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search.filters.applied.f.access: openAccess × End date: 2022 × Start date: 2020 × Has files: Yes × Subject: Adsorption ×

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    Solubility 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, Dana
    The 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.
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    Two-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, Oliver
    In2O3 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.
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    Waterborne 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, Dana
    Highly 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.