@article{LippoldEidnerKumkeetal.2017, author = {Lippold, Holger and Eidner, Sascha and Kumke, Michael Uwe and Lippmann-Pipke, Johanna}, title = {Dynamics of metal-humate complexation equilibria as revealed by isotope exchange studies - a matter of concentration and time}, series = {Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society}, volume = {197}, journal = {Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society}, publisher = {Elsevier}, address = {Oxford}, issn = {0016-7037}, doi = {10.1016/j.gca.2016.10.019}, pages = {62 -- 70}, year = {2017}, abstract = {Complexation with dissolved humic matter can be crucial in controlling the mobility of toxic or radioactive contaminant metals. For speciation and transport modelling, a dynamic equilibrium process is commonly assumed, where association and dissociation run permanently. This is, however, questionable in view of reported observations of a growing resistance to dissociation over time. In this study, the isotope exchange principle was employed to gain direct insight into the dynamics of the complexation equilibrium, including kinetic inertisation phenomena. Terbium(III), an analogue of trivalent actinides, was used as a representative of higher-valent metals. Isotherms of binding to (flocculated) humic acid, determined by means of Tb-160 as a radiotracer, were found to be identical regardless of whether the radioisotope was introduced together with the bulk of stable Tb-159 or subsequently after pre-equilibration for up to 3 months. Consequently, there is a permanent exchange of free and humic-bound Tb since all available binding sites are occupied in the plateau region of the isotherm. The existence of a dynamic equilibrium was thus evidenced. There was no indication of an inertisation under these experimental conditions. If the small amount of Tb-160 was introduced prior to saturation with Tb-159, the expected partial desorption of Tb-160 occurred at much lower rates than observed for the equilibration process in the reverse procedure. In addition, the rates decreased with time of pre-equilibration. Inertisation phenomena are thus confined to the stronger sites of humic molecules (occupied at low metal concentrations). Analysing the time-dependent course of isotope exchange according to first-order kinetics indicated that up to 3 years are needed to attain equilibrium. Since, however, metal-humic interaction remains reversible, exchange of metals between humic carriers and mineral surfaces cannot be neglected on the long time scale to be considered in predictive transport models.}, language = {en} } @article{VacogneSchlaad2017, author = {Vacogne, Charlotte D. and Schlaad, Helmut}, title = {Controlled ring-opening polymerization of alpha-amino acid N-carboxyanhydrides in the presence of tertiary amines}, series = {Polymer : the international journal for the science and technology of polymers}, volume = {124}, journal = {Polymer : the international journal for the science and technology of polymers}, publisher = {Elsevier}, address = {Oxford}, issn = {0032-3861}, doi = {10.1016/j.polymer.2017.07.062}, pages = {203 -- 209}, year = {2017}, abstract = {The mechanism of the primary ammonium/tertiary amine-mediated ring-opening polymerization of gamma-benzyl-L-glutamate N-carboxyanhydride (BLG-NCA) was investigated. Kinetic analyses revealed that the normal amine mechanism (NAM) together with a dormant-active chain end equilibrium were responsible for the controlled nature of this polymerization pathway, but that the polymerization also proceeded via the activated monomer mechanism (AMM). Mixtures of primary amines (1 equiv) and tertiary amines (0-1.5 equiv) were therefore tested to confirm the co-existence of the NAM and AMM and determine the limits for a controlled polymerization. For tertiary amine molar fractions smaller than 0.8 equiv, the reaction times were greatly reduced (compared to primary amine-initiated polymerization) without compromising the control of the reaction. Hence, the polymerization of NCA can proceed in a controlled manner even when the AMM contributes to the overall chain growth mechanism. (C) 2017 Elsevier Ltd. All rights reserved.}, language = {en} } @article{OmorogieBabalolaUnuabonahetal.2016, author = {Omorogie, Martins O. and Babalola, Jonathan Oyebamiji and Unuabonah, Emmanuel I. and Gong, Jian R.}, title = {Clean technology approach for the competitive binding of toxic metal ions onto MnO2 nano-bioextractant}, series = {Clean technologies and environmental policy}, volume = {18}, journal = {Clean technologies and environmental policy}, publisher = {Springer}, address = {New York}, issn = {1618-954X}, doi = {10.1007/s10098-015-1004-z}, pages = {171 -- 184}, year = {2016}, abstract = {The competitive extraction of Cr(III) onto Nauclea diderrichii seed epicarp doped with MnO2 nanoparticles (MnO2 nano-bioextractant (MNB)) in a single and binary batch system was studied. For validity of experimental data, chi square test, root mean square error, sum of the square errors, hybrid fractional error function, Marquart's percent standard deviation and standard absolute error were used. Among the kinetic models used, pseudo-second-order and Langmuir equations gave the best fits for the experimental data, with qe (mg g) for the uptake of Cr(III) in single metal system onto MNB, then Cr(III) with Cd(II), Pb(II), Hg(II), KCl and CaCl2 in binary metal systems onto MNB were 2.611, then 1.989, 1.016, 2.208, 1.249 and 1.868 from kinetic standpoint, respectively. The initial sorption rates, h (mg/g/min), and half lives, t1/2 (min), for the uptake of Cr(III) in single metal system onto MNB, then Cr(III) with Cd(II), Pb(II), Hg(II), KCl and CaCl2 in binary metal system onto MNB were 3.497, then 2.311, 2.274, 0.242, 2.956, 45.568 and 0.747, then 5.769, 1.766, 12.144, 1.762, and 2.415, respectively. Physicochemical surface analyses such as pH of point of zero charge, Brunauer-Emmett-Teller single point and multi-point techniques for surface area analyses, scanning electron microscopy and transmission electron microscopy were done on MNB and MnO2 nanoparticles in order to understand their surface microstructures. Desorption study showed that MNB can be recycled and used for future study. Hence, MNB showed good potential to remediate Cr(III) from wastewaters and polluted water.}, language = {en} } @article{OmorogieBabalolaUnuabonahetal.2016, author = {Omorogie, Martins O. and Babalola, Jonathan Oyebamiji and Unuabonah, Emmanuel I. and Song, Weiguo and Gong, Jian Ru}, title = {Efficient chromium abstraction from aqueous solution using a low-cost biosorbent: Nauclea diderrichii seed biomass waste}, series = {Journal of Saudi Chemical Society}, volume = {20}, journal = {Journal of Saudi Chemical Society}, publisher = {Elsevier}, address = {Amsterdam}, issn = {1319-6103}, doi = {10.1016/j.jscs.2012.09.017}, pages = {49 -- 57}, year = {2016}, abstract = {Toxic Cr(III) which poses environmental hazard to flora and fauna was efficiently abstracted by low-cost Nauclea diderrichii seed biomass (NDS) with good sequestral capacity for this metal was investigated in this study. The NDS surface analyses showed that it has a specific surface area of 5.36 m(2)/g and pHpzc of 4.90. Thermogravimetric analysis of NDS showed three consecutive weight losses from 50-200 degrees C (ca. 5\%), 200-400 C (ca. 35\%), >400 degrees C (ca. 10\%), corresponding to external water molecules, structural water molecules and heat induced condensation reactions respectively. Differential thermogram of NDS presented a large endothermic peak between 20-510 degrees C suggesting bond breakage and dissociation with the ultimate release of small molecules. The experimental data showed kinetically fast biosorption with increased initial Cr(III) concentrations, indicating the role of external mass transfer mechanism as the rate controlling mechanism in this adsorption process. The Langmuir biosorption capacity of NDS was 483.81 mg/g. The use of the corrected Akaike Information Criterion tool for ranking equilibrium models suggested that the Freundlich model best described the experimental data, which is an indication of the heterogeneous nature of the active sites on the surface of NDS. N. diderrichii seed biomass is an easily sourced, cheap and environmental friendly biosorbent which will serve as a good and cost effective alternative to activated carbon for the treatment of polluted water and industrial effluents. (C) 2012 King Saud University. Production and hosting by Elsevier B.V. All rights reserved.}, language = {en} } @article{SchafferIdzikWilkeetal.2016, author = {Schaffer, Mario and Idzik, Krzysztof R. and Wilke, Max and Licha, Tobias}, title = {Amides as thermo-sensitive tracers for investigating the thermal state of geothermal reservoirs}, series = {Geothermics : an international journal of geothermal research and its applications}, volume = {64}, journal = {Geothermics : an international journal of geothermal research and its applications}, publisher = {Elsevier}, address = {Oxford}, issn = {0375-6505}, doi = {10.1016/j.geothermics.2016.05.004}, pages = {180 -- 186}, year = {2016}, abstract = {The application of thermo-sensitive tracers is a promising technique for evaluating the thermal state of geothermal reservoirs. To extend the compound spectrum for hydrolyzable compounds to reservoir temperatures between 100 and 200 degrees C carboxamides were studied. The kinetic parameters of 17 self-synthesized amides were determined in hydrothermal batch and autoclave experiments. The influence of the molecular structure and the role of pH/pOH on hydrolysis kinetics were studied. Additionally, the thermal stabilities of the hydrolysis products were evaluated. The results demonstrate the high potential of tracers based on amide hydrolysis for use in medium enthalpy reservoirs. (C) 2016 Elsevier Ltd. All rights reserved.}, language = {en} } @article{ShkilnyySchoeneRumplaschetal.2011, author = {Shkilnyy, Andriy and Sch{\"o}ne, Stefanie and Rumplasch, Claudia and Uhlmann, Annett and Hedderich, Annett and G{\"u}nter, Christina and Taubert, Andreas}, title = {Calcium phosphate mineralization with linear poly(ethylene imine) a time-resolved study}, series = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, volume = {289}, journal = {Colloid and polymer science : official journal of the Kolloid-Gesellschaft}, number = {8}, publisher = {Springer}, address = {New York}, issn = {0303-402X}, doi = {10.1007/s00396-011-2403-2}, pages = {881 -- 888}, year = {2011}, abstract = {We have earlier shown that linear poly(ethylene imine) (LPEI) is an efficient growth modifier for calcium phosphate mineralization from aqueous solution (Shkilnyy et al., Langmuir, 2008, 24 (5), 2102). The current study addresses the growth process and the reason why LPEI is such an effective additive. To that end, the solution pH and the calcium and phosphate concentrations were monitored vs. reaction time using potentiometric, complexometric, and photometric methods. The phase transformations in the precipitates and particle morphogenesis were analyzed by X-ray diffraction and transmission electron microscopy, respectively. All measurements reveal steep decreases of the pH, calcium, and phosphate concentrations along with a rapid precipitation of brushite nanoparticles early on in the reaction. Brushite transforms into hydroxyapatite (HAP) within the first 2 h, which is much faster than what is reported, for example, for calcium phosphate precipitated with poly(acrylic acid). We propose that poly(ethylene imine) acts as a proton acceptor (weak buffer), which accelerates the transformation from brushite to HAP by taking up the protons that are released from the calcium phosphate precipitate during the phase transformation.}, language = {en} } @article{BalckeHahnOswald2011, author = {Balcke, Gerd U. and Hahn, M. and Oswald, Sascha Eric}, title = {Nitrogen as an indicator of mass transfer during in-situ gas sparging}, series = {Journal of contaminant hydrology}, volume = {126}, journal = {Journal of contaminant hydrology}, number = {1-2}, publisher = {Elsevier}, address = {Amsterdam}, issn = {0169-7722}, doi = {10.1016/j.jconhyd.2011.05.005}, pages = {8 -- 18}, year = {2011}, abstract = {Aiming at the stimulation of intrinsic microbial activity, pulses of pure oxygen or pressurized air were recurrently injected into groundwater polluted with chlorobenzene. To achieve well-controlled conditions and intensive sampling, a large, vertical underground tank was filled with the local unconfined sandy aquifer material. In the course of two individual gas injections, one using pure oxygen and one using pressurized air, the mass transfer of individual gas species between trapped gas phase and groundwater was studied. Field data on the dissolved gas composition in the groundwater were combined with a kinetic model on gas dissolution and transport in porous media. Phase mass transfer of individual gas components caused a temporary enrichment of nitrogen, and to a lower degree of methane, in trapped gas leading to the formation of excess dissolved nitrogen levels downgradient from the dissolving gas phase. By applying a novel gas sampling method for dissolved gases in groundwater it was shown that dissolved nitrogen can be used as a partitioning tracer to indicate complete gas dissolution in porous media.}, language = {en} } @article{OmorogieBabalolaUnuabonahetal.2012, author = {Omorogie, Martins O. and Babalola, Jonathan Oyebamiji and Unuabonah, Emmanuel I. and Gong, Jian Ru}, title = {Kinetics and thermodynamics of heavy metal ions sequestration onto novel Nauclea diderrichii seed biomass}, series = {BIORESOURCE TECHNOLOGY}, volume = {118}, journal = {BIORESOURCE TECHNOLOGY}, number = {8}, publisher = {ELSEVIER SCI LTD}, address = {OXFORD}, issn = {0960-8524}, doi = {10.1016/j.biortech.2012.04.053}, pages = {576 -- 579}, year = {2012}, abstract = {This study reports the sequestration of Cd(II) and Hg(II) using a new biosorbent. Nauclea diderrichii seed biomass. Experimental data obtained were fitted into kinetic and thermodynamic models. Experimental data fitted best into pseudo-second order kinetic model among others. Results obtained kinetically revealed that the biosorption of Cd(II) and Hg(II) using N. diderrichii seed biosorbent increased with increase in temperature. At the highest temperature, which was 333 K. the highest amount of metal biosorbed, q(e), for Cd(II) and Hg(II) obtained were 6.30 and 6.15 mg/g respectively. The biosorption of Cd(II) was kinetically faster than that of Hg(II), the highest initial biosorption rates for Cd(II) and Hg(II) were 56.19 and 4.39 mg/g min respectively. Thermodynamic parameters obtained by Erying equation from this study revealed that the biosorption process was spontaneous, feasible, endothermic with a decrease in the degree of chaos in the biosorption system. (C) 2012 Elsevier Ltd. All rights reserved.}, language = {en} } @article{UnuabonahGuenterWeberetal.2013, author = {Unuabonah, Emmanuel I. and G{\"u}nter, Christina and Weber, Jens and Lubahn, Susanne and Taubert, Andreas}, title = {Hybrid Clay - a new highly efficient adsorbent for water treatment}, series = {ACS sustainable chemistry \& engineering}, volume = {1}, journal = {ACS sustainable chemistry \& engineering}, number = {8}, publisher = {American Chemical Society}, address = {Washington}, issn = {2168-0485}, doi = {10.1021/sc400051y}, pages = {966 -- 973}, year = {2013}, abstract = {New hybrid clay adsorbent based on kaolinite clay and Carica papaya seeds with improved cation exchange capacity (CEC), rate of heavy metal ion uptake, and adsorption capacity for heavy metal ions were prepared. The CEC of the new material is ca. 75 meq/100 g in spite of the unexpectedly low surface area (approximate to 19 m(2)/g). Accordingly, the average particle size of the hybrid clay adsorbent decreased from over 200 to 100 pm. The hybrid clay adsorbent is a highly efficient adsorbent for heavy metals. With an initial metal concentration of 1 mg/L, the hybrid clay adsorbent reduces the Cd2+, Ni2+, and Pb2+ concentration in aqueous solution to <= 4, <= 7 and <= 20 mu g/L, respectively, from the first minute to over 300 min using a fixed bed containing 2 g of adsorbent and a flow rate of approximate to 7 mL/min. These values are (with the exception of Pb2+) in line with the WHO permissible limits for heavy metal ions. In a cocktail solution of Cd2+, and Ni2+, the hybrid clay shows a reduced rate of uptake but an increased adsorption capacity. The CEC data suggest that the adsorption of Pb2+, Cd2+, and Ni2+ on the hybrid clay adsorbent is essentially due to ion exchange. This hybrid clay adsorbent is prepared from materials that are abundant and by a simple means that is sustainable, easily recovered from aqueous solution, nonbiodegradable (unlike numerous biosorbent), and easily regenerated and is a highly efficient alternative to activated carbon for water treatment.}, language = {en} }