24 results on '"Ulrike, Kunz"'
Search Results
2. Catalytic recycling of medical plastic wastes over La0.6Ca0.4Co1–Fe O3− pre-catalysts for co-production of H2 and high-value added carbon nanomaterials
- Author
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Xiao Yu, Guoxing Chen, Marc Widenmeyer, Isabel Kinski, Xingmin Liu, Ulrike Kunz, Dominique Schüpfer, Leopoldo Molina-Luna, Xin Tu, Gert Homm, and Anke Weidenkaff
- Subjects
Process Chemistry and Technology ,Catalysis ,General Environmental Science - Published
- 2023
3. Layer-selective functionalisation in mesoporous double layer via iniferter initiated polymerisation for nanoscale step gradient formation
- Author
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Annette Andrieu-Brunsen, Ulrike Kunz, and Mathias Stanzel
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Double layer (biology) ,chemistry.chemical_classification ,Materials science ,Polymers and Plastics ,Organic Chemistry ,General Physics and Astronomy ,Ionic bonding ,Polymer ,Mesoporous silica ,Nanopore ,chemistry ,Chemical engineering ,Materials Chemistry ,Thin film ,Mesoporous material ,Layer (electronics) - Abstract
Functionalisation of technological nanopores and investigation of their transport properties have attracted considerable interest from scientific as from technological point of view, among others due to their potential regarding molecular transport design. Asymmetric design of nanopore structure and functionalisation is expected to trigger increased and directed transport of ionic species. Based on this motivation, we demonstrate a layer-selective polymer functionalisation in a mesoporous double layer thin film to generate nanoscale step gradient architectures with asymmetric charge distribution by taking advantage of co-condensation and polymer modification techniques. Thereby, mesoporous silica and co-condensed mesoporous amino silica thin films are combined to double layered films with a film thickness of 300 – 400 nm in both sequential arrangements, respectively. Iniferter initiated polymerisation is used to selectively functionalise only the amino silica layer with polymers such as poly(2-(methacryloyloxy)ethyltrimethylammonium chloride) (PMETAC) in a grafting from approach. Investigation of the ionic pore accessibility of the mesoporous double layered films before and after layer-selective polymer functionalisation shows that the ionic pore accessibility is dominated by the bottom layer when overcoming the electrostatic repulsion of the top layer.
- Published
- 2023
- Full Text
- View/download PDF
4. 3D NiCo-Layered double Hydroxide@Ni nanotube networks as integrated free-standing electrodes for nonenzymatic glucose sensing
- Author
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Falk Muench, Ulrike Kunz, Khaled M. Amin, and Wolfgang Ensinger
- Subjects
Nanotube ,Materials science ,Layered double hydroxides ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Catalysis ,Biomaterials ,chemistry.chemical_compound ,Nickel ,Colloid and Surface Chemistry ,chemistry ,Electrode ,engineering ,Hydroxide ,0210 nano-technology ,Layer (electronics) ,Cobalt - Abstract
Nickel cobalt layered double hydroxide (NiCo-LDH)-based materials have recently emerged as catalysts for important electrochemical applications. However, they frequently suffer from low electrical conductivity and agglomeration, which in turn impairs their performance. Herein, we present a catalyst design based on integrated, self-supported nickel nanotube networks (Ni-NTNWs) loaded with NiCo-LDH nanosheets, which represents a binder-free, hierarchically nanostructured electrode architecture combining continuous conduction paths and openly accessible macropores of low tortuosity with an ultrahigh density of active sites. Similar to macroscale metallic foams, the NTNWs serve as three-dimensionally interconnected, robust frameworks for the deposition of active material, but are structured in the submicron range. Our synthesis is solely based on scalable approaches, namely templating with commercial track-etched membranes, electroless plating, and electrodeposition. Morphological and compositional characterization proved the successful decoration of the inner and outer nanotube surfaces with a conformal NiCo-LDH layer. Ni-NTNW electrodes and hydroxide-decorated variants showed excellent performance in glucose sensing. The highest activity was achieved for the catalyst augmented with NiCo-LDH nanosheets, which surpassed the modification with pure Ni(OH)2. Despite its low thickness of 20 µm, the optimized catalyst layer provided an outstanding sensitivity of 4.6 mA mM−1 cm−2, a low detection limit of 0.2 µM, a fast response time of 5.3 s, high selectivity and stability, and two linear ranges covering four orders of magnitude, up to 2.5 mM analyte. As such, derivatized interconnected metal nano-networks represent a promising design paradigm for highly miniaturized yet effective catalyst electrodes and electrochemical sensors.
- Published
- 2021
5. Electroless Nanoplating of Iridium: Template‐Assisted Nanotube Deposition for the Continuous Flow Reduction of 4‐Nitrophenol
- Author
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Falk Muench, Tim Hellmann, Jan P. Hofmann, Wolfgang Ensinger, Ulrike Kunz, and Martin Christoph Scheuerlein
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Nanotube ,Materials science ,Nanostructure ,chemistry.chemical_element ,engineering.material ,Borohydride ,Catalysis ,chemistry.chemical_compound ,chemistry ,Coating ,Chemical engineering ,Plating ,Electrochemistry ,engineering ,Methyl orange ,Iridium ,Microreactor - Abstract
Electroless plating is a powerful tool in nanofabrication and is available for many of the noble transition metals. There is, however, a striking lack of electroless plating procedures for the rarer platinum-group metals. In this work, two plating baths for nanoscale iridium coatings are developed and their conformality and nanofabrication potential are showcased by coating ion-track-etched polycarbonate membranes, creating Ir nanotubes in the process. Both plating solutions yield morphologically different deposits, indicating that the microstructure of the film can be tuned by adjusting the composition of the plating bath. The catalytic performance of the deposited materials is investigated by using membrane-embedded nanotubes as catalysts for the reduction of 4-nitrophenol and methyl orange by borohydride, showing remarkable activity and stability. Operation in flow-through configuration, in which the metallized membrane is implemented as a microreactor greatly enhances the interaction with the catalyst surface, considerably increasing product yield. The results highlight the potential of Ir nanoplating for realizing sophisticated nanostructures and heterogeneous catalysts, but also illustrate the intricacies related to the complex chemistry of electroless Ir plating baths.
- Published
- 2020
6. Insights into the interplay of wetting and transport in mesoporous silica films
- Author
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Annette Andrieu-Brunsen, Adnan Khalil, Matthias Zimmermann, Peter Stephan, Robert W. Stark, Steffen Hardt, Ulrike Kunz, Hans-Joachim Kleebe, and Alena K. Bell
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Materials science ,Condensation ,Nucleation ,Ionic bonding ,02 engineering and technology ,Mesoporous silica ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Biomaterials ,Nanopore ,Colloid and Surface Chemistry ,Chemical engineering ,Boiling ,Wetting ,0210 nano-technology ,Mesoporous material - Abstract
The understanding and design of wetting-transport and wetting-charge-transport interplay in nanometer-sized pores is a still not fully understood key step in improving nanopore transport-related applications. A control of mesopore wettability accompanied by pore filling and ionic mesopore accessibility analysis is expected to deliver major insights into this interplay of nanoscale pore wetting and transport. For a systematic understanding, we demonstrate a gradual adjustment of nanopore ionic accessibility by gradually tuning silica nanopore wettability using chemical vapor phase deposition of 1H,1H,2H,2H-perfluorooctyl dimethylchlorosilane. The mutual influence of wetting on liquid imbibition, condensation, and molecular transport as well as on heat transfer were studied by ellipsometry, cyclic voltammetry and boiling experiments, respectively. A multi-methodical analytic approach was used to directly couple wetting properties of mesoporous silica thin films to ionic mesopore accessibility allowing us to determine two different ion transport mechanisms based on three defined wetting regimes as well as a threshold hydrophobicity suppressing pore accessibility. Furthermore, boiling experiments showed a clear increase in nucleation site density upon changing the wettability of the mesoporous surfaces from hydrophilic to hydrophobic. Hence, these results provide insights into the complex interplay of pore wall functionalization, wetting, and charge-dependent nanopore properties.
- Published
- 2022
- Full Text
- View/download PDF
7. Electroless Nanoplating of Pd−Pt Alloy Nanotube Networks: Catalysts with Full Compositional Control for the Methanol Oxidation Reaction
- Author
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Ulrike Kunz, Markus Antoni, Falk Muench, Christian Lohaus, Oliver Clemens, Andreas Klein, Angelina Fischer, Stephan Wollstadt, Tobias Stohr, and Wolfgang Ensinger
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chemistry.chemical_classification ,Nanotube ,Materials science ,Nanostructure ,Alloy ,Polymer ,engineering.material ,Catalysis ,Nanomaterials ,Metal ,Chemical engineering ,chemistry ,visual_art ,Plating ,Electrochemistry ,visual_art.visual_art_medium ,engineering - Abstract
Due to its simplicity, flexibility and conformity, electroless plating presents itself as an attractive route towards functional metal nanostructures. Despite the importance for creating multimetallic materials with enhanced properties, the complex interactions between the components in electroless plating baths make alloy formations a challenging objective. In this work, we outline an electroless plating strategy fabricating Pd−Pt alloy nanomaterials, which is based on arbitrarily miscible plating baths for the individual metals. To demonstrate the excellent nanoscale conformity and homogeneity of our plating system, we apply it to ion track‐etched polymer templates with large inner surfaces as ambitious substrates, resulting in the formation of 3D free‐standing PdₓPt₁₀₀₋ₓ‐nanotube‐networks (NTNWs). Based on the electro‐oxidation of methanol as a model reaction, we utilize the compositional freedom provided by our syntheses for optimizing the catalytic performance of our metal NTNWs, which heavily depends on the Pd−Pt ratio. Within our system, the highest surface normalized activity was found for the Pd₂₀Pt₈₀ NTNW, reaching more than a two‐fold increase of the peak current density in comparison to pure Pt. Overall, our reaction system provides a versatile toolkit for fabricating intricate Pd−Pt nanostructures of arbitrary elemental composition, and constitutes a starting point for designing new electroless alloy plating baths.
- Published
- 2022
8. Simultaneous Nanolocal Polymer and
- Author
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Mathias, Stanzel, Lucy, Zhao, Reza, Mohammadi, Raheleh, Pardehkhorram, Ulrike, Kunz, Nicolas, Vogel, and Annette, Andrieu-Brunsen
- Subjects
Article - Abstract
Bioinspired solid-state nanopores and nanochannels have attracted interest in the last two decades, as they are envisioned to advance future sensing, energy conversion, and separation concepts. Although much effort has been made regarding functionalization of these materials, multifunctionality and accurate positioning of functionalities with nanoscale precision still remain challenging. However, this precision is necessary to meet transport performance and complexity of natural pores in living systems, which are often based on nonequilibrium states and compartmentalization. In this work, a nanolocal functionalization and simultaneous localized sensing strategy inside a filtering mesoporous film using precisely placed plasmonic metal nanoparticles inside mesoporous films with pore accessibility control is demonstrated. A single layer of gold nanoparticles is incorporated into mesoporous thin films with precise spatial control along the nanoscale layer thickness. The local surface plasmon resonance is applied to induce a photopolymerization leading to a nanoscopic polymer shell around the particles and thus nanolocal polymer placement inside the mesoporous material. As near-field modes are sensitive to the dielectric properties of their surrounding, the in situ sensing capability is demonstrated using UV–vis spectroscopy. It is demonstrated that the sensing sensitivity only slightly decreases upon functionalization. The presented nanolocal placement of responsive functional polymers into nanopores offers a simultaneous filtering and nanoscopic readout function. Such a nanoscale local control is envisioned to have a strong impact onto the development of new transport and sensor concepts, especially as the system can be developed into higher complexity using different metal nanoparticles and additional design of mesoporous film filtering properties.
- Published
- 2021
9. Simultaneous Nanolocal Polymer and In Situ Readout Unit Placement in Mesoporous Separation Layers
- Author
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Raheleh Pardehkhorram, Annette Andrieu-Brunsen, Nicolas Vogel, Ulrike Kunz, Mathias Stanzel, Lucy Zhao, and Reza Mohammadi
- Subjects
Chemistry ,010401 analytical chemistry ,Nanotechnology ,010402 general chemistry ,01 natural sciences ,0104 chemical sciences ,Analytical Chemistry ,Nanopore ,Surface modification ,Surface plasmon resonance ,Thin film ,Functional polymers ,Mesoporous material ,Nanoscopic scale ,Plasmon - Abstract
Bioinspired solid-state nanopores and nanochannels have attracted interest in the last two decades, as they are envisioned to advance future sensing, energy conversion, and separation concepts. Although much effort has been made regarding functionalization of these materials, multifunctionality and accurate positioning of functionalities with nanoscale precision still remain challenging. However, this precision is necessary to meet transport performance and complexity of natural pores in living systems, which are often based on nonequilibrium states and compartmentalization. In this work, a nanolocal functionalization and simultaneous localized sensing strategy inside a filtering mesoporous film using precisely placed plasmonic metal nanoparticles inside mesoporous films with pore accessibility control is demonstrated. A single layer of gold nanoparticles is incorporated into mesoporous thin films with precise spatial control along the nanoscale layer thickness. The local surface plasmon resonance is applied to induce a photopolymerization leading to a nanoscopic polymer shell around the particles and thus nanolocal polymer placement inside the mesoporous material. As near-field modes are sensitive to the dielectric properties of their surrounding, the in situ sensing capability is demonstrated using UV–vis spectroscopy. It is demonstrated that the sensing sensitivity only slightly decreases upon functionalization. The presented nanolocal placement of responsive functional polymers into nanopores offers a simultaneous filtering and nanoscopic readout function. Such a nanoscale local control is envisioned to have a strong impact onto the development of new transport and sensor concepts, especially as the system can be developed into higher complexity using different metal nanoparticles and additional design of mesoporous film filtering properties.
- Published
- 2021
- Full Text
- View/download PDF
10. Electrodeposition of palladium-dotted nickel nanowire networks as a robust self-supported methanol electrooxidation catalyst
- Author
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Prashant Khadke, Wolfgang Ensinger, Tim Boettcher, Falk Muench, Ulrike Kunz, Christina Roth, Matthew T. Mayer, and Sasho Stojkovikj
- Subjects
inorganic chemicals ,Materials science ,Nanowire ,chemistry.chemical_element ,Nanoparticle ,02 engineering and technology ,Electrocatalyst ,Electrochemistry ,Catalysis ,chemistry.chemical_compound ,0502 economics and business ,General Materials Science ,050207 economics ,Mechanical Engineering ,05 social sciences ,021001 nanoscience & nanotechnology ,Nickel ,nanowire networks ,chemistry ,Chemical engineering ,Mechanics of Materials ,electrodeposition ,Chemical Energy Carriers ,methanol electrooxidation catalyst ,Methanol ,0210 nano-technology ,500 Naturwissenschaften und Mathematik::540 Chemie::540 Chemie und zugeordnete Wissenschaften ,Palladium - Abstract
Abstract Mass activity and long-term stability are two major issues in current fuel cell catalyst designs. While supported catalysts normally suffer from poor long-term stability but show high mass activity, unsupported catalysts tend to perform better in the first point while showing deficits in the latter one. In this study, a facile synthesis route towards self-supported metallic electrocatalyst nanoarchitectures with both aspects in mind is outlined. This procedure consists of a palladium seeding step of ion track-etched polymer templates followed by a nickel electrodeposition and template dissolution. With this strategy, free-standing nickel nanowire networks which contain palladium nanoparticles only in their outer surface are obtained. These networks are tested in anodic half-cell measurements for demonstrating their capability of oxidising methanol in alkaline electrolytes. The results from the electrochemical experiments show that this new catalyst is more tolerant towards high methanol concentrations (up to $${5}\,\hbox{mol}\,\hbox{L}^{-1}$$ 5 mol L - 1 ) than a commercial carbon supported palladium nanoparticle catalyst and provides a much better long-term stability during potential cycling. Graphical Abstract
- Published
- 2021
- Full Text
- View/download PDF
11. Electrocatalytic applications of platinum-decorated TiO2 nanotubes prepared by a fully wet-chemical synthesis
- Author
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Markus Antoni, Falk Muench, Joachim Brötz, Wolfgang Ensinger, Wolfgang Donner, and Ulrike Kunz
- Subjects
Materials science ,Mechanical Engineering ,Analytical chemistry ,chemistry.chemical_element ,02 engineering and technology ,Type (model theory) ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Potassium tetrachloroplatinate ,0104 chemical sciences ,Catalysis ,chemistry.chemical_compound ,Crystallinity ,chemistry ,Mechanics of Materials ,General Materials Science ,0210 nano-technology ,Bifunctional ,Platinum ,Chemical bath deposition ,Titanium - Abstract
Pt-decorated $$\hbox {TiO}_{2}$$ nanotubes Pt@TiO2 are prepared only by applying a set of facile wet-chemical redox reactions to ion track-etched polycarbonate templates. First, a homogeneous layer of Pt nanoparticles is deposited onto the complex template surface by reducing potassium tetrachloroplatinate with absorbed dimethylaminoborane. Second, the template is coated with a conformal $$\hbox {TiO}_{2}$$ layer, using a chemical bath deposition reaction based on titanium(III) chloride. After the removal of the template, the rutile-type $$\hbox {TiO}_{2}$$ nanotubes remain decorated with Pt nanoparticles and nanoparticle-clusters on their outside. During the process, neither vacuum techniques nor external current sources or addition of heat are employed. The crystallinity, composition, and morphology of the composite nanotubes are analysed by X-ray diffraction, scanning and transmission electron microscopy as well as by energy-dispersive X-ray spectroscopy. Finally, the obtained materials are examplarily applied in the electrooxidation of ethanol and formic acid, and their performances have been evaluated. Compared to conventional carbon black-supported Pt nanoparticles, the Pt@TiO2 nanotubes show higher reaction rates. Mass activities of 2.36 $$\hbox {A}\hbox { mg}_{\rm Pt}^{-1}\hbox { cm}^{-2}$$ are reached in ethanol oxidation and 7.56 $$\hbox {A}\hbox { mg}_{\rm Pt}^{-1}\hbox { cm}^{-2}$$ in the formic acid oxidation. The present structures are able to exploit the synergy of Pt and $$\hbox {TiO}_{2}$$ with a bifunctional mechanism to result in powerful but easy-to-fabricate catalyst structures. They represent an easily producible type of composite nanostructures which can be applied in various fields such as in catalytics and sensor technology.
- Published
- 2017
12. Fluid Flow Programming in Paper-Derived Silica–Polymer Hybrids
- Author
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Christelle Dubois, Markus Biesalski, Hans-Joachim Kleebe, Annette Andrieu-Brunsen, Nicole Herzog, Eléonor Grange, Christian Rüttiger, Tobias Meckel, Torsten Gutmann, Andreas Geißler, Markus Gallei, and Ulrike Kunz
- Subjects
Grammage ,Capillary action ,Chemistry ,Nanotechnology ,02 engineering and technology ,Surfaces and Interfaces ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,0104 chemical sciences ,visual_art ,Electrochemistry ,visual_art.visual_art_medium ,Fluid dynamics ,Surface modification ,General Materials Science ,Fiber ,Ceramic ,Composite material ,0210 nano-technology ,Porosity ,Mesoporous material ,Spectroscopy - Abstract
In paper-based devices, capillary fluid flow is based on length-scale selective functional control within a hierarchical porous system. The fluid flow can be tuned by altering the paper preparation process, which controls parameters such as the paper grammage. Interestingly, the fiber morphology and nanoporosity are often neglected. In this work, porous voids are incorporated into paper by the combination of dense or mesoporous ceramic silica coatings with hierarchically porous cotton linter paper. Varying the silica coating leads to significant changes in the fluid flow characteristics, up to the complete water exclusion without any further fiber surface hydrophobization, providing new approaches to control fluid flow. Additionally, functionalization with redox-responsive polymers leads to reversible, dynamic gating of fluid flow in these hybrid paper materials, demonstrating the potential of length scale specific, dynamic, and external transport control.
- Published
- 2016
13. Templated synthesis of pure and bimetallic gold/platinum nanotubes using complementary seeding and plating reactions
- Author
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Wolfgang Ensinger, Ingeborg Gärtner, L. Hussein, Hans-Joachim Kleebe, Tobias Stohr, Ulrike Kunz, Sevda Ayata, and Falk Muench
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Nanotube ,Nucleation ,Nanoparticle ,chemistry.chemical_element ,Nanotechnology ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Platinum nanoparticles ,01 natural sciences ,0104 chemical sciences ,Nanomaterials ,Catalysis ,Colloid and Surface Chemistry ,chemistry ,Plating ,0210 nano-technology ,Platinum - Abstract
The application of electroless plating to porous template membranes displays an important route towards one-dimensional metal nanostructures such as nanotubes. For this reaction class, activation pretreatments are required to introduce catalyst seeds, which initiate surface-selective metal deposition from the metastable plating baths. Hitherto, these pretreatments are performed as a means to an end to ensure reliable metal film nucleation, and introduce often undesired contaminations. In this work, we demonstrate that the seeding step can be recognized as a synthetic tool to purposefully adjust the chemical composition of electrolessly plated nanomaterials. By consecutive application of several interfacial reactions (polymer swelling, reducing agent absorption, metal nanoparticle nucleation, autocatalytic metal deposition), we fabricate gold-platinum nanotubes of well-defined composition. Aside strictly monometallic gold and platinum nanotubes, bimetallic nanotubes are produced which consist of platinum nanoparticies embedded in gold walls. As shown in the electrooxidation of formic acid, the nanotube composition has a pronounced impact on the properties of the resulting materials and can be used to enhance the catalyst performance. The outlined strategy provides a versatile route towards sets of compositionally varying metal nanostructures and allows to examine and to exploit multi-element synergies. (C) 2016 Elsevier B.V. All rights reserved.
- Published
- 2016
14. NiCo nanotubes plated on Pd seeds as a designed magnetically recollectable catalyst with high noble metal utilisation
- Author
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Ulrike Kunz, Sandra Schaefer, Wolfgang Ensinger, Joachim Brötz, Falk Muench, I. Gärtner, Markus Antoni, Christian Lohaus, and Eva-Maria Felix
- Subjects
chemistry.chemical_classification ,Materials science ,General Chemical Engineering ,Nucleation ,Nanotechnology ,02 engineering and technology ,General Chemistry ,Polymer ,engineering.material ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Catalysis ,Metal ,Template ,Chemical engineering ,X-ray photoelectron spectroscopy ,chemistry ,visual_art ,engineering ,visual_art.visual_art_medium ,Noble metal ,0210 nano-technology ,Porosity - Abstract
Electroless plating of magnetic materials on catalytically active noble metal seeds is a powerful tool to design highly efficient recyclable catalysts. For the electroless plating procedure of metallic nanotubes in porous polymer templates, a sensitisation and activation process of the template is necessary. Therefore, metallic seeds are created on the surface of the polymer, which then enable the selective heterogeneous nucleation of a metal film on the template's surface. By choosing the metals for seeds and structures wisely, different functional materials can be purposefully combined. In this work magnetically recoverable catalysts were designed, which consist of magnetic NiCo nanotubes as carrier for catalytically active Pd seeds. The synthesised catalyst structures were thoroughly characterised by SEM, TEM, EDX, XRD, XPS, ICP-OES, VSM and then tested in the 4-nitrophenol reduction reaction, which was monitored by UV-Vis spectroscopy. After the reaction the structures were recycled and reused without a decrease in activity.
- Published
- 2016
15. Influence of Nanoconfinement on the pKa of Polyelectrolyte Functionalized Silica Mesopores
- Author
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Hans-Joachim Kleebe, Grit Baier, Ulrike Kunz, Annette Andrieu-Brunsen, Martin Brodrecht, Adnan Khalil, Gerd Buntkowsky, Robert Brilmayer, and Sonja Kübelbeck
- Subjects
chemistry.chemical_classification ,Materials science ,Mechanical Engineering ,Polymer ,Mesoporous silica ,Methacrylate ,Oligomer ,Polyelectrolyte ,chemistry.chemical_compound ,chemistry ,Chemical engineering ,Polymerization ,Mechanics of Materials ,Hybrid material ,Mesoporous material - Abstract
Functionalized ordered mesoporous materials are relevant in technologies, such as drug release, sensing, and separation. To design functionality, the silica framework can be functionalized with responsive molecules or polymers. Often, the pH value in those hybrid materials determines performance. Even though pH/pKa differences between polymers in bulk solutions and nanoscale confinement have been observed, the influence of confinement on pH- and pore filling dependent polyelectrolyte oligomer chain charge has yet not been investigated systematically. Here, mesoporous silica films are functionalized with (2-dimethylamino)ethyl methacrylate) (DMAEMA) and 2-(methacryloyloxy)ethyl phosphate (MEP) oligomers using photoiniferter initiated polymerization. This approach allows a controlled and environmentally friendly mesopore functionalization in water. The obtained oligomer functionalized pores are tunable with respect to pore filling. For both, poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) and poly(2-(methacryloxy)ethyl phosphate) (PMEP), the charge generation inside mesopore confinement is significantly delayed toward harsher pH conditions resulting in pKa shifts of 1���2 pH units. Polymer amount and ionic strength show to further influence the pKa of PDMAEMA in mesopores. The technological importance of the pH value in confinement and its effect on enzyme stabilization is demonstrated. Lipase from Aspergillus oryzae loses its activity upon encapsulation in silica nanoparticles at pH values where the enzyme is stable in bulk solution.
- Published
- 2020
16. Electron microscopy techniques for the analysis of the polymer electrolyte distribution in proton exchange membrane fuel cells
- Author
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Christina Roth, Frieder Scheiba, Nathalie Benker, Ulrike Kunz, and Hartmut Fuess
- Subjects
chemistry.chemical_classification ,Renewable Energy, Sustainability and the Environment ,Scanning electron microscope ,Analytical chemistry ,Energy Engineering and Power Technology ,Proton exchange membrane fuel cell ,Electrolyte ,Polymer ,Conductivity ,Chemical engineering ,chemistry ,Transmission electron microscopy ,Proton transport ,Electrode ,Electrical and Electronic Engineering ,Physical and Theoretical Chemistry - Abstract
The polymer electrolyte distribution in PEMFC electrodes plays an important role for the catalyst utilization and various transport processes in the electrode. Moreover, its influence on the transport processes is not only limited to proton transport but it may also affect gas transport, electron conductivity and water management of the cell. However, experimental techniques to study the polymer electrolyte distribution are scarce. In this paper we present various approaches based on scanning electron microscopy (SEM) and transmission electron microscopy (TEM) to characterize the polymer electrolyte distribution. The methods presented include staining of the polymer electrolyte with heavy metal ions, energy dispersive X-ray (EDX) mapping and energy filtered imaging (EFI). Their use for the analysis of the polymer electrolyte distribution and electrode structure will be presented and current limitations of these techniques will be discussed.
- Published
- 2008
17. A new route towards nanoporous TiO2 as powders or thin films from the thermal treatment of titanium-based hybrid materials
- Author
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Bernard Jousseaume, Christine Labrugère, Thierry Toupance, Odile Babot, Ulrike Kunz, Sana Ahmad, Guy Campet, Joachim Brötz, Institut des Sciences Moléculaires (ISM), Centre National de la Recherche Scientifique (CNRS)-École Nationale Supérieure de Chimie et de Physique de Bordeaux (ENSCPB)-Université Sciences et Technologies - Bordeaux 1-Université Montesquieu - Bordeaux 4-Institut de Chimie du CNRS (INC), Institut de Chimie de la Matière Condensée de Bordeaux (ICMCB), Institut de Chimie du CNRS (INC)-Centre National de la Recherche Scientifique (CNRS)-Institut Polytechnique de Bordeaux-Université de Bordeaux (UB), Fachbereich Material- und Geowissenschaften, and Technische Universität Darmstadt (TU Darmstadt)
- Subjects
Materials science ,Thin films ,chemistry.chemical_element ,Nanoparticle ,Nanotechnology ,02 engineering and technology ,Thermal treatment ,010402 general chemistry ,01 natural sciences ,law.invention ,Inorganic Chemistry ,law ,TiO2 ,Calcination ,Porous materials ,Thin film ,Nanoporous ,[CHIM.MATE]Chemical Sciences/Material chemistry ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,chemistry ,Chemical engineering ,Hybrid materials ,0210 nano-technology ,Porous medium ,Hybrid material ,Titanium - Abstract
International audience; Calcination of cyclopentadienyltitanium-based organic-inorganic hybrid materials at 450-500 °C led to the formation of anatase titanium dioxide as white powders consisting of a porous network of aggregated nanoparticles, the nanoporosity detected being related to the inter-particle space. Depending on the calcination temperatures, the surface area of the titanium dioxide particles varied from 65 to 158 m(2) g(-1).
- Published
- 2012
18. Platinum nanowires with pronounced texture, controlled crystallite size and excellent growth homogeneity fabricated by optimized pulsed electrodeposition
- Author
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Stefan Lauterbach, Hans-Joachim Kleebe, Martin Hottes, Ulrike Kunz, Wolfgang Ensinger, Falk Muench, Markus Rauber, Joachim Brötz, and Christian Stegmann
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Materials science ,Nanoporous ,General Chemical Engineering ,Nanowire ,Nucleation ,Pulse duration ,chemistry.chemical_element ,Nanotechnology ,General Chemistry ,Crystallinity ,chemistry ,Chemical engineering ,Crystallite ,Platinum ,Current density - Abstract
Platinum nanowires with controlled texture and crystallite size were fabricated in nanoporous ion-track etched polycarbonate membranes by electrochemical deposition with different potential pulse sequences. The application of specific potential pulses ranging from −0.5 V to −1.3 V and reverse pulses with +0.2 V allows switching between a light 〈111〉 texture and a pronounced 〈100〉 texture along the nanowire axis. At the same time, the crystallite size determined by XRD was significantly increased from approx. 20 nm to 45 nm, yielding oligocrystalline wires, which are very difficult to obtain with Pt electrodeposition due to its pronounced tendency towards instantaneous nucleation. TEM verified the increase of the calculated average crystallite size of the Pt nanowires. We have been able to prove the necessity of each potential pulse and pulse duration by changing them in a systematical way. Key strategy to achieve large crystallite sizes and a pronounced texture was to reduce oversaturation of Pt adatoms during the reduction step and to preferentially dissolve lattice defects and nucleation sites by anodic removal. Additionally, the homogeneity of the Pt nanowire growth was evaluated for the applied pulse sequences by SEM. The results show that by reducing the deposition current density, the uniformity of the Pt nanowires was strongly enhanced. The proposed rational synthetic strategy allows to optimize the crystallinity, texture and monodispersity of Pt nanowires and is thus of considerable relevance for tailoring the functional properties of these structures.
- Published
- 2014
19. Analytical electron microscopical investigations on the apoplastic pathways of lanthanum transport in barley roots
- Author
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Stephan Holzamer, Ralf Stelzer, Heiner Lehmann, Ulrike Kunz, and Markus Gierth
- Subjects
Ion Transport ,Tight junction ,Hordeum ,Plant Science ,Biology ,Plant Roots ,Apoplast ,Cell wall ,Microscopy, Electron ,Membrane ,Biochemistry ,Lanthanum ,Exodermis ,Genetics ,Biophysics ,Endodermis ,Hordeum vulgare ,Ion transporter - Abstract
In transmission electron microscopy studies, lanthanum ions have been used as electron-opaque tracers to delineate the apoplastic pathways for ion transport in barley (Hordeum vulgare L.) roots. To localize La3+ on the subcellular level, e.g. in cell walls and on the surface of membranes, electron-energy-loss spectroscopy and electron-spectroscopic imaging were used. Seminal and nodal roots were exposed for 30 min to 1 mM LaCl3 and 10 mM LaCl3, respectively. In seminal roots, possessing no exodermis, La3+ diffusion through the apoplast was stopped by the Casparian bands of the endodermis. In nodal roots with an exodermis, however, La3+ diffusion through the cortical apoplast had already stopped at the tight junctions of the exodermal cell walls resembling the Casparian bands of the endodermis. Therefore, we conclude that in some specialized roots such as the nodal roots of barley, the physiological role of the endodermis is largely performed by the exodermis.
- Published
- 2001
20. Imaging the Electrode-GDL Interface by a Modified Wood's Intrusion Process
- Author
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Ulrike Kunz, Frieder Scheiba, Nathalie Benker, Hartmut Fuess, and Christina Roth
- Abstract
not Available.
- Published
- 2010
21. Specific procedures of TEM sample preparation for fuel cell electrodes and components
- Author
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Christina Roth, Frieder Scheiba, Nathalie Benker, Ulrike Kunz, and Hartmut Fuess
- Subjects
Materials science ,Chemical engineering ,Structural Biology ,Electrode ,Analytical chemistry ,Fuel cells ,Sample preparation - Published
- 2009
22. Electron microscopy techniques for the detailed study of fuel cell electrodes and components
- Author
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Frieder Scheiba, Nathalie Benker, Ulrike Kunz, Christina Roth, and Hartmut Fuess
- Subjects
Materials science ,Chemical engineering ,Structural Biology ,law ,Electrode ,Analytical chemistry ,Fuel cells ,Electron microscope ,law.invention - Published
- 2009
23. Investigation of the Polymer Electrolyte Distribution in Polymer Electrolyte Fuel Cells (PEFC)
- Author
-
Frieder Scheiba, Nathalie Benker, Ulrike Kunz, and Christina -. Roth
- Abstract
not Available.
- Published
- 2008
24. Identification of D-glucose-binding polypeptides which are components of the renal Na+-D-glucose cotransporter
- Author
-
Martin Neeb, Ulrike Kunz, and Hermann Koepsell
- Subjects
Azides ,Kidney Cortex ,Monosaccharide Transport Proteins ,Swine ,Phlorizin ,Renal cortex ,Biochemistry ,Acetylglucosamine ,chemistry.chemical_compound ,medicine ,Animals ,Molecular Biology ,Gel electrophoresis ,Glucosamine ,Affinity labeling ,Microvilli ,Molecular mass ,Chemistry ,Isoelectric focusing ,Sodium ,Affinity Labels ,Cell Biology ,Molecular Weight ,Glucose ,Isoelectric point ,medicine.anatomical_structure ,Electrophoresis, Polyacrylamide Gel ,Isoelectric Focusing ,Cotransporter - Abstract
D-Glucose-binding polypeptides in the Na+-D-glucose cotransporter from pig renal cortex were identified by affinity labeling with two D-glucose analogs, 10-N-(N-[4-azido-2-nitrophenyl]-beta-alanyl)amino-1-decyl-beta-D- glucopyranoside (NapADG) and 10-N-(bromoacetyl)amino-1-decyl-beta-D-glucopyranoside (BADG). During short-term incubation in the dark, NapADG and BADG are reversible inhibitors of Na+ gradient-dependent D-glucose uptake and Na+-dependent phlorizin binding with Ki values of about 40 and 400 microM, respectively. Irreversible inhibition of Na+-dependent phlorizin binding, which was prevented by D-glucose or phlorizin, was measured after a 1-h incubation with BADG. Both NapADG and BADG selectively labeled polypeptides with apparent molecular weights of 82,000, 75,000, 64,000, and 47,000. Since labeling of the Mr 82,000 and 75,000 polypeptides by both analogs was partially dependent on the presence of Na+ and was partially protected by D-glucose or phlorizin but not by L-glucose or D-mannose, these polypeptides are thought to be components of the renal Na+-D-glucose cotransporter which contain D-glucose-binding sites. For the Mr 64,000 and 47,000 polypeptides, Na+ dependence and D-glucose protection were not constantly observed. However, also, these polypeptides are thought to be components or proteolytic splitting products of the Na+-D-glucose cotransporter since we observed that three monoclonal antibodies showed cross-reaction with the BADG-labeled Mr 82,000, 64,000, and 47,000 polypeptides (K. Korn, A. Raszeja-Specht, S. Bernotat-Danielowski, and H. Koepsell, manuscript in preparation). When the BADG-labeled Mr 82,000 and 75,000 polypeptides were analyzed after two-dimensional separation by isoelectric focusing and sodium dodecyl sulfate-polyacrylamide gel electrophoresis, three-labeled, D-glucose-protectable polypeptides with the respective molecular weights and isoelectric points of 82,000 and 5.6, 75,000 and 5.4, and 75,000 and 6.9 were distinguished. The data indicate that renal brush-border membranes contain several polypeptides which are components of the Na+-D-glucose cotransporter and contain D-glucose-binding sites.
- Published
- 1987
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