How Grain Boundaries and Interfacial Electrostatic Interactions Modulate Water Desalination via Nanoporous Hexagonal...

Area of Science:

• Materials Science
• Nanotechnology
• Environmental Engineering

Background:

• Growing global demand for freshwater necessitates advanced desalination technologies.
• Nanoporous two-dimensional materials like hexagonal boron nitride (hBN) show promise for desalination membranes.
• Understanding material defects and surface properties is key to optimizing membrane performance.

Purpose of the Study:

• To investigate the impact of grain boundaries (GBs) and interfacial electrostatic interactions on the desalination performance of bicrystalline nanoporous hBN.
• To analyze how different GB misorientation angles affect nanopore structure and water/ion transport.
• To evaluate the role of surface charge on hBN desalination efficiency.

Main Methods:

• Classical molecular dynamics simulations were employed to study water and Na+ ion transport.
• Quantum-mechanical density functional theory (DFT) calculations were used to determine atomic partial charges.
• Lattice dynamics calculations analyzed nanopore alterations due to GBs.

Main Results:

• Grain boundaries alter nanopore size and shape in bicrystalline hBN compared to monocrystalline hBN.
• A 13.2° GB in hBN increased water flow by ~30% but decreased Na+ rejection by ~6%.
• Interfacial electrostatic interactions significantly influenced water flow rate, with DFT-derived charges yielding the highest flow.

Conclusions:

• GBs in hBN membranes can decrease ion rejection, while surface charge affects water permeation.
• Nanopore shape, influenced by GBs, plays a critical role in balancing water flow and ion selectivity.
• Optimizing hBN membrane design requires careful consideration of both structural defects and surface electrostatics for efficient desalination.