Investigation on the Mechanisms of Mg(OH) 2 Dehydration and MgO Hydration by Near-Infrared Spectroscopy

作者：Atsushi Kondô, Ryo Kurosawa, Junichi Ryu, Masaya Matsuoka, Masato Takeuchi · 发表于：The Journal of Physical Chemistry C · 年份：2021 · DOI：10.1021/acs.jpcc.1c01470 · 被引用次数：64 · 研究领域：Magnesium Oxide Properties and Applications、Layered Double Hydroxides Synthesis and Applications、Calcium Carbonate Crystallization and Inhibition

The mechanism for the dehydration of Mg(OH) 2 and hydration of MgO was investigated by near-infrared (NIR) spectroscopy. Mg(OH) 2 showed three absorption bands in the NIR region at 7339, 7306, and 7157 cm –1, due to the different hydroxyl groups (7339 cm –1: OH( e ) and OH( c ) located on the edge and corner of the Mg(OH) 2 sheet, 7306 cm –1: OH( t ) located on the terrace of Mg(OH) 2 sheet, 7157 cm –1: OH( i ) located on the interlayer of Mg(OH) 2 sheets). During the phase transition from Mg(OH) 2 to MgO at approximately 400 °C, the interlayer OH( i ) of Mg(OH) 2 disappeared by a dehydration reaction and the OH( t ) on the (001) plane of Mg(OH) 2 was converted to the hydrogen-bonded hydroxyl groups on the (111) plane of MgO (7309 cm –1 ). Furthermore, when MgO was in contact with water vapor at 85 and 50 °C (RH 85%), the isolated hydroxyl groups of the MgO surface (7360 cm –1 ) were easily hydrated to form hydrogen-bonded ones (7309 cm –1 ). When a monolayer Mg(OH) 2 sheet was formed on the MgO surface, OH( e ), OH( c ), and OH( t ) were observed at 7345 and 7309 cm –1 . As the hydration reaction proceeded, the intermediate state like stacking of several Mg(OH) 2 sheets, which are related to the decrease in the OH( t ) and the spontaneous increase in the interlayer OH( i ), was experimentally confirmed.