Seamless Rim-Functionalization of h-BN with Silica-Experiment and Theoretical Modeling

Boron nitride contains six-ring layers, which are isostructural to graphene, and it exhibits similar extraordinary mechanical strength. Unlike graphene, hexagonal boron nitride (h-BN) is an insulator and has some polar features that make it a perfect material for those applications graphene is not suitable for, for example, purely ionic conductors, insulating membranes, transparent coatings, composite ceramics, high oxidation resistance materials. We report here a selective rim-functionalization of h-BN with SiO2 by using the Stöber process. A closed, protruding ring of SiO2 is formed covering all edges perpendicular to the [001] zones of the h-BN stacks and thus shield the most reactive centers of BN layers. SEM and HAADF-STEM images, X-ray spectroscopy, and atomic force microscopy confirm the rim-functionalization by SiO2 . XRD demonstrates the absence of any intercalation phenomenon of BN and reveals the glassy nature of the SiO2 rims. Selected variations of synthesis and theoretical modeling both confirm that rim activation by water prior to the Stöber condensation is crucial. First-principles calculations also confirm that dangling bonds of clean BN edges merge to give interlayer bonds that make further functionalization much more difficult. The reported reaction pathway should allow for other new functionalizations of pure BN and of the rimmed SiO2 /h-BN composites.