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- ItemPreliminary Study on the Application of Temperature Swing Adsorption in Aqueous Phase for Pesticide Removal(London [u.a.] : Institute of Physics, 2018) Aumeier, B.; Dang, H.Q.A.; Wessling, M.Temperature swing adsorption (TSA) is a well-established process for gas purification. In this work, the feasibility of TSA in aqueous phase was studied. This concept could enable in situ adsorbent regeneration and thus fostering sustainable decentralized adsorption processes applied to water treatment. The adsorption processes with the use of granular activated carbon (GAC) have been widely applied to remove the residual amounts of pesticides in water treatment. Amitrole was chosen as a typical pesticide in this study, GAC was selected as the main adsorbent for amitrole removal. Adsorption isotherm experiments were conducted at different temperatures of 20°C, 57°C and 94°C to identify the most appropriate sorptive – sorbent system for dynamic adsorption and TSA research. Once the isotherm experiments were accomplished, breakthrough curve experiments were subsequently investigated. Finally, TSA process was conducted with the activated carbon regeneration at the elevated temperature of 125°C. Consequently, initial obtained results proved the feasibility of the proposed TSA technique for pesticide removal in aqueous phase.
- ItemCriticial Assessment of the Photocatalytic Reduction of Cr(VI) over Au/TiO2(Basel : MDPI, 2018-12-3) Ngo, Anh Binh; Nguyen, Hong Lien; Hollmann, DirkThe purification of drinking water is one of the most urgent challenges in developing countries, for which the efficient removal of traces of heavy metals, e.g., Cr(IV), represents a key technology. This can be achieved via photocatalysis. In this study, we compare the performance of Au/TiO2 to bare TiO2 P25 catalysts. Furthermore, the influence of the sacrificial reagent citric acid under UV-Vis and Vis excitation was investigated and a detailed investigation of the catalysts before and after reaction was performed. During the photocatalytic reduction of Cr(IV) under acidic conditions, both leaching of Au, as well as absorption of Cr, occur, resulting in new catalyst systems obtained in situ.
- ItemSolubility and selectivity effects of the anion on the adsorption of different heavy metal ions onto chitosan(Basel : MDPI, 2020) Weißpflog, Janek; Gündel, Alexander; Vehlow, David; Steinbach, Christine; Müller, Martin; Boldt, Regine; Schwarz, Simona; Schwarz, DanaThe biopolymer chitosan is a very efficient adsorber material for the removal of heavy metal ions from aqueous solutions. Due to the solubility properties of chitosan it can be used as both a liquid adsorber and a solid flocculant for water treatment reaching outstanding adsorption capacities for a number of heavy metal ions. However, the type of anion corresponding to the investigated heavy metal ions has a strong influence on the adsorption capacity and sorption mechanism on chitosan. In this work, the adsorption capacity of the heavy metal ions manganese, iron, cobalt, nickel, copper, and zinc were investigated in dependence on their corresponding anions sulfate, chloride, and nitrate by batch experiments. The selectivity of the different heavy metal ions was analyzed by column experiments. © 2020 by the authors.
- ItemTwo-dimensional electron gas of the In2O3 surface: Enhanced thermopower, electrical transport properties, and reduction by adsorbates or compensating acceptor doping(Woodbury, NY : Inst., 2020) Papadogianni, Alexandra; Rombach, Julius; Berthold, Theresa; Polyakov, Vladimir; Krischok, Stefan; Himmerlich, Marcel; Bierwagen, OliverIn2O3 is an n-type transparent semiconducting oxide possessing a surface electron accumulation layer (SEAL) like several other relevant semiconductors, such as InAs, InN, SnO2, and ZnO. Even though the SEAL is within the core of the application of In2O3 in conductometric gas sensors, a consistent set of transport properties of this two-dimensional electron gas (2DEG) is missing in the present literature. To this end, we investigate high-quality single-crystalline as well as textured doped and undoped In2O3(111) films grown by plasma-assisted molecular beam epitaxy to extract transport properties of the SEAL by means of Hall effect measurements at room temperature while controlling the oxygen adsorbate coverage via illumination. The resulting sheet electron concentration and mobility of the SEAL are ≈1.5×1013cm−2 and ≈150cm2/Vs, respectively, both of which are strongly reduced by oxygen-related surface adsorbates from the ambient air. Our transport measurements further demonstrate a systematic reduction of the SEAL by doping In2O3 with the deep compensating bulk acceptors Ni or Mg. This finding is supported by x-ray photoelectron spectroscopy (XPS) measurements of the surface band bending and SEAL electron emission. Quantitative analyses of these XPS results using self-consistent, coupled Schrödinger-Poisson calculations indicate the simultaneous formation of compensating bulk donor defects (likely oxygen vacancies), which almost completely compensate the bulk acceptors. Finally, an enhancement of the thermopower by reduced dimensionality is demonstrated in In2O3: Seebeck coefficient measurements of the surface 2DEG with partially reduced sheet electron concentrations between 3×1012 and 7×1012cm−2 (corresponding average volume electron concentration between 1×1019 and 2.3×1019cm−3) indicate a value enhanced by ≈80% compared to that of bulk Sn-doped In2O3 with comparable volume electron concentration.
- ItemWaterborne phenolic, triazine-based porous polymer particles for the removal of toxic metal ions(Amsterdam : Elsevier, 2022) Borchert, Konstantin B.L.; Frenzel, Robert; Gerlach, Niklas; Reis, Berthold; Steinbach, Christine; Kohn, Benjamin; Scheler, Ulrich; Schwarz, Simona; Schwarz, DanaHighly functional and also highly porous materials are presenting great advantages for applications in energy storage, catalysis and separation processes, which is why a continuous development of new materials can be seen. To create a material combining the promising potential interactions of triazine groups with the electrostatic or hydrogen bonding interactions of phenolic groups, a completely new polymeric resin was synthesized. From an eco-friendly dispersion polymerization in water, a copolymer network was obtained, which includes nine hydroxyl groups and one s-triazine ring per repetition unit. The polymer forms highly porous particles with specific surface areas up to 531 ​m2/g and a negative streaming potential over a great pH range. The adsorption isotherms of Ni2+, Cd2+, and Pb2+ were studied in more detail achieving very good adsorption capacities (16 mg Ni2+/g, 24 mg Cd2+/g, and 90 mg Pb2+/g). Demonstrating excellent properties for adsorption applications. The adsorbent exhibited selectivity for the adsorption of Pb2+ over more commonly occurring but non-toxic metal ions such as Fe2+, Ca2+, Mg2+, and K+. Furthermore, reusability of the material was demonstrated by facile, quantitative desorption of adsorbed Pb2+ with a small amount of diluted HCl, circumventing organic chelators. Subsequently, adsorption was carried out without decrease in adsorption performance.
- ItemInteraction between immobilized polyelectrolyte complex nanoparticles and human mesenchymal stromal cells(Auckland : DOVE Medical Press, 2014) Woltmann, B.; Torger, B.; Müller, M.; Hempel, U.Background: Implant loosening or deficient osseointegration is a major problem in patients with systemic bone diseases (eg, osteoporosis). For this reason, the stimulation of the regional cell population by local and sustained drug delivery at the bone/implant interface to induce the formation of a mechanical stable bone is promising. The purpose of this study was to investigate the interaction of polymer-based nanoparticles with human bone marrow-derived cells, considering nanoparticles' composition and surface net charge. Materials and methods: Polyelectrolyte complex nanoparticles (PECNPs) composed of the polycations poly(ethyleneimine) (PEI), poly(L-lysine) (PLL), or (N,N-diethylamino)ethyldextran (DEAE) in combination with the polyanions dextran sulfate (DS) or cellulose sulfate (CS) were prepared. PECNPs' physicochemical properties (size, net charge) were characterized by dynamic light scattering and particle charge detector measurements. Biocompatibility was investigated using human mesenchymal stromal cells (hMSCs) cultured on immobilized PECNP films (5-50 nmol·cm-2) by analysis for metabolic activity of hMSCs in dependence of PECNP surface concentration by MTS (3-[4,5-dimethylthiazol-2-yl]-5-[3-carboxymethoxyphenyl]-2-[4-sulfophenyl]-2H-tetrazolium, inner salt) assay, as well as cell morphology (phase contrast microscopy). Results: PECNPs ranging between ~50 nm and 150 nm were prepared. By varying the ratio of polycations and polyanions, PECNPs with a slightly positive (PEC+NP) or negative (PEC-NP) net charge were obtained. The PECNP composition significantly affected cell morphology and metabolic activity, whereas the net charge had a negligible influence. Therefore, we classified PECNPs into "variant systems" featuring a significant dose dependency of metabolic activity (DEAE/CS, PEI/DS) and "invariant systems" lacking such a dependency (DEAE/DS, PEI/CS). Immunofluorescence imaging of fluorescein isothiocyanate isomer I (FITC)-labeled PECNPs suggested internalization into hMSCs remaining stable for 8 days. Conclusion: Our study demonstrated that PECNP composition affects hMSC behavior. In particular, the PEI/CS system showed biocompatibility in a wide concentration range, representing a suitable system for local drug delivery from PECNP-functionalized bone substitute materials.
- ItemSurface Functionalization by Stimuli-Sensitive Microgels for Effective Enzyme Uptake and Rational Design of Biosensor Setups(Basel : MDPI, 2018) Sigolaeva, Larisa V.; Pergushov, Dmitry V.; Oelmann, Marina; Schwarz, Simona; Brugnoni, Monia; Kurochkin, Ilya N.; Plamper, Felix A.; Fery, Andreas; Richtering, WalterWe highlight microgel/enzyme thin films that were deposited onto solid interfaces via two sequential steps, the adsorption of temperature- and pH-sensitive microgels, followed by their complexation with the enzyme choline oxidase, ChO. Two kinds of functional (ionic) microgels were compared in this work in regard to their adsorptive behavior and interaction with ChO, that is, poly(N-isopropylacrylamide-co-N-(3-aminopropyl)methacrylamide), P(NIPAM-co-APMA), bearing primary amino groups, and poly(N-isopropylacrylamide-co-N-[3-(dimethylamino) propyl]methacrylamide), P(NIPAM-co-DMAPMA), bearing tertiary amino groups. The stimuli-sensitive properties of the microgels in the solution were characterized by potentiometric titration, dynamic light scattering (DLS), and laser microelectrophoresis. The peculiarities of the adsorptive behavior of both the microgels and the specific character of their interaction with ChO were revealed by a combination of surface characterization techniques. The surface charge was characterized by electrokinetic analysis (EKA) for the initial graphite surface and the same one after the subsequent deposition of the microgels and the enzyme under different adsorption regimes. The masses of wet microgel and microgel/enzyme films were determined by quartz crystal microbalance with dissipation monitoring (QCM-D) upon the subsequent deposition of the components under the same adsorption conditions, on a surface of gold-coated quartz crystals. Finally, the enzymatic responses of the microgel/enzyme films deposited on graphite electrodes to choline were tested amperometrically. The presence of functional primary amino groups in the P(NIPAM-co-APMA) microgel enables a covalent enzyme-to-microgel coupling via glutar aldehyde cross-linking, thereby resulting in a considerable improvement of the biosensor operational stability.
- ItemAdsorption characteristics of Er3N@C80on W(110) and Au(111) studied via scanning tunneling microscopy and spectroscopy(Frankfurt, M. : Beilstein-Institut zur Förderung der Chemischen Wissenschaften, 2017-5-23) Schimmel, Sebastian; Sun, Zhixiang; Baumann, Danny; Krylov, Denis; Samoylova, Nataliya; Popov, Alexey; Büchner, Bernd; Hess, ChristianWe performed a study on the fundamental adsorption characteristics of Er3N@C80 deposited on W(110) and Au(111) via room temperature scanning tunneling microscopy and spectroscopy. Adsorbed on W(110), a comparatively strong bond to the endohedral fullerenes inhibited the formation of ordered monolayer islands. In contrast, the Au(111)-surface provides a sufficiently high mobility for the molecules to arrange in monolayer islands after annealing. Interestingly, the fullerenes modify the herringbone reconstruction indicating that the molecule–substrate interaction is of considerable extent. Investigations concerning the electronic structure of Er3N@C80/Au(111) reveals spatial variations dependent on the termination of the Au(111) at the interface.
- ItemInsulin adsorption to catheter materials used for intensive insulin therapy in critically ill patients: Polyethylene versus polyurethane - possible cause of variation in glucose control?(Sharjah : Bentham Science Publishers B.V., 2014) Ley, S.C.; Ammann, J.; Herder, C.; Dickhaus, T.; Hartmann, M.; Kindgen-Milles, D.Introduction: Restoring and maintaining normoglycemia by intensified insulin therapy in critically ill patients is a matter of ongoing debate since the risk of hypoglycemia may outweigh positive effects on morbidity and mortality. In this context, adsorption of insulin to different catheter materials may contribute to instability of glucose control. We studied the adsorption of insulin to different tubing materials in vitro and the effects on glycemic control in vivo. Materials and Methods: In vitro experiments: A syringe pump was filled with 50 IU insulin diluted to 50 ml saline. A flow of 2 ml/h was perfused through polyethylene (PET) or polyurethane (PUR) tubing. Insulin concentrations were measured at the end of the tube for 24 hours using Bradford's protein assay. In vivo study: In a randomized double-blinded cross-over design, 10 intensive care patients received insulin via PET and PUR tubes for 24 hours each, targeting blood glucose levels of 80-150 mg/dl. We measured blood glucose levels, the insulin dose required to maintain target levels, and serum insulin and C-peptide levels. Results: In vitro experiments: After the start of the insulin infusion, only 20% (median, IQR 20-27) (PET) and 22% (IQR 16-27) (PUR) of the prepared insulin concentration were measured at the end of the 2 meter tubing. Using PET, after one hour infusion the concentration increased to 34% (IQR 29-36) and did not increase significantly during the next 24 hours (39% (IQR 39-40)). Using PUR, higher concentrations were detected than for PET at every measurement from 1 hour (82% (IQR 70-86)) to 24 hours (79% (IQR 64-87)). In vivo study: Glycemic control was effective and not different between groups. Significantly higher volumes of insulin solution had to be infused with PET compared to PUR (median PET 70.0 (IQR 56-82) ml vs. PUR 42 (IQR 31-63) ml; p=0.0015). Serum insulin concentrations did not decrease significantly one hour after changing to PET or PUR tubing. Conclusion: Polyurethane tubing systems allow application of insulin with significantly lower adsorption rates than polyethylene tubing systems. As a consequence, less insulin solution has to be infused to patients for effective blood glucose control. Tubing material of the insulin infusion may be crucial for safe and effective glycemic control in critically ill patients.
- ItemPolyelectrolyte complex nanoparticles of poly(ethyleneimine) and poly(acrylic acid): Preparation and applications(Basel : MDPI AG, 2011) Müller, M.; Keßler, B.; Fröhlich, J.; Poeschla, S.; Torger, B.In this contribution we outline polyelectrolyte (PEL) complex (PEC) nanoparticles, prepared by mixing solutions of the low cost PEL components poly(ethyleneimine) (PEI) and poly(acrylic acid) (PAC). It was found, that the size and internal structure of PEI/PAC particles can be regulated by process, media and structural parameters. Especially, mixing order, mixing ratio, PEL concentration, pH and molecular weight, were found to be sensible parameters to regulate the size (diameter) of spherical PEI/PAC nanoparticles, in the range between 80-1,000 nm, in a defined way. Finally, applications of dispersed PEI/PAC particles as additives for the paper making process, as well as for drug delivery, are outlined. PEI/PAC nanoparticles mixed directly on model cellulose film showed a higher adsorption level applying the mixing order 1. PAC 2. PEI compared to 1. PEI 2. PAC. Surface bound PEI/PAC nanoparticles were found to release a model drug compound and to stay immobilized due to the contact with the aqueous release medium.