Removal of Pb(II) and methylene blue from aqueous solution by magnetic hydroxyapatite-immobilized oxidized multi-walled carbon nanotubes.

Magnetic hydroxyapatite-immobilized oxidized multi-walled carbon nanotubes (mHAP-oMWCNTs), an excellent adsorbent for Pb(II) and methylene blue (MB) removal, was synthesized in the present work. It was characterized by SEM, XRD, FTIR, BET, TGA and zeta potential analysis. mHAP-oMWCNTs displayed better adsorption performance than mHAP, mMWCNTs and HAP-oMWCNTs. The adsorption of Pb(II) and MB mainly depend on the ion-exchange property of HAP and the abundant oxygenic functional groups on oMWCNTs surface. Besides, good magnetic performance of mHAP-oMWCNTs makes it easy to achieve the solid-liquid separation. The adsorption kinetic data described well with the pseudo-second-order model and the equilibrium data fitted well with Frendlich and Langmuir isotherms for Pb(II) and MB, respectively. The maximum adsorption capacity was 698.4mgg-1 for Pb(II) and 328.4mgg-1 for MB from Langmuir isotherm. Thermodynamic studies (ΔG<0, ΔH>0, ΔS>0) implied the both adsorption was endothermic and spontaneous process. Furthermore, the excellent reusability of mHAP-oMWCNTs was confirmed by the desorption experiments. All the results showed mHAP-oMWCNTs has a promising application in water treatment.