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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: 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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  • 3
    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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  • 4
    Language: English
    In: Environmental science & technology, 19 August 2014, Vol.48(16), pp.8946-62
    Description: This contribution critically reviews the state of knowledge on interactions of natural colloids and engineered nanoparticles with natural dissolved organic materials (DOM). These interactions determine the behavior and impact of colloids in natural system. Humic substances, polysaccharides, and proteins present in natural waters adsorb onto the surface of most colloids. We outline major adsorption mechanisms and structures of adsorption layers reported in the literature and discuss their generality on the basis of particle type, DOM type, and media composition. Advanced characterization methods of both DOM and colloids are needed to address insufficiently understood aspects as DOM fractionation upon adsorption, adsorption reversibility, and effect of capping agent. Precise knowledge on adsorption layer helps in predicting the colloidal stability of the sorbent. While humic substances tend to decrease aggregation and deposition through electrostatic and steric effects, bridging-flocculation can occur in the presence of multivalent cations. In the presence of DOM, aggregation may become reversible and aggregate structure dynamic. Nonetheless, the role of shear forces is still poorly understood. If traditional approaches based on the DLVO-theory can be useful in specific cases, quantitative aggregation models taking into account DOM dynamics, bridging, and disaggregation are needed for a comprehensive modeling of colloids stability in natural media.
    Keywords: Humic Substances ; Colloids -- Chemistry ; Nanoparticles -- Chemistry ; Water Pollutants, Chemical -- Chemistry
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 5
    Language: English
    In: Reviews in Environmental Science and Bio/Technology, 2013, Vol.12(3), pp.235-256
    Description: A main objective in the field of mixture toxicity is to determine how well combined effects are predictable based on the known effects of mixture constituents. Conducting toxicity tests for all conceivable combinations of chemicals, to understand all mechanisms in the combined toxicity of environmental pollutants, is virtually unfeasible due to cost- and time-consuming procedures. Therefore, predictive tools for mixture toxicity are required to be developed within the applicable range of predictive toxicology. The concept of concentration addition (CA) model is often considered a general method for estimating mixture toxicity at the regulatory level. In the long run, however, the possibility of toxicological synergism between mixture components actually occurs, especially from the no-effect level or non-toxic substances. This is ignored under the CA concept, and needs to be examined and integrated into existing addition models at a scientific level, this paper reviews existing integrated models for estimating the toxicity of complex mixtures in literature. Current approaches to assess mixture toxicity and the need for new research concepts to overcome challenges which recent studies have confronted are discussed, particularly those involved in computational approaches to predict mixture toxicity in an environment risk assessment based on mixture components.
    Keywords: Mixture toxicity ; Mixture risk assessment ; Prediction model ; Computational toxicology
    ISSN: 1569-1705
    E-ISSN: 1572-9826
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  • 6
    Language: English
    In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 20 August 2013, Vol.431, pp.150-160
    Description: The effect of grain water repellency on transport and deposition of hydrophilic colloids was studied by analyzing the breakthrough behavior of carboxylate-modified microspheres in water-saturated wettable and hydrophobic sand columns at different ionic strengths. Interaction free energies calculated from zeta ( )-potential and contact angle data were used to explain the specific colloid breakthrough behavior. Experimental breakthrough data could be well described with the finite-element code HYDRUS-1D using a one kinetic site model with attachment and detachment kinetics. Higher colloid deposition rates found for the hydrophobic sand could primarily be explained by its small electron-donor component of surface free energy ( = 1.6 × 10 mJ m , compared to = 64.1 mJ m for the wettable sand), leading to strongly attractive acid–base interactions at separation distances 〈 5 nm. Increasing ionic strength reduced the repulsive electrostatic interactions and generally increased colloid deposition with the effect being more pronounced in the hydrophobic sand. It can be concluded that grain water repellency tends to increase the deposition of negatively charged hydrophilic colloids, which can be ascribed to specific acid–base interactions. However, our results further revealed that the calculated interaction free energy profiles should be considered only as an approximation showing general trends because surface chemical heterogeneity as detected by atomic forces microscopy impeded the determination of the actual interaction energy conditions, resulting in an overestimation of electrostatic repulsion.
    Keywords: Acid–Base Interaction ; Carboxylate-Modified Microspheres ; Colloid Breakthrough ; Interaction Free Energy ; Surface Free Energy Components ; Wettability ; Engineering ; Chemistry
    ISSN: 0927-7757
    E-ISSN: 1873-4359
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  • 7
    Language: English
    In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2005, Vol.265(1), pp.163-170
    Description: In this study, hydration of a peat sample was investigated with differential scanning calorimetry (DSC) in terms of glass transition behavior and the formation of freezable and unfreezable water. Special attention was drawn to the development of these characteristics in the course of hydration and to plasticizing and antiplasticizing effects of water. Freezable water was formed above a water content threshold of = (23 ± 7)% and revealed structured melting peaks indicating freezable bulk-like water and freezable bound water. The freezable bound water revealed a broad, kinetically controlled melting endotherm, and the melting barrier increased with increasing hydration time. Glass transitions were found in between 43 °C and 68 °C with a change in heat capacity of Δ = (0.13 ± 0.08) J g K . Glass transition behavior does not fully match the theoretical expectations and is linked with water binding. Water reveals a short-term plasticizing function in the range of days as well as a slow antiplasticizing function in the range of weeks or even months. The findings are consistent with the hydrogen bond based cross-linking model (HBCL) suggested in a previous study. Non-equilibrium and matrix relaxation are considered the rule rather than the exception in nature and underline the ecological relevance of hydration, the relevance for sorption and transport phenomena was well as possibly for soil development.
    Keywords: Hydration ; Peat ; Plasticizer ; Antiplasticizer ; Unfreezable Water ; Glass Transition ; Engineering ; Chemistry
    ISSN: 0927-7757
    E-ISSN: 1873-4359
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  • 8
    Language: English
    In: Reviews in Environmental Science and Bio/Technology, 2012, Vol.11(1), pp.41-54
    Description: Interactions between cations and natural organic matter (NOM) are central for the stability of organic matter, formation of supramolecular NOM structure, formation of organo-mineral associations, soil aggregation and binding of organic contaminants. The effect of multivalent cations on environmental functionalities of NOM strongly depends on the relative importance between intramolecular complexation and intermolecular cross-linking, the degree of which will be determined by the spatial arrangement of the hydrophilic functional groups in NOM. This literature review seeks to evaluate the current state of the art regarding the relevance of intermolecular cross-links via bridges of multivalent cations. Cross-linking has been suggested to explain among others aggregate stability, retarded dissolved organic matter release, reduced organic matter (OM) solubility as well as increase in degree and nonlinearity of sorption or organic chemicals to NOM. Although the cross-linking mechanism has been suggested in numerous studies, it has not yet been verified directly. The dynamics of the intermolecular cross-links, their persistence as well as their interplay with OM and their influence on stability and bioavailability of organic chemicals is up to now unknown. The major challenge in this context is the development of a suitable combination of experimental and instrumental techniques and relating the results to molecular and physicochemical models on the basis of targeted combination of spectroscopic, molecular modelling and thermoanalytical methods.
    Keywords: Cations ; Natural organic matter ; Cross-linking ; Water molecule bridges ; Cation bridges ; NMR ; Thermal analysis
    ISSN: 1569-1705
    E-ISSN: 1572-9826
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  • 9
    Language: English
    In: Environmental science & technology, 21 May 2013, Vol.47(10), pp.5083-91
    Description: The fate of engineered nanoparticles in environmental systems is controlled by changes in colloidal stability and their interaction with different environmental surfaces. Little is known about nanoparticle-surface interactions on the basis of sorption isotherms under quasi-equilibrium conditions, although sorption isotherms are a valuable means of studying sorbate-sorbent interactions. We tested the extent to which the sorption of engineered silver nanoparticles (nAg) from stable and unstable suspensions to model (sorbents with specific chemical functional groups) and environmental (plant leaves and sand) surfaces can be described by classical sorption isotherms. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) qualitative and quantitative analyses were also used to assess the morphology and nanomechanical parameters of the covered surfaces. The sorption of nAg from stable suspensions was nonlinear and best described by the Langmuir isotherm. Langmuir coefficients varied with sorbent surface chemistry. For nAg sorption from an unstable suspension, the sorption isotherms did not follow any classical sorption models, suggesting interplay between aggregation and sorption. The validity of the Langmuir isotherm suggests monolayer sorption, which can be explained by the blocking effect due to electrostatic repulsion of individual nanoparticles. In unstable suspensions, aggregates are instead formed in suspension and then sorbed, formed on the surface itself, or formed in both ways.
    Keywords: Models, Chemical ; Metal Nanoparticles -- Chemistry ; Silver -- Chemistry
    ISSN: 0013936X
    E-ISSN: 1520-5851
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  • 10
    Language: English
    In: Journal of Contaminant Hydrology, December 2016, Vol.195, pp.31-39
    Description: Engineered nanoparticles released into soils may be coated with humic substances, potentially modifying their surface properties. Due to their amphiphilic nature, humic coating is expected to affect interaction of nanoparticle at the air-water interface. In this study, we explored the roles of the air-water interface and solid-water interface as potential sites for nanoparticle attachment and the importance of hydrophobic interactions for nanoparticle attachment at the air-water interface. By exposing Ag nanoparticles to soil solution extracted from the upper soil horizon of a floodplain soil, the mobility of the resulting “soil-aged” Ag nanoparticles was investigated and compared with the mobility of citrate-coated Ag nanoparticles as investigated in an earlier study. The mobility was determined as a function of hydrologic conditions and solution chemistry using column breakthrough curves and numerical modeling. Specifically, we compared the mobility of both types of nanoparticles for different unsaturated flow conditions and for pH = 5 and pH = 9. The soil-aged Ag NP were less mobile at pH = 5 than at pH = 9 due to lower electrostatic repulsion at pH = 5 for both types of interfaces. Moreover, the physical flow field at different water contents modified the impact of chemical forces at the solid-water interface. An extended Derjaguin-Landau-Verwey-Overbeek (eDLVO) model did not provide satisfactory explanation of the observed transport phenomena unlike for the citrate-coated case. For instance, the eDLVO model assuming sphere-plate geometry predicts a high energy barrier (〉 90 ) for the solid-water interface, indicating that nanoparticle attachment is less likely. Furthermore, retardation through reversible sorption at the air-water interface was probably less relevant for soil-aged nanoparticles than for citrate-coated nanoparticles. An additional cation bridging mechanism and straining within the flow field may have enhanced nanoparticle retention at the solid-water interface. The results indicate that the mobility of engineered Ag nanoparticles is sensitive to solution chemistry, especially pH and the concentration of multivalent cations, and to the unsaturated flow conditions influencing particle interaction at biogeochemical interfaces.
    Keywords: Unsaturated Transport ; Water Dynamics ; Cation Bridging ; Amphiphilic ; Edlvo ; Engineering ; Environmental Sciences ; Geography
    ISSN: 0169-7722
    E-ISSN: 1873-6009
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