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Restructuring of a peat in interaction with multivalent cations: effect of cation type and aging time.

Kunhi Mouvenchery Y, Jaeger A, Aquino AJ, Tunega D, Diehl D, Bertmer M, Schaumann GE - PLoS ONE (2013)

Bottom Line: The maximum uptake increased with pH of cation addition and decreased with increasing cation valency.Molecular modeling demonstrates that large average distances between functionalities (∼3 nm in this peat) cannot be bridged 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.

View Article: PubMed Central - PubMed

Affiliation: University of Koblenz-Landau, Institute for Environmental Sciences, Department of Environmental and Soil Chemistry, Landau, Germany.

ABSTRACT
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.

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A comparison of cation uptake with respect to the amounts remained in treatment solution in aluminium (SP-Al), calcium (SP-Ca) and sodium (SP-Na) treated samples at different cation addition pH.
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pone-0065359-g004: A comparison of cation uptake with respect to the amounts remained in treatment solution in aluminium (SP-Al), calcium (SP-Ca) and sodium (SP-Na) treated samples at different cation addition pH.

Mentions: The dependence of efficiency of cation uptake on amount of added cations is shown in sorption isotherms in Figure 4. The higher uptake of the respective cation at higher cation addition pH demonstrated by Figure 3 is even clearer in the sorption isotherm. Shapes of the isotherms were non-linear, but similar for all conditions. The sorbed amount increased with equilibrium solution concentration and appeared to approach a limit value, for higher equilibrium solution concentrations, which depends on cation type and cation addition pH. Only for Na+, the limit value was not reached under the conditions applied in the current study. Sorption isotherms for cation addition at pH 1.9 resulted in lower limit values and the final value were already reached at low equilibrium concentrations.


Restructuring of a peat in interaction with multivalent cations: effect of cation type and aging time.

Kunhi Mouvenchery Y, Jaeger A, Aquino AJ, Tunega D, Diehl D, Bertmer M, Schaumann GE - PLoS ONE (2013)

A comparison of cation uptake with respect to the amounts remained in treatment solution in aluminium (SP-Al), calcium (SP-Ca) and sodium (SP-Na) treated samples at different cation addition pH.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3672098&req=5

pone-0065359-g004: A comparison of cation uptake with respect to the amounts remained in treatment solution in aluminium (SP-Al), calcium (SP-Ca) and sodium (SP-Na) treated samples at different cation addition pH.
Mentions: The dependence of efficiency of cation uptake on amount of added cations is shown in sorption isotherms in Figure 4. The higher uptake of the respective cation at higher cation addition pH demonstrated by Figure 3 is even clearer in the sorption isotherm. Shapes of the isotherms were non-linear, but similar for all conditions. The sorbed amount increased with equilibrium solution concentration and appeared to approach a limit value, for higher equilibrium solution concentrations, which depends on cation type and cation addition pH. Only for Na+, the limit value was not reached under the conditions applied in the current study. Sorption isotherms for cation addition at pH 1.9 resulted in lower limit values and the final value were already reached at low equilibrium concentrations.

Bottom Line: The maximum uptake increased with pH of cation addition and decreased with increasing cation valency.Molecular modeling demonstrates that large average distances between functionalities (∼3 nm in this peat) cannot be bridged 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.

View Article: PubMed Central - PubMed

Affiliation: University of Koblenz-Landau, Institute for Environmental Sciences, Department of Environmental and Soil Chemistry, Landau, Germany.

ABSTRACT
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.

Show MeSH
Related in: MedlinePlus