Agnes Schulze
Leibniz Association
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Featured researches published by Agnes Schulze.
Macromolecular Rapid Communications | 2010
Agnes Schulze; Barbara Marquardt; Sven Kaczmarek; Rolf Schubert; Andrea Prager; Michael R. Buchmeiser
Poly(ethersulfone) membranes were surface modified in a one-step procedure. For this purpose, the membranes were soaked with aqueous solutions of different low-molecular weight molecules bearing diverse hydrophilic functionalities and subject to electron beam treatment. No catalysts, photoinitiators, organic solvents or other toxic reagents were used, and no additional synthetic or purification steps were required.
RSC Advances | 2013
Agnes Schulze; Manfred F. Maitz; Ralf Zimmermann; Barbara Marquardt; Marion Fischer; Carsten Werner; Marco Went; Isabell Thomas
Electron-beam-induced grafting of hydrophilic polymers was applied to modify PVDF membranes for biomedical applications. Grafting was performed by immersing the membrane in an aqueous solution of different hydrophilic polymers followed by electron-beam irradiation. The two polymer types are able to cross-link by recombination of adjacent radicals formed via the irradiation. Although the untreated membrane was already quite hydrophilic, the modification resulted in even lower water contact angles at the membrane surface indicating improved water wettability. The presence of different functional groups originating from the hydrophilic polymers was detected on the membrane surface by electrokinetic measurements. SEM investigations as well as porosimetry experiments showed that the grafted hydrophilic polymer layer is very thin; therefore, the membrane pore structure is not negatively affected. Soxhlet extraction revealed the stability of the modification for selected polymers: surface contact angles were comparable after extraction, and total organic carbon investigation of the extraction water revealed no significant loss of organic material. Investigated mechanical properties confirmed an increased stability due to cross-linking of the polymers. Undesired hemolysis was not detected with hemocompatibility tests, and coagulation was decreased with selected hydrophilic polymers. Because of the absence of any toxic material during surface modification and the high stability of the product, this method is believed to be suitable for the modification of membranes for medical applications, e.g. for improving the hemo- or biocompatibility.
RSC Advances | 2015
Kristina Fischer; M. Kühnert; Roger Gläser; Agnes Schulze
Diclofenac is a commonly used anti-inflammatory drug, which has been found in surface waters. Advanced oxidation processes (AOPs) seem to be the most suitable technique to prevent the entry of diclofenac and other pollutants into surface waters. TiO2 is especially reliable in mineralizing many organic molecules. The combination of TiO2 nanotubes with a polymer microfiltration membrane (polyethersulfone, PES) showed high photocatalytic activity by degrading diclofenac combined with an excellent membrane performance and long-term stability. By continuously degrading pollutants from water via a cross-flow setup, the molecules to be degraded are transported right to the membrane surface so that the overall reaction rate is increased. The toxicity of diclofenac was reduced by photocatalysis and photolysis; however, photocatalysis had greater impact. Moreover, the complete degradation of pollutants is very important to avoid highly toxic intermediate products.
Water Science and Technology | 2012
Agnes Schulze; Barbara Marquardt; Marco Went; Andrea Prager; Michael R. Buchmeiser
A new electron beam-based approach for the direct functionalization of polyethersulfone, polyvinylidene fluoride, polysulfone as well as polyacrylonitrile membranes in a one-step procedure is presented. Aqueous solutions of functional molecules were immobilized on the membrane surface by electron beam treatment. The resulting membranes show significantly increased flux and water wettability accompanied by decreased protein adsorption. Stability tests demonstrated the permanence of the modification. This new method neither requires any preceding surface functionalization nor the use of catalysts/photoinitiators or other toxic reagents. In addition, it avoids the synthesis of hydrophilic monomers/polymers, thus avoiding additional synthetic and purification steps as well as the use of organic solvents.
Synthetic Communications | 2006
Agnes Schulze; Georgia Pagona; Athanassios Giannis
Abstract An efficient method for the oxidation of alcohols is presented. The use of catalytic amounts of sodium chloride in combination with oxone allows the conversion primary aliphatic alcohols to symmetric esters. Secondary alcohols can be easily oxidized to ketones, and benzylic alcohols are converted to the corresponding aldehydes. The method is cost effective and enviromentally benign.
Polymers | 2017
Agnes Schulze; Daniel Breite; Yongkyum Kim; Martin Schmidt; Isabell Thomas; Marco Went; Kristina Fischer; Andrea Prager
To generate polyethersulfone membranes with a biocatalytically active surface, pancreatin was covalently immobilized. Pancreatin is a mixture of digestive enzymes such as protease, lipase, and amylase. The resulting membranes exhibit self-cleaning properties after “switching on” the respective enzyme by adjusting pH and temperature. Thus, the membrane surface can actively degrade a fouling layer on its surface and regain initial permeability. Fouling tests with solutions of protein, oil, and mixtures of both, were performed, and the membrane’s ability to self-clean the fouled surface was characterized. Membrane characterization was conducted by investigation of the immobilized enzyme concentration, enzyme activity, water permeation flux, fouling tests, porosimetry, X-ray photoelectron spectroscopy, and scanning electron microscopy.
Polymers | 2017
Juliane Schmidt; Ren Wei; Thorsten Oeser; Lukas Dedavid e Silva; Daniel Breite; Agnes Schulze; Wolfgang Zimmermann
Polyurethanes (PU) are widely used synthetic polymers. The growing amount of PU used industrially has resulted in a worldwide increase of plastic wastes. The related environmental pollution as well as the limited availability of the raw materials based on petrochemicals requires novel solutions for their efficient degradation and recycling. The degradation of the polyester PU Impranil DLN by the polyester hydrolases LC cutinase (LCC), TfCut2, Tcur1278 and Tcur0390 was analyzed using a turbidimetric assay. The highest hydrolysis rates were obtained with TfCut2 and Tcur0390. TfCut2 also showed a significantly higher substrate affinity for Impranil DLN than the other three enzymes, indicated by a higher adsorption constant K. Significant weight losses of the solid thermoplastic polyester PU (TPU) Elastollan B85A-10 and C85A-10 were detected as a result of the enzymatic degradation by all four polyester hydrolases. Within a reaction time of 200 h at 70 °C, LCC caused weight losses of up to 4.9% and 4.1% of Elastollan B85A-10 and C85A-10, respectively. Gel permeation chromatography confirmed a preferential degradation of the larger polymer chains. Scanning electron microscopy revealed cracks at the surface of the TPU cubes as a result of enzymatic surface erosion. Analysis by Fourier transform infrared spectroscopy indicated that the observed weight losses were a result of the cleavage of ester bonds of the polyester TPU.
Materials | 2016
Agnes Schulze; Marco Went; Andrea Prager
Polymer membranes have been modified with hyperbranched polymers with the aim to generate a high density of hydrophilic functional groups at the membrane surface. For this purpose hyperbranched polymers containing amino, alcohol, and carboxylic acid end groups were used for membrane modification, respectively. Thus, surface potential and charges were changed significantly to result in attractive or repulsive interactions towards three different proteins (albumin, lysozyme, myoglobin) that were used to indicate membrane fouling properties. Our studies demonstrated that hydrophilization alone is not effective for avoiding membrane fouling when charged proteins are present. In contrast, electrostatic repulsion seems to be a general key factor.
Science of The Total Environment | 2018
Elham Jahangiri; Isabell Thomas; Agnes Schulze; Bettina Seiwert; Hubert Cabana; Dietmar Schlosser
Laccase from Phoma sp. UHH 5-1-03 was cross-linked to polyvinylidene fluoride membranes by electron beam irradiation. Immobilised laccase displayed a higher stability than the non-immobilised enzyme with respect to typical wastewater temperatures, and pH at a range of 5 to 9. Batch tests addressed the removal of pharmaceutically active compounds (PhACs; applied as a mixture of acetaminophen, bezafibrate, indometacin, ketoprofen, mefenamic acid, and naproxen) by both immobilised and non-immobilised laccase in municipal wastewater. High removal rates (>85%) of the most efficiently oxidised PhACs (acetaminophen and mefenamic acid) indicated a high efficiency of the immobilised laccase in wastewater. Continuous elimination of the aforementioned PhACs by the immobilised enzyme in a continuously operated diffusion basket reactor yielded a PhAC removal pattern qualitatively similar to those observed in batch tests. Clearly higher apparent Vmax values and catalytic efficiencies (in terms of both Vmax/S0.5 as well as Vmax/Km values obtained from data fitting according to the Hill and the Michaelis-Menten model, respectively) observed for acetaminophen oxidation by the immobilised compared to the non-immobilised enzyme are in support of a considerably higher functional stability of the immobilised laccase especially in wastewater. The potential influence of acetaminophen on the removal of comparatively less laccase-oxidisable water pollutants such as the antimicrobial triclosan (TCS) was investigated. TCS was increasingly removed upon increasing the initial acetaminophen concentration in immobilised as well as non-immobilised laccase reaction systems until saturation became evident. Acetaminophen was consumed and not recycled during laccase reactions, which was accompanied by the formation of various acetaminophen-TCS cross-coupling products. Nevertheless, the simultaneous presence of acetaminophen (and potentially even more pollutant removal-enhancing laccase substrates) and more recalcitrant pollutants in wastewater represents an interesting option for the efficiency enhancement of enzyme-based wastewater treatment approaches.
RSC Advances | 2016
Daniel Breite; Marco Went; Andrea Prager; Agnes Schulze
The zeta potential of membrane surfaces and the resulting electrostatic interactions are determining factors of membrane fouling. This study investigates the influence of environmental parameters like pH value, salt concentration, or ion valence on the zeta potential of polymer membranes and the resulting fouling. To control electrostatic forces charged polystyrene beads were used as fouling reagents. Also, polyethersulfone and polyvinylidene fluoride membranes were modified to possess an either positive or negative surface charge. Afterwards, suspensions of beads were filtered through the membranes in different electrolytic environments. Fouling occurred when membrane and beads are oppositely charged. Bead adsorption was not observed when both surfaces are evenly charged. The latter was found to be influenced by electrolyte concentration. High salt concentrations or present bivalent ions reduced the electrostatic repulsion between evenly charged surfaces and led to membrane fouling. Low salt concentrations did not influence the electrostatic repulsion. Thus, critical salt concentrations were determined and used to identify the critical zeta potential. In addition, the fouling of a zwitterionic membrane surface was investigated regarding its pH dependence. A critical zeta potential that is associated with membrane fouling was identified. The critical zeta potentials are similar for both pH and salt concentration dependence.