Aqueous Dispersions of Few-Layered and Monolayered Hexagonal Boron Nitride Nanosheets from Sonication-Assisted Hydrolysis: Critical Role of Water

Abstract

Hexagonal boron nitride (h-BN) is traditionally considered to be insoluble in water. However, here we demonstrate that water is effective to exfoliate the layered h-BN structures with the assistance of bath sonication, forming “clean” aqueous dispersions of h-BN nanosheets without the use of surfactants or organic functionalization. Besides few-layered h-BN nanosheets, there was also evidence on the presence of monolayered nanosheet and nanoribbon species. Most nanosheets were of reduced lateral sizes, which was attributed to the cutting of parent h-BN sheets induced by the sonication-assisted hydrolysis (evidenced by the ammonia test and spectroscopy results). The hydrolysis effect also assisted in the exfoliation of h-BN nanosheets in addition to the solvent polarity effect. The h-BN nanosheets in such “clean” aqueous dispersions were demonstrated to be conveniently processed via solution methods with retained physical properties. The dispersed h-BN nanosheets in water also exhibited strong affinity toward proteins such as ferritin, suggesting that the nanosheet surfaces were available for further bioconjugations. The above findings may pave the way for the applications of these novel 2-dimensional nanomaterials in various fields such as composites, electronics, and biology.