Spatial distribution of bipolar functional groups modulates water and ion transport in carbon nanotube

Functional group modification in carbon nanotubes alters charge distribution and steric hindrance, which strongly influence the transport of water molecules and ions. Molecular dynamics simulations are used to examine how the number and spatial arrangement of carboxyl and amino groups in carbon nanotubes influence transport behavior in the channel. As the number of functional groups increases, water transport efficiency decreases, whereas ion rejection increases. Bipolar functionalization enhances ion selectivity while improving the continuity of water migration. Further comparison of double-ring, linear, helical, and coupled distributions shows that the linear and semi-helical coupled distribution constructs continuous low-resistance channels and optimizes the local charge regulation network, thereby reducing the energy barrier for water migration and enhancing ion selectivity, which leads to the best overall transport performance. This study reveals the intrinsic mechanisms by which the spatial distribution of bipolar functional groups regulates transport behavior in nanochannels, providing a theoretical basis for the design of functionalized nanochannels.