On the Structure and Lithium Adsorption Mechanism of Layered H₂TiO₃

Layered H 2 TiO 3 has been studied as an ionic sieve material for the selective concentration of lithium from solutions. The accepted mechanism of lithium adsorption on H 2 TiO 3 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 H 2 TiO 3 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 H 2 TiO 3 contains isolated OH groups and hydrogen-bonded OH groups. Among these two hydroxyl groups, isolated OH groups present in the HTi 2 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 H 2 TiO 3 contains a high concentration of stacking faults and structural disorders which play a crucial role in controlling lithium adsorption properties.