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SOME REMARKS ON THE ORIGIN OF LIGNITE HUMIC ACIDS OPTICAL PROPERTIES

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Author(s): Hana Čechlovská | Dana Válková | Laurent Grasset | Naděžda Fasurová | Jiří Kučerík

Journal: Petroleum and Coal
ISSN 1337-7027

Volume: 51;
Issue: 1;
Start page: 33;
Date: 2009;
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Keywords: synchronous fluorescence spectroscopy | lignite humic acids | extractions | supramolecular structure

ABSTRACT
Humic acids (HA) isolated from lignite of South Moravian and North Czech region(leonardite) were characterized by elemental analysis and fluorescence spectroscopyanalysis. From both humic acids there were sequentially extracted water solublefractions, free and bond fatty acids which were consequently characterized by CPMAS13C-NMR spectroscopy and GC-MS analysis. The respective rests were dissolved insodium hydroxide and the synchronous fluorescence spectroscopy (SFS) was used toanalyze the character of present fluorophores and assess the influence of extractedmolecules on the fluorescence of humic acids. The results has revealed a number ofessential outcomes for the elaboration of fluorescence records of humic matter: i) basedon our and other measurements, the optical properties of humic acids could not be aresult of the superposition of numerous independent chromophores, but rather of theirmutual interactions; it seems, that SFS evaluates predominantly hydrophobic core ofhumic aggregates which has apparently highly aromatic character, ii) the inner core of ahumic aggregate do not necessarily consists of condensed structures, the higharomaticity degree can be a consequence of weak interactions of simple aromaticmoieties such as π-π stacking and CH-π; iii) the crucial factor in SFS measurement isquenching which can be caused both by molecules present outside and inside of a humicaggregate; iv) due to the unique and complicated secondary structure of humic acids themolecules which are not primarily fluorophores can significantly affect the fluorescencedue to their interaction with fluorophores.
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