Water Transport Dynamics in Layered Nanoporous Graphene: An In-Depth Molecular Dynamics Study

Two-dimensional graphene nanomaterials are relevant to substantial applications for water purification and selective ionic sieving. However, it remains challenging to precisely tune the geometrical features of graphene and to isolate the effects of individual structural parameters experimentally, and also to have a deep understanding of the water-membrane interactions. Here in this work, we employ molecular dynamics simulations to investigate the water permeation through alternately stacked, three-layer graphene/graphene oxide membranes without externally applied pressure or electric fields. Our findings reveal a nuanced interplay among different key factors such as layer spacing, pore size, oxidation degree, pore modification, and temperature. The permeation dynamics of water molecules is fundamentally governed by long-range electrostatic interactions, which act in concert with van der Waals interactions to facilitate the transport process. We report that strategic pore alignment and an increased hydroxyl content enhance the water flux, with optimal performance observed at room temperature for well-spaced layers. Moreover, we found that the hydroxyl groups are more influential than the epoxy groups, and can modulate the energy landscape for water transport. We further demonstrated that precise control over pore geometry and chemical functionalization can dramatically improve the permeability, which furnishes insights for the rational design of graphene-based membranes. We also discussed flexible models and nonperiodic models, proving that interlayer spacing is the crucial determinant of water flux, with permeability being subject to the transport pathways of water molecules. Consequently, our study provides a roadmap for the development of high-performance membranes for advanced water treatment and selective separation applications.