The direct adsorption mechanism of chlorides (LiCl, NaCl, KCl, CsCl, MgCl2, CaCl2, SrCl2 and BaCl2) on carbon nanotubes (CNTs) was investigated with first-principles calculations. The dipole moment, the adsorption energy and the Coulomb interaction energy were calculated. The value of the adsorption energy ranges from 0.2 to 0.6 eV. Considering the structure change of chlorides before and after adsorption, we find that the adsorption energy, just as the Coulomb energy, is proportional to the ratio of chloride's dipole moment to the square of adsorption distance. So, we conclude that the direct adsorption of chlorides on CNTs occurs mainly through long-range electrostatic interactions. (C) 2013 Elsevier B.V. All rights reserved.