Publication detail

Lignite humic acids aggregates studied by high resolution ultrasonic spectroscopy. Thermodynamic stability and molecular feature.

KUČERÍK, J. ČECHLOVSKÁ, H. BURSÁKOVÁ, P. PEKAŘ, M.

Original Title

Type

journal article in Web of Science

Language

English

Original Abstract

The thermodynamic stability of lignite humic acids (sodium salt) aggregates was studied by high resolution ultrasonic spectroscopy within the temperature interval from 5 to 90C. The changes in differential ultrasonic velocity (U12) showed strong differences among humic solutions within the concentration range from 0.005 to 10 g/L. Measurement revealed several transitions which were attributed to the weakening of humic secondary structure. Concentration around 1 g/L seemed to be a limit under which the change of the prevalence and importance of hydration occurred. Above this concentration the difference in U12 decreased following the temperature increase which was explained as a dominance of hydrophilic hydration. In contrast, below this concentration, the temperature dependence of U12 resulted in increasing tendency which was attributed to the prevalence of hydrophobic hydration, i.e. uncovering of apolar groups towards surrounding water. Additional experiments in which the humic sample was modified by hydrochloric acid resulted in a slight structural stabilization which lead to the conclusion that humic micelle-like subaggregates form an open-layer assemblies easily accessible for interaction with an extraneous molecule. That was partly verified by addition of propionic acid which brought about even larger reconformation of humic aggregates and exhibition of polar groups towards hydration water. The reversible changes in humate solutions induced by elevated temperatures provided the evidence about the existence of significant physical interactions among humic molecules resulting in formation of various kinds of aggregates. The nature of aggregates, mainly the stability and conformation, strongly depends on the concentration. Evidently, the changes observed in this work cannot be simply explained as expansions or conformational changes of macromolecular coils.

Keywords

aggregation; hydrophilic hydration; hydrophobic hydration; lignite humic acids; stability; ultrasonic spectroscopy

Authors

KUČERÍK, J.; ČECHLOVSKÁ, H.; BURSÁKOVÁ, P.; PEKAŘ, M.

RIV year

2009

Released

2. 8. 2009

Publisher

Springer

Location

Nizozemí

ISBN

1388-6150

Periodical

Journal of Thermal Analysis and Calorimetry

Year of study

Number

State

Hungary

Pages from

637

Pages to

643

Pages count

BibTex

@article{BUT48901,
  author="Jiří {Kučerík} and Hana {Čechlovská} and Petra {Bursáková} and Miloslav {Pekař}",
  title="Lignite humic acids aggregates studied by high resolution ultrasonic spectroscopy. Thermodynamic stability and molecular feature.",
  journal="Journal of Thermal Analysis and Calorimetry",
  year="2009",
  volume="96",
  number="2",
  pages="637--643",
  issn="1388-6150"
}