Hydration of LiOH and LiCl─Near-Infrared Spectroscopic Analysis

リチウム化合物の脱水／水和反応に関する論文が公開されました．
M. Takeuchi, R. Kurosawa, J. Ryu and M. Matsuoka, ACS Omega, 6, 33075-33084 (2021).

Abstract
The hydration behavior of LiOH, LiOH·H₂O, and LiCl was observed by near-infrared (NIR) spectroscopy. Anhydrous LiOH showed two absorption bands at 7340 and 7171 cm^–1. These NIR bands were assigned to the first overtone of surface hydroxyls and interlayer hydroxyls of LiOH, respectively. LiOH·H₂O showed two absorption bands at 7137 and 6970 cm^–1. These NIR bands were assigned to the first overtone of interlayer hydroxyls and H₂O molecules coordinated with Li⁺, respectively. The interlayer OH^– and the coordinated H₂O of LiOH·H₂O were not modified even when the LiOH·H₂O was exposed to air. In contrast, anhydrous LiOH was slowly hydrated for several hours, to form LiOH·H₂O under ambient conditions (RH 60%). Kinetic analysis showed that the hydration of the interlayer OH^– of LiOH proceeded as a second-order reaction, indicating the formation of intermediate species─[Li(H₂O)_x(OH)₄]^_3– (x = 1 or 2). However, the hydration of the LiOH surface did not follow a second-order reaction because the chemisorption of H₂O molecules onto the defect sites of the LiOH surface does not need to crossover the energy barrier. Furthermore, we succeeded in observing the hydration of deliquescent LiCl, including the formation of LiCl solution for several minutes by NIR spectroscopy.