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Effect of electric or magnetic field on desalination efficiency was studied by molecular dynamics simulation. A restricted double-walled carbon nanotube (CNT) was selected, then strong and weak external field regime were applied on simulated system. Results of simulation showed that strong electric field increases water flow rate two times than untreated system. Magnetization of water decreases water flow rate because of the increase in number of hydrogen bond. In addition, it was observed that applying electric field or magnetization of water completely rejects the ions. In fact, electric field moved back Na+ ions because of the force acting on the ion opposite to the direction of reverse osmotic forces. Magnetization of water leads to a more stable hydration shell around the Na+ ion that prevents passing through the carbon nanotube. In comparison with a single-walled CNT, considering a double-walled CNT enhances the experimental agreement of simulated water flow rate.

Effect of carbon nanotube (CNT) shape on desalination efficiency was investigated by computer simulation. Three shapes of CNT including tubular, cone, and hetero-junction (a combination of two different diameter CNTs which connected by a diverged CNT) shaped were simulated at high pressure (> 50 MPa). For the first time, we placed neutral charge CNT between two inert walls to illustrate support of CNT that is an inert polymer. Cone shaped CNT conducted water ~ 4 times faster than (6,6) CNT and rejected the ions similar to (6,6) CNT. Actually, cone-shaped CNT possesses the shorter residence time and higher number of water in the tube. This is because of the higher capacity and lower energy barrier against water to pass through it. However, hetero-junction CNT showed a slower water conductance because of the formation of water cluster at the large end of CNT that implies a high-energy barrier against water. In addition, H-bond number is also responsible for energy barrier. H-bond number in bulk of water is 4 and should be decreased to 2 to penetrate in the tubular and hetero-junction shaped CNT. Nevertheless, in a cone shaped CNT H-bond number falls down to 3 only at the entrance of the tube.