Nature of Natural Organic Matter Interactions with Mineral Surfaces
EMSL Project ID
50761
Abstract
The interactions of organic- and bio-molecules with minerals play a central role in controlling soil biogeochemistry; plant nutrition; chemical processes in sediments, soils, sedimentary rocks and the oceans; the transport and fate of heavy metals, radionuclides, and many organic and pharmaceutical contaminants in the environment; and the global carbon cycle. Natural organic matter (NOM) is a significant chemical component of many near-surface geochemical environments and consists of a complex mixture of compounds with a wide range of functionality, molecular weight, structure, and composition. NOM is often intimately associated with minerals in soils and natural waters, however, details regarding the mechanisms behind these associations and how those associations change with properties such as pH, cations present, and the types of mineral surfaces are not fully understood. In this proposal, we use the unique capabilities of EMSL to study NOM-carbonate and NOM-clay associations and the chemical factors that control them. To study NOM-carbonate association, we will use 43Ca, 25Mg, 207Pb, and 13C NMR along with helium ion and transmission electron microscopy, X-ray diffraction, and total organic carbon analysis to test the idea that NOM associates with carbonates via a cation bridging mechanism, where a cation is bound to both the inorganic phase and NOM molecule, and what cation properties affect the association mechanism. We will also examine the relative roles of cation bridging versus hydrophobicity-driven association mechanisms in NOM-clay samples by performing a systematic study of the structure and dynamics of model NOM molecules that contain specific functionalities. The most important objective is to investigate the pH and cation dependence of the relative importance of cation bridging and hydrophobic interactions for the common functional groups found in NOM. This study takes advantage of the sensitivity and resolution offered by the high-field NMR spectrometers at EMSL to perform variable temperature 43Ca, 23Na, and 13C NMR experiments that permit us to simultaneously characterize NOM adsorption and the dynamic behavior of all species involved. The results of our studies will be closely coupled with molecular dynamics computations performed in our home laboratories to provide detailed insight unobtainable with simulations or spectroscopy alone.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2019-10-01
End Date
2021-12-31
Status
Closed
Released Data Link
Team
Principal Investigator
Co-Investigator(s)
Related Publications
Bowers G.M., E.D. Walter, S.D. Burton, K.C. Schwarz, D.W. Hoyt, and R.J. Kirkpatrick. 2020. "Probing Pore Size and Connectivity in Porous Silicas Using 13C MAS NMR Spectroscopy of Supercritical Methane." Journal of Physical Chemistry C 124, no. 21:11536-11543. PNNL-SA-153506. doi:10.1021/acs.jpcc.0c02718