2H and 7Li Solid-State MAS NMR Study of Local Environments and Lithium Adsorption on the Iron(III) Oxyhydroxide, Akaganeite (β-FeOOH)

H-2 and Li-7 MAS NMR spectroscopy have been applied to characterize the surface and bulk hydroxyl groups and Li+ sorption on the iron oxyhydroxide akaganeite (beta-FeOOH), a common soil.mineral with a large surface area and uptake capacity for toxic cations and anions. The formation of both inner and outer-sphere complexes on the surface of akaganeite was confirmed, the former giving rise to Li-7 NMR signals with large Li-7 hyperfine shifts. The concentrations of these complexes was determined as a function of pH and possible Li+ binding modes and sites are proposed based on their Li-7 hyperfine shifts. The binding is compared with those of the other FeOOH polymorphs, goethite and lepidocrocite. The modes or binding are similar to those of :goethite, except that sites at the entrances to the tunnels become available for binding, particularly for nanosized akaganeite particles.