Efficient removal of heavy metal ions by thiol-functionalized superparamagnetic carbon nanotubes

Thiol-functionalized multiwall carbon nanotube/magnetite nanocomposites (CNTs/Fe ₃O ₄) were synthesized, and were investigated by power X-ray diffraction, transmission electron microscopy, energy-dispersive X-ray spectrometer, Fourier transform infrared spectroscopy, thermogravimetric analyses, BET analysis and physical properties measurement system. The results showed that the 3-mercaptopropyltriethoxysilane (MPTS) was successfully grafted on the surface of CNTs/Fe ₃O ₄ nanocomposites. The as-synthesized thiol-functionalized CNTs/Fe ₃O ₄ (MPTS-CNTs/Fe ₃O ₄) nanocomposites exhibited superparamagnetic property and higher specific surface area than that of CNTs/Fe ₃O ₄ nanocomposites at room temperature. The adsorption properties of Hg ²⁺ and Pb ²⁺ as a function of contact time, pH value and initial metal concentration were characterized by an inductively coupled plasma optical emission spectroscopy (ICP-OES). The pseudo-first-order kinetic equation could better than that of pseudo-second-order kinetic equation to describe the adsorption kinetics of the before and after thiol-functionalized nanocopmposites. The removal efficiency of CNTs/Fe ₃O ₄ nanocomposites and MPTS-CNTs/Fe ₃O ₄ nanocomposites was highly pH dependent and the optimal pH value for adsorption was 6.5. The adsorption isotherms of Hg ²⁺ and Pb ²⁺ by MPTS-CNTs/Fe ₃O ₄ nanocomposites matched well with the Langmuir model with the maximum adsorption capacities of 65.52 and 65.40mg/g, respectively.