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

在土壤中，中孔和微孔（2-50 nm和<2 nm）在控制土壤有机质（SOM）稳定性方面很重要，但更具体的孔隙性质（如连通性或结构）的影响仍然大多未解决使用普通方法。作为一种替代方法，对孔隙尺寸和形状高度敏感的“常规”129 NMR直到最近才成功地引入土壤科学。我们打算促进这一学科的创新技术，并将其应用于孔隙表面的化学和物理性质对SOM封存效率的影响的研究。使用超极化（HP）129大大提高了灵敏度，我们将能够探索具有低表面积（<10 m2）的样品并进行变温实验。后者可以提供关于吸附物的迁移率和吸附参数的信息。在增加的压力下应用Xe吸附将扩大探测的孔类型的范围。脉冲场梯度（PFG）NMR将用于确定>63 μ m的级分中的弯曲度和孔表面积与体积比。结合更传统的土壤科学方法（穆斯堡尔光谱，X射线衍射，N2吸附）和固态13 C NMR有望在理解土壤孔隙的微观结构特性及其在碳封存中的作用方面取得可靠的突破。

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.