Studies on the removal of tetracycline by multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) were used for the sorption of tetracycline (TC) from aqueous solution. A systematic 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 pi-pi dispersion interaction and hydrophobic interaction between TC and MWCNT. The adsorption efficiency could reach 99.8%, suggesting that MWCNT is excellent adsorbents for TC removal from water. TC adsorption kinetics were found that the equilibrium was reached within 20 min following the pseudo-second-order model with observed rate constants (k(2)) of 0.026-0.032 g mg(-1) min(-1) (at varied temperatures). The whole rate process appeared to be influenced by both intraparticle diffusion and boundary layer diffusion. The sorption data could be well interpreted by the Langmuir model with the maximum adsorption capacity of 269.54 mg g(-1) (293 K) of TC on MWCNT. The mean energy of adsorption was calculated to be 0.029 kJ mol(-1) (293 K) from the Dubinin-Radushkevich adsorption isotherm. Moreover, the thermodynamic parameters for the adsorption were estimated, and the Delta H degrees and Delta G degrees values indicated the endothermic and spontaneous nature of the sorption process. (C) 2011 Elsevier B.V. All rights reserved.