The Role of Concentration and Solvent Character in the Molecular Organization of Humic Acids
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Date
2016-10-21
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Mark
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MDPI AG
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Abstract
Bylo studováno chování huminových kyselin ve třech různých prostředích lišících se chemickým složením a způsobem přípravy. Byly zjištěny dva důležité zlomy v chování těchto systémů, první při nízkých koncentracích kolem 0,02 g/dm3, kdy dochází ke změnám v hydratačním obalu a druhý kolem koncentrace 1 g/dm3, který je spojen s počátkem agregace huminových částic.
The molecular organization of humic acids in different aqueous solutions was studied over a wide concentration range (0.01–10 g/dm3). Solutions of humic acids were prepared in three different media: NaOH, NaCl, and NaOH neutralized by HCl after dissolution of the humic sample. Potentiometry, conductometry, densitometry, and high resolution ultrasound spectrometry were used in order to investigate conformational changes in the humic systems. The molecular organization of humic acids in the studied systems could be divided into three concentration ranges. The rearrangements were observed at concentrations of ~0.02 g/dm3 and ~1 g/dm3. The first “switch-over point” was connected with changes in the hydration shells of humic particles resulting in changes in their elasticity. The compressibility of water in the hydration shells is less than the compressibility of bulk water. The transfer of hydration water into bulk water increased the total compressibility of the solution, reducing the ultrasonic velocity. The aggregation of humic particles and the formation of rigid structures in systems with concentrations higher than 1 g/dm3 was detected.
The molecular organization of humic acids in different aqueous solutions was studied over a wide concentration range (0.01–10 g/dm3). Solutions of humic acids were prepared in three different media: NaOH, NaCl, and NaOH neutralized by HCl after dissolution of the humic sample. Potentiometry, conductometry, densitometry, and high resolution ultrasound spectrometry were used in order to investigate conformational changes in the humic systems. The molecular organization of humic acids in the studied systems could be divided into three concentration ranges. The rearrangements were observed at concentrations of ~0.02 g/dm3 and ~1 g/dm3. The first “switch-over point” was connected with changes in the hydration shells of humic particles resulting in changes in their elasticity. The compressibility of water in the hydration shells is less than the compressibility of bulk water. The transfer of hydration water into bulk water increased the total compressibility of the solution, reducing the ultrasonic velocity. The aggregation of humic particles and the formation of rigid structures in systems with concentrations higher than 1 g/dm3 was detected.
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en