Removal of heavy metals from aqueous solutions by multi-walled carbon nanotubes modified with 8-hydroxyquinoline

Multi-walled carbon nanotubes (MWCNTs) were modified with 8-hydroxyquinoline and used for the removal of Cu(II), Pb(II), Cd(II) and Zn(II) from aqueous solutions. Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy showed the successful modification of the MWCNTs with 8-hydroxyquinoline. The adsorption parameters, such as the amount of MWCNTs used, temperature, pH, ionic strength, metal ion concentration, and competition among metal ions, were studied and optimized. The results showed that most of the metals were removed from aqueous solution using 250 mg of MWCNTs at pH 7.0 and 298 K in 0.01 M KNO3 after 10 min of adsorption. The results also showed that the competition between the target heavy metals was in the order of Cu(II) > Pb(II) ≈ Zn(II) > Cd(II) for % adsorption. The recycling, desorption and regeneration of the MWCNTs were evaluated and the results demonstrated that most of the metal ions desorbed at pH values lower than 2.0, and the MWCNTs could be used for up to three cycles of adsorption/desorption without losing efficiency. The pristine and modified MWCNTs were used to remove the target heavy metals from two real samples collected from the Red Sea and a wastewater treatment plant. Both pristine and modified MWCNTs were capable of removing the heavy metals from the real samples. In general, the modification of MWCNTs with 8-hydroxyquinoline significantly enhanced the removal of heavy metals from aqueous solution.