Influence of Adsorbed Organic Acids on Soil Mineral Wettability
EMSL Project ID
51896
Abstract
Soil wettability is dictated by the extent to which hydrophilic mineral surfaces are covered by hydrophobic soil organic carbon (SOC) from bacterial decomposition, decaying plant matter, or root exudates. This proposed work will use an integrated experimental and computational approach to investigate how the fundamental process of water adsorption on soil minerals is influenced by the presence of adsorbed organic acids at humidities below water saturation. Carboxylic functional groups of organic acids are key moieties determining the binding strength of water-repellent SOC to mineral surfaces. Target systems will be combinations of model carboxylic acids (acetic, benzoic, phthalic, oxalic, and citric) and Al(III)- and Fe(III)-hydroxide minerals. Experiments will test (1) the hypothesis that coverage and coordination mode of organic acids adsorbed at mineral surfaces will impact amounts of adsorbed H2O and diffusive mass transport; and (2) the corollary that the amount of adsorbed H2O will impact the binding mode of organic acids. Minerals will be characterized at EMSL pre- and/or post-reaction using surface area measurements, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. In operando magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy at EMSL will provide molecular-level information about how organic acids are bound at Al(III)-hydroxide mineral surfaces. In operando infrared spectroscopy at PNNL will precisely measure adsorbed H2O concentrations and complement NMR measurements with additional molecular-level information regarding organic acid coordination and protonation state. In operando electrical impedance spectroscopy at PNNL will give unique information about the H2O coverage at the onset of diffusive mass transport within adsorbed H2O films that will be correlated to molecular-scale information about organic acid binding from NMR and IR spectroscopy. Finally, computational modeling at EMSL will provide spectra of energetically optimized structures of organic acids at mineral surfaces that will be used to interpret NMR and IR spectra. This work supports EMSL's goal to advance the understanding of mineral-organic matter interactions and will provide fundamental insights relevant to organic nutrient bioavailability in soils and global carbon cycling.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2021-10-01
End Date
N/A
Status
Active
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
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