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Berlin Brandenburg

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  • 1
    Language: English
    In: Analytical chemistry, 19 November 2013, Vol.85(22), pp.10643-7
    Description: Studying the environmental fate of engineered or natural colloids requires efficient methods for measuring their size and quantifying them in the environment. For example, an ideal method should maintain its correctness, accuracy, reproducibility, and robustness when applied to samples contained in complex matrixes and distinguish the target particles from the natural colloidal background signals. Since it is expected that a large portion of nanoparticles will form homo- or heteroagglomerates when released into environmental media, it is necessary to differentiate agglomerates from primary particles. At present, most sizing techniques do not fulfill these requirements. In this study, we used online coupling of two promising complementary sizing techniques: hydrodynamic chromatography (HDC) and single-particle ICPMS analysis to analyze gold nanoparticles agglomerated under controlled conditions. We used the single-particle mode of the ICPMS detector to detect single particles eluted from an HDC-column and determine a mass and an effective diameter for each particle using a double calibration approach. The average agglomerate relative density and fractal dimension were calculated using these data and used to follow the morphological evolution of agglomerates over time during the agglomeration process. The results demonstrate the ability of HDC coupled to single-particle analysis to identify and characterize nanoparticle homoagglomerates and is a very promising technique for the analysis of colloids in complex media.
    Keywords: Nanopartikel ; Einzelpartikel ; Chromatographie ; Partikelanalyse ; Eichen (Abgleichen) ; Agglomerieren ; Fraktale Dimension ; Kolloid ; Gold ; Basis (Grundlage) ; Agglomerat ; Flankendurchmesser ; Massenspektrometrie Mit Induktiv Gekoppeltem Plasma ; Engineering ; Chemistry;
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 2
    Language: English
    In: The Science of the Total Environment, Dec 1, 2015, Vol.535, p.35(10)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.scitotenv.2014.11.058 Byline: George Metreveli, Allan Philippe, Gabriele E. Schaumann Abstract: Silver nanoparticles (Ag NPs) could be found in aquatic systems in the near future. Although the interplay between aggregate formation and disaggregation is an important factor for mobility, bioavailability and toxicity of Ag NPs in surface waters, the factors controlling disaggregation of Ag NP homoaggregates are still unknown. In this study, we investigated the reversibility of homoaggregation of citrate coated Ag NPs in a Rhine River water matrix. We characterized the disaggregation of Ag NP homoaggregates by ionic strength reduction and addition of Suwannee River humic acid (SRHA) in the presence of strong and weak shear forces. In order to understand the disaggregation processes, we also studied the nature of homoaggregates and their formation dynamics under the influence of SRHA, Ca.sup.2+ concentration and nanoparticle concentration. Even in the presence of SRHA and at low particle concentrations (10[mu]gL.sup.-1), aggregates formed rapidly in filtered Rhine water. The critical coagulation concentration (CCC) of Ca.sup.2+ in reconstituted Rhine water was 1.5mmolL.sup.-1 and was shifted towards higher values in the presence of SRHA. Analysis of the attachment efficiency as a function of Ca.sup.2+ concentration showed that SRHA induces electrosteric stabilization at low Ca.sup.2+ concentrations and cation-bridging flocculation at high Ca.sup.2+ concentrations. Shear forces in the form of mechanical shaking or ultrasound were necessary for breaking the aggregates. Without ultrasound, SRHA also induced disaggregation, but it required several days to reach a stable size of dense aggregates still larger than the primary particles. Citrate stabilized Ag NPs may be in the form of reaction limited aggregates in aquatic systems similar to the Rhine River. The size and the structure of these aggregates will be dynamic and be determined by the solution conditions. Seasonal variations in the chemical composition of natural waters can result in a sedimentation-release cycle of engineered nanoparticles. Article History: Received 29 September 2014; Revised 16 November 2014; Accepted 16 November 2014
    Keywords: Water – Analysis ; Humic Acids – Analysis
    ISSN: 0048-9697
    Source: Cengage Learning, Inc.
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  • 3
    Language: English
    In: The Science of the Total Environment, Dec 1, 2015, Vol.535, p.54(7)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.scitotenv.2014.10.108 Byline: Sondra Klitzke, George Metreveli, Andre Peters, Gabriele E. Schaumann, Friederike Lang Abstract: Nanoparticles enter soils through various pathways. In the soil, they undergo various interactions with the solution and the solid phase. We tested the following hypotheses using batch experiments: i) the colloidal stability of Ag NP increases through sorption of soil-borne dissolved organic matter (DOM) and thus inhibits aggregation; ii) the presence of DOM suppresses Ag oxidation; iii) the surface charge of Ag NP governs sorption onto soil particles. Citrate-stabilized and bare Ag NPs were equilibrated with (colloid-free) soil solution extracted from a floodplain soil for 24h. Nanoparticles were removed through centrifugation. Concentrations of free Ag ions and DOC, the specific UV absorbance at a wavelength of 254nm, and the absorption ratio [alpha].sub.254/[alpha].sub.410 were determined in the supernatant. Nanoparticle aggregation was studied using time-resolved dynamic light scattering (DLS) measurement following the addition of soil solution and 1.5mM Ca.sup.2+ solution. To study the effect of surface charge on the adsorption of Ag NP onto soil particles, bare and citrate-stabilized Ag NP, differing in the zeta potential, were equilibrated with silt at a solid-to-solution ratio of 1:10 and an initial Ag concentration range of 30 to 320[mu]g/L. Results showed that bare Ag NPs sorb organic matter, with short-chained organic matter being preferentially adsorbed over long-chained, aromatic organic matter. Stabilizing effects of organic matter only come into play at higher Ag NP concentrations. Soil solution inhibits the release of Ag.sup.+ ions, presumably due to organic matter coatings. Sorption to silt particles was very similar for the two particle types, suggesting that the surface charge does not control Ag NP sorption. Besides, sorption was much lower than in comparable studies with sand and glass surfaces. Article History: Received 29 September 2014; Revised 30 October 2014; Accepted 30 October 2014 Article Note: (miscellaneous) Editor: D. Barcelo
    Keywords: Nanoparticles ; Adsorption
    ISSN: 0048-9697
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: PLoS ONE, 01 January 2014, Vol.9(2), p.e90559
    Description: In this study, we evaluated hydrodynamic chromatography (HDC) coupled with inductively coupled plasma mass spectrometry (ICP-MS) for the analysis of nanoparticles in environmental samples. Using two commercially available columns (Polymer Labs-PDSA type 1 and 2), a set of well characterised calibrants and a new external time marking method, we showed that flow rate and eluent composition have few influence on the size resolution and, therefore, can be adapted to the sample particularity. Monitoring the agglomeration of polystyrene nanoparticles over time succeeded without observable disagglomeration suggesting that even weak agglomerates can be measured using HDC. Simultaneous determination of gold colloid concentration and size using ICP-MS detection was validated for elemental concentrations in the ppb range. HDC-ICP-MS was successfully applied to samples containing a high organic and ionic background. Indeed, online combination of UV-visible, fluorescence and ICP-MS detectors allowed distinguishing between organic molecules and inorganic colloids during the analysis of Ag nanoparticles in synthetic surface waters and TiO₂ and ZnO nanoparticles in commercial sunscreens. Taken together, our results demonstrate that HDC-ICP-MS is a flexible, sensitive and reliable method to measure the size and the concentration of inorganic colloids in complex media and suggest that there may be a promising future for the application of HDC in environmental science. Nonetheless the rigorous measurements of agglomerates and of matrices containing natural colloids still need to be studied in detail.
    Keywords: Sciences (General)
    E-ISSN: 1932-6203
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  • 5
    Language: English
    In: The Science of the Total Environment, Dec 1, 2015, Vol.535, p.1(2)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.scitotenv.2015.06.006 Byline: Gabriele E. Schaumann, Thomas Baumann, Friederike Lang, George Metreveli, Hans-Jorg Vogel
    Keywords: Soils
    ISSN: 0048-9697
    Source: Cengage Learning, Inc.
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  • 6
    Language: English
    In: The Science of the Total Environment, Dec 1, 2015, Vol.535, p.113(9)
    Description: To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.scitotenv.2015.03.023 Byline: Samuel K. Kumahor, Pavel Hron, George Metreveli, Gabriele E. Schaumann, Hans-Jorg Vogel Abstract: Chemical factors and physical constraints lead to coupled effects during particle transport in unsaturated porous media. Studies on unsaturated transport as typical for soils are currently scarce. In unsaturated porous media, particle mobility is determined by the existence of an air-water interface in addition to a solid-water interface. To this end, we measured breakthrough curves and retention profiles of citrate-coated Ag nanoparticles in unsaturated sand at two pH values (5 and 9) and three different flow rates corresponding to different water contents with 1mM KNO.sub.3 as background electrolyte. The classical DLVO theory suggests unfavorable deposition conditions at the air-water and solid-water interfaces. The breakthrough curves indicate modification in curve shapes and retardation of nanoparticles compared to inert solute. Retention profiles show sensitivity to flow rate and pH and this ranged from almost no retention for the highest flow rate at pH=9 to almost complete retention for the lowest flow rate at pH=5. Modeling of the breakthrough curves, thus, required coupling two parallel processes: a kinetically controlled attachment process far from equilibrium, responsible for the shape modification, and an equilibrium sorption, responsible for particle retardation. The non-equilibrium process and equilibrium sorption are suggested to relate to the solid-water and air-water interfaces, respectively. This is supported by the DLVO model extended for hydrophobic interactions which suggests reversible attachment, characterized by a secondary minimum (depth 3-5kT) and a repulsive barrier at the air-water interface. In contrast, the solid-water interface is characterized by a significant repulsive barrier and the absence of a secondary minimum suggesting kinetically controlled and non-equilibrium interaction. This study provides new insights into particle transport in unsaturated porous media and offers a model concept representing the relevant processes. Article History: Received 9 December 2014; Revised 5 March 2015; Accepted 5 March 2015 Article Note: (miscellaneous) Editor: D. Barcelo
    Keywords: Nanoparticles – Analysis ; Multiprocessing – Analysis
    ISSN: 0048-9697
    Source: Cengage Learning, Inc.
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  • 7
    Language: English
    In: Langmuir : the ACS journal of surfaces and colloids, 09 October 2018, Vol.34(40), pp.12174-12182
    Description: Adsorption is the main mechanism of capturing water in soil organic matter (SOM) under arid conditions. This process is governed by hydrophilic sites, which are gradually bridged via water molecule bridges (WaMB). Until now, the link between WaMB and other types of water molecules occurring in SOM during sorption has not been systematically investigated. In this work, we compared the formation and stability of WaMB simultaneously with the total water content, strength of water binding, and kinetics of water sorption in a vacuum-dried model SOM (sapric histosol) exposed to different relative water pressures. The same parameters were then determined in SOM exposed to reduced relative pressures. The adsorption resulted in an adsorption isotherm with a Langmuir-like part below a relative pressure of 0.5 and a Brunauer-Emmett-Teller-like isotherm at higher relative pressures. The WaMB formation was observed at a relative pressure of 0.32, which represented the pressure at which Langmuir-like part reached a plateau. The binding energy showed a linear decrease with an increasing pressure; the slope increased at a relative pressure of 0.46. Reduction of relative pressures above 0.46 showed that the water content remained constant, but the binding energy was lowered. In contrast, below a relative pressure of 0.46, the water content decreased, but the binding energy was not changed. The results indicate that in SOM exposed to different relative pressures, water exists in three types: first, it is strongly bound to primary sorption sites (Langmuir-like), second, it occurs in the form of WaMB water, which bridges functional groups and where predominates water-water interactions, and third, it occurs in the form of phase water, which is located in larger pores similar to the pure water phase. The latter either surrounds the WaMB and destabilizes it or, for higher water content, links individual WaMB and successively reduces their stabilizing effect. Formation of phase water leads to swelling processes including plasticizing effects and potential volume changes of SOM. Accordingly, the results suggest that at lower water relative pressures WaMB stabilizes the SOM structure, whereas at higher water relative pressures, it influences the formation of phase water and thereby the total water content in SOM.
    ISSN: 07437463
    E-ISSN: 1520-5827
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  • 8
    Language: English
    In: Analytical chemistry, 07 August 2018, Vol.90(15), pp.8793-8799
    Description: The use of plastic materials in daily life, industry, and agriculture can cause soil pollution with plastic fragments down to the micrometer scale, i.e., microplastics. Quantitative assessment of microplastics in soil has been limited so far. Until now, microplastic analyses in soil require laborious sample cleanup and are mostly restricted to qualitative assessments. In this study, we applied thermogravimetry-mass spectrometry (TGA-MS) to develop a method for the direct quantitative analysis of poly(ethylene terephthalate) (PET) without further sample pretreatment. For this, soil samples containing 1.61 ± 0.15 wt % organic matter were spiked with 0.23-4.59 wt % PET bottle recyclate microplastics. dl-Cysteine was used as the internal standard (IS). Sample mixtures were pyrolyzed with a 5 K min ramp (40-1000 °C), while sample mass loss and MS signal intensity of typical PET pyrolysis products were recorded. We found MS signal intensities linearly responding to microplastic concentrations. The most-promising results were obtained with the IS-corrected PET pyrolysis product vinylbenzene/benzoic acid ( m/ z = 105, adj. R = 0.987). The limits of detection and quantification were 0.07 and 1.72 wt % PET, respectively. Our results suggest that TGA-MS can be an easy and viable complement to existing methods such as pyrolysis or thermogravimetry-thermal desorption assays followed by gas chromatography/mass spectrometry detection or to spectral microscopy techniques.
    Keywords: Microplastics ; Quantitative-Analysis ; Pyrolysis ; Terephthalate ; Soil-Pollution ; Soil-Analysis ; Ground-Samples ; Mass-Reduction ; Cysteine ; Benzoic-Acid ; Agricultural-Industry ; Fragment ; Organic-Medium ; Detection-Limit ; Thermogravimetric-Analysis ; Spectral-Technique ; Mikroplastik ; Quantitative Analyse ; Pyrolyse ; Terephthalat ; Bodenverschmutzung ; Bodenanalyse ; Bodenprobe ; Massenverringerung ; Cystein ; Benzoesäure ; Agrikultur ; Fragment ; Organisches Material ; Nachweisgrenze ; Thermogravimetrie ; Spektralverfahren ; Engineering ; Chemistry;
    ISSN: 00032700
    E-ISSN: 1520-6882
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  • 9
    Language: English
    In: The journal of physical chemistry. A, 30 March 2017, Vol.121(12), pp.2367-2376
    Description: Water molecules in soil organic matter (SOM) can form clusters bridging neighboring molecular segments (water molecule bridges, WaMBs). WaMBs are hypothesized to enhance the physical entrapment of organic chemicals and to control the rigidity of the SOM supramolecular structure. However, the understanding of WaMBs dynamics in SOM is still limited. We investigated the relation between WaMBs stability and the physicochemical properties of their environment by treating a sapric histosol with various solvents and organic chemicals. On the basis of predictions from molecular modeling, we hypothesized that the stability of WaMBs, measured by differential scanning calorimetry, increases with the decreasing ability of a chemical to interact with water molecules of the WaMBs. The interaction ability between WaMBs and the chemicals was characterized by linear solvation energy relationships. The WaMBs stability in solvent-treated samples was found to decrease with increasing ability of a solvent to undergo H-donor/acceptor interactions. Spiking with an organic chemical stabilized (naphthalene) or destabilized (phenol) the WaMBs. The WaMBs stability and matrix rigidity were generally reduced strongly and quickly when hydrophilic chemicals entered the soil. The physicochemical aging following this destabilization is slow but leads to successive WaMBs stabilization and matrix stiffening.
    Keywords: Humus – Research ; Organic Compounds – Chemical Properties ; Polar Molecules – Chemical Properties;
    ISSN: 10895639
    E-ISSN: 1520-5215
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  • 10
    Language: English
    In: Journal of Colloid And Interface Science, 15 April 2018, Vol.516, pp.446-455
    Description: Soil water repellency originating from organic coatings plays a crucial role for soil hydraulics and plant water uptake. Focussing on hydrophobicity in the rhizosphere induced by root-mucilage, this study aims to explore the link between macroscopic wettability and nano-microscopic surface properties. The existing knowledge of the nanostructures of organic soil compounds and its effect on wettability is limited by the lack of a method capable to assess the natural spatial heterogeneity of physical and chemical properties. In this contribution, this task is tackled by a geostatistical approach via variogram analysis of topography and adhesion force data acquired by atomic force microscopy and macroscopic sessile drop measurements on dried films of mucilage. The results are discussed following the wetting models given by Wenzel and Cassie-Baxter. Undiluted mucilage formed homogeneous films on the substrate with contact angles 〉90°. For diluted samples contact angles were smaller and incomplete mucilage surface coverage with hole-like structures frequently exhibited increased adhesion forces. Break-free distances of force curves indicated enhanced capillary forces due to adsorbed water films at atmospheric RH (35 ± 2%) that promote wettability. Variogram analysis enabled a description of complex surface structures exceeding the capability of comparative visual inspection.
    Keywords: Soil Water Repellency ; Root-Mucilage ; Contact Angle ; Atomic Force Microscopy ; Adhesion ; Nanomechanical Mapping ; Variogram ; Engineering ; Chemistry
    ISSN: 0021-9797
    E-ISSN: 1095-7103
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