Exploring the influence of silver nanoparticles on water dynamics within carbon nanotubes

Abstract

Water confined inside carbon nanotubes (CNTs) exhibits structural and dynamical properties that differ substantially from those of bulk water, with important implications for nanoscale transport and membrane applications. In this work, molecular dynamics simulations were used to investigate how externally anchored silver (Ag) nanoparticles influence the behavior of water confined inside CNTs of about 1 and 2 nm diameter over the temperature range 220–300 K. In the 1 nm CNT, Ag enhances near-wall water layering and depletes the pore center across the full temperature range, narrowing and steepening the radial free-energy well and localizing water into a tight annular shell. In the 2 nm CNT, Ag only modestly sharpens the near-wall region, leaving interior water largely unperturbed. Despite these structural changes, first-shell oxygen–oxygen coordination remains bulk-like, and the 6 radial distribution function reveals a stable hydration shell around Ag with weak temperature dependence. Ag has a modest effect on the average hydrogen-bond count, but significantly alters kinetics in a diameter-dependent manner: in the 1 nm CNT, reduced hydrogen-bond lifetimes accompany faster axial diffusion and dipole reorientation, whereas in the 2 nm CNT, lifetimes increase modestly, orientational relaxation slows, and translational mobility remains high because of the larger pore cross-section. Notably, Ag suppresses a structural crossover near 250 K observed in the pristine 1 nm CNT, consistent with our previously reported findings. Overall, these findings show that Ag nanoparticles tune nanoconfined water into a structurally more ordered but dynamically responsive state, providing useful insights for CNT-based nanofluidic and membrane system design.