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

2H and 7Li MAS NMR spectroscopy have been applied to characterize the surface and bulk hydroxyl groups and Li+ sorption on the iron oxyhydroxide akaganeite (β-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 7Li NMR signals with large 7Li 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 7Li hyperfine shifts. The binding is compared with those of the other FeOOH polymorphs, goethite and lepidocrocite. The modes of 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.