Tuning Physicochemical Properties of Boron Nitride-Based Membranes via Scalable One-Step Exfoliation for Ionic and Molecular Nanofiltration.

Two-dimensional (2D) nanomaterials, such as graphene, have been widely used in various applications, such as electrodes for energy storage and laminar membranes for separations. Hexagonal boron nitride (hBN), one of the 2D materials possessing properties similar to graphene, can be used as laminar stacking laminates for separation processes due to its high filtration efficiency and solvent flow. Herein, we prepared 2D-hBN nanosheets using different nitrogen-containing precursors via facile liquid-phase exfoliation for the preparation of hBN membranes. We found that the as-prepared hBN samples exhibit unique physicochemical properties, as determined by various spectroscopic techniques, particularly near-edge X-ray absorption fine structure spectroscopy, which was used to identify the presence of defects on the hBN nanosheets. The elemental compositions of each hBN nanosheet were also revealed by an X-ray photoelectron spectroscopic technique, indicating significant changes in the B:N and B:C ratios. The hBN membranes exhibit high stability in aqueous solutions without membrane deformation. The nanochannel height of the hBN membranes was found to be 0.34 nm, as determined by X-ray diffraction analysis. The membranes demonstrate excellent rejection performance for charged dye molecules (acid orange 7 and methylene blue) with high water permeation rates. This is due to electrostatic repulsion between the negatively charged surface of the hBN membranes and the charged species, as well as size exclusion from the narrow capillary channels between the stacked layered hBN nanosheets. Therefore, the hBN membranes, with their unique physicochemical properties, are promising for applications in water purification.