Enhancing desalination performance in nanoporous membranes requires a fundamental understanding of how nanoscale geometry and external driving fields jointly regulate water and ion transport. In this work, atomistic molecular dynamics simulations were performed to investigate the selective transmembrane transport of water molecules and ions through graphene nanopores with different geometries, including circular, triangular, rectangular, and cross-shaped pores. The effects of driving pressure and lateral electric field were systematically examined. The results show that water flux increases approximately linearly with pressure, whereas ion rejection decreases to some extent under higher pressure. Under the same pressure, nanopore geometry strongly affects transport behavior. Circular and cross-shaped nanopores exhibit higher water flux than triangular and rectangular pores, which is closely related to their distinct water occupation patterns and effective migration pathways inside the nanopores.
To further improve ion rejection, a lateral electric field was introduced perpendicular to the pressure-driven transport direction. The lateral electric field significantly suppresses ion permeation while only moderately reducing water flux. This difference originates from the distinct responses of water molecules and ions to the electric field. Ions are driven toward the nanopore edge, leading to compressed effective transmembrane pathways, enhanced ion–graphene interactions, and increased migration resistance. In contrast, water molecules are mainly affected through dipole reorientation, and their density distribution and migration pathways are less disturbed. Among the four nanopore geometries, the cross-shaped nanopore achieves the best overall desalination performance under the combined regulation of pressure and lateral electric field, maintaining relatively high water flux while achieving high ion rejection. These findings reveal the coupled roles of nanopore geometry and lateral electric field in regulating nanoscale selective transport, and provide theoretical guidance for the rational design of next-generation high-performance desalination membranes with non-circular nanopores and field-assisted separation strategies.