On the Structure and Lithium Adsorption Mechanism of Layered H₂TiO₃

Layered H₂TiO₃ has been studied as an ionic sieve material for the selective concentration of lithium from solutions. The accepted mechanism of lithium adsorption on H₂TiO₃ ion sieves is that it occurs via Li⁺-H⁺ ion exchange with no chemical bond breakage. However, in this work, we demonstrate that lithium adsorption on H₂TiO₃ occurs via O-H bond breakage and the formation of O-Li bonds, contrary to previously proposed mechanisms. Thermogravimetric analysis results show that the weight loss due to dehydroxylation decreases from 2.96 wt % to 0.8 wt % after lithium adsorption, indicating that surface hydroxyl groups break during lithium adsorption. Raman and Fourier transform infrared spectroscopy studies indicate that H₂TiO₃ contains isolated OH groups and hydrogen-bonded OH groups. Among these two hydroxyl groups, isolated OH groups present in the HTi₂ layers are more actively involved in lithium adsorption than hydrogen-bonded OH groups. As a result, the actual adsorption capacity is limited by the number of isolated OH groups, whereas hydrogen-bonded OH groups involved are for stabilizing the layered structure. We also show that H₂TiO₃ contains a high concentration of stacking faults and structural disorders which play a crucial role in controlling lithium adsorption properties.