TY - JOUR
T1 - Evaluating pore structures of soil components with a combination of "conventional" and hyperpolarised 129Xe NMR studies
AU - Filimonova, Svetlana
AU - Nossov, Andrei
AU - Dümig, Alexander
AU - Gédéon, Antoine
AU - Kögel-Knabner, Ingrid
AU - Knicker, Heike
N1 - Funding Information:
We are indebted to Dr. Werner Häusler for the XRD-analyses. The German Science Foundation ( DFG, KN 463/8-1 ) is gratefully acknowledged for the financial support. Charcoal materials were taken from the DFG project KN 463/5-2.
PY - 2011/4/15
Y1 - 2011/4/15
N2 - 129Xe nuclear magnetic resonance (NMR) spectroscopic studies of xenon gas adsorbed on model systems representing soil porous components (Al (hyrd)oxides and charcoals) as well as natural soil materials (derived from a non-allophanic Andosol) were performed with the aim of characterising their micro- (<2nm) and mesopores (2-50nm). Both conventional, i.e. thermally polarised (TP), and laser-polarised or hyperpolarised (HP) 129Xe NMR was applied. The latter technique significantly increased sensitivity of the measurements. Information on the pore size range was derived from the 129Xe resonance shifts, δ, monitored as function of Xe loading, whereas the temperature dependences of δ provided information on the nature of xenon-pore surface interactions in terms of effective adsorption enthalpies. Dissolved organic matter (DOM) sorption on the mesoporous Al2O3 was shown to proceed inhomogeneously indicative by the Xe adsorption enthalpies corresponding to the co-existing "empty" pores and pores coated with organic species. In AlOOH, an interconnected system of micro- and mesopores was tested. The enhanced sensitivity of HP 129Xe NMR allowed us detecting micropores in charcoals, where N2 adsorption method underestimated porosity due to the restricted N2 diffusion at 77K. The interconnected pore structure of charcoals was attributed to the voids formed by both polyaromatic and aliphatic domains (evidenced by 13C NMR). The observed differences between the TP- and HP 129Xe NMR patterns were explained by the restricted xenon diffusion through charcoal particles caused by the constricted pore openings. Their suggested size is of the order of one or two diameters of the Xe atom. For the Andosol clay fractions, the large low-field 129Xe shifts (up to 175ppm) increasing with Xe pressure indicated a developed porosity most obviously comprised by the interconnected micro- and mesopores. Such porous network may originate from the "multi-domain" structure of soil clay particles, i.e. particles formed by agglomerated nano-sized crystallites. The latter are assumed to be the polynuclear Alx(H2O)y(OH)z clusters formed by hydrolysis reactions of Al3+ species after the destroying of Al-humus complexes by the H2O2-oxidation.
AB - 129Xe nuclear magnetic resonance (NMR) spectroscopic studies of xenon gas adsorbed on model systems representing soil porous components (Al (hyrd)oxides and charcoals) as well as natural soil materials (derived from a non-allophanic Andosol) were performed with the aim of characterising their micro- (<2nm) and mesopores (2-50nm). Both conventional, i.e. thermally polarised (TP), and laser-polarised or hyperpolarised (HP) 129Xe NMR was applied. The latter technique significantly increased sensitivity of the measurements. Information on the pore size range was derived from the 129Xe resonance shifts, δ, monitored as function of Xe loading, whereas the temperature dependences of δ provided information on the nature of xenon-pore surface interactions in terms of effective adsorption enthalpies. Dissolved organic matter (DOM) sorption on the mesoporous Al2O3 was shown to proceed inhomogeneously indicative by the Xe adsorption enthalpies corresponding to the co-existing "empty" pores and pores coated with organic species. In AlOOH, an interconnected system of micro- and mesopores was tested. The enhanced sensitivity of HP 129Xe NMR allowed us detecting micropores in charcoals, where N2 adsorption method underestimated porosity due to the restricted N2 diffusion at 77K. The interconnected pore structure of charcoals was attributed to the voids formed by both polyaromatic and aliphatic domains (evidenced by 13C NMR). The observed differences between the TP- and HP 129Xe NMR patterns were explained by the restricted xenon diffusion through charcoal particles caused by the constricted pore openings. Their suggested size is of the order of one or two diameters of the Xe atom. For the Andosol clay fractions, the large low-field 129Xe shifts (up to 175ppm) increasing with Xe pressure indicated a developed porosity most obviously comprised by the interconnected micro- and mesopores. Such porous network may originate from the "multi-domain" structure of soil clay particles, i.e. particles formed by agglomerated nano-sized crystallites. The latter are assumed to be the polynuclear Alx(H2O)y(OH)z clusters formed by hydrolysis reactions of Al3+ species after the destroying of Al-humus complexes by the H2O2-oxidation.
KW - Adsorption
KW - Andosol
KW - Charcoals
KW - Meso- and micropores
KW - Nuclear magnetic resonance
KW - Xenon
UR - http://www.scopus.com/inward/record.url?scp=79952899848&partnerID=8YFLogxK
U2 - 10.1016/j.geoderma.2011.01.009
DO - 10.1016/j.geoderma.2011.01.009
M3 - Article
AN - SCOPUS:79952899848
SN - 0016-7061
VL - 162
SP - 96
EP - 106
JO - Geoderma
JF - Geoderma
IS - 1-2
ER -