The importance and impact of the application of CNT membranes with sub-nanometer pores for effective water purification are marvelous. Here we demonstrate, by reactive MD simulations, that CNT membranes can efficiently reject phenol due to molecular size exclusion effects and yield high permeability of water. The water flux in armchair CNTs with a pore diameter of about 7 Å is 1.3 orders of magnitude greater than that of the zigzag counterparts, and pore chemistry plays an important role in moderating the water flux. Nanotubes with H-capped atoms on their rims lead to higher fluxes (50 times) than that of the C-passive counterpart. In nanotubes of larger diameters (8 Å), the pore size is large enough to permit phenol molecules to permeate without any restraint. A series of evidence-based investigations on the interaction nature of the systems under consideration was performed to explain the specific molecular factors as well as systematically reliable relationships for water molecules penetrating through various nanotubes. DFT calculations were also performed to evaluate the validity of the reactive potential employed here. We expect these findings to establish a basis for the design of novel energy-efficient nanotube based membranes as an economical means for the removal of organic contaminants from water, and they can be a benchmark for directing experimental efforts, which are presently restricted by the difficulty associated with creating sub-nanometer pores of a specific size for water treatments.
