Marthi Rajashekhar, Asgar Hassnain, Gadikota Greeshma, Smith York R
Material Science & Engineering, University of Utah, Salt Lake City, Utah 84112, United States.
School of Civil and Environmental Engineering, Cornell University, Ithaca, New York 14853, United States.
ACS Appl Mater Interfaces. 2021 Feb 24;13(7):8361-8369. doi: 10.1021/acsami.0c20691. Epub 2021 Feb 11.
Layered HTiO has been studied as an ionic sieve material for the selective concentration of lithium from solutions. The accepted mechanism of lithium adsorption on HTiO 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 HTiO 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 HTiO contains isolated OH groups and hydrogen-bonded OH groups. Among these two hydroxyl groups, isolated OH groups present in the HTi 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 HTiO contains a high concentration of stacking faults and structural disorders which play a crucial role in controlling lithium adsorption properties.
层状HTiO已被作为一种离子筛材料进行研究，用于从溶液中选择性富集锂。关于锂在HTiO离子筛上的吸附，公认的机理是通过Li-H离子交换发生，且无化学键断裂。然而，在本研究中，我们证明锂在HTiO上的吸附是通过O-H键断裂和O-Li键的形成发生的，这与先前提出的机理相反。热重分析结果表明，锂吸附后由于脱羟基导致的重量损失从2.96 wt%降至0.8 wt%，这表明锂吸附过程中表面羟基会断裂。拉曼光谱和傅里叶变换红外光谱研究表明，HTiO含有孤立的OH基团和氢键结合的OH基团。在这两种羟基中，HTi层中存在的孤立OH基团比氢键结合的OH基团更积极地参与锂吸附。因此，实际吸附容量受孤立OH基团数量的限制，而参与其中的氢键结合OH基团则用于稳定层状结构。我们还表明，HTiO含有高浓度的堆垛层错和结构无序，它们在控制锂吸附性能方面起着关键作用。
