Adsorption of Ni(II) from aqueous solution using oxidized multiwall carbon nanotubes

In this work, oxidized multiwall carbon nanotubes (MWCNTs) were used as a novel adsorbent for removing Ni(II) from aqueous solution. The adsorption of Ni(II) onto oxidized MWCNTs was studied as a function of contact time, pH, ionic strength, MWCNT concentration, and temperature. The results showed that Ni(II) adsorption onto MWCNTs is strongly dependent on pH and oxidized MWCNT concentration and, to a lesser extent, ionic strength. Kinetic data indicated that the adsorption process achieved equilibrium within 40 min and follows a pseudo-second-order rate equation. The adsorption data fit the Langmuir model and its linearized form well, together with thermodynamic data indicating the spontaneous and endothermic nature of the process. Results of a desorption study showed that Ni(II) adsorbed onto oxidized MWCNTs could be easily desorbed at pH < 2.0. Ion exchange may be the predominant mechanism of Ni(II) adsorption on oxidized MWCNTs. Oxidized MWCNTs may be a promising candidate for concentration of heavy metal ions from industrial wastewater.