Adsorption behavior of multi-walled carbon nanotubes for the removal of olaquindox from aqueous solutions.

Multi-walled carbon nanotubes (MWCNT) were employed for the sorption of olaquindox (OLA) from aqueous solution. A detailed study of the adsorption process was performed by varying pH, ionic strength, sorbent amount, sorption time and temperature. The adsorption mechanism is probably the non-electrostatic π-π dispersion interaction and hydrophobic interaction between OLA and MWCNT. The adsorption efficiency could reach 99.7%, suggesting that MWCNT is excellent adsorbents for effective OLA removal from water. OLA adsorption kinetics were found to be very fast and equilibrium was reached within 2.0 min following the pseudo-second-order model with observed rate constants (k) of 0.169-1.048 g mg(-1)min(-1) (at varied temperatures). The overall rate process appeared to be influenced by both external mass transfer and intraparticle diffusion, but mainly governed by intraparticle diffusion. A rapid initial adsorption behavior occurred within a short period of time in this adsorption system. The sorption data could be well interpreted by the Langmuir model with the maximum adsorption capacity of 133.156 mg g(-1) (293 K) of OLA on MWCNT. The mean energy of adsorption was calculated to be 0.124 kJ mol(-1) (293 K) from the Dubinin-Radushkevich adsorption isotherm. Moreover, the thermodynamic parameters showed the spontaneous, exothermic and physical nature of the adsorption process.