larvae (79%) compared to the other porous materials (93–98%) was determined, suggesting a non-ideal surface topography. While alumina foam samples (HAPES) exhibit the most promising results in terms of settlement and survival of larvae, clay-based substrates provide a more economic solution for the sexual propagation of corals in aquaculture.Wissenschaftlicher ArtikelBand:44Heft:14121 172 - 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:217122 119 - Some of the metrics are blocked by yourconsent settings
Item-typ:Veröffentlichung, Ceramic capillary membranes with tailored pore sizes and functionalizations for virus retention(2020-02-19); ; ; The aim of this work is the design of a versatile and effective virus filtration system based on ceramic which offers both high membrane throughput rates and high retention capacities for a wide variety of viruses. For this purpose, an extrusion process based on yttria stabilized zirconia (YSZ) powders with particle sizes of 30 nm, 40 nm or 90 nm is implemented to shape tubular membranes. After sintering at 1050 °C for 2 h a defect-free homogenous structure with open porosities of around 50 % is achieved. By increasing the initial YSZ particle size, increased average membrane pore sizes ranging from 24 nm to 146 nm are obtained. A high membrane pore size leads to reduced virus retention capacities in combination with increased water permeate fluxes. Capillaries made of YSZ-40nm are promising candidates as they fulfill the virus filter criterion of 4 log reduction values (LRVs) required by the World Health Organization in combination with a membrane flux of ~30 L/(m2hbar). Capillaries made of YSZ-90nm do not fulfill the virus filter criterion due to their average pore size of ~150 nm. However, they show a membrane flux of ~150 L/(m2hbar) and can therefore be used for high flux filtration applications, if an adequate adsorption capacity for viruses by a membrane surface functionalization is provided. Therefore, a straightforward chemical functionalization strategy using aminosilanes with one, two or three amino groups per silane molecule, namely 3-aminopropyltriethoxysilane (APTES), N-(2-aminoethyl)-3-aminopropyltriethoxysilane (AE-APTES) and n-(3-trimethoxysilylpropyl)diethylenetriamine (TPDA), is used. The zeta-potential of the membrane surface is converted from negative to positive. Therefore, the virus retention capacity for the model virus MS2 (diameter = 25 nm, isoelectric point (IEP) = 3.9) is significantly increased for neutral feed solutions based on monovalent and divalent salts (NaCl, MgCl2) from a LRV of <0.3 for non-functionalized membranes to LRVs of up to 9.6 ± 0.3 for the TPDA functionalized capillaries due to electrostatic interactions. A lower LRV of 6.4 is observed for feed solutions which are based on only monovalent ions (NaCl). Therefore, the TPDA functionalized surface is simulated at the atomistic scale using explicit-solvent molecular dynamics in the presence of either Na+ or Mg2+ ions. This shows that the binding free energy reveals that the Mg2+ ions remain adsorbed to the membrane surface, whereas Na+ ions form only a weakly bound with the surface. Due to the adsorbed Mg2+ ions an upright orientation of the TPDA molecules and opposed to that a more tilted orientation in the presence of Na+ ions is found. Therefore, a better accessibility of the TPDA molecules for the viruses and thus a better virus retention capacity is found when using feed solutions based on Mg2+ ions. The retention capacity for the model virus PhiX174 (diameter = 26 nm, IEP = 6.2) viruses cannot be increased by TPDA functionalized membranes due to the repulsion between the positively charged bacteriophages and the positively charged pore wall surfaces at a neutral pH. Therefore, a hydrophobic functionalization of the ceramic membranes with silanes offering carbon chains is performed. Virus retention increases most strongly for capillaries functionalized with C8-chains (n-octyltriethoxysilane, OTS), showing LRVs of ~9 for both viruses (MS2 and PhiX174) with throughput rates of up to ~400 L/(m²h) even under varying feed conditions. Accordingly, such hydrophobic ceramic membranes are a versatile alternative to conventional polymeric membranes for virus retention applications.Dissertation282 300