Auflistung nach Autor:in "Stark, Wendelin J."

Gerade angezeigt 1 - 8 von 8

Ferromagnetic inks facilitate large scale paper recycling and reduce bleach chemical consumption
(American Chemical Society, 2013) Zeltner, Martin; Toedtli, Laura M.; Hild, Nora; Fuhrer, Roland; Rossier, Michaël; Gerber, Lukas C.; Raso, Renzo; Grass, Robert N.; Stark, Wendelin J.
Deinking is a fundamental part of paper recycling. As the global paper consumption rises and exceeds even the annual paper production, recycling of this raw material is of high importance. Magnetic ink based on carbon coated magnetic nanoparticles enables an alternative approach to state of the art paper deinking. Magnetic deinking comprises three steps (preselection, washing, and magnetic separation of fibers). Preseparation of printed from nonprinted scraps of paper is feasible and reduces the paper mass which has to be fed into a deinking process. A consecutive washing process removes surficial magnetic ink that can be collected by application of a permanent magnet. Still, printed parts are subjected to a further continuous magnetic deinking step, where magnetic and nonmagnetic paper fibers can be separated. Magnetic deinking of a model print allows recovery of more than 80% of bright fibers without any harsh chemical treatment and the re-collection of more than 82% of magnetic ink.
01A - Beitrag in wissenschaftlicher Zeitschrift
Fibers mechanically similar to sheep wool obtained by wet spinning of gelatin and optional plasticizers
(Wiley, 2014) Stoessel, Philipp R.; Raso, Renzo; Kaufmann, Tim; Grass, Robert N.; Stark, Wendelin J.
AbstractGelatin is an exceptional and versatile biopolymer with applications in various industries. As the most abundant structural protein in vertebrates it is available in megaton quantities. On these grounds, it would be a plausible substitute for synthetic polymers. Gelatin processing into fibers seems promising as continuous protein filaments do not have the limitation of natural fibers, i.e., small staple fiber length. Instead of spinning an aqueous gelatin solution, a protein precipitate from a phase‐separated system is used. Robust wet spinning with subsequent fiber drawing allows production of a gelatin filament with similar mechanical properties as sheep wool. Different degrees of fiber drawing and addition of plasticizers enable to tailor the mechanical and thermal fiber properties and demonstrate the versatility of the proposed spinning process.
01A - Beitrag in wissenschaftlicher Zeitschrift
Indoor air purification using activated carbon adsorbers: Regeneration using catalytic combustion of intermediately stored VOC
(American Chemical Society, 2014) Raso, Renzo; Zeltner, Martin; Stark, Wendelin J.
In this study, we demonstrate a two-step process where activated carbon based air purifier systems can be regenerated in situ and eliminate volatile organic compounds (VOCs) from indoor air in an energy efficient way. A carbon based adsorber was combined in series with a CeO2/TiO2 oxidative catalyst for total oxidation of the previously adsorbed and periodically released volatile organic compounds during regeneration runs. We investigated the adsorption and desorption behavior of five different VOCs (diethyl ether, limonene, linalool, hexanoic acid, triethylamine and n-decane) with thermogravimetric measurements, mass spectrometry and elemental analysis. Cyclic loading and regeneration experiments were carried out with selected VOCs (limonene, linalool and n-decane) for testing regeneration at elevated temperature. We showed that in situ thermal regeneration and subsequent oxidation of released VOC is a sustainable and easy applicable technology for indoor air purification. This two-step approach allows energy saving as the VOCs are eliminated discontinuously (enriching VOCs; periodic catalytic combustion), and is of high environmental and economic interest, as much less maintenance services are required.
01A - Beitrag in wissenschaftlicher Zeitschrift
Limestone nanoparticles as nanopore templates in polymer membranes. Narrow pore size distribution and use as self-wetting dialysis membranes
(Royal Society of Chemistry, 2014) Kellenberger, Christoph R.; Pfleiderer, Florian C.; Raso, Renzo; Burri, Cornelia H.; Schumacher, Christoph M.; Grass, Robert N.; Stark, Wendelin J.
Limestone nanoparticles can be used as nanopore templates to prepare porous polymeric films. Their application as membranes is so far strongly limited by the fact that these films are highly hydrophobic. In this study, a simple method is reported to directly produce self-wetting membranes by the template removal method. Triethyl citrate modified polyethersulfone and cellulose acetate membranes were produced using dissolvable limestone nanoparticles as pore templates. The nanoporous polymer films were used as dialysis membranes and characterized by means of buffer exchange rate, molecular weight cut-off, protein adsorption, pore size distribution and water contact angle. The herein prepared membranes were further benchmarked against commercially available dialysis membranes with comparable average pore size. They showed narrow pore size distributions, fast dialysis rates at low protein adsorption and molecular weight cut-off of around 12 kDa. Interestingly, the triethyl citrate modified polyethersulfone membranes displayed only moderate change in pore size distribution as a result of the plasticizer additive compared to pure polyethersulfone membranes. This is a matter of substantial interest considering the fact that additive modifications of membranes produced by the predominant phase inversion process typically show alterations in morphology that lead to undesired changes in membrane performance. Furthermore, dextran recovery analysis proved to meet the specific requirements for dialysis membrane characterization and benchmarking.
01A - Beitrag in wissenschaftlicher Zeitschrift
Magnetic superbasic proton sponges are readily removed and permit direct product isolation
(American Chemical Society, 2014) Schneider, Elia M.; Raso, Renzo; Hofer, Corinne J.; Zeltner, Martin; Stettler, Robert D.; Hess, Samuel C.; Grass, Robert N.; Stark, Wendelin J.
Workup in organic synthesis can be very time-consuming, particularly when using reagents with both a solubility similar to that of the desired products and a tendency not to crystallize. In this respect, reactions involving organic bases would strongly benefit from a tremendously simplified separation process. Therefore, we synthesized a derivative of the superbasic proton sponge 1,8-bis(dimethylamino)naphthalene (DMAN) and covalently linked it to the strongest currently available nanomagnets based on carbon-coated cobalt metal nanoparticles. The immobilized magnetic superbase reagent was tested in Knoevenagel- and Claisen-Schmidt-type condensations and showed conversions of up to 99%. High yields of up to 97% isolated product could be obtained by simple recrystallization without using column chromatography. Recycling the catalyst was simple and fast with an insignificant decrease in catalytic activity.
01A - Beitrag in wissenschaftlicher Zeitschrift
Nanoparticle-assisted, catalytic etching of carbon surfaces as a method to manufacture nanogrooves
(American Chemical Society, 2012) Schumacher, Christoph M.; Koehler, Fabian M.; Rotzetter, Aline C. C.; Raso, Renzo; Stark, Wendelin J.
A simple structuring method for graphitic structures based on the catalytic properties of cerium oxide nanoparticles under oxidizing conditions is presented. Highly oriented pyrolytic graphite chips were impregnated with well-dispersed ceria nanoparticles and then treated at elevated temperatures for several hours. Oxidation activities on the particle surface appeared as crystallographically independent traces that were formed on the graphite and provide a simple method to manufacture nanogrooves at large scale. By altering treatment durations and temperatures, the optimal conditions and activity parameters of the particles were determined. A systematic AFM evaluation allowed formulating of a mechanism of the etching process. The findings provide a simple procedure for the patterning of graphitic structures, formation of nanogrooves and thereby a basic tool for material science with respect to the manufacturing of atmospheric nanofilters and ion-selective membranes.
01A - Beitrag in wissenschaftlicher Zeitschrift
Programmable living material containing reporter micro-organisms permits quantitative detection of oligosaccharides
(Elsevier, 2015) Mora, Carlos A.; Herzog, Antoine F.; Raso, Renzo; Stark, Wendelin J.
The increasing molecular understanding of many diseases today permits the development of new diagnostic methods. However, few easy-to-handle and inexpensive tools exist for common diseases such as food disorders. Here we present a living material based analytical sensor (LiMBAS) containing genetically modified bacteria (Escherichia coli) immobilized and protected in a thin layer between a nanoporous and support polymer membrane for a facile quantification of disease-relevant oligosaccharides. The bacteria were engineered to fluoresce in response to the analyte to reveal its diffusion behavior when using a blue-light source and optical filter. We demonstrated that the diffusion zone diameter was related semi-logarithmically to the analyte concentration. LiMBAS could accurately quantify lactose or galactose in undiluted food samples and was able to measure food intolerance relevant concentrations in the range of 1-1000 mM requiring a sample volume of 1-10 μL. LiMBAS was storable for at least seven days without losing functionality at 4 °C. A wide range of genetic tools for E. coli are readily available thus allowing the reprogramming of the material to serve as biosensor for other molecules. In combination with smartphones, an automated diagnostic analysis becomes feasible which would also allow untrained people to use LiMBAS.
01A - Beitrag in wissenschaftlicher Zeitschrift
Template-particle stabilized bicontinuous emulsion yielding controlled assembly of hierarchical high-flux filtration membranes
(American Chemical Society, 2015) Hess, Samuel C.; Kohll, A. Xavier; Raso, Renzo; Schumacher, Christoph M.; Grass, Robert N.; Stark, Wendelin J.
A novel solvent-evaporation-based process that exploits template-particle stabilized bicontinuous emulsions for the formation of previously unreached membrane morphologies is reported in this article. Porous membranes have a wide range of applications spanning from water filtration, pharmaceutical purification, and battery separators to scaffolds for tissue engineering. Different situations require different membrane morphologies including various pore sizes and pore gradients. However, most of the previously reported membrane preparation procedures are restricted to specific morphologies and morphology alterations require an extensive optimization process. The tertiary system presented in this article, which consists of a poly(ether sulfone)/dimethylacetamide (PES/DMAc) solution, glycerol, and ZnO-nanoparticles, allows simple and exact tuning of pore diameters ranging from sub-20 nm, up to 100 nm. At the same time, the pore size gradient is controlled from 0 up to 840%/μm yielding extreme asymmetry. In addition to structural analysis, water flux rates of over 5600 L m–2 h–1 are measured for membranes retaining 45 nm silica beads.
01A - Beitrag in wissenschaftlicher Zeitschrift