Hydration and dehydration of water of bentonite: A solid-state 1H magic-angle spinning NMR study

Abstract

Molecular-level interactions of interlayer water near the montmorillonite surfaces were investigated on commercial bentonite using solid-state 1H magic-angle spinning NMR spectroscopy. It was observed that when the water content was higher than about 3 wt%, the chemical shift of samples increases as the increase in water content, while it decreases when the water content was lower than about 3 wt% with the increase of water content. Dehydration experiments at low water content and theoretical calculation showed that there might be two types of interaction in the interlayer space of montmorillonite: the water-water interaction and cation-water interaction. Water-water interaction was dominant at relatively high water content and cation-water interaction was dominant at relatively low water contents. The water-water interaction formed loosely bound water and the water-cation interaction formed tightly bound water near the montmorillonite surfaces.