Advanced 129Xe NMR techniques for examing soil meso- and micro porosity and its role in hosting soil organic matter

• Applicant: Professorin Dr. Heike Knicker
• Subject Area: Soil Sciences
• Term: from 2008 to 2010
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 55108979

In soils, meso- and micropores (2-50 nm and <2 nm) are important in controlling soil organic matter (SOM) stabilization but the impact of more specific pore properties such as connectivity or structure remains mostly unresolved using common methods. As an alternative, “conventional” 129Xe NMR being highly sensitive to pore dimensions and shape was only recently successfully introduced into soil science. We intend to promote innovative technologies of this discipline and to apply them for the study of the effect of chemical and physical properties of the pore surface on the SOM sequestration efficiency. The use of hyperpolarized (HP) 129Xe considerably increases the sensitivity and we will be able to explore samples with low surface area (<10 m2) and perform variable temperature experiments. The latter can provide information on the mobility of the adsorbate and the adsorption parameters. Applying Xe-adsorption at increased pressures will expand the range of probed pore-types. Pulsed field gradient (PFG) NMR will be used to determine the tortuosity and pore surface area-to-volume ratios in the fractions >63 Jm. Combination with methods more traditional for soil science (Mössbauer spectroscopy, X-ray diffraction, N2 adsorption) and solid-state 13C NMR is expected to achieve a reliable break-through in understanding the microstructural properties of soil pores and their role in C-sequestration.

• DFG Programme: Research Grants
• Participating Person: Professorin Dr. Ingrid Kögel-Knabner