Water Icing Triggered Scalable and Controllable Exfoliation of Hexagonal Boron Nitride Nanosheets

Abstract

Herein, a scalable and controllable approach is proposed to exfoliate high quality hexagonal boron nitride nanosheets (h-BNNSs) from h-BN flakes, which relies on the efficient reduction of h-BNNS interlayer interaction by rapid volume expansion of water in icing. Water can enter into the h-BNNS interlayer through the “entry” caused by the hydroxyl induced local structure distortion as demonstrated by molecular dynamics simulations. The entered water could form fairly compact initial nuclei, and then ice and rapidly expand as temperature drops sharply, resulting in the interlayer space increase and interlayer force reduction between h-BNNSs and thus achieving efficient exfoliation of h-BNNSs in subsequent ultrasonication. The thicknesses of h-BNNSs are dominated by freezing and exfoliation cycles, and monolayer h-BNNSs can be obtained after five cycles of freezing and exfoliation currently. The as-obtained h-BNNSs have excellent dispersibility in water enabling their versatile applications as polymer additives, thermal conductive fillers, and flame-retardants, etc.