One Dimensional Confinement Inhibits Water Dissociation in Carbon Nanotubes

PEREZ SIRKIN, YAMILA A.; ALI HASSANALI; DAMIAN A SCHERLIS

Journal of Physical Chemistry Letters

American Chemical Society

Año: 2018 vol. 9

1948-7185

The eect of nanoconnement on the self-dissociation of water constitutes an openproblem whose elucidation poses a serious challenge to experiments and simulationsalike. In slit pores of width 1 nm, recent rst-principles calculations have predictedthat the dissociation constant of H2O increases by almost two orders of magnitude[Phys. Rev. Lett. 2017, 119, 056002]. In the present study, QM-MM moleculardynamics combined with a biased sampling strategy, are employed to compute thedissociation free-energy prole of water in a (6,6) carbon nanotube. According to ourresults, the equilibrium constant Kw drops by 3 orders of magnitude with respect tothe bulk phase value, at variance with the trend predicted for connement in two di-mensions. The higher barrier to dissociation can be ascribed to the undercoordinationof the hydroxide and hydronium ions in the nanotube, and underscores that chemi-cal reactivity does not exhibit a monotonical behavior with respect to pore size, butmay vary substantially with the characteristic length-scale and dimensionality of theconning media.