Increasing applications of multiwalled carbon nanotubes (MWCNTs) and thallium (TI) would raise their exposure risks to aquatic environment. MWCNTs might affect the environmental behavior of TI(I) by adsorption, and it is critical to understand the interactions between them. The adsorption kinetics, isotherms, thermodynamics, and desorption of TI(I) by three MWCNTs were studied. In addition, the influences of solution pH, ionic strength on adsorption were also evaluated. The adsorption of TI(I) on MWCNTs started at very low pH values and increased abruptly, then maintained high level with increasing pH values at pH > 6.5. MWCNTs with more hydrophilic groups and negative surface charges had the greatest TO) absorption capacity. The existence of K+ significantly inhibited TO) adsorption on purified-MWCNTs. TI(I) adsorption on MWCNTs was spontaneous occurred by ion exchange with H+/Na+/K+ at the exchange sites and forming outer-sphere surface complex. Moreover, TO) could be easily desorbed from MWCNTs and the lower pH benefited the desorption. (C) 2013 Elsevier B.V. All rights reserved.