Hydration of LiOH and LiCl-Near-Infrared Spectroscopic Analysis

The hydration behavior of LiOH, LiOH center dot 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 center dot 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 center dot H2O were not modified even when the LiOH center dot H2O was exposed to air. In contrast, anhydrous LiOH was slowly hydrated for several hours, to form LiOH center dot 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.

Automated summary

The hydration behavior of LiOH, LiOH•H2O, and LiCl was studied using NIR spectroscopy. Anhydrous LiOH slowly hydrated to form LiOH•H2O under ambient conditions, while interlayer OH- and coordinated H2O of LiOH•H2O remained unchanged even when exposed to air. The hydration of LiOH surface did not follow a second-order reaction due to the lack of energy barrier for the chemisorption of H2O molecules onto defect sites. Additionally, hydration of deliquescent LiCl and formation of LiCl solution were successfully observed by NIR spectroscopy.