Water molecules in boron nitride interlayer space: ice and hydrolysis in super confinement

Abstract

Development of nano-sized channels and filters in the recent years has made the role of water immensely important as water molecules affect their performance and durability. Here, we take advantage of molecular dynamics and density functional theory methods to demonstrate the shift in behavior of water molecules confined between hexagonal boron nitride (HBN) sheets spaced at 3.0 to 6.5 Å. Our results demonstrate that lower interlayer spaces cause higher amounts of charge transferred between the species, while at extreme degrees of confinement, these interactions cause the disintegration of trapped water molecules. Consequently, the inner face of the HBN sheets is functionalized with hydroxyl groups, releasing hydrogens in the form of protons that travel the interlayer space by Grotthuss mechanism. This is the first-hand evidence of a mechanical form of hydrolysis that corresponds with a nucleophilic attack (on boron atoms) to relieve water from extreme confined conditions. This process unveils a previously unknown behavior of water within extremely confined spaces and reveals new considerations concerning nanofilters and nanochannels.