Ion transport through functionalized carbon nanotubes in an external electric field is studied using all atom molecular dynamics simulations. The surface of carbon nanotubes has been functionalized with hydrogens and hydroxyl groups, and ionic current passing through the nanochannels has been examined with respect to the extent of surface modification. We are able to dramatically increase the ionic current passing through the nanotube via the appropriate surface modification. An analysis of the electrostatic potential within the tube shows higher ionic currents result from an increase in accessible pathways coupled with a global shift toward more direct ion passage. Moreover, through judicious choice of structure, the current can be modulated to a large degree with ion selectivity. (C) 2017 Elsevier B.V. All rights reserved.