High-performance desalination through tortuous pathways in multilayer ABC-stacked large-pore covalent organic frameworks: a theoretical study

Abstract

The scarcity of freshwater poses a significant threat to sustainable development and human well-being. Exploring and developing state-of-the-art semipermeable materials for seawater desalination could be a potential solution to address this issue. In this study, we unveil the desalination potential of a newly synthesized multilayer covalent organic framework (COF), named ABBPM, showcasing remarkable water permeance reaching 52 L cm⁻² day⁻¹ MPa⁻¹ alongside a NaCl rejection rate of 97%. This outstanding performance can be attributed to the advantageous combination of its large pore size (∼3 nm), wide organic skeleton (∼0.94 nm), and the ordered ABC stacking pattern, which creates tortuous yet express water pathways, significantly enhancing filtration efficiency. Free energy analysis reveals that compared to the energy barriers (∼4 kJ mol⁻¹) faced by water molecules, ions encounter higher energy barriers (∼9 kJ mol⁻¹ to ∼11 kJ mol⁻¹) when traversing the 3L ABBPM membrane, which can be primarily attributed to the broad organic skeleton. Moreover, the translocation velocity of water across the multilayer ABBPM membranes surpasses that observed in nanopores on a single-layer graphene or MoS₂. Therefore, this study not only presents the multilayer ABBPM COF as a promising candidate for efficient desalination but also proposes a strategic design approach for layered porous structures, with pore sizes exceeding the diameters of hydrated ions, for desalination technology advancement.