Understanding Aqueous Dispersibility of Boron Nitride Nanosheets from ¹H Solid State NMR and Reactive Molecular Dynamics

Stable aqueous dispersions of BN nanosheets can be obtained by the sonication assisted exfoliation of hexagonal BN powders in water without the need of stabilizers: a phenomenon not observed for the isoelectronic graphite, of comparable hydrophobicity. We show here that the aqueous dispersions are stabilized by electrostatic repulsive interactions and establish from ζ potential measurements that the BN nanosheets are positively charged on delamination with the medium turning increasingly basic as sonication proceeds. We have investigated how charge develops on the sheets by reactive force-field (ReaxFF) molecular dynamics simulations of the interaction of water with BN nanosheets and independently identified the major chemical species present on the nanosheets from ¹H and ¹¹B solid-state NMR measurements. Charges develop on the sheets as a consequence of the dissociation of water molecules at the edges of the sheet that leave the nitrogen edge atoms protonated and the release of hydroxyl groups into the bulk leading to an increased basicity of the medium