Impact of −C2H5 and −OH Functionalizations on the Water Flow Blockage in Carbon Nanotubes

Carbon nanotube (CNT) filter membranes are excellent promising materials for efficient desalination. In our previous studies (Phys. Rev. Lett. 2015, 115, 164502) we showed that Na+ cations in seawater would easily bind at the entrance of the pristine CNT due to cation−π interaction, resulting in the blocking of water flow through the nanotube. Here, we systematically investigate the binding behavior of ions and blockage effects of water flow in much more chemically realistic CNTs that are functionalized at the ends with various density of hydrophilic −OH or hydrophobic −C2H5 groups. Our findings show that hydrophobic −C2H5 groups will weaken the cation−π interaction between Na+ ions and CNTs, and accordingly, water flows through the CNTs fluently. CNTs functionalized with −C2H5 groups in moderate density are expected to work excellently in desalination application, whereas functionalization with hydrophilic −OH groups cannot prevent the blockage of water. This finding brings insights in designing efficien...