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  • 1
    Language: English
    In: Environmental Chemistry, 2014, Vol.11(6), p.709
    Description:  The supramolecular structure and resulting physicochemical properties of soil organic matter (SOM) significantly control storage and buffer functions of soils, e.g. for nutrients, organic molecules and water. Multivalent cations, able to form complexes, are suggested to form inter- and intramolecular cross-links in SOM. At present, specific effects of the valence and type of cation on SOM properties are incompletely understood. We investigated changes in SOM interfacial properties, its ability to release mobile colloids in aqueous solutions and its sorption affinity towards organic chemicals in dependence on cation–SOM interactions, temperature and aging time.
    Keywords: colloids; contact angle; sorption; X-ray photoelectron spectroscopy.;
    ISSN: 1448-2517
    E-ISSN: 14498979
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  • 2
    Language: English
    In: Journal of Thermal Analysis and Calorimetry, 2014, Vol.118(2), pp.1203-1213
    Description: Multivalent cations are suggested to influence the supramolecular structure of soil organic matter (SOM) via inter- and intra-molecular interactions with SOM functional groups. In this study, we tested the combined effect of cations, temperature treatment, and isothermal aging on SOM matrix properties. Samples from a peat and a mineral soil were either enriched with Na, Ca, and Al or desalinated in batch experiments. After treatment at 25, 40, 60, and 105 °C and after different periods of aging at 19 °C and 31 % relative humidity, we investigated the physicochemical matrix stability and the thermal stability against combustion. We hypothesized that multivalent cations stabilize the SOM matrix, that these structures disrupt at elevated temperatures, and that aging leads to an increase in matrix stability. The results show that cation-specific effects on matrix rigidity started to evolve in the peat only after 8 weeks of aging and were significantly lower than the temperature effects. Temperature treatment above 40 °C caused a non (or not immediately) reversible loss of water molecule bridges (WaMB) and above 60 °C a partly reversible melting process probably of semi-crystalline poly(methylene). Thermal stability increased with increasing cation valence and degree of protonation and was much less affected by temperature. Generally, Na-treated and control samples revealed lower thermal stability and lower increase in matrix rigidity with aging than those treated with Ca, Al, and H. We conclude that drying at elevated temperatures (〉40 °C) may irreversibly change SOM structure via disruption of labile cross-links and melting of semi-crystalline domains.
    Keywords: Cation ; Combustion enthalpy ; Differential scanning calorimetry (DSC) ; Soil organic matter (SOM) ; Step transition
    ISSN: 1388-6150
    E-ISSN: 1588-2926
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