Multiwalled carbon nanotubes as adsorbents for removal of herbicide diuron from aqueous solution

The adsorption of diuron onto as-prepared and oxidized multiwalled carbon nanotubes (MWCNTs) from aqueous solution has been studied through batch experiments, in which the effect of contact time, temperature, pH and coexisting Cu2+ were investigated. The adsorption performance of diuron onto MWCNTs fitted the pseudo-second-order model and apparent equilibrium was reached within 1 h. The experimental data showed good correlation with Freundlich, Langmuir and Polanyi–Manes models in the range of experimental concentrations, but followed Polanyi–Manes model most appropriate. The calculated thermodynamic parameters showed adsorption of diuron onto MWCNTs was exothermic and spontaneous. Except for the introduction of oxygen-containing functional groups onto the surfaces of MWCNTs, the oxidized treatment of as-prepared MWCNTs can also increase the surface area and the pore volume, which resulted in the increase adsorption of diuron in this study. The adsorption of diuron was found to be pH dependent, and more adsorption was observed under neutral and basic conditions. The presence of Cu2+ has no significant effect on the adsorption of diuron onto as-prepared MWCNTs, on the contrary, the presence of Cu2+ can greatly decrease the adsorption of diuron onto oxidized MWCNTs. In addition, competitive adsorption was greater at higher than at lower diuron concentrations.

► The pseudo-second-order model can well describe the adsorption performance of diuron onto MWCNTs.
► The Polanyi–Manes isotherm showed the best fitting with the equilibrium data.
► The thermodynamic parameters indicated that the adsorption of diuron onto MWCNTs was spontaneous and exothermic.
► The adsorption of diuron onto MWCNTs was found to be pH dependent and favorable under neutral and basic conditions.
► The presence of Cu2+ had different effect on the adsorption of diuron onto as-prepared and oxidized MWCNTs.