Monitoring MgCl₂ hydrate formation from aqueous solutions using terahertz time-domain spectroscopy

The interaction of MgCl₂ with H₂O is heavily involved in biological and chemical processes. In this work, freezing-induced hydrate formation from MgCl₂ aqueous solution was monitored using terahertz time-domain spectroscopy. At low temperatures, two phase transitions from brine to hydrate formation could be clearly observed, and the formation of hydrate was accompanied by the emergence of new THz fingerprint peaks at 1.02, 1.56, and 1.84 THz, respectively. Integrating XRD and quantum chemical calculations, we attributed the absorption peaks to the vibrational modes of the formed MgCl₂·12H₂O. This demonstrates the potential of THz spectroscopy for application in the detection of biological processes in low-temperature environments, such as cell freezing.