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

TL;DR

This paper shows how to make boron nitride membranes with tunable properties for efficient water purification using a simple one-step method.

Contribution

A scalable one-step exfoliation method to tune hBN membranes for nanofiltration with unique physicochemical properties.

Findings

hBN membranes show high rejection of charged dyes due to electrostatic repulsion and size exclusion.

Membranes have a nanochannel height of ~0.34 nm and high water permeation rates.

X-ray techniques revealed changes in B:N and B:C ratios and the presence of defects on hBN nanosheets.

Abstract

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.

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