Adsorption and desorption of dimethyl phthalate on carbon nanotubes in aqueous copper(II) solution

The adsorption and desorption of dimethyl phthalate (DMP) on five types of carbon nanotubes (CNTs) were studied in the absence and presence of 50 mg/L copper(II) (Cu2+) ion. The adsorption and desorption data are well described by the Freundlich model and the first-order two-compartment model, respectively. The adsorption capacity of CNTs for DMP is inversely related to the average outer diameter of the CNTs. The surface acidic functional groups of CNTs increases in the order of lactones < hydroxyl < carboxyl functionalities and decreases with the increase in the outer diameter. The adsorption of DMP on CNTs increases in the presence of Cu2+ ions. The adsorption coefficient increases in pH 3–6 and is nearly the same at pH > 6 for all CNTs. The presence of Cu2+ ions decreases the amounts of desorbed DMP from CNTs, inferring that Cu2+ ions could suppress the DMP desorption from CNTs and reduce DMP toxicity to our environment.