Formation Mechanism of Boron-Based Nanosheet through the Reaction of MgB₂ with Water

Abstract

A recent experiment demonstrated that ultrasonication of MgB2 in water yields Mg-deficient hydroxyl-functionalized boron nanosheets at room temperature. Herein, we examined the mechanism of nanosheet formation. Analysis of the reaction products and temporal variation in pH and H2 production shows that the reaction between MgB2 and water comprises two steps: (i) an ion-exchange process between protons and a part of Mg cations of MgB2 with its exfoliation and (ii) the hydrolysis reaction between Mg-deficient boron hydride and water to produce H2 and Mg-deficient hydroxyl-functionalized boron sheets. The sheets with a stacking periodicity of 0.70 nm were obtained as the supernatant of the reaction product of water with MgB2. The stacking sheets can be further exfoliated if the reaction is conducted under ultrasonication. The derived nanosheets are composed of sp2-bonded boron framework and possess a disordered structure containing hydroxyl species and oxidized magnesium.