Inhaltszusammenfassung

Cross-linking of humic substances with organic bridging groups is hypothesized to contribute to the humification of soil organic matter. Model cross-linked humic substances were prepared by cross-linking Amherst soil humic acid by a diepoxide and a polycarboxylic acid in the solid state, applying procedures established for cross-linking of polymers and textile fabrics. Products of the crosslinking reactions were analyzed by FTIR and 13C CPMAS NMR. Physicochemical properties of t...Cross-linking of humic substances with organic bridging groups is hypothesized to contribute to the humification of soil organic matter. Model cross-linked humic substances were prepared by cross-linking Amherst soil humic acid by a diepoxide and a polycarboxylic acid in the solid state, applying procedures established for cross-linking of polymers and textile fabrics. Products of the crosslinking reactions were analyzed by FTIR and 13C CPMAS NMR. Physicochemical properties of the products were determined by solubility experiments and thermal analysis. The incorporation of the cross-linker into the matrix of the humic acid by covalent linkages was confirmed by both the disappearance of bands of the reactive functional groups of the cross-linker in the FTIR spectrum and the increase of signals related to the incorporation of the cross-linker into the matrix of the humic acid in the FTIR and 13C-CPMAS-NMR spectra. The formation of covalent ester and ether linkages by the cross-linking reaction was indicated. Water solubilities at pH 6.2 of the cross-linked samples as determined by UV/Vis spectrometry were reduced compared to controls. Fewer water molecule bridges were formed in the cross-linked samples, which was attributed to a lower number of available functional groups and increased distances between humic acid strands caused by the cross-linking molecules. Reduced reactivities of humic acid strands in the cross-linked samples further indicated successful cross-linking. The reactions investigated in this study can be regarded as models for reactions occurring in natural soils to test the significance of cross-linking reactions in the humification process of soil organic matter.» weiterlesen» einklappen

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