Enhanced water permeation through the terahertz-induced phase and diffusion transition in metal-organic framework membranes.

Abstract

Freshwater scarcity is a pressing global concern, and water desalination has emerged as a promising solution. Metal-organic framework (MOF) membranes have demonstrated exceptional potential in this regard. However, previous efforts to improve the permeability of MOFs have primarily focused on chemical modifications and synthesis rather than exploring physical methods. Using molecular dynamics simulations, we propose that the use of terahertz waves at a specific frequency of 7.5 ± 1.0 THz significantly enhances water permeability across MOF membranes, up to 27-fold, while maintaining effective ion rejection capabilities throughout the process. The mechanism behind this enhancement involves the resonance between the terahertz wave and the hydrogen bond vibrations of water within the MOF. This resonance amplifies the rotational kinetic energy of water molecules, disrupting the hydrogen bonds and causing a phase transition from quasi 1D square ice to a gas-like phase. Additionally, the diffusion behavior shifts from Fickian diffusion to sub-diffusion, resulting in improved water permeation across the MOF membrane. This study highlights the potential of terahertz waves as a physical tool to enhance the permeability of MOFs in water desalination, providing new avenues for efficient water treatment and resource sustainability.