Size, shape, and stability of organic particles formed during freeze–thaw cycles

Model experiments with tannic acid

authored by: Stefan Dultz, Myriam Speth, Klaus Kaiser, Robert Mikutta, Georg Guggenberger
Abstract: Hypothesis: Freeze-thaw cycles (FTC) in soils can cause the aggregation of dissolved organic matter but controlling factors are little understood. Experiments: In freeze–thaw experiments with tannic acid (TA) as model substance, we studied the effect of TA concentration, pH, electrolytes (NaCl, CaCl₂, AlCl₃), and number of FTC on particle formation. Tannic acid (0.005 to 10 g L⁻¹) was exposed to 1–20 FTC at pH 3 and 6. The size and shape of particles was determined by confocal laser scanning microscopy. Particle stability was deduced from the equivalent circle diameter (ECD) obtained in dry state and the hydrodynamic diameter measured in thawing solutions. Findings: Tannic acid particles occurred as plates and veins, resembling the morphology of ice grain boundaries. Low pH and presence of electrolytes favored the formation of large particles. The freeze-concentration effect was most intense at low TA concentrations and increased with the number of FTC. While ECD of particles formed at low TA concentrations were smaller than at high concentrations, it was vice versa in the thawed state. At low TA concentrations, higher crystallization pressure of ice caused enhanced stability of large particles. We conclude that FTC can strongly alter the physical state of dissolved organic matter, with likely consequences for its bioavailability.
Organisation(s): Institute of Earth System Sciences
Soil Science Section
External Organisation(s): Justus Liebig University Giessen
Martin Luther University Halle-Wittenberg
Type: Article
Journal: Journal of Colloid and Interface Science
Volume: 667
Pages: 563-574
No. of pages: 12
ISSN: 0021-9797
Publication date: 08.2024
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Electronic, Optical and Magnetic Materials, Biomaterials, Surfaces, Coatings and Films, Colloid and Surface Chemistry
Electronic version(s): https://doi.org/10.1016/j.jcis.2024.04.080 (Access: Open)

BibTeX

@article{c75591a01d8b4a0a8e82da8dfd5949e8,
title = "Size, shape, and stability of organic particles formed during freeze–thaw cycles: Model experiments with tannic acid",
abstract = "Hypothesis: Freeze-thaw cycles (FTC) in soils can cause the aggregation of dissolved organic matter but controlling factors are little understood. Experiments: In freeze–thaw experiments with tannic acid (TA) as model substance, we studied the effect of TA concentration, pH, electrolytes (NaCl, CaCl2, AlCl3), and number of FTC on particle formation. Tannic acid (0.005 to 10 g L−1) was exposed to 1–20 FTC at pH 3 and 6. The size and shape of particles was determined by confocal laser scanning microscopy. Particle stability was deduced from the equivalent circle diameter (ECD) obtained in dry state and the hydrodynamic diameter measured in thawing solutions. Findings: Tannic acid particles occurred as plates and veins, resembling the morphology of ice grain boundaries. Low pH and presence of electrolytes favored the formation of large particles. The freeze-concentration effect was most intense at low TA concentrations and increased with the number of FTC. While ECD of particles formed at low TA concentrations were smaller than at high concentrations, it was vice versa in the thawed state. At low TA concentrations, higher crystallization pressure of ice caused enhanced stability of large particles. We conclude that FTC can strongly alter the physical state of dissolved organic matter, with likely consequences for its bioavailability.",
keywords = "Equivalent circle diameter, Freeze-concentration, Hydrodynamic diameter, Ice exclusion, Particle shape, Particle stability, Self-aggregation",
author = "Stefan Dultz and Myriam Speth and Klaus Kaiser and Robert Mikutta and Georg Guggenberger",
note = "Funding Information: This study was carried out within the framework of the Deutsche Forschungsgemeinschaft funded research unit RU 2179 \u201CMAD Soil \u2013 Microaggregates: Formation and turnover of the structural building blocks of soils\u201D (DFG RU 2179) under the project 251268514. ",
year = "2024",
month = aug,
doi = "10.1016/j.jcis.2024.04.080",
language = "English",
volume = "667",
pages = "563--574",
journal = "Journal of Colloid and Interface Science",
issn = "0021-9797",
publisher = "Academic Press Inc.",
}