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  • 1
    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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  • 2
    Language: English
    In: Journal of Soils and Sediments, 2012, Vol.12(1), pp.115-115
    Description: Byline: Gabriele Ellen Schaumann (1), Yamuna Kunhi Mouvenchery (1) Author Affiliation: (1) Department of Environmental and Soil Chemistry, Institute for Environmental Sciences, Universitat Koblenz-Landau, Fortstr. 7, 76829, Landau, Germany Article History: Registration Date: 01/12/2011 Online Date: 09/12/2011 Article note: The online version of the original article can be found at http://dx.doi.org/ 10.1007/s11368-011-0443-3.
    Keywords: Humic Acids ; Soils ; Soil Chemistry;
    ISSN: 1439-0108
    E-ISSN: 1614-7480
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  • 3
    Language: English
    In: Journal of Soils and Sediments, Jan, 2012, Vol.12(1), p.48(15)
    Description: Byline: Gabriele Ellen Schaumann (1), Yamuna Kunhi Mouvenchery (1) Keywords: Atomic force microscopy; Glass transition; Nanothermal analysis; Soil organic matter; Thermal analysis; Thermomechanical analysis Abstract: Purpose This exploratory study evaluates the potential of nanothermal analysis (nTA) coupled with atomic force microscopy (AFM) of soil samples for understanding physicochemical processes in soil and for linking the nanospatial and microspatial distribution of thermal characteristics with the macroscopic properties of soil samples. Materials and methods Soil and reference samples were investigated by differential scanning calorimetry and AFM-nTA. nTA was conducted on 16 points of each AFM image in two subsequent heating cycles (55--120degC and 55--300degC, respectively). Thermograms were subdivided into characteristic types and their spatial distribution was compared between sample replicates and materials. Results and discussion Thermogram types consisted of partly structured expansion and compression phases, suggesting material-specific thermal profiles. The distribution of thermogram types reflected sample-dependent nanoscale and microscale heterogeneity. Indications for water molecule bridge transitions were found by nTA in peat and soil. Organic materials generally revealed strong expansion and irreversible compression phases, latter probably due to the collapse of pore and aggregate structures. In contrast to charcoal and manure, peat shows strong expansion below 120degC and compression only above 120degC. Conclusions All investigated samples are heterogeneous on the nanoscale and microscale with respect to thermal behaviour. AFM-nTA allows distinguishing numerous different materials on nanometre and micrometre scales in soil samples. The material-dependent characteristics will help in understanding and learning more about the nanoscale distribution of different materials and properties. Related to the macroscopic thermal behaviour, this will allow studying links between the properties of biogeochemical interfaces and the processes governed by them. Author Affiliation: (1) Department of Environmental and Soil Chemistry, Institute for Environmental Sciences, Universitat Koblenz-Landau, Fortstr. 7, 76829, Landau, Germany Article History: Registration Date: 28/10/2011 Received Date: 30/08/2011 Accepted Date: 28/10/2011 Online Date: 16/11/2011 Article note: Responsible editor: Michael Kersten An erratum to this article can be found at http://dx.doi.org/10.1007/s11368-011-0459-8
    Keywords: Peat ; Soil Chemistry ; Soil Carbon ; Soils ; Humic Acids ; Atomic Force Microscopy
    ISSN: 1439-0108
    Source: Cengage Learning, Inc.
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  • 4
    Language: English
    In: PLoS ONE, 01 January 2013, Vol.8(6), p.e65359
    Description: It is assumed to be common knowledge that multivalent cations cross-link soil organic matter (SOM) molecules via cation bridges (CaB). The concept has not been explicitly demonstrated in solid SOM by targeted experiments, yet. Therefore, the requirements for and characteristics of CaB remain unidentified. In this study, a combined experimental and molecular modeling approach was adopted to investigate the interaction of cations on a peat OM from physicochemical perspective. Before treatment with salt solutions of Al(3+), Ca(2+) or Na(+), respectively, the original exchangeable cations were removed using cation exchange resin. Cation treatment was conducted at two different values of pH prior to adjusting pH to 4.1. Cation sorption is slower (〉〉2 h) than deprotonation of functional groups (〈2 h) and was described by a Langmuir model. The maximum uptake increased with pH of cation addition and decreased with increasing cation valency. Sorption coefficients were similar for all cations and at both pH. This contradicts the general expectations for electrostatic interactions, suggesting that not only the interaction chemistry but also spatial distribution of functional groups in OM determines binding of cations in this peat. The reaction of contact angle, matrix rigidity due to water molecule bridges (WaMB) and molecular mobility of water (NMR analysis) suggested that cross-linking via CaB has low relevance in this peat. This unexpected finding is probably due to the low cation exchange capacity, resulting in low abundance of charged functionalities. Molecular modeling demonstrates that large average distances between functionalities (∼3 nm in this peat) cannot be bridged by CaB-WaMB associations. However, aging strongly increased matrix rigidity, suggesting successive increase of WaMB size to connect functionalities and thus increasing degree of cross-linking by CaB-WaMB associations. Results thus demonstrated that the physicochemical structure of OM is decisive for CaB and aging-induced structural reorganisation can enhance cross-link formation.
    Keywords: Sciences (General)
    E-ISSN: 1932-6203
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  • 5
    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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  • 6
    Language: English
    In: Journal of Soils and Sediments, 2013, Vol.13(9), pp.1579-1588
    Description: Purpose: Nutrient release, soil wettability, water binding, and matrix rigidity of soil organic matter (SOM) can be affected by cross-links between segments of SOM, cations, and water molecule bridges (WaMB). Not all cation effects on SOM can be explained with the currently accepted idea that multivalent cations cross-link organic matter segments via direct cation bridges (CaB). The objective was to understand these interactions and their effect on SOM matrix rigidity and wettability. Materials and methods: We modified cation composition of two peats and an organic surface layer (OSL) using cation exchange resin to remove cations and solutions of Na super(+), Ca super(2+), or Al super(3+) to enrich samples with cations. SOM matrix rigidity was determined at 4 and 〉8 weeks after treatment via the WaMB transition temperature T*, using differential scanning calorimetry. Wettability was measured via sessile drop contact angle (CA). Results and discussion: The effect of cation removal on T* depended on cation exchange capacity and initial cation content. Cation addition to OSL increased T*. This effect increased with increasing cation loading and valency, and T* correlated with CA. Classical cross-linking can neither explain the higher heterogeneous matrix of Ca-treated than Al-treated samples nor the aging-induced convergence of T* for different cations and concentrations. The latter is likely due to interaction between CaB and WaMB in SOM. Conclusions: Associations of CaB and WaMB evolve slowly and form a supramolecular network in SOM. Those dynamic associations can fix molecular arrangements inducing water repellency and increase kinetic barriers for the release and uptake of water and nutrients from aged soil.
    Keywords: Cross-links ; Differential scanning calorimetry ; Matrix rigidity ; Multivalent cation ; Soil organic matter ; Water molecule bridges (WaMB) ; Water repellency
    ISSN: 1439-0108
    E-ISSN: 1614-7480
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  • 7
    Language: English
    In: Journal of Soils and Sediments, 2012, Vol.12(1), pp.48-62
    Description: Purpose: This exploratory study evaluates the potential of nanothermal analysis (nTA) coupled with atomic force microscopy (AFM) of soil samples for understanding physicochemical processes in soil and for linking the nanospatial and microspatial distribution of thermal characteristics with the macroscopic properties of soil samples. Materials and methods: Soil and reference samples were investigated by differential scanning calorimetry and AFM-nTA. nTA was conducted on 16 points of each AFM image in two subsequent heating cycles (55-120 degree C and 55-300 degree C, respectively). Thermograms were subdivided into characteristic types and their spatial distribution was compared between sample replicates and materials. Results and discussion: Thermogram types consisted of partly structured expansion and compression phases, suggesting material-specific thermal profiles. The distribution of thermogram types reflected sample-dependent nanoscale and microscale heterogeneity. Indications for water molecule bridge transitions were found by nTA in peat and soil. Organic materials generally revealed strong expansion and irreversible compression phases, latter probably due to the collapse of pore and aggregate structures. In contrast to charcoal and manure, peat shows strong expansion below 120 degree C and compression only above 120 degree C. Conclusions: All investigated samples are heterogeneous on the nanoscale and microscale with respect to thermal behaviour. AFM-nTA allows distinguishing numerous different materials on nanometre and micrometre scales in soil samples. The material-dependent characteristics will help in understanding and learning more about the nanoscale distribution of different materials and properties. Related to the macroscopic thermal behaviour, this will allow studying links between the properties of biogeochemical interfaces and the processes governed by them.
    Keywords: Atomic force microscopy ; Glass transition ; Nanothermal analysis ; Soil organic matter ; Thermal analysis ; Thermomechanical analysis
    ISSN: 1439-0108
    E-ISSN: 1614-7480
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  • 8
    Language: English
    In: Journal of Plant Nutrition and Soil Science, June 2018, Vol.181(3), pp.441-452
    Description: A soil's cation exchange capacity (CEC) is expected to be relatively inert against changes in cation loading. In this study, we treated a soil sample originating from the organic layer of a forest soil with various bivalent cations after removing the native cations. Sorption isotherms and cation exchange capacity were determined, the latter using the BaCl method. Sorption showed Langmuir characteristics, with the maximum coverage () increasing in the order Ba 〈 Ca 〈 Mg, but being clearly smaller than the initial load of native exchangeable cations. The Langmuir coefficient, , depended oppositely to the order obtained for . CEC increased upon cation treatment and it varied by a factor of almost two. The unexpected variation of CEC was explained by the low cation exchange capacity of the organic matter such that not all functional groups are close enough to be bridged and the second charge of a bivalent cation is not neutralized by the organic functional group. The Langmuir sorption type, and being smaller than the content of sorption sites and being largest for Mg, suggested that only a part of the sites can be cross‐linked and at least part of the cross‐links are formed by hydrated cations. Thermodynamic considerations allowed reconstruction of two contrasting processes during CEC determination by Ba: : the disruption of cross‐links, which increases with the cationic strength and the cation load before CEC determination, but does not require structural re‐orientation in the SOM matrix, and the formation of new cross‐links during CEC determination, depending only on the content of unoccupied sites before CEC determination and requiring structural re‐organization of the matrix and thus a minimum matrix flexibility. The use of bivalent cations for CEC determination may thus result in an overestimation of CEC for organic matter with low CEC. This has, however, promising potential when comparing CEC determined with monovalent cations and bivalent cations. Using a set of bivalent cations, may allow probing distribution of distances between functional groups in the organic matter and even characterize the matrix rigidity of the cation‐cross‐linked network.
    Keywords: Bivalent Cations ; Cation Exchange Capacity ; Cross‐Linking ; Langmuir ; Soil Organic Matter ; Sorption
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 9
    Language: English
    In: Journal of Plant Nutrition and Soil Science, April 2014, Vol.177(2), pp.141-149
    Description: The objective of this study was to investigate the effects of mono‐ and polyvalent cations on sorption of the two hydrophobic compounds nonylphenol (NP) and phenanthrene (Phe). To this end, exchange sites of a sandy soil were saturated with either Na, Ca, or Al and excess salts were removed by washing. The samples were then sterilized and either stored moist, dried at room temperature, or at 20°C, 60°C, or 105°C in a vented oven. Saturation with Na led to an increase of dissolved organic C (DOC) concentration in the soil water extracts, whereas the polyvalent cations Ca and Al decreased it. The H‐NMR relaxometry analyses showed that Al restricted the mobility of water molecules that are confined within the SOM structure to a higher extent than Ca or Na. According to contact‐angle (CA) analyses, cation treatment did not significantly change the wetting properties of the samples. Batch sorption–desorption experiments showed no clear salt‐treatment effects on the sorption and desorption equilibria or kinetics of NP and Phe. Instead, the sorption coefficients and sorption hysteresis of NP and Phe increased in dry soil. With increasing drying temperature the CA of the soils and the sorption of both xenobiotics increased significantly. We conclude that structural modifications of SOM due to incorporation of polyvalent cations into the interphase structure do not modify the sorption characteristics of the soil for hydrophobic compounds. Instead, increasing hydrophobization of organic soil constituents due to heat treatment significantly increased the accessible sorption sites for nonpolar organic compounds in this soil.
    Keywords: Soil Organic Matter ; Sodium ; Calcium ; Aluminum ; Contact Angle ; Wettability ; Relaxation Time
    ISSN: 1436-8730
    E-ISSN: 1522-2624
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  • 10
    Language: English
    In: Analytical and Bioanalytical Chemistry, 2012, Vol.403(9), pp.2529-2540
    Description: Biogeochemical interfaces in soil are dynamic in the spatial and temporal domain and require advanced visualisation and quantification tools to link in vitro experiments with natural systems. This study presents the development, characterization and application of functional nanoparticles coated with monoclonal antibodies to visualise the distribution of benzo[a]pyrene in porous media using magnetic resonance imaging. The labelled particles are 450 nm in diameter and interact with benzo[a]pyrene covalently bound to silanized silica gel. They did not bind to benzo[a]pyrene adsorbed to plain silica gel. Although unspecific filtration was low, washing steps are required for visualisation. The ability to visualise benzo[a]pyrene is inversely correlated to the heterogeneity of the soil materials. There are access restrictions to narrow pore spaces which allow the visualisation of only those pathways which are also accessible to bacteria and hydrocolloids. The production of the particles is applicable to other antibodies which extends the range of potential target contaminants.
    Keywords: PAH ; Magnetic resonance imaging (MRI) ; MRI label ; NMR relaxometry ; Anti-B[a]P antibody ; Biogeochemical interface
    ISSN: 1618-2642
    E-ISSN: 1618-2650
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