The adsorption behavior of lithium on spinel titanium oxide nanosheets with exposed (1-14) high-index facets.

The ion-exchange process is usually influenced by the surface properties of the adsorbents. In particular, the prophase adsorption/desorption process is confined by different crystal facets. In this research, spinel Li4Ti5O12 nanosheets with an exposed (1-14) high-index facet were prepared by a hydrothermal method followed by calcination treatment. Then, a H4Ti5O12 adsorbent was obtained, covered with the same (1-14) facets, after treatment with 0.2 M HCl. This special facet-exposed H4Ti5O12 has high cycling ability, with the adsorption uptake remaining at 96.84% after four cycles, a fast adsorption equilibrium time (equilibrium time < 60 min), excellent ion adsorption selectivity for Li+ uptake (separation factor: Li+ > K+ > Ca2+ > Na+ > Mg2+), and good adsorption capacity for Li+ uptake (21.57 mg g-1 ). With the help of X-ray photoelectron spectroscopy analyses, the Li+ adsorption process on the H4Ti5O12 nanosheets is shown to be an ion-exchange process. In addition, the coordination relationship between lithium and oxygen ions was investigated, illustrating that the four-coordinated structure is more stable than other complexes. These results indicate that hydrogen ions are exchanged for lithium ions at tetrahedral 8a sites, leading to the H4Ti5O12 structure with high stability in the adsorption-desorption cycling process.