Investigation on the mechanism of LiOH hydration using near infrared spectroscopy

Abstract

Anhydrous LiOH showed NIR absorption bands at 7340 and 7171 cm^–1, which were assigned to the surface OH^– and interlayer OH^– of LiOH, respectively. LiOH·H₂O showed NIR absorption bands at 7137 and 6970 cm^–1, which were assigned to the interlayer OH^– and H₂O coordinated with Li⁺, respectively. Based on the assignments, the hydration behavior of LiOH under ambient conditions was investigated by NIR spectroscopy. 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 surface OH^– did not because the coordination of H₂O molecules onto the defect sites of LiOH surface does not require any activation energy.